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Forestry engineering

Finite stock in the Amazon

Two species of tree take more than a century to grow and replace the quantity of cut wood

Simulations made by computer indicate that the commercial extraction of certain top class Amazonian trees might not be a sustainable activity in the long term. Not even the adoption of the techniques recommended today for managing the forest, a group of measures, which in theory should reduce the effects of lumber activities upon the forest to acceptable levels, is capable of smoothing over the marks left by the human hand: rapid and effective, the chainsaw always wins out, and by a long way, the race against nature. In the virtual scenarios, created in the micro computers of the researchers involved with the Dendrogene Project – Genetic Conservation in the Managed Forests of the Amazon, the populations of two tree species, the tatajuba  and the native variety of the West Indian bully tree, the maçaranduba, were submitted to a single cutting cycle, carried out in accordance with the concepts considered rational by current sustainable growth. This situation was represented with the help of a ecology and genetics modeling program, named Eco-Gene, which calculated how long it would be necessary for the remaining trees of each species to re-grow and multiply and the forest to return to have the original quantity of tatajuba and maçaranduba trees. The results have lit up an orange warning light: a century of tranquility was not sufficient to again endow the forest with the same stock of wood of the two species that they had previously.

The situation of the Bagassa guianensis, the scientific name of the scarce tatajuba tree, which produces a yellowish wood, much appreciated in the construction of boats and floorboards, is particularly worrying. In the simulation, the forest needed some two hundred years to recover 80% of the original quantity of wood. The regeneration process was so slow that the species did not manage to recoup all of its initial stock. More abundant, the Manilkara huberi, the popular maçaranduba tree, the owner of a very hard and resistant wood, dark red in color, had a better performance, but not very exciting: one hundred and thirty years were necessary for it to again exhibit the original quantity of wood. “We need to review some ideas about wood exploration”, says Milton Kanashiro, a forestry engineer with Embrapa (the Brazilian Agricultural Research Corporation) – Eastern Amazon, of Belem, who coordinated over a five-year period the work of approximately fifty researchers and collaborators in the Dendrogene Project. “We have indications that, even with the adoption of management, in the framework practiced by companies today, there is a major reduction in the commercial stock of some tree species explored economically.”

Sun and shade
The tatajuba and the maçaranduba trees are species of high commercial value from the Amazon, sometimes found side by side in areas of firm ground, as the strips of the forest lands that are never flooded are called. In their maturity they reach forty to fifty meters in height cutting through the forest canopy. They have thick trunks with diameters varying from 1.4 meters to 2.0 meters for adult examples, and their fruit are edible, especially that of the maçaranduba. In spite of having points in common, the two species are conspicuous by the differences in their dynamics of reproduction and growth rate. “One is the contrary of the other” says the biologist Marivana Borges Silva, who is taking her doctorate degree at the Federal University of Pará (UFPA), and who worked on the simulations. In adult forests, the tatajuba is rare; it loves sunlight and grows rapidly. The maçaranduba is abundant, tolerates shade well and develops slowly. In an area of 500 hectares of the National Forest of Tapajós, close to the town of Santarém, in Pará State, where the field work of the Dendrogene Project was concentrated, among the trees with more than 10 centimeters of diameter, the number of examples of the fist named species is ten times less than that of the second.

In this stretch of forest, close to fifty researchers and project collaborators, from here and abroad, have been studying in depth, for five years, the many varied aspects of biology and genetics of seven arboreal species, all of them explored by the lumber dealers. As well as the tatajuba and maçaranduba trees, whose work is at the most advanced stage, the jatoba tree (Hymenaea courbaril), the cumaru (Dipteryx Odorata), the anani (Symphonia globulifera), the andiroba (Carapa guianensis) and the parapara (Jacaranda copaia) are the targets of the researchers. Each tree has occurrence and reproductive dynamics that are distinct from the others, forming, according to the scientists, a representative framework of a good part of the diversity of the arboreal species of Amazonia. The main objective of the Dendrogene Project, a scientific enterprise to the tune of R$ 6 million funded mainly with resources from Embrapa itself and from the International Development Department of the British government, is to understand the greatest number possible of variables that influence in the birth, growth, death and regeneration of trees of commercial interest. And, in this manner, design specific management plans for the groups of trees that show themselves capable of being explored over a long period of time. “One of the problems of current management is to view the forest as something homogeneous, without taking into consideration the particularities of each species”, suggests Kanashiro. “Our data, although preliminary, shows that forestry management could be viable if we to follow two pathways: reduce the intensity of extraction, diminishing the quantity of wood removed or elongate the cutting cycle, and promote rotation among the species that will be commercially explored in the future, concentrating activities on those with rapid growth.”

The problem is that it is still not known which species could be managed in a sustainable manner. Hence the importance of having scientific projects that attempt to respond to this difficult question. For now, it is not yet clear which type of management it would be possible to recommend for the exploration of the tatajuba and maçaranduba trees. The analysis of another series of simulations carried out during the Dendrogene Project indicate that both cases are delicate. With the help of the Eco-Gene program, which was fed with the biological and molecular data of the two species, the researchers compared the impact of the adoption of nine distinct scenarios of exploration over a period of three hundred (300) years. The objective was to see if some change of behavior would produce significant reductions in the effects of the lumber activities on the populations of tatajuba and maçaranduba trees. Once again, at the end of the simulations, there was nothing to commemorate: in all of the scenarios tested, even in the apparently least aggressive situations, there were no more trees remaining in sufficient enough quantity for commercial exploration after the third cycle of cuts. “The results did not change much as a function of the adopted scenario” comments Vânia Azevedo, who is taking her master’s degree at the University of Brasilia (UnB), and who participated in the simulations. “After the third cycle of cuts, it would not have been possible to take almost nothing from the forest.”

In each simulation, at least one of the three main parameters of the forestry management plan was altered. These central directives define the interval of time between each extraction of the wood, the minimum diameter of the tree trunks that can be cut down and the percentage of trees that passed through the cut that were preserved (left as reserve). Among the few companies that have adopted management plans in the Amazon, where 70% of the lumber extraction is irregular, according to some estimates, the standard adopted is to follow what the law demands: adopt a cycle cut of thirty years, to consider as a candidate for extraction, all of the trees with at least 45 centimeters in diameter at the so-called diameter at breast height (DBH) and to maintain as reserve only one in every ten trees that have attained the cutting point. The first scenario tested served as a control. In this case the Eco-Gene program calculated what would happen with populations of five hundred (500) tatajuba and five hundred (500) maçaranduba trees that would remain untouched over three centuries. In the other scenarios, from the second to the ninth, distinct management plans were tested that were more or less restrictive to the lumber activity. That of number two simulated exactly the parameters used today in management. In the others the extraction cycle varied between 30, 60 and 90 years, the minimum diameter for cutting oscillated between 45, 55 and 65 centimeters and the section of the uncut trees left as reserve fluctuated between 10%, 30% and 50% of the adult examples.

After some three hundred years of virtual exploration of the trees, the general picture painted by the Eco-Gene program was not good. In relation to scenario number one, in which there were no cuts made at all of the wood, the tatajuba, and to a lesser extend the maçaranduba, showed in the other simulations significant reductions in stock of wood and in the number of trees that made up their respective populations. The quantity of wood of B. guianensis available in the forest shrunk between 82% and 90% and the number of trees between 63% and 78%. The stock of wood of M. huberi receded between 58% and 80% and the number of trees decreased at the maximum by 12%. It appeared that there had been a paradox – or an error – surrounding the two indices calculated by the modeling program for the maçaranduba tree. How, after three centuries of exploration, can the number of trees of a species almost not diminish whilst the stock of the wood dwindles in front of our eyes? The answer: it’s true that at the end of the simulations there was almost the same number of maçaranduba trees as in the past, only that they were much smaller than before.

If the forestry management as it is practiced today radically alters the stock of wood in the forest, its impact upon the genetic diversity of the tatajuba and maçaranduba trees did not appear to have the same magnitude. In both species, the loss of molecular information was at the maximum some 15% of the so-called genotype combinations that there were in the trees before the start of the logging activity. A genotype combination is a particular form of a gene found in an individual. In other parameters, such as consanguinity, there were no statistically significant changes. “The simulations indicate there are no strong threats to the genetic conservation of these trees” ponders Kanashiro. “But we can’t as yet say this with all certainty.”

Complex reality
The results of the simulations need to be put into perspective. The reality, everyone knows, above all the researchers involved with the Dendrogene Project, is more complex than the scenarios built up through a computer program that attempts to forecast the effects of the controlled extraction of wood. The Eco-Gene program was fed with data about the genetic and biological characteristics of the tatajuba and maçaranduba trees studied in a natural area of the forest. The ideal would be if the software were to be fed with information of trees coming from managed areas, which should present distinctive dynamic reproduction. Shortly this should be possible. At the end of 2003, the researchers accompanied the cutting down of 90% of the adult trees of the seven studied species that exist inside 500 hectares of the forest, in which the project had concentrated its fieldwork. “Later this year, or in 2006, I should be returning to the area to see the impact of the extraction of the wood upon the insects and animals responsible for the pollination of the trees”, says the biologist Márcia Motta Maués, from Embrapa-Eastern Amazon.

It may seem to be against common sense to the layman, but the extraction of wood stimulates the germination of seeds in the soil of Amazon and, in the first instance, favors the growth of seedlings of trees in the stretch of the forest that had been explored. The cutting of a maçaranduba or a tatajuba of large size opens up a clearing in the sawed jungle and the rays of the sun strike the land more easily. The forestry engineer, José do Carmo Alves Lopes, also from Embrapa, has measured at Tapajós the levels of regeneration of the seven studied species in detail during the Dendrogene Project, before and after having made the cutting down of trees there. Ten months after the chainsaw had done its job, all of the varieties had increased their levels of regeneration. The tatajuba, which loves sunlight, showed the highest index of appearance and growth of the little seedlings. There were sixty two times more seedlings of the specie than before (the number of off-shoots per hectare rose from 0.3 to 19.0). The crabwood, the species that had the lowest level of regeneration, increased more 5% in its number of plantulas (jumped from 106 off-shoots per hectare to 112). “Now we need to know how these growth levels will fit in over time. They will drop off, but we just don’t know when”, affirmed engineer Carmo. As the crown of the forest again becomes dense, species that do not tolerate shadow begin to show alarming levels of mortality. Only the few examples that are tallest, which literally manage a permanent place in the sun, survive. This is the situation of the tatajuba, contrary to the maçaranduba that likes the shadow.

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