There are several dams in the ecoregion whose effect has been not only to flood large extensions of native forest, but also to impose new barriers that increase the fragmentation of the forest and reduce the dispersal capacity of flora and fauna that live on opposite sides of the newly-formed reservoir (Fahey & Langhammer in press). There are plans for the construction of several new dams in the ecoregion whose negative effects would likely be similar to those that have been already built (FVSA 1996, Bertonatti & Corcuera 2000, Fahey & Langhammer in press).
Roads constitute an important cause of native forest fragmentation and degradation, not only for their direct effect (edge effect, fragmentation and isolation of populations, and road kills) but also because they facilitate the process of colonization and invasion of lands to obtain squatters’ rights (Chebez & Hilgert in press). There are almost no areas in the ecoregion without road access. Soil erosion along poorly-designed and poorly-maintained dirt roads is also a cause of concern.
There are plans to develop major engineering work such as dredging and channelization in the Paraná-Paraguay waterway (Hidrovía), enhancing the transportation of goods from the heart of South America to the Atlantic Ocean, and vice-versa. Such plans have the potential of seriously affecting the natural resources of the region (Huszar et al. 1999). This large channel and navigation infrastructure, if implemented, will have a large indirect impact on biodiversity because it will create economic incentives for the expansion of large-scale agriculture and conversion of the last forest remnants in the ecoregion.
Unsustainable exploitation of the native forest
The unsustainable exploitation of the native forest through “conventional” or “traditional” logging has also degraded the forest remnants. Native forest exploitation has traditionally been conducted in a predatory and unsustainable manner (see Rice et al. 2001). It is well documented that conventional logging has severe impacts on biodiversity (Putz et al. 2000). In the Upper Paraná conventional logging of native forest has, as its most direct effect, the impoverishment of the forest and changes in forest structure and soil composition. It may also increase the dominance of some tree species and may reduce the natural regeneration of the forest (Mac Donagh et al. 2001).
Originally, only a few species of native trees (e.g., four in Misiones) were harvested for timber, but as these species became scarce, the number of species exploited has increased. Between 20 and 40 species are now harvested regularly (Laclau 1994). Native forests that have been exploited usually suffer a process of invasion by native bamboo species that fill the gaps and apparently preclude the natural regeneration of the forest. It is known that different bird communities are associated with forests in different successional stages; second growth forests contain more edge species and have lost primary forest species in relation to primary forests (Protomastro 2001). However, little is known about changes in species compositions in relation to different types and degrees of primary forest exploitation (see Mac Donagh et al. 2001). One of the main impediments to reversing this trend of unsustainable exploitation and consequent degradation of the forests is that there is insufficient scientific information on forest composition and structure, forest dynamics, and on the best ways to responsibly manage the forests.
There are laws that protect the native forest cover in all three countries and require management plans for native forest exploitation. However, these plans or laws are insufficient or are not effectively enforced. The situation of native forest exploitation is different in the three countries.
In Argentina the native forest is exploited only outside strictly protected areas. The Misiones provincial authority (Dirección de Bosques) requires a management plan to exploit the native forest, but these plans generally do not ensure the sustainable use of the forests because they are usually clearly non-sustainable and/or they are not well implemented as a result of lack law enforcement. Also, anecdotal evidence suggests that there is likely an important fraction of the timber that is illegally extracted and marketed.
In Paraguay, the native forest is effectively protected in some reserves or in areas of difficult accessibility (e.g., Cordillera San Rafael). However, most fragments of native forest are suffering a process of unsustainable, and in most cases illegal, exploitation, including forests within implemented national parks. Most of the illegally harvested wood is transported to the Brazilian markets, facilitated by the lack of controls, widespread corruption among public officials responsible for law enforcement, and the existence of several roads on the terrestrial border with Brazil.
In Brazil, the situation is very different due to the almost complete absence of remaining large primary forest remnants with valuable wood outside strictly protected areas. Most forest fragments outside these protected areas are small patches of secondary forests. Although prohibited by Brazil’s Forest Code, most privately-owned riparian forests have been clearcut. A 1990 Brazilian Presidential decree also prohibits any cutting of primary and secondary Atlantic Forest.
São Paulo, in Brazil, is the main market for the wood irresponsibly exploited in Paraguay and Argentina. Buenos Aires also receives an important portion of the timber extracted in Misiones. Local markets play only a minor role in the consumption of wood from this ecoregion.
Besides the extraction of timber for construction or furniture, the remaining patches of forest are under heavy pressure for the extraction of fuel wood. For example, in the state of Santa Catarina, Brazil, there are no oil or gas pipelines to supply energy. Fuel wood or charcoal (produced locally) is used by the majority of the rural people for heating, cooking, and drying food. The production of tobacco, one of the main products in Santa Catarina, requires large amounts of fuel wood that is obtained locally in the secondary forest remnants (Hodge et al. 1997). In Misiones, yerba mate is also dried with fuel wood obtained from secondary forests, which is becoming a scarce resource for yerba mate producers (S. Holz pers. com.).