110 research outputs found

    Climate modulates the effects of tree diversity on forest productivity

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    1. Despite growing evidence that, on average, diverse forests tend to be more productive than species-poor ones, individual studies often report strongly contrasting relationships between tree species richness and above-ground wood production (AWP). In the attempt to reconcile these apparently inconsistent results, we explored whether the strength and shape of AWP–diversity relationships shifts along spatial and temporal environmental gradients in forests across Europe. 2. We used tree ring data from a network of permanent forest plots distributed at six sites across Europe to estimate annual AWP over a 15-year period (1997–2011). We then tested whether the relationship between tree species richness and AWP changes (i) across sites as a function of large-scale gradients in climatic productivity and tree packing density and (ii) among years within each sites as a result of fluctuating climatic conditions. 3. AWP–species richness relationships varied markedly among sites. As predicted by theory, the relationship shifted from strongly positive at sites where climate imposed a strong limitation on wood production and tree packing densities were low, to weakly negative at sites where climatic conditions for growth were most suitable. In contrast, we found no consistent effect of interannual fluctuations in climate on the strength of AWP–species richness relationships within sites. 4. Synthesis. Our results indicate that the shape and strength of the relationship between tree diversity and forest productivity depends critically on environmental context. Across Europe, tree diversity shows the greatest potential to positively influence forest productivity at either end of the latitudinal gradient, where adverse climatic conditions limit productivity and lead to the development of less densely packed stands.The research leading to these results received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 265171.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1111/1365-2745.1252

    Strength in numbers:combining multi-source remotely sensed data to model plant invasions in coastal dune ecosystems

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    International audienceA common feature of most theories of invasion ecology is that the extent and intensity of invasions is driven by a combination of drivers, which can be grouped into three main factors propagule pressure (P), abiotic drivers (A) and biotic interactions (B). However, teasing apart the relative contribution of P, A and B on Invasive Alien Species (IAS) distributions is typically hampered by a lack of data. We focused on Mediterranean coastal dunes as a model system to test the ability of a combination of multi-source Remote Sensing (RS) data to characterize the distribution of five IAS. Using generalized linear models, we explored and ranked correlates of P, A and B derived from high-resolution optical imagery and three-dimensional (3D) topographic models obtained from LiDAR, along two coastal systems in Central Italy (Lazio and Molise Regions). Predictors from all three factors contributed significantly to explaining the presence of IAS, but their relative importance varied among the two Regions, supporting previous studies suggesting that invasion is a context-dependent process. The use of RS data allowed us to characterize the distribution of IAS across broad, regional scales and to identify coastal sectors that are most likely to be invaded in the future. © 2019 by the authors

    Drivers of aboveground wood production in a lowland tropical forest of West Africa:teasing apart the roles of tree density, tree diversity, soil phosphorus, and historical logging

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    This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Wiley.1. Tropical forests currently play a key role in regulating the terrestrial carbon cycle and abating climate change by storing carbon in wood. However, there remains considerable uncertainty as to whether tropical forests will continue to act as carbon sinks in the face of increased pressure from expanding human activities. Consequently, understanding what drives productivity in tropical forests is critical. 2. We used permanent forest plot data from the Gola Rainforest National Park (Sierra Leone) – one of the largest tracts of intact tropical moist forest in West Africa – to explore how (i) stand basal area and tree diversity, (ii) past disturbance associated with past logging and (iii) underlying soil nutrient gradients interact to determine rates of aboveground wood production (AWP). We started by statistically modelling the diameter growth of individual trees and used these models to estimate AWP for 142 permanent forest plots. We then used structural equation modelling to explore the direct and indirect pathways which shape rates of AWP. 3. Across the plot network, stand basal area emerged as the strongest determinant of AWP, with densely packed stands exhibiting the fastest rates of AWP. In addition to stand packing density, both tree diversity and soil phosphorus content were also positively related to productivity. By contrast, historical logging activities negatively impacted AWP through the removal of large trees, which contributed disproportionately to productivity. 4. Synthesis. Understanding what determines variation in wood production across tropical forest landscapes requires accounting for multiple interacting drivers – with stand structure, tree diversity and soil nutrients all playing a key role. Importantly, our results also indicate that logging activities can have a long-lasting impact on a forest’s ability to sequester and store carbon, emphasizing the importance of safeguarding old-growth tropical forests.This study was funded through a grant from the Cambridge Conservation Initiative Collaborative Fund entitled “Applications of airborne remote sensing to the conservation management of a West African National Park”. T.J. was funded in part through NERC grant NE/K016377/1. A.C.S. was funded in part through a grant from the Percy Sladen Memorial Fund

    Riparian buffers act as microclimatic refugia in oil palm landscapes

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    1. There is growing interest in the ecological value of set-aside habitats around rivers in tropical agriculture. These riparian buffers typically comprise forest or other non production habitat, and are established to maintain water quality and hydrological processes, whilst also supporting biodiversity, ecosystem function and landscape connectivity. 2. We investigated the capacity for riparian buffers to act as microclimatic refugia by combining field-based measurements of temperature, humidity, and dung beetle communities with remotely-sensed data from LiDAR across an oil palm dominated landscape in Borneo. 3. Riparian buffers offer a cool and humid habitat relative to surrounding oil palm plantations, with wider buffers characterised by conditions comparable to riparian sites in continuous logged forest. 4. High vegetation quality and topographic sheltering were strongly associated with cooler and more humid microclimates in riparian habitats across the landscape. Variance in beetle diversity was also predicted by both proximity-to-edge and microclimatic conditions within the buffer, suggesting that narrow buffers amplify the negative impacts that high temperatures have on biodiversity. 5. Synthesis and applications. Widely-legislated riparian buffer widths of 20-30 m each side of a river may provide drier and less humid microclimatic conditions than continuous forest. Adopting wider buffers and maintaining high vegetation quality will ensure set-asides established for hydrological reasons bring co-benefits for terrestrial biodiversity, both now, and in the face of anthropogenic climate change.This work was funded by the Natural Environmental Research Council (NERC) through the Human Modified Tropical Forests programme (NE/K016261/1; NE/K016377/1), as well as the Newton--Ungku Omar Fund via the British Council and Malaysian Industry -Government Group for High Technology (216433953). NERC also funded the PhD studentship for JW (NE/L002485/1) and research fellowship of TJ (NE/S01537X/1)
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