Land-sparing agriculture sustains higher levels of avian functional diversity than land sharing

The ecological impacts of meeting rising demands for food production can potentially be mitigated by two competing land-use strategies: off-setting natural habitats through intensification of existing farmland (land sparing), or elevating biodiversity within the agricultural matrix via the integration of 'wildlife-friendly' habitat features (land sharing). However, a key unanswered question is whether sparing or sharing farming would best conserve functional diversity, which can promote ecosystem stability and resilience to future land-use change. Focusing on bird communities in tropical cloud forests of the Colombian Andes, we test the performance of each strategy in conserving functional diversity. We show that multiple components of avian functional diversity in farmland are positively related to the proximity and extent of natural forest. Using landscape and community simulations, we also show that land-sparing agriculture conserves greater functional diversity and predicts higher abundance of species supplying key ecological functions than land sharing, with sharing becoming progressively inferior with increasing isolation from remnant forest. These results suggest low-intensity agriculture is likely to conserve little functional diversity unless large blocks of adjacent natural habitat are protected, consistent with land sparing. To ensure the retention of functionally diverse ecosystems, we urgently need to implement mechanisms for increasing farmland productivity whilst protecting spared land

Optimizing carbon storage and biodiversity protection in tropical agricultural landscapes

With the rapidly expanding ecological footprint of agriculture, the design of farmed landscapes will play an increasingly important role for both carbon storage and biodiversity protection. Carbon and biodiversity can be enhanced by integrating natural habitats into agricultural lands, but a key question is whether benefits are maximized by including many small features throughout the landscape ('land-sharing' agriculture) or a few large contiguous blocks alongside intensive farmland ('land-sparing' agriculture). In this study, we are the first to integrate carbon storage alongside multi-taxa biodiversity assessments to compare land-sparing and land-sharing frameworks. We do so by sampling carbon stocks and biodiversity (birds and dung beetles) in landscapes containing agriculture and forest within the Colombian Chocó-Andes, a zone of high global conservation priority. We show that woodland fragments embedded within a matrix of cattle pasture hold less carbon per unit area than contiguous primary or advanced secondary forests (>15 years). Farmland sites also support less diverse bird and dung beetle communities than contiguous forests, even when farmland retains high levels of woodland habitat cover. Landscape simulations based on these data suggest that land-sparing strategies would be more beneficial for both carbon storage and biodiversity than land-sharing strategies across a range of production levels. Biodiversity benefits of land-sparing are predicted to be similar whether spared lands protect primary or advanced secondary forests, owing to the close similarity of bird and dung beetle communities between the two forest classes. Land-sparing schemes that encourage the protection and regeneration of natural forest blocks thus provide a synergy between carbon and biodiversity conservation, and represent a promising strategy for reducing the negative impacts of agriculture on tropical ecosystems. However, further studies examining a wider range of ecosystem services will be necessary to fully understand the links between land-allocation strategies and long-term ecosystem service provision

Biodiversity-ecosystem service relationships in degraded and recovering ecosystems.

Biodiversity loss is occurring at an unprecedented rate and most of this loss is due to human induced pressure. This loss in biodiversity had led to concerns that the provision of ecosystem services that humans depend upon might be negatively affected. As such much modern conservation science focusses on preserving biodiversity whilst protecting priority ecosystem services. However, there may be spatial and temporal trade-offs between these services and the biodiversity that is considered important. Characterisation of such the relationships between biodiversity and ecosystem services is vital in order to improve management and policies which aim to protect and restore both biodiversity and ecosystem services. The broad aims of the thesis were to explore biodiversity-ecosystem service relationships in (1) ecosystems invaded by non-native plant species and (2) tropical forests affected by human exploitation and disturbance. Specifically this thesis aimed to answer the questions: 1. What effect do non-native plant invasions have on aboveground carbon storage, belowground carbon storage, carbon sequestration, water quality and water provision? 2. How do changes in species richness affect this ecosystem service provision? 3. How do these changes relate to the woodiness and traits of invasive and native dominant species, and the type of ecosystem invaded? 4. What factors drive differences in residual stand damage, biomass loss and species richness change following selective logging? 5. After deforestation how long do carbon stocks and plant biodiversity take to recover in tropical forests? 6. Do carbon and plant biodiversity differ in their recovery rates? 7. Which areas are priorities for restoration of tropical carbon? All chapters in this thesis make use of large datasets that I collated from the literature and other authors in order to draw broad conclusions about trade-offs and relationships between services and biodiversity In the section concentrating on invasive species my results suggest that non-native invasive plants generally increase the storage of carbon, whilst reducing water quality and availability. This may indicate a fundamental trade-off between services where increased biomass of plants results in higher evapotranspiration and thus water loss, while also enhancing the carbon cycle and nitrogen production of microorganisms. In addition my results suggest that aboveground carbon storage increases as species richness is reduced, showing the opposite relationship to that shown in many biodiversity ecosystem functioning experiments. This is the first time any such relationship has been found between community change and ecosystem level impacts in the context of species invasions. However, it seems likely that this relationship depends on the identity and traits of the species, with invasions in open habitats by woody species likely to drive a negative relationship between richness change and biomass change with the opposite true when grassy species invade woodlands. This result presents a trade-off between conservation priorities that managers will need to consider. In Chapter 3 I investigated the possibility of predicting the impact of non-native invasive plant impacts on ecosystem services by using characteristics and functional traits of both invasive and native species. This work suggested that aboveground carbon storage is most easily predicted by traits and characteristics of native and non-native species, with few other ecosystem services well explained by models. Results suggested that transition from woody to non-woody dominant species resulted in most dramatic changes in aboveground carbon storage. However, interestingly aboveground carbon storage also tended to increase where native species were replaced by species of similar woodiness. Similarly, given that woodiness and size of species are related, there was a positive relationship between the invasive species height and increases in aboveground carbon storage. However, all other ecosystem services were poorly predicted by species traits and characteristics. This work suggests that the most dramatic changes in carbon storage may result from shifts in ecosystems that resemble regime shifts. Future work addressing invasive species from this perspective is warranted as many invasions resemble such shifts. In Chapter 4 I investigated the relationships between logging intensity and methods and residual stem damage, biomass loss and species richness change in tropical logged forests. Many syntheses of the logging literature have made little distinction between logged sites, and only one has explored any of the mechanisms that may drive heterogeneity in logging impacts. This is particularly surprising given that Reduced Impact Logging (RIL) has been implemented relatively widely principally to reduce carbon loss from logged forests. My results from this chapter suggest that the principal driver of logging impacts is the intensity at which logging is carried out, showing broadly negative relationships with biomass and tree species richness change and a positive relationship with residual stem damage. Interestingly, RIL appeared to reduce residual stem damage slightly but evidence for this effect was weaker in other analyses. These analyses also suggest a slight increase in tree species richness at low logging intensities, showing some similarities to intermediate disturbance hypothesis type relationships. This is suggestive of a complex relationship between tree species richness and biomass changes during logging that deviated substantially from that suggested in grassland biodiversity-ecosystem function experiments. This is as far as I know the first time this relationship has been suggested in the context of logged forests. The result from this chapter also suggest that there is weak support that RIL reduces logging damage at low intensities but little evidence that this is reflected by changes in biomass. Further studies are needed to discern the effect of RIL over a wide range of logging intensities. Chapter 5 investigates tropical forest recovery following agricultural clearance. In this chapter I aimed to identify the recovery times of different above and belowground carbon pools and tree and epiphyte species richness as well as tree species composition using studies that had paired mature forest sites as comparators. Surprisingly this chapter represents the first attempt to generalise about this recovery rate. The results suggest that following clearance carbon and species richness of plants recovers relatively quickly (<100 years), but species indicative of old forests are rarely present in recovering forests and show few signs of recovery. Thus, while carbon recovery goals may be achievable full recovery of plant biodiversity may require centuries. This slow recovery may be aided by active restoration. Finally in Chapter 6 I investigated which areas should be considered as priorities when restoring tropical forests for carbon storage and bird biodiversity. In this chapter I found evidence of spatial trade-offs between carbon storage and bird species recovery. Empirical models suggested that carbon is accumulated most rapidly in forests with long growing seasons, while probability of bird species presence was primarily driven by habitat specificity, range size and forest cover. Model projections suggested that areas that should be considered a priority for restoration targeting carbon storage are found in the wet tropics while priorities for restoration of bird biodiversity are found in mountainous areas. These analyses indicated that there was no relationship between the two goals, but that by using model projections it was possible to identify areas that maximised both. In summary work in this thesis provides the best synthesis of the relationships between biodiversity and ecosystem services in the context of non-native invasive plants, and selective logging and recovery from tropical forest clearance to date. This is of particular value because such relationships have rarely been explored in these contexts despite widespread and of global importance for conservation

Rubber plantations in the Indo-Burma biodiversity hotspot: habitat loss, biodiversity and economics

Natural rubber is in high demand for the manufacture of tyres, and rubber plantations are expanding globally. Southeast Asia is the epicentre of rubber cultivation, where deforestation to make way for rubber has been occurring for decades. This process has caused substantial biodiversity loss and carbon emissions. Expansion has recently shifted northwards into mainland Southeast Asia (the Indo-Burma biodiversity hotspot) due to the development of hardier rubber varieties that can survive longer dry seasons and cooler climates. The northward shift has been exacerbated by replacement of rubber with oil palm further south. Profitability and extent of rubber are comparable to oil palm, but rubber has received far less attention and scrutiny from civil society. Future demand for natural rubber is predicted to require 4.3 – 8.5 million ha of additional plantation area by 2024, relative to a 2010 baseline. Profits accruing from logging and conversion of forest to rubber in Cambodia are shown to be very high. The carbon prices that would be needed for a REDD+ program in Indo- Burma to match costs of forest conservation where rubber is a threat, are $30 – 51 tCO2-1. These prices are far higher than those currently paid on carbon markets or through carbon funds, highlighting the importance of supply-chain initiatives, environmental governance and full valuation of ecosystem services for defending forests from conversion to rubber. Agroforestry methods for cultivating rubber in Thailand were found to produce yields comparable to monocultural methods, while providing modest benefits for bird and butterfly diversity. Agroforests did not support any species of conservation concern, and contiguous forests are irreplaceable for the conservation of forest biodiversity. Functional diversity of birds was found not to differ between rubber agroforests and monocultures, and species that feed primarily on nectar and fruit were extremely scarce in both types of rubber plantation

Ecosystem services and disservices in small-scale tropical agriculture

Small-scale farmlands are dynamic systems crucial to the food-security and livelihoods of more than two billion people and there is political pressure in many developing nations to consolidate and expand small farms into larger units of management. This could have consequences for agro-ecosystem processes and the ecosystem services and disservices that regulate crop production. This thesis aims to highlight and address these issues in smallholder farming landscapes, which are poorly studied and represent significant knowledge gaps. Research on pollination and biological control is biased towards large-scale systems, and biological control research shows a strong geographic bias to temperate developed nations, whilst pollination research is geographically more balanced. To have more impact on global issues of poverty and food-security, agricultural ecosystem service research needs to have a greater focus on small-scale farmed landscapes. In a low-input, small-scale farmed area of Kenya, the response to land-use intensification of insect groups important to ecosystem services and disservices for crop production was examined. Small ecotone pollinators responded negatively to intensification, but larger bees did not. Natural enemies did not show a strong negative response to land-use intensification, which suggested that low pesticide application rates allowed cultural species to persist in croplands. The functional richness of Hymenoptera and Coleoptera was highest in the most intensified land-use context, which provides support for the intermediate landscape complexity hypothesis. Functional evenness and trait-environment associations showed that phytophagous traits increased with land-use intensification and could be linked to increased ecosystem disservice if crops are consumed. Smallholder interviews showed that ecosystem disservices due to crop-raiding animals were a major problem and that attitudes to wildlife, elephants and protected areas became more negative with increasing proximity to large areas of wilderness. However, increasing the proportion of natural habitat in the vicinity of smallholdings moderated the negative effect of proximity to wilderness on attitudes towards protected areas. Thus, perceived ecosystem disservices may vary with land-sparing at different spatial scales (i.e., conserved habitat). Whilst this thesis demonstrates that land-use intensification of early stage small-scale farming landscapes affects human perceptions and attitudes towards nature and the taxonomic and functional composition of cropland insect communities, direct quantification of the crop yield and economic consequences of this is sorely needed. Assessment of actual vs. perceived ecosystem disservices would also aid the conservation measures needed to make land-sparing work