Predicting geographic distribution and habitat suitability due to climate change of selected threatened forest tree species in the Philippines
Introduction
The Philippines has very rich biodiversity in terms of number and percentage. It is regarded as one of 17 mega biodiversity countries accruing to its geographical isolation, diverse habitats and high rates of endemism (ASEAN Centre for Biodiversity, 2010, Protected Areas and Wildlife Bureau, 2009). It ranks 5th globally in terms of the number of plant species and maintains 5% of the world's flora. However, due to anthropogenic activities as well as natural disturbances, it continues to lose its rich biodiversity resources (Conservation International [CI], 2012). The presence of large number of endangered and threatened species brings down the country into one of the global biodiversity hotspots in the world, thus making it one of the top global conservation priority areas (ASEAN Centre for Biodiversity, 2010, International Union for Conservation of Nature, 2003, Myers et al., 2000). The official country listing of threatened plant species, Department of Environmental and Natural Resources Administrative Order Number [DAO] 2007-01 (2007), lists 176 vulnerable species, 99 critically endangered species, 187 endangered species and 64 other threatened plant species in the Philippines.
In addition to anthropogenic habitat alteration, climate change has been identified as well as one of the major threats facing biodiversity worldwide (ASEAN Centre for Biodiversity, 2010, Convention on Biological Diversity, 2010, Intergovernmental Panel on Climate Change, 2007, Millennium Ecosystem Assessment, 2005). It has been estimated that 20–30% of plant and animal species, globally, will be at higher risk of extinction due to global warming and that a significant proportion of endemic species may become extinct by 2050 or 2100 as a consequence as global mean temperatures exceed 2–3 °C above pre-industrial levels (Fischlin et al., 2007, Vié et al., 2008). As evidenced by the increasing mean temperature observed over time, climate change is said to be also occurring in the country (Philippines Atmospheric, Geophysical, and Astronomical Services Administration [PAGASA], 2011). Hence, there is a greater risk of extinction for species that are already vulnerable, particularly those with strict habitat requirements and restricted ranges (CBD, 2010).
An aspect that scientists and researchers look into to evaluate the potential impacts of climate change on natural systems is in the understanding of the likely shift in geographic distributions and habitat suitability of species due to future climate (Martinez-Meyer, 2005). In recent years, multiple modelling programs have been developed to predict the impacts of climate change on species distribution, even for areas that suffer from incomplete and biased samplings, or for areas where no collections have been made (Araujo and Guisan, 2006, Elith et al., 2006, Trisurat et al., 2011). Species-distribution models (SDMs) are based on the assumption that the relationship between a given pattern of interest (e.g. species abundance or presence/absence) and a set of factors assumed to control it can be quantified (Anderson et al., 2003, Anderson and Martinez-Meyer, 2004, Guisan and Zimmermann, 2000, Raxworthy et al., 2003). Maxent, one popular SDM based on presence-only modelling method involves maximum entropy modelling and has been used successfully to predict the distributions of different floral and faunal species (Baldwin, 2009, Trisurat et al., 2011, Weber, 2011). According to the study of Trisurat et al. (2011), from 26.6 °C 2008 to 28.7 °C in 2100 nine forest plant species have suitable distribution ranges in more than 15% of the region, 20 species have suitable ecological niches in less than 10% while the ecological niches of many Dipterocarpus species cover less than 1% of the region. Additionally, Maxent has been found to be robust to changes in sample size, and still have good predictive ability at low sample sizes, making it the ideal model for the prediction of distributions for rare species (Hernandez et al., 2006, Wisz et al., 2008).
Threats to vulnerable forest tree species and their habitat in the Philippines caused by anthropogenic activities and climate change could be exacerbated as well by modest research and conservation interest. Since 1997, only two studies on potential impacts of climate change on forests ecosystems in the Philippines have been conducted: Cruz (1997) and Lasco et al. (2008). Cruz (1997) hypothesized that tropical forest areas will likely expand as temperature and precipitation increase in many parts of the country. Temperature change may lead to a loss of a few species of plants and animals that may significantly erode the biodiversity of these forests. The study of Lasco et al. (2008) employed the Holdridge Life Zone system. Using GIS, they simulated how the forest types will change under increasing rainfall and temperature. The results demonstrated that dry forests are the most vulnerable terrestrial ecosystems in the Philippines which will disappear even with just 25% increase in rainfall. However, with regards to potential impacts of climate change on specific forest tree species, no research has been done yet in the country. In fact, a research gap identified by the Philippine Council for Agriculture, Forestry, and Natural Resources Research and Development (PCARRD) in 2010 that cross-cuts forest ecosystem, climate change and biodiversity is that future studies need to look at how climate change and the accompanying change in forest types will affect the biodiversity at the species level with special emphasis on rare, threatened, and endangered species.
With the research gap in mind, the main objective of this study was to assess the geographic distribution and habitat suitability due to climate change of selected threatened forest tree species in the Philippines. It is hoped that the results will be useful in developing science-based conservation strategies that could enhance the resilience of those threatened forest tree species and their natural ecosystems to current and future climate. This could provide options for the conservation of such species in areas that are continuously pressured by human activities and potentially by climate change. Information and maps describing habitat suitability and species distributions in such areas are essential for habitat conservation and species management.
Section snippets
Study area
The Philippines is located between 116° 40′, and 126° 34′ E. longitude and 4° 40′ and 21° 10′ N. latitude. It is bordered by the Philippine Sea to the east, the South China Sea to the west, and the Celebes Sea to the south. Relative to other countries in Southeast Asia, Philippines is located in east of Vietnam and north of Indonesia and Malaysia (Fig. 1). The Philippines has 7107 islands covering a total of 30 million ha. Owing to its archipelagic nature, topographic variations characterize
Variables with higher contribution to the geographical distribution of the 14 threatened forest tree species
Based on the results, the distributions of the threatened forest tree species are largely determined by biophysical variables (80%) more than bioclimatic variables (20%). Among the bioclimatic variables, Bio 2 (mean diurnal temperature range) has the highest average percent contribution (5.2%) in most of the 14 threatened forest tree species followed by Bio 6 (minimum temperature of coldest month) with average contribution of 4.6% (Fig. 3). This means that these two bioclimatic variables
Conclusions and recommendations
This study aimed to evaluate the consequences of climate change on geographical distributions and habitat suitability of selected 14 threatened forest tree species in the Philippines. Based on the principle of maximum entropy, it utilized a machine algorithm called Maxent to estimate a target probability distribution of the selected species. Three research questions were formulated as the framework of this study namely: 1) which variable has the highest contribution in the geographical
Acknowledgements
This research is part of the project Mainstreaming Climate Change in Biodiversity Planning and Management implemented by World Agroforestry Centre-Philippines and funded by the United States Agency for International Development.
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