I first went to the Pando in the Bolivian Amazon in 1988 as a young undergraduate. Returning in 2013 as a middle-aged botanist it was a pleasant surprise to find that although the capital Cobija had grown a lot much of the forest remained and that sustainable Brazil nut harvesting remained the major source of income for rural communities. It also remained one of the forests with the highest diversity of primates in the World. A single locality having up to thirteen species of monkey! That all looks about to change though as a triple whammy of semi-legal gold-mining, oil exploration and road building took off in 2015 and which by 2018 will have completely transformed the infrastructure, economy and likely the social fabric of one of the least deforested parts of the Amazon.
Asphalt roads are clearly of benefit to Amazonian communities, providing improved access to healthcare, education and markets and assist with the seasonal Brazil nut harvest. Roads also, however push back the frontiers of the forest and facilitate currently unsustainable agriculture, such as slash-and-burn, cattle-ranching or intensive soya / oil-palm production. Finding a balance between the opportunities and risks posed by asphalt roads is very difficult and rarely achieved. Oil extraction and transportation will also have an impact, changing the economy of the Pando and possibly replacing natural forest with its Brazil Nut and rubber trees as a major souce of employment and incomes. It also of course brings with it the risks of any large mining operations.
The rapid growth of semi-legal artesanal gold mining in the Pando could have a far greater impact. The mercury used to separate gold from the river sediment has profound health risks for those mining but also for the whole ecosystem downstream, and for decades to come. Artesanal gold mining also attracts people desperate for money, from all over South America, together with many other strands of the black economy leading to social and political instability.
In addition to getting the timing right it is also important to pollard at the right height, point on the stem and using the right tools. Pollarding involves cutting the top and branches off of a tree. Normally this is done to promote resprouting at the top of the stem but in the case of our agroforest system we want to allow light into our plot for the cultivation of annual crops or fruit trees. This means that we need to cut the stem at the right height so as to shade the crops below and to give them enough time to grow and be harvested before the branches have regrown to their original length. For this purpose we are aiming to pollard at approximately 1.30 m in height, the height of somebody’s chest.
The best place to cut the stem is a couple of centimetres above or below a branch or branch scar. The reason for this is that new branches will sprout from these points. If you cut through the branch point or scar then the tissue from which new branches will develop will be damaged and new branches will be generated at the nearest point above or below it, meaning that it will be higher or lower than desired. The choice of implement is also important. Whilst it is much quicker and more natural to want to use a machete, this is not the ideal way to cut the branch. The reason for this is that it is hard to get a clean clut with a machete as Inga wood splits very easily and the split wood is vulnerable to insect and fungal infections.
The Inga trees in the first plot that we planted at the end of February 2014 have been big enough to pollard since July. We have not pollarded, however, as the conditions have not been right to do so. As Dr Terry Pennington, Inga agroforest expert explained, you should not pollard trees during the dry season and the best time to do so is a couple of weeks into the wet season. The reason for this is that when you remove all of the leaves and main branches of a tree, the above-ground loss is mirrored below ground. That is the roots die back comensurate with what was lost above. During the dry season there is little water in the soil and the tree needs all its roots to obtain the moisture it needs. Therefore if you have pruned during the dry season, the tree is left without enough roots to survive.
In the case of the Bolivian Amazon, the dry season normally runs from April/May to October/November. This year has been particularly hot and dry, possible a consequence of the El Niño phenomenon, and so pollarding our plot would likely kill all of the trees. We will therefore wait until the middle of November when the rains should have started before pollarding.
At another of our sites, Palacio, the timing of pollarding is also important. The reason for this is that it is a site which floods for a couple of weeks each February. We therefore have to be careful that we leave enough time between pollarding and the floods. Or at least make sure that we pollard high enough so that the new shoots emerge above the floodwaters. So here again the timing of pollarding and the associated planting of crops needs careful thought!
Alex Monro's blog about the documenting and conservation of biodiversity