Inter-Individual Budburst Variation in Fagus sylvatica Is Driven by Warming Rate

Phenological response of European beech (Fagus sylvatica L.) to climate change in the Western Carpathian climatic-geographical zones

Introduction

The paper analyzes the results of 26 years (1996-2021) of phenological observations of the vegetative organs of European beech (Fagus sylvatica L.) in the Western Carpathians. It evaluates the influence of the heterogeneity of this territory, including relief and elevation, based on climatic-geographical types.

Methods

Phenological stages, including leaf unfolding, full leaves, leaf coloring, and leaf fall, were monitored at 40 phenological stations across eight elevation zones. The study assesses trends in the occurrence of phenological stages, the length of the growing season, and phenological elevation gradients.

Results

The results indicate a statistically significant earlier onset of spring phenological phases and delay in autumn phases, resulting in an average extension of the beech growing season by 12 days. Our findings confirm that the lengthening of the growing season due to warming, as an expression of climate change, is predominantly attributed to the warming in the spring months. The detected delayed onset of autumn phenophases was not due to warming in the autumn months, but other environmental factors influence it. The trend of elongation of the growing season (p<0.01) is observed in all elevation zones, with a less significant trend observed only in zones around 400 and 600 m a.s.l, signaling changes in environmental conditions across most of the elevation spectrum. Moreover, the heterogeneity of climatic-geographical types within each elevation zone increases the variability in the duration of the growing season for sites with similar elevations. By extending the growing season, it is assumed that the beech area will be changed to locations with optimal environmental conditions, especially in terms of adverse climatic events (late spring frosts, drought) during the growing season. The phenological elevation gradients reveal an earlier onset of 2.2 days per 100 m for spring phenophases and a delay of 1.1-2.9 days per 100 m for autumn phenophases.

Discussion

These findings highlight the specific environmental conditions of European beech in the Western Carpathians and their potential for anticipating changes in its original area. Additionally, these observations can aid in forecasting the further development of phenological manifestations related to climate change.

Late autumn warming can both delay and advance spring budburst through contrasting effects on bud dormancy depth in Fagus sylvatica L

The current state of knowledge on bud dormancy is limited. However, expanding such knowledge is crucial in order to properly model forest responses and feedback to future climate. Recent studies have shown that warming can decrease chilling accumulation and increase dormancy depth, thereby inducing delayed budburst in European beech (Fagus sylvatica L). Whether fall warming can advance spring phenology is unclear. To investigate the effect of warming on endodormancy of deciduous trees, we tested the impact of mild elevated temperature (+2.5-3.5 °C; temperature, on average, kept at 10 °C) in mid and late autumn on the bud dormancy depth and spring phenology of beech. We studied saplings by inducing periods of warming in greenhouses over a 2-year period. Even though warming reduced chilling accumulation in both years, we observed that the response of dormancy depth and spring budburst were year-specific. We found that warming during endodormancy peak could decrease the bud dormancy depth and therefore advance spring budburst. This effect appears to be modulated by factors such as the date of senescence onset and forcing intensity during endodormancy. Results from this study suggest that not only chilling but also forcing controls bud development during endodormancy and that extra forcing in autumn can offset reduced chilling.

How consistently do species leaf-out or flower in the same order? Understanding the factors that shape this characteristic of plant communities

Plant species are frequently reported to undergo leaf-out and flowering in a consistent order from 1 year to the next; however, only a limited number of these findings arise from studies encompassing many species or sites. Here, we evaluate the consistency in the order species leafed out in the northeastern United States using observations contributed to the USA National Phenology Network's Nature's Notebook platform. We repeated this analysis for flowering, evaluating a total of 132 species across 84 sites. We documented a relatively high degree of consistency in the order of both events among individual plants, with higher consistency in flowering. A small number of species pairs exhibited very high consistency in phenological order across several sites. The majority of species pairs exhibited variability in how consistently they underwent either leaf-out or flowering from site to site, which could be the result of either plastic or locally adaptive responses. Our investigation revealed that neither functional type nor seasonal position played a major role in shaping how consistently species leafed out or flowered in the same order. Instead, we found the number of days separating the events and interannual variability in timing to be the most influential factors driving the consistency in ordering.

Temperature sensitivity of leaf flushing in 12 common woody species in eastern China

Leaf phenology is one of the most reliable indicators of global warming in temperate regions because it is highly sensitive to temperatures. Temperature sensitivity (S_T) is defined as the values of changed days of leaf flushing date (LUD) per degree increase in temperatures. Climate warming substantially advanced LUD in the temperate region, but its effect on S_T of LUD is still not clear. We used spring phenological records of 12 woody plants in eastern China in the years of 1983-2014 to explore temporal and spatial changes of LUD and S_T. Furthermore, we compared the difference of S_T and preseason temperatures in two periods (1983-1997 and 2000-2014), and explored the main factors regulating S_T. The results showed that the average LUD significantly advanced (-2.7 days per decade). The mean LUD over the period 1983-2014 was in day of the year (DOY) 87 ± 7 across sites and species for the early leaf flushing species (EFS), and mean DOY 102 ± 5 for the late leaf flushing species (LFS). LUD was earlier in low latitude than that in high latitude. S_T of Armeniaca vulgaris was the most sensitive to temperature across all sites (-3.66 d °C^-1), while Firmiana simplex was the most insensitive (-2.37 d °C^-1). LUD of EFS was more sensitive to temperature warming than that of LFS. At the same site, LUD of EFS would advance more obviously than that of LFS under global warming. For all species, S_T decreased significantly with shorter preseason length and warmer temperatures at the preseason end. Our results had demonstrated a strong relationship between S_T and the preseason length (mean temperature at the preseason end).