Forests' Retreat: Page 9 Endangered Species Handbook

Forest

Forests' Retreat: Page 9

Until the 1970s, no one knew what the effects of clearcutting forests would be on various species of rainforest wildlife. The US government's Smithsonian Institution, with ornithologist Dr. Thomas Lovejoy supervising, conducted the first scientific studies of the effects of forest destruction in the Amazon on a wide range of wildlife. Blocks of interior forest of various sizes were inventoried by teams of biologists with mist nets and live animal traps. After each inventory was completed, the blocks were isolated by clearcutting the forests surrounding them. Then, after a period, they were inventoried again to discover the effects of clearcutting on the wildlife in the newly isolated forest patches. This type of research aims to discover how large reserves must be to preserve the diversity of ecosystems.

The results of Lovejoy's research in Amazonian primary forest indicated that small reserves of 2.5 acres or less lose a large percentage of their wildlife, and the larger the reserve, the fewer the number of species that disappear (Lovejoy et al. 1984). Certain species are dependent on large areas of primary, old-growth forest and are quick to disappear as soon as forests are disturbed or fragmented. Bird populations tended to decline in most reserve sizes, and species composition changed. In the smallest plot, 39 species of birds dwindled to 18 species after three years, and in the larger plot of 25 acres, 48 species declined to 38 (Lovejoy et al. 1984). The understory species were censused, as opposed to the canopy birds which seem less vulnerable to fragmentation of forest. Ecological dependencies caused some extinctions. For example, army ants thrive in large areas but disappear from smaller ones, and birds that feed on these ants, such as antbirds which are diverse and numerous in primary forests, disappeared within a short period from smaller plots (Lovejoy et al. 1984).

In another chain reaction, the White-lipped Peccary (Tayassu albirostris) proved to be a keystone forest species. It digs small waterholes to wallow in when ponds dry up, providing habitat for other wildlife. Peccaries travel in large groups seeking their diet of fruits, especially palm fruits, and act as seed dispersers. The key to their survival is territory size: a herd of 100 animals requires a territory of 97 square miles (Fragoso and Silvius 1995). They disappear from smaller forests causing the local extinction of frogs, who lay their eggs in these waterholes. In the Amazon study, four species of frogs disappeared from areas where peccaries had insufficient habitat to survive (Lovejoy et al. 1984).

Many other mammals are affected by forest fragmentation. Twenty species of mammals occupied a large, undisturbed forest plot, while only five were left in an isolated 25-acre-forest; a mere three mammal species remained in a 2.5-acre-forest (Lovejoy et al. 1984).

Theoretically, extinctions also can be caused when species have limited distributions which are destroyed by logging. A number of birds and mammals, including several newly discovered marmoset species in the upper Amazon forests, inhabit extremely restricted ranges of only a few square miles. Some species of primates will refuse to cross a road, such as a logging road, or an open clearing. Should a road be built in the middle of their tiny ranges, they would face extinction. Since tropical forests have not been thoroughly inventoried, the endemic species at risk most probably number in the tens of thousands.

Butterflies that live only in deep, virgin rainforest are so intolerant of fragmented forest that they disappear from areas less than 250 acres and, even there, survive only in the central core area (Laurance and Bierregaard 1997, Lovejoy et al. 1984). Forest butterflies, which exist in amazing diversity, are highly sensitive to the disappearance of their host plants, upon which they lay their eggs, and thrive in greatest number when vegetation is highly diverse. Some cannot tolerate the penetration of light into forests, and others require such large territories to feed that they disappear from small reserves, according to research by Keith Brown and Roger Hutchings (Laurance and Bierregaard 1997).

In small forest blocks, trees on the forest edge become vulnerable to the effects of wind and fire, fall in far greater numbers than those in the center and succumb to fires that spread from neighboring grasslands. Fires consumed large areas of rainforest in the Amazon during the late 1990s as a result of fragmentation. This was the first record of rainforest fires in this region. Storms blow down trees adjacent to the edges of fragmented forests and, over a period, will destroy the inner primary forest (Lovejoy et al. 1984).

Research on forest fragmentation is now taking place in Africa, Asia, Australia, the Indian Ocean islands and elsewhere in the world. Numerous scientific papers on the subject were gathered in a book entitled Tropical Forest Remnants. Ecology, Management, and Conservation of Fragmented Communities (Laurance and Bierregaard 1997). Many of these studies paint a grim picture of the effects of forest fragmentation on biodiversity.

Bats are important forest pollinators but are extremely vulnerable to extinction. They are rarely protected and often persecuted. The valuable Durian fruit of Asia is one such plant pollinated by a declining species of rainforest bat. Other food plants pollinated by bats include wild bananas, breadfruit, mangoes, guavas, avocados, almonds, cashews and cloves, according to Bat Conservation International, which is dedicated to changing the negative image of bats and preserving wild populations (see Organizations list for address).