Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Abstract:

Aim Progress has been made in understanding the relationship between biodiversity and ecosystem functioning (BEF) in both experimental and real-world ecosystems. Yet, we have a limited understanding of the extent to which biodiversity affects ecosystem functioning in heterogeneous environments and whether variation in ecosystem functioning between communities is related to variation in species richness or turnover. Here, we quantify the relative contribution of variation in species richness and species turnover to variation in ecosystem functioning between communities (i.e., the diversity effect) along two tropical elevational gradients. Location Andes (Ecuador) and Mt. Kilimanjaro (Tanzania). Taxa studied Woody plants, springtails, soil arthropods, ants, and frugivorous birds. Methods We collected data on seven ecosystem functions, including biomass and process rates, across six ecosystem types along the two elevational gradients. We then combine the ecological Price equation with the concept of β-diversity to quantify how the diversity effect is shaped by environmental heterogeneity within and across ecosystem types, and whether the effect of environmental heterogeneity is primarily mediated by variation in species richness or species turnover. Results The diversity effect on ecosystem functioning increased consistently with environmental heterogeneity on both mountains. Species richness and turnover, on average, contributed similarly to the diversity effect on ecosystem functioning in both mountain regions, but effect sizes varied across functions. The increase in the diversity effect with environmental heterogeneity was primarily mediated by species richness, while species turnover played a secondary role in mediating the effects of environmental heterogeneity. Main Conclusions Our study reveals that the diversity effect on ecosystem functioning increases with environmental heterogeneity and that species richness, rather than species turnover, primarily drives this relationship. The dominant role of species richness in mediating the effect of environmental heterogeneity indicates that BEF relationships along environmental gradients are strongly influenced by environmental filters that limit local species coexistence.

Abstract:

Root anatomical traits regulate water transport and resource acquisition in forest ecosystems, yet their variation and coordination with aboveground traits remain poorly understood in tropical forests. We investigated patterns of interspecific variation in four root anatomical traits (vessel diameter, vessel density, vessel lumen fraction, and theoretical hydraulic conductivity) across 20 tree species representing contrasting growth strategies in a premontane tropical forest of southern Ecuador. Using 160 root samples from transport roots (4–8 mm diameter), we quantified anatomical traits through microscopy and calculated theoretical hydraulic conductivity. We analyzed correlations with wood density and leaf functional traits and performed principal component analyses to assess trait coordination. Species exhibited substantial variation in root anatomical traits, ranging from acquisitive strategies with large vessel diameters (67.6 μm in Ocotea sp.) and high hydraulic conductivity (73.9 kg m−1 MPa−1 s−1 in Alchornea glandulosa) to conservative strategies with high vessel density (>185 vessels/mm2 in Leonia crassa and Aspidosperma rigidum). However, 60% of species displayed intermediate trait values, suggesting compensatory strategies rather than extreme specialization. We documented strong negative correlations between vessel diameter and both vessel density (r = −0.74) and wood density (r = −0.51), pointing at hydraulic efficiency-safety trade-offs. Principal component analysis revealed that leaf traits operated orthogonally to root anatomical traits, indicating independent axes of functional variation rather than coordinated whole-plant strategies. These decoupling challenges traditional plant economics spectrum assumptions and evidence that plants optimize above- and belowground functions through independent evolutionary pathways. Our findings highlight the prevalence of intermediate hydraulic strategies in tropical tree communities and provide new insights into the functional organization of diverse forest ecosystems.

Abstract:

Plant communities of the tropical dry forest (TDF) host a great diversity of species which show a large variety of morphological traits. While most TDF species produce wind-dispersed fruits or seeds, bearing some kind of structure that facilitates their travel by wind others produce fleshy fruits mainly consumed and dispersed by animals. Fruits may bear just one large seed or up to many tiny ones and also the shape, size or germination process of seedlings vary greatly between species of the TDF in southern Ecuador. Despite their relevance for plant regeneration, there is very little information facilitating species identification of fruits, seeds and seedlings of TDF species. Identification tools are therefore needed to foster local knowledge, maintain biodiversity for future generations and support conservation and restoration efforts. This project aimed to produce a scientific identification guide available to both the local and the scientific community to facilitate taxonomic determination of fruits, seeds and seedlings of woody TDF species. It will be useful to future research projects carried out in the Laipuna reserve and will contribute to public outreach. Uncompressed version can be requested from Lea Kerwer.

Abstract:

Tropical dry forests are among the most threatened terrestrial ecosystems worldwide. This study applies robust multi-objective optimization and Pareto frontier analysis to support sustainable land-use planning in dry forest ecosystems, taking as an example the drylands of southern Ecuador. By integrating ecological and socioeconomic indicator bundles, we modeled optimal land-use compositions under uncertainty and compared them to observed allocations derived from GIS, field data, and farmer input. The observed landscape, dominated by silvopasture (57%) and maize (32%), contrasts with the model’s optimal allocation, which prioritizes shaded cocoa (25%) and coffee (23%), reduces silvopasture (15%), and modestly increases maize (37%). The model enhanced a land-use performance index across different levels of considered uncertainty (low: 22–48%; moderate: 10–32%; high: 16–32%), revealing the method’s strength in generating valuable farm-level insights. The Pareto frontier analysis indicated trade-offs between bundles of ecological and economic indicators, mirroring real-world tensions. While observed land use aligns closely with optimized socioeconomic objectives, it underperforms ecologically. Agroforestry emerges as a promising compromise, though incentives and policy support will be key for adoption. Our findings illustrate how robust multi-objective optimization can strengthen intuitive diversification strategies, balance short- and long-term goals, and guide transitions to more resilient land uses. This is especially critical in vulnerable, data-scarce dry ecosystems increasingly affected by environmental and socioeconomic stressors.

Abstract:

Plant roots have a large diversity of form and function, which is also related to their degree of mycorrhizal association. This is known as the fungal collaboration gradient, where thinner roots acquire resources by themselves, and thicker roots depend on mycorrhizae. In this study, we, for the first time, implement the fungal collaboration gradient in a trait-based dynamic vegetation model (DVM, LPJ-GUESS-NTD). We test if the DVM can predict fine-root-trait distributions and estimate the effects of arbuscular-mycorrhiza-fungus (AMF)-mediated nutrient uptake on ecosystem processes along an elevation gradient in a tropical montane forest in southern Ecuador. The model reproduces the observed fine-root traits of specific root length (SRL) and AMF colonization along the elevation gradient, which ranges from low AMF colonization at 1000 m (25 %) to high AMF colonization at 3000 m (61 %). When AMF-mediated nutrient uptake is deactivated, site average biomass values are reduced by up to 80 %. Accounting for AMF-related belowground traits also affects simulated community leaf traits, suggesting linkages between below- and aboveground traits as AMF promotes more leaf-acquisitive traits. In addition, deactivation of AMF uptake reduced simulated soil C stocks by up to 68 %. The model suggests that the collaboration gradient has a substantial influence on vegetation diversity and functioning as well as soil carbon in the study system. We thus advocate more explicit treatment of fine-root traits and mycorrhizae in DVMs. The model scheme here is based on general trade-offs and could be implemented in other DVMs and be tested for other study regions.

Abstract:

The effective conservation and management of critical ecosystems, such as tropical mountain forests, depends on informed decision-making in order to reduce biodiversity loss, protect ecosystem services, and mitigate socio-economic impacts. However, providing decision-makers with reliable, site-specific data to navigate the uncertainties of forest management remains a significant challenge. This study aimed to address this gap by translating optimized, non-spatial land-use scenarios from a previous study into spatially explicit deforestation projections for a mountain forest landscape in southern Ecuador. These scenarios represent three distinct management perspectives, including: (a) prioritizing socio-economic benefits and costs (SE), (b) balancing ecosystem services and socio-economic objectives (ES-SE), and (c) emphasizing biodiversity conservation alongside socio-economic considerations (B-SE). We generated spatial projections of forest loss over a 25-year period for each scenario, by integrating remote sensing and modeling techniques. The results offer graphical representations of forest cover changes, highlighting areas where deforestation is most likely to occur. By spatializing these forest trajectories, we provide a valuable tool for conservation planning, enabling stakeholders not only to anticipate the potential impacts of land-use management decisions but also to develop targeted strategies and evidence-based policies for the sustainable management of tropical mountain forests.

Abstract:

Latent heat flux is a central element of land-atmosphere interactions under climate change. Knowledge is particularly poor in the biodiversity hotspot of the Andes, where heat flux measurements using eddy covariance stations are scarce and land surface models (LSMs) often oversimplify the complexity of the ecosystems. The main objective of this study is to perform latent heat flux simulations for the tropical South Eastern (SE) Ecuadorian Andes using a coupled LSM framework, and to test the performance with heat flux and soil moisture data collected from a tropical high-altitude pasture. Prior to testing, we applied multi-criteria model calibration of sensitive model parameters, focusing on improving simulated soil water conditions and radiation fluxes as a prerequisite for proper heat flux simulations. The most sensitive parameters to improve soil moisture and radiation flux simulations were soil porosity, saturated hydraulic conductivity, leaf area index, soil colour and NIR (Near Infrared) leaf optical properties. The best calibrated model run showed a very good performance for half-hourly latent heat flux simulations with an R2 of 0.8 and an RMSE of 34.0 W m−2, outperforming simulations with uncalibrated and uncoupled LSM simulations in comparable areas. The slight overall overestimation in the simulated latent heat flux can be related to (i) simulation uncertainties in the canopy heat budget, (ii) an imbalance in the observed flux data and (iii) slight overestimations in the simulated soil moisture. Although our study focuses on latent heat fluxes and their relation to simulated radiation fluxes and soil moisture, model outputs of sensible heat fluxes were also discussed. The systematic overestimation of sensible heat flux in the model seems to be mainly a result of overestimated canopy temperatures. The improved simulation for latent heat flux has a high translational potential to support land use strategies in the tropical Andes under climate change.

Abstract:

Understanding the partitioning of downward shortwave radiation into direct and diffuse components is essential for modeling ecosystem energy fluxes. Accurate partitioning functions are critical for land surface models (LSMs) coupled with climate models, yet these functions often depend on regional cloud and aerosol conditions. While data for developing semi-empirical partitioning functions are abundant in mid-latitudes, their performance in tropical regions, particularly in the high Andes, remains poorly understood due to scarce ground-based measurements. This study analyzed a unique dataset of shortwave radiation components from a tropical mountain rainforest (MRF) in southern Ecuador, developing and testing a locally adapted partitioning function using Random Forest Regression. The model achieved high accuracy in predicting the percentage of diffuse radiation (%Dif; R2=0.95, RMSE = 5.33, MAE = 3.74) and absolute diffuse radiation (R2=0.99, RMSE = 5.30, MAE = 14). When applied to simulate upward shortwave radiation, the model outperformed commonly used partitioning functions achieving the lowest RMSE (8.62) and MAE (5.82) while matching the highest R2 (0.97). These results underscore the importance of regionally adapted radiation partitioning functions for improving LSM performance, particularly in complex tropical environments. The adapted LSM will be further utilized for studies on heat fluxes and carbon sequestration.

Abstract:

To predict future changes in nutrient availability in the young soils of the tropical Andes, it is important to study the response of weathering rates to climate and land-use change. This is particularly true in highly biodiverse tropical forests, where increasing nutrient availability can threaten their biodiversity. Hence, our objectives were to compare the kinetics of element release by weathering along an elevation gradient and between forest and pasture in a tropical montane forest region in south Ecuador. We collected soil samples from three plots in both natural forest and pasture, at elevations of 1000, 2000, and 3000 m above sea level (a.s.l., i.e., 18 in total). The sites at 2000 and 3000 m a.s.l. had similar parent material and allowed for evaluating the climatic effect. To assess element mobilization from the soil, we conducted a weathering experiment at a constant pH value (pHstat). During the experiment, ions were released from the soil into solution at pH 3 and removed from the solution using an ion-exchange resin. We described the release of base cations (Ca, Mg, K), Mn, Al, and Fe with a two-step first-order reaction, distinguishing a fast-reacting pool (FP) and a slow-reacting pool (SP), with their associated rate constants. The FP of Ca, Mg, K, and Mn closely correlated with and corresponded in size to the concentrations of the exchangeable cations of these elements (r = 0.78 – 0.96). The FP of Ca, Mg, K, and Mn was significantly larger in the soils under pasture than under forest vegetation, likely because of the input of alkaline ashes during slash-and-burn practices. The sizes of the FP and the SP of all studied elements under both land covers/uses were not significantly different between the sites at 2000 and 3000 m a.s.l., possibly because the opposing effects of increasing precipitation and decreasing temperature canceled each other out. Metal release kinetics differed markedly among sites with different parent materials, indicating that weathering is strongly influenced by the chemical composition of the parent rocks. Our study illustrates that element release by weathering in the soils of south Ecuador is strongly influenced by differences in land cover/use and chemical composition of parent rocks.

Abstract:

Los bosques secos tropicales, son ecosistemas únicos y diversos, pese a su importancia biológica se encuentran entre los más amenazados del mundo, las presiones sociales y económicas han provocado una reducción significativa de su cobertura, lo que ha afectado su capacidad de proporcionar servicios ecosistémicos. El objetivo de este estudio fue conocer los cambios de contenido de carbono en la biomasa aérea en dos pisos altitudinales 600 y 1200 m s.n.m. en la Reserva Natural Laipuna de Naturaleza y Cultura Internacional. Se registró el diámetro a la altura del pecho (DAP) y altura total de todos los individuos arbóreos con DAP ≥ 10 cm en seis parcelas permanentes de una hectárea. Para la estimación del carbono en la biomasa aérea se usó la ecuación de Chave, considerando el DAP (cm) y la altura de los árboles (m), así como también la densidad de madera (g/cm3) de cada una de las especies presentes dentro de las parcelas. No se encontraron diferencias estadísticas entre los contenidos de carbono dentro del área evaluada estas reservas fueron entre 35,6 Mg C ha-1 y 43,2 Mg C ha-1 a 600 m s.n.m. y 1 200 m s.n.m. respectivamente, demostrando así que la altitud es un factor que no influye en el almacenamiento de carbono aéreo. Se considera que este tipo de bosque representa una opción para contrarrestar el aumento de CO2 atmosférico, siendo este un justificativo importante para su conservación, más aún cuando el bosque se encuentra bajo procesos dinámicos de crecimiento.

Abstract:

Purpose of the Review The escalating impacts of human activities and climate change, particularly increased nutrient leaching and deposition, could significantly alter the productivity, structure, and function of tropical vegetation. To better understand how nutrient deposition affects regeneration in tropical ecosystems, we synthesised studies that added N, P, NP, or NPK to the seedlings of tropical tree and shrub species. Recent Findings In the tropics, nutrient limitation leads to multiple resource constraints. Our systematic review and hierarchical meta-analyses aimed to: (1) test the effect of nutrient addition on the growth rate and biomass allocation of seedlings of tropical species; (2) examine seedling responses across climate-defined groups; (3) quantify the effects of experimental methods and wood density on species’ responses to experimental fertilisation. Summary Overall, nutrient addition increased seedling shoot biomass by 26% and growth rates by 14%. Pot and transplantation experiments demonstrated stronger positive effects than in-situ observational studies. Nutrient combinations yielded the highest growth rates (NPK: 27%, and NP: 18%), and N was critical for shoot biomass (N: 38%, and NP: 48%). The responses of shoot biomass indicated co-limitation of N and P, but also high variability in seedling responses to individual nutrients. Temperature and precipitation had indirect regulating effects, while seasonality showed the strongest impact in seasonally dry sites (38% growth rate and 70% shoot biomass). Species showed individual responses to nutrients, influenced by biotic and abiotic interactions. Finally, we suggest tracking additional parameters, like forest successional status, that may intensify nutrient deposition effects on tropical soils due to climate change.

Abstract:

The co-evolutionary arms race between herbivores and plants forces plants to evolve protection strategies that reduce the palatability of the plant modules attacked by the herbivores. These characteristics of traits have consequences for both the survival of plant individuals and the composition of plant communities. Thus, correlating traits of for instance leaves with herbivory is an important step toward understanding the dynamics of plant populations and communities. Traits can either be measured using conventional lab methods or recently developed spectral sensing techniques. We examined whether leaf traits of trees are related to herbivory in a multispecies approach. Furthermore, we explored whether leaf traits characterized by spectral sensing provide similar relations to herbivory as lab-based leaf traits. We established nine 1-ha square plots evenly distributed over three different forest types in Ecuadorian tropical montane rainforests where we estimated herbivory as the leaf area loss (in square centimeters) of 20 (±5) leaves sampled from the canopies of 380 tree individuals belonging to 51 tree species (7 ± 1 individuals/species) using lab- and spectral-sensing-based methods. For each methodological approach, we ran 100 linear mixed-effects models with all respective leaf traits as predictor and herbivory as response variables for data subsets containing one randomly selected tree individual of each species to estimate the range of the regression coefficients for each trait. Automated stepwise backward selections determined the frequency of each trait having an important influence on herbivory. We found no clear relations between leaf traits and herbivory for neither lab- nor spectral-sensing-based traits. A nested variance component analysis demonstrated that the observed variability was mainly due to the variation in trait concentrations between tree individuals of a species. Our results suggest that snapshot data lead to a mismatch between herbivory and the concentrations of traits during the peak of herbivory. Another explanation could be that environmental conditions or processes along the food web are more important in structuring herbivory than leaf traits.

Abstract:

High spatio-temporal variability is a characteristic of extreme rainfall. In mountainous regions like the Tropical Andes, where intricate orography and mesoscale atmospheric dynamics greatly impact rainfall systems, this particularly holds for mountain areas like the Tropical Andes. Thus, the absence of operational rainfall monitoring networks with high spatio-temporal resolution has imposed difficulties for a proper analysis of extreme rainfall events in the Ecuadorian Andes. Nowhere, we present our improved knowledge on rainfall extremes based on newly available rainfall radar data of this region. In our study we employ a clustering approach to identify types of extreme rainfall events and analyze their spatio-temporal characteristics. Based on 3 years of data obtained from an X-band scanning weather radar data, the study was conducted in the southern Ecuadorian Tropical Andes at 4450 m a.s.l. By applying a rainfall threshold, 67 extreme rainfall events were selected. The rainfall characteristics of each extreme rainfall event, such as the amount of rain, its duration, its hour, and month of occurrence were determined and used as input variables of a k-means clustering analysis to group the events into different classes. The result revealed three main classes of extreme rainfall events. The first class is characterized by highest rain intensity and lowest duration. The second class is characterized by its month of occurrence, during the first 5 months of the year. The third class showed lowest rain intensity and highest duration mainly occurred at higher elevations. The typology of events advances our understanding of the spatio-temporal characteristics of extreme rainfall in the Tropical Andes.

Abstract:

The globally increasing reactive N richness affects even remote ecosystems such as the tropical montane forests in Ecuador. We tested whether the δ15N values of total dissolved N (TDN), measured directly in solution with a TOC‐IRMS, can be used to help elucidate N sources and sinks along the water path and thus might be suitable for ecosystem monitoring. From 2013 to 2016, the δ15N values of TDN in bulk deposition showed the most pronounced temporal variation of all ecosystem solutions (δ15N values: 1.9–5.9‰). In throughfall (TF), TDN was on average 15N‐depleted (-1.8 ± s.d. 0.4‰) relative to rainfall (3.4 ± 0.9‰), resulting from net retention of isotopically heavy N, mainly as NH4+. Simultaneously, N‐isotopically light NO3‐N and dissolved organic nitrogen (DON) with a δ15N value between NO3‐N and NH4‐N were leached from the canopy (leaves: -3.5 ± 0.5‰). The increasing δ15N values in the order, TF < stemflow (SF, 0.1 ± 0.6‰) < litter leachate (LL, 1.3 ± 0.7‰) concurred with an increasing DON contribution to TDN reflecting the δ15N value of the organic layer (1.9 ± 0.9‰). The lower δ15N value of the mineral soil solution at the 0.15 m soil depth (SS15, -1.5 ± 0.3‰) than in LL can be explained by the retention of DON and NH4+ and the addition of NO3- from mineralization and nitrification. The increasing δ15N values in the order, SS15 < SS30 (-0.6 ± 0.2‰) < streamflow (ST, 0.5 ± 0.6‰) suggested gaseous N losses because of increasing denitrification. There was no seasonality of the δ15N values. Our results demonstrate that the δ15N values of TDN in ecosystem solutions help identify N sources and sinks in forest ecosystems.

Abstract:

There is evidence to suggest that vascular epiphytes experience low competition for resources (light, water, and nutrients) compared to terrestrial plants. We tested the hypothesis that low resource competition may lead to higher nestedness among vascular epiphyte assemblages compared to trees. We studied the species composition and biomass of epiphytes and trees along an elevation gradient in a tropical dry forest in SW Ecuador. Both life-forms were inventoried on 25 plots of 400 m2 across five elevation levels (550–1250 m). Tree species density and total species richness increased with elevation, whereas basal area and biomass did not show significant trends. Epiphyte species density and richness both increased strongly with elevation, in parallel to biomass. Plot-level compositional changes were similarly strong for both life-forms. We attribute elevational increases in the species richness of trees and epiphytes to increasing humidity, i.e., more mesic growth conditions. We attribute the more pronounced elevational increase in epiphyte biomass, species density, and richness—the latter coupled with a higher degree of nestedness—to the greater moisture dependency of epiphytes and relatively low direct competition for resources. Our study provides a first comparison of elevational trends in epiphyte and tree diversity and biomass for a tropical dry forest.

Abstract:

We introduce the FunAndes database, a compilation of functional trait data for the Andean flora spanning six countries. FunAndes contains data on 24 traits across 2,694 taxa, for a total of 105,466 entries. The database features plant-morphological attributes including growth form, and leaf, stem, and wood traits measured at the species or individual level, together with geographic metadata (i.e., coordinates and elevation). FunAndes follows the field names, trait descriptions and units of measurement of the TRY database. It is currently available in open access in the FIGSHARE data repository, and will be part of TRY’s next release. Open access trait data from Andean plants will contribute to ecological research in the region, the most species rich terrestrial biodiversity hotspot.

Abstract:

Ensuring the integrity of the world’s forests is indispensable for mitigating climate change, combatting biodiversity loss, and protecting the livelihoods of rural communities. While many strategies have been developed to address deforestation across different geographic scales, measuring their impact against a fluctuating background of market-driven forest loss is notoriously challenging. In this article, we (1) asses deforestation in Ecuador using a dynamic, counterfactual baseline that excludes non-market factors, (2) identify periods of reduced and excess deforestation, and (3) assess the economic consequences of associated CO2 emissions using the social cost of carbon metric. We construct a counterfactual market-forces-only reference scenario by simulating heterogeneous profit-seeking agents making satisficing land-use allocation decisions under uncertainty. The model simulates a reference scenario for 2001–2022, a period encompassing dollarization, the beginning of a constitution granting inalienable rights to nature, and the launch of the largest payments for ecosystem services program in Ecuador’s history. On this period, total deforestation was approximately 20% lower than expected in a market-forces-only scenario (9540 vs.12,000 km2). The largest deviation occurred in 2001–2009, when observed deforestation was 43.6% lower than expected (3720 vs 6590 km2). From 2010 onwards, deforestation appears to be market-driven. We assess the economic value of avoided CO2 emissions at US $5.7 billion if the reduction is permanent, or US $3.1 billion considering a 1% risk of loss from 2022 onwards. We discuss contributing factors that likely shaped periods of reduced and excess deforestation and stress the need to use realistic baselines.