Are we saving forests at the expense of rivers?

For the last five years, I’ve been working on research related to the conservation of aquatic ecosystems in Southeast Asia, and I'm happy to announce that the first chapter of my dissertation has recently been published. While it's only available online at the moment, it should be making its way onto a printing press at Ecosystems in the coming months. A big thank you to my collaborators Joel Moore (Towson U.), Naparat Suttidate (formerly at UW-Madison now in Thailand), Robyn Hannigan (U. Mass-Boston) and my advisor Pete McIntyre (UW-Madison), my field assistant, Jack Siddoway, and the International Sustainable Development Studies Institute for logistical support.

Ngao River Valley | Not long ago these swidden fields would have grown mostly rice and vegetables for local subsistence. Now, farmers with reduced access to land increasingly choose to grow cash crops, like the soy pictured here, on their remaining land.

Much of the work of conservation is figuring out how to balance human needs for resources like food, water, and timber with the need to maintain the organisms and ecosystems that produce these goods. There have been a lot of studies that have specifically looked at how to meet the future food demand of humans while maintaining sufficient areas for wildlife. Many scientists argue that the best way to do this is to maximize the amount of food produced from the minimum amount of land. By doing this, there will be more land with high-quality habitats for wildlife. Achieving this goal would require substantial centralization of agriculture as well as substantial fertilization and irrigation effort in most places. Other researchers have suggested that we should mix agricultural landscapes with conserved areas, because these sorts of arrangements can be better for both wildlife and for the farmers. This may just sound like an academic argument, but land managers from all over the world have to deal with these types of questions.

The question that I and my collaborators were interested in trying to answer was, What happens to the aquatic ecosystems when you try to intensify agricultural production and maximize forest cover?  This scenario is currently playing out in much of Southeast Asia as the historical swidden farming system common in northern Thailand and throughout Southeast Asia is being converted to more industrialized corn and soybean farming. Swidden is a long-standing process of cultivating plots of land that depends on forest regeneration to maintain the fertility of soils. Swidden is sometimes referred to as rotational farming because farmers rotate their cultivation among 5-20 different patches of forest, one of which is cut and burned each year to provide a pulse of nutrients at the beginning of the growing season before laying fallow for several years.

Karen State, Myanmar (Burma) | Fish, like those pictured on the left, have supported people in Southeast Asia for millennia. Now, landscapes and farming practices are being converted in order to grow the soy and corn used for feeding chickens and pigs, pictured at right.

There are lots of forms of swidden, but they all typically don't require the use of commercial fertilizers like more conventional, or modern, farming techniques. Because of the increased pressure on many regional governments to increase agricultural production while also increasing forest cover, people practicing swidden have often been incentivized, or in some cases forced, to adopt conventional farming practices. While this might have benefits for increasing the extent of forest cover, which in turn may help conserve terrestrial biodiversity, the necessity of using commercial fertilizers may result in losses of water quality in these areas, and thereby negatively impact freshwater biodiversity.

Mun River, Thailand | Many people throughout Southeast Asia depend on rivers to provide them with food. This man is collecting snails and aquatic insects from these water plants.

Our results strongly suggest that areas with low swidden coverage and high levels of commercial farming have higher nutrient concentrations in the rivers that drain those landscapes.  More importantly they have potentially altered ratios of nutrients like nitrogen and phosphorus, which have been shown to affect the production of algae, the bottom of the food web in these tropical aquatic systems. At low concentrations, these nutrients might actually increase the food resources available to the rest of the organisms in the rivers, but, in most aquatic systems around the world, having too much nutrient availability often results in hazardous algal blooms. So, while curtailing swidden and concentrating agriculture production on smaller patches of land might provide more forest habitat for things like birds and mammals, the impact may actually be negative on all freshwater organisms both in the immediate area and downstream of farmed areas. Unfortunately, the ongoing debates regarding terrestrial management that either favors swidden or alternatively intensive forms of farming have rarely considered the effects of these transitions on aquatic systems.

Conservation planners face the continual challenge of maintaining biodiversity and important ecosystem functions, while also ensuring there is enough land for producing the food our growing human population needs. However, our research suggests that there may be costs to aquatic systems if we just try to maximize our agricultural production on less land in order to increase the amount of land for conservation. With additional consideration of aquatic ecosystems in our land management strategies we can make sure we aren't just saving our forests at the expense of our rivers.