The Current and Future Status of Floristic Provinces in Thailand

1. Introduction

Species are generally not randomly distributed. Plants and animals originate via evolution and this always happens in a geographically restricted area. Thus, it is not surprising that man has searched for patterns in these distributions, that is in the areas in which species are found. One means of finding these patterns is to examine if certain areas can be characterized by species which are in combination typical for the area. The resulting regions are called, in the case of plants, floristic or phytogeographical regions. Usually, a country/continent is completely subdivided into these areas and these are mutually exclusive.

Thailand has a species rich and complex biodiversity that differs in various parts of the country (MacKinnon, 1997; Wikramanayake et al., 2002; Maxwell, 2004). Thailand harbours one of the 25 global hotspots of biodiversity (Myers et al., 2000) known as the Indo-Burmese Region. Unfortunately, the biodiversity of Thailand is under severe threat (Stibig et al., 2007). Indeed, the whole of Southeast Asia is on the verge of losing approximately three-quarters of its original forest cover by 2100, and up to 42% of its biodiversity (Sodhi et al., 2004). In Thailand, clearance for agriculture and other uses has reduced forest cover to perhaps as low as 20% (Santisuk et al., 1991), much of which may be degraded (Parnell et al., 2003). According to Middleton (2003), forest cover has declined from 50% in the 1950’s to 25% in 2000, as detected by Landsat-TM images, and this is one of the fastest rates of deforestation in the tropics (Middleton, 2003). Maxwell’s (2004) view is even more dramatic as he estimates forest cover to be reduced to 15%. Currently, the 115 National Parks and Wildlife Sanctuaries in Thailand together cover 6.72 M ha and the forest therein is protected, which equates to 53% of the remaining forest area or 8% of the total land area (Middleton, 2003). Even though little remains of the original deciduous and evergreen forests of Thailand, it is still one of the biodiverse countries in Southeast Asia (estimates by Middleton, 2003, and Parnell, 2000, are that, 10,250 and 12,500 higher plant species, respectively are found). The reason for the high level of species richness in Thailand is that the country is situated on the borders or at the cross-roads between four major biogeographical regions: the Himalayas in the northwest, China in the north, Indochina in the east, and Sundaland in the south. The flora is therefore influenced by Indochinese, Indo-Burmese and Malesian elements.

Based on these influences Smitinand (1958) discriminated seven floristic regions in Thailand (Figure 1). His delimitation of these regions was based on a manuscript by Dr. A.F.G. Kerr, which is present in the Royal Botanic Gardens Kew, UK, but which we were unable to retrieve. Kerr distinguished six regions to which Smitinand added a seventh, the South-western region. The regions are still in use by botanists (e.g., Maxwell, 2004) and the Flora of Thailand Project (e.g., Santisuk & Larsen, 2009) today. The regions can be characterized as follows (sequences as used in the present floras; text largely after Smitinand, 1958):

Figure 1.

Phytogeographical areas of Thailand as used in the Flora of Thailand project. Provincial borders are indicated. N = Northern (yellow), NE = North-eastern (dark green), E = Eastern (green), SW = South-western (middle blue), C = Central (light blue), SE = South-eastern (dark blue), P = Peninsular (red)