Suresh Chandra Subedi

To better understand successional changes and drivers of changes in forests, we must (1) test assumptions of successional studies and (2) quantify patterns in species and functional traits in stands varying in successional age. Successional changes are commonly approximated by quantifying changes along chronosequences, or space‐for‐time substitutions. These assumed successional patterns, however, are rarely tested through longitudinal studies of individual sites. To identify drivers of successional trajectories and to address questions of deterministic vs. stochastic community assembly, species composition data must be supplemented with data such as species functional traits. We examined patterns in species composition and functional traits along a chronosequence of tropical dry forest (TDF) sites in North Key Largo, Florida in 1993. To test patterns identified along the chronosequence, we quantified longitudinal change in species and functional traits by remeasuring the sites in 2013. We tested the following predictions: (1) dynamic changes within sites in species composition and functional trait composition will corroborate a pattern indicated by the chronosequence; (2) a growth‐survival demographic tradeoff will be consistent with increasing dominance of evergreen species over the course of succession; and (3) forest succession will demonstrate convergence in both composition and function. As predicted, dynamic changes in species composition and functional traits within sites corroborated patterns quantified over the chronosequence, and species functional groups showed a growth‐survival demographic tradeoff between deciduous species early in succession and evergreen species late in succession. Surprisingly, however, although species composition converged late in succession, functional traits showed greatest divergence late in succession. We suggest that this divergence is due to functionally disparate evergreen and leaf exchanger species coexisting with high abundances for the first time late in succession, and to interspecific competition in an environment of limited resources late in succession. Synthesis. This is the first study in TDF to corroborate compositional and functional changes measured along a chronosequence with results of longitudinal measurements within sites. Additionally, this TDF ecosystem shows a rare successional pattern of convergence in species composition but divergence in functional traits, likely due to the coexistence of different functional groups and interspecific competition late in succession.

Introduction: The endangered Quercus oglethorpensis is a narrowly distributed tree species endemic to the southeastern United States, persisting in fragmented, poorly drained hardwood forests. Reconstructing climatic suitability across past, present, and future periods provides insight into how long-term climatic legacies and ongoing warming constrain its range dynamics. Methods: We modeled climatic suitability during the Last Glacial Maximum (LGM), Mid-Holocene (MH), present, and a projected future period (2071–2100, SSP3-7.0) using species distribution models parameterized with bioclimatic variables. Results: Results indicate a restricted Gulf Coast refugium during the LGM, with a secondary extension into the southern Appalachian foothills, followed by northward expansion into the interior Southeast during the MH. Present-day suitability is highly fragmented, and future projections suggest a pronounced northeastward shift toward the Piedmont and Appalachian regions, with an estimated centroid displacement of ∼672 km from the LGM to the projected future. Although total climatically suitable area is projected to decline modestly (∼5%), the representation of suitable habitat within protected areas declines disproportionately (∼64%), from 0.9% of the current suitable range to 0.3% under future conditions. Multi-period overlap analysis identifies only a single persistent refugium (2.83 km ² ), underscoring the rarity of long-term climatic stability. Discussion: These findings demonstrate how Quaternary climate dynamics and ongoing warming interact to drive range shifts and fragmentation, exposing substantial conservation gaps. Effective conservation of Q. oglethorpensis will require integrating in situ protection of remnant populations with ex situ conservation, connectivity planning, and adaptive forest management under future climate change.

Oak ( Quercus ) diversity is a defining feature of North American forests, comprising over 75% of the region's vegetation. Oaks play a vital role in supporting numerous wildlife species by providing essential food and habitat resources, while also contributing to carbon storage, soil stabilization, and cultural and economic values. Arkansas, with its highly diverse biogeography, offers suitable conditions for a wide range of oak species, leading to the formation of varied vegetation communities. The purpose of this study is to assess the diversity (species richness) of the Quercus genus across the state of Arkansas using multi species niche modeling. Geographic coordinates of 5,987 herbarium records, representing 26 native Oak species, were compiled. We employed an ensemble species distribution modeling approach to predict suitable habitat areas for oak species and to identify hotspots. Our results showed that mean temperature of driest month, precipitation of warmest month, and mean diurnal range contributed > 80% the model prediction. The highest oak richness in Arkansas was found in Crowley's Ridge and Mississippi Valley Loess Plains, each supporting 20 Quercus species, followed by Arkansas River Valley and Ozark highlands with 18 species each. Considering growing concerns over oak forest decline due to anthropogenic and climate change, this study offers valuable insights for conservation, assessment, management strategies, and silviculture planning of oak species in the region.

The tiger Panthera tigris is an apex predator categorized as Endangered on the IUCN Red List. The availability of sufficient prey is a key requirement for its survival. The tiger diet landscape refers to a dynamic ecological picture of the diverse prey species consumed by tigers in a specific region, reflecting the complex relationships between tiger populations and their prey. It can provide information on the tiger’s preferred prey as well as the conservation status of prey species across boundaries. To draw up a road map for the conservation and management of tigers across the Indian subcontinent, where the Bengal tiger Panthera tigris tigris occurs, we identified which prey species make up the majority of the tiger’s diet and answered questions relating to prey density, distribution and conservation status. We reviewed 48 studies published over 30 years (1992–2022) on tiger diet and prey availability. We recorded c. 30 mammalian prey species, with chital Axis axis , sambar Rusa unicolor , wild boar Sus scrofa , Tarai gray langur Semnopithecus hector , northern red muntjac Muntiacus vaginalis and domestic livestock contributing c. 90% of the total relative biomass consumed. Nearly half of the prey species are of conservation concern (categorized as Near-Threatened, Vulnerable or Endangered on the IUCN Red List), and 11 prey species are listed on CITES Appendix I. As part of a sustainable tiger conservation road map, we suggest that the tiger’s major prey species should be incorporated into government protection schemes.

Aim and Questions: Sea‐level rise has been responsible for extensive vegetation changes in coastal areas worldwide. The intent of our study was to analyze vegetation dynamics of a South Florida coastal watershed within an explicit spatiotemporal framework that might aid in projecting the landscape's future response to restoration efforts. We also asked whether recent transgression by mangroves and other halophytes has resulted in reduced plant diversity at local or subregional scales.Location: Florida’'s Southeast Saline Everglades, USA.Methods: We selected 26 locations, representing a transition zone between sawgrass marsh and mangrove swamp, that was last sampled floristically in 1995. Within this transition zone, leading‐ and trailing‐edge subzones were defined based on plant composition in 1995. Fifty‐two site × time combinations were classified and then ordinated to examine vegetation–environment relationships using 2016 environmental data. We calculated alpha‐diversity using Hill numbers or Shannon–Weiner index species equivalents and compared these across the two surveys. We used a multiplicative diversity partition to determine beta‐diversity from landscape‐scale (gamma) diversity in the entire dataset or in each subzone.Results: Mangrove and mangrove associates became more important in both subzones: through colonization and establishment in the leading edge, and through population growth combined with the decline of freshwater species in the trailing edge. Alpha‐diversity increased significantly in the leading edge and decreased nominally in the trailing edge, while beta‐diversity declined slightly in both subzones as well as across the study area.Conclusions: Recent halophyte encroachment in the Southeast Saline Everglades continues a trend evident for almost a century. While salinity is an important environmental driver, species’ responses suggest that restoration efforts based on supplementing freshwater delivery will not reverse a trend that depends on multiple interacting factors. Sea‐level‐rise‐driven taxonomic homogenization in coastal wetland communities develops slowly, lagging niche‐based changes in community structure and composition.

Quercus arkansana (Arkansas oak) is at risk of becoming endangered, as the total known population size is represented by a few isolated populations. The potential impact of climate change on this species in the near future is high, yet knowledge of its predicted effects is limited. Our study utilized the biomod2 R package to develop habitat suitability ensemble models based on bioclimatic and topographic environmental variables and the known locations of current distribution of Q. arkansana. We predicted suitable habitats across three climate change scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5) for 2050, 2070, and 2090. Our findings reveal that the current suitable habitat for Q. arkansana is approximately 127,881 km² across seven states (Texas, Arkansas, Alabama, Louisiana, Mississippi, Georgia, and Florida); approximately 9.5% is encompassed within state and federally managed protected areas. Our models predict that all current suitable habitats will disappear by 2050 due to climate change, resulting in a northward shift into new regions such as Tennessee and Kentucky. The large extent of suitable habitat outside protected areas suggests that a species-specific action plan incorporating protected areas and other areas may be crucial for its conservation. Moreover, protection of Q. arkansana habitat against climate change may require locally and regionally focused conservation policies, adaptive management strategies, and educational outreach among local people.

Coastal dry tropical forests (CDTFs) are important yet vulnerable ecosystems. In this paper, we highlight the special conservation issues facing CDTFs by focusing on one variant of the type, those that occupy limestone substrate in the northeastern Caribbean. Our analysis draws largely from the coastal terrestrial broadleaf forests of the northern Bahamas, the Florida Keys, and southwestern Puerto Rico. Based on the surveys of storm surge recorded during major hurricanes during the last 50 years, we define CDTFs as coastal terrestrial broadleaf forests on ground surfaces elevated up to 5 m above sea level and occurring within 5 km of the coast. These forests are not only threatened by land‐use change from urbanization but also climate‐driven sea level rise (SLR) and hurricanes, which have degraded them and reduced their extent. CDTFs are distinguished from other dry tropical forests by the occasional influence of marine water incursion during periodic storms, requiring species common to these forests to have some level of salt tolerance despite experiencing well‐drained, fresh water conditions during most of their life span. With precipitation being the sole freshwater source for most CDTFs, SLR and the resulting salinization in the rooting zone subjects these forests to increasingly stressful conditions. Hence, even a modest rise in sea level can push numerous imperiled and endangered species and coastal terrestrial broadleaf communities to the edge of their tolerance, causing a decline in extent or their complete disappearance. Outside of protected areas, rapid urbanization has fragmented these forests and reduced their extent, which in turn have modified the interaction between rising seas and forest function. This work emphasizes the need for refined risk assessments to be completed and for conservation measures to be enforced so that resources can be directed appropriately to prevent further loss of CDTFs.Abstract in Spanish is available with online material.

Climate change could amplify the extinction risk of endemic species, and the risk is even greater for species occupying high elevations and mountain ranges. In this study, we assessed the climatically suitable habitat of the only endemic Nepalese bird species, the spiny babbler (Turdoides nipalensis), and predicted the extent of the future (2050 and 2070) habitat of this species under two climate change scenarios (SSP2‐4.5 and SSP5‐8.5). We used georeferenced occurrence points alongside ecologically meaningful climatic and topographic variables to develop an ensemble suitable habitat model using different species distribution modeling algorithms in BIOMOD2. We identified 22,488.83 km² (15%) of Nepal's total land area as suitable habitat for this endemic species, where the nonprotected regions incorporated the largest extent of suitable habitat (88%), with a majority of this suitable area within the central Mid‐Hill region. Under the SSP2‐4.5 scenario, 21.58% and 34.08% of the current suitable habitat range are projected to be lost by 2050 and 2070, respectively. Whereas under the SSP5‐8.5 scenario, our projections suggest that 40.45% and 52.18% of habitat will be lost by 2050 and 2070, respectively. Habitat suitability increased with a rise in warmest quarter precipitation (above 1000 mm), coldest quarter precipitation between 50 and 100 mm, and warmest quarter temperature between 20 and 30°C. Given our results, it is crucial to review the conservation policy of nonprotected areas and formulate a spiny babbler‐specific conservation action plan with a special focus on protecting their primary habitat in human‐dominated landscapes and nonprotected areas.

The Maple-leaf oak, Quercus acerifolia (E.J.Palmer) Stoynoff & Hess, is listed as Critically Imperiled by the State of Arkansas and considered endangered in the IUCN Red List of Threatened Oak Species. It is endemic to the interior highlands of the Ouachita Mountains in west-central Arkansas, where it is reported to occur in only four isolated locations. No specific research exists regarding predicted climate change impacts on the Q. acerifolia, but given its small range and habitat specificity, such climate change-driven impacts will likely pose significant risks to remaining populations. We used an ensemble species distribution modeling (SDM) approach to predict climatically suitable habitat for Q. acerifolia within its native range. We investigate how future changes in climate may impact habitat suitability. Currently, the estimated area of climatically suitable habitat area for Q. acerifolia is 2,523 km2. By 2050, the predicted climatically suitable habitat area is 749 km2, a 70% reduction in habitat extent. By 2100, the model ensemble predicts a suitable habitat of only 285 km2 or an 89% loss of present suitable habitat. The model ensemble also predicted climatically suitable habitat area in 20 counties (14 in Arkansas and six in Oklahoma), including the currently known four locations in Arkansas. Although Q. acerifolia is rare and is at risk of extinction due to potential climate-change driven habitat reduction, the SDM ensemble identified several new habitat areas for the species. New habitat information can be used to search for existing Q. acerifolia populations or guide reintroduction efforts, leading to enhanced focus on long-term management, conservation, and restoration of this critically-imperiled species.