Future global biodiversity may be intrinsically linked to the adaptive and resilience capacities of island ecosystems.
Yet, terrestrial biodiversity of islands is often under-represented within climate change impact assessments, being largely overshadowed by a focus on marine diversity, especially coral reefs.
Unconstrained habitat destruction and degradation cannot be sustained and will be to the detriment of both island communities and the local biodiversity upon which these communities depend.
By Dr. Shobha Maharaj, IPCC 6th Assessment Lead Author, Islands
Islands across the world (with the exception of Greenland) cover approximately two to four percent of the Earth’s terrestrial surface, yet, oceanic and some continental-shelf islands (many of which are Small Island Developing States (SIDS) are estimated to harbor more than 20% of existing species (e.g., ~25% extant global flora) (Wetzel, 2013; Kumar and Tehrany, 2017). This is largely due to exceptionally high rates of insular terrestrial endemism — averaging around 9.5 times higher for vascular plants and 8.1 times higher for vertebrates than continents (Bellard, 2014; Wetzel, 2013).
However, up to 80% of historical extinctions (Wetzel, 2013) and almost half of all species currently considered to be at risk of extinction occur on islands; with these primarily due to human-induced factors such as invasive species, overexploitation, and habitat loss (Spatz et al. 2017). Now, with the exacerbating impacts of climate change being added to the mix, current projections suggest that further losses could contribute disproportionally to global biodiversity decline (Pouteau and Birnbaum 2016). Hence, future global biodiversity may be intrinsically linked to the adaptive and resilience capacities of island ecosystems.
Yet, terrestrial biodiversity of islands is often under-represented within climate change impact assessments, being largely overshadowed by a focus on marine diversity, especially coral reefs. This is a brief overview of the terrestrial island biodiversity conundrum.
Insular biodiversity is more vulnerable and faces more severe threats from changing climate conditions than continental regions. Island ecosystems tend to be structurally simple, which makes them fragile to both stochastic and deterministic threats. Characterized by high levels of endemism but with both low species diversity and functional redundancy, many of these ecosystems typically contain species with inherently high sensitivity to rapid environmental change such as: characteristic narrow habitat ranges, small population sizes, low genetic diversity and poor adaptive, dispersal and defensive capabilities (Harter et al 2015). These factors are compounded by limited resources within already very small, restricted, often fragmented, and degraded terrain — together with deteriorating conditions and habitat loss stemming from synergies between climate change and both natural and human-induced disturbances. Insular species therefore have limited opportunities for autonomous adaptation and are much less likely to shift their ranges to the relevant latitudinal, longitudinal, and/or altitudinal extents required for continued population size and genetic variability. When combined with even small losses of habitat from climatic change drivers such as extreme events, sea level rise (SLR), and in particular, increased competition from invasive alien species (IAS), this amplifies vulnerability to extirpations – which can translate to extinctions (and reduced global biodiversity) in the case of endemics located on one or a few nearby islands (Manes et al 2021 and Costello et al 2022).
Climate-smart conservation on islands, however, remains hindered due to data paucity issues. Foremost among these is the chronic unavailability of up-to-date, adequately downscaled data from the most recent suite of global climate models (GCMs) (RCPs and especially SSPs). The grid spacing of GCMs generally span hundreds of kilometers (Maharaj and New 2013, Pouteau and Birnbaum 2016) and hence without adequate downscaling, these data are unable to simulate future microclimate variation across the often complex topography of many SIDS — which contain high habitat heterogeneity and climate refugia. As such, there is a continued inability to robustly model and comprehensively assess the increasingly dynamic impacts of changing climate, including synergistic interactions with continued habitat loss, degradation, SLR, IAS and extreme events. Without such models, the development of robust conservation and adaptation strategies remain out of reach for local conservation planners and managers, and this in turn, negatively and directly impacts upon the resilience potential of SIDS’ ecosystems . For example, without future projections indicating which regions are less likely to support biodiversity under changing climate conditions, conservation planners are unable to adjust their management (and even allocation of new) of protected areas.
One of the key reasons given for the unavailability of such adequately downscaled GCM data is the lack of historical observation data, particularly for precipitation. However, based on this author’s experience, at least within the Caribbean SIDS, it is not that these historical data do not exist, but more so, that these have not been collected, collated, and made available to the global modelling communities that generate GCMs. For example, on the island of Trinidad in the southern Caribbean, the local water resources agency (WASA) has a vast collection of location points across the island that have, for many decades, been collecting precipitation data. Yet these data are difficult to access and can only be done so with extensive amounts of red tape involved. Likewise, other local and regional institutions that do have collations of precipitation and temperature data, both government and private, often flatly refuse to share these data with researchers or require arduous amounts of documentation and time, with no guarantee of receipt at the end.
This territoriality over data and ‘turf protection’ perpetuate a vicious cycle. Continued paucity of adequately downscaled GCM data is, in large part, due to an ongoing non-collation (and hence unavailability) of historical observation data from local agencies — together with a persistent disconnect and non-cooperation among government agencies, academic institutions, and others with such data. This continues to be a major driver of SIDS being underrepresented within global reports such as those developed by the Intergovernmental Panel on Climate Change (IPCC) and similar — where material within such reports rely on published, often peer-reviewed work related to climate change. With adequately downscaled GCM data lacking, robust studies, and hence publications, on future impacts of climate change on SIDS remain sparse at best. This resulting inadequate representation of islands within these global reports, in turn, leads to the provision of little support to SIDS governments by way of much needed evidence for international funding to address adaptation needs and similar. For example, the recently released Summary for Policy Makers of the IPCC’s AR6, Working Group II clearly states in Figure 3 (f) that the development of risk diagrams (burning embers) for Small Islands was not possible due to “the paucity of adequately downscaled climate projections, with uncertainty in the direction of change, the diversity of climatologies and socioeconomic contexts … resulting in few numbers of impact and risk projections from different warming levels.” (IPCC, 2022)
Additionally, on many islands, there is a pervading lack of baseline data on species’ distributions, ecology, and endemic status, especially those with restricted ranges and locations (Kumar and Taylor 2015). This paucity stems, in many cases from a lack of local capacity and resources for funding the intensive surveys required to identify and map species distribution and overall biogeography. As such, very little has been published on the biogeography and physiology of insular species in relation to projected climatic changes. Additionally, many islands have incomplete and/or outdated national species lists and hence, incomplete current International Union for Conservation of Nature (IUCN) Red Lists — which is reflected within the respective National Biodiversity Strategic Action Plans of these nations (e.g. Russel et al 2017, Kumar and Taylor 2015). Without these data, informed assessment, planning, prioritization, and adaptation strategies cannot be effectively devised. This continues to delay the development of effective policy towards not only biodiversity conservation strategies but for other important cross-sectoral issues within these resource-limited, highly vulnerable nations.
The limited terrain of islands in today’s globalized, warming world implies that large proportions of insular biodiversity will often require conservation across mosaics of human-impacted, heavily degraded, and fragmented landscapes. Traditional conservation measures such as protection, restoration, and increasing permeability for species across landscape matrices via expanded/shifted protected areas, dispersal corridors and buffer zones, in isolation, may be of limited effectiveness within island settings (Vogiatzakis et al 2016). The above mentioned disconnect amongst government and other agencies also contributes to conservation management occurring within silos on many islands, at least at the coarse scale, with terrestrial and marine/coastal conservation efforts often occurring independently of each other. The tight interconnectivity of insular ecosystems with each other implies that a switch to more holistic, whole-of-island conservation strategies may be likely to increase the adaptation and resilience potentials of SIDS (Streubig et al 2015B; Ferreira et al 2019). Climate-smart Ecosystem-Based or Nature-Based adaptation strategies such as ridge-to-reef conservation, which integrate conservation inside, outside, and between protected areas across terrestrial, freshwater, and coastal/marine ecosystems are much needed — as these can help to increase the interconnectivity of natural and semi-natural habitats and reduce land use impacts (Costello et al 2022).
As seen with the dialogue developing around the ongoing Covid-19 pandemic, wiser, more sustainable use of natural resources presents an opportunity towards a transformational future. Islands represent a wide range of development and governance status, from dependents of continental states to semi- and non-autonomous islands, as well as having unique socio-political power relations and inter-island connections, that all influence their potentials to adapt to climate change (Petzold and Magnan 2019). The key insular commonality of limited resources implies that unconstrained habitat destruction and degradation cannot be sustained and will be to the detriment of both island communities and the local biodiversity upon which these communities depend. As climate continues to change, there is increasing urgency to re-think how progress can be measured, and develop opportunities to build on synergies with disaster risk reduction, social justice and food/water security – to maximize benefits from their natural resources in a sustained manner. A green post-Covid recovery offers hope for adaptation that focuses on investing in island-based human capital, with nature-based solutions as a way forward that harnesses the resiliency of both humans and ecosystems. This however cannot be adequately achieved unless data paucity issues are quickly addressed, keeping in mind that the world has just a brief window (~a decade) to get on track if global warming is to be limited to 1.5°C (IPCC, 2022).
This article was written for Perry World House’s 2022 Global Shifts Colloquium, ‘Islands on the Climate Front Line: Risk and Resilience,’ and made possible in part by a grant from the Carnegie Corporation of New York. The views expressed are solely the author’s and do not reflect those of Perry World House, the University of Pennsylvania, or the Carnegie Corporation of New York.
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