Land management in Xishuangbanna
The legend says one day, two Dai hunters saw a golden deer in the forest. They followed his track for several days, and finally, they found a beautiful place, everything was green , the landscape was made of small mountains, rivers and waterfalls. The Dai people settled in this little paradise, they built terraces on the steep hills and called this kingdom ''Sipsongbanna'', the land of 12000 rice fields.
Originally, the entire Xishuangbanna was covered by dense forests, tropical forests. Traditionally, the hill tribes used slash and burn agriculture to produce food. This method consists in cutting a piece of forest, burning the vegetation to bring nutrients to the soil, and use that rich soil to grow cereals, fruits and vegetables. During the first year, the yield is very good, then, the nutrients being fewer, it would gradually decrease. When the soil is too poor, the farmers find another piece of land and start the process again: slashing, burning, cultivation and fallow. In Xishuangbanna's tropical climate, the vegetation can grow fast, and after ten years, the land can be used again. This is a very ancient technique of agriculture and it works perfect and is sustainable in lowly populated areas.
Another way to grow rice is to use paddy fields, this method give a better yield/ha than slash and burn agriculture but a very flat ground is required. Unlike standard fields, paddy fields don't need to have a fallow period to recover, but to achieve high yields, a good irrigation system is important.
Slash and burn and paddy fields are the two main ways in which people grow food in Xishuangbanna, yet, the farmers of Xishuangbanna have many permanent plantations: mostly bananas, rubber and tea trees. This kind of agriculture is different, it is what is called ''cash crop'', unlike subsistence agriculture, the product of those plantations is to be sold, it is the main source of revenue for the farmers. Hevea plantations is the most important cash crop in Xishuangbanna, the farmers make a good profit from the rubber extracted. The rubber tree plantations are expanding at a high pace.
In 15 years (from 1988 to 2003), the average income per person has tripled in Xishuangbanna. This development has been faster than the average in China and still is (in 2010 Xishuangbanna had 12% growth while China had 9%). This economic success is due to the diversity of activities in Banna: agriculture (rubber, tea, fruits), industry (mining, logging) and services (tourism, retail).
The tourists come to Xishuangbanna to admire its preserved nature, beautiful landscapes, mysterious forests and rich biodiversity. They are like the two Dai hunters following the golden deer. Tourism accounts for 16.5% of Xishuangbanna's GDP. Meanwhile, the huge plantations of rubber trees damage the natural landscape, usually made of jungle and paddy fields, it also damage the very nature.
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This is a satellite photo taken around Menglun, all those curves are rubber trees. You can imagine the size of those plantations. Scientists found out that such large scale projects had significant impacts on the environment. |
First, the soil cover is different in a hevea plantation and in a tropical forest is different. The tropical forest has a thick canopy, the forest is dark even by day. When a rainfall occurs, part of the rainwater is captured by the canopy, the thick layer of leaves forms a sort of buffer and the water falls on the ground after a while. In a rubber tree plantation, the cover ground is much more exposed, hence, the rainwater strikes the ground directly. During the rainy season, the rain falls mostly during short and intense showers. If all the water reaches the ground in a short timescale, the soil becomes flooded and the water runs off. In this way, each kind of terrain has different run-off characteristics which can be assessed by scientists. In the hevea plantations, the run off is high, therefore, the rainwater is not absorbed by the soils, it quickly reaches the nearby river. Why is it a problem?
It is for three reasons:
-The excessive run off can dramatically raise the level of the river, creating floods (the 2011 floods in Bangkok are partly due to this phenomena)
-Water has an important role for soil: it distributes nutrients. When the rainwater runs down the slope, it takes a lot of organic matter with it, if this matter enters in the river, the nutrients are taken from the area and eventually end up in the seas and oceans (see eutrophication in the Baltic sea or in the Gulf of Thailand). It is therefore important that water penetrates the soil.
-Rainwater recharges the groundwater reserves. Those reserves are used for irrigation and drinking, if the water runs off, it becomes polluted and cannot be used for drinking (tap water most often comes from groundwater because it is generally the cleanest water found in large quantity).
Second, tropical forest intercepts fog (it means it ''creates'' fog), hevea plantations do not. Fog is important during the dry season because it brings water to the plants. As a result of the massive development of rubber plantations, there is much less foggy days in Xishuangbanna, its misty atmosphere has vanished. This is probably the most noticeable change in the Banna weather, old people talk a lot about it.
Third, the tropical forest supports biodiversity, it sustains life much better than the rubber plantations do. Xishuangbanna is at the border between temperate climate (like in northern Yunnan) and tropical climate (like in Thailand). As a consequence, it has a particularly rich biodiversity and is the home of many rare species. Tropical rainforest is the main habitat of those unique plants (5000 species in Banna) and animals (1000 species) and it must be protected.
The benefit of biodiversity is a bit hard to quantify, to do this, the scientists use a tool called ''ecosystem services value''. Each type of environment is attributed a price in,for example, dollar per hectare per year. For example, the ecosystem of one hectare of tropical forest gives a service to humanity equivalent to 2007$/year, while in a rubber tree plantation, the ecosystem is only estimated to 92$/year. In 1988, the total amount of ecosystem service in Xishuangbanna was worth 2474 million dollars while in 2003, it was estimated to 2084 million dollar.
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Global ecosystem services value, notice that tropical forests are high priced while deserts have a low value. |
Moreover, the land filled with rubber trees cannot be used for slash and burn agriculture, as a consequence, the farmers must rely on the paddy fields to produce their food. Even though the yield is lower, the slash and burn agriculture allows the farmers to cultivate a wide range of vegetables and rice varieties. The paddy field cultivation is less diverse and is more dependent on water and fertilizers. This is a big change for farmers because they are leaving the traditional methods which were complex and required a lot of knowledge about soils, varieties and nature in general. Instead, they choose more simple and efficient methods, which have been satisfying so far but might not be as sustainable. Now, the farmers cultivate only a few species and earn money with rubber, then, they buy what they need in the market. This new way of living makes them more dependent on the price of rubber and on the weather. What would happen in case of very poor yield on their unique cash crops? The traditional agriculture involved dozens of species and having bad yields due to pest on one crop had no serious consequences. In terms of agriculture, diversity is safety.
The picture on the left represents Xishuangbanna as it was thousands years ago: only tropical and mountain rain forest. The central map is a model of the land use in 2003, as you can see, the rubber tree plantations are concentrated in the south of Xishuangbanna, the western area is mostly tea gardens. Scientists have assessed the consequences of two scenarios. In the ''rubber plantation scenario'' , no regulation is made and the price of rubber is high. The hevea plantations expand up to 1500m high, only the established natural reserves and the tea gardens are preserved. In the second scenario, the government decides to control and restrain the production of rubber, and to start forest conservation projects. In this case, the area occupied by rubber trees stays roughly the same as in 2003 and many other plantations and fields are restored to tropical forest.
The expansion of hevea plantations in Xishuangbanna can have a positive short term economic impact because the demand for natural rubber is high. On the long term though, the tendency is uncertain, what would be the impact of the landscape change on tourism? How about retail? Tea industry? Wood carving? Jade and jewelery? If the tourists don't come to Xishuangbanna because of the damaged environment, the economic improvement made on the rubber might well be offset by the slow down of other sectors.
Why is Banna tea more expensive than Lincang tea? Probably because Xishuangbanna has prestige, every Chinese has heard about this tiny prefecture, at the tip of China. Xishuangbanna is the land of Dai people, of Pu Er tea, of elephants, of tropical forest, not the land of rubber trees. Xishuangbanna is a 'place to go' in Yunnan, like Dali and Lijiang, more than any other areas, for the sake of their reputation, those regions have to invest in environment conservation.
A research program assessed that in the area around Menglun (a typical town in central Banna), the economic development has been achieved at the expense of ecosystem services.
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Development and land use in Menglun area between 1988 and 2003 |
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Ecosystem services value in Menglun area in 1988 and 2003 |
In this area, for 1$/y GDP earned, 2$/y of ecosystem services have been lost. Can we consider this development sustainable? The answer is not that easy because this model is not perfect. To a certain extent, the value attributed to ecosystem services is variable, concerning aesthetic value for example, how much would you pay to have a piece of tropical forest next to your home? Nonetheless, ecosystem service value includes the extra spending if this forest was not here. In a poor environment, people fall sick more often because of polluted air/water, poor soils makes yields lower, implies the buying of agrochemicals to prevent pests and diseases and give extra work to the farmers. Dozens of parameters are included in the calculation of this ecosystem service value, this kind of assessment is relatively new in Science (just like all branches of environmental science) and there is room for improvement.
Meanwhile, decisions must be taken, policies must be established, the precautionary principle suggests that people start to act without waiting for complete scientific knowledge. We might never be able to estimate what will happen...until it happens. But what is sure is that changes in the climate of Xishuangbanna are observed and they are faster than those expected by global warming. Scientists believe that in this place, at the limit of two types of climate, the forest creates and sustains its own micro-climate, if it is destroyed, the climate will be dramatically affected. Present actions dictate the future, humans must take the right decisions now to achieve a more developed world, this is the key of sustainable development.
references:
-Fu et al,2005, Fallow agroecosystem dynamics and Socioeconomic development in China
-Hu H.,2008,Impact of Land Use and Land Cover Changes on Ecosystem Services in Southwest China
-Xu et al, 2005,Land-use and land-cover change and farmer vulnerability in Xishuangbanna prefecture in southwestern China
-Li et al. 2007, Past, present and future land-use in Xishuangbanna, China and the implications for carbon dynamics
-Liu et al, 2002,Practice of conserving plant diversity through traditional beliefs: a case study in Xishuangbanna, southwest China
-Liu et al,2009,Runoff generation in small catchments under a native rain forest and a rubber plantation in Xishuangbanna