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Ecology

The resistance of the forest

Degraded ecosystems ,as long as they remain close to original woods, are to keep their biodiversity

In the south of Bahia, those interested in ecology enjoy a further attraction in addition to the tourist enchantments of Ilhéus, the land of Jorge Amado: the Una Biological Reserve, a priority to the conservation of the Atlantic forest system. One of the last great continuous stretches still preserved in the Northeast, the reserve survives in the midst of cacao and rubber plantations and pasture in use or abandoned. A fragmented landscape has been formed, the effect of which on biodiversity is surprisingly less that we might have imagined.

Researchers on the Remains of the Una Forest Region (RestaUna) project have observed that in the neighboring or surrounding regions, fragmentation of the forest has not led, as it was feared, to the complete isolation of animal and plant populations: species from the original forest are also found in stretches where the forest has been modified. Conceived by young São Paulo researchers and maintained since 1988 by the Santa Cruz State University (Uesc) of Ilhéus, RestaUna suggests that the mosaic formed by the set of environments resulting from the deterioration of the forest have managed to maintain most of their original biodiversity: provided that they are close to areas of original forest, the modified environments are home to around 70% of the animal species found in the original forest.

So far, the researchers have identified around 420 species of animal and 600 species of plants. In Una, they have discovered 12 new species of animal and another 12 of plants, described in articles due to be published coming months. Among those found, for example, two species of lizard, two toads of the genus Chiasmocleis , and three species of bata of the family Phyllostomidae and two Nymphalidae butterflies, previously only found in the Amazon region. The work includes a list of endangered species, which diminish in relation to the interior inside of continuous areas: 48 animals (including 26 birds) and 46 vegetables (including 18 bromeliads and 19 tress and shrubs).

Forest, cacao and cleared land
To understand why this discovery has caused such an impression it is necessary yo explore the region in a pickup truck and, at the cost of much sweat and shaking about, learn first hand about the region’s environments: conserved forest, cacao plantations (or cabrucas) and shrubbery on cleared land (where the forest has been cleared and is regenerating). The intact forest is sultry, humid, and dense, with trees of all sizes: those with thick trunks and 20 to 30 meters tall next to young trees, still slim, integrated with networks of vines and clouds of small mosquitoes. On the trails, once one’s eyes have become accustomed, the diversity is clear, if we move into a previously cleared area, the environment is hotter and clearer – you can almost see the sun – and the vegetation changes, young trees with slim trunks predominate and there are lots of vines. Sometimes the clearing already seems like a young forest, other times it is like pasture so scant is the vegetation.

Further on we go into a cacao plantation, also hot and sultry, but less diverse; the landscape is dominated by cacao trees, two or three meters tall, in the space previously occupied by trees in the sub-forest, up to 10 meters tall. Taller trees are preserved, to give shade which the cacao trees need. It is a despoiled environment, still with the persistent mosquitoes, and we can walk about relatively easily. The problem with this type of use where part of the forest is preserved is that it tends not to last: fragmentation advances with the decline of cacao growing, devastated since the 80’s by the filamentous fungi, vassoura-de-bruxa (witch’s broomstick – Crinipellis perniciosa) – which may explain why it is rare to run into anyone in the cacao plantations.

In satellite photos or on maps, we see the marks of forests separated by extensive unforested areas. Thus, the cacao plantations and clearings – in Una, always close to native forest – work as corridors between the remaining areas of original forest. But the RestaUna group warns of the danger of generalizing these results: very extensive forests, far from any stretch of native forest, are unlikely to retain the same diversity of forest species that the project observed.

The risk remains
The work of the 12 members of the project have the support of the American biologist William Laurance, of the National Amazon Research Institute (Inpa), one of the world authorities on the fragmentation of tropical forests. And his basis is around 35,000 records of collections, forming one of the largest animal databases of a Brazilian ecosystem in existence.

The diversity found in degraded oiled areas has limits. “Animals of the Atlantic coast forest are highly sensitive to fragmentation”, warns Laurance. There may not be any reduction in the total number of species in each group of animals, but fragmentation unsettles the population of animals and plants in Una: numerically rare species within each group may become dominant over others that used to dominate, or they may even disappear in response the changes in humidity and light.

The lizard Enyalius catenatus picus and the butterflies of the genus Morpho, for example, found relatively easily in the rain forests, are extremely rare in the cacao plantations. The three small mammals that predominate in virgin forest – the rodent Oryzomys laticeps and the marsupials Marmosops incanus and Monodelphis americana – have become rare on the edges of the remaining forests which have been invaded by non-forest species more typical of open areas.

The findings counter settled ideas, in particular the Theory of Island Biogeography, still one of the guidelines for those that work with fragmentation. Formulated in 1967 by Robert MacArthur and Edward Osborne Wilson, of Harvard University, in the United States, the theory maintains that, on islands, the number of species is proportional to the area and to the distance between each habitat. Over time, their conclusions have covered continental “islands”, or stretches of habitat. But according to the RestaUna group, the theory would only be valid where the environments surrounding the islands are really inhospitable – as is the case of a pasture, but not of a forest clearings or cacao plantations.

The effect of the borders
In Una, they believe that what most affects the population of plants and animals is not the reduction of the original habitat, but the border effect – the change to the forest caused by contact with open areas that arise through deforestation. At the borders – stretches of disturbed forest that are hotter and lighter than inside the original forest – the mortality rate of trees increases and the microclimate changes from the effect of the wind and brighter light.

In this point, the RestaUna results reinforce the theories of a work that is a reference in tropical forest fragmentation: the Biological Dynamics of Forest Fragments (PDBFF), that has been undertaken since 1979 by the Inpa in collaboration with the Smithsonian Institution, of the United States. To determine the consequences of deforestation and forest fragmentation in the Amazon region, 11 areas north of Manaus, measuring 1, 10 or 100 hectares (1 hectare is 10,000 square meters) were isolated.

It was clear that slashing the forest by opening up pasture causes a substantial loss to the number of species, especially of birds, although the isolation can also maintain the number of species constant or even increase the population of some animals, such as toads and small mammals. The effect of the borders was also established; smaller reserves, of 1 hectare cannot maintain the original biodiversity because they let in too much light, which lowers humidity, alters the microclimate and increases the mortality rate of trees, especially fully-grown trees close to the edges of the fragments.

Detail: the fragments studied in the Amazon region were surrounded by pasture – a more marked contrast than in the south of Bahia, where the remnant forests are surrounded by previous clearances and cabrucas, the cacao forests. “This difference reinforces the idea that the cabrucas are an ‘environmentally friendly’ alternative use, since they enable many forest species to be shifted or even to reside and reproduce in them”, comments Heraldo Vasconcelos, the PDBFF’s scientific coordinator. But he himself warns, “I don’t mean that we should replace forest with cacao forest, but only that the cabrucas increase the value of conservation in the forest fragments, in contrast to other land uses, such as pasture, which reduces it”.

Nowadays, 40% of what is left of the forest in the south of Bahia is used for cacao growing, covering around 600,000 hectares in the region. Not all behave in the same way. “An isolated cacao cabruca is less rich in bat species that others, located between stretches of forest”, points out Deborah Faria, RestaUna’s technical coordinator.

Opposite paths
“It is notable that a project like this has been begun and organized entirely by postgraduate student, who have done extraordinary work”, recognizes Laurance. The first conversations between doctoral students at the University of São Paulo (USP) and the State University of Campinas (Unicamp), willing to pool their theses in a single project, took place in 1996. “The fact of being doctoral students, which was a weakness for the group, became an advantage: we had to do the survey fast and well to complete our theses”, says Renata Pardini, responsible for surveying small mammals, who did her doctorate under the guidance of Eleonora Trajano, of USP.

After studying the PDBFF’s approach – in which surveys were carried out one after the other and, in part because of logistical difficulties, years went by until all the areas for the study were found, located on private estates – the team decided to adopt a different approach; that of studying groups of animals and plants at the same time and in the same places as the collection. Thus, they managed to limit the influence of fragmentation on the biology of the species, without interfering in the transformation of the forest, since pasture can be turned into a recovering clearing from one year to the next.

FAPESP supported the project with two doctoral grants and two masters’ degree grants. Over time the group obtained the support of the Ministry of the Environment and the National Scientific and Technological Development Council (CNPq) and of the World Bank (Ibrd), among others, which enabled the infrastructure for the field surveys to be created, including the purchase of two jeeps to travel over the difficult terrain of the Una reserves.

Conservation with use
Sticking to the design of the project suggested by Laurance, the 12 biologists worked with 36 sampling areas, including continuous forest, borders, recovering clearings, and cabrucas. These spaces were located in three 5-km-sided squares, which together represented 49% forest, 27% pastures, 15% recovering clearings, 6% cabrucas and 2% rubber plantations. The region includes still intact portions of forest, most of them on private estates, as well as the 7,000-hectare Una reserve.

For three years, they undertook expeditions lasting up to two or three weeks. The sampling used to study the effects of fragmentation involves ten groups: birds, bats, small mammals, toads and lizards, beetles and butterflies, land invertebrates, bromeliads, ferns, trees and shrubs. Four hundred and forty buckets were buried to catch lizards and 2,500 hours were spent observing bats, collected by net at night.

Little by little it became clear that the animals react to human action on the environment. For toads (2,448, of 18 species were collected), cacao forest and clearings seem to work as extensions of the forest. “Both work like a patchwork quilt, in bringing together the patches and enabling the population of the different parts of the region’s forest to be connected”, comments Deborah. The borders – important because 63% of the perimeterof all the forest is in contact with open areas, one can see the loss or decline of certain species. There are no Fringe-lipped bats (Trachops cirrhosus), hairy little big-eared bats (Micronycteris hirsute) and Tonatia salrophila bats there.

Typical of conserved forest they do not do well on the borders because the great density of leaves and vines makes it difficult to fly and maneuver to capture arthropods which is their favorite food, found on leaves and branches. There are fewer ferns in these areas than inside the forest – a consequence of the increased temperature and lower humidity. The borders are, however, the favorite areas of invading species typical of open areas, such as the rodents Akodon cursor and Oligoryzomys sp and the butterflies Hermeuptychia hermes, Yphthimoides ca. ochracea and Yphthimoides renata.

But there are also species that do not respond to the fragmentation and that occur in all the environments in the Una mosaic, such as the Archaeopreona spp. and Colobura dirce butterflies. The marsupial Marmosa murina is a forest species that lives in trees, but which does well in disturbed areas; its presence increases both at the borders and in cacao forest and in the recovering clearings.

Disappearing mammals
Another human activity having a substantial impact is hunting, which especially threatens the large mammals. For example, there are no more tapirs (Tapirus terrestris) and white lipped peccaries (Tayassu pecari), even though the Una forest is big enough to be home to them. Hunting is an important food supplement there, according to a survey conducted by Renata and by Gabriel Rodrigues dos Santos: most of the 204 families interviewed live on nearby farms and have an average monthly income of two minimum wages. Based on the results, they included suggestion to reduce hunting in the proposed biological guidelines for the region, sent last year to the administrators and environmental technicians in Bahia.

They recommend, for example, concentrated action with estate owners, for them to ban hunting – today, 70% of them impose no restrictions. Another measure is to encourage residents of the reserve to raise domestic animals more intensively, such as chickens and pigs. The survey suggested that the head of a family that has food at home will not readily go out hunting and may even think about conservation.

The Projects
1. Effects of Fragmentation and Anthropic Conversion of Natural Environments on the Bat Population of the Atlantic Forest of the South of Bahia (nº 97/07075-1); Modality Postgraduate grant; Coordinator
Wesley Rodrigues Silva – Unicamp’s Institute of Biology; Investment
R$ 56,102.22
2. Fragmentation of the Forest and Uses of the Land in the Environmental Mosaic of the Una Region, South Bahia – Effects of the Population of Land Mammals (nº 97/03258-4); Modality Postgraduate grant; Coordinator Eleonora Trajano – USP’s Biosciences Institute; Investment R$ 98,307.11

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