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82 results for “tree density”

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dryad36/100

Demographic consequences of heterogeneity in conspecific density dependence among mast fruiting tropical trees

The role of conspecific density dependence (CDD) in the maintenance of species richness is a central focus of tropical forest ecology. However, tests of CDD often ignore the integrated effects of CDD over multiple life-stages and their long-term impacts on population demography. We combined a 10-year time series of seed production, seedling recruitment and sapling and tree demography of three dominant Southeast Asian tree species that adopt a mast fruiting phenology. We used these data to construct individual-based models that examine the effects of CDD on population growth rates (λ) across life-history stages. Recruitment was driven by positive CDD for all species, supporting the predator satiation hypothesis, while negative CDD affected seedling and sapling growth of two species, significantly reducing λ. This negative CDD on juvenile growth overshadowed the positive CDD of recruitment, suggesting the cumulative effects of CDD during seedling and sapling development has greater importance than the positive CDD during infrequent masting events. Overall, CDD varied between positive and negative across life-history stages for all species, suggesting that assessments of CDD on transitions between just two stages (e.g. seeds-seedlings or juveniles-mature trees) likely misrepresents the importance of CDD on population growth and stability.

opencc-zeroMay 2022View details →

zenodo36/100

Potential map generated by the RF spatial model to define ideal zones for the occurrence of high density of giant trees in the Amazon

The provided image is a theoretical map of giant tree density in the Amazon, generated from a spatial model based on the **Random Forest** algorithm. The map displays the spatial distribution of tree density, representing the number of trees taller than 60 meters per square kilometer (trees/km²). The model was developed using climatic, topographic, and soil variables to predict areas with higher concentrations of these giant trees. The areas are color-coded according to different density ranges, where: - Lighter shades indicate lower tree density (≤ 5 trees/km²), - Darker shades indicate higher density (up to 141 trees/km²). Biogeographic provinces within the Amazon biome, such as the **Guiana Shield**, **Xingu-Tapajós**, and **Roraima**, are highlighted, showing distinct density patterns across the Amazon region. This map is a valuable tool for understanding the spatial distribution of giant trees in the Amazon and plays a crucial role in conservation efforts and ecological monitoring in the region.

opencc-by-4.0Sep 2024View details →

dryad36/100

Data and R scripts for: Ant invasions is associated with lower root density and different root distribution of a foundational savanna tree species

Some invasive ants have worldwide distributions and impose substantial impacts on human society and native biodiversity. Yet we know little about how ants impact soil ecosystems in general, much less how soil ecosystems shift when invasive ants move in. We excavated the coarse roots of a monodominant savanna tree in invaded and uninvaded areas to test the hypothesis that the presence of invasive ants would be associated with changes in root distribution and biomass across the landscape. We found that in the presence of invasive ants, trees had a shifted distribution of lateral coarse roots, with proportionally less root biomass near the surface and far from tree stems. In addition, the density of lateral coarse-root biomass was ~20% lower for trees within invaded landscapes. Our results suggest that soil-nesting invasive ants can drive important changes in rooting strategy for a tree species that serves a foundational role in the biogeochemical cycles of vertisol savannas.

opencc-zeroDec 2022View details →

dryad36/100

Effects of long-term fixed fire regimes on African savanna vegetation biomass, vertical structure and tree stem density

<ol> <li>Fire plays an integral role in shaping the vegetation structure of savanna ecosystems. However, effects of fire regime characteristics, such as frequency and season of burn, on savanna vegetation structure, biomass and tree abundance across landscape types are largely unknown. </li> <li>We used high-resolution airborne Light Detection and Ranging (LiDAR) to investigate the long-term effects of fire manipulation on savanna vegetation in Kruger National Park, South Africa. We analysed the effects of fire exclusion and experimental burns every 1, 2, 3, 4 and 6 years and during different seasons on aboveground biomass (AGB), tree stem densities and vegetation vertical height profiles across a rainfall gradient and on contrasting geologies. </li> <li>Across savanna types, and especially in drier savannas, fire season was more influential for constraining AGB than was fire frequency. Plots experiencing fires during the late- and mid-dry season had 44.50% and 43.60%, respectively, lower AGB relative to unburnt plots than wet-season fires. However, in mesic savannas, fire frequency interacted with fire season to influence AGB: plots subjected to high frequency, dry season fires had 55.35% lower AGB than unburnt plots, whereas plots burnt in the wet season at lower frequencies had lower AGB (24.40% lower than unburnt plots) than plots subjected to high frequency, wet-season fires (13.74% lower AGB than unburnt plots). </li> <li>Fire regimes had variable effects on tree densities, and effects varied with savanna type. Woody vertical vegetation profiles showed the largest differences in response to dry season fires, with the greatest divergence in vegetation height classes < 5m. </li> <li>Synthesis and applications. Understanding the influence of fire regimes on vegetation structure has important implications for the management of savanna heterogeneity, and for predicting trajectories of change in savanna vegetation as fire regimes vary with climate change. We show that the magnitude of the effect of fire on woody vegetation structure varies with savanna context. Our results suggest that heterogeneous vegetation structure can be achieved by applying fires in the dry season in mesic savannas, whereas in dry savannas, variation in fire regimes is less consequential for constraining biomass accumulation and altering vegetation structure. </li> </ol>

opencc-zeroMay 2023View details →

dryad36/100

Effects of tree species diversity and conspecific seedling density on insect herbivory and pathogen infection on big-leaf mahogany seedlings

The Janzen-Connell Hypothesis (JCH) predicts that attack by specialist enemies on seedlings increases with conspecific seedling density, but studies have rarely experimentally tested for the contingency of such effects on tree community context (e.g., diversity, composition) and measured responses by different enemies (e.g. herbivores, pathogens). We conducted a field study in a large-scale system evaluating tree species diversity and conspecific density effects on leaf damage on mahogany (Swietenia macrophylla) seedlings. We established quadrats of eight levels of seedling density across mahogany tree monocultures and species polycultures including mahogany, and recorded percent leaf damage by insects and percent leaf necrosis by a pathogenic fungus on mahogany seedlings. We found contrasting effects of tree species diversity on insects and pathogens. Whereas diversity did not affect leaf damage by insects, it had a significant negative effect on leaf necrosis by pathogens. On average, percent leaf necrosis on mahogany seedlings in polyculture was half of that observed in monoculture. We discuss the potential influences of changes in mahogany tree density vs. frequency (relative to other tree species) driving this diversity effect. Unexpectedly, we found no effect of seedling conspecific density on either leaf insect or pathogen damage (i.e., density-independent attack). Likewise, we found no significant tree diversity by seedling density interaction, indicating that attackers were consistently unresponsive to variation in seedling density across two levels of tree diversity. Overall, this study provides a unique test of the JCH by experimentally evaluating seedling density and tree diversity effects on contrasting plant enemies, shedding light on enemy controls over plant recruitment.

opencc-zeroJun 2023View details →

dryad36/100

Data to: Remotely sensed tree height and density explain global gliding vertebrate richness

In vertebrates, gliding evolved as a mode of energy-efficient locomotion to move between trees. Gliding vertebrate richness is hypothesised to increase with tree height and decrease with tree density but empirical evidence for this is scarce, especially at a global scale. Here, we test the ability of tree height and density to explain species richness of gliding vertebrates globally compared to richness of all vertebrates, while controlling for biogeographical and climatic factors. We compiled a global database of 193 gliding amphibians, mammals and reptiles and created maps of species richness from extent-of-occurrence range maps. We paired species richness of gliding vertebrates with spatial estimates of global tree height and density and biogeographical regions as covariates to account for ecological differences among global regions. We used univariate linear and multivariate generalised linear mixed-effect models to evaluate relationships between species richness and tree height and density and the interaction between both. We found that richness of all gliding vertebrate species increased significantly with tree height, while results for richness of amphibians, mammals and reptiles alone indicated mixed responses, especially among different biogeographical regions. Mixed-effect models mirrored these results for richness of all species combined, while also revealing the mixed responses to tree height and density of richness of amphibians, mammals and reptiles. Richness of all vertebrate species – gliding and non-gliding – also increased with tree height and density but at a lesser rate than richness of gliding vertebrates indicating a greater influence of forest structure on richness patterns of gliding vertebrates. Our results support hypotheses stating that gliding in vertebrates globally evolved in tall forests as energy-efficient locomotion between trees and provide further evidence for the importance of forest structure to explain the distribution of gliding vertebrates.

opencc-zeroSep 2023View details →

dryad36/100