Montane Forest Research Articles

Epiphytic CAM bromeliads indicate vulnerability of tropical forest communities to climate change.

Vascular epiphytes have a variety of mechanisms to trap and retain water, including crassulacean acid metabolism (CAM). Niche segregation was investigated for epiphytic bromeliads on the tropical Caribbean island of Trinidad, where habitats range from lowland deciduous forests to high-rainfall montane tropical forests, ~1000 m in elevation. Four tank-impounding bromeliad epiphytes in the genus Aechmea (Ae. aquilega, Ae. fendleri, Ae. nudicaulis and Ae. dichlamydea) with CAM were mapped across their distinct geographical and elevational zonations in northern Trinidad and Tobago. Species distribution modelling was used to determine environmental limitations for each species. Anatomical and physiological measurements included leaf succulence traits, gas exchange and CAM activity; hydraulic conductance and vulnerability; stomatal sensitivity and quantum yield responses to nocturnal temperature and long-term water deficits. A total of 2876 field observations identified the transitions between the lowland Ae. aquilega and montane Ae. fendleri, occurring >500 m a.s.l. at the drier western end of the Northern Mountain Range and at progressively lower elevations towards the wetter, eastern region. Anatomical and physiological sensitivities of gas exchange, CAM activity and water use, and responses to elevated nocturnal temperatures and drought, were markedly different for Ae. fendleri compared with Ae. aquilega or the ubiquitous Ae. nudicaulis. The species distribution model highlighted the susceptibility of Ae. fendleri to a changing climate. For each species, physiological and anatomical traits were tailored to environmental tolerances, consistent with specialist or generalist niche preferences. Using Intergovernmental Panel on Climate Change scenarios, we predict that rapid rainfall and temperature changes will lead to the loss of Ae. fendleri and associated lower (and upper) montane forest communities from Trinidad, seriously impacting both biodiversity and critical ecosystem functions here and in other tropical island habitats. Epiphytic bromeliads act as markers for threatened communities, and their physiological tolerances represent key indicators of climate change impacts.

Another Recently Recognized Monotypic Genus Is No Longer Monotypic: A Second Species of Pachycaulos (Gesneriaceae) from the Huancabamba Depression in Northern Peru

Abstract— A new species is described from the Huancabamba Pass, a relict montane forest in northwest Peru, near the southwestern border of Ecuador. Pachycaulos huancabambae J.L.Clark & Moonlight is a terrestrial or lithophytic herb with scandent stems that grows in dense mats of bryophytes. This is the second species of Pachycaulos and renders that taxon as non-monotypic. We discuss several other genera of Gesneriaceae that are also no longer monotypic because of recent exploratory research in tropical forests and increased taxon sampling from ongoing phylogenetic studies. A molecular phylogenetic analysis based on nrDNA ITS is presented that strongly supports the monophyly and sister-group relationship of P. huancabambae and P. nummularia. Based on IUCN guidelines, a preliminary conservation status is assigned as Critically Endangered (CR).

A New Miniature Species of Arthroleptis (Anura: Arthroleptidae) from Nyungwe National Park, Rwanda

A new, very small-sized species of Arthroleptis is described from western Rwanda. The new species occurs locally endemic in Nyungwe Forest and Cyamudongo Forest, where it inhabits the leaf litter of montane forests between 1800 and 2200 m a.s.l. It differs from all other members of the genus by a unique combination of morphological characters, including size (SVL of adult males 16.0–16.5 mm), skin texture, length of hindlimbs, and ventral colour pattern; by characteristics of its advertisement call that consists of a single note lasting 17.4 ± 6.4 [11–32] ms and has a dominant frequency of 5861 ± 188 [5531–6029] Hz; and also in the sequence of the 16S rRNA gene that differs from available homologous sequences of other species of the genus by an uncorrected p-distance of at least 4.6%. Details of the natural history as well as two additional call types are described.

Tropical montane forest (Shola) tree species can regenerate under abandoned exotic tree plantations in the Western Ghats of India

Abstract Whether environmental conditions under exotic tree plantations abandoned in the Western Ghats of India can facilitate the natural regeneration of tropical montane forest (Shola forest) tree species is being debated. In many cases, the exotic tree plantations are being cleared to allow for the restoration of native ecosystems. In this paper, we examined whether exotic tree plantations have indeed a negative effect on the regeneration of Shola forest tree species. For this, we assessed the abundance, diversity, and composition of the regeneration of Shola forest tree species in plantations, each with different dominant tree species (Acacia mearnsii, Pinus sp., and Eucalyptus sp.). We tested the abundance of regenerating native tree species against the main plantation canopy species (plantation type) as well as other environmental factors (aspect, distance to nearest Shola forest, structural diversity, slope, elevation, presence of herbivores, and canopy closure). We found that the number of native tree species regenerating in all plantation types was at an acceptable level: 1960, 1773, and 462 individuals ha−1 for Acacia, Eucalyptus, and Pinus plantations, respectively. A rare fraction analysis showed that the highest number of Shola tree species were regenerating under Acacia mearnsii (25) followed by Eucalyptus (19) and Pinus (8) plantations. The density and diversity of regenerating Shola trees was greatest under Acacia plantations and northern aspects but declined with increasing elevation. The presence of herbivores also reduced the density and diversity of Shola tree regeneration. We concluded that the restoration of Shola forest in the Western Ghats is possible in existing stands of exotic tree species and this process can be accelerated with appropriate silvicultural methods. We additionally recommend that studies involving long-term exclosures can provide valuable insights into the effects of browsing on regeneration and species composition.

Near-field variability of evaposublimation in a montane conifer forest

Methods that combine in-situ measurements, statistical methods, and model simulations with remotely sensed data provide a pathway for improving the robustness of surface flux products. For this research, we acquired eddy-covariance fluxes along a five-tower transect in a snowy montane forest over three consecutive winters to characterize near-field variability of the subcanopy environment. The novel experiment design enabled discriminating near-field evaposublimation sources. Boosted regression trees reveal that the predictive capacity of state variables change with season and storm cycle frequency. High rates of post-storm evaposublimation of canopy-intercepted snow at this site were constrained by short residence time of snow in the canopy due to throughfall and melt. The snow melt-out date for open vs. closed canopy conditions depended on total snowfall accumulation. Compared with low accumulation years, the snow melt-out date under the dense canopy during the high accumulation winter was later than for the open area, as shading became more important later in the season. The field experiments informed an environmental response function that was used to integrate ERA5-Land latent heat flux data at 20-km nominal resolution with USFS Tree Canopy Fraction data at 30-m resolution and showed near-field flux variability that was not resolved in model simulations. Previous evaposublimation results from experiments in alpine and subalpine environments do not directly translate to a montane forest due to differences in process rates.

Twenty‐five years of change in forest structure and nesting behavior of Hawaiʻi ʻelepaio

Long‐term ecological studies are invaluable for detecting changes over time. Forest restoration has been a conservation priority in Hawaiʻi, where invasive species have negatively impacted native bird habitat. During 1993–1994, a study was conducted of Hawaiʻi ʻelepaio (Chasiempis sandwichensis) nest site selection and forest composition in mesic montane forest along Mauna Loa Road in Hawaiʻi Volcanoes National Park. We returned to the site and repeated the methods used in the earlier study to record Hawaiʻi ʻelepaio nest site selection (tree species, tree and nest height, and tree girth [diameter at breast height, DBH]) from 2015 to 2017, and measured forest composition (tree density, relative abundance, height, and DBH) in 2019. Three times as many nests were found in ʻaʻaliʻi (Dodonaea viscosa) as in koa (Acacia koa) in both time periods. Heights of koa and ʻaʻaliʻi did not change, but their DBH increased over time. The relative height of nests in ʻaʻaliʻi trees did not change, but nests in koa were placed higher in the crown during the later study. Overall tree density increased from 1,619 (95% confidence interval [CI] = 1,499–1,740) trees/ha to 2,583 (95% CI = 2,176–3,096) trees/ha. Koa relative abundance was 53% of total trees earlier and 45% later, ʻaʻaliʻi remained at 47%, and māmane (Sophora chrysophylla) increased from 0 to 8% over time. Our results indicate that changes in forest composition affect nesting behavior, but in ways that are not necessarily simple or consistent.

Dynamic response of root-associated fungal community structure to nitrogen and phosphorus additions in a subtropical forest

The impacts of nitrogen (N) and phosphorus (P) additions on root-associated fungi (RAF) of mixed roots in forest soils remain poorly understood. We investigated how RAF communities respond to N and P inputs in a subtropical montane forest using a time-series sampling approach. Our results showed that sampling time had a significant effect on total fungal richness, while the N addition had significant impacts on symbiotrophic rather than saprotrophic fungal richness. RAF community composition was strongly influenced by P addition treatments regardless of sampling time. Furthermore, we found that RAF community structure was mainly affected by soil NO3–-N, C/N and N/P ratios. This influence could be ascribed to the direct control of fungal activities and the indirect effects of fertilization on soil properties. Together, our findings highlight the importance of considering temporal variation in RAF responses to fertilization for a more comprehensive understanding of fungal community dynamics.

A new high elevation species of Oreophryne Boettger (Anura: Microhylidae) from Sulawesi, Indonesia.

We examined the morphology of 50 specimens of Sulawesian Oreophryne and recognize a distinct, undescribed species. Based on morphological data and supported with phylogenetic analysis of the 16S rRNA gene, it is herein described and named as Oreophryne riyantoi sp. nov. The new species is diagnosed by having a combination of rounded snout in dorsal and lateral view, indistinct tympanum, narrow interorbital distance, small hands, small terminal discs on fingers and toes, toes without webbing, short legs, and dorsal surfaces of head, body and limbs irregularly tuberculated in life. It was found in leaf litter on the forest floor in extremely wet primary montane forest on Mount Mekongga at an altitude of 2528 m asl. The forest-dwelling habit of this terrestrial frog is unusual because other terrestrial Oreophryne occuring at high-altitude live in open grassy or fern dominated meadows. Four endemic species of Oreophryne are now known from Sulawesi. However, herpetological research activities, including high elevation surveys and additional taxonomic work, are necessary to achieve a comprehensive understanding of Oreophryne diversity and phylogeography in Sulawesi.

Evaluating community-wide temporal sampling in passive acoustic monitoring: A comprehensive study of avian vocal patterns in subtropical montane forests

Background: Passive acoustic monitoring (PAM) has become a popular tool for bird monitoring, with vocal activity rate (VAR) being a key metric to gauge bird populations. However, the effective temporal sampling design at the community level for representative VAR data remains underexplored. Methods: In this study, we used vocalizations extracted from recordings of 12 bird species, taken at 14 PAM stations situated in subtropical montane forests over a four-month period, to assess the impact of temporal sampling on VAR across three distinct scales: seasonal, diel, and hourly. For seasonal sampling analysis, we employed hierarchical clustering analysis (HCA) and the coefficient of variation (CV). Generalized additive models (GAMs) were utilized for diel sampling analysis, and we determined the average difference in VAR values per minute for the hourly sampling analysis. Results: We identified significant day and species-specific VAR fluctuations. The survey season was divided into five segments; the earliest two showed high variability and are best avoided for surveys. Data from days with heavy rain and strong winds showed reduced VAR values and should be excluded from analysis. Continuous recordings spanning at least seven days, extending to 14 days is optimal for minimizing sampling variance. Morning chorus recordings effectively capture the majority of bird vocalizations, and hourly sampling with frequent, shorter intervals aligns closely with continuous recording outcomes. Conclusions: While our findings are context-specific, they highlight the significance of strategic sampling in avian monitoring, optimizing resource utilization and enhancing the breadth of monitoring efforts.

A new Andean species of Merostachys Spreng. from Bolivia (Poaceae: Bambusoideae: Bambuseae): Merostachys nigricans

Based on fieldwork and examination of herbarium specimens, a new Andean species, Merostachys nigricans, from the humid montane forest of Bolivia is described and illustrated. We provide notes about distribution, habitat, ecology, conservation status, phenology, common names, uses, and taxonomic affinities with M. ramosa and M. yungasensis. A distribution map is also included. The presence of an unusually black internal surface of basal internodes distinguishes it from all other species in the genus and gives rise to its name.

Bird communities in a selectively logged tropical montane forest are dominated by small, low-elevation species

Tropical montane forests are critical centres of terrestrial biodiversity and endemism, and face a range of threats, including selective logging and climate change. However, few studies have explored the joint influence of these threats, particularly in tropical mountains, despite how crucial it is to understand the cumulative impact of forest loss and climate change on biodiversity. We used mist-netting and bird ringing data from a long-term (10-year) community and population monitoring program to examine how the composition of the mid-elevation Eastern Himalayan understorey bird community changed in the mid-elevation primary and logged forest. Because logged forest is warmer than primary forest, we hypothesised that the bird community would shift towards lower elevation species, with a faster transition in logged forest. Further, because logged forest has lower arthropod abundance, we hypothesised that the primary forest community would have larger species than the logged forest community. Our study shows that the bird community in the logged forest shifted towards lower-elevation species than in the primary forest (although this was not statistically significant). Moreover, we found that smaller species were better able to colonise warmer logged forest, whereas larger species reached higher densities in primary forest. These trends are likely to be driven by climate change causing upslope range shifts and logged forest selecting for species that are likely to tolerate the consequently altered abiotic (higher temperatures) and biotic (lower resources) environment. These findings have significant implications for understanding the impacts of forest loss and climate change on biodiversity, particularly in tropical montane forests.

DINAMIKA PERTUMBUHAN POHON DI HUTAN RESTORASI BODOGOL TAMAN NASIONAL GUNUNG GEDE PANGRANGO, JAWA BARAT

The Restored Forest (RF) in Bodogol, Gunung Gede Pangrango National Park (GGPNP) is located in the degraded lowland forest area. The Bodogol RF constituted the area of the ecosystem restoration program, where the initial tree planting was carried out by Mrs. Megawati Soekarnoputri the 5th President of the Republic of Indonesia. In that restored forest area, a study was conducted by establishing one hektare plots. We recorded 26 tree species and 16 families, including 14 tree species that were used in the restoration, four cultivated species, and eight species that naturally enter the site as new arrival (recruitment). The total basal area was 7.47 m2/Ha and tree density was 256 trees/Ha. The mean diameter growth was 1.78 cm/year, and the highest diameter growth was Hibiscus tilliaceus (2.42 cm/year). The mean total height growth was 0.52 m/year, and the highest was Paraserianthes falcataria (0.85 m/year). The density of Toona sureni was very high (61 trees/Ha) and in the future it ay dominate the forest will, therefore other tree species native to Mt. Gede-Pangrango should be planted to enrich the present restored forest so as to encourage the development of mixed lowland or montane forests similar to the original climax forests with high species diversity. Structurally, about 50 % of the RF has been achieved, but species composition still needs further enrichment either by active intervention of planting native TNGGP species if deemed necessary or by allowing succession to take place naturally, although it will take a very long time.

Stable functional structure despite high taxonomic variability across fungal communities in soils of old-growth montane forests

BackgroundMajor advances over the past decade in molecular ecology are providing access to soil fungal diversity in forest ecosystems worldwide, but the diverse functions and metabolic capabilities of this microbial community remain largely elusive. We conducted a field survey in montane old-growth broadleaved and conifer forests, to investigate the relationship between soil fungal diversity and functional genetic traits. To assess the extent to which variation in community composition was associated with dominant tree species (oak, spruce, and fir) and environmental variations in the old-growth forests in the Jade Dragon Snow Mountain in Yunnan Province, we applied rDNA metabarcoding. We also assessed fungal gene expression in soil using mRNA sequencing and specifically assessed the expression of genes related to organic matter decomposition and nutrient acquisition in ectomycorrhizal and saprotrophic fungi.ResultsOur taxonomic profiling revealed striking shifts in the composition of the saprotrophic and ectomycorrhizal guilds among the oak-, fir-, and spruce-dominated forests. The core fungal microbiome comprised only ~ 20% of the total OTUs across all soil samples, although the overlap between conifer-associated communities was substantial. In contrast, seasonality and soil layer explained only a small proportion of the variation in community structure. However, despite their highly variable taxonomic composition, fungal guilds exhibited remarkably similar functional traits for growth-related and core metabolic pathways across forest associations, suggesting ecological redundancy. However, we found that the expression profiles of genes related to polysaccharide and protein degradation and nutrient transport notably varied between and within the fungal guilds, suggesting niche adaptation.ConclusionsOverall, our metatranscriptomic analyses revealed the functional potential of soil fungal communities in montane old-growth forests, including a suite of specialized genes and taxa involved in organic matter decomposition. By linking genes to ecological traits, this study provides insights into fungal adaptation strategies to biotic and environmental factors, and sheds light on the importance of understanding functional gene expression patterns in predicting ecosystem functioning.BiaDVnGNFcTVJp_FejwVZqVideo

Plant Diversity, Aboveground Biomass and Carbon Stock in an Isolated Tropical Sub Montane Forest in Sri Lanka

This study was conducted at Rilagala conservation forest, Nawalapitiya to assess and compare the plant diversity, above ground biomass and carbon stock in the periphery and interior of an isolated sub montane forest in Sri Lanka. All trees above 5 cm Diameter at Breast Height (DBH) in eleven randomly demarcated 25 m × 25 m plots were recorded. Distance up to 100 m from the forest boundary considered as the periphery (8 plots) and over 200 m as the core (3 plots). A total of 1,583 trees belonging to 29 species were recorded and aboveground biomass (AGB) and carbon stocks were calculated using allometric equations. The tree diversity of each plot was calculated using the Shannon diversity index (H’). Results were statistically analysed using single factor ANOVA. The species richness and H’ were the highest at the periphery (n=23, H’= 2.55) while the lowest at forest interior (n=11, H’= 1.97). The highest tree density was recorded at periphery (2,992 trees ha-1) and it decreased to 1,408 trees ha-1 towards the core. The average DBH was 8.5 ± 3.33 cm and it increased towards the forest interior (9.7 ± 4.51 cm) from the periphery (7.2 ± 3.74 cm). Estimated aboveground biomass ranged from 63.99 - 108.13 Mg ha-1 with a mean of 82.53 ± 14.39 Mg ha-1. The above ground C stock was estimated from 31.99 - 54.07 Mg ha-1 with a mean of 41.26 ± 7.2 Mg ha-1. However, there was no significant difference between forest periphery and core in variables, except species richness (p<0.05). The study revealed that the diversity and density of trees decreased towards the forest interior and vice versa was recorded for DBH, AGB and carbon stock. The study highlights the importance of conserving isolated tropical sub montane forest patches for carbon sequestration.

Carbon Stable Isotope Ratio of Dissolved Organic Matter as a Tool To Identify Its Sources and Transformations in a Tropical Montane Forest in Ecuador.

Dissolved organic matter (DOM) contributes to forest C cycling. We assessed temporal variability, sources, and transformations of DOM during four years in a tropical montane forest with the help of stable C isotope ratios (δ13C values). We measured δ13C values of DOM in rainfall (RF), throughfall (TF), stemflow (SF), litter leachate (LL), soil solutions at the 0.15 and 0.30 m depths (SS15, SS30), and streamflow (ST) with TOC-IRMS. The δ13C values of DOM did not vary seasonally. We detected an event with a high δ13C value likely attributable to black carbon from local pasture fires. The mean δ13C values of DOM outside the event decreased in the order, RF (-26.0 ± 1.3‰) > TF (-28.7 ± 0.3‰) > SF (-29.2 ± 0.2‰) > LL (-29.6 ± 0.2‰) because of increasing leaching of C-isotopically light compounds. The higher δ13C values of DOM in SS15 (-27.8 ± 1.0‰), SS30 (-27.6 ± 1.1‰), and ST (-27.9 ± 1.1‰) than in the above-ground solutions suggested that roots and root exudates are major belowground DOM sources. Although in DOM the C/N ratios correlated with the δ13C values when all solutions were considered, this was not the case for SS15, SS30, and ST alone. Thus, the δ13C values of DOM provide an additional tool to assess the sources and turnover of DOM.

Inclusions and exclusions in treeline definitions

AbstractKörner and Hoch's (2023) definition of “treeline” to include only forest edges that are arctic or alpine, globally distributed and thermally limited is reconsidered for the alpine, with attention to the alpine treeline ecotone. They characterize the alpine treeline and the ecotone as a single phenomenon at a single fundamental niche limit, with all other montane forest edges at realized niche limits. The framework restricts treeline and the treeline ecotone to narrow but interesting ecophysiological questions but leaves other fundamentally limited edges, those in disequilibrium with a changed temperature regime, and the extensive zone of krummholz and tree‐species seedlings now often referred to as the treeline ecotone, without terminology. Recognizing other fundamental niche limited edges as treelines, if not alpine, and defining “alpine treeline” as a zone or line within the broader “alpine treeline ecotone”, are proposed to promote synergies in research in these related systems.

Avian biodiversity losses from grazing of high Andean páramo

Páramos are high-elevation grassland-dominated ecosystems of the northern Andes that harbour large numbers of small-ranged and endemic species and provide important ecosystem services. Though páramos are increasingly managed with a conservation focus, they remain ecologically threatened, in part due to overgrazing. Here, we assess the impacts of grazing on bird communities using data collected from three páramo complexes in the Eastern Andes of Colombia. We (1) assess how densities of shrubs and frailejones—a keystone group of plants in the páramo—are impacted by grazing, (2) determine the influence of these vegetation features on bird occupancy, and (3) examine how bird species richness and community composition are impacted by páramo grazing. We find that grazing status strongly influences the vegetation characteristics of the páramo, resulting in large reductions in the abundance of shrubs and frailejones. These vegetation changes have significant impacts on páramo bird communities, with reduced shrub abundance resulting in lower occupancy for most species (4 out of 48). As a consequence, grazed páramo communities contain fewer bird species and vary in composition relative to those of natural páramo. However, the magnitudes of these differences are modest and it is possible that low-intensity grazing remains compatible with conservation management. We suggest that it is important to consider how páramo conservation may interact with management of adjacent montane forests and the potential for leakage effects resulting in increased deforestation outside of protected areas.

Seasonal patterns in the leaf C:N:P stoichiometry of four conifers on the northeastern Tibetan Plateau

Research into leaf traits, especially carbon (C), nitrogen (N), and phosphorus (P), are essential for understanding the nutrient uptake strategies and ecosystem functions, such as the rates of photosynthesis, transpiration, and nutrient intake in plants. However, seasonal patterns of leaf C:N:P stoichiometry in arid and semiarid forest ecosystems remain unclear. In this study, temporal scale monitoring was conducted on four conifer species (Picea wilsonii, Pinus tabuliformis, Picea crassifolia, and Juniperus przewalskii) within the Qilian Mountains to determine the seasonal patterns of leaf C:N:P stoichiometry and their driving forces. The seasonal patterns of the leaf N and P contents were asynchronous among the species. The C content and C:N and C:P ratios in the leaves in Tulugou (relatively wet and fertile) were lower than those in Langchaigou (extremely infertile and dry), whereas the N and P contents in the leaves displayed an inverse pattern (p < 0.05). The results confirmed that the leaf economics spectrum gradually transitions from high resource acquisition to high resource conservation as the environmental stress increased. Additionally, the leaf N and P contents were found to be positively correlated with the precipitation and soil water content during the growing seasons (p < 0.01), whereas the soil temperature negatively impacted the leaf N and P contents (p < 0.01). A two-way analysis of variance indicated that the species was the main driving factor of variation in the leaf C:N:P stoichiometry in the four conifers. The redundancy analysis revealed that soil properties explained 50.9 % of the total variability in the leaf stoichiometry, with the soil N pool having the strongest effect on the leaf traits. Overall, our results indicated that the tree species and soil N pools were the key driving factors affecting the leaf stoichiometry of the conifers, and the trees adapted to the changing environment through a trade-off in the leaf functional traits. These findings provide a temporal and spatial perspective for understanding how the leaf functional traits of conifers respond to environmental changes in arid and semi-arid montane forest ecosystems.

The Influence of Winter Snowpack on the Use of Summer Rains in Montane Pine Forests Across the Southwest U.S.

AbstractA two decade‐long megadrought, with likely anthropogenic causes, has impacted forest growth and mortality across the southwestern U.S. Given this event, and the future likelihood of similar climate challenges, it is important to understand how different water resources are used by semi‐arid forests in this region. Within the geographic domain of the North American Monsoon climate system, we studied seasonal water‐use in eight different Pinus ponderosa montane forests distributed across a climate gradient with varying contributions from winter and summer precipitation. We collected oxygen isotopes from precipitation, soil, and xylem water during two contrasting hydrologic years to determine how trees differentially use winter versus summer precipitation sources. Most trees switched from using snowmelt water as the primary source during the early‐summer hyper‐arid period, to monsoon rainwater during the late‐summer. However, during the low snowpack year, which represents the most common climate phenomenon during the megadrought, trees at all sites used less summer rain when compared to the higher snowpack year, demonstrating a drought‐induced antecedent influence of winter precipitation on the uptake of summer rain. A possible mechanism to explain the antecedent effect is an earlier snow disappearance during the low snowpack year weakening hydrologic connectivity within the soil profile, decreasing the soil infiltration of summer rains. However, in years with higher snowpack, the snow lasts longer, and this can improve the hydrologic connectivity within the soil profile. As a result, there is more infiltration of summer rains into the soils. This can enhance the maintenance of active shallow fine‐root biomass during the period when snowpack disappears, and monsoon rains have yet to arrive. These findings provide insight into how the seasonal interactions between major seasonal climate systems influence forest tree water use in the face of an extreme megadrought.

Co-occurrence of climate-change induced and anthropogenic pressures in Central American key biodiversity areas

Central America hosts many key biodiversity areas (KBAs), areas which represent unique and irreplaceable ecosystems of global importance for species conservation. However, large extents of these areas are not under legal protection and could be threatened by pressures from land use change (e.g. deforestation and agricultural expansion), high human population density (e.g. population growth and urban sprawl) and climate-driven biome shifts. Here, we simulated future biome stability under the influence of climate change across KBAs in the Mesoamerican biodiversity hot spot and combined the results with projections of land use and population density up to the end of the 21st century. We applied four forcing scenarios based on two global climate models (GFDL-ESM4 and IPSL-CM6A-LR) and two shared socio-economic pathways (SSP1-2.6 and SSP3-7.0), which represent a range from low to high emission pathways. Our model projected decreased biome stability in 39%–46% of protected areas in KBAs, whereas this number even increased to 59%–60% for unprotected areas in KBAs (depending on the climate scenario). While human interferences in protected parts of KBAs are expected to be limited, large parts of unprotected areas in KBAs were projected to be pressured by multiple factors at once and are reason for concern. In particular, high human population pressures (>10 people km−2) emerged as a main threat over 30%–44% of the unprotected area in KBAs. These were largely accompanied by pressures from land use and sporadically reinforced by pressures from climate-driven biome shifts. Among the hot spots facing multiple high pressures are some of the last tropical dry and montane forest ecosystems in Central America, which stresses the need for urgent conservation action.