Forests exist on almost every part of the globe’s land. Forest complexity causes scientists to classify forests in more than one way, by location, the type of wood they produce, or their age. Sometimes these three classifications interconnect. Ecology uses a forest classification system based on climate, determined by precipitation and temperature. This classification system correlates to where on the globe the forests grow. Each of the three main classifications contain subcategories based on more detailed climatic conditions: tropical, subtropical, Mediterranean, temperate, coniferous, boreal, and montane (cloud forest). Some of these groups contain additional subtypes.
Forests also belong to categories according to the types of trees that predominate; for example, coniferous, mixed broadleaf, aspen, oak, or mangrove forest. Finally, forest age determines characteristics of this habitat, so forests may be identified as immature, secondary, primary, or old-growth.
The World Resources Institute’s Global Forest Watch program states on its Web site that the Earth has lost almost 50 percent of its forests in the last 8,000 years, the same time period in which civilization developed. The highest rates of today’s forest loss occur in Africa and South America; every five years Africa and South America lose 3.2 and 2.5 percent, respectively. These numbers can be deceptive because in some African nations the combined grassland and forest loss tops a rate of 10 percent annually. Grasslands have in fact undergone more drastic reductions than forests in some places, particularly Africa. If these current disappearance rates continue, many countries will lose all their forests within a few decades.
Forest loss has a devastating impact on biodiversity because forests, especially the tropical rain forests near the equator, make a great contribution to the world’s plant and animal diversity. These tropical rain forests account for at least half of all the Earth’s biodiversity even though they cover only about 2 percent of the Earth’s surface. These forests have also become the most threatened by deforestation.
Deforestation refers to any removal of trees without replacement, and it threatens forests in direct and indirect ways. Direct deforestation comes from four main causes: clearing of tropical forests for crops, livestock, and timber; clearing of temperate deciduous forests for timber, crops, and urban development; clearing of evergreen coniferous forests for timber; and conversion of forests to monoculture (vineyards, commercial tree farms). Illegal logging makes up part of the deforestation problem, much as exotic animal poaching decimates protected wildlife populations. Logging is the process of cutting and removing logs from the forest.
Indirect causes affect forests similarly to how they affect animal species. Three important indirect threats to forests are roads, climate change, and habitat fragmentation. Indirectly, off-road vehicles used to build roads damage seedlings and new growth, increase soil erosion, and fragment habitat. Climate change affects environment by shifting the optimal temperature range in habitats. Wildlife can migrate to a different elevation or latitude to find the ideal temperature. Trees, however, do not possess the luxury of moving; entire species can slowly die as a result of continuous temperature changes. Climate change also makes conditions suitable for invasive species to enter a habitat and may additionally open the door to increased incidence of disease or pest infestation. Habitat fragmentation from urban growth or agriculture reduces the ability of tree populations to propagate and lessens their genetic diversity.
All of these effects caused the world to lose 3 percent of its forests in a 15-year period from 1990 to 2005, a rate of 0.2 percent a year. At present, the world’s forested areas continue to decrease but the disappearance rate has been slowing; Europe and North America have now reversed centuries of forest loss. The most threatened forests reside in Africa, Latin America, and the Caribbean. Fortunately, national governments in Africa have started cooperative programs for forest conservation, and individual nations have adapted new forest policies and forest laws. New forestry management programs help save forests to some extent, but fires, regional conflicts, and legal and illegal industries have continued the deforestation crisis. The table on the next page provides details on today’s major threats to forests and their primary location, though all of these threats can be found to some degree in almost every part of the world.
Many people may assume forest fires pose the greatest threat to forests. In the United States, the Smokey Bear campaign began in the 1940s to remind people of the dangers of forest fires. Illegal campsite fires, arson, and blazes cause damage each year in dry areas of the United States that have dense human populations. But fires in general, natural or human-caused, do not threaten the overall population of forests, and fire management makes up an important sector of overall forest management. Fires actually contribute to the health of forests and plant communities by
• enhancing nutrient recycling
• allowing for small plants to spread
• regulating the succession of new tree growth
• developing new habitat
• reducing biomass buildup
• enriching soils
• reducing parasites and disease-causing organisms
In North America and Europe, forestry programs work in conjunction with the government. The success of slowing forest loss in these places varies, however. Forest area stabilized in Canada and the United States in the mid-2000s, but forest area continues to shrink in Mexico, although fortunately the rate has slowed. In Europe, lands set aside for protected forests have increased slightly in the past five to 10 years. Asia and the Pacific have halted an alarming trend of forest loss that took place during the past 30 years, and in these places forested land may now be increasing in area. However, part of East Asia’s statistics may be misleading. China has planted large forest plantations, and while these plantations add to the total amount of land that forests cover, such monocultures do little to improve biodiversity.
Trees in the forest interact with other living things in ecosystems just as plants, animals, and microbes do. An imbalanced ecosystem can therefore harm trees. For example, if a predator were to disappear, other animals may grow to higher population numbers and graze all the young seedlings needed to regenerate the forest in 100 years. An alteration to a plant community in the forest likely alters the birds and reptiles living there, which can affect populations of tree pests and parasites. Trees weakened by a parasite become more vulnerable to infection by disease-causing microbes.
Climate change holds paramount importance in forest health because it affects seasons, normal temperature ranges, and tree reproduction. Climate change has also influenced the world’s availability of clean water. Like all living things, trees cannot survive long without water, but equally important, trees play a crucial role in the Earth’s water cycle.
Source of Information : Green Technology Conservation Protecting Our Plant Resources