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An example of decrease in drought resistance with increase in drought severity A tree-ring site (32.43°N, 110.79°W, Ponderosa pine) in Arizona, USA presents a decrease in drought resistance with increase in drought severity during three periods (i.e. 1950-1969, 1970-1989, and 1990-2009). The name of the tree-ring site is az598 in the ITRDB tree-ring database. Blue bars (upper panel) denote the mean drought severity during each period and orange bars (lower panel) denote the mean resistance during each period. Arrows show the directions of changes in drought severity (blue) and resistance (orange) over time.
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The frequency and intensity of droughts have increased over the decades, leading to increased forest decline. The response of forest to drought can be evaluated by both its sensitivity to drought (resistance) and its post-drought recovery rate (resilience). However, it remains uncertain how drought resistance and resilience of forests change over t...
Citations
... At the same time, the NDVI and NPP of vegetation increased based on satellite data and numerical models [33,34]. Furthermore, the responses of vegetation to drought changes presented various instances of spatial heterogeneity in the TP, which varies with the different vegetation types in different regions [14,[35][36][37][38][39]. For instance, Wang et al. [40] and Wang et al. [41] found enhanced drought caused the vegetation degradation in the southern and western regions, while Fang and Zhang [42] observed a negative impact of drought on vegetation in the southeastern areas. ...
The Tibetan Plateau (TP) is a climate-sensitive and ecologically fragile area. Studying drought and its effects on vegetation over the TP is of great significance for ecological conservation. However, there were large uncertainties in previous studies on the drought characteristics and their impacts on alpine vegetation in this region. This study explored the drought changes and their impacts on alpine vegetation during the growing season over the TP in 1982–2018. The results showed that the TP has experienced a wetting trend in most regions of the TP. Correspondingly, the vegetation has become greener in most areas. The wetting and drying trend in the growing season changed around 1995. Before 1995, the TP experienced an overall drying trend with a spatial pattern of a drying trend in the northern regions and a wetting trend in the southern regions, while it showed an overall wetting trend after 1995, with a reversed spatial pattern to that before 1995. After 1995, wetting and drying trends affected the vegetation in 61% of the TP. However, before 1995, the NDVI presented an increasing trend in most areas of the TP under a drying trend. Therefore, a drying trend was not the primary factor affecting vegetation growth in this period. Instead, changes in the cryosphere induced by warming could be the main factor. In addition, the distribution of vegetation across the TP was primarily influenced by drought intensity, which had the greatest impact on sparse vegetation, followed by meadow and grassland. This study enhances our understanding of the impact of drought changes on alpine vegetation on the TP.
... For example, Wang et al., (2022) found that species with higher specific leaf area (SLA) and leaf nitrogen concentration (LN) (i.e., fast-growing strategies) have higher growth variability. Recent studies showed that functional traits significantly influence tree growth response to climate change at both short-term and long-term scales (Li et al., 2020;Serra-Maluquer et al., 2022;Wang et al., 2022), and that species with higher wood density (WD) have stronger drought sensitivity. Moreover, different functional groups (e.g., needleleaf vs. broadleaf, and evergreen vs. deciduous tree species) can also reveal rather different radial growth responses to climate change, even under a same climate (Cahoon et al., 2018;Wang et al., 2022). ...
... For each variable retained in the model, the result of Chi-square test (Type III ANOVA) was reported. DN and EN, plots with deciduous and evergreen needleleaf species, respectively; For abbreviations see Table 2. evergreen coniferous species generally adopt conservative strategy, which allows them to be highly resistant to climate stress (Li et al., 2020;Song et al., 2021), resulting in lower growth spatiotemporal variability. However, other studies have reported that species with conservative (i. ...
... Ecological resilience examines the ability of an ecosystem to absorb large disturbances without shifting to a different domain of attraction in structure or functioning, while engineering resilience examines the departure and return of an ecosystem to its reference state after small disturbances (1)(2)(3). Engineering resilience is often employed to quantify the short-term responses of vegetation to climate extremes (4)(5)(6)(7), and the concept requires quantifying both the concurrent vegetation response, i.e. during the disturbance, and the delayed response, i.e. after the disturbance (2,8). Many metrics have been established for both types of responses. ...
... The differences between Evergreen Forest and the other land cover groups may be because in the southeastern United States, the evergreen forest species were mainly gymnosperms (loblolly and short leaf pines) (68). Gymnosperms have more conservative water use strategy that made them less sensitive to drought than angiosperms (7). Given the important role of moisture (Moisture and temperature controls on the urban-rural differences in resilience metrics section), the same mechanisms might have caused the gymnosperms to be less sensitive to hot months, and thus exhibit similar or even lower magnitudes of resilience than the urban vegetation (Figs. ...
With continuing global warming and urbanization, it is increasingly important to understand the resilience of urban vegetation to extreme high temperatures, but few studies have examined urban vegetation at large scale or both concurrent and delayed responses. In this study, we performed an urban-rural comparison using the Enhanced Vegetation Index and months that exceed the historical 90th percentile in mean temperature (referred to as “hot months”) across 85 major cities in the contiguous U.S. We found that hot months initially enhanced vegetation greenness but could cause a decline afterwards, especially for persistent (≥ 4 months) and intense (≥ +2°C) episodes in summer. The urban responses were more positive than rural in the western U.S. or in winter, but more negative during spring-autumn in the eastern U.S. The east-west difference can be attributed to the higher optimal growth temperatures and lower water stress levels of the western urban vegetation than the rural. The urban responses also had smaller magnitudes than the rural responses, especially in deciduous forest biomes, and least in evergreen forest biomes. Within each biome, analysis at 1km pixel level showed that impervious fraction and vegetation cover, local urban heat island intensity, and water stress were the key drivers of urban-rural differences. These findings advance our understanding of how prolonged exposure to warm extremes, particularly within urban environments, affects vegetation greenness and vitality. Urban planners and ecosystem managers should prioritize the long and intense events and the key drivers in fostering urban vegetation resilience to heat waves.
... The BRT model is an ML method that effectively connects environmental variables with monthly scale NEE data. It can capture physically complex and nonlinear relationships as well as interactions among variables (Kong et al., 2022;Li et al., 2020). This advantage makes it particularly suitable for quantifying the contribution of predicted variables to monthly NEE. ...
Upscaling flux tower measurements based on machine learning (ML) algorithms is an essential approach for large‐scale net ecosystem CO2 exchange (NEE) estimation, but existing ML upscaling methods face some challenges, particularly in capturing NEE interannual variations (IAVs) that may relate to lagged effects. With the capacity to characterize temporal memory effects, the Long Short‐Term Memory (LSTM) networks are expected to help solve this problem. Here we explored the potential of LSTM for predicting NEE across various ecosystems using flux tower data over 82 sites in North America. The LSTM model with differentiated plant function types (PFTs) demonstrates the capability to explain 79.19% (R² = 0.79) of the monthly variations in NEE within the testing set, with RMSE and Mean Absolute Error values of 0.89 and 0.57 g C m⁻² d⁻¹ respectively (r = 0.89, p < 0.001). Moreover, the LSTM model performed robustly in predicting cross‐site variability, with 67.19% of the sites that can be predicted by both LSTM models with and without distinguished PFTs showing improved predictive ability. Most importantly, the IAV of predicted NEE highly correlated with that in flux observations (r = 0.81, p < 0.001), clearly outperforming that by the random forest model (r = −0.21, p = 0.011). Among all nine PFTs, solar‐induced chlorophyll fluorescence, downward shortwave radiation, and leaf area index are the most important variables for explaining NEE variations, collectively accounting for approximately 54.01% in total. This study highlights the great potential of LSTM for improving carbon flux upscaling with multi‐source remote sensing data.
... Consequently, gymnosperms are now exhibiting greater mortality and more severe reduction in growth. 45 Trade-offs related to resilience are also well-documented by the fast-slow lifestyle continuum across species, an empirical pattern of interspecific differences in either physiological responses, such as metabolic rate or stress reactivity, or demographically, via vital rates and offspring size. 46,47 For example, Capdevila et al. ...
There is increasing interest in applying resilience concepts at different scales of biological organization to address major interdisciplinary challenges from cancer to climate change. It is unclear, however, whether resilience can be a unifying concept consistently applied across the breadth of the biological sciences, or whether there is limited capacity for integration. In this review, we draw on literature from molecular biology to community ecology to ascertain commonalities and shortcomings in how resilience is measured and interpreted. Resilience is studied at all levels of biological organization, although the term is often not used. There is a suite of resilience mechanisms conserved across biological scales, and there are tradeoffs that affect resilience. Resilience is conceptually useful to help diverse researchers think about how biological systems respond to perturbations, but we need a richer lexicon to describe the diversity of perturbations, and we lack widely applicable metrics of resilience.
... For example, species with lower P50 (water potential at 50% loss of conductivity) and higher HSM (hydraulic safety margin) are more droughttolerant and are generally associated with low drought-induced mortality (Serra-Maluquer et al., 2022). Recent studies showed that functional traits can regulate tree growth responses to climate change at both short-and long-term scales, and that species displaying stronger growth-drought sensitivity episodes tended to have higher wood density (WD) (Li et al., 2020;Serra-Maluquer et al., 2022). Meanwhile, traits of different plant organs (e.g. ...
... Tree-ring data provide long-term records of radial growth and are widely used to study forest dynamics in response to climate change (Li et al., 2020). Here, we focus on conifers as they are important components of many temperate and boreal forests. ...
... org) (Kattge et al., 2020), and mean trait values of the species were calculated and used in data analysis. For stand factors, the stand age of each chronology was calculated as the mean age for all tree rings used to build the chronology, and tree age of each tree-ring series was estimated as the number of rings (Li et al., 2020). The ITRDB data set did not provide the stand height data, and the canopy height for each site was extracted from a global canopy height map with the geographic coordinates of each chronology. ...
Temporal growth variability is an important indicator of ecosystem function under climate change. However, we still lack a unified understanding of how climate conditions, climate change (trends and variability), nitrogen (N) deposition, functional traits and stand factors together affect radial growth variability.
Using global conifer tree‐ring records (123 species from 1780 sites) during 1970–2010 to calculate growth variability, we assessed how abiotic and stand factors affect growth variability directly and indirectly via functional traits with boosted regression tree and structural equation models, and examined the differences among continents (North America, Asia and Europe).
We found: (a) growth variability was mainly affected by warm‐induced drought and increased at lower latitudes. Climate warming in winter could decrease growth variability, but this effect is by far not enough to offset the threat of hotter drought; (b) there existed a trade‐off between fast‐ and slow‐growing (drought tolerance) strategies for global conifer species, and abiotic and stand factors affected growth variability via functional traits. Contrary to common conjecture, species with higher drought tolerance revealed higher growth variability due to their occupation of more xeric sites, and may also because higher investment in drought tolerance leads to less investment remaining for growth; (c) older trees revealed higher growth variability due to their more conservative growth strategy, while at large scales, taller trees showed lower growth variability due to occupying more productive sites; and (d) moderate N deposition could reduce growth variability by leading conifers to adopt a more fast‐growing strategy (e.g. in Asia), but long‐term and excessive N deposition led to increased growth variability (e.g. in North America and Europe).
Synthesis . Our results suggest that coniferous forests in water‐limited regions should be more vulnerable to hotter drought, and the ‘fast–slow’ growth strategies may be key in regulating the effects of various abiotic and stand factors on ecosystem stability. Moreover, future hotter drought and N deposition will severely threaten conifer growth, especially for old trees and conifers at lower latitudes.
... The differential drought sensitivities between gymnosperms and angiosperms had been explored, but the conclusions were controversial. For instance, Li et al. (2020) suggested that the growth of gymnosperms was more resistant to drought than that of angiosperms, with other evidence showing wider hydraulic safety margins in gymnosperms than angiosperms (Choat et al., 2012). In contrast, Anderegg et al. (2020) demonstrated that gymnosperms were more vulnerable to multiple droughts than angiosperms. ...
Divergent responses of plant biomass to drought were found across hundreds of manipulative experiments. While many researchers have explored the influences of plant functional types (PFTs) and climatic conditions, few focus on the importance of evolutionary history. Here we compiled a global dataset of the responses of plant biomass and biomass allocation to the experimental drought from 281 studies conducted on 329 wild species and conducted both traditional and phylogenetic meta-analyses to explore the potential role of evolutionary history in affecting the differences among PFTs and the regulation effects of environmental conditions. We found that there were no consistent differences in biomass responses to drought between gymnosperm and angiosperm woody plants when the traditional meta-analysis was applied. Taking the phylogenetic information (the proxy of evolutionary history) into account resulted in more sensitive responses in gymnosperms than angiosperms but with great uncertainty, probably due to the high hydraulic diversity in both groups. The observed higher drought sensitivity in evergreen gymnosperms than deciduous ones, and in C3 herbs than in C4 ones were mainly derived from the phylogenetic relatedness among species. The influences of drought intensity were prevalent in both traditional and phylogenetic meta-analyses. These results highlight the vital role of plant evolutionary history played in affecting plant responses to drought. Given the potentially complicated interactions of climatic change and evolutionary history, we call for experiments that aim to investigate the role of phylogenetic relatedness on plant and ecosystem functions in future studies.
... SPEI-6) for classifying ECEs because the maximum correlation of SPEI-ANPP appeared at SPEI-6 ( Figure S2). The thresholds for ECEs were derived using the tenth percentile method Li et al., 2020) based on the historical SPEI-6 distribution (i.e. past 40 or 60 years in our study) at each weather station ( Figure S3). ...
Aim
Chronic directional climate changes in temperature and precipitation are predicted to increase the frequency of extreme climatic events (ECEs); however, their co‐occurring effects on the temporal stability of community productivity (i.e. ANPP stability) are still unclear. Here, we evaluate whether the increased frequency of ECEs reduces ANPP stability, and how it modulates the effects of chronic directional climate factors on ANPP stability in natural grassland.
Location
Twenty‐two sites in Asia and 14 sites in North America.
Time period
1980s–2010s.
Major taxa studied
Herbaceous plant.
Methods
We collected 36 long‐term observational and consecutive ANPP data (at least 10 years) and resampled yearly ANPP via a consecutive resampling method of nested time windows for each field. We used linear mixed‐effect models, partial regression analysis and structure equation models to explore the interactive effects of three climatic factors on ANPP stability and their associated intermediate processes of sensitivity, asymmetry, resistance and resilience.
Results
The increased frequency of ECEs was observed within the long‐term rising temperature and elevating precipitation trend across sites in the past several decades. Elevating precipitation rather than rising temperature was the primary driver influencing ANPP stability. Elevating precipitation increased ANPP stability through increasing mean ANPP and decreasing the standard deviation (i.e. SD) of ANPP due to a decrease in sensitivity of ANPP to precipitation. The increased frequency of ECEs decreased ANPP stability mainly by increasing the SD of ANPP, and it reduced the positive effect of elevated precipitation on ANPP stability via a decrease in resilience.
Main conclusion
Our results demonstrated that recurrent and discrete ECEs had cumulatively negative effects on ANPP stability, and the decreased resilience was identified as the primary factor reducing the grassland community stability under long‐term climate change. This highlighted the potential risks of increased frequency of ECEs for grassland ecosystem functions.
... Woody plants may be able to sustain aerobic respiration and water absorption via adventitious roots or aerenchyma induced by auxin and ethylene signals [92,93,94]. An example of a tree species that can withstand flooding is Larix laricina. ...
Abiotic stressors may have intricate and varied impacts on the growth and development of forest trees. This article provides a comprehensive summary of the effects of abiotic stressors, such as flood, drought, severe temperature, salt, heavy metal, combination stresses, and microplastics, on the morphological, physiological, and anatomical features of woody plants. The focus is particularly on evaluating these effects from the viewpoint of the xylem. During abiotic stress, the ability of xylem to transport water declines, which is linked to the control of leaf stomata and the suppression of aquaporin (AQP) function. Concurrently, woody plants maintain control over the dimensions and structure of their roots and leaves in order to achieve a harmonious equilibrium between water intake and evaporation. The anatomical characteristics are modified as well, including increased density of leaf stomata, smaller conduits, and thicker cell walls. Furthermore, various types of stressors elicit distinct responses in plants. For instance, flooding leads to the development of adventitious roots and aeration tissues, while forest fires cause irreparable damage to the xylem. Low temperatures result in tissue freezing, salt stress hinders ion absorption, and exposure to heavy metals induces biological toxicity. Woody plants' growth may be periodically enhanced in conditions of drought, floods, and exposure to heavy metals. The impact of combined stress on the physiological, morphological, and anatomical characteristics of woody plants is not only cumulative. The underlying mechanism behind this phenomenon requires additional investigation, particularly in natural or near-natural environments.
... However, they ignored forest sustainability under multiple and interactive disturbances in the dynamic process, which was mainly due to the lack of a dynamic comprehensive evaluation system of forest sustainability under temporal dynamic disturbances (Anderegg et al., 2020;Wingfield et al., 2015). Although a few studies have discussed the changes in forest resistance and resilience over time under dynamic changes in drought disturbance (Forzieri et al., 2022;Tao et al., 2022), most have focused on the trade-off relationship between resistance and resilience and the comparison of differences among forest structures (Gazol et al., 2018;Haberstroh & Werner, 2022;Li et al., 2020). ...
