Mapping Impacts of Climate Change on the Distributions of Two Endemic Tree Species under Socioeconomic Pathway Scenarios (SSP)

Effects of topography and spatial processes on structuring tree species composition in a diverse heterogeneous tropical karst seasonal rainforest

Ecological communities are composed of complex vegetation that differs from community to community and also within the community. The variability of tree species in the community in relation to their environments can be studied by using different statistical tools. The present study was conducted to describe and also to quantify the spatial pattern, abundance and diversity of tree species in the Western Ghats of Karnataka. The spatial pattern of tree species was studied by using Poisson and Negative binomial distributions. Results indicate that most of the selected tree species followed Negative binomial distribution having clumped pattern. The Species abundance distribution was studied by using log series and lognormal distributions in six different forest types (Evergreen, semievergreen, moist deciduous, dry deciduous, scrub and shola forest types). All six different forest types followed lognormal distribution where as evergreen and shola forest types followed log series distribution also. Diversity of the tree species in different forest types was quantified by different diversity indices; it was found that evergreen forest is most diverse.

Inferring the processes underlying the spatial distribution patterns of tree species is fundamental for understanding species coexistence. Here, we examined spatial distribution patterns of woody plants by using the univariate pair correlation function to quantify spatial patterns of species in a fullly mapped 25 ha subtropical plot in China. We analyzed the relationships between the species attributes and spatial distribution patterns of 137 tree species with at least one individual per hectare. The results showed that aggregated distributions were the dominant pattern for species in the Badagongshan subtropical forests, and that the percentage of significantly aggregated species decreased with increasing spatial scales. Rare species were more aggregated than intermediate and abundant species, but they were more easily influenced by habitat heterogeneity. Also, there was significantly negative relationship between species abundance and species aggregation intensity. The aggregation intensity showed negative relationships to species mean diameter at breast height (DBH) and maximum DBH, i.e., species became more regularly spaced as species stature increased. Species functional traits (e.g., growth form and phenological guild) also had obvious effects on the spatial patterns of species. However, spatial patterns of tree species were not related to the dispersal mode. Our results partially conformed to the prediction that species’ attributes influenced species’ spatial patterns following similar laws, even after controlling for the effects of habitat heterogeneity. Consequently, species attributes (species abundance, mean DBH, maximal DBH, growth form, phenological guild, etc.) and habitat heterogeneity may primarily contribute to spatial patterns and species coexistence in natural forests.

QuestionsHow do spatial patterns of tree distribution and species co‐occurrence differ between primary and secondary tropical rain forests? What signatures of ecological processes might be discerned by comparing the spatial patterns of trees between primary and secondary forest plots?LocationTropical rain forest vegetation, lowlands of Papua New Guinea.MethodsAll trees over 5 cm DBH were surveyed in two non‐replicated 1‐ha plots situated in primary and secondary forest. Grid location, DBH, height and species identity were recorded for all surveyed trees. Analysis of the spatial pattern and the autocorrelation of tree sizes and identities were used to assess the structure of the forest found within the plots. Functions combining Ripley's K and the individual species–area relationship were applied to study the spatial distribution of trees and species diversity.ResultsThe spatial distribution of common species, and all stems collectively, was aggregated in the secondary forest plot but not different from random in the primary forest plot. Diameter and height were also strongly spatially auto‐correlated in the secondary forest plot but not in the primary forest plot. Conspecific aggregations were more common in the secondary forest plot. Finally, the secondary forest plot was characterized by the presence of diversity‐repelling species and lower diversity than the primary forest plot, where diversity‐accumulating species were present.ConclusionsWe attribute the weaker autocorrelation of tree size in the primary forest to the development of size hierarchies throughout the course of stand aging. The conspecific aggregation and low local diversity within the secondary forest plot are likely caused by dispersal limitation during a brief period of establishment after disturbance. The higher local diversity of the primary forest can be explained by the reduction of species aggregation through increased mortality of conspecifics. This is caused by strong intraspecific competition, supporting the spatial segregation hypothesis (interspecific spatial segregation).

Summary 1 The Bogue Chitto River, Louisiana, USA, is a meandering river with 16 early successional tree species having > 1% relative dominance. We hypothesized that geomorphic processes associated with river planform promote predictable spatial patterns of tree species within each river bend by influencing the physical conditions under which the forest is initially established. We predicted that (i) species of trees differ in their location of recruitment along the point bar, and trees on older land reflect the spatial patterns of recent recruits; (ii) the location of recruitment differs among tree species in elevation, soil texture, herbaceous cover and light; and (iii) a specific pattern of elevation, soil texture and tree species in the earliest stage of forest succession characterizes multiple river bends in a reach. 2 On the floodplain interior to one bend, we mapped all trees and sampled seedlings and saplings, elevation, soil texture, herbaceous cover and light. In newly established forest adjacent to the point bars of eight bends, we surveyed spatial patterns of tree species, elevation and soil texture. 3 Trees of most species had characteristically become established along either the upstream or downstream segment of each point bar. Variation in tree species composition was gradual both along the point bar and along an axis of increasing age of land. The locations of recruitment and mature trees were the same for eight of 11 common species on the focal river bend. 4 The locations of tree recruitment and of mature trees of specific species on the focal bend were related to spatial patterns of elevation (corresponding to flood regime), soil texture, light, herbaceous cover and the inferred pattern of shear stress by flood water on the point bar. The same patterns of elevation and soil texture and locations of tree species characterized multiple river bends. 5 Geomorphic processes related to the river planform of the Bogue Chitto River promote spatially complex but predictable patterns of primary forest succession.

Disturbance related vegetation dynamics differs with Azorean mountain forest communities, where each tree species has its own regeneration strategy. Knowledge of the spatial distribution of tree species may help us to generate hypotheses on the relation between disturbance, regeneration and spatial organization and on the possible underlying ecological mechanisms. In view of this, we asked the following questions regarding the spatial pattern of tree species: What is the spatial distribution of saplings and adults? Are there any spatial associations or exclusions between saplings and adults of the same and different species? To what extent do the disturbance regimes and regeneration strategies of each species explain its spatial pattern? Six 225 m (15×15 m) plots were placed in each of three different forest types in three Islands (Pico, Terceira and Flores). Patterns of tree individuals were analysed through Morisita’s index of dispersion (Iδ) and Iwao ω index. With the exception of Laurus azorica and Frangula azorica. saplings are in most cases aggregated. Erica azorica is the only species whose adults are aggregated at short distances. Spatial distribution is mostly random for the other species. At short distances, few strong associations or exclusions were detected. Pioneer species such as Juniperus brevifolia tend to be more aggregated due to their dependence on gaps to germinate and recruit new individuals. In fact, increasing disturbance and gap size enhances the regeneration of J. brevifolia. Primary species tend to be randomly distributed in part due to their strategy of forming seedling-sapling banks. Spatial pattern of tree species is largely explained by disturbance regimes and regeneration strategies of each species. However, factors such as habitat related patchiness, competition and dispersion limitation may also explain many of the observed patterns.

Termite mounds have been poorly studied in tropical rainforest in contrast to those of savannahs where they create fertility hotspots and influence the spatial pattern of vegetation. An inventory of termite mounds and of 15 tree species with a diameter at breast height ≥ 10 cm was carried out in two 800-ha blocks, in two rainforest sites located in northern Congo. We used inhomogeneous and intertype K functions to study the spatial pattern of termite mounds and of tree species around mounds, respectively. We found that mounds in Loundoungou were over-dispersed within a radius of less than 70 m, while those in Mokabi were randomly spaced. Tree species within a 20-m radius around a mound were aggregated towards the mound, e.g. Entandrophragma cylindricum, randomly distributed, or even repulsed by the mound. The specific responses also differed in the two sites. These results suggest that (i) the mounds in Loundoungou were created by savannah termite species 3,000-2,000 years BP during the Late Holocene Rainforest Crisis and (ii) the mounds in Mokabi are characteristic of forest mounds. The impact of termite mounds on the spatial pattern of tree species is thus site-dependent, and these differences might be due to species seed dispersal strategies and to soil calcium concentrations.

Tree species were assembled into forest communities by various processes, and it was found that trees are spatially arranged in a community by the abiotic and biotic conditions within that community. Here, we explore the abiotic processes and biotic interactions in the spatial patterning of tree species across six old‐growth forest types in a tropical nature reserve. Four spatial point process models (the homogeneous Poisson process, inhomogeneous Poisson process, homogeneous Thomas process, and inhomogeneous Thomas process) were used to evaluate the potential contribution of the random processes, habitat heterogeneity, dispersal limitation, and the joint effects of dispersal and habitat heterogeneity to the formation of the spatial patterns of tree species. A combination of the null model and size–distance regression analysis was applied to assess the effect of competition and facilitation on the tree species assembly. We found that the homogeneous and inhomogeneous Thomas processes were the best models for describing the spatial patterns of more than 85% tree species across the six tropical forests. The combination of the null model and size–distance regression analysis showed that 37–44% of tree species were affected by competition and 9–24% of tree species were affected by facilitation across the six tropical forest types. Competition was the dominant form of species interactions in forests with mild abiotic conditions such as the tropical montane rain forest and tropical lowland rain forest. Meanwhile, facilitation was the most important biotic interaction in the abiotically harsh tropical montane dwarf forest on mountaintops. Our study suggests that dispersal limitation and the joint effects of dispersal and habitat heterogeneity were the dominant abiotic processes in controlling the spatial patterning of trees in tropical forests. Moreover, the relative importance of competition and facilitation in the assembly of the tree species varied among the forest types with different abiotic conditions.

Double-edged effects of climate change on plant invasions: Ecological niche modeling global distributions of two invasive alien plants

Designing sustainable management strategies in groundwater-dependent socio-economic systems in areas with scarce water resources and protected wetlands is a challenging issue. The high vulnerability of these systems to droughts will be exacerbated even further under future climate change (CC) and socio-economic scenarios. A novel integrated bottom-up/top-down approach is used to identify “climate resilient pathways”, from which to co-design adaptation strategies to reduce the impact of potential future CC and socio-economic scenarios. The approach followed two steps (1) the generation of local CC and socio-economic scenarios by downscaling global/regional climate models and (2) the identification and assessment of potential adaptation strategies through an iterative bottom-up/top-down approach. Top-down assessments of the impact of CC have been undertaken by propagating local scenarios within a chain of mathematical models based on expert criteria/assumptions. This allowed us to analyse of the physical vulnerability of the system under different potential CC and socio-economic scenarios by simulating them with a sequential modelling of rainfall–recharge, agriculture, and hydrological processes through a distributed groundwater finite difference model. These model results were discussed with the stakeholders at a first workshop, which aimed to identify potential adaptation strategies. The influence of the adaptation strategies on the future hydrological status was assessed by simulating them through the chain of models. These results were the inputs into the discussions at a second workshop, which aimed to validate and/or improve the results of the first workshop. The methodology was applied in the Upper Guadiana River Basin, where there is a long-standing conflict between wetland conservation and groundwater overexploitation for intensive agriculture. The future horizon 2016–2045 is analysed with the scenarios compatible with the emission scenario RCP4.5. The research has allowed us to conclude that groundwater pumping reduction would be the most robust and effective measure to reduce the impact of CC in the area.

We characterized the dispersal modes and spatial patterns of 128 tree species in a tropical semi-evergreen forest of Arunachal Pradesh, northeastern India. A high percentage of species are animal-dispersed (78%), while about 22% (28) are dispersed abiotically (wind or gravity-dispersed). Of the animal-dispersed species, 54 species were primarily bird-dispersed, 25 were mammal-dispersed, and 21 were dispersed by both groups. We hypothesized that adult tree distribution patterns were related to dispersal mode and fruit size. We predicted that tree species with mechanisms for long-distance seed dispersal are likely to show more uniform or random spatial patterns than those with limited seed dispersal. Tree species with large fruits were also predicted to have greater levels of clumping than those that have small fruits. However, all tree species had a clumped distribution pattern. At the community level, we found no differences in spatial patterns based on dispersal mode for a subset of 50 tree species. Fruit size was, however, positively correlated with higher levels of spatial aggregation suggesting that tree species distributions are to an extent limited by dispersal. The importance of dispersal mode in determining adult tree distribution patterns at the community level may be obscured by interacting effects of other factors such as patchy habitat conditions and density-dependent mortality factors at different life-history stages that ultimately determine adult tree distributions.

Competitive interactions significantly impact plant diversity, playing a crucial role in community assembly. This study, conducted in the evergreen broadleaved forest of Bidoup-Nui Ba National Park in southern Vietnam, aimed to investigate neighborhood competition and spatial patterns of tree species. In 2024, a 4-ha study plot was established within the strictly protected zone of the national park for data collection purposes. A total of 7,666 trees with a diameter at breast height (DBH) ≥2.5 cm, representing sixty-six species from thirty-one families, were identified, measured for DBH, and mapped for stem location. Unmarked and marked point-pattern analyses were employed to examine the spatial patterns of the most abundant species. The results revealed that the fifteen most abundant species exhibited an aggregated distribution at small scales (0–30 m), with their spatial patterns correlating with their life-history stages. Specifically, the spatial arrangements shifted from aggregation during the juvenile stage to randomness or regularity at the subadult and adult stages. Intra- and interspecific competition were found to be closely tied to spatial scale, showcasing instances of both symmetric and asymmetric competition. Notably, interspecific associations mainly exhibited spatial independence, especially at 0–50 m scales. This study identified several vital ecological processes governing the spatial distribution and neighborhood competition among broadleaved tree species in the study area, including dispersal limitations, symmetric and asymmetric competition, and self-thinning of tree species.

Mountain forest ecosystems provide us with life-supporting ecosystem services that are valuable for local, regional, and global communities. Ecological niche-based models have been used extensively, with remarkable success, in understanding the influence of climate change on potential distribution of species. In this study, we used maximum entropy (MaxEnt) modelling to predict the potential distribution of ecologically important tree species, Abies, Picea, and Juniperus, at the eastern edge of the Tibetan Plateau in China. The potential distribution of tree species was modelled and predicted on genus level for current and three representative concentration pathway (RCPs) based future (2050s and 2070s) climate conditions. The model performed well and gave reliable results for current and potential species’ distribution. Precipitation of wettest month was the most important environmental variable for determining the habitat suitability of all tree species, with 30.3% (Abies), 51.2% (Picea), and 57% (Juniperus) contribution to model output, respectively. Temperature seasonality, temperature annual range, and soil type also made the most significant contribution to model outputs. Model projections under current climate highlight that the total suitable habitats, which included regions with different probability of species occurrence, for Abies (3234.2 km2) was much higher than Picea (2003.7 km2) and Juniperus (1784.8 km2). However, projections of habitat suitability under current climate scenario projected onto future climate change scenarios for all concentration pathways in 2050s and 2070s, showed a clear decline in potentially suitable habitats for all three species. The shifts in geographic distributions under future climate scenarios showed an unusual pattern, with slight downward shift of the mean elevation with high habitat suitability for the occurrence of tree species in most RCPs, accompanied by a decrease in the elevational range of suitable habitats. The results of this study highlight the urgent need for forest management strategies to conserve the habitats of these species. Our study offers base-line information on the impact of climate-change on major tree species which can aid in guiding adaptation strategies for forest conservation and management in order to sustain the delivery of ecosystem services in the future.

Aims Understanding processes underlying spatial distribution of tree species is fundamental to the study of spe-cies coexistence and diversity.Our objective was to determine the spatial structure and identify the processes that may generate spatial patterns of trees in a tropical lowland rain forest community on Hainan Island of South China.Methods Based on four models of point pattern analysis (homogenous Poisson process,inhomogenous Poisson process,homogenous Thomas process and inhomogenous Thomas process),we evaluated the potential contribu-tion of habitat heterogeneity and dispersal limitation to the formation of spatial patterns of tree species in two 1-hm2 stem-mapped forest dynamic plots.The relative importance of each process was assessed at six different spatial scales ( 2 m,2-5 m,5-10 m,10-15 m,15-20 m and 20-25 m).Important findings All stems combined revealed a strong aggregation at short distance (≤2 m),and the degree of aggregation decreased with increasing distance.Among the four models simulating tree distribution and pat-terning,the homogeneous Thomas process was the best-fit model.This result suggested that spatial patterns of tree species in tropical lowland rain forest might be formed by dispersal limitation.The homogeneous Poisson process that models the effect of spatial complete randomness was the second-best model.The inhomogeneous Thomas process and inhomogeneous Poisson process were equally important to forming spatial patterns of trees;they simulated the joint effects of habitat associations and dispersal limitation and modeled heterogeneity,respec-tively.The proportion of best-fit models differed across different scales.The dispersal limitation was a most im-portant mechanism in spatial patterning of tree species at most scales,while complete randomness process was second in importance.The joint effects of habitat associations and dispersal limitation mainly influenced tree dis-tribution at small scales (0-5 m).However,habitat heterogeneity only affected the distribution at larger scales (15-25 m).

Understanding processes underlying spatial distribution of tree species is fundamental to studying species coexistence and diversity. This study modeled point patterns of tree distribution, expressed by Cartesian coordinates of individual trees within a mapped forest stand, for the purpose of identifying processes that may generate spatial patterns of tree communities. We used four primary point pattern processes (homogeneous Poisson process, inhomogeneous Poisson process, homogeneous Thomas process, and inhomogeneous Thomas process) to model tree distribution in two stem-mapped forests in Taiwan, Republic of China. These four models simulate spatial processes of habitat association and seed dispersal, allowing us to evaluate the potential contribution of habitat heterogeneity and dispersal limitation to the formation of spatial patterns of tree species. The results showed that the inhomogeneous Thomas process was the best fit model and described most of the species studied, suggesting that spatial patterns of tree species might be formed by the joint effects of habitat associations and dispersal limitation. The homogeneous Thomas process that models the effect of dispersal limitation was the second best model. We also found that the best fit models could be predicted by species attributes, including species abundance and dispersal mode. The significant traits, however, differed between the two study plots and demonstrated site-specific patterns. This study indicated that the interactive operation of niche-based (habitat heterogeneity) and neutral-based (dispersal limitation) may be important in generating spatial patterns of tree species in forest communities.