Tree Growth In Forests Research Articles

Phosphorus limitation promotes soil carbon storage in a boreal forest exposed to long‐term nitrogen fertilization

AbstractForests play a crucial role in global carbon cycling by absorbing and storing significant amounts of atmospheric carbon dioxide. Although boreal forests contribute to approximately 45% of the total forest carbon sink, tree growth and soil carbon sequestration are constrained by nutrient availability. Here, we examine if long‐term nutrient input enhances tree productivity and whether this leads to carbon storage or whether stimulated microbial decomposition of organic matter limits soil carbon accumulation. Over six decades, nitrogen, phosphorus, and calcium were supplied to a Pinus sylvestris‐dominated boreal forest. We found that nitrogen fertilization alone or together with calcium and/or phosphorus increased tree biomass production by 50% and soil carbon sequestration by 65% compared to unfertilized plots. However, the nonlinear relationship observed between tree productivity and soil carbon stock across treatments suggests microbial regulation. When phosphorus was co‐applied with nitrogen, it acidified the soil, increased fungal biomass, altered microbial community composition, and enhanced biopolymer degradation capabilities. While no evidence of competition between ectomycorrhizal and saprotrophic fungi has been observed, key functional groups with the potential to reduce carbon stocks were identified. In contrast, when nitrogen was added without phosphorus, it increased soil carbon sequestration because microbial activity was likely limited by phosphorus availability. In conclusion, the addition of nitrogen to boreal forests may contribute to global warming mitigation, but this effect is context dependent.

Hydraulic conductivity regulates tree growth and drought resistance in semi-arid mixed forests of northern China

With the intensification of climate warming, drought has become increasingly severe. Drought seriously impacts tree growth and may even result in tree mortality. However, our understanding of how the hydraulic structure of xylem in different tree species regulates growth and drought resistance remains incomplete. Here, we collected tree-ring samples from three semi-arid natural Chinese pine (Pinus tabuliformis)-broadleaf mixed forests in northern China. We selected Chinese pine (non-porous wood), white birch (Betula platyphylla, diffuse-porous wood), and Liaodong oak (Quercus liaotungensis, ring-porous wood) as target tree species. Using dendrochronology and wood anatomy methods, we evaluated interspecies differences in tree growth, climate sensitivity, and drought resistance, and analyzed the relationships between tree growth, drought resistance, and theoretical xylem-specific hydraulic conductivity (Ks). Our findings revealed distinct differences in the hydraulic structure of xylem among these three tree species as well as their resilience to drought. Liaodong oak exhibited less sensitive to drought compared to Chinese pine and white birch. Meanwhile both Chinese pine and Liaodong oak demonstrated greater resistance to drought than white birch. The positive correlation between specific xylem hydraulic conductivity and both tree growth and drought resistance were observed for Chinese pine, but Liaodong oak was the opposite. This suggested that specific hydraulic conductivity of xylem cannot serve as a consistent or robust predictor of tree growth or drought resistance across different species. As climate warming intensifies, it is anticipated that white birch may experience severe and significant irreversible decline in growth, while Liaodong oak may exhibit the highest potential growth performance. Given the projected intensification of future warming trends along with more frequent extreme climate events, safeguarding biodiversity and productivity within semi-arid Chinese pine-broadleaf mixed forests may hinge on the prioritizing protection efforts for Chinese pine.

Trading off nature for nature‐based solutions: The bioeconomics of forest management for wildlife, timber, and carbon

AbstractNature‐based solutions are attracting interest for their potential to enlist ecological processes as cost‐effective and safe ways to capture and store carbon in forest ecosystems. Such solutions often need to be implemented in landscapes in which there are longer established values for other ecosystem services including wildlife and timber production. Here we develop an integrative model that illustrates the inherent trade‐offs that will arise among the competing values for landscape space and how to resolve them. The analysis characterizes boreal forest ecosystem dynamics involving interactions among the main trophic compartments of an intact boreal ecosystem, aka “nature.” The model accounts for carbon accumulation via biomass growth of forest trees (timber), carbon loss due to controls from moose herbivory that varies with moose population density (hunting), and soil carbon inputs and release, which together determine the carbon sink strength of the ecosystem. We link the ecological dynamics with an economic analysis by assigning a price to carbon stored within the intact boreal forest ecosystem. We then weigh these carbon impacts against the economic benefits of timber production and hunting across a range of moose population densities. Combined, this carbon‐bioeconomic program calculates the total ecosystem benefit of a modeled boreal forest system, providing a framework for examining how different forest harvest and moose densities influence the achievement of carbon storage targets, under different levels of carbon pricing. The analysis shows that promoting nature‐based solutions merely for carbon storage may result in loss of a key part of “nature” via loss of the trophic structure and key functional controls in the ecosystem.

Neighborhood Diversity Promotes Tree Growth in a Secondary Forest: The Interplay of Intraspecific Competition, Interspecific Competition, and Spatial Scale.

Understanding the biodiversity-productivity relationship (BPR) is crucial for biodiversity conservation and ecosystem management. While it is known that diversity enhances forest productivity, the underlying mechanisms at the local neighborhood level remain poorly understood. We established a 9.6 ha dynamic forest plot to study how neighborhood diversity, intraspecific competition, and interspecific competition influence tree growth across spatial scales using linear mixed-effects models. Our analysis reveals a significant positive correlation between neighborhood species richness (NSR) and relative growth rate (RGR). Notably, intraspecific competition, measured by conspecific neighborhood density and resource competition, negatively impacts RGR at finer scales, indicating intense competition among conspecifics for limited resources. In contrast, interspecific competition, measured by heterospecific density and resource competition, has a negligible impact on RGR. The relative importance of diversity and intra/interspecific competition in influencing tree growth varies with scale. At fine scales, intraspecific competition dominates negatively, while at larger scales, the positive effect of NSR on RGR increases, contributing to a positive BPR. These findings highlight the intricate interplay between local interactions and spatial scale in modulating tree growth, emphasizing the importance of considering biotic interactions and spatial variability in studying BPR.

Impact of extreme pre-monsoon drought on xylogenesis and intra-annual radial increments of two tree species in a tropical montane evergreen broad-leaved forest, southwest China.

Tropical montane evergreen broad-leaved forests cover the majority of forest areas and have high carbon storage in Xishuangbanna, southwest China. However, stem radial growth dynamics and their correlations with climate factors have never been analyzed in this forest type. By combining bi-weekly microcoring and high-resolution dendrometer measurements, we monitored xylogenesis and stem radius variations of the deciduous species Betula alnoides Buch.-Ham. ex D. Don and the evergreen species Schima wallichii (DC.) Korth. We analyzed the relationships between weekly climate variables prior to sampling and the enlarging zone width or wall-thickening zone width, as well as weekly radial increments and climate factors during two consecutive years (2020 to 2021) showing contrasting hydrothermal conditions in the pre-monsoon season. In the year 2020, which was characterized by a warmer and drier pre-monsoon season, the onset of xylogenesis and radial increments of B. alnoides and S. wallichii were delayed by three months and one month, respectively, compared with the year 2021. In 2020, xylem formation and radial increments were significantly reduced for B. alnoides, but not for S. wallichii. The thickness of enlarging zone and wall-thickening zone in S. wallichii were positively correlated with relative humidity, and minimum and mean air temperature, but were negatively correlated with vapor pressure deficit during 2020 to 2021. The radial increments of both species showed significant positive correlations with precipitation and relative humidity, and negative correlations with vapor pressure deficit and maximum air temperature during two years. Our findings reveal that drier pre-monsoon conditions strongly delay growth initiation and reduce stem radial growth, providing deep insights to understand tree growth and carbon sequestration potential in tropical forests under a predicted increase in frequent drought events.

Demographic and net primary productivity dynamics of primary and secondary tropical forests in Southwest China under a changing climate

AbstractTropical forests are major carbon sinks on the Earth's land surface. However, our understanding of how the demographic rate and carbon sink capacities of tropical forests respond to climate change remains limited. In this study, we investigated the impacts of environmental drivers on forest growth, mortality, recruitment, and stem net primary productivity (NPPstem) over 16 years at five tropical forest plots in Xishuangbanna, Southwest China. These plots are along a successional gradient spanning three tropical secondary forests (tropical secondary forest‐1 [TSF‐1], tropical secondary forest‐2 [TSF‐2], and tropical secondary forest‐3 [TSF‐3]) and two primary forests (tropical rainforest [TRF] and tropical karst forest [TKF]). Our results showed that early successional secondary forests (TSF‐2 and TSF‐3) had higher diameter growth rates and relative mortality rates. An extreme drought event during 2009–2010 reduced the growth rate, relative recruitment rate, and NPPstem for most plots while increasing mortality in early successional forest plots. We observed significant negative effects of maximum temperature (Tmax) on NPPstem and diameter growth rate across all plots. Additionally, we found that precipitation had significant positive effects on diameter growth rate across all plots. Furthermore, tree mortality increased with rising Tmax, whereas precipitation significantly enhanced tree recruitment. Our findings highlight the vulnerability of tree growth, mortality, recruitment, and productivity in tropical forests to extreme drought events in Southwest China. Continued climate warming and more frequent droughts will induce higher mortality rates and impede growth, thus reducing the carbon sink capacity of tropical forests, especially in early successional stage tropical secondary forests.

Disturbance history, neighborhood crowding and soil conditions jointly shape tree growth in temperate forests.

Understanding how different mechanisms act and interact in shaping communities and ecosystems is essential to better predict their future with global change. Disturbance legacy, abiotic conditions, and biotic interactions can simultaneously influence tree growth, but it remains unclear what are their relative contributions and whether they have additive or interactive effects. We examined the separate and joint effects of disturbance intensity, soil conditions, and neighborhood crowding on tree growth in 10 temperate forests in northeast China. We found that disturbance was the strongest driver of tree growth, followed by neighbors and soil. Specifically, trees grew slower with decreasing initial disturbance intensity, but with increasing neighborhood crowding, soil pH and soil total phosphorus. Interestingly, the decrease in tree growth with increasing soil pH and soil phosphorus was steeper with high initial disturbance intensity. Testing the role of species traits, we showed that fast-growing species exhibited greater maximum tree size, but lower wood density and specific leaf area. Species with lower wood density grew faster with increasing initial disturbance intensity, while species with higher specific leaf area suffered less from neighbors in areas with high initial disturbance intensity. Our study suggests that accounting for both individual and interactive effects of multiple drivers is crucial to better predict forest dynamics.

Environmental predictors of forest structure, tree growth and wood production for Xylocarpus granatum in mixed-species mangrove forests

Environmental predictors of forest structure, tree growth and wood production for Xylocarpus granatum in mixed-species mangrove forests

Diminishing legacy effects from forest fertilization on stand structure, vegetation community, and soil function

While there is consensus that fertilization with nitrogen (N) is a cost-effective way of increasing both forest biomass yield and timber harvest profitability, the strength and longevity of legacy effects are debated. To quantify legacy effects of past fertilization, we analysed 21 mixed Pinus sylvesteris and Picea abies stands. The stands, on average 23 years old at the time of this study, were either unfertilized (n=7), fertilized with 150 kg N ha−1 once 36 years ago (n=7), or twice, 45 and 36 years ago, respectively (n=7), during the previous stand rotation. We performed measurements on soil N mineralisation and N availability, forest growth, ground vegetation community composition, soil and vegetation C/N ratios and soil C and N stocks, many of which responded to legacy N fertilization earlier in stand development. Our results show that the legacy effects of fertilization during the previous stand rotation have diminished through time, indicating an eventual convergence of stand properties. Specifically, all significant effects present in the previous measurement period (over a decade ago), were weaker or completely absent in the current study (i.e. 36 years after fertilization and 23 years after initiation of the new stands). None-the-less, this indicates a longer legacy effect of N fertilization than what is normally considered and suggests that care should be taken to mitigate unwanted, long-term effects when utilizing N addition to promote tree growth in boreal forests.

Restoration thinning accelerates small tree growth but may slow large tree growth in a multi‐age flood‐dependent forest

Abstract Large tree decline is occurring globally with critical implications for biodiversity and carbon sequestration. Restoration thinning is a potential management action to accelerate tree growth and promote large tree development in forests, yet trials have been limited and results have been mixed. We conducted a large‐scale trial to determine whether restoration thinning could accelerate the development of large trees in river red gum forests in Australia that had experienced widespread woody thickening and a decline of large trees due to long‐term commercial timber harvesting and river regulation. Thinning was conducted on 44 9‐ha plots by removing trees <40 cm diameter from around retained trees at a range of spacings. Initial tree densities ranged from ~260 to ~1860 trees per ha and 8%–86% of trees were removed by thinning. We monitored 1980 trees prior to thinning, and annually for 5 years post‐thinning. We tested the effects of thinning intensity on diameter growth of different sized trees and explored whether long‐ and short‐term water availability affected outcomes. Thinning promoted the growth of small trees <56 cm diameter, especially in drier sites during wet years. Higher thinning intensities reduced the growth rates of large trees (no smaller than 79.5 cm diameter) in wetter sites. For medium‐ and large‐sized trees, long‐ and short‐term water availability were stronger drivers of tree growth than competition due to tree density. Synthesis and applications. Restoration thinning may accelerate tree growth in young river red gum forests where all trees are small. But restoration thinning may be ineffective or detrimental in multi‐aged forests where the goal is to promote the growth rates of trees that are already medium to large in size.

PagPXYs improve drought tolerance by regulating reactive oxygen species homeostasis in the cambium of Populus alba × P. glandulosa

PXY (Phloem intercalated with xylem) is a receptor kinase required for directional cell division during the development of plant vascular tissue. Drought stress usually affects plant stem cell division and differentiation thereby limiting plant growth. However, the role of PXY in cambial activities of woody plants under drought stress is unclear. In this study, we analyzed the biological functions of two PXY genes (PagPXYa and PagPXYb) in poplar growth and development and in response to drought stress in a hybrid poplar (Populus alba × P. glandulosa, ‘84K’). Expression analysis indicated that PagPXYs, similar to their orthologs PtrPXYs in Populus trichocarpa, are mainly expressed in the stem vascular system, and related to drought. Interestingly, overexpression of PagPXYa and PagPXYb in poplar did not have a significant impact on the growth status of transgenic plants under normal condition. However, when treated with 8 % PEG6000 or 100 mM H2O2, PagPXYa and PagPXYb overexpressing lines consistently exhibited more cambium cell layers, fewer xylem cell layers, and enhanced drought tolerance compared to the non-transgenic control ‘84K’. In addition, PagPXYs can alleviate the damage caused by H2O2 to the cambium under drought stress, thereby maintaining the cambial division activity of poplar under drought stress, indicating that PagPXYs play an important role in plant resistance to drought stress. This study provides a new insight for further research on the balance of growth and drought tolerance in forest trees.

Process-Based Modeling of Phenology and Radial Growth in Pinus tabuliformis in Response to Climate Factors over a Cold and Semi-Arid Region.

(1) Background: Climate change significantly impacts the phenology and dynamics of radial tree growth in alpine dryland forests. However, there remains a scarcity of reliable information on the physiological processes of tree growth and cambial phenology in response to long-term climate change in cold and semi-arid regions. (2) Methods: We employed the process-based Vaganov-Shashkin (VS) model to simulate the phenology and growth patterns of Chinese pine (Pinus tabuliformis) in the eastern Qilian Mountains, northeastern Tibetan Plateau. The model was informed by observed temperature and precipitation data to elucidate the relationships between climate factors and tree growth. (3) Results: The simulated tree-ring index closely aligned with the observed tree-ring chronology, validating the VS model's effectiveness in capturing the climatic influences on radial growth and cambial phenology of P. tabuliformis. The model outputs revealed that the average growing season spanned from mid-April to mid-October and experienced an extension post-1978 due to ongoing warming trends. However, it is important to note that an increase in the duration of the growing season did not necessarily result in a higher level of radial growth. (4) Conclusions: While the duration of the growing season was primarily determined by temperature, the growth rate was predominantly influenced by water conditions during the growing season, making it the most significant factor contributing to ring formation. Our study provides valuable insights into the potential mechanisms underlying tree growth responses to climate change in cold and semi-arid regions.

Sex-dependent resilience to extreme drought events: implications for climate change adaptation of a South American endangered tree species

BackgroundRecent changes in climatic trends are resulting in an increased frequency and intensity of extreme events, with unknown effect on ecosystem dynamics in the near future. Extreme drought episodes are recognized as disturbance factors capable of modifying forest dynamics and tree growth. Within this context, dioecious tree species may be impacted by climatic extremes, affecting male/female proportions and, consequently, reproductive processes and species persistence. Therefore, there is an urgent need for species-specific assessments of growth tolerance to extreme dry spells in dioecious tree species, to establish effective conservation strategies for these particular natural resources. Araucaria araucana (araucaria), an endangered dioecious Patagonian tree species, has recently undergone decay and mortality episodes in response to increasing dry climatic conditions. While sex-dependent tolerance to extreme drought episodes has been assessed in the species’ humid distribution range, there is still a lack of information on the gender-based resilience of trees growing in the drier environments of the species’ distribution.MethodsWe reconstructed, through dendrochronological methods, the sex-dependent response of 105 araucaria individuals (55 female and 50 male trees) to five regional extreme dry spells employing a set of different indices. Resistance, recovery period, and average growth reduction of standardized tree-ring growth were examined, analysing the effect of biotic (sex, pre-drought stem tree growth) and abiotic (local climatic conditions before, during, and after extreme climatic episodes) factors on tree resilience.ResultsSex influences only the species resistance to climatic disturbance, with male individuals showing lower tolerance to extreme drought events. Pre-drought radial growth rates and local meteorological conditions preceding, during, and following extreme dry spells strongly modulated araucaria radial growth resilience regardless of tree sex, influencing the species resistance, recovery period, and average growth reduction.ConclusionsWe provide novel and crucial information for the species conservation and management in the current climate change scenario, and contribute to the debate regarding the role of tree sex as a factor influencing woody species growth under particularly adverse climatic conditions. In the face of climate change, an increase in extreme drought events is expected in the easternmost araucaria xeric end distribution area, which will likely decrease the species resilience.

Abiotic Stress Responses in Woody Plants: Morphological, Physiological, and Anatomical Features

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.

Responses of belowground fine root biomass and morphology in Robinia pseudoacacia L. plantations to aboveground environmental factors

The adaptation of fine roots to a variety of environmental conditions is crucial for promoting the growth and long-term survival of forest trees. To achieve sustainable forest ecology management requires a comprehensive understanding of the intricate relationships between belowground and aboveground factors in the forest ecosystem. Equally important is identifying the factors that directly affect the growth and development of fine roots belowground. This study was carried out in 25-year-old pure plantations of Robinia pseudoacacia L. within the Caijiachuan watershed, Jixian County, Shanxi Province, China. Twenty-seven permanent sample plots were established, with each plot measuring 20 × 20 m. These plots covered nine different stand densities ranging from 775 to 2975 trees/ha, with three replicates per density. Through field surveys and multivariate analysis, along with the use of a simplified Generalized Linear Model, this study revealed the alterations in belowground fine root biomass and morphology resulting from variations in stand density. Additionally, it explored the mutual relationships between belowground fine root biomass and morphology and aboveground environmental characteristics. The results show that, under different stand densities, only fine root biomass, specific fine root length, fine root tissue density, and fine root tip density displayed significant differences (P < 0.05), while specific fine root surface area exhibited a decreasing trend with increasing stand density. Moreover, lower densities (1025 and 1175 trees/ha) promoted the growth of specific fine root length and specific fine root surface area, while higher densities (2100 and 2475 trees/ha) supported the development of fine root biomass and fine root tip density. The combined contributions of semi-decomposition layer litter layer thickness (contribution value: 0.1340), mean tree height (contribution value: 0.2710), and neighborhood comparison (contribution value: 0.1840) significantly explain the variations in fine root biomass (P = 0.014) and specific fine root surface area (P = 0.031). Fine root biomass shows statistically significant correlations only with total phosphorus and available phosphorus (P < 0.05). The influence of soil factors (contribution value: 0.0306) on subterranean fine roots is much less pronounced compared to that of stand structure (contribution value: 0.1152) and other environmental factors (contribution value: 0.1128). These factors together account for the variations in subterranean fine roots, with stand structure and other environmental factors making the most significant contributions (contribution value: 0.5840). These research findings offer valuable insights into the connections between subterranean fine roots and aboveground biotic and abiotic factors in Robinia pseudoacacia L. plantations in the northern Loess Plateau region. Furthermore, they provide vital information for the prudent management and operation of low-efficiency Robinia pseudoacacia L. plantations.

Dendrochronological studies in North Africa: reality and prospects

The southern Mediterranean region, particularly North Africa, is a crucial area for biodiversity conservation. However, the impacts of climate change on plant species in this region are not well understood. Dendroecology, the study of tree rings, is a valuable technique for analyzing the effects of environmental changes on woody plants over time. In this study, we intend to assess the state of the art in dendrochronological research in North Africa and identify knowledge gaps and limitations in the field. The period of analysis spans from 1979 to 2023. We used all the available literature in Dendrobox and Google Scholar during this period. Our study revealed several research gaps in the region, including the need for more studies on the history of forest fires and their relationship to climate conditions in Morocco, Algeria, and Tunisia, the impact of climate on the anatomical characteristics of growth rings, and the effects of climate change on tree species diversity and forest health. Applying this technique in the future would allow for detailed insights into the effect of climate on the internal structure and growth of forest trees. The findings of this study will help guide future research and contribute to a better understanding of the climate-growth relationship of woody plants in North Africa.

Response of L. Scoparium and K. Robusta to biosolids and dairy shed effluent application in a low fertility soil

Biosolids and Dairy Shed Effluent (DSE) can contain high concentrations of plant nutrients, making them potential resources for enhancing forest tree species growth and soil fertility. This study aimed to investigate the effects of biosolids and DSE application on the growth and nutrient uptake of Leptospermum scoparium and Kunzea robusta, while also considering the potential accumulation of contaminants. The results demonstrated that amending low-fertility soil with 2600 kg N ha-1 of biosolids and 200 kg N ha-1 of DSE positively influenced the growth of both L. scoparium and K. robusta. This improvement was evident through increased biomass production and enhanced uptake of essential elements such as calcium (Ca), potassium (K), and sulfur (S). Notably, L. scoparium exhibited superior growth when combined with DSE, while both species showed similar positive responses when combined with biosolids. However, it should be noted that the application of biosolids resulted in elevated concentrations of certain trace elements in the plants, whereas DSE did not. These trace elements included cadmium (Cd), copper (Cu), manganese (Mn), and zinc (Zn). Despite the increase, the levels of these elements did not exceed unacceptable thresholds. Considering the potential influence of biosolids on plant rhizodeposition, it is recommended that future studies investigate the interactions between plant roots and microbes, particularly in relation to plant element uptake. This line of research would further enhance our understanding of the underlying mechanisms involved. In conclusion, the findings suggest that the application of biosolids and DSE can effectively improve forest tree growth and nutrient uptake. However, careful management is necessary to mitigate the potential accumulation of trace elements. These results provide valuable insights for optimizing the use of biosolids and DSE in forestry practices, with potential economic and environmental benefits.

Increasing radial growth in old-growth high-elevation conifers in Southern California, USA, during the exceptional "hot drought" of 2000-2020.

Hot droughts, droughts attributed to below-average precipitation and exceptional warmth, are increasingly common in the twenty-first century, yet little is known about their effect on coniferous tree growth because of their historical rarity. In much of the American West, including California, radial tree growth is principally driven by precipitation, and narrow ring widths are typically associated with either drier or drought conditions. However, for species growing at high elevations (e.g., Larix lyalli, Pinus albicaulis), growth can be closely aligned with above-average temperatures with maximum growth coinciding with meteorological drought, suggesting that the growth effects of drought span from adverse to beneficial depending on location. Here, we compare radial growth responses of three high-elevation old-growth pines (Pinus jeffreyi, P. lambertiana, and P. contorta) growing in the San Jacinto Mountains, California, during a twenty-first-century hot drought (2000-2020) largely caused by exceptional warmth and a twentieth-century drought (1959-1966) principally driven by precipitation deficits. Mean radial growth during the hot drought was 12% above average while 18% below average during the mid-century drought illustrating that the consequences of environmental stress exhibit spatiotemporal variability. We conclude that the effects of hot droughts on tree growth in high-elevation forests may produce responses different than what is commonly associated with extended dry periods for much of western North America's forested lands at lower elevational ranges and likely applies to other mountainous regions (e.g., Mediterranean Europe) defined by summer-dry conditions. Thus, the climatological/biological interactions discovered in Southern California may offer clues to the unique nature of high-elevation forested ecosystems globally.

Climate Sensitivity and Drought Legacy of Tree Growth in Plantation Forests in Northeast China Are Species- and Age-Dependent

The occurrence, frequency, and severity of drought are accelerating due to global warming. Understanding the vulnerability of plantation forests to climate change, particularly to drought events, is critical to revealing the underlying mechanisms of tree resilience, recovery, and acclimation, which are important for plantation management. How the stand age affects the climate sensitivity of tree growth, as well as the direction, magnitude, and duration of the drought legacy, in plantation forests in northeast China is still unclear. In this study, we used MODIS-derived NDVI time series with gridded climate data from 2000 to 2020 to fill this knowledge gap. The selected plantation forests were dominated by four coniferous species: Korean pine (Pinus koraiensis), Scots pine (Pinus sylvestris), Japanese larch (Larix kaempferi), and Dahurian larch (Larix gmelinii). The results show that the climate sensitivity of tree growth differed among species and age groups. The growth of Korean pine and Scots pine was mostly dependent upon precipitation, while the growth of Japanese larch and Dahurian larch was determined primarily by temperature. Old Japanese larch (21–40 years) and Dahurian larch trees (31–60 years) were more sensitive to temperature and precipitation than young conspecifics, whereas old Korean pine (41–60 years) and Scots pine (31–60 years) were less sensitive to precipitation and temperature than young conspecifics. Furthermore, the legacy of drought lasted one year for Korean pine, Japanese larch, and Dahurian larch and over three years for Scots pine. Old trees were more severely affected by drought, particularly Scots pine and Dahurian larch. The findings of the study can help improve plantation forest management for better adaptation to future climate change.

Tree regeneration and ontogenetic strategies of northern European hemiboreal forests: transitioning towards closer-to-nature forest management.

Tree ontogeny is the genetic trajectories of regenerative processes in trees, repeating in time and space, including both development and reproduction. Understanding the principles of tree ontogeny is a key priority in emulating natural ecological patterns and processes that fall within the calls for closer-to-nature forest management. By recognizing and respecting the growth and development of individual trees and forest stands, forest managers can implement strategies that align with the inherent dynamics of forest ecosystem. Therefore, this study aims to determine the ontogenetic characteristics of tree regeneration and growth in northern European hemiboreal forests. We applied a three-step process to review i) the ontogenetic characteristics of forest trees, ii) ontogenetic strategies of trees for stand-forming species, and iii) summarise the review findings of points i and ii to propose a conceptual framework for transitioning towards closer-to-nature management of hemiboreal forest trees. To achieve this, we applied the super-organism approach to forest development as a holistic progression towards the establishment of natural stand forming ecosystems. The review showed multiple aspects; first, there are unique growth and development characteristics of individual trees at the pre-generative and generative stages of ontogenesis under full and minimal light conditions. Second, there are four main modes of tree establishment, growth and development related to the light requirements of trees; they were described as ontogenetic strategies of stand-forming tree species: gap colonisers, gap successors, gap fillers and gap competitors. Third, the summary of our analysis of the ontogenetic characteristics of tree regeneration and growth in northern European hemiboreal forests shows that stand-forming species occupy multiple niche positions relative to forest dynamics modes. This study demonstrates the importance of understanding tree ontogeny under the pretext of closer-to-nature forest management, and its potential towards formulating sustainable forest management that emulates the natural dynamics of forest structure. We suggest that scientists and foresters can adapt closer-to-nature management strategies, such as assisted natural regeneration of trees, to improve the vitality of tree communities and overall forest health. The presented approach prioritizes ecological integrity and forest resilience, promoting assisted natural regeneration, and fostering adaptability and connectivity among plant populations in hemiboreal tree communities.