## 2 Study Area  
Nan is one of the 17 provinces situated in northern Thailand, covering approximately 12,000 km\({}^{2}\). The province has an elongated shape surrounded by high mountains, except for the southern part (Figure 1). Nan Province accounts for one third of the Nan River Basin, which flows from north to south and joins the Ping, Wang, and Yom Rivers to form the Chao Phraya River in Nakhon Sawan Province. The lowlands (< 400 m) occupy about 18% of the province's area, while elevations greater than 800 m cover approximately 40%. The highest altitude of 1,980 m above mean sea level is in Doi Phu Kha National Park. The mean annual rainfall during 1961-2013 was 1,268.8 mm. The rainy season begins in May and ends in September. Mean annual temperature is 25.9\({}^{\circ}\)C; maximum temperature is 33.1\({}^{\circ}\)C, and minimum temperature is 20\({}^{\circ}\)C [36].  
The population of Nan Province is approximately 478,000 persons, and 55% of the households engage in agriculture. Agricultural sector contributes about 32% of the Gross Provincial Product (GPP) [7]. Mean population density is low at 39 persons/km\({}^{2}\) compared to the national population density (130 persons/km\({}^{2}\)) due to mountainous topography, which is a barrier to development. An important social problem in the province is poverty. In 2015, 28.8% of Nan's population lived under the poverty line (USD 1,057 per person per year in 2015), considerably greater than the national proportion of 8.6% [37]. An increased density of households living in poverty was found in steeper terrain because of low income from agriculture and lack of job opportunities.  
Agriculture plays a key role in the economy and livelihood of most of the population, particularly tribal people (e.g., Lua, Khmog, Mien and Khmu). Most of the lowlands are dominated by ethnic Thai, whereas the highlands and mountainous territories are populated by other ethnic groups. Land suitable for cultivation is limited: agricultural land in 1977 covered 5.3% of the province. In 2007 agricultural land increased to 10%, with 42% of this area used for maize cultivation. In the last decade, the province faced a maize boom and rapid expansion of rubber plantations. In 2016 maize cultivation covered approximately 127,000 ha, which was nearly fivefold and two-fold greater area than in 2005 and 2007, while the rubber plantations increased over four-fold during 2005-2016 [38; 39]. Agricultural land increased to 27.3% of the province's area, with 13% of this area irrigated.  
Long-term monitoring by the Land Development Department (LDD) and the Royal Forest Department (RFD) showed that forest cover in Nan province declined from 92% in 1977 [40] to 61% in 2016 [11]. The greatest deforestation rate of 33% (or 14% per annum) was recorded during 2009-2012 [33]. Protected areas (national parks) and class 1 watersheds cover about 35% and 45% of the area. These two land-use types are recognized as conservation forests [12] and agricultural development, extraction of non-timber products and human settlement are prohibited in these areas. Rapid agricultural expansion driven by favorable market price for maize and government incentives for rubber plantations [35] in the last decade has triggered extensive deforestation in conservation forests.