About this site
Providing tropical forest news, statistics, photos, and information, rainforests.mongabay.com is the world's most popular rainforest site. [more]
Weekly Newsletter
Mongabay will never distribute your email address or send spam.
Share
Anak Krakatau (son of Krakatoa) eruption in 1992. (Photo by N. Butler)
NATURAL FORCES
Throughout their existence, tropical rainforests have been affected by natural forces like fire, drought, and storms. These events occur on a random basis and can damage large stretches of rainforest. However, the damage caused by these natural occurrences is generally different from that caused by human activities; namely in that the forest loss is not complete and parts of the ecosystem continue to function. From the surviving remnants of the ecosystem, the forest can usually rapidly regenerate. Within a few years, the forest diversity can return to or exceed the diversity that existed before the disturbance. Some studies have suggested that these periodic occurrences are an important ingredient to a forest's diversity. Without these events, scientists believe, some forests cannot reach their fully dynamic state. Researches have found that forest turnover rates may be as short as 65-135 years.
Natural forest fires occur in rainforests, despite their humid nature. Generally, when forest burns in smaller fires, ground vegetation, shrubbery, saplings, and smaller trees are eradicated, while the larger canopy species are spared. The fire has the effect of clearing the forest floor and weaker trees, thus allowing new growth.
A forest, stressed by drought or some other factor, is most susceptible to fire, usually sparked by lightening or small human fires that escape neighboring agricultural zones and burn out of control. For example, the great Bornean fires of 1982-83, destroyed more than 9 million acres (3.6 million hectares) of forest (2.81 million ha of dipterocarp forest) in Kalimantan (Indonesia). These fires, like the wildfires of 1997-98, was ignited by land-clearers setting fires in and around forest heavily degraded by logging under el Niño-induced drought conditions. Research has recently found that over half the Amazon rainforest is at risk of burning during extreme droughts, like the one that struck from July—November in 2005.
VOLCANIC ACTIVITY
Volcanic eruptions and subsequent lava flows sometimes burn large tracts of forest, while the gases released from the activity can kill wildlife. An interesting phenomenon, documented by a National Geographic expedition in Zaire's (now the Democratic Republic of Congo) Virunga National Park, and undoubtedly in other areas with volcanic activity, involves carbon dioxide, a gas that is poisonous in high concentrations. Since carbon dioxide is heavier than air and tends to hug the ground, it forms deadly sink areas when released via volcanic vents. In these areas, green grass grows vigorously due to the abundance of C02 and the lack of herbivores, which are attracted to the untouched grass, but are quickly asphyxiated by the toxic gas. Other animals come, including predators attracted to the dead animals, but they, too, perish. The sink becomes a death trap. However, these carbon dioxide sinks are rare, so they do not pose a major threat to most animals. In 1999, lava flows in Cameroon destroyed sections of virgin rainforest, while there is evidence of large-scale lava damage in the rainforests of Costa Rica.
Drought can affect forests by weakening the system to the point where it is more susceptible to other events like fire and disease. Drought is often partially induced by human activities like deforestation, but it is also a natural occurrence, like El Niño, which periodically causes drought in Asian and American tropical rainforests. El Niño is usually named as one of the influences behind the great Bornean fires of 1982-1983 and 1997-1998.
Drought initially weakens canopy plants by reduction of local humidity and rainfall. If the drought is long enough, the leaf litter dries out, killing off decomposers and reducing the effectiveness of nutrient recycling within the system as a whole.
Drought can bring benefits to the forest. Studies have shown that El Niño may enhance fruit production in forests affected by seasonal differences in rainfall. El Niño events produce dry sunny years in Central America, northern South America, the Amazon, Malesia (Indonesia and Malaysia), New Guinea, parts of equatorial west Africa, and India. The reduced cloudiness is beneficial to fruit production in that higher levels of photosynthetically active radiation (PAR) reach plants. El Niño and high levels of PAR have been associated with mast fruiting.
However it is a different case in the years following El Niño events since dry, sunny El Niño events tend to alternate with wet, cloudy years in the tropics. In addition, high fruit production consumes stored reserves for plants, limiting the next reproductive event.
Some scientists are concerned that climate change could worsen droughts in the Amazon. In 2005, the accumulation of warm waters in the tropical Atlantic helped fuel a record hurricane season while reducing the availability of moisture to the Amazon basin. These conditions could worsen as global temperatures increase. Research published in December 2005 suggests that warmer sea temperatures in the tropical Atlantic are likely to become increasingly prevalent as currents normally carrying warm water from equatorial regions towards the Arctic weaken. One simulation by researchers at the University of Illinois, Urbana-Champaign, found that 45 percent chance that existing water currents in the North Atlantic Ocean could shut down by the end of the century if nothing is done to slow greenhouse gas emissions. Such a collapse of the so-called "Atlantic heat conveyor belt" could plunge parts of Europe into significantly colder winters while exacerbating drought conditions in equatorial Africa. Back in the Amazon, the usually moist rainforest could become drier and more susceptible to forest fires.
Deforestation emissions should be shared between producer and consumer, argues study
(11/19/2009) Under the Kyoto Protocol the nation that produces carbon emission takes responsibility for them, but what about when the country is producing carbon-intensive goods for consumer demand beyond its borders? For example while China is now the world's highest carbon emitter, 50 percent of its growth over the last year was due to producing goods for wealthy countries like the EU and the United States which have, in a sense, outsourced their manufacturing emissions to China. A new study in Environmental Research Letters presents a possible model for making certain that both producer and consumer share responsibility for emissions in an area so far neglected by studies of this kind: deforestation and land-use change.
Oil palm workers still below poverty line, despite Minister's statements
(11/19/2009) On October 19th, Plantation Industries and Commodities Minister Tan Sri Bernard Dompok told parliament that oil palm harvesters and rubber tappers are living above Malaysia's national poverty line, according to a story in the Malaysian Insider. But now representatives of the workers are saying Dompok lied.
Indonesian government suspends license of logging company in controversial forest area
(11/19/2009) The Indonesian government today temporarily suspended the license of Asia Pacific Resources International Holding Limited (APRIL) for developing an area of forest and peatland in Sumatra pending a review of the company's permits, reports Greenpeace.
Pygmy hippo shot and killed in…Australia
(11/17/2009) Hunters going after pigs in Australia's Northwest Territories got a big surprise when they shot an animal they mistook for a pig, only to find out it was a pygmy hippopotamus, reports the Northwest Territory News.
