Environmental stratification to model climate change impacts on biodiversity and rubber production in Xishuangbanna, Yunnan, China

Highlights

• Xishuangbanna Prefecture, Yunnan, in southwest China, is renowned for rich biodiversity, both natural and within traditional agroecosystems.

• From 2002 to 2012 the area under rubber plantations has increased from 8% to 22%.

• Rubber currently occupies most of the area where climatic conditions are conducive to rubber production.

• Rubber production is limited by colder climatic conditions at higher elevations.

• By 2050, 75% of Xishuangbanna will become conducive to rubber production.

Abstract

An analysis and multi-model approach, based on a statistically derived Global Environmental Stratification (GEnS) and using a downscaled ensemble (n = 63) of CIMP5 Earth System Models applied across four representative concentration pathways (RCP), has been used to project the impact of climate change on spatial distribution of bioclimatic zones and ecosystems within the biodiverse rich Xishuangbanna Prefecture, Yunnan Province, by the year 2050. Four bioclimatic zones and 9 strata were identified, overlaid with protected areas, and associated with on-going landuse change, i.e. a rapid increase in rubber plantation from 8% to 22% of total area between 2002 and 2010. Significant changes in the areal extent and distribution of all zones and strata are projected, with an averaged mean annual temperature increase ranging from 1.6 °C to 2.4 °C. By 2050, there are significant geographical shifts in all identified strata, with an average upward shift of 309 m of elevation for all strata. On average, more than 75% of Xishuangbanna is predicted to shift to a different zone, with 96% shifting to a different stratum. The area conducive to rubber plantations, currently limited by climatic conditions, expands to nearly 75% of the total area. Climatic change potentially removes the bioclimatic barriers to further expansion of rubber plantations within the area and increases pressure on remaining biodiversity both within and outside of protected areas. The analysis provides the basis for understanding potential impacts of changing bioclimatic conditions on managed and unmanaged ecosystems and landuse change trends, within the context of ongoing rapid change and agricultural expansion in the area. Current efforts to conserve forests, biodiversity and traditional landuse systems require an improved understanding of both the projected climatic changes and the responses of biodiversity and traditional agricultural systems to changing conditions.

Introduction

Improved understanding of the impact of climate change on landuse change processes in Xishuangbanna, Yunnan, China is required for effective conservation planning within the context of a rapidly changing environment. Habitat loss through landuse and landcover change is a major driving factor accelerating biodiversity loss across the globe, as it is within Xishuangbanna (Xu et al., 2012), an area recognized as China’s “Treasure House” of biological diversity, and one of the richest in number of flowering species in the world. At the same time, it is generally agreed that climate change will have major impacts on ecosystems throughout this mountainous region (Xu et al., 2009, Xu et al., 2012). Although more than 12% of Xishuangbanna’s land area is designated as various types of protected areas (Guo et al., 2002), the impacts of climate change could undermine current and future conservation efforts if changing conditions, such as shifts in species ranges (Körner, 2007, La Sorte and Jetz, 2010, La Sorte and Jetz, 2012) are not considered in planning and implementation of conservation policies and initiatives. Likewise, understanding the impact climate might have on agricultural suitability and landcover change, particularly the expansion of agricultural land area, is required if sustainable development and climate adaptation policies are to be effectively “biodiversity friendly” upon implementation.

Integration and coordination of environmental and biodiversity data, in conjunction with an understanding of landuse change trends, have been highlighted as being essential to respond to the major challenges of climate change and biodiversity decline (Beier and Brost, 2010). The Global Environmental Stratification (GEnS) (Metzger et al., 2013) is a globally consistent classification of land into relatively homogenous units, based upon a statistical clustering of climate variables (Metzger et al., 2013). It was developed in support of the Global Earth Observation – Biodiversity Observation Network (GEO-BoN) (GEOBON, 2010, Scholes et al., 2008, Scholes et al., 2012) to provide a framework for comparison and analysis of ecological and environmental data across large heterogeneous areas, and to facilitate the integration of global biodiversity data collection and monitoring efforts. In this paper, a geospatial modeling approach (Zomer et al., 2013) based upon the GEnS is used to analyze projected climate changes and their impact on bioclimatic conditions within Xishuangbanna by the year 2050. The geographic shift of bioclimatic strata as a result of changed climatic conditions can be used as a surrogate measure for inferring potential impacts on the spatial distribution of biomes, ecoregions, ecosystems, vegetation communities or wildlife habitat. An analysis of remote sensing data from 2002 to 2010 is used to assess the direction and magnitude of the landuse and landcover changes in Xishuangbanna. The potential impact of projected climate change on landuse, particularly expansion of rubber plantation area, as well as on efforts to conserve forests, biodiversity, and traditional landuse systems, is examined and compared with current and historic landuse change. The analysis provides a geospatially articulated basis for discerning potential impacts of medium-term climate change (i.e. by 2050) on terrestrial ecosystems, rubber production, and biodiversity conservation efforts in Xishuangbanna.

Xishuangbanna Prefecture is located on the southern margins of China’s Yunnan Province, bordering Laos and Myanmar (Fig. 1a). Xishuangbanna lies in a transition zone from sub-tropical to tropical climates, and like the whole of Yunnan, it is within the transition zone from the Eastern Himalaya flora and fauna to the biota of mainland Southeast Asia. The region is dominated by mountains, with an elevation range from 542 to 2415 m asl (Fig. 1b), has a generally warm and moist climate, and harbors exceptionally high levels of biodiversity. There are over 5000 flowering plant and fern species, accounting for approx. 35% of all of Yunnan’s higher plants, including 153 endemic species and 56 rare and endangered species (Zhang and Cao, 1995). The region contains China’s largest area of diverse types of mature tropical forest, which mainly lie within the Xishuangbanna Biosphere Reserve. This reserve features eight vegetation types and twelve sub-types, including tropical rain forest, tropical monsoon forest, and sub-tropical monsoon evergreen broadleaf forest. It is home to the northernmost tropical rainforest in the world. Various measures have been adopted by the government to preserve biodiversity in the area, e.g. the expansion of formally protected areas. Nevertheless, forest area has been decreasing and forest patches have become increasingly fragmented, with the populations of many species reduced (Zhang and Cao, 1995, Pu et al., 2007, Li et al., 2008). There have been dramatic changes in landuse and landcover since the 1950s, with many forests in this area heavily impacted and converted to rubber plantations and other cash crops (Xu et al., 2012).

In conjunction with these landuse changes, Xishuangbanna, being one of the poorest regions in China, is also experiencing a rapid socioeconomic transformation. However, much of the population is still living in relatively poor conditions. Deforestation, fragmentation of forests, and landuse changes, particularly the expansion of agricultural and industrial crops such as rubber, occurring over the last sixty years, led to severe negative impacts on biodiversity and ecosystem services throughout Yunnan, including Xishuangbanna (Chapman, 1991, Fox and Vogler, 2005, Li and Fox, 2012). Rubber (Hevea brasiliensis) is the main crop replacing traditional agriculture and forest vegetation in Xishuangbanna (Fox and Vogler, 2005, Xu et al., 2005, Li et al., 2006), and is among the major drivers of deforestation and biodiversity loss throughout Southeast Asia (Li et al., 2006, Hu et al., 2007). The impacts of this landuse change, beyond decreasing biodiversity (Li et al., 2006, Hu et al., 2007), include deterioration of watershed services (Guardiola-Claramonte et al., 2008), and a decline in livelihood options (Xu et al., 2005). Rubber production in Xishuangbanna has increased dramatically in the last decades, and is continuing to increase, heavily impacting natural ecosystems (Li et al., 2008). Climate change has the potential to substantially exacerbate the impacts of these processes, undermining current landuse planning and conservation efforts (Dale, 1997, Hannah, 2010). The average temperature over Yunnan Province has been increasing since the late 1980s and it has become markedly warmer since the 1990s (Cheng and Xie, 2008). The trend of temperature increase in Yunnan is parallel to the trends for the global, northern hemisphere, and China as a whole, with temperatures in Yunnan changing slightly more than the global average and a little less than the averages for the northern hemisphere and China (Lin et al., 2007). As a result of this warming trend, the elevational distribution of bioclimatic zones in this mountainous region is likely to shift markedly (Xu et al., 2009).

Traditionally managed agro-ecosystems, supporting high levels of biodiversity, are found throughout Xishuangbanna, primarily swidden-fallow systems, but also agroforestry systems such as the Dai home gardens, traditional firewood management systems based on Cassia siamea, sacred forests, and forest-based tea production (Yu et al., 1985, Guo, 1993, Long, 1993, Cui et al., 2000, Zeng et al., 2001). The area is considered a center of diversity for rice, with over 400 varieties of upland rice found (Dai, 1998). The areal extent of traditional swidden-fallow systems decreased considerably over the past decades due to changes in economic policies, demographic processes, and conservation actions (Ye and Dai, 2000). In recent years, there has been a very large increase in the land devoted to rubber production (Guo et al., 2002, Xu et al., 2012). Rubber planting began in the late 1950s, and by 2010 rubber plantations occupied over 424,000 ha in Xishuangbanna (Xu et al., 2012). Before the 1980s, rubber was grown almost exclusively on state farms. Under new economic and land polices beginning in 1980s local smallholder farmers started to cultivate rubber. While in 1965 only 42 ha were managed as smallholder plantations (0.5% of total rubber plantation area), by 1998 this area had already increased to over 41,000 ha (45% of total rubber plantation). Much of these plantations were established on lands designated as collective forest or swidden-fallow successional forest. In turn, these subsistence activities have been displaced to higher elevations less suitable for growing rubber. Recently, the transition to a market–driven economy has encouraged a transition from swidden-fallow, upland rice, and other subsistence crops to industrial and market oriented crops such as tea, and in particular, rubber.