|In the last post, I wrote up an explanation of slash and burn (shifting cultivation) agriculture based on a lecture by agroecologist Daniel Robison. The day after he gave that presentation, he accompanied our group into the rainforest (or jungle, as it is more commonly referred to in Bolivia) to visit the indigenous community of San Miguel del Bala, a Tacana-speaking community that practices slash and burn agriculture. A guide from San Miguel del Bala joined us to give us a tour of his community (including a delightful visit to his home to meet his family, which I will share in another post), and Daniel acted as a translator in more ways than one, translating our guide's words from Spanish to English but also explaining the ecological significance of what we were seeing.
We arrived in the Amazon a few days after the first rains. Those who are responsible about burning wait until a few days after the first rains and then burn the areas they wish to burn. Clearly, many people are not so responsible, as an awful lot of burning took place before we arrived - and before the first rains. Below are a few pictures of areas of forest being burned. Daniel said these are likely examples of responsible burning - given the timing - although the latter two pictures show a burn taking place too close to the banks of the Beni River, which might result in unwanted erosion.
Burning (perhaps too close to the river)
A closer view of the same burn
So what happens after the forest is burned? We saw several examples of areas in various stages of fallow. The picture below shows an area that was slashed and burned a year ago. (Daniel said "Last year this time it would have been a smoking stubble.") Then, the people of San Miguel del Bala planted rice here, which they harvested in March. As you can see, the forest has already started to reclaim the area.
An area that was burned a year ago.
In contrast, here is another area that was burned a year ago. However, it was not left fallow long enough before it was burned. As a result, grasses are dominating the area now.
Another picture of the area burnt last year that wasn't left fallow long enough.
Once an area is burned (around October), they plant rice and cassava and perhaps some fruit trees. They harvest the rice in March. The cassava continues growing for a total of 18 months, thus giving them two crops from one area. While the cassava grows, you can see grasses already beginning to take over the forest floor (in the picture below). In the area where the photo was taken, the rice was already harvested, the cassava was growing, and we also saw pineapple, bananas, cacao, sugarcane, papaya, and pacay (ice cream bean) growing.
Grass growing on the ground in an area burned a year ago.
Next, I've got a picture of an area that has been left fallow for seven years. It is also an area that was planted in rice. The soil here is fairly poor. On better soil, there would be denser vegetation after seven years. The people of San Miguel del Bala plan to let this area remain fallow for a total of 15 to 20 years, because with poor soil, they would not get much of a yield if they slashed and burned it again sooner.
An area with poor soil that has been fallow for 7 years
As I wrote yesterday, slashing and burning forces succession. That means that after an area is burned, there are a few species that come in first, and those create the right conditions for other species. The next set of species enters the area, and those create the right conditions for even more species to grow, and so on, until ultimately the ecosystem reaches a climax state.
Here, there are a few key pioneer species that enter an area soon after it has been burned. One is the cecropia tree, a tree that grows to incredible heights in just two years. Cecropia trees have leaves that can look silvery if you are looking at them from below, and I think the entire tree looks like something that Dr. Seuss might have made up. The leaves are enormous, and when they fall on the forest floor and decompose, they create the right conditions for other species' seeds to germinate.
Cecropia trees, I think
Daniel holding a cecropia tree leaf and pointing up at a cecropia tree above
The cecropia tree Daniel was pointing at, which is nearly impossible to see through the thick vegetation.
One of the other main pioneer species here is the balsa tree, shown below.
Often tropical soils are very poor, which may come as a surprise given how much life (both in quantity and variety) thrives here. One explanation I've heard is that the frequent rain beating down on the soil tends to leach out the nutrients. So how does so much life burst from such poor soil? The nutrients are usually held in the plants themselves. There is a constant recycling of nutrients with plants dying, decomposing, and other plants taking up the nutrients as they become available. (This also happens as animals eat the plants, poop, and make nutrients available that way.) In slash and burn agriculture, burning releases the nutrients that are held in the vegetation, making them available to whatever crop you wish to grow.
I took the picture below to show an example of how thickly covered the forest floor is with decomposing plant matter. The area that is cleared is the path we were walking on, and I can only imagine that trail maintenance is a constant job for the people of San Miguel del Bala.
A thick layer of litter on the forest floor
Below, you can see a photo I took of an area left fallow for 25 years. It was tall forest 25 years ago, when it was burned, planted in rice, and then left fallow ever since. Our guide told us that his community did not plan to ever burn this area again because it was near the Eco-Lodge they operated for tourists. In exchange for not burning this area, they were given land inside the nearby Madidi National Park that they were allowed to slash and burn.
An area that has been left fallow for 25 years.
Poor soil is only one reason why slash and burn is practiced. The other main reason is that the forest plants move so quickly in reclaiming any area that is burned and cultivated that weeding is nearly impossible. It's far easier to slash, burn, plant, harvest, and then walk away and let the forest take over. One alternative to slash and burn that the people of San Miguel del Bala have tried is using tropical kudzu to crowd out weeds. This is a different species from the type of kudzu that has taken over the American South.
Daniel pointing out tropical kudzu, a possible alternative to slash and burn agriculture.
As noted yesterday and hopefully made clear here, slash and burn agriculture can be done in an ecological way. It works very well with nature instead of treating nature as an obstacle to overcome. However, as you can see here, problems occur when areas are left fallow for too short a time.
Fallow periods tend to be shortened due to population pressures or another other pressure that might leave the group practicing slash and burn agriculture with too little land to leave each area fallow for a long enough time. frequently areas with better soils are left fallow for shorter periods of time, and that isn't a problem because, with better soil, the forest is still able to return after the burn. Also, as we saw while visiting San Miguel del Bala, areas closer to one's home tend to be burned more frequently than areas further away. Aside from the fact that it takes longer to walk to far away areas, there's also the fear that someone may come along and steal your crop if you aren't nearby to protect it.
The long story short is that slash and burn agriculture itself (when practiced properly) is not the problem that is causing rainforest destruction. My diaries over the next several days will show a number of other things happening in the Amazon that are problems resulting in rainforest destruction, as well as a discussion of how to stop these practices.