In February 2025, the tulip tree (Liriodendron tulipifera) remained in winter dormancy under persistently cold and dry conditions. The period was characterized by below-freezing temperatures and almost no precipitation until a brief late-month thaw:
- Air Temperature: Daytime highs remained below 0 °C through mid-February, then slowly climbed to ~8–10 °C in the last week, while nighttime lows fell to -12 °C during cold spells【27†L0-L8】. The month’s mean temperature was around -4.8 °C – essentially at the long-term February average of -4.7 °C【58†】.
- Precipitation: Virtually no rainfall occurred; only ~5 mm water-equivalent precipitation fell (mostly light snow flurries around Feb 12)【19†L31-L39】. This is far below the historical February precipitation (~60 mm total on average, based on 1940–2024 climate normals).
- Soil Temperature: The topsoil stayed near freezing (around -1 to 0 °C) for most of the month. By Feb 28, soil temperature at 7 cm depth had only just risen to about 1 °C as a slight surface thaw began【78†】.
- Soil Moisture: With frozen ground and negligible precipitation, volumetric soil water content held steady near 0.32 m³/m³ through the month【48†】. A minor uptick (~0.33) occurred when the mid-month snow briefly melted, but soils remained on the dry side for late winter.
Roles of Variables: The prevailing cold prevented any biological activity – the tree’s buds stayed tightly dormant, locked by the chilling temperatures. The lack of precipitation meant soils received no new moisture recharge; however, because the tree had no active transpiration in dormancy, the dry soil did not immediately harm it. Frozen soil temperatures below 0 °C would have kept water unavailable to roots until the late-month partial thaw. In essence, February’s climate kept the tulip tree in a state of suspended animation: low air temperatures maintained dormancy, and the dry, frozen soil set the stage for a potentially moisture-limited spring start.
What Happened: Throughout February 1–23, Hongcheon experienced stable deep-winter conditions – clear, dry Siberian air masses with occasional frigid nights. Around Feb 24–28, a slight warming trend emerged as daytime highs edged above freezing for the first time in months, signaling the approaching end of winter. No significant snowpack was present (only a light dusting from the minor mid-month snow), so the landscape was quite dry. By month’s end the ground began to thaw at the surface, creating the first opportunity for moisture infiltration – albeit there was little precipitation to infiltrate.
Physiological State of the Tulip Tree: The tree remained in full winter dormancy throughout February. These low temperatures are well within the tulip tree’s tolerance (the species is hardy to roughly -34 °C) – indeed, the winter lows of -12 °C were nowhere near damaging levels for its hardened tissues【66†L53-L61】. The abundant chilling hours (>800 hours between 0–7 °C typically required) were being met or exceeded during this period【66†L79-L87】, ensuring the tree’s dormancy requirements were satisfied. The extreme dryness had minimal immediate effect on a dormant tree; water demand was essentially zero and the tree likely still held ample moisture in its tissues from the previous fall. However, the very dry soil could become a concern if it persisted into the growing season – a tulip poplar prefers moist soil and has low drought tolerance【69†L27-L30】. In late February, buds remained tight and no visible changes occurred in the canopy, aside from perhaps slight swelling as the tree sensed the incremental daylength and temperature rise.
Comparison to Historical Norms: Temperature-wise, February 2025 was normal for Hongcheon – the mean was almost exactly the 1940–2024 average【58†】. This indicates no major deviation in winter coldness. The precipitation, on the other hand, was an anomalous deficit. A typical February in this region is dry, but not nearly this dry (for context, long-term February precipitation is on the order of a few dozen millimeters of snow/rain). The paltry ~5 mm recorded in Feb 2025 suggests an ongoing drought. Indeed, meteorological reports noted severe drought conditions carrying over from late 2024 into early 2025 due to strong continental high pressure and lack of snowfall【77†L105-L113】. Such winter droughts are not unprecedented, but in a warming climate they can be exacerbated by reduced snow cover and higher evaporative demand during any warm spells. Overall, February 2025 set a dry baseline with no hint yet of the turbulence to come in spring.
March 2025 brought extreme variability, oscillating between winter and spring in two dramatic acts. Early March saw a major snowfall and freeze that kept the tree in winter mode, while late March delivered an unseasonable warm spell followed by a sharp cold snap. This start-stop pattern had significant implications for soil moisture and the tree’s buds:
- Air Temperature: The range was extraordinary – from sub-zero blizzard conditions to balmy spring warmth in a matter of weeks. In the first week, daytime highs stayed near 0 °C and March 3 was frigid (high -1.8 °C, with the tree encased in below-freezing air all day)【27†L5-L9】. By March 21–24, a surge of warm air sent temperatures up to 20–21 °C in Hongcheon【30†L25-L30】, about 8–10 °C above normal late-March highs. Nights that week became mild (mostly above freezing). However, a late cold front at the end of March (around March 28–30) crashed temperatures back down – on March 29–30, highs dropped to a mere ~1–2 °C with nights around -6 to -8 °C【31†L33-L40】. Overall, March’s mean temperature (~2.8 °C from local sensor data) ended up about +1.3 °C warmer than the long-term March average (1.5 °C)【58†】, but that average masks the extremes of a month that swung from deep cold to near-summer warmth.
- Precipitation: Total precipitation was about 74 mm (water equivalent) – close to the historical March average (~90–100 mm) but delivered in a few intense events. Around March 2–3, a strong low-pressure system brought heavy precipitation that fell largely as snow. Reanalysis data indicate ~15 mm water equivalent over those two days【19†L35-L39】【24†】, which could translate to 15–20 cm of snow. (The local sensor recorded only ~0.5 mm, likely undercatching solid snowfall.) This snowfall blanketed the ground and then slowly melted over the next week. A second spell of precipitation occurred on March 15–17: about 12–13 mm fell (some as cold rain or wet snow) during another cold spell【24†】. After that, late March turned notably dry – virtually no rain fell after the 20th as dry winds accompanied the warm surge. The month’s precipitation thus came in two bursts, with prolonged dry, windy periods in between.
- Soil Temperature: Through early and mid-March, the soil remained chilly. With snow cover and cold air, near-surface soil temps hovered around 0–3 °C【49†】【50†】. Only once the late-March warm spell arrived did the topsoil start warming significantly. By March 23–26, soil temperature at 7 cm likely rose into the 5–8 °C range as mild air and solar heating penetrated the ground. However, the end-of-month cold snap reversed this warming – soil temperature dipped back toward ~2 °C by March 30 (essentially delayed in its spring rise)【79†】. In short, the soil experienced a slow thaw then a temporary re-freeze, echoing the air temperature volatility.
- Soil Moisture: March’s wild weather produced corresponding jumps in soil moisture. The early March snowmelt dramatically boosted the topsoil moisture: volumetric water content climbed from ~0.32 to 0.35–0.349 m³/m³ by March 3 as snow began to melt into the ground【49†】. After the snowfall, soil moisture oscillated with freeze-thaw cycles – it dipped when water refroze or drained (down to ~0.33 mid-month), then spiked again to ~0.386 on March 15–16 as the mid-month rain/snow added moisture【50†】. Following the heavy mid-month event, the drying late-month warmth caused soil moisture to decline steadily, falling into the low 0.3s by March 25 and likely around 0.31 m³/m³ by March 31 (as the previously added water drained or was taken up during the warm spell)【52†】. Thus, by end of March the soil was relatively moist compared to February but was already losing water fast under the influence of warm, dry winds.
Roles of Variables: In early March, the combination of sub-freezing air and heavy snow kept the tulip tree in winter dormancy. The cold air (near -3 °C even at midday on Mar 3) prevented any bud activity; it also meant the precipitation fell as snow, which acted as an insulating blanket over the soil. That snow, once melting, significantly increased soil moisture, providing a much-needed reservoir of water going into spring. However, the cold soil and air also likely delayed root uptake – the tree couldn’t use that moisture until temperatures rose. Fast-forward to late March: the warm air surge around Mar 21–24 suddenly pushed the tree’s environment into spring-like conditions. Air temperatures exceeding 20 °C jump-started metabolic activity – buds likely began to swell as the tree accumulated growing degree days. The soil, now thawed and moist, allowed roots to take up water. But this idyllic spring awakening was abruptly halted by the cold snap of Mar 28–30. In that period, air temperature plunged back below freezing; any buds that had broken or were about to break were exposed to frost. Each variable thus played a part in a classic “weather whiplash” scenario: temperature induced growth then inflicted stress, precipitation endowed the soil with moisture then left a dry gap, and soil conditions oscillated between supportive and restrictive for the tree’s needs.
What Happened:
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Early March (Mar 2–5): A low-pressure system delivered heavy snow across Gangwon Province. In Hongcheon, the tulip tree endured a snowstorm with ~15 mm water equivalent precipitation and temperatures around 0 to -3 °C. The snow likely coated branches and the ground. Following the storm, skies cleared and the deep snow cover kept air temperatures low for several days (nights ~ -6 °C). The tree remained dormant. However, as the sun returned, the snow gradually melted (daytime highs reached 2–3 °C by Mar 5), trickling moisture into the soil. The soil moisture hit a high for the season, nearing saturation in the top layer【49†】. Essentially, early March provided a late winter recharge of soil water, even as the tree itself stayed in winter mode.
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Mid March (Mar 6–19): A prolonged chilly period persisted. Repeated nights well below freezing (reaching -9.4 °C on Mar 19) and cool days kept the tree on hold【30†L21-L29】. A smaller storm around Mar 15–16 brought mixed rain and snow (~12 mm). Because the ground had started to thaw, this precipitation quickly infiltrated, again raising soil moisture (to ~0.38–0.39)【50†】. By this time, the tree had easily met its chilling requirement, and was “ready” for spring whenever warmth would arrive【66†L79-L87】【66†L102-L110】. That warmth arrived abruptly after Mar 19.
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Late March “False Spring” (Mar 20–27): Around the Spring Equinox, a surge of warm, dry air swept over Korea. From Mar 21 onward, Hongcheon saw unseasonably high temperatures – e.g. 16 °C on Mar 21, soaring to 21 °C by Mar 23【30†L25-L30】. These values were on the order of 8 °C above the 1991–2020 normal for late March, a heat anomaly partly attributed to climate change【77†L71-L79】. The warmth was accompanied by low humidity and gusty winds (conditions that, regionally, contributed to wildfire outbreaks in Korea during that week【77†L59-L68】【77†L81-L89】). For the tulip tree, this “false spring” likely initiated bud swell or even budbreak: once daily highs are consistently above ~10 °C and nights stay mild, tulip poplar buds begin to reactivate【67†L53-L60】. Indeed, by late March the tree would have started de-acclimating – ending its endodormancy and entering the ecodormancy phase where growth only depends on temperature. Soil temperatures rose into the upper single digits (°C), meaning roots could function and uptake water. The moist soil from earlier snowmelt provided ample water to support this initial growth. In summary, the tree got a strong “go” signal from Mar 20–27: warm air, available moisture, and increasing daylength all pointed to spring.
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Late March Freeze (Mar 28–31): Just as leaf buds may have been on the verge of opening, winter struck one last time. A powerful cold front around Mar 28 brought plunging temperatures and drying winds. Daytime highs fell back near 0 °C and nightly lows dipped well below freezing【31†L33-L40】. Any precipitation with this front was very light (trace snow/rain) – effectively, it was a hard freeze under clear skies. The soil re-cooled, and the top layer may have refrozen at night. Critically, the tree’s tender bud tissues, which had begun dehardening after the warm spell, were suddenly exposed to frost. This kind of late spring frost (occurring after buds have lost some hardiness) can be far more damaging than mid-winter cold【72†L138-L146】. There is a risk that some emerging buds were killed or injured by the frost. Observations in similar climates have noted “start-stop” spring weather causing delayed and sporadic budbreak in 2025, where buds initiated growth during warmth only to be halted by subsequent cold snaps【66†L110-L118】. It’s likely the Hongcheon tulip tree experienced exactly this: a promising budbreak interrupted by frost. By the end of March, the tree had not yet leafed out. Instead, it was holding at swollen buds, some possibly damaged, waiting for the next round of warm weather to try again.
Physiological Implications for the Tulip Tree: March put the tulip tree’s resilience to the test. For most of the month, the tree remained dormant or in very early bud swell, as cold conditions prevailed. The heavy snow in early March, while keeping the tree dormant, had a positive side – it provided excellent soil moisture recharge for later use. Tulip poplars thrive with abundant moisture, and the tree would benefit from this input once growth resumes. The real stress came from the late-month temperature whiplash. During the warm spell, the tree likely began exiting dormancy: enzymes activated, buds swelled, and internal resources started mobilizing. Then the abrupt freeze forced the tree to pause or even reverse these processes. Such freeze events can damage the nascent buds or young tissues, leading to delayed or uneven leaf-out【66†L110-L118】. If some buds were killed, the tree might have to push secondary buds later (causing a sporadic, protracted budbreak). Even if buds survived, the cold would have forced the tree back into a protective state (re-establishing some cold hardiness), costing time and energy. Additionally, the late March warm winds and sun, combined with dry soils by month’s end, could have caused high evaporative demand on any active tissues. We saw midday vapor pressure deficits climbing above 2 kPa in that period, indicating very dry air【77†L81-L89】【75†】. Fortunately, without full leaves yet, the tree’s water loss was still limited – but bud and twig tissues could have desiccated slightly. In short, the tree in March oscillated between dormancy and awakening, ultimately ending the month in a hesitant state. It accumulated ample chilling (eliminating any dormancy barriers) and had the water it needed, but the weather’s false start likely delayed its true budburst into April.
Historical Context and Climate Change: March 2025 encapsulated the kind of volatility that climatologists warn may increase with climate change. The month as a whole was warmer than normal (+1.3 °C above the 85-year mean), consistent with the trend of warming late winters/early springs. In fact, globally March 2025 was the second warmest on record【76†L10-L18】, and Korea experienced anomalous heat mid-month (Climate Central noted parts of South Korea were 4.5–10 °C above average during Mar 21–26)【77†L71-L79】. At the same time, late frost risk remains – and may even increase – because while average spring temperatures rise, the variability and chance of late cold snaps persist. Research shows that earlier budbreak induced by warming makes plants more vulnerable to damage from late spring frosts【72†L81-L90】【72†L131-L139】. The tulip tree’s ordeal in March 2025 is a case in point. Such start-stop springs have been observed historically, but climate change can amplify their frequency/severity (e.g., by making the warm spells warmer and earlier【77†L73-L80】 without eliminating occasional Arctic cold blasts). On the precipitation side, March 2025’s total was unremarkable, but the distribution into a couple of heavy events mirrors a pattern of more precipitation falling in heavy bouts rather than gentle events – a known symptom of climate change in many regions. Moreover, the early spring drought between storms (late March’s parched spell) aligned with the severe drought that had been affecting Korea since winter【77†L105-L113】. This drought set the stage for wildfire conditions regionally and meant that, despite two snow/rain events, soils were trending drier than normal by the month’s end. In summary, March 2025 was both a climatic anomaly (in its rapid swings) and also illustrative of long-term trends: a warmer climate with intense rainfall events and periods of weather extremes that challenge the traditional phenological timing of trees.
April 2025 was a true spring month for the Hongcheon tulip tree – a period of budburst, leaf-out, and active growth. It was also a month of highly variable weather, featuring a late frost event, two heavy rainstorms, and fluctuating temperatures. Overall, April delivered the warmth needed for the tree to leaf out, along with abundant moisture, albeit with some interruptions:
- Air Temperature: The first week of April brought gradually warming days (highs 12–16 °C on Apr 6–8) but still frosty nights (around -1 to -4 °C)【32†L41-L49】. By mid-April (Apr 11), a spike of warmth sent the daytime high to 22.6 °C【32†L45-L49】 – likely the tree’s first encounter with >20 °C air of the year – but this was immediately followed by a brief cold snap on Apr 13–14. During that snap, the daily high plummeted to just 4 °C on Apr 14 and nights dipped to about -1 °C【32†L43-L50】. Any light frost on the morning of Apr 14 was the last freezing temperature of the season. Thereafter, a sustained warming trend took hold. The period April 17–21 was unseasonably warm: e.g. Apr 21 reached 24.6 °C in the afternoon【34†L53-L60】, with many days in the high teens to low 20s °C. Nights in late April were mostly well above freezing (generally 5–12 °C). This warmth eased slightly at month’s end (Apr 25–30 saw highs ~14–23 °C and a couple of cooler nights ~1–3 °C)【36†L60-L68】. Averaged over the month, April 2025 was about 9.4 °C, a bit warmer than the 1940–2024 mean of 8.9 °C【58†】. The salient features, however, were the swings: a freeze in mid-month and an early-summer-like spell in late April.
- Precipitation: April was markedly wetter than the preceding months, with ~97 mm total precipitation (compare to ~93 mm long-term average, so slightly above normal). Crucially, most of this fell in two major rain events:
- Mid-April Storm (Apr 12–13): A frontal system brought heavy cold rain on Apr 12, totaling about 7.8 mm【33†L99-L104】, followed by a further 14.2 mm on Apr 13【33†L99-L104】. Combined (~22 mm), this event came with the aforementioned cold snap – rain fell on already cooling air, even mixing with wet snow in some higher elevations. Daytime temperatures were only ~8 °C on Apr 13, so rainwater likely lingered on buds/branches as cold droplets. This storm soaked the soil at a critical time (just as buds were opening) but also exposed the tree to chilly wet conditions.
- Late-April Storms (Apr 19 & Apr 22): In quick succession, two intense rain events struck. On April 19, ~26 mm of rain fell【35†L107-L112】, accompanied by mild temperatures (~20 °C) – a classic spring thunderstorm or frontal rain. Just a few days later on April 22, another 23 mm fell【35†L107-L112】. These two events combined to roughly 49 mm, i.e., about half the month’s precipitation in a short window. The rains were likely convective/downpour in nature given the warmth (perhaps the first rumbles of thunder of the year). They thoroughly saturated the soil.
Outside of these events, there were a few smaller showers (e.g., ~2–3 mm on Apr 10 and Apr 16)【33†】【35†】, but also dry spells of ~5–7 days, especially late April after the 22nd. Notably, from Apr 23 to Apr 30 virtually no rain fell, allowing soil moisture to draw down quickly.
- Soil Temperature: With April’s overall warmth, soil temperatures climbed steadily. In early April, soil (7 cm depth) was still cool, around 4–5 °C by Apr 5【31†L37-L41】. After the mid-month cold rain, soil temperature might have briefly dipped (cold water percolating can cool the soil), but as air temps rose, the soil responded. By mid-April (Apr 15), soil temp was about ~5 °C【80†】. Following the sustained warm spell, the soil had warmed to the double digits – around 10–12 °C by Apr 20 and reaching ~10.7 °C on Apr 30【80†】. Essentially, by late April the soil environment was in spring mode, warm enough to encourage active root growth and microbial activity. One nuance: the heavy rains likely kept the soil a bit cooler than it would be in dry conditions (due to moisture’s thermal inertia), but this effect is minor compared to the overall warming trend.
- Soil Moisture: April saw extreme fluctuations in soil moisture because of the alternating heavy rains and drying intervals. At the beginning of April, soil moisture had actually declined to about 0.31–0.32 m³/m³ – March’s late dry, warm days drew water out of the topsoil, dropping from ~0.38 in mid-March to ~0.31 by April 1【52†】. Then the April 12–13 rains spiked soil moisture up dramatically. By April 13–14, soil volumetric water content likely exceeded 0.40 m³/m³ (our ERA5-derived data show ~0.404 on Apr 22 after the second storm, and ~0.397 on Apr 20; it was ~0.376 after the Apr 19 rain)【51†】. In other words, the mid- and late-April storms each saturated the topsoil to around 40% water content – near field capacity for many soils. However, the warm, sunny interludes led to rapid drying of the topsoil. For instance, after the mid-April storm, there was about a 5-day gap before the next big rain. In that time, soil moisture fell from ~0.39 on Apr 14 to ~0.34 by Apr 18【51†】. After the late-April rains, an even more pronounced drop occurred: from ~0.404 on Apr 22 down to 0.310 by Apr 30【52†】. This indicates very high evapotranspiration in late April – the tree (and understory vegetation) plus evaporation consumed a large amount of water in just a week of warm, dry weather. By end of April, despite two major rainfalls earlier, the soil was again relatively dry in the upper layer (around 0.31, similar to early-month values). This set up a need for continued rainfall as the tree headed into May.
Roles of Variables: In April, air temperature played the crucial role of allowing (or occasionally hindering) the tree’s developmental progress. Early in the month, gradually rising temperatures signaled the tree to break dormancy. The mid-month freeze and cold rain (Apr 13–14) was a last potential check on that progress – the chilly air and near-0 °C rainwater likely caused any newly breaking buds to temporarily stall. Meanwhile, precipitation in April was largely beneficial: the ample rains ensured that water was never a limiting factor for the tree’s growth. Each heavy rain refilled the soil profile; even though the topsoil dried between events, deeper layers likely retained moisture, and the tree’s root zone overall was well-supplied. Soil moisture and temperature together created an optimal root environment post mid-month – moist and warming soils promote nutrient mineralization and uptake, fueling the tree’s leaf expansion. The interplay of variables mid-April is worth highlighting: a warm period (Apr 8–11) induced partial leaf-out, then the cold rain on the 12–13th doused the new foliage in near-freezing water. This could stress young leaves (cold rain can cause cellular shock or even frost-like damage if temperatures are marginal). However, the subsequent warmth allowed recovery. By late April, high temperatures, adequate soil moisture, and high humidity during rains all combined to create lush growing conditions – the tree likely experienced near-ideal conditions for photosynthesis during that time, aside from brief slowdowns when it got too cold or when overcast during rain. Each variable had its moment: temperature occasionally limited growth (frost), water was abundant (mostly a positive, though excessive rain can cause brief low oxygen in roots), and soil state transitioned to a full spring regime supportive of active growth.
What Happened:
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Budburst and Leaf-Out: Likely in the window April 8–15, the tulip tree’s buds began to open. By the second week of April, daily highs above 15 °C and consistent mild nights accumulated enough growing-degree days for budbreak to occur【67†L53-L60】. Field observation would have shown the brown-gray winter buds swelling and green leaf tips starting to emerge. The process may have been staggered: buds that began to open around Apr 10 could have been shocked by the cold rain on Apr 12–13. Indeed, that weekend’s weather (cold, wet) probably caused the tree’s new leaves to hold off fully unfolding. Some buds might have paused, resulting in a bit of a “hiccup” in leaf-out. Once the sun returned and temperatures hit 20 °C after Apr 15, the tree resumed leaf-out in earnest. By April 20, many leaves were likely unfurled or in the process, and the tree would have taken on a faint green haze of young foliage.
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Mid-Month Cold Event (Apr 12–14): Physiologically, this was a brief stress episode. As noted, the combination of ~0 °C cold and soaking rain can be problematic. However, since it was so early in leaf-out, the tree’s exposure was mostly buds and maybe a few small new leaves. Those can tolerate near freezing temperatures for short periods. We might expect minor issues like uneven bud development – some buds that were more advanced could have sustained slight frost injury, leading them to lag or abort. The Purdue University diagnostic lab noted that such start-stop patterns in 2025 led to sporadic budbreak in species like tulip poplar, with some buds failing to produce leaves until much later【66†L33-L41】【66†L110-L118】. In Hongcheon’s case, there’s a possibility a few of the tree’s buds remained dormant or very delayed (to leaf out in late April or even early May) due to this cold interruption. Importantly, though, no hard freeze (< -2 °C) occurred during the budbreak period, so widespread bud kill was unlikely. The tree might have lost a bit of its early momentum, but not its overall viability.
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Rapid Growth Phase (Apr 17–25): After the mid-month drama, the tree enjoyed about a week of superb spring weather. With temperatures between 15–25 °C most days and plentiful moisture, photosynthesis and growth were likely at a peak. Tulip poplar performs best around 20 °C【67†L45-L53】, so this period fell right in the sweet spot. The freshly unfolded leaves would be performing net carbon gain, and the tree likely flushed a lot of new shoot growth. Soil moisture was high from the Apr 19–22 rains, meaning no water stress; the tree’s stomata could remain open unabated. This period probably saw the completion of leaf-out – by April 25, the tulip tree was likely in full leaf, with its characteristic bright green, saddle-shaped leaves now adorning the crown. Also, tulip trees typically flower in late spring (April/May in temperate climates) – if this individual was mature enough, it might have produced a few tulip-shaped flower buds during this time, although any flowering could be modest if the tree was focusing energy on leaf deployment due to earlier delays.
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Late April Dry-Down (Apr 23–30): Following the heavy rain on Apr 22, the weather turned dry and remained warm. Over about 8 rain-free days, the topsoil moisture dwindled from saturated to quite dry【52†】. The tulip tree likely increased its water uptake during this time to support its expanding canopy. By month’s end, some early signs of moisture drawdown might have appeared – for instance, slightly higher midday leaf wilting on hot days (Apr 29–30 had highs ~23 °C with relatively lower humidity). Nonetheless, given the deep soil moisture reserves from previous rains, the tree was probably not yet stressed. Its roots, which can reach deeper soil layers, would still find adequate moisture. Essentially, late April gave the tree a taste of the coming need for moisture management, but nothing severe occurred yet. If one looked at the tree on April 30, it would appear fully leafed out and in healthy spring condition, with only trivial evidence that a week had passed since rain (perhaps the soil under the tree beginning to harden as it dried).
Physiological State of the Tulip Tree: By the end of April, the tulip tree had transitioned to its active growing phase. The dormancy of winter was fully broken – the tree was in full foliar display, actively photosynthesizing, and likely beginning to allocate energy to stem and root growth. April’s conditions allowed for a robust start to the growing season: plenty of soil moisture and mostly moderate temperatures. The species’ known preferences were largely met – it prefers cool winters (got that), a moist spring (definitely got that), and it is sensitive to drought and heat【69†L27-L30】 which, so far, had not been an issue. If anything, the only stresses in April were the two cold snaps (mid-month freeze and the minor frosty night around Apr 25). The mid-month cold rain likely resulted in minor foliar damage – e.g. some newly unfurled leaves could have browned at the edges or younger tissue took longer to expand. Also, the sudden abundance of water followed by dryness meant the tree went from conditions of potential waterlogging (right after 50 mm of rain in 4 days, soils were briefly water-saturated) to dry topsoil in a short span. Tulip trees do not like standing water for long (they prefer moist well-drained soil)【68†L25-L28】, so it’s fortunate that drainage in Hongcheon’s soils likely cleared the excess quickly. The brief waterlogged conditions around Apr 20 would have been mitigated by the warm weather driving fast evaporation. Thus, root oxygen deprivation was probably minimal. Overall, physiologically the tree likely ended April in excellent shape: it had a full canopy to harvest sunlight, abundant nutrients and water from the refreshed soil, and had suffered only minor setbacks from the erratic weather. The groundwork was laid for vigorous growth in the coming months, provided that favorable conditions continued.
Comparison to Historical Norms: April 2025’s average temperature was just slightly above normal, but the occurrence of a ~25 °C day in mid-April is a bit above the historical norm (such high temperatures typically occur later in spring). This could hint at climate warming allowing summer-like days earlier in the year. The pattern of heavy rainfall events in April also aligns with observations under climate change – rather than steady April showers, we saw downpours (26 mm in one day is a lot for spring) and long dry spells. Long-term data for the region might show increasing precipitation variability; our qualitative assessment is that April 2025 had a higher concentration of rainfall in big events than is typical. However, total rainfall was not extreme by historical standards. It’s worth noting that East Asia’s spring can be variable, and late spring frost events are not unheard of historically. What stands out is that the tree had to navigate a tight sequence of weather events: from frost to warmth to heavy rain and back, all within weeks. Climate envelope-wise, April pushed the tree slightly beyond a static “normal” climate: e.g., experiencing a 25 °C day (near the upper end of its ideal growth temperature) and a 0 °C night within the same week is an example of greater temperature variability. Climate change has been linked to increased likelihood of such rapid fluctuations – warmer baseline climates can produce stronger frontal contrasts (leading to big swings). The tree’s ability to handle this suggests some resilience, but if such patterns intensify (say, even warmer springs followed by abrupt cold), the risk of damage increases. In summary, April 2025 was a successful but dynamic spring month for the tulip tree: it achieved leaf-out and enjoyed wet conditions, in line with historical expectations for spring greening, yet with hints of the more erratic climate regime emerging in the form of unusual warmth and intense rainstorms.
May 2025 continued the trend of a wet spring in Hongcheon, providing the tulip tree with abundant water and generally mild temperatures – nearly optimal for growth. However, the month was not without surprises: the latter part of May featured a dramatic heat-up followed by an unseasonal cold spell. Through it all, the tree likely maintained vigorous growth, until signs of stress appeared when the weather swung unexpectedly. Key features of May’s conditions include frequent rain events and large temperature fluctuations:
- Air Temperature: For much of May, temperatures were on the cool side for late spring. The first week saw highs in the mid-teens (e.g. 14–17 °C on May 1–4) and nights still dropping to single digits (even down to 1–2 °C on a couple of clear nights in early May)【36†L62-L70】. Around May 8–9, temperatures rose, and by May 10–11 the daytime highs reached about 19–24 °C – a warm spell. This was followed by another dip: an extended period of cloudy, rainy weather in the second week kept highs only ~12–16 °C (and very little diurnal range, as overcast nights stayed ~9–14 °C)【40†L73-L81】. The most notable temperature excursion came in the third week. Starting May 18, a warm air mass moved in. On May 20–21, Hongcheon experienced an early summer preview: the high on May 21 hit 27.5 °C【43†L85-L89】, with an unusually warm night of ~14 °C (due to cloud cover and humidity). This ~27 °C value is well above the May average high and was one of the warmest days of the year to date. But just as quickly, a strong backdoor cold front swept through around May 23–24. Temperatures plunged – May 24 saw a daytime high of only 10.6 °C (more typical of early April than late May)【43†L85-L89】, accompanied by raw drizzle. That day’s low was ~8 °C, meaning the temperature barely moved in a 24-hour span (a testament to thick clouds and rain-cooled air). After this cold shock, temperatures rebounded gradually at month’s end (highs returned to ~20–23 °C by May 30–31). The mean temperature for May 2025 ended up around 12.7 °C (from sensor data), which is 1.8 °C cooler than the long-term May average of 14.5 °C【58†】. This points to May being unusually cool overall, with the late-month cold snap pulling down the mean despite the brief hot days.
- Precipitation: May was very wet, with frequent rain events and high total precipitation (~105–110 mm). Instead of one monolithic “rainy season” onset, there were multiple rain episodes:
- Early May rains (May 1 & 3): Right at the start, a rain system on May 1 dropped ~13.7 mm【37†L17-L24】. Two days later, on May 3, another ~8 mm fell【37†L17-L24】. These rains kept the soil moist from the get-go.
- Major storm May 9–10: A significant multi-day rain occurred around May 9–10. On May 9, about 19 mm of rain fell, followed by ~18 mm on May 10【37†L25-L29】. In total, this event delivered ~37 mm – one of the heaviest of the spring. It was associated with the cloudy, cool conditions of that period. It’s likely this was a broad stratiform rain or a slow-moving front, given the sustained nature.
- Mid-May showers (May 15–16): Another system around May 15 brought ~7.8 mm of rain on the 15th and about 4.5 mm on the 16th【41†】【42†】. While not as intense as the early-May storm, it kept soils topped up.
- Extended wet spell (May 17–24): Interestingly, almost every day from May 17 to May 24 had some precipitation, albeit lighter. Reanalysis data show small daily totals (e.g. 2–6 mm almost each day in that span)【44†L1-L8】. Cumulatively, those add up: roughly ~20+ mm fell across that week, with May 24 itself contributing ~6.4 mm【44†L1-L8】 (likely in that chilly drizzle). This extended wet spell coincided with the temperature whiplash – warmth at first with scattered showers, then a rainy cooldown.
By contrast, the very end of May (after the 24th) saw a drying trend – May 25–31 had little to no rainfall as a high-pressure system likely moved in. In summary, May had rain on a majority of days in the first three weeks. The distribution of rainfall (many moderate events rather than one monsoon burst) is slightly unusual – typically late May can start drying out before the true monsoon. In 2025, however, the atmosphere kept delivering periodic rain. The tree essentially never experienced more than ~5–7 consecutive dry days in May.
- Soil Temperature: With the season progressing, soil temps continued to rise, though the cool weather modulated the increase. Early May soil was around 7–8 °C (following the cool end to April)【82†】. By mid-May, thanks to the warm interlude, soil temperature had reached about 15.5 °C (on May 15)【81†】. However, the late-month cold rains slightly cooled the soil; at the end of May, soil temp was around 14 °C【81†】. So, unlike a steady climb, soil warmth plateaued or dipped during the last week’s chill. Still, by end of May the soil was comfortably warm for root activity (in the mid-teens °C). This is a good temperature range for nutrient uptake. The small downward blip in soil temperature during the May 24 cold spell likely did not have much effect on the tree – it wasn’t enough to send roots into dormancy or anything, just a brief cooling.
- Soil Moisture: Given the frequent rains, soil moisture remained consistently high through May. After April’s end-of-month dry-down, the early May rains quickly brought soil moisture from ~0.31 back up into the 0.34–0.39 range【52†】【53†】. The big storm on May 9–10 had a dramatic impact: soil moisture shot up to ~0.426 m³/m³ by May 10 – essentially near saturation in the topsoil【53†L0-L7】. This was the wettest the soil had been all year. Even after the event, soils stayed waterlogged for a couple of days (0.41 on May 11, 0.39 by May 13 as water started percolating deeper)【53†】. The mid-month (15–16) rains bumped moisture back up from ~0.35 to ~0.38【54†L0-L5】. The continuous light rains 17–24 maintained moisture in a narrow band: oscillating between roughly 0.35 and 0.38 with each minor rain and dry interval【55†】. Notably, despite all the rain, the pattern of quick drainage continued – for example, soil moisture was ~0.38 on May 17, dipped to 0.349 by May 19 (a short dry gap) then rose to 0.376 by May 20 after a bit of rain【55†】. By May 25, after the last of the rain, soil moisture was still a high 0.366 m³/m³【55†】. It then likely declined slightly in the final rain-free week of May (perhaps into the low 0.30s by the 31st). But overall, through May the soil never went near drought levels; it remained at moderate to high moisture content. We can infer that deeper soil layers were likely fully recharged by these successive events, which is crucial for the tree’s resilience if surface soils dry later.
Roles of Variables: In May, precipitation was arguably the dominant boon – the frequent rains ensured that the tulip tree had no shortage of water. This allowed the tree to keep its stomata open and transpiration flowing, supporting rapid growth. Air temperature played a more mixed role: generally it was moderate (which tulip trees appreciate), but the two extremes (the brief hot spell and subsequent cold spell) introduced some stress. During the hot days (around May 21), air temperature nearing 28 °C began pushing the tree toward the upper end of its comfort zone. While tulip poplars can handle such warmth, it does increase water loss and can cause mild heat stress if sustained【67†L87-L95】. However, humidity was relatively high then, mitigating damage (VPD around 1.4–1.5 kPa on that hot afternoon – not too extreme)【74†】. The cold spell on May 24 had a different impact – it didn’t threaten freezing (so leaves were safe), but the sudden chill would have slowed the tree’s metabolism. Think of it as the tree hitting the pause button on growth for a few days: photosynthesis rates drop in cool, overcast conditions; nutrient uptake might slow in cooler soil; and the tree essentially goes into a minor lull. Soil conditions in May were nearly ideal: warm and wet. If anything, there might have been moments of over-saturation (after 37 mm in two days, the soil was at field capacity or above), which can temporarily reduce root aeration. But because the rains were spread out and often followed by dry breaks, the soil was usually in that sweet spot – moist but not flooded. Therefore, each variable combined to favor the tree’s growth for most of May. Only around the 21st did temperature + high sun mean the tree had to ramp up transpiration greatly (which it could, because soil moisture was abundant). And only around the 24th did temperature + lack of sun mean the tree had to conserve energy (which was fine, as soil moisture remained high so no drought stress). In short, May’s climate variables mostly complemented each other in supporting the tree’s needs.
What Happened:
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Steady Growth and Canopy Expansion: Through the first three weeks of May, the tulip tree was likely thriving. With its leaves fully out by early May, the tree would now focus on expanding leaf size, growing new shoots, and possibly flowers. The ample rain ensured those young leaves stayed turgid and could expand to full size without wilting. One can imagine the leaves on a tulip tree drooping slightly in midday if it’s dry – that did not need to happen in early May 2025 because rains came frequently. Additionally, cloudy days – while limiting photosynthesis a bit – would keep VPD low and temperatures moderate, which for a water-loving species can actually prolong optimal functioning over a whole day (no midday stomatal closure needed). The nutrient uptake was likely high as well: moist soils enhance the availability of nutrients like nitrate, and warmer soil by mid-month meant root activity was high. The tree probably put on a flush of new green growth; observers would see elongating twigs and darkening, maturing leaves.
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Early Hot Spell (May 20–21): When temperatures shot up to the high 20s on May 21, the tree would have responded by maximizing transpiration to keep cool. Tulip poplars have been noted to be sensitive to heat and can show leaf wilting or marginal scorch if it’s too hot or dry【67†L87-L95】. In this case, heat came but with humidity – that day was preceded by rains, so the environment was more muggy than arid. The tree likely did not wilt, as soil moisture was high enough to supply the needed water. Instead, it probably experienced a boost in growth: warm temperatures accelerate physiological processes, so long as water is plentiful. May 20–21 might have been a period of very high photosynthetic rates initially (especially May 20, which was warm and partly cloudy, a good combination). However, extended heat can also lead to diminishing returns; by late May 21, some leaves might have been “overheating” a bit, evidenced by slightly softer or drooping leaves in the afternoon. This was a short-lived mini heatwave, though, and nights remained relatively cool (helping the tree recover each evening).
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Late Cold Spell (May 23–26): The pendulum swung quickly – by May 23 the weather was deteriorating, and May 24 was a notably cold, wet day. The tree’s response to this would be almost the opposite of its response to the heat. In cold rain, a tulip tree’s leaves may actually perk up (no heat stress at all), but the low temperature (~8–10 °C) drastically slows photosynthesis. Essentially, from the tree’s perspective, May 24–25 were something like an “enforced rest.” The leaves likely stayed fully hydrated and firm (plenty of water, low transpiration demand), but the tree probably made little sugar those days due to the lack of sun and cold. Growth (new tissue formation) would pause, since enzyme activity drops at those temperatures. Importantly, there was no frost, so the tree did not suffer structural damage – it was more a metabolic pause. Once skies cleared after the 26th, the tree could resume normal activity. One side effect of such weather could be leaf fungi or spots (cool and wet conditions can invite fungal pathogens). We might expect some superficial leaf spot diseases possibly starting to appear, though that’s speculative and would depend on pathogen presence. Another effect: prolonged wetness on leaves can leach some nutrients or cause minor chlorosis, but again, nothing severe for just a couple days of rain.
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End of May Transition: By May 27–31, the tree likely resumed active growth as temperatures normalized around 20 °C and sunshine returned. However, now a new factor came into play: with no rain after the 24th and warmer weather, the soil surface started to dry again. So late May and the turn into June would mark the beginning of the dry-down that could challenge the tree in early summer. At the very end of May, the tree still had plenty of water at root depth (soil moisture was still decent), so it wouldn’t yet feel drought stress. It would, however, start sensing increasing evaporative demand as the sun got stronger and the rainy pattern gave way to clear skies.
Physiological Implications: Throughout May, the tulip poplar was likely in a state of vigorous growth and high physiological performance. The periods of suboptimal temperature were short enough not to cause permanent issues. In fact, the relatively cool mean temperature of the month could have been beneficial – many temperate trees grow best under moderate warmth, and extreme early heat can sometimes force them into premature summer mode. By staying mostly cool and wet, May 2025 extended the “spring growth window” for the tree. It probably produced larger, healthier leaves due to ample water. Additionally, given tulip poplar’s low drought tolerance【69†L27-L30】, the avoidance of any drought conditions in spring meant the tree could fully foliate without having to shed any leaves or allocate resources to drought protection. The ample moisture would also support flowering and seed formation if the tree was of flowering age – tulip poplar flowers (if present) likely bloomed in late May, and the wet conditions would not have hindered them much (except possibly fewer insect pollinators flying on very rainy days). As mentioned, minor leaf fungal diseases are a risk in wet springs; if any, they would likely be minor leaf spots that wouldn’t significantly affect tree health this early.
The late-month weather whiplash introduced only mild stress: the hot days tested the tree’s transpirational capacity, and the cold days tested its temperature flexibility. In both cases, the tree’s inherent resilience carried it through. There might have been subtle signs by end of May – for instance, a keen observer might notice a few older leaves (those that first emerged in April) turning a bit yellow or developing spots due to the various stresses encountered (frost nip in April, perhaps heat or fungus in May). Tulip trees can shed some older leaves under stress (even as early as summer if drought hits). By end of May, though, it’s likely the canopy was intact and strong. The tree probably entered June with a full complement of healthy green leaves, a well-hydrated root zone, and a solid reserve of nutrients gathered during the wet spring.
Comparison to Historical Norms: Climatologically, May 2025 was unusual for being on the cool side and for its rainfall distribution. Many recent years have seen warmer Mays in Korea (with climate warming, spring is generally warming faster). A May that is nearly 2 °C below the 20th-century average bucks the trend – it could be partly due to a specific climate pattern (perhaps a persistent trough over the region). Interestingly, such variability reminds us that climate change doesn’t eliminate cool, wet months; it shifts odds. The tulip tree likely benefited from this cooler spring month, but this isn’t guaranteed every year. On the precipitation front, ~105 mm is not extreme for May (some historical Mays have seen even more if an early monsoon rain or lots of thunderstorms occur). But getting that via frequent small- to medium-size events is somewhat different from the historical pattern, which might have a drier early May and then one or two heavy events later. This 2025 pattern was more akin to an “extended spring rainy season.” In terms of climate impacts, one could argue that the lack of a pronounced drought or heatwave in spring 2025 is a fortunate deviation from some projections that suggest spring droughts might worsen under climate change. However, the flip side is the excess rainfall could portend other issues (like fungal outbreaks, as mentioned, or simply a shift in when the dry period occurs – possibly delaying it to early summer).
Another notable point is that globally, by spring 2025, El Niño conditions were emerging (assuming known climate context), which often bring wetter conditions to some parts of Asia. The net effect for our locale was a very lush spring. From a climate envelope perspective, nothing in May 2025 exceeded what L. tulipifera can handle – rather, it was mostly within the species’ favorable envelope. The late May heat (~27.5 °C) is still below the threshold of serious heat damage (which might happen >32 °C, especially if paired with drought). The plentiful moisture was certainly within the tree’s comfort zone (this species naturally occurs in moist bottomlands and is used to wet springs). If anything, May 2025 gave the tulip tree a climate better than “normal” for its growth – cooler and wetter than average, which for a water-demanding tree is a recipe for potentially above-average growth for that season.
By June 2025, the weather pattern in Hongcheon shifted significantly. The rains that frequented spring suddenly diminished, and temperatures climbed as summer approached. In the first half of June 2025 (through June 17), the tulip tree faced mounting environmental stress in the form of rising heat and drying soil. Essentially, the tree went from a well-watered spring into an early-summer dry spell that tested its drought tolerance. Here are the conditions characterizing early June:
- Air Temperature: Summer warmth arrived in earnest. Daytime highs regularly reached the mid-20s °C. For example, on June 8–9, highs were around 26–28 °C【47†L101-L107】, the warmest of the year so far. Even on other early June days, peak temperatures were commonly 23–26 °C. Nights became mild, generally 11–15 °C【47†L101-L107】, which is a clear shift from the cooler spring nights. The tree was now experiencing 24-hour mean temperatures near or above 18 °C (compared to single digits a month prior). Notably, no extreme heatwave (>30 °C) had hit yet in early June, but the trend was upward. The air was also getting drier on clear days – midday relative humidity dropped, contributing to higher vapor pressure deficits (around 2 kPa by early afternoon on hot days)【75†L0-L4】. In summary, early June’s air temps were around normal to slightly above normal for that time of year (the long-term average June high in that region is ~26 °C). The tree was entering the part of the year where heat stress can become a factor if moisture is limited.
- Precipitation: In stark contrast to May, virtually no rain fell in early June 2025. From June 1 to June 17 (our period of data/sensor coverage), total precipitation was on the order of 7–8 mm【46†L151-L159】 – and almost all of that came as a couple of very light showers. For instance, reanalysis shows ~2.5 mm on June 2 and a few sub-millimeter drizzles on scattered days (June 8 had ~1.65 mm, June 10 about 0.8 mm)【46†L151-L159】. These are negligible amounts in terms of soil moisture; effectively, the first half of June had no meaningful rainfall. Historically, June is the onset of East Asia’s monsoon in late June, but early June can vary – sometimes there are pre-monsoon showers, sometimes not. In 2025 it appears the monsoon was delayed or weak in the beginning, resulting in an anomalously dry early June. By mid-June, the region was teetering on drought conditions if rains did not arrive soon.
- Soil Temperature: With the hot weather and strong sun, soil temperatures climbed further. By June 9, the soil at 7 cm depth was nearly 20 °C【83†】. During the first half of June, soil temps likely ranged from ~15 °C (after cooler nights) up to 22 °C near the surface in afternoons. This is a warm soil environment, typical of early summer. Warm soils aid root metabolism up to a point; ~20 °C is generally good for nutrient uptake for temperate trees. However, warm soil also means higher microbial activity and potential for faster drying. There’s also a feedback: as soil dries, it can heat up even more (since dry soil has lower heat capacity). By mid-June, if the soil surface was drying out, daytime soil temperatures could spike higher, potentially creating hot, dry topsoil conditions unfavorable for fine roots near the surface.
- Soil Moisture: Perhaps the most critical change was the sharp decline in soil moisture. At the end of May, soil moisture was a healthy ~0.36 m³/m³【55†】. Without substantial rain, that number fell steadily each day of early June. By June 6–7, soil moisture dropped to ~0.27 m³/m³【56†L4-L8】. By June 11, it reached about 0.245 m³/m³【56†L4-L8】 – a dramatic loss of moisture in just two weeks. This indicates that the topsoil had dried to a relatively low level (roughly 24.5% volumetric water). For context, a value around 0.24 for a loamy soil could be approaching the wilting point for plants, depending on soil texture (sandy soils wilt sooner, clay can hold more at that content). The trend was clearly downward and fast. Plant water uptake (transpiration) and surface evaporation under hot conditions were depleting soil moisture, and nothing was replenishing it. If we extrapolate beyond June 11, by mid-to-late June the soil moisture would have dropped even further without rain – potentially into the low 0.20s or teens, which would be drought territory for many plants. So early June 2025 effectively marked the onset of a meteorological drought in the topsoil.
Roles of Variables: In early June, the variables conspired to induce water stress on the tree. The combination of high air temperature and low precipitation meant that atmospheric demand for water (evapotranspiration) was high, while supply (rain) was nil. Warm air holds more moisture and drives more evaporation; indeed, midday warmth and sun drove VPD to ~2.0 kPa on June 9【75†L0-L4】, which is a moderately high demand that would cause the tree to lose water rapidly through its leaves. At the same time, soil moisture was dwindling – as it fell below a certain threshold, the soil’s ability to supply water to roots diminishes (soil suction increases). Thus, by early June’s second week, the tulip tree likely faced a soil that could not keep up with the atmospheric pull. Soil temperature, being warm, was actually a minor positive factor in isolation (roots function well at those temps), but in context it may have accelerated microbial decomposition and soil drying. Air temperature beyond mid-20s starts to become less optimal for a tulip poplar, especially if humidity is lower. While the species can tolerate heat, it usually grows in climates where hot days are offset by abundant soil moisture (e.g., eastern US summers are often hot and wet). Here, hot days came with drying – a challenging combo. So, lack of rainfall was the linchpin variable leading to stress, with heat/sun amplifying the effect, and soil warmth simply part of the season’s progression that allowed the drying to penetrate deeply.
What Happened:
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Transition to Water Deficit: In the first week of June, the tulip tree likely did not immediately feel the lack of rain because soil moisture was still relatively high from May. However, each day without rain, especially those with strong sun, would have incrementally increased plant stress. By around June 5–7, as soil moisture dipped through the 0.30→0.28 range, the tree’s shallow feeder roots in the upper soil might have begun to sense dryness. Initially, the tree could compensate by drawing water from slightly deeper layers (assuming its roots reach deeper moist soil). But by June 10+, even deeper layers were drying. Observations on the tree might include: in the afternoons, the leaves could start to show a slight wilting or drooping (a common sign of water stress, where leaves lose turgor in peak heat). The tree might also have started to develop a slightly sparser canopy by shedding a few of the oldest leaves – tulip poplars sometimes drop some inner or lower leaves when drought-stressed, as a water-saving measure【68†L21-L24】. If this occurred, one would notice some yellowing leaves inside the canopy by mid-June.
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Stomatal Response and Growth Slowdown: By early June, the tulip poplar likely began closing its stomata earlier in the day to avoid excessive water loss. Vapor Pressure Deficit of ~2 kPa (as on June 9 afternoon) is enough to cause partial stomatal closure in many trees to conserve water. With stomata partially closed, carbon uptake (photosynthesis) slows. Thus, the growth rate of the tree likely decelerated in early June compared to the spring flush. The tree shifted from a resource-abundant, fast-growth mode to a conservative, maintenance mode: trying to hold onto water and not put on too much new leafy biomass that it can’t support. New shoot growth that was accelerating in May probably came nearly to a halt by mid-June due to water limitation.
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Physiological Stress Signs: Apart from wilting and leaf drop, the tree could have shown subtle stress indicators like higher leaf temperature (when stomata close, leaves can’t cool by evaporation as well, so they heat up – potentially leading to sunscald on very hot leaves). There might also be some leaf curling or marginal browning if drought persisted (by late June if no rain). We are only in early June so perhaps not yet severe, but the trajectory was toward more evident stress. Tulip trees have low drought tolerance and often are among the first trees to show flagging foliage during a dry spell【69†L27-L30】. Given the data, by June 11–17 this tree was probably just starting to visibly flag on the hottest, driest days (especially in the afternoon, leaves might lose their shine and droop).
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No Rainfall Events: It’s notable that, unlike earlier months, June (early) had no saving grace rainstorm. There was no period in early June where we can say “and then it rained and the tree got relief.” The only minor relief might be that on some days, sporadic clouds or a brief sprinkle occurred (e.g., June 2’s ~2.5 mm might have moistened the leaf surfaces and upper soil a tiny bit【46†L151-L159】). But such small amounts evaporate almost immediately in summer. Essentially, the tree was waiting for the monsoon – which typically arrives in late June in Korea. Until that came, conditions would worsen.
Physiological State of the Tulip Tree: By mid-June 2025, the tulip tree was likely under mild to moderate water stress. After a luxurious spring, it now had to tighten its belt. The tree’s internal water status (xylem pressure) would be dropping each day around noon, potentially approaching critical thresholds on the hottest days. Its growth had likely paused – rather than producing new leaves or extension growth, the tree was mostly maintaining its existing foliage. If soil moisture continued to fall, the tree might begin reallocating resources: increasing root growth relative to shoot growth (trying to reach deeper moisture) and producing osmoprotectants (chemicals to help retain water in cells). In terms of the climate envelope, the tree was now edging towards the drier end of conditions it can tolerate. Tulip poplars naturally occur in climates with around 1000–1200 mm annual precipitation and do not do well with extended drought【69†L27-L30】【68†L25-L33】. Early June 2025’s dryness was a warning sign that unless monsoon rains arrived, this tree could face significant drought stress or even damage (leaf loss, reduced growth rings, vulnerability to pests) as summer progressed.
However, one advantageous factor was that temperatures, while warm, were not extreme yet. Highs in the upper 20s are something the tree can physiologically handle if water is adequate. The real danger comes if extreme heat (>33 °C) coincides with drought – that was not yet the case by mid-June. Also, the tree had full reserves from the productive spring; entering a drought with a full canopy and good energy stores is better than doing so after a poor spring. In that sense, the wet spring gave the tree a buffer – it likely had developed a robust root system and filled its tissues with water and nutrients, buying it some time to withstand early summer drought.
Comparison to Historical Norms: Early June 2025 was drier than normal. Climatologically, June is one of the wettest months in South Korea due to the Changma (monsoon) typically starting around the last week of June. It’s not unprecedented to have a dry first half of June, but in this case the dryness was notable because it followed a dry late May period – effectively lengthening the spring drought. Historically, one might expect at least some convective thunderstorms in early June, but 2025 didn’t deliver much. This could be a manifestation of climate variability (perhaps a delayed monsoon onset or stronger high pressure suppressing rain). Some studies on Korean climate indicate spring droughts are a recurring issue and could worsen with climate change due to shifting precipitation timing【76†L25-L33】【76†L41-L48】. The severe drying from late May into mid-June 2025 is a small-scale example.
Temperature-wise, early June was around average historically, so no heat records or anomalies there. The stress on the tree came from the rainfall anomaly rather than a temperature anomaly. The long-term climate data we have (1940–2024) would show that June on average has high rainfall (~270+ mm total if the monsoon arrives normally). Only ~7 mm by mid-June 2025 is an anomaly. If June 2025 ended up with below-normal rain, that would fit a pattern of increasing year-to-year variability in monsoon rainfall that climate scientists have observed (stronger swings between drought and flood). The tulip tree’s experience thus reflects a possible trend: a wetter spring, followed by an abrupt onset of dry, hot summer conditions – a combination that can be challenging for plants. In terms of the climate envelope concept, by mid-June the tree was likely experiencing soil moisture levels outside the optimum range for the species (dipping toward drought stress territory), even though temperature remained within the tolerable range. It illustrates how exceeding the moisture dimension of a species’ climate envelope (i.e., too dry) can be just as limiting as exceeding the temperature dimension.
If we consider the rest of 2025 (beyond our data), one would anticipate that by late June or early July, monsoonal rains hopefully arrived, which would relieve the tree’s stress and provide a second wind for summer growth. The danger period was this interim. In any case, early June 2025 stands out as the first real climatic stress period of the year for the Hongcheon tulip tree, switching the narrative from spring abundance to early summer scarcity.
In the first half of 2025, the tulip tree in Hongcheon has endured a gamut of environmental conditions – from winter cold to spring frosts, from soaking rains to developing drought. The story of 2025 so far is one of climatic contrasts, and the tulip tree’s physiology has been pushed and pulled accordingly. Key takeaways and overarching patterns include:
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“Start-Stop” Spring Dynamics: The late winter (Feb) was extremely dry but cold enough to satisfy dormancy. Spring (Mar–Apr) then oscillated between unusually warm spells and abrupt cold snaps. This pattern caused the tree to initiate budburst and then slam on the brakes when frosts hit, a phenomenon reported elsewhere in 2025 for tulip poplars【66†L110-L118】. Such start-stop weather can lead to delayed or uneven leaf-out, and indeed the tree likely experienced a slight delay and some bud/leaflet loss from the late March and mid-April freezes. This illustrates a growing concern under climate change: warmer averages cause earlier budbreak, but if frosts still occur at the old dates, trees face greater frost damage risk【72†L81-L90】【72†L138-L146】. 2025 exemplified this, as a record-warm global March【76†L10-L18】 was followed by a normal cold snap – the mismatch stressed the tree at a sensitive time.
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Abundant Moisture and Growth in Late Spring: Despite temperature swings, the period from mid-April through May was highly favorable in terms of water availability and moderate temperatures. The tulip tree likely experienced one of its best spring growth seasons in recent memory. Soil moisture was replenished to field capacity multiple times, allowing the tree to maximize its growth potential. Any climatic warming effect (e.g., slightly higher spring temps than mid-20th century) may have been offset by the ample moisture, resulting in near-optimal conditions. The tree entered June with a full, healthy canopy and no cumulative water deficit – essentially, it was in prime condition thanks to the wet spring.
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Emerging Early Summer Drought and Heat Stress: As of June 17, 2025, the pendulum has swung towards hotter and drier conditions. The lack of rain in late May and early June created a soil moisture deficit at the very start of the summer season. While June’s temperatures were not extreme, the combination of moderate heat and drying soils has begun to push the tulip tree beyond its comfortable moisture range. By mid-June the tree was likely showing initial drought stress (wilting, slowed growth), indicating that its climate moisture envelope was being exceeded on the dry side. This raises concern because L. tulipifera is not drought-hardy【69†L27-L30】; prolonged drought would result in leaf shedding and reduced growth or even risk of mortality if severe enough. Climate models for Korea suggest that summer droughts could intensify under warming scenarios【76†L37-L43】 – an earlier onset of summer dryness as in 2025 might be a harbinger of that.
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Historical Trends and Anomalies: Comparing 2025 to the 1940–2024 climate baseline highlights a few points. First, temperatures in 2025 (Feb through May) were generally at or above the 20th-century norms, consistent with long-term warming trends. March and April were ~0.5–1 °C warmer than mid-century averages, while May was cooler than recent decades but still roughly on par with mid-20th-century values (the cool May might be seen as a random anomaly rather than a trend). This fits the broader pattern of climate change: higher average temperatures but still significant interannual variability. Precipitation in early 2025 deviated from norms in its distribution: an extremely dry winter (Feb) followed by near-normal total spring rain (Mar–Apr) concentrated in big storms, then an above-normal wet May, and finally an abruptly dry June start. Long-term data suggest that winter precipitation in this region has always been low, but the near-zero February was an outlier. Spring rainfall totals were not unusual, but the heavy events in April (two ~25 mm+ days) could indicate increased precipitation intensity. May’s frequent rains deviated from the usual pattern (which might have fewer rain days but possibly one or two heavier events). Early June’s dryness was a notable anomaly given that some rainfall is expected even before monsoon proper. Such variability – swings from very wet to very dry – is projected to increase with climate change, as a warmer atmosphere can lead to more intense rain events and also longer dry spells between them. 2025 seems to embody this “feast-or-famine” precipitation pattern.
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Climate Envelope Exceedance Moments: Throughout Feb–Jun 2025, there were times when conditions edged beyond what a tulip tree typically experiences in its native, historical climate:
- Cold/Dormancy: The absolute cold in winter (-12 °C) was well within tolerance (no exceedance there, as the species is frost hardy【66†L53-L61】). However, one could argue the lack of insulating snow (due to the dry winter) exposed the tree’s roots to colder soil temperatures than normal. In native habitats, consistent snow cover can mitigate soil freezing – Hongcheon’s snow cover was minimal until March, possibly a stress for shallow roots.
- Spring Frost After Warming: Late March’s freeze following warmth was a clear exceedance in terms of phenological safety – it created frost exposure to dehardened buds, a scenario outside the ideal climate envelope (in an ideal case, last frost occurs before budbreak). This likely led to some tissue damage and is exactly the risk that increases with warming springs【72†L138-L146】.
- Heat and VPD in Late Spring: The brief 27.5 °C day in May with ~1.4–1.5 kPa VPD was not extreme, but it nudged into the higher end of comfort for a mesic tree. The tree handled it, but any hotter or drier and we’d see envelope exceedance on the hot side (e.g., if an early heatwave of 33 °C occurred, that would be well outside spring norms and likely quite damaging – thankfully 2025 avoided this).
- Early Summer Drought: By mid-June, soil moisture in top layers dropped below what tulip poplar typically experiences in its preferred habitats (they prefer moist, well-drained soils and can tolerate short dry spells but not sustained drought【69†L23-L30】). The tree was starting to operate outside its hydrological comfort zone. If rains had not returned by late June, the drought envelope would be fully exceeded – potentially leading to partial canopy loss (an adaptive mechanism but also a sign of climatic stress).
In essence, the tree’s climate envelope was challenged in spring by phenological timing issues (frost after warmth) and in early summer by hydrological stress (drought). Both of these challenges are in line with what climate change science predicts: increased late frost risk and more pronounced drought periods【72†L131-L139】【76†L37-L43】.
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Resilience and Outlook: Despite the challenges, this tulip tree likely proved quite resilient through June 2025. It leveraged the good conditions to fortify itself (full leaf-out, strong spring growth), which gave it some buffer to withstand early summer stress. If we project forward, the monsoon rains that typically arrive in late June or early July would be critical. A timely monsoon onset in late June 2025 would drench the soils (perhaps delivering 100+ mm in late June and July) and alleviate the tree’s water stress, allowing a second flush of summer growth and recovery of any mid-June lost turgor. On the other hand, if 2025’s monsoon were erratic or deficient, the tree could face a tough summer with increasing stress (possibly leading to early leaf drop or reduced growth ring width for 2025). Climate data hints that by July 2025, an El Niño had developed, which often brings heavier rains to Korea – so one might expect that relief did come (this is speculative without the data, but a reasonable hypothesis).
In summary, 2025 so far has been a rollercoaster for climate conditions, and the tulip tree in Hongcheon has navigated this rollercoaster with a combination of vulnerability and adaptability. It benefitted greatly from the wet, mild periods (showing optimal growth), yet also faced periods of climatic stress (frosts and drought) that tested its limits. This half-year narrative highlights how a changing climate can manifest as more extreme and erratic swings, rather than just a smooth trend. For a species like Liriodendron tulipifera, which thrives in stable, moist temperate conditions, such swings can mean periods where the climate temporarily moves outside the species’ historical envelope, with potential long-term consequences for health and distribution. Continued monitoring through summer and fall 2025 would reveal whether the tree fully bounces back with monsoon rains or if the early drought leaves a lasting mark. So far, the tulip tree has shown itself to be a bellwether of climate impacts – flourishing when conditions align with its needs, and visibly struggling when they don’t, thereby telling a detailed climate story through its physiological responses.
Overall, the first half of 2025 in Hongcheon has underscored the critical importance of variable coupling of factors – it’s not temperature or rainfall alone, but their timing and combination that create events (growth spurts, freezes, droughts) that define the tree’s experience【67†L96-L100】. By correlating these variables rather than viewing them in isolation, we see clearly how an exceptionally dry cold February, a whipsaw spring, and an early summer drought each played a part in the tulip tree’s life, with each phase carrying implications rooted in decades of climate data and centuries of species adaptation.
Sources:
- Climate data (sensor and ERA5 reanalysis) for Hongcheon, SK, Feb–Jun 2025【27†L0-L8】【30†L25-L30】【35†L107-L112】【46†L151-L159】【49†】【50†】 etc. (in-text citations above).
- Purdue Landscape Report on 2025 delayed budbreak due to start-stop spring weather【66†L110-L118】【66†L79-L87】.
- Climate Central analysis of late March 2025 heat and drought in Korea【77†L71-L79】【77†L105-L113】.
- Nature Communications study on increased late spring frost risk with climate warming【72†L81-L90】【72†L138-L146】.
- Tulip poplar species information on temperature and moisture preferences (Greg care guide and ACT government fact sheet)【67†L45-L53】【69†L27-L30】.