Tropical Montane Forest Research Articles

Possible carnivory in the epiphytic liverwort Pleurozia acinosa (Mitt.) Trevis. is not confirmed

ABSTRACT Introduction. Although in all proven cases of carnivory in plants the relevant species are in the Angiospermae, it has been posited that this phenomenon occurs in two genera of liverworts, Colura and Pleurozia. The suggested occurence of zoophagy in these groups is largely based on their trap-like water sacs, leaf modifications, and the positive results of ‘feeding’ experiments; however, no evidence of nitrogen uptake has been presented. Methods. We measured δ13C, δ15N, %C and %N in Pleurozia acinosa (Mitt.) Trevis. from tropical montane forests in Vietnam, and in representatives from several reference plant groups, both carnivorous and non-carnivorous, and including epiphytes and terrestrial plants. Key results and conclusions. δ13C values in Pleurozia acinosa were significantly higher than in all other groups of plants studied. However, δ15N was significantly lower in P. acinosa than in both groups of true carnivorous plants, and it did not differ from that in non-carnivorous vascular epiphytes and phorophyte trees, being even lower than in other epiphytic bryophytes. Thus, our results do not support the suggestion of carnivory in the genus Pleurozia.

Litter mixture effects on decomposition change with forest succession and are influenced by time and soil fauna in tropical mountain Andes

Abstract In highly transformed regions, such as the tropical Andes, identifying the influence of forest succession and soil fauna on non-additive effects of litter decomposition is crucial for gaining a more realistic understanding of carbon dynamics and nutrient cycles. The objective of this paper was to analyze the changes of litter mixture effects on decomposition between different soil fauna treatments (macrofauna inclusion vs macrofauna exclusion) and successional stages (mature forests vs secondary forests) in upper Andean tropical forests along time by using a reciprocal translocation experiment of 1,344 litterbags that ran for 18 months with six common native Andean species. Thought t-tests, linear regressions, and linear mixed models, I found that litter mixture effects vary among sites and increase with time in secondary forests until the year of decomposition in litterbags with macrofauna exclusion. Mature forests exhibited strong antagonistic effects, while pronounced synergistic effects were observed in secondary forests. Although soil macrofauna did not increase significantly litter decomposition and synergistic effects in the mixtures at any of the stages of decay, it is likely that soil macrofauna may impact litter mixtures through top-down effects within soil food webs, rather than exerting a direct effect in the litter consumption as has been reported in tropical lowland ecosystems. Overall, this study supports the idea that litter mixtures exhibit significant variability across sites, can change with successional stage, and are influenced by soil fauna depending on the stage of decay in tropical Andean montane forests.

The relationship between the abundance of non-native tree species and the community structure of resident woody species in tropical montane forest of West Usambara Mountains, Tanzania

Non-native tree species are globally claimed as liable to the encroachment of natural forests in their proximity resulting to the loss of biodiversity. This study was conducted in Magamba Nature Forest Reserve (MNFR) in West Usambara Mountains of Tanzania. A total of 96 (20 m x 20 m) plots were established to record all woody plants with Diameter at Breast Height (DBH) ≥ 5 cm while two nested plots of 2 m x 5 m were set to measure any plant with DBH ≥ 1 cm but less than 5 cm. Furthermore, two nested plots of 1 m x 1 m were established within the bigger plot in order to assess and record seedlings (DBH < 1 cm). Generalized Linear Models (GLMs) were used to assess the relationship between total abundance, species diversity, richness, evenness, and biomass of resident species and the abundance of Acacia melanoxylon and Eucalyptus grandis. Findings show a significant (p < 0.05) decrease of abundance of all resident woody species, adults, saplings and seedlings with an increase in the abundance of A. melanoxylon. The study also showed that the species richness and diversity of all resident species decreased with increasing the abundance of non-native species (p < 0.05). The abundance of E. grandis did not show significant (p > 0.05) association when assessed against the total abundance, species diversity, richness and evenness of all the resident woody species. This non-significant result may not necessarily mean no effect. This is because the P-value does not explain the size of the effect in biological data. Further analysis revealed that, the biomass of resident species was negatively related to the abundance of non-native species A. melanoxylon (p = 0.003) and E. grandis (p = 0.038). The negative relationship between the abundance, richness, diversity, evenness, and biomass of the resident woody species and the abundance of non-native species portrayed in this study raise an alarm. Therefore, there is need for setting monitoring and control mechanism to stop further spread of the non-native tree species in MNFR and hence, save the remaining biodiversity of the area.

Variable thermal plasticity of leaf functional traits in Andean tropical montane forests.

Tropical montane forests (TMFs) are biodiversity hotspots and provide vital ecosystem services, but they are disproportionately vulnerable to climate warming. In the Andes, cold-affiliated species from high elevations are being displaced at the hot end of their thermal distributions by warm-affiliated species migrating upwards from lower elevations, leading to compositional shifts. Leaf functional traits are strong indicators of plant performance and at the community level have been shown to vary along elevation gradients, reflecting plant adaptations to different environmental niches. However, the plastic response of such traits to relatively rapid temperature change in Andean TMF species remains unknown. We used three common garden plantations within a thermosequence in the Colombian Andes to investigate the warming and cooling responses of key leaf functional traits in eight cold- and warm-affiliated species with variable thermal niches. Cold-affiliated species shifted their foliar nutrient concentrations when exposed to warming, while all other traits did not significantly change; contrastingly, warm-affiliated species were able to adjust structural, nutrient and water-use efficiency traits from acquisitive to conservative strategies in response to cooling. Our findings suggest that cold-affiliated species will struggle to acclimate functional traits to warming, conferring warm-affiliated species a competitive advantage under climate change.

Recovery of aboveground biomass, soil carbon stocks and species diversity in tropical montane secondary forests of East Africa

Tropical montane forests are fragile ecosystems that provide a wide range of ecosystem services including hydrological services, biodiversity protection and storing carbon in the above and belowground and soils contributing to climate change mitigation. The world’s tropical montane forests are increasingly exposed to degradation and their recovery after disturbance has not been adequately quantified. Here, using information from 47 plots in three blocks of the Mau Forest Complex of Kenya, we assessed the changes in aboveground biomass (AGB), tree species diversity, soil carbon and nitrogen stocks following forest clearance. AGB recovered at an annual rate of 6.42 Mg ha−1 yr−1 in the first 20 years, the rate then slowed down to 4.46–4.67 Mg ha−1 yr−1 at around 25–30 years. Around 25 years after disturbance, AGB in recovering forests was 70 % (198.32 ± 78.11 Mg ha−1) of the AGB in the old secondary forest (OSF) (282.86 ± 71.64 Mg ha−1) and was statistically indistinguishable. Stem density, species diversity and richness indices did not show significant differences across recovery classes. There was no significant difference in soil carbon and nitrogen stocks across classes with the soil carbon (184.1 ± 41 Mg ha−1) of the young secondary forest (<10 years) being 84.5 % of that of the OSF (217.9 ± 51.8 Mg ha−1). This study reports a rapid rate of AGB and carbon accumulation within 20 years of disturbance, and high levels of species richness in these previously disturbed fragments of tropical montane forests of East Africa.

Fundamental but underrepresented: root carbon stocks in African montane forests

African montane forests harbor some of the greatest biodiversity worldwide, with high levels of species endemism. However, the loss of these forests through fragmentation, deforestation and climate change has been rapidly increasing in recent years. Montane forests in Africa are more susceptible to changes in climate than their lowland counterparts, yet their ecological value is still underrepresented. These montane forests have recently been highlighted as a major aboveground carbon (C) stock. The estimated 149.4 Mg C ha−1 from aboveground live trees surpasses estimates from the Intergovernmental Panel on Climate Change for these endangered forests, and exceeds reported values for neotropical montane and lowland forests by up to 70%. Despite the tremendous implications of these findings, coordinated and available research on the C storage potential of the other share of African montane forest biomass, that is in tree roots, is largely missing. Broadly estimated from the allometry of aboveground C stocks and from root:shoot ratios in lowland forests, more than 60 Mg C ha−1 can be stored in African montane forest roots, about 40% more than previously determined. While this broad estimation points at the potential importance of root C stocks in African montane forests, it also unveils a far-reaching knowledge gap. Here, we advocate for a more quantitative representation of the root C stock from dominant forest tree species of African tropical montane forests and ultimately for a better grasp on tree C stocks from this endangered ecosystem.

Post-fire assessment of recovery of montane forest composition and stand parameters using in situ measurements and remote sensing data

Tree diversity in the tropical forests face escalating threats from wildfires. This study assessed post-fire impacts and recovery patterns in Tanzanian Eastern Arc Mountains forests from 2017 to 2022 using field measurements and remote sensing techniques. Tree species diversity, composition, and forest stand parameters were compared between burned and unburned forest plots across two reserves. A predictive model utilizing 14 key variables derived from multispectral satellite data was developed to accurately map burned areas and spatial fire patterns. Results revealed significantly lower tree density, aboveground biomass, species richness, and Shannon diversity in burned areas compared to unburned forests. However, compositional analysis showed extensive species overlap between burned and unburned sites, with burned areas containing more indicative pioneer and disturbance-adapted species such as Apodytes dimidiata. Over time since fire events, tree density, basal area, aboveground biomass, species richness, evenness, and diversity increased markedly, evidencing active tree recovery. The remote sensing model effectively delineated approximately 1430 hectares of burned areas concentrated near villages, suggesting prevalent anthropogenic fire ignitions. Although wildfires substantially impacted forest structure and biodiversity, the limited compositional shifts point to resilience of these tropical montane forests. Integration of diverse spectral bands and textural metrics from multispectral satellite data can support precise mapping of fire effects and forest recovery dynamics in these ecologically vital yet threatened ecosystems, aiding conservation and management. Overall, this study provides novel insights into post-fire responses in Eastern Arc Mountain forests using a synergistic field and remote sensing approaches.

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.

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.

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.

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&lt;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.

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.

Patterns and consequences of invasion of tropical montane forests by Cestrum aurantiacum Lindl. in the Western Ghats

In the montane forest-grassland mosaics of the Western Ghats, land cover conversion to silviculture and agriculture over the last five decades has resulted in both loss of natural habitats and widespread invasion of remnant habitat patches. While invasion of the grassland habitats of the mosaic has been relatively well studied, there have been few attempts to understand the extent to which forest habitats (locally known as sholas) have been affected by the spread of exotic species. Here we examine the patterns and impacts of invasion of shola forest understoreys by Cestrum aurantiacum Lindl., an exotic shrub species. At the landscape scale, we demonstrate that the presence and abundance of this invasive in shola understories is negatively related to distance from tea plantations. Further, the intensity of invasion is higher in areas with greater seasonality of temperature and lower mean annual precipitation. At the patch scale, invasion is greatest at shola edges and away from stream courses. We find that C. aurantiacum abundance has negatively affected the regeneration of native shola tree species as well as the abundance of native shola understorey shrubs. Fifty three percent of invaded plots had no native shrubs present. In plots where both C. aurantiacum and native shrubs were present in large enough numbers, we found evidence of negative spatial dependence between stem locations of C. aurantiacum and native shrubs. Our findings have important implications for the management and conservation of these mosaics.

Burn severity and proximity to undisturbed forest drive post-fire recovery in the tropical montane forests of northern Vietnam

BackgroundIn recent decades, fire has increasingly occurred in the tropical montane rainforests of northern Vietnam. However, there are few studies of the effects of fire on forest composition and recovery in this region, and understanding these effects is critical for effective forest fire management and conservation. Forest plant species richness, structure (density, basal area), and composition were quantified for 133 forest plots randomly located in unburned (> 20 years since last fire) and recently burned (3–9 years since fire) vegetation associated with ten selected wildfires in three provinces of northern Vietnam where fires since 2000 were most frequent. Linear mixed effect models and nonmetric multidimensional scaling (NMDS) ordination were used to explore the structure, richness, and composition of burned and unburned forests and their environmental drivers, and to explore the key drivers of regeneration patterns in burned forest, including time since fire occurrence, fire severity, and distance to unburned forest edge.ResultsTotal species richness and diversity, tree species richness, tree density, and basal area were higher in unburned (vs. burned) forest plots, low (vs. high) severity burn areas, near (vs. far) from the closest unburned forest edge, and longer (vs. shorter) time since last fire. Results suggest that while burned forests were recovering on a trajectory back towards unburned forest composition, recovery was likely to be markedly slowed where fires were large (distance from edge effects) and/or of high severity, and forests may shift towards a different state (i.e., composition and structure) where more than one fire affects the same area over short time intervals.ConclusionsThis study provides insights into the effects of fire and other environmental factors on forest composition and recovery in the tropical montane forests of northern Vietnam, crucial for informing policymakers involved in forest conservation and management.

Mapping deforestation and recovery of tropical montane forests of East Africa

Deforestation poses a major threat to the tropical montane forest ecosystems of East Africa. Montane forests provide key and unique ecological and socio-economic benefits to the local communities and host diverse flora and fauna. There is evidence of ongoing deforestation and forest clearance in these montane forests although estimates diverge among different sources suggesting rates of 0.4%–3% yr−1. Quantifying deforestation rates and forest disturbance is critical to design conservation and sustainable management policies for forest management. This study quantified the rate of deforestation and forest recovery over the last three decades for the Mau Forest Complex and Mount Elgon forests in Kenya and Uganda using Landsat time-series satellite imagery. With the analysis, classification accuracies of 86.2% and 90.5% (kappa 0.81 and 0.88) were achieved for the Mau Forest Complex and the Mt Elgon forests, respectively. 21.9% (88,493 ha) of the 404,660 ha of Mau forest was lost at an annual rate of −0.82% yr−1 over the period between 1986 and 2017. More positively, 18.6% (75,438 ha) of the forest cover that was disturbed during the same period and is currently undergoing recovery. In Mt Elgon forest, 12.5% (27,201 ha) of 217,268 ha of the forest cover was lost to deforestation at an annual rate of −1.03% yr−1 for the period between 1984–2017 and 27.2% (59,047 ha) of the forest cover disturbed is undergoing recovery. The analysis further demonstrated agriculture (both smallholder and commercial) was the main driver of forest cover loss in Mau forest, accounting for 81.5% (70,612 ha) of the deforestation, of which 13.2% was due to large scale and 68.3% was related to the smallholders. For the Mt Elgon forest, agriculture was also the main driver accounting for 63.2% (24,077 ha) of deforestation followed by the expansion of human settlements that contributed to 14.7% (5,597 ha) of forest loss. This study provides accurate and novel estimates of the rate of deforestation for the Mau forest complex and Mt Elgon forest ecosystems. These rates are higher than previously estimated and recent deforestation has been identified, which provides a quantitative basis for forest restoration programs and to design conservation policies.

Comparison of multi-source remote sensing data for estimating and mapping above-ground biomass in the West Usambara tropical montane forests

Above-ground biomass (AGB) estimation is important to better understand the carbon cycle and improve the efficiency of forest policy and management activities. AGB estimation models, using a combination of field data and remote sensing data, can largely replace traditional survey methods for measuring AGB. There are, however, critical steps for mapping AGB based on satellite data with an acceptable degree of accuracy, such as choice of remote sensing data, the proper statistical modelling method, and remote sensing predictor variables, at known field locations. This study sought to identify the optimal optical and synthetic aperture radar (SAR) remote sensing imagery from five sensors (PlanetScope, Sentinel-2, Landsat 8 OLI, ALOS-2/PALSAR-2, and Sentinel-1) to model 159 field-based AGB values from two montane forests under semiparametric (Generalized Additive Model; GAM) and non-parametric (eXtreme Gradient Boosting; XGB) approaches using information from four groups of predictor variables (spectral bands/polarizations, vegetation indices, textures, and a combination of all). The study's results showed that PlanetScope (rRMSE = 69.19%; R2 = 0.161) was the most precise optical sensor while ALOS-2/PALSAR-2 (rRMSE = 70.76; R2 = 0.165) was the most precise amongst the SAR sensors. XGB models generally resulted in those with lower prediction errors as compared to GAMs for the five sensors. Models having textures of vegetation indices and polarization bands achieved greater accuracy than models that incorporated spectral bands/polarizations and vegetation indices only. The study recommends that PlanetScope and ALOS-2/PALSAR-2 remote sensing data using the XGB-based technique is an appropriate approach for accurate local and regional estimation of tropical forest AGB particularly for complex montane forest ecosystems.

Sap flow responses in pioneer and late-successional tree species in secondary tropical montane forests of Eastern Himalaya, India.

The interactive role of life-history traits and environmental forcing on plant-water relations is crucial for understanding species response to climate change but remains poorly understood in secondary tropical montane forests (TMFs). Comparing contrasting life-history traits (pioneer vs late-successional species) in a biodiverse Eastern Himalayan secondary TMF, we investigated sap flow responses in co-occurring pioneer species, Symplocos racemosa (n=5) and Eurya acuminata (n=5), and late-successional species, Castanopsis hystrix (n=3), using modified Granier's Thermal Dissipation probes. The fast-growing pioneers S. racemosa and E. acuminata) had 2.1- and 1.6-times higher sap flux density than the late-successional C. hystrix, respectively, and exhibited characteristics of long-lived pioneer species. Significant radial and azimuthal variability in sap flow (V) between species was observed and attributed to life history traits and the canopy's access to sunlight. Nocturnal V (1800-0500hr) was 13.8 % of daily V and is attributed to stem recharge for evening V (1800-2300hr) and to endogenous stomatal controls for pre-dawn V (0000-0500hr). Both the shallow-rooted pioneer species exhibited midday depression in V attributed to photosensitivity and diel moisture stress response. In contrast, deep-rooted C. hystrix transpired unaffected across the dry season likely accessing groundwater. Thus, the secondary broadleaved TMFs, with the dominance of shallow-rooted pioneers, are more prone to the negative impacts of drier and warmer winters than primary forests, which are dominated by deep-rooted species. The study provides an empirical understanding of life-history traits and microclimate modulating plant-water use in widely distributed secondary TMFs in Eastern Himalaya and highlights their vulnerability against warmer winters and reduced snowfall due to climate change.

Developing a more complete understanding of tropical montane forest disturbance ecology through landslide research

Landslides are a central component of tropical montane forest disturbance regimes, including in the tropical Andes biodiversity hotspot, one of the most biodiverse ecosystems in the world. Technological developments in remote sensing have made landscape-scale landslide studies possible, unlocking new avenues for understanding montane biodiversity, ecosystem functioning, and the future effects of climate change. Here, we outline three axes of inquiry for future landslide ecology research in Andean tropical montane forest. We focus exclusively on the Andes due to the vast floral diversity and high endemicity of the tropical Andes biodiversity hotspot, and its importance for global biodiversity and regional ecosystem service provisioning; the broad elevational, latitudinal, and topographic gradients across which landslide dynamics play out; and the existence of long-term plot networks that provide the necessary baseline data on mature forest structure, composition, and functioning to contextualize disturbance impacts. The three lines of study we outline, which draw heavily on remote sensing data and techniques, will deepen scientific understanding of tropical montane forest biodiversity and ecosystem functioning, and the potential impacts of climate change on both. They are: (1) tracking landslide biodiversity dynamics across time and space with high spatial and temporal resolution satellite and unoccupied aerial vehicle imagery; (2) assessing the ecological influence of landslides through the lens of plant functional diversity with imaging spectroscopy; and (3) understanding current and predicting future landslide regimes at scale by building a living landslide inventory spanning the tropical Andes. The research findings from these three axes of inquiry will shed light on the role of landslides and the process of forest recovery from them in both the Andes and worldwide.

Satellite-derived forest canopy greenness shows differential drought vulnerability of secondary forests compared to primary forests in Peru

Understanding tropical secondary forest canopy greenness and responses to climatic conditions is important for climate change mitigation, particularly in the tropics where secondary forest growth is a substantial carbon sink and a promoted natural climate solution. We here test three hypotheses: (a) forest canopy greenness is higher in younger, secondary forests than in older, primary or mature forests, (b) secondary forests are more vulnerable to climatic pressures and (c) there are significant differences between forest types regarding primary–secondary canopy greenness and their differential responses to drought anomalies. To explore these relationships, we monitored wet and dry seasonal greenness from 2001 to 2020, estimated through the enhanced vegetation index (EVI), of Peruvian tropical dry, montane and lowland secondary forests and compared it to nearby primary forests. We developed predictive models of seasonal EVI using remotely sensed variables, including land surface temperature (LST), evapotranspiration (ET), potential evapotranspiration (PET), ratio of ET and PET (ETn), and the standard precipitation index (SPI). Overall, there was a higher change in annual and seasonal EVI for secondary forests compared to primary forests. However, primary forests maintained relatively stable EVI levels during the wet season despite drought anomalies. When decoupling forest type canopy greenness and drought response, primary forest greenness in dry and lowland ecosystems were temporally more stable. Secondary montane had a lower increase in greenness when drought anomalies held during different seasons. Stepwise multiple linear regression models indicated that LST and ETn, a plant water use index, were the most significant factors to predict greening fluctuations in dry and montane forest types. ET and SPI mostly drove wet season mean EVI across all forest types. Predictors of dry season mean EVI varied, but mostly including water availability. Our results suggest that tropical secondary forests are more productive overall yet more vulnerable to prolonged drought.