Leland Werden

Last Name

Werden

First Name

Leland

ORCID

0000-0002-3579-4352

Organisational unit

09625 - Crowther, Thomas Ward (ehemalig) / Crowther, Thomas Ward (former)

Show all metadata

Search Results

Publications1 - 10 of 17

An open-source method for spatially and temporally explicit herbivory monitoring in semi-arid savannas
Weber, Manuel; Strijbis, Jonathan; Osner, Nicholas; et al. (2025)
Journal of Environmental Management
Effective management of protected areas is crucial for addressing the global biodiversity crisis. In water-limited savannas, altered herbivory regimes contribute to ecosystem degradation, creating a need for tools to track herbivore impact on vegetation. Here, we present the Spatially and Temporally Explicit Herbivory Monitoring (STEHM) tool, a novel methodology for monitoring herbivory pressure in near real-time. This approach combines herbivore abundance estimates, derived using a detection algorithm (YOLO v10) performed on imagery collected with camera traps placed at waterpoints across protected areas, with satellite imagery (Sentinel-2) to classify vegetation cover. STEHM enables weekly herbivory assessments, facilitating adaptive herbivore management at scales down to a few square kilometers. By linking herbivore dynamics to surface water availability—a primary factor influencing large herbivore distributions—STEHM provides a framework to disentangle ecological drivers of plant-herbivore interactions. Over one year, we collected and applied STEHM to a total of 2,275,309 individual camera trap images across two case study sites in northern Namibia, leading to the detection of 100,826 waterpoint visits by ten focal species. These observations revealed consistent differences in herbivory pressure between waterpoints, with some areas experiencing concentrated pressure, and a seasonal decline in less water-dependent species during the rainy season, while water-dependent species remained present. Findings indicate that water availability manipulation can alleviate pressure in high-impact areas as non-selective grazers shift to other waterpoints. This refined monitoring capability supports adaptive conservation strategies, providing spatially explicit, near real-time data on herbivore densities to enable targeted management and promote savanna restoration.
Increasing air-filled vessels has little influence on vulnerability to drought-induced embolism in two species with long maximum xylem vessel length but low vessel connectivity
Smith-Martin, Chris M.; Johnson, Kate M.; Urquhart, Shelley; et al. (2025)
Tree Physiology
Perennial woody plants accumulate native xylem embolisms over time. However, whether this makes the water transport system more vulnerable to drought-induced dysfunction as the percentage of gas-filled vessels increases is unclear. We tested whether increasing the proportion of open (air-filled) vessels changes the overall embolism vulnerability in stems of angiosperm species with long maximum vessel lengths but relatively low vessel connectivity. Using optical vulnerability curves, we measured xylem vulnerability of 57 branches ranging in length from ~10 to over 300 cm, from two adult trees (Acacia mearnsii De Wild. and Eucalyptus globulus Labill.) known to have long maximum vessel length (>75 cm) but low vessel connectivity. The fraction of open vessels at different branch lengths was estimated by staining open vessels under suction and with X-ray micro-computed tomography (μCT). To relate this to native field conditions, the percentage of pre-existing native embolisms was measured with μCT on a different set of branches. Our results show that even when a large proportion (> 25%) of open (air-filled) vessels are present, the xylem-embolism thresholds (water potential at 12% (P$_{12}$), 50% (P$_{50}$) and 88% (P$_{88}$) embolized xylem area) resemble those of branches with no open vessels. Scanning of native embolism with μCT revealed 10% (E. globulus) and 20% (A. mearnsii) native embolism under natural conditions. We conclude that even when approximately one-quarter of vessels are air-filled, there is no discernable effect on the overall xylem vulnerability of stem segments with long vessels and low vessel connectivity. Xylem vulnerability to embolism among all the branches measured from each of the two trees was relatively homogeneous with a ~10-20% variation. Our findings also suggest that the presence of pre-existing native embolisms, at the percentages observed in the field (<25%), would not increase vulnerability to xylem embolism in these species with largely isolated individual xylem vessels.
Leaf habit affects the distribution of drought sensitivity but not water transport efficiency in the tropics
Vargas G., German; Kunert, Norbert; Hammond, William M.; et al. (2022)
Ecology Letters
Considering the global intensification of aridity in tropical biomes due to climate change, we need to understand what shapes the distribution of drought sensitivity in tropical plants. We conducted a pantropical data synthesis representing 1117 species to test whether xylem-specific hydraulic conductivity (KS), water potential at leaf turgor loss (ΨTLP) and water potential at 50% loss of KS (ΨP50) varied along climate gradients. The ΨTLP and ΨP50 increased with climatic moisture only for evergreen species, but KS did not. Species with high ΨTLP and ΨP50 values were associated with both dry and wet environments. However, drought-deciduous species showed high ΨTLP and ΨP50 values regardless of water availability, whereas evergreen species only in wet environments. All three traits showed a weak phylogenetic signal and a short half-life. These results suggest strong environmental controls on trait variance, which in turn is modulated by leaf habit along climatic moisture gradients in the tropics.
Effects of landscape structure on restoration success in tropical premontane forest
San-José, Miriam; Werden, Leland; Joyce, Francis H.; et al. (2022)
Scientific Reports
Reversing large-scale habitat degradation and deforestation goes beyond what can be achieved by site-level ecological restoration and a landscape ecology perspective is fundamental. Here we assess the relative importance of tree cover and its configuration on forest-dependent birds and late-successional tree seedlings in restoration sites in southern Costa Rica. The abundance and species richness of birds increased in landscapes with more corridors, higher tree cover, and lower levels of fragmentation, highlighting the importance of riparian corridors for connectivity, and continuous tree cover as suitable habitat. Landscape variables affected abundance and species richness of seedlings similarly, but effects were weaker, possibly because seedlings face establishment limitation in addition to dispersal limitation. Moreover, the scale of landscape effects on seedlings was small, likely because proximal individual trees can significantly influence recruitment in restoration plots. Results underscore the importance of incorporating landscape-level metrics to restoration projects, as knowing the extent, and how the landscape may affect restoration outcomes can help to infer what kind of species will arrive to restoration plots.
Accounting for albedo change to identify climate-positive tree cover restoration
Hasler, Natalia; Williams, Christopher A.; Denney, Vanessa Carrasco; et al. (2024)
Nature Communications
Restoring tree cover changes albedo, which is the fraction of sunlight reflected from the Earth’s surface. In most locations, these changes in albedo offset or even negate the carbon removal benefits with the latter leading to global warming. Previous efforts to quantify the global climate mitigation benefit of restoring tree cover have not accounted robustly for albedo given a lack of spatially explicit data. Here we produce maps that show that carbon-only estimates may be up to 81% too high. While dryland and boreal settings have especially severe albedo offsets, it is possible to find places that provide net-positive climate mitigation benefits in all biomes. We further find that on-the-ground projects are concentrated in these more climate-positive locations, but that the majority still face at least a 20% albedo offset. Thus, strategically deploying restoration of tree cover for maximum climate benefit requires accounting for albedo change and we provide the tools to do so.
The Evolution of Forest Restoration in Europe: A Synthesis for a Step Forward Based on National Expert Knowledge
Erdozain, Maitane; Alberdi, Iciar; Aszalós, Réka; et al. (2024)
Current Forestry Reports
Purpose of review: We are amid a historical momentum encouraging forest restoration, yet the translation of ambitious targets into reality is hindered by poor documentation and understanding of the success and failure of past restoration efforts. This review aims to evaluate the ecological, social, political and economic characteristics of forest restoration across Europe, their development over time and key lessons learned to guide future restoration initiatives. The analysis is based on the synthesis of expert assessments from 18 European countries. Recent findings: Early restoration initiatives in central and southern Europe were largely reactive to natural disasters or timber shortages, and while effective in erosion control and timber production, their ecological benefits were often limited due to monoculture plantations and short-rotation systems. Geopolitical crises intensified timber production, with nationalized and centrally managed forests in several countries, but often at the cost of biodiversity. Since the 1990s, a shift toward multifunctionality has emerged driven by the convergence of environmental, social, political and economic events. Summary: Forest restoration in Europe has transitioned from disaster reduction and production-driven efforts to a more multifunctional approach that promotes biodiversity. Changes have been driven by a combination of environmental (e.g., catastrophic consequences following natural disasters), political (e.g., wars, forest nationalization and management centralization), legal (e.g., strict and ambitious national and international policies), social (e.g., rural abandonment and changes in societal values) and economic (e.g., new funding mechanisms or market fluctuations) events. Despite the development, conflicting goals, insufficient funding, climate change and short-term thinking persist as key barriers.
A comprehensive analysis of forest restoration practices across Europe: Ecological, economic, social and policy dimensions
Menéndez-Miguélez, María; Rubio-Cuadrado, Álvaro; Bauhus, Jürgen; et al. (2025)
Ecological Indicators
Scaling up ecosystem restoration is essential to halt and reverse land degradation and biodiversity loss and ensure future functionality and resilience. However, the implementation of concrete restoration initiatives will present many challenges, such as setting appropriate and realistic goals, selecting or developing the most effective and efficient restoration practices, as well as carrying out effective short- and long-term monitoring of success. Furthermore, there is a lack of information to facilitate the implementation of effective restoration interventions. To address this knowledge gap we gathered information on the ecological, economic, social and policy challenges faced by restoration practitioners across Europe using a widely distributed online survey. Based on the 398 responses received from practitioners working in 31 countries we assessed how practical and scientific knowledge form an integral part of restoration initiatives. The focus of more than 40% of respondents from restoration projects was on increasing the population of species (plant species) and promoting their regeneration. Two common elements emerged across the wide diversity of responses: 1) a prevalent belief that restoration enhances multiple ecological aspects simultaneously, and subsequently, 2) the importance of developing monitoring frameworks that holistically evaluate restoration effectiveness, given the difficulty in defining a single, exclusive indicator of restoration success, as this could oversimplify the outcomes in complex ecosystems. Furthermore, respondents emphasized the importance of taking a holistic approach to restoration design, encompassing not only ecological aspects but also social, economic, and policy dimensions. The findings from the analysis of this survey provide, for the first time, a comprehensive view of the ecosystems and restoration activities that European countries are prioritizing, along with evaluation by the stakeholders involved.
Physiological and Growth Responses of Tropical Dry Forest Tree Seedlings to Water and Nutrient Additions: Comparisons Between Nitrogen Fixers and Non-Fixers
Calderón-Morales, Erick; Werden, Leland; Smith-Martin, Chris M.; et al. (2025)
Biotropica
Belowground resources are key determinants of seedling growth and survival in tropical forests. Nutrients and light may limit plant growth the most in tropical wet forests, whereas water may limit plant growth more in tropical dry forests. Nitrogen (N)-fixing species play an important role in the nitrogen and carbon cycles across tropical dry forests. However, studies investigating the joint effects of water and nutrients on the physiology and performance of N-fixing species are scarce. We implemented a full factorial shade house experiment that manipulated water and nutrients (NPK 20:20:20 and complete micronutrients) using eight tree species representing N-fixing and non-fixing tree species in the tropical dry forest of Costa Rica to determine: (1) How plant responses to water and nutrient availability vary between N-fixing and non-fixing tree species?; and (2) How nutrient and/or water availability influences seedling water- and nutrient-use traits? We found that growth and physiological responses to water and nutrient addition depended directly on the capacity of species to fix atmospheric N2. N-fixing species responded more strongly to nutrient addition, accumulating 67% more total biomass on average (approximately double that of non-fixing taxa) and increasing average height growth rate by 41%. N-fixing species accumulated more biomass without compromising water-use efficiency, taking full advantage of the increased nutrient availability. Interestingly, results from our experiment show that increased water availability rarely influenced tropical dry forest seedling performance, whereas nutrient availability had a strong effect on biomass and growth. Overall, our results highlight the ability of N-fixing seedlings to take advantage of local soil resource heterogeneity, which may help to explain the dominance of N-fixing trees in tropical dry forests.
Assisted restoration interventions drive functional recovery of tropical wet forest tree communities
Werden, Leland; Zarges, Sebastian; Holl, Karen D.; et al. (2022)
Frontiers in Forests and Global Change
Choosing appropriate forest restoration interventions is challenging. Natural regeneration can rapidly facilitate forest recovery in many situations. However, barriers such as dispersal limitation and competition with non-native species can require assisted restoration approaches to facilitate plant community recovery. We used a study that has directly compared the outcomes of tropical wet forest restoration interventions across 11 replicate sites in southern Costa Rica. Within this framework, we examined the functional recovery trajectories of recruiting tree sapling communities across a gradient of restoration interventions including low (natural regeneration), intermediate (applied nucleation), and high (plantation) initial resource-investment, which we compared to remnant reference forest. We collated leaf and stem functional traits for tree species that comprised the bulk of recruiting saplings, then determined how community-weighted trait means and functional diversity metrics changed over a decade across treatments. Results show that assisted restoration approaches (applied nucleation, plantation) sped the development of more functionally diverse tree communities, more than tripling the functional richness (FRic) of recruiting communities when compared to natural regeneration. However, functional dispersion (i.e., the trait range of dominant species) was equivalent across interventions, and between 28 and 44% lower than remnant forest, indicating that increases in FRic under assisted restoration were driven by species recruiting in low abundances (<10 individuals across treatments). Recruits in assisted restoration treatments also had 10-15% tougher, less-palatable leaves, and leaves were even tougher in reference forest, which could be driven by increasing herbivory pressure along the gradient of interventions. Results show that tracking simple metrics such as species richness can mask a more mechanistic understanding of ecosystem recovery that is elucidated by taking a functional trait-driven approach toward evaluating outcomes. For example, our work identified a paucity of dense-wooded species recruiting across restoration interventions, wood density was 11-13% lower in restoration treatments than reference forests, underscoring such species as prime targets for enrichment planting. Overall, findings suggest that assisted restoration can catalyze the functional recovery of naturally recruiting tree communities in landscapes that are slow to recover naturally and highlight the importance of evaluating how different components of functional diversity shift over time to fully understand restoration outcomes.
Ten simple rules for using large language models in science, version 1.0
Smith, Gabriel Reuben; Bello, Carolina; Bialic-Murphy, Lalasia; et al. (2024)
PLoS Computational Biology

Publications1 - 10 of 17

Leland Werden

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results