Riparian buffers act as microclimatic refugia in oil palm landscapes

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)

Leech blood-meal invertebrate-derived DNA reveals differences in Bornean mammal diversity across habitats.

The application of metabarcoding to environmental and invertebrate-derived DNA (eDNA and iDNA) is a new and increasingly applied method for monitoring biodiversity across a diverse range of habitats. This approach is particularly promising for sampling in the biodiverse humid tropics, where rapid land-use change for agriculture means there is a growing need to understand the conservation value of the remaining mosaic and degraded landscapes. Here we use iDNA from blood-feeding leeches (Haemadipsa picta) to assess differences in mammalian diversity across a gradient of forest degradation in Sabah, Malaysian Borneo. We screened 557 individual leeches for mammal DNA by targeting fragments of the 16S rRNA gene and detected 14 mammalian genera. We recorded lower mammal diversity in the most heavily degraded forest compared to higher quality twice logged forest. Although the accumulation curves of diversity estimates were comparable across these habitat types, diversity was higher in twice logged forest, with more taxa of conservation concern. In addition, our analysis revealed differences between the community recorded in the heavily logged forest and that of the twice logged forest. By revealing differences in mammal diversity across a human-modified tropical landscape, our study demonstrates the value of iDNA as a noninvasive biomonitoring approach in conservation assessments

Failed replacement enhances tropical tree diversity

The Janzen-Connell (JC) hypothesis is a leading explanation for plant-species diversity in tropical forests. It predicts that host specialist natural enemies drive the disproportionate mortality of con specific juveniles close to adults, particularly when density is high. The survival of heterospecifics is thought to be unaffected because apparent competition is generally weak or absent. Consequently, if the JC effect is sufficiently intense, adults will not be replaced by conspecific individuals and species turnover will be promoted at forest sites, which has the potential to greatly enhance diversity. This thesis first demonstrates experimentally that natural enemies are capable of driving overcompensating density dependence in the seedlings of a tropical tree and that these natural enemies do not generate apparent competition. The potential for these short-term processes to develop into long-term recruitment inhibition is assessed by showing that adults are rarely replaced by con specific individuals, using Barro Colorado Island 50 ha plot datatset. However, self-replacement rates are shown to vary with landscape-scale abundance, adult-tree size and growth form. Finally, the diversity enhancing potential of self-replacement inhibition is measured using a simulation model in which the strength of density dependence is manipulated and the JC mechanism is compared to several alternative mechanisms for enhancing coexistence.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Failed replacement enhances tropical tree diversity

The Janzen-Connell (JC) hypothesis is a leading explanation for plant-species diversity in tropical forests. It predicts that host specialist natural enemies drive the disproportionate mortality of con specific juveniles close to adults, particularly when density is high. The survival of heterospecifics is thought to be unaffected because apparent competition is generally weak or absent. Consequently, if the JC effect is sufficiently intense, adults will not be replaced by conspecific individuals and species turnover will be promoted at forest sites, which has the potential to greatly enhance diversity. This thesis first demonstrates experimentally that natural enemies are capable of driving overcompensating density dependence in the seedlings of a tropical tree and that these natural enemies do not generate apparent competition. The potential for these short-term processes to develop into long-term recruitment inhibition is assessed by showing that adults are rarely replaced by con specific individuals, using Barro Colorado Island 50 ha plot datatset. However, self-replacement rates are shown to vary with landscape-scale abundance, adult-tree size and growth form. Finally, the diversity enhancing potential of self-replacement inhibition is measured using a simulation model in which the strength of density dependence is manipulated and the JC mechanism is compared to several alternative mechanisms for enhancing coexistence.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Realising the social value of impermanent carbon credits

Efforts to avert dangerous climate change by conserving and restoring natural habitats are hampered by concerns over the credibility of methods used to quantify their long-term impacts. We develop a novel, flexible framework for estimating the net social benefit of impermanent nature-based interventions that integrates three substantial advances: (1) conceptualising the permanence of a project’s impact as its additionality over time; (2) risk-averse estimation of the social cost of future reversals of carbon gains; and (3) post-credit monitoring to correct errors in deliberately pessimistic release forecasts. Our framework generates incentives for safeguarding already-credited carbon while enabling would-be investors to make like-for-like comparisons of diverse carbon projects. Preliminary analyses suggest nature-derived credits may be competitively priced even after adjusting for impermanence.The Royal Society, ESRC, NERC, Grantham Research Institute on Climate Change and the Environment, Frank Jackson Trust, Dragon Capital, and the Tezos Foundatio

Conflicts and opportunities for commercial tree plantation expansion and biodiversity restoration across Brazil

Publication status: PublishedSubstantial global restoration commitments are occurring alongside a rapid expansion in land‐hungry tropical commodities, including to supply increasing demand for wood products. Future commercial tree plantations may deliver high timber yields, shrinking the footprint of production forestry, but there is an as‐yet unquantified risk that plantations may expand into priority restoration areas, with marked environmental costs. Focusing on Brazil—a country of exceptional restoration importance and one of the largest tropical timber producers—we use random forest models and information on the economic, social, and spatial drivers of historic commercial tree plantation expansion to estimate and map the probability of future monoculture tree plantation expansion between 2020 and 2030. We then evaluate potential plantation‐restoration conflicts and opportunities at national and biome‐scales and under different future production and restoration pathways. Our simulations show that of 2.8 Mha of future plantation expansion (equivalent to plantation expansion 2010–2020), ~78,000 ha (3%) is forecast to occur in the top 1% of restoration priority areas for terrestrial vertebrates, with ~547,500 ha (20%) and ~1,300,000 ha (46%) in the top 10% and 30% of priority areas, respectively. Just ~459,000 ha (16%) of expansion is forecast within low‐restoration areas (bottom 30% restoration priorities), and the first 1 Mha of plantation expansion is likely to have disproportionate impacts, with potential restoration‐plantation overlap starkest in the Atlantic Forest but prominent in the Pampas and Cerrado as well. Our findings suggest that robust, coherent land‐use policies must be deployed to ensure that significant trade‐offs between restoration and production objectives are navigated, and that commodity expansion does not undermine the most tractable conservation gains under emerging global restoration agendas. They also highlight the potentially significant role an engaged forestry sector could play in improving biodiversity outcomes in restoration projects in Brazil, and presumably elsewhere

Conflicts and opportunities for commercial tree plantation expansion and biodiversity restoration across Brazil.

Substantial global restoration commitments are occurring alongside a rapid expansion in land-hungry tropical commodities, including to supply increasing demand for wood products. Future commercial tree plantations may deliver high timber yields, shrinking the footprint of production forestry, but there is an as-yet unquantified risk that plantations may expand into priority restoration areas, with marked environmental costs. Focusing on Brazil-a country of exceptional restoration importance and one of the largest tropical timber producers-we use random forest models and information on the economic, social, and spatial drivers of historic commercial tree plantation expansion to estimate and map the probability of future monoculture tree plantation expansion between 2020 and 2030. We then evaluate potential plantation-restoration conflicts and opportunities at national and biome-scales and under different future production and restoration pathways. Our simulations show that of 2.8 Mha of future plantation expansion (equivalent to plantation expansion 2010-2020), ~78,000 ha (3%) is forecast to occur in the top 1% of restoration priority areas for terrestrial vertebrates, with ~547,500 ha (20%) and ~1,300,000 ha (46%) in the top 10% and 30% of priority areas, respectively. Just ~459,000 ha (16%) of expansion is forecast within low-restoration areas (bottom 30% restoration priorities), and the first 1 Mha of plantation expansion is likely to have disproportionate impacts, with potential restoration-plantation overlap starkest in the Atlantic Forest but prominent in the Pampas and Cerrado as well. Our findings suggest that robust, coherent land-use policies must be deployed to ensure that significant trade-offs between restoration and production objectives are navigated, and that commodity expansion does not undermine the most tractable conservation gains under emerging global restoration agendas. They also highlight the potentially significant role an engaged forestry sector could play in improving biodiversity outcomes in restoration projects in Brazil, and presumably elsewhere

Accurate measurement of tropical forest canopy heights and aboveground carbon using structure from motion

© 2019 by the authors. Unmanned aerial vehicles are increasingly used to monitor forests. Three-dimensional models of tropical rainforest canopies can be constructed from overlapping photos using Structure from Motion (SfM), but it is often impossible to map the ground elevation directly from such data because canopy gaps are rare in rainforests. Without knowledge of the terrain elevation, it is, thus, difficult to accurately measure the canopy height or forest properties, including the recovery stage and aboveground carbon density. Working in an Indonesian ecosystem restoration landscape, we assessed how well SfM derived the estimates of the canopy height and aboveground carbon density compared with those from an airborne laser scanning (also known as LiDAR) benchmark. SfM systematically underestimated the canopy height with a mean bias of approximately 5 m. The linear models suggested that the bias increased quadratically with the top-of-canopy height for short, even-aged, stands but linearly for tall, structurally complex canopies ( > 10 m). The predictions based on the simple linear model were closely correlated to the field-measured heights when the approach was applied to an independent survey in a different location (R 2 = 67% and RMSE = 1.85 m), but a negative bias of 0.89 m remained, suggesting the need to refine the model parameters with additional training data. Models that included the metrics of canopy complexity were less biased but with a reduced R 2 . The inclusion of ground control points (GCPs) was found to be important in accurately registering SfM measurements in space, which is essential if the survey requirement is to produce small-scale restoration interventions or to track changes through time. However, at the scale of several hectares, the top-of-canopy height and above-ground carbon density estimates from SfM and LiDAR were very similar even without GCPs. The ability to produce accurate top-of-canopy height and carbon stock measurements from SfM is game changing for forest managers and restoration practitioners, providing the means to make rapid, low-cost surveys over hundreds of hectares without the need for LiDAR.The study was financed by faculty of Technology and Environment, Prince of Songkla Universit