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Deciduous Forest
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Monday, 5 March 2007
The Human Impact on Temperate Deciduous Forests
Deforestation and Its Consequences:
Deforestation in temperate deciduous forests has obviously had a large impact on the species composition of the zonobiome. However, the adverse effects of deforestation and logging are far graver than would be expected solely based on the amount of land lost to agricultural purposes. This is because agriculture and grazing require a relatively flat grassland, which interrupts the continuous distribution of the deciduous forest.

These sparse areas of forest vegetation, in which humans live side-by-side with the forest, also contain many invasive species of plant life. Such alien plants have been introduced by humans, intentionally or otherwise, severely altering the natural pattern of the forest vegetation. These factors, taken as a whole, dramatically increase the prevalence of fire (a typically periodic event in temperature deciduous forests) in areas already lacking a high forest density. Thus, fires, while typically rejuvenating to the ecosystem as a whole, are now occurring so frequently that they pose a threat to many of the forest?s remaining animal species.

Centris Bees: A Genus in Danger
A notable example of a type of animal whose distribution has been hindered by the deforestation and its subsequent increase in fire frequency are bees of the genus Centris, who utterly depend on the forest and its resources for their survival. Aside from the pollen and nectar they must acquire from flowering plants in the forest, bees have an increased reliance on the structure and composition of the forest to maintain optimal survival conditions. That is, Centris bees create nests in deadwood portions of tree holes and in protected sites near the ground, both of which are destroyed by frequent fires. Additionally, fires also scorch oil-producing plants, which female bees use to maintain the young cells growing in their nests. Excessive fires decrease the amount of oil produced by these plants, limiting the ability of the bees to offer sustenance to their young.

Thus, as a whole, the increased frequency of fires due to deforestation has had drastic consequences on the distribution of Centris bees, whose populations over the past 2 decades have declined by almost 90% in temperate deciduous forests.

Alien Species: A Threat to Forest Diversity
In addition to changing the distribution of the vegetation in temperate deciduous forests, humans have further impacted these ecosystems by introducing alien species, both accidentally and intentionally.

African Honey Bees:
Over the last 2 decades, Mayans in the Yucatan region have imported the aggressive African honey bees as a substitute to the native stingless bees. The African bees produce higher quantities of quality honey, making them a more valuable resource to residents of this region who invest in the honey market.

However, the introduction of a new species has not been without its costs. As a result, there has been a breakdown in the diversity of stingless bees, to a point where they are now rare in the Yucatan, that correlates directly to the presence of the African honey bees. The breakdown of stingless bee populations has been caused by the aggressive nature of the African bees, who attack the passive native bees, thus lowering their diversity.

Red Fire Ants:
On the other hand, some alien species are introduced into foreign environments unintentionally, as is the case with the red imported fire ant, Solenopsis invicta. Over the last 60 years, this species of ants has increased dramatically in North America. However, this has come at a cost, as the presence of fire ants has led to a decreased diversity of other species of ants. Moreover, in the presence of the fire ants, the co-occurrence of many ant species has been random. This is because the invasive ants, foreign to their new habitat, fail to acknowledge the domains of other ant species. Instead, they inhabit land randomly, leading to aggressive behavior between ants that would otherwise not have occurred.

The presence of invasive species can drastically affect the species composition of native plants and animals, leading to an imbalance in the native species distribution as the indigenous flora and fauna greatly decreased in diversity.

Posted by planet/bruinsavannahs at 12:01 AM PST
Updated: Thursday, 15 March 2007 12:32 AM PDT
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