Forest restoration has the potential to mitigate the impact of deforestation and forest degradation. Various global policies have been sought to put restoration into the mainstream agenda including under the Convention on Biological Diversity (CBD) and the program for Reducing Emissions from Deforestation and forest Degradation (REDD+). The Aichi Target of the CBD set a target for at least 15% of degraded ecosystems to be restored by 2020 for key goals including biodiversity conservation, carbon enhancement and the provision of livelihoods. A theoretical framework to underpin decision-making for landscape-scale restoration has been slow to emerge, resulting in a limited contribution from science towards achieving such policy targets. My thesis develops decision frameworks to guide the restoration of degraded tropical forests to enhance biodiversity and the delivery of ecosystem services. In this thesis, three critical questions on how to make better decisions for landscape-scale restoration are addressed by: (a) considering landscape heterogeneity in terms of degradation condition, restoration action and cost, and temporally-explicit restoration benefits; (b) leveraging restoration within competing land uses using emerging policy for offsetting; and (c) enhancing feasibility by accounting for the social and political dimensions related to restoration.
I use Kalimantan (Indonesian Borneo) as a case study area, as it represents a region that is globally important in terms of biodiversity and carbon storage. Kalimantan’s forests also provide essential livelihoods for local people. Yet, rapid deforestation and forest degradation threaten the forests in this region. Chapter 2 verifies that forest loss and degradation is the most significant threat to biodiversity in Kalimantan, impacting more than 80% of threatened animal species and 60% of threatened plant species. The future of Kalimantan’s wildlife depends on the survival of species in human-modified landscapes including in restored forest.
Quantifying carbon benefit in a policy, such as forest restoration under the REDD+, requires a standardised tool, which has not been available for data-poor regions including Kalimantan. In Chapter 3, I examine a process-based model, called 3-PG (physiological principles for predicting growth), to estimate the above-ground biomass (AGB) content of the major forest types occurring on the island of Borneo. Using readily available climate and soil data, the results indicate the 3-PG model accurately predicts AGB compared with field-measured data, revealing the potential application of this model for carbon sequestration analyses. The datasets along with a set of parameters used in this chapter are employed in the subsequent chapters.
Degraded tropical forests are characterised by a broad spectrum of forest condition states, mainly as a result of varying intensities of logging and fire. In Chapter 4, I develop a new framework to optimally allocate restoration investments to forests of varying condition, with two contrasting objectives: carbon and biodiversity. The work takes into account a diverse suite of restoration techniques and their costs and quantifies time-dependent restoration benefits in terms of carbon sequestration and the improvement of habitat for threatened mammals. I find that the distribution of investments is highly dependent on the restoration objective, which inevitably involves trade-offs between objectives. Nonetheless, for greatest achievement of both objectives, I demonstrate that restoring highly degraded Bornean lowland forest should receive the greatest investment.
Environmental offsetting is an emerging opportunity to leverage restoration over economic activities. Employing a backcasting approach, Chapter 5 presents the first investigation of the potential application of restoration as a policy tool to offset carbon and biodiversity loss from agricultural development at a landscape scale. Using an oil-palm case study in Kalimantan, I find offsetting biodiversity loss from past oil-palm plantation developments requires 8.7% of Kalimantan’s landmass to be restored at a cost of US$7.6 billion. In contrast, compensating carbon emissions would require an area of less than 2% of the region at a cost of US$1.8 billion by restoring degraded peatlands, including the failed Ex-Mega Rice Project in Central Kalimantan. My findings raise questions on the overall capacity of the oil-palm industry, and the agriculture sector more broadly, to fully offset biodiversity loss.
Forest restoration has had variable success, with performance strongly moderated by specific socio-ecological and political contexts within a region. To enhance social feasibility and political permissibility in restoration, Chapter 6 demonstrates the first integration of a socio-ecological systems framework with systematic decision-making to develop a context-specific restoration plan for livelihoods provision. I compare areas that were prioritised for restoration identified solely on the basis of biophysical criteria with those that combine socio-political and biophysical criteria. It emerges that incorporating the socio-political context alters the identification of priority areas for restoration, with only half the priority areas remaining the same with, and without, the socio-political factors. While the social feasibility and political permissibility can be enhanced, accounting for these constraints is likely to incur substantial opportunity costs. My framework reveals significant deficiencies and inefficiencies associated with existing restoration policies for Kalimantan.
My thesis demonstrates that the best decisions for landscape-scale restoration are not simply made as the result of a binary answer: restore or not restore. Using carefully developed frameworks, I have shown how and where restoration should be carried out, with cost-effective implementation and with opportunities for landscape-scale projects. By putting the theoretical analyses undertaken in my thesis into the context of a globally important case study, my research provides evidence for science-based restoration policy that is transparent and transferable to achieve ambitious global policy targets.