Coexistence Of Tree Species Research Articles

Conserved responses of water use to evaporative demand in mixed forest across seasons in low subtropical China

The positive correlation between diversity and production has been extensively documented. Given the intrinsic relationship between production and plant water consumption, it was anticipated that mixed forests would exhibit different water use compared to pure forests. In this study, the responses of water use to vapour pressure deficit were analyzed by monitoring the sap flow of Schima superba in both pure and mixed forests, as well as Castanopsis chinensis in mixed forest. Additionally, the relationships among leaf and stem traits were examined by measuring specific leaf area (SLA), N and P concentration per unit leaf mass, leaf δ18O and δ13C and wood density of sapwood (WD) during both wet and dry seasons. The results showed that S. superba demonstrated a comparable regulation of water use during both wet and dry seasons in mixed forest, whereas it exhibited less strict water use regulation during the wet season in comparison to the dry season in pure forest. Regardless of whether the forests were pure or mixed, both leaf δ13C and WD remained consistent across seasons, while there was an increase in SLA during the wet season compared to the dry season for S. superba. There was a different seasonal change in leaf δ18O for S. superba in pure and mixed forests. Water use and leaf economic spectrum may determine the adaptive strategies of coexisting species, and the coexisting tree species in mixed forest exhibited a resource-use differentiation, as indicated by seasonal variations in leaf and stem traits, likely explaining the conserved responses of sap flow to evaporative demand. Our research might provide insights into the impact of tree interaction on water use strategies and the water use-based forest management under current climate change.

Quercus acutissima exhibits more adaptable water uptake patterns in response to seasonal changes compared to Pinus massoniana

BackgroundSeasonal precipitation variability significantly affects water use in forests; however, whether water uptake is adapted to changes in precipitation, particularly whether it could affect the coexistence of tree species, has rarely been quantified in forest systems. MethodIn this study, dual stable isotopes and the Li-6400 portable photosynthesis system were used to determine the water sources of a mixed conifer (Pinus massoniana) and broadleaf (Quercus acutissima) forest and changes in hydraulic characteristics during the dry and wet seasons in a southern hilly region of China. ResultsAlthough the hydraulic characteristics of P. massoniana were lower than those of Q. acutissima, it maintained a stable water source from the deep soil layer and a higher stomatal conductance (Gs), leading to a higher transpiration rate (Tr) during the growing seasons. Q. acutissima mainly absorbed water from deeper soil layers in the dry season and took up from shallow soil layers in the wet season. Its Gs values exhibited sensitivity to precipitation, while it maintained a lower Tr value during the growing seasons. The excessive water-use strategy observed in P. massoniana may confer weak drought-tolerance during higher frequency and more intense extreme precipitation events, whereas Q. acutissima may exhibit better ecological adaption to precipitation changes. ConclusionsThe overlap of water niches in mixed forests did not appear to affect the coexistence of tree species. The present study provides insights into reforestation and water management in the southern hilly regions of China.

Seasonal and interspecific variations in the water uptake depth of trees in a moist cool-temperate mixed forest in Japan

ABSTRACT The water uptake depth of trees affects their overall water use and the water cycle of forest ecosystems. However, empirical data on the depth from which water is drawn are lacking for many moist forests. In this study, we estimated the water uptake depths of 24 coexisting tree species in a moist cool-temperate mixed forest in Japan using stable oxygen isotopes. Our goal was to clarify the factors influencing water uptake depth including season, species, slope position, and tree height under moist conditions. Water uptake depth was determined during three periods in which temperatures differed but soil moisture levels remained similar. Season was shown as one of the factors affecting water uptake depth, which was shallowest in August, when temperatures reached maximum values, and deepest during May, when temperatures were lowest. This seasonal variation is likely to be related to physiological processes such as increasing transpiration which leads to water uptake shifting to the water-rich shallow soil layer and/or activation of fine root production at the soil surface, where temperatures are high. Water uptake depth also varied with tree species, suggesting the occurrence of belowground resource segregation among moist forest tree species. Slope position and tree height did not affect water uptake depth. This study highlights the importance of considering temperature-driven physiological processes when examining water uptake depth in moist forests, which could have implications for predicting the responses of these ecosystems to climate change.

Species-Specific Root Distribution and Leaf Iso/Anisohydric Tendencies Shape Transpiration Patterns Across Heterogeneous Karst Habitats.

The driving forces of transpiration are not only atmospheric evaporation but also root zone water supply and stomatal regulation among species. However, the biophysiological drivers of transpiration remain incompletely understood in heterogeneous karst habitats. This study investigated the commonly coexisting tree species Mallotus philippensis and Celtis biondii in two typical karst habitats: rock-dominated (RD) habitat and control soil-dominated (SD) habitat. Over 2 years, soil moisture, transpiration, root distribution, and leaf water potential were measured. The results showed that soil moisture in the RD habitat was significantly lower than in the SD habitat. Transpiration patterns also differed between habitats, with species-specific distinctions driven by biophysiological traits. M. philippensis showed small hydroscape areas and its root system mainly distributed in the soil zone in both habitats. The isohydric behaviour and lower root density in the RD habitat drove M. philippensis to reduce transpiration in response to soil water deficiency. Conversely, C. biondii had large hydroscape areas and roots capable of penetrating bedrock. It transpired higher relying on ample accessible water through anisohydric behaviour and having a more robust root system both in soil and bedrock zones in the RD habitat. Our study highlights the critical role of root water accessibility and leaf iso/anisohydric tendencies in driving transpiration.

Phylogenetic relatedness and habitat affect seedling abundance of a mid-montane humid evergreen broad-leaved forest in the Gaoligong Mountains, Southwestern China

The neighborhood effect has become an important framework with which to study the mechanisms that maintain the coexistence of tree species. Phylogenetic relatedness among neighboring plants directly affects species coexistence and the maintenance of tree diversity. And some studies have reported that seedling performance is negatively correlated with phylogenetic relatedness, which termed phylogenetic negative density dependence. Soil-borne fungal pathogens affected seedling performance of phylogenetically related host species, i.e., phylogenetic Janzen–Connell effect. Seedlings may be particularly vulnerable to habitat and neighbor characteristics. Although previous studies have demonstrated the influence of neighborhood effects, phylogenetic relatedness, and habitat filtering on seedling survival, growth, and mortality, the effect of variation in these factors on seedling abundance remains unclear. To address this question, we used a 4-ha (200 m × 200 m) and monitored four-year (2020–2023) seedling dataset from a mid-montane humid evergreen broad-leaved subtropical forest in the Gaoligong Mountains, Yunnan, Southwestern China, and which consisted of 916 seedlings belonging to 56 species. The results of generalized linear mixed models showed no significant effect of conspecific adult neighbors on seedling abundance at any of the intervals evaluated. In contrast, we found evidence of phylogenetic distance density dependence in the forests of the Gaoligong Mountains. Specifically, there was a significant positive effect of the relative average phylogenetic distance between heterospecific adult neighbors and focal seedlings on focal seedling abundance in 2020; however, the relative average phylogenetic distance between heterospecific seedling neighbors and focal seedlings had a significant negative effect on seedling abundance over the four-year period (2020–2023). Among the habitat factors, only light (canopy opening) had a negative effect on seedling abundance in all four years. Light resources may be a limiting factor for seedlings, and determine seedling dynamics in subtropical forests. Overall, our results demonstrated that phylogenetic density dependence and habitat filtering affected subtropical seedling abundance. Our findings provide new evidence of the impact of phylogenetic density dependence on seedling abundance in a subtropical mid-montane humid evergreen broad-leaved forest and highlight the need to incorporate the neighborhood effect, phylogenetic relatedness, and habitat factors in models assessing seedling abundance.

Introduction of broadleaf tree species can promote the resource use efficiency and gross primary productivity of pure forests.

Long-term pure forest (PF) management and successive planting has result resulted in "low-efficiency artificial forests" in large areas. However, controversy persists over the promoting effect of introduction of broadleaf tree species on production efficiency of PF. This study hypothesised that introduced broadleaf tree species can significantly promote both water-nutrient use efficiency and gross primary productivity (GPP)of PF. Tree ring chronologies, water source, water use efficiency and GPP were analysed in coniferous Cunninghamia lanceolata and broadleaved Phoebe zhennan growing over the past three decades. The introduction of P. zhennan into C. lanceolata plantations resulted in inter-specific competition for water, probably because of the similarity of the main water source of these two tree species. However, C. lanceolata absorbed more water with a higher nutrient level from the 40-60-cm soil layer in mixed forests (MF). Although the co-existing tree species limited the basal area increment and growth rates of C. lanceolata in MF plots, the acquisition of dissolved nutrients from the fertile topsoil layer were enhanced; this increased the water use efficiency and GPP of MF plots. To achieve better ecological benefits and GPP, MFs should be constructed in southern China.

Effects of stem size and age on resprouting ability of different tree species after clear-cutting in a warm temperate secondary forest

ABSTRACT Understanding the resprouting abilities of various tree species provides valuable insights into managing coppice forests and predicting forest dynamics. Clear-cutting was conducted in a secondary forest comprising warm-temperate broadleaf trees, and the stump size, age, and traits of the resprouts were measured to study their effects on resprouting ability. The number of resprouts that emerged from a stump was not significantly different when comparing different tree forms (canopy and shrub) or leaf longevity (evergreen and deciduous). Taller species generated taller and fast-growing resprouts. The ability to generate more resprouts with age was more important for species dominance than the ability to generate more resprouts with increase in stem size. Most shrub layer species exhibited age-related reductions in resprouting ability. Evergreen canopy species tended to have a larger number of resprouts and higher stump survival rate. The results suggest that the diversity of the resprouting traits among tree species could largely influence the stand dynamics and contribute to the coexistence of tree species.

Different phosphorus preferences among arbuscular and ectomycorrhizal trees in a subtropical forest

Phosphorus (P) is one of the most limiting elements for efficient plant growth and regeneration, coexisting plants are found to be able to partition soil P components through different types of mycorrhizal symbiosis. However, previous evidences were mostly based on artificial addition of different forms of P chemicals, there is still a lack of observational and experimental verifications on how tree species respond to soil P heterogeneity in natural soils. Herein, we conducted a field survey to investigate how spatial distribution of tree species with different types of mycorrhizal associations are related with soil P compositions. We found that arbuscular mycorrhizal (AM) trees tend to distribute in soils rich in inorganic P, while ectomycorrhizal (ECM) trees distribute in habitats with low inorganic P. We further established a shade-house experiment to evaluate how P availability of field soils affects seedling performance of AM and ECM trees. Biomass of AM seedlings was highest when grew in soil with the medium level of inorganic P, while ECM seedlings grown best in soil with the lowest inorganic P level. Seedling survival and mycorrhizal colonisation rates decreased, while specific root length and specific area of seedling roots increased, with increasing inorganic P concentrations. Using field soil with natural composition of P-forms and spatial heterogeneity, our findings confirmed the hypothesis that AM trees prefer inorganic P while ECM trees are able to utilise organic P in a more realistic setting, which regulated spatial distributions and promoted coexistence of subtropical tree species at local scale.

Above‐ and belowground strategies of tropical montane tree species are coordinated and driven by small‐scale nitrogen availability

Abstract The question whether the strategies of above‐ and belowground plant organs are coordinated as predicted by the plant economics spectrum theory is still under debate. We aim to determine the leading dimensions of tree trait variation for above‐ and belowground functional traits, and test whether they represent spectra of adaptation along a soil fertility gradient in tropical Andean forests. We measured leaf, stem and fine root functional traits, and individual‐level soil nutrient availability for 433 trees from 52 species at three elevations between 1000 and 3000 m a.s.l. We found close coordination between above– and belowground functional traits related to the trade‐off between resource acquisition and conservation, whereas root diameter and specific root length formed an independent axis of covarying traits. The position of a tree species along the acquisition–conservation axis of the trait space was closely associated with local soil nitrogen, but not phosphorus, availability. Our results imply that above‐ and belowground plant functional traits determine at which edaphic microhabitats coexisting tree species can grow, which is potentially crucial for understanding community assembly in species‐rich tropical montane forests. Read the free Plain Language Summary for this article on the Journal blog.

Variations in the plasticity of functional traits indicate the differential impacts of abiotic and biotic factors on the structure and growth of trees in tropical dry forest fragments

Abiotic and biotic factors have considerable impact on the plasticity of plant functional traits, which influences forest structure and productivity; however, their inter-relationships have not been quantified for fragmented tropical dry forest (TDF) ecosystems. We asked the following questions: (1) what are the variations in the plasticity of functional traits due to soil moisture availability in TDF fragments? (2) what are the roles of soil nutrients and forest disturbances in influencing variations in the plasticity of functional traits in the TDF fragments? and (3) how do the variations in the plasticity of functional traits influence the structure and productivity of TDF fragments? Based on linear mixed-effects results, we observed significant variations among tree species for soil moisture content (SMC) under the canopy and selected functional traits across forest fragments. We categorized tree species across fragments by principal component analysis (PCA) and hierarchical clustering on principal components (HCPC) analyses into three functional types, viz., low wood density high deciduous (LWHD), high wood density medium deciduous (HWMD), and high wood density low deciduous (HWLD). Assemblage of functional traits suggested that the LWHD functional type exhibits a drought-avoiding strategy, whereas HWMD and HWLD adopt a drought-tolerant strategy. Our study showed that the variations in functional trait plasticity and the structural attributes of trees in the three functional types exhibit contrasting affinity with SMC, soil nutrients, and disturbances, although the LWHD functional type was comparatively more influenced by soil resources and disturbances compared to HWMD and HWLD along the declining SMC and edge distance gradients. Plasticity in functional traits for the LWHD functional type exhibited greater variations in traits associated with the conservation of water and resources, whereas for HWMD and HWLD, the traits exhibiting greater plasticity were linked with higher productivity and water transport. The cumulative influence of SMC, disturbances, and functional trait variations was also visible in the relative abundance of functional types in large and small sized fragments. Our analysis further revealed the critical differences in the responses of functional trait plasticity of the coexisting tree species in TDF, which suggests that important deciduous endemic species with drought-avoiding strategies might be prone to strategic exclusion under expected rises in anthropogenic disturbances, habitat fragmentation, and resource limitations.

Differences in photosynthetic and water use characteristics of four co-existing tree species at the treeline of the Japanese Alps

ABSTRACT Physiological characteristics of trees in the alpine treeline are critical for assessing the vulnerability of alpine forest ecosystems, but differences in water relations between co-existing deciduous and evergreen trees remain poorly understood. In this study, we analyzed the photosynthetic and water use characteristics of two deciduous broad-leaved (Sorbus matsumurana and Betula ermanii) and two evergreen coniferous (Abies mariesii and Pinus pumila) tree species at the treeline – i.e. the line connecting the highest patches of forest composed of trees at least three meters high – of Mt. Norikura in central Japan, to explore the physiological adaptations of trees to alpine environments. We monitored diurnal changes in leaf gas exchange rates and leaf and soil water potentials in each tree species during the growing season, as well as bulk leaf water relations based on pressure – volume curves and whole-tree hydraulic structures. The four species under study relied on different physiological characteristics at both leaf and plant levels for adaptation to their natural habitat. For maintaining water in leaves, S. matsumurana showed higher water use efficiency (WUE; the ratio of photosynthesis to transpiration) and osmotic adjustment. In contrast, B. ermanii showed lower WUE, while maintaining higher soil-to-leaf hydraulic conductivity with less stomatal control. In turn, A. mariesii showed higher WUE and leaf succulence. Meanwhile, P. pumila showed lower WUE but compensated for water loss through higher leaf hydraulic capacitance and tissue elasticity. Our observations demonstrate that tree species rely on specific physiological characteristics to adapt to the alpine treeline environment.

Adaptive strategies to freeze-thaw cycles in branch hydraulics of tree species coexisting in a temperate forest

Freeze-thaw cycles (FTCs) limit the distribution and survival of temperate tree species. Tree species with different wood types coexist in temperate forests and are subjected to the same FTCs. It is essential to understand how these trees differentially cope with xylem hydraulic failure induced by FTCs in the field. The branch hydraulic traits and nonstructural carbohydrate concentration of six coexisting tree species in a temperate forest were measured from mid-winter to early spring when the FTCs occurred from January to April. The percentage loss of hydraulic conductivity (PLC) was lower, and the water potential inducing a 50% loss of hydraulic conductivity (P50) was more negative in tracheid trees than in ring- and diffuse-porous trees, suggesting tracheid trees with narrow tracheid diameters showed less vulnerable to embolism and provided a lower degree of hydraulic failure during FTCs (stronger resistance). Ring-porous trees always showed lower hydraulic conductivity and higher PLC and P50, and these traits did not change during FTCs, suggesting that they might lose the hydraulic functions in winter and abandon the last year xylem. The P50 in diffuse-porous increased after several FTCs (frost fatigue), but that in tracheid species continued to increase (or even decrease) until the end of FTCs (69 cycles), suggesting that tracheid trees were less sensitive to frost fatigue than diffuse-porous trees. Soluble sugar concentration in deciduous trees negatively correlated with PLC at the end of FTCs, indicating that the effect of soluble sugar on refilling embolism occurred in early spring. While the soluble sugar concentration of deciduous trees decreased, that of two evergreen tracheid trees gradually increased, possibly due to the winter photosynthesis of evergreen leaves. Our results suggest temperate trees adopt different strategies to cope with the same FTCs. These findings enrich the understanding of plant hydraulics and carbon physiology in winter and provide insights into the response of different species coexisting in temperate forests under climate change.

Effect of Gap Size and Elevation on the Regeneration and Coexistence of Abies, Betula, and Acer Tree Species in a Subalpine Coniferous Forest

Forest gaps play an important role in species regeneration and forest succession. Gap size has a primary influence on tree species coexistence and community assembly along an elevation gradient. In this study, we evaluated the regeneration and coexistence of Abies faxoniana, Betula utilis, and Acer maximowiczii at different life history stages in varied gap sizes along an elevation gradient (between 3000 and 3500 m a.s.l). We found that gap size can positively enlarge the effects of elevation on the regeneration density of the three species. In the process of regeneration from seedling to sapling, Abies had stronger regeneration capability, with regeneration niche breadths of more than 0.6 in different gap sizes. A factor analysis of mixed data indicated that regeneration density, soil nutrient contents, and air humidity were mainly related to gap size, but habitat temperature was largely determined by elevation. The connection between the species regeneration density and habitat conditions was due to differences in their regeneration niches, reflecting the selective preemption of environmental resources of different species in different life stages. Microhabitat heterogeneity, controlled by the characteristics of forest gaps along an elevation, affected the regeneration niche differences of the tree species, which contributed to the species coexistence and community assembly processes.

Rcontroll: An R interface for the individual‐based forest dynamics simulator TROLL

Abstract A central challenge in ecology is understanding the emergence of patterns as the result of interactions among individuals. Dynamic forest models can provide a fine‐scale description of the ecological, physiological and environmental processes that explain the demography of coexisting tree species. This in turn helps predict changes under future scenarios. However, model accessibility is a major obstacle to a wide use and communication across scientific disciplines and for educational purposes. Here, we present the R package rcontroll, which provides access to the TROLL forest simulator in the R environment. TROLL is individual‐based and spatially explicit and leverages knowledge of ecology, biogeochemistry and tree ecophysiology through a trait‐based parameterisation. TROLL has been used to simulate carbon fluxes and tree diversity in tropical and subtropical forests and to explore forest resilience to disturbance and environmental changes more generally. rcontroll provides a user‐friendly environment to set up and analyse TROLL simulations with varying community compositions, ecological parameters and climate conditions. We show how to test parameter sensitivity in TROLL using the rcontroll R package. We also demonstrate the flexibility and ease of use of rcontroll by replicating a previously published study based on the TROLL simulator. Both examples are included with reproducible code documents. Complex forest simulators are important scientific tools for science and education, and wide access to these tools is an important condition for their adoption. TROLL is designed to address a wide range of ecological and environmental questions, and the new R package rcontroll is designed to be an entry point for TROLL model users.

Species-specific growth responses to local and regional climate variability indicate the presence of a diversity portfolio effect in mediterranean tree assemblages

Understanding the role of tree biodiversity in stabilizing ecosystem processes is of paramount importance in forest ecology, especially because of increasing temperatures and droughts. The portfolio effect is one of the main hypotheses explaining the biodiversity-stability relationship that has been defined as a variance reduction effect of biodiversity in an ecosystem process, so that fluctuations over time in highly diverse communities become significantly smaller in low-diversity communities. In this work, two main objectives were established: to analyze a potential portfolio effect in a tree assemblage through functional mechanisms of compensation, and to identify the local climatic factors and teleconnections responsible for the interannual variations in the growth of tree species. The study was carried out in a region of the Iberian Peninsula with transitional climatic characteristics that allow the coexistence of needleleaf and broadleaf tree species with a wide variety of strategies and functional traits allowing them to respond differentially to climatic conditions. A dendrochronological approach was followed to analyze tree growth in relation to climate factors. We found that the magnitude and sensitivity of the response to both local climatic elements and teleconnections were species-dependent and that during climatically extreme years, the species exhibited marked differences in tree growth and compensatory responses that contributed to an increase in temporal stability. These results point to the existence of a portfolio effect in Mediterranean woodlands that supports tree diversity as an effective driver of ecosystem stability. Although the combination of dry and hot years always has a negative effect on tree growth, the association of coniferous and broadleaved (evergreen and marcescent) species at our study site could have a significantly positive influence by increasing temporal stability at landscape level through complementary functional responses.

Coexistence of Tree Species Promotes the Similarity of the Elementome in Soil Profiles

Coexistence of Tree Species Promotes the Similarity of the Elementome in Soil Profiles

Spatial determinants of tree recruitment in mixed stands in southeastern Poland- silver fir's interaction with lowland tree species

Silver fir (Abies alba Mill.) is a typical mountain tree species, but it can also grow in lowlands below 300 m a.s.l., where it must coexist with a variety of competitors. Much less were studied in the northeastern part of its natural range, where annual precipitation varies between 500 and 600 mm, distinctly less than in the mountains. The general objective of this study was to investigate the regeneration process of silver fir in mixed lowland forests in regions with water shortage. The evaluation of spatial relationships between old, dominant and newly established trees was used to clarify the mechanisms of tree species coexistence. The study was conducted in managed and protected stands in Janów Forests in the southeastern part of Poland. We selected mature forest stands (oldest trees older than 100 years) representing three types of mixed stands in nature reserves, as well as in comparable managed forests. Data was collected on 500 m2 sample plots established randomly in each stand category (20 sample plots × 6 stands). Silver fir as the target tree showed statistically significant segregation from other species in 15 cases. Small silver fir trees were associated with large pines in two forest types and segregated form large firs in one. The spatial relationships between fir and black alder were negative. Black alder was the second species with the most statistically significant spatial relationships with other tree species (11 cases). Alders separated from large pines and large firs and from medium and small silver firs. Strong segregation of medium-sized hornbeam from the small class of silver fir was observed. Our study showed that silver fir natural regeneration and colonization of new areas at the northeastern limit of its range are limited by low seed rain density, interactions with other competing species, and local site conditions. Areas with moderately high water table are potentially suitable for fir regeneration, but black alder has a competitive advantage in wetter parts of forest stand. The major advantage of such sites is the absence of beech populations, which are an important competitor to fir in the central European mountains, but a likely equally important limitation would be the presence of hornbeam populations. Our results suggest that less intensive cuttings at carefully selected places are more conducive to fir regeneration than more intensive salvage cuttings.

Some of the Mechanisms for Coexistence of Tree Species Diversity in Tropical Forests: A Review of Effects of Tree Density Dependence

Tree communities contribute to maintenance of species diversity in tropical forests. Coexistence of many tree species is not without competition. Therefore, coexistence of tree species and size diversities occur sequentially or simultaneously in tropical natural forests. Understanding coexistence and competition mechanisms of tree species requires knowledge of interactions within and between species. However, many conservation efforts and strategies failed due to inability to identify and maintain functional coexistence mechanisms among tree species in the forest. Also, most trees died because of pressure on their habitats and not because of limiting growth resources. Hence, species identity, minimum distance and size of the neighbouring trees which are responsible for coexistence of competing trees in most tropical forests have not been explicitly reviewed. Therefore, this review evaluated some of the density dependent mechanisms for coexistence of tree species alpha diversity in tropical forests. Many interactive mechanisms are responsible for coexistence tree species in tropical forests. Inter- and intra-specific competitions are the most significant and both facilitate positive and negative density dependence. Therefore, switching from negative to positive density dependence may occur in some situations. Positive and negative density effects regulate species abundance and coexistence through conspecific and heterospecific structures. Aggregates of conspecific and heterospecific neighbours constitute forest spatial structure. Negative density interactions are mutually exclusive and basically ranged from effect of species identity of neighbours, distance to neighbours and tree size of the neighbours to reference trees in the community structures. Some mechanisms shorten distances for heterospecific than conspecific interactions. Conspecific structures improved survival and growth of rare tree species. Interactive mechanisms in tree community and population structures facilitate species diversity and size inequality, respectively.

Structuring mechanism of tree species diversity pattern in an evergreen broadleaved forest in Con Dao National Park, Vietnam

The spatial structure of a community and the ecological mechanisms that control it are central themes in community ecology. This study aimed to investigate the ecological mechanisms driving the coexistence of tree species in the evergreen broadleaved forests in Con Dao National Park, Vietnam. We employed two null models: complete spatial randomness and inhomogeneous Poisson process within the framework of the individual species-area relationship model. The analyses focused on the effects of habitat filtering and species interactions. We discovered habitat heterogeneity in a 4-ha study plot that contained 5,653 tree individuals belonging to sixty-four plant families. The results demonstrated the critical role of habitat filtering and species interactions in maintaining species diversity within the plant community. The study also indicated that the local diversity structure of tree species depended on the spatial scale. This study went beyond niche and neutral theories by emphasizing the significance of ecological field theory and the principle of asymmetric competition in explaining the coexistence of tree species in evergreen broadleaved forests. Our findings may provide valuable insights into biodiversity conservation and the management of evergreen broadleaved forests, helping to improve further plant diversity conservation activities in the study area.

Growth phenology adjusts to seasonal changes in water availability in coexisting evergreen and deciduous mediterranean oaks

Different leaf (evergreen vs. deciduous habit) and xylem (diffuse-vs. ring-porous wood) traits represent contrasting strategies to face seasonal changes in water availability and temperature. However, how contrasting leaf and xylem habits of coexisting tree species affect stem wood formation and tree-ring development remains poorly understood. Here, we investigated the spatio-temporal patterns of wood formation in two deciduous oaks (Quercus faginea and Quercus petraea) and two evergreen oaks (Quercus ilex and Quercus suber) coexisting in seasonally dry Mediterranean forests along an aridity gradient in Spain. We hypothesized that growth responses to drought and intra- and inter-annual growth patterns would differ between functional groups. We simulated intra- and inter-annual growth using a modified version of the Vaganov-Shashkin (VS) process-based, growth model. The VS model simulations were used to estimate growth changes under a high emission scenario (RCP 8.5) for the current distribution of the study oak species and to forecast their future performance under warm (4.8 ​°C) conditions in the Iberian Peninsula. Our simulations indicate that climate warming would induce a shortening of the ring-growth season and a reduction of radial growth in evergreen and deciduous Mediterranean oaks, particularly in dry sites from southern and eastern Iberia currently occupied by Q. ilex and Q. faginea. Evergreen oaks may better recover after dry periods than deciduous oaks by resuming growth after the summer drought. Low soil water availability in spring would be more detrimental to growth of deciduous oaks. Process-based growth models should be refined and validated to better forecast changes in tree growth as a function of climate.