Showing papers by "Andy Hector published in 2019"

Drought cuts back regeneration in logged tropical forests

Abstract: Logged tropical forests represent a major opportunity for preserving biodiversity and sequestering carbon, playing a large role in meeting global forest restoration targets. Left alone, these ecosystems have been expected to undergo natural regeneration and succession towards old growth forests, but extreme drought events may challenge this process. While old growth forests possess a certain level of resilience, we lack understanding as to how logging may affect forest responses to drought. This study examines the drought–logging interaction in seedling dynamics within a landscape of logged and unlogged forests in Sabah Malaysia, based on 73 plots monitored before and after the 2015-16 El Nino drought. Drought increased seedling mortality in all forests, but the magnitude of this impact was modulated by logging intensity, with forests with lower canopy leaf area index (LAI) and above ground biomass (AGB) experiencing greater drought induced mortality. Moreover, community traits in more heavily logged forests shifted towards being more ruderal after drought, suggesting that the trajectory of forest succession had been reversed. These results indicate that with reoccurring strong droughts under a changing climate, logged forests that have had over half of their biomass removed may suffer permanently arrested succession. Targeted management interventions may therefore be necessary to lift the vulnerable forests above the biomass threshold.

Not even wrong: Comment by Loreau and Hector.

Abstract: In a new paper entitled \"Not even wrong: The spurious measurement of biodiversity's effects on ecosystem functioning\", Pillai & Gouhier (2019) question the validity of the additive partition of biodiversity effects that we proposed 18 years ago (Loreau and Hector 2001) and that has become a classic in the biodiversity and ecosystem functioning (BEF) research field. Here we show that their critique misinterprets the goal of the BEF research program; in effect, they propose another research program that is both fundamentally different from BEF and logically inconsistent. In particular, they seek to measure biodiversity effects beyond and above those of species coexistence, an impossible task because biodiversity and coexistence are inseparable concepts. Therefore, once the direct and indirect effects of species coexistence are fully accounted for, the residual effect of biodiversity that they propose to study should be zero. We conclude that BEF research should rejuvenate and develop in new directions, but this effort will be successful only if it builds upon the foundations laid down by past research. This article is protected by copyright. All rights reserved.

Positive effects of liana cutting on seedlings are reduced during El Niño-induced drought

Abstract: 1. Liana cutting is a management practice currently applied to encourage seedling regeneration and tree growth in some logged tropical forests. However, there is limited empirical evidence of its effects on forest demographic rates in Southeast Asia. 2. We used 22 four-hectare plots in the Sabah Biodiversity Experiment (a reduced impact logging site) enrichment line planted with 16 dipterocarp species to assess the effects of complete liana cutting on tree growth and survival. We compared plots where lianas were only cut along planting lines (standard enrichment line planting) with those with one (2014) or two rounds (2011 and 2014) of complete liana cutting. 3. We found increased seedling growth following the first complete liana cut in 2011 relative to the enrichment line planting, consistent with previous studies. The response after three years to the cutting in 2014 depended on whether lianas had been previously cut or not: in twice-cut plots, seedling growth was not significantly different from the standard enrichment planting controls, whereas growth in plots with only one complete cut in 2014 was significantly slower. Seedling survival decreased through time for both once- and twice-cut liana treatments but remained stable in controls. 4. Sapling growth after the 2014 liana cutting showed a similar pattern to seedling growth, while tree growth following the 2014 liana cutting was significantly lower than controls regardless of whether lianas were cut twice (2011 and 2014) or once (2014). 5. Differences in response between the two rounds of liana cutting were likely due to changes in precipitation - 2011 was followed by consistent rainfall while 2014 was followed by two severe droughts within 2 years. 6. Synthesis and applications. Our results generally support the widely-reported positive effects of liana cutting on tree growth and survival. However, reduced growth and survival after the 2015/16 El Nino suggests that drought may temporarily undermine the benefits of liana cutting in logged tropical forests. Managers of similar areas in SE Asia should consider halting liana cutting during El Nino events. In other tropical areas, seedling survival should be monitored to assess to what extent results from SE Asia are transferable.

Individual tree traits shape insect and disease damage on oak in a climate-matching tree diversity experiment.

Abstract: Diversifying planted forests by increasing genetic and species diversity is often promoted as a method to improve forest resilience to climate change and reduce pest and pathogen damage. In this study, we used a young tree diversity experiment replicated at two sites in the UK to study the impacts of tree diversity and tree provenance (geographic origin) on the oak (Quercus robur) insect herbivore community and a specialist biotrophic pathogen, oak powdery mildew. Local UK, French, and Italian provenances were planted in monocultures, provenance mixtures, and species mixes, allowing us to test whether: (a) local and nonlocal provenances differ in their insect herbivore and pathogen communities, and (b) admixing trees leads to associational effects on insect herbivore and pathogen damage. Tree diversity had variable impacts on foliar organisms across sites and years, suggesting that diversity effects can be highly dependent on environmental context. Provenance identity impacted upon both herbivores and powdery mildew, but we did not find consistent support for the local adaptation hypothesis for any group of organisms studied. Independent of provenance, we found tree vigor traits (shoot length, tree height) and tree apparency (the height of focal trees relative to their surroundings) were consistent positive predictors of powdery mildew and insect herbivory. Synthesis. Our results have implications for understanding the complex interplay between tree identity and diversity in determining pest damage, and show that tree traits, partially influenced by tree genotype, can be important drivers of tree pest and pathogen loads.