Glen Reynolds

A large-scale forest fragmentation experiment: the Stability of Altered Forest Ecosystems Project

Opportunities to conduct large-scale field experiments are rare, but provide a unique opportunity to reveal the complex processes that operate within natural ecosystems. Here, we review the design of existing, large-scale forest fragmentation experiments. Based on this review, we develop a design for the Stability of Altered Forest Ecosystems (SAFE) Project, a new forest fragmentation experiment to be located in the lowland tropical forests of Borneo (Sabah, Malaysia). The SAFE Project represents an advance on existing experiments in that it: (i) allows discrimination of the effects of landscape-level forest cover from patch-level processes; (ii) is designed to facilitate the unification of a wide range of data types on ecological patterns and processes that operate over a wide range of spatial scales; (iii) has greater replication than existing experiments; (iv) incorporates an experimental manipulation of riparian corridors; and (v) embeds the experimentally fragmented landscape within a wider gradient of land-use intensity than do existing projects. The SAFE Project represents an opportunity for ecologists across disciplines to participate in a large initiative designed to generate a broad understanding of the ecological impacts of tropical forest modification.

The Sabah Biodiversity Experiment: a long-term test of the role of tree diversity in restoring tropical forest structure and functioning

Relatively, little is known about the relationship between biodiversity and ecosystem functioning in forests, especially in the tropics. We describe the Sabah Biodiversity Experiment: a large-scale, long-term field study on the island of Borneo. The project aims at understanding the relationship between tree species diversity and the functioning of lowland dipterocarp rainforest during restoration following selective logging. The experiment is planned to run for several decades (from seed to adult tree), so here we focus on introducing the project and its experimental design and on assessing initial conditions and the potential for restoration of the structure and functioning of the study system, the Malua Forest Reserve. We estimate residual impacts 22 years after selective logging by comparison with an appropriate neighbouring area of primary forest in Danum Valley of similar conditions. There was no difference in the alpha or beta species diversity of transect plots in the two forest types, probably owing to the selective nature of the logging and potential effects of competitive release. However, despite equal total stem density, forest structure differed as expected with a deficit of large trees and a surfeit of saplings in selectively logged areas. These impacts on structure have the potential to influence ecosystem functioning. In particular, above-ground biomass and carbon pools in selectively logged areas were only 60 per cent of those in the primary forest even after 22 years of recovery. Our results establish the initial conditions for the Sabah Biodiversity Experiment and confirm the potential to accelerate restoration by using enrichment planting of dipterocarps to overcome recruitment limitation. What role dipterocarp diversity plays in restoration only will become clear with long-term results.

Selective-logging and oil palm: multitaxon impacts, biodiversity indicators, and trade-offs for conservation planning

Strong global demand for tropical timber and agricultural products has driven large-scale logging and subsequent conversion of tropical forests. Given that the majority of tropical landscapes have been or will likely be logged, the protection of biodiversity within tropical forests thus depends on whether species can persist in these economically exploited lands, and if species cannot persist, whether we can protect enough primary forest from logging and conversion. However, our knowledge of the impact of logging and conversion on biodiversity is limited to a few taxa, often sampled in different locations with complex land-use histories, hampering attempts to plan cost-effective conservation strategies and to draw conclusions across taxa. Spanning a land-use gradient of primary forest, once- and twice-logged forests, and oil palm plantations, we used traditional sampling and DNA metabarcoding to compile an extensive data set in Sabah, Malaysian Borneo for nine vertebrate and invertebrate taxa to quantify the biological impacts of logging and oil palm, develop cost-effective methods of protecting biodiversity, and examine whether there is congruence in response among taxa. Logged forests retained high species richness, including, on average, 70% of species found in primary forest. In contrast, conversion to oil palm dramatically reduces species richness, with significantly fewer primary-forest species than found on logged forest transects for seven taxa. Using a systematic conservation planning analysis, we show that efficient protection of primary-forest species is achieved with land portfolios that include a large proportion of logged-forest plots. Protecting logged forests is thus a cost-effective method of protecting an ecologically and taxonomically diverse range of species, particularly when conservation budgets are limited. Six indicator groups (birds, leaf-litter ants, beetles, aerial hymenopterans, flies, and true bugs) proved to be consistently good predictors of the response of the other taxa to logging and oil palm. Our results confidently establish the high conservation value of logged forests and the low value of oil palm. Cross-taxon congruence in responses to disturbance also suggests that the practice of focusing on key indicator taxa yields important information of general biodiversity in studies of logging and oil palm.

A sequential study of the pathology associated with the infection of sheep with adult and larval Ostertagia circumcincta

Disturbances in the physiology of the abomasa of sheep infected with either adult Ostertagia circumcincta given via abomasal cannulae, or larvae (L3) given intraruminally were matched by pathological changes in tissues collected by repeated mucosal biopsy. Within 2-3 days of the transplant of adult worms, abomasal pH had increased markedly in five out of six animals, and there also had been rapid increases in serum gastrin and pepsinogen concentrations in all animals. Reductions in parietal cell number were recorded as early as 1 day after the transplant of adults and were associated with the rapid accumulation of many neutrophils and eosinophils. Mucosal hyperplasia, with increased numbers of cells closer in appearance to mucous/mucous neck cells, was a relatively late development, being most pronounced in the latter part of the infection. In sheep given larvae, changes in secretory physiology were again matched by a concurrent fall in parietal cell number and by the accumulation of inflammatory cells. Changes became maximal when most worms could be expected to be present as adults, confirming the role of adults in the natural disease. Some abnormalities were detected in biopsies collected from animals maintained free of parasites and, although milder in degree, there were similarities to those observed in parasitised tissues, there being fewer parietal cells, a modest degree of mucous cell hyperplasia and inflammatory infiltrates of predominantly neutrophils. These changes were the likely result of trauma to the tissues in the immediate vicinity of the cannula, due either to the presence of the cannula itself or to the frequent collection of biopsy material from areas close to it.

Effects of adult and larval Haemonchus contortus on abomasal secretion

Abomasal pH and serum pepsinogen and gastrin were increased in parasite-naive sheep by infection with either larval or adult H. contortus. Four sheep received 10000 larvae intraruminally and 9000 adult worms were given directly via an abomasal cannula to another 4 sheep. The latter animals were dosed orally with 0.4 mg kg-1 ivermectin 4 days after worm transfer and their recovery was monitored for a further 8 days. Whereas the presence of adult worms rapidly induced changes in the secretory activity of the abomasum, the early larval stages had minimal effects up to the 4th day post-infection. After either larval or adult infection, the initial hypergastrinaemia began at the same time as the increase in abomasal pH, but serum gastrin continued to increase after abomasal pH had reached a maximum and returned more slowly to normal values after drenching. The increase in serum pepsinogen did not precede those in the other parameters, unlike the earlier hyperpepsinogenaemia which occurs with Ostertagia infection. Three of the 8 infected sheep had no detectable serum pepsinogen increase during the parasitism while showing typical effects on abomasal pH and serum gastrin. The rapidity of the responses to the transfer of adult worms and to their removal by treatment with anthelmintic supports a role for worm excretory/secretory (ES) products which possibly are not produced by the early larval stages. The similarity of responses to H. contortus and O. circumcincta infection suggests the involvement of the same or very similar ES products.

Abomasal secretion in sheep receiving adult Ostertagia circumcincta that are prevented from contact with the mucosa.

AIMS Both adult and larval Ostertagia circumcincta infections raise abomasal pH and serum gastrin and pepsinogen concentrations, either because of physical effects of the worms or from their chemical secretions. The study was designed to examine whether adult worms require contact with the gastric mucosa to effect changes in gastric secretion. METHODS Abomasal pH and serum gastrin and pepsinogen concentrations were measured in four groups of sheep: Group A (n = 4): abomasal contents containing about 18,000 adult O. circumcincta were obtained from donor sheep, concentrated and infused into 5 microm mesh porous bags attached to surgically implanted abomasal cannulae. A second worm transplantation was carried out 1 week later to assess worm survival after 16 hours. Group B (n = 4): about 9000 adult worms, recovered after migration out of abomasal contents set in agar, were placed in small 5 microm mesh bags which were inserted through indwelling abomasal cannulae and left for 3 days. Group C (n = 2): about 3000 adult worms from the population recovered from agar were infused through abomasal cannulae which allowed. free movement in the abomasum. Group D (n = 3) was left uninfected. RESULTS Worms transplanted directly into the abomasum (Group C) caused rapid and marked effects on abomasal secretion. Adult O. circumcincta died within 16 hours of transfer into the abomasum when they were restrained within porous bags. Nevertheless, in sheep receiving 18,000 worms, abomasal pH increased soon after new feed was presented on Days 1, 2 and 4 after worm transfer; serum gastrin was elevated in three sheep from 113 hours and serum pepsinogen increased in one animal. Sheep receiving 9000 worms showed similar trends but the results were equivocal. CONCLUSIONS Adult O. circumcincta prevented from physical contact with the gastric mucosa by restraint in porous bags are able to raise abomasal pH. This study implicates parasite excretory-secretory products in mediating changes in gastric secretion caused by adult abomasal worms.

A trait-based trade-off between growth and mortality: evidence from 15 tropical tree species using size-specific relative growth rates

A life-history trade-off between low mortality in the dark and rapid growth in the light is one of the most widely accepted mechanisms underlying plant ecological strategies in tropical forests. Differences in plant functional traits are thought to underlie these distinct ecological strategies; however, very few studies have shown relationships between functional traits and demographic rates within a functional group. We present 8 years of growth and mortality data from saplings of 15 species of Dipterocarpaceae planted into logged-over forest in Malaysian Borneo, and the relationships between these demographic rates and four key functional traits: wood density, specific leaf area (SLA), seed mass, and leaf C:N ratio. Species-specific differences in growth rates were separated from seedling size effects by fitting nonlinear mixed-effects models, to repeated measurements taken on individuals at multiple time points. Mortality data were analyzed using binary logistic regressions in a mixed-effects models framework. Growth increased and mortality decreased with increasing light availability. Species differed in both their growth and mortality rates, yet there was little evidence for a statistical interaction between species and light for either response. There was a positive relationship between growth rate and the predicted probability of mortality regardless of light environment, suggesting that this relationship may be driven by a general trade-off between traits that maximize growth and traits that minimize mortality, rather than through differential species responses to light. Our results indicate that wood density is an important trait that indicates both the ability of species to grow and resistance to mortality, but no other trait was correlated with either growth or mortality. Therefore, the growth mortality trade-off among species of dipterocarp appears to be general in being independent of species crossovers in performance in different light environments.

The effects of catchment and riparian forest quality on stream environmental conditions across a tropical rainforest and oil palm landscape in Malaysian Borneo

Abstract Freshwaters provide valuable habitat and important ecosystem services but are threatened worldwide by habitat loss and degradation. In Southeast Asia, rainforest streams are particularly threatened by logging and conversion to oil palm, but we lack information on the impacts of this on freshwater environmental conditions, and the relative importance of catchment versus riparian‐scale disturbance. We studied 16 streams in Sabah, Borneo, including old‐growth forest, logged forest, and oil palm sites. We assessed forest quality in riparian zones and across the whole catchment and compared it with stream environmental conditions including water quality, structural complexity, and organic inputs. We found that streams with the highest riparian forest quality were nearly 4 °C cooler, over 20 cm deeper, had over 40% less sand, greater canopy cover, more stored leaf litter, and wider channels than oil palm streams with the lowest riparian forest quality. Other variables were significantly related to catchment‐scale forest quality, with streams in the highest quality forest catchments having 40% more bedrock and 20 times more dead wood, along with higher phosphorus, and lower nitrate‐N levels compared to streams with the lowest catchment‐scale forest quality. Although riparian buffer strips went some way to protecting waterways, they did not maintain fully forest‐like stream conditions. In addition, logged forest streams still showed signs of disturbance 10–15 years after selective logging. Our results suggest that maintenance and restoration of buffer strips can help to protect healthy freshwater ecosystems but logging practices and catchment‐scale forest management also need to be considered.

The value of biodiversity for the functioning of tropical forests: insurance effects during the first decade of the Sabah biodiversity experiment

One of the main environmental threats in the tropics is selective logging, which has degraded large areas of forest. In southeast Asia, enrichment planting with seedlings of the dominant group of dipterocarp tree species aims to accelerate restoration of forest structure and functioning. The role of tree diversity in forest restoration is still unclear, but the ‘insurance hypothesis’ predicts that in temporally and spatially varying environments planting mixtures may stabilize functioning owing to differences in species traits and ecologies. To test for potential insurance effects, we analyse the patterns of seedling mortality and growth in monoculture and mixture plots over the first decade of the Sabah biodiversity experiment. Our results reveal the species differences required for potential insurance effects including a trade-off in which species with denser wood have lower growth rates but higher survival. This trade-off was consistent over time during the first decade, but growth and mortality varied spatially across our 500 ha experiment with species responding to changing conditions in different ways. Overall, average survival rates were extreme in monocultures than mixtures consistent with a potential insurance effect in which monocultures of poorly surviving species risk recruitment failure, whereas monocultures of species with high survival have rates of self-thinning that are potentially wasteful when seedling stocks are limited. Longer-term monitoring as species interactions strengthen will be needed to more comprehensively test to what degree mixtures of species spread risk and use limited seedling stocks more efficiently to increase diversity and restore ecosystem structure and functioning.

Resistance of tropical seedlings to drought is mediated by neighbourhood diversity.

Occasional periods of drought are typical of most tropical forests, but climate change is increasing drought frequency and intensity in many areas across the globe, threatening the structure and function of these ecosystems. The effects of intermittent drought on tropical tree communities remain poorly understood and the potential impacts of intensified drought under future climatic conditions are even less well known. The response of forests to altered precipitation will be determined by the tolerances of different species to reduced water availability and the interactions among plants that alleviate or exacerbate the effects of drought. Here, we report the response of experimental monocultures and mixtures of tropical trees to simulated drought, which reveals a fundamental shift in the nature of interactions among species. Weaker competition for water in diverse communities allowed seedlings to maintain growth under drought while more intense competition among conspecifics inhibited growth under the same conditions. These results show that reduced competition for water among species in mixtures mediates community resistance to drought. The delayed onset of competition for water among species in more diverse neighbourhoods during drought has potential implications for the coexistence of species in tropical forests and the resilience of these systems to climate change.Reduced competition for water among species in mixed tropical plant communities mediates community resistance to drought: weaker competition permits growth maintenance in drought, whereas stronger competition inhibits it.