4. Regulation services

Through plant-soil-atmosphere interactions, tropical forests have a major role in regulating atmospheric gases and therefore climate. Carbon emissions due to deforestation in the tropics were 810 Tg C year−<sup>1</sup> between 2000 and 2005 [30], in which Brazil and Indonesia were the first two contributing countries with an emission rate of 340 and 105 Tg C year−<sup>1</sup> , respectively. Soil carbon loss due to land use change in the tropical area was estimated to be 79 Pg CO2 during the past 150 years (1860–2101, averaged from three different models) [31].

Peat swamp forests in Southeast Asia are an important carbon stock due to their predominant wet soil condition. However, the need for more farmland has largely changed the peatlands into different agricultural uses such as rice fields and oil palm plantations. Hergoualc'h and Verchot [32] demonstrated a very clear change in greenhouse gases (CO2 + CH4 + N2O) budgets when original peatlands were converted to six different land use types including degraded forest, croplands and shrublands, rice fields, oil palm plantation, Acacia crassicarpa plantation, and Sago palm plantation. On average, the undisturbed peatlands are the strongest CH4 source, which, however, could be offset by the CO2 sink strength and thus remain the only net greenhouse gas sink of the magnitude of −1.3 ± 5.9 Mg CO2-Eq ha<sup>−</sup><sup>1</sup> year−<sup>1</sup> . The conversion of peatland into Acacia crassicarpa plantation turns the sink into the largest source of 72.0 ± 12.8 Mg CO2-Eq ha<sup>−</sup><sup>1</sup> year−<sup>1</sup> .

Coastal mangroves in many tropical countries have been destroyed and the land been used for aquafarming or other purposes like harbor construction. Kauffman et al. [33] showed an extremely high carbon emission accompanying the conversion of mangroves to shrimp ponds in the Dominican Republic. The carbon stocks of mangroves ranged from 706 to 1131 Mg C ha−<sup>1</sup> , while that in the abandoned shrimp ponds were only 95 Mg C ha−<sup>1</sup> . The estimated carbon emission of 2244–3799 Mg CO2-Eq ha<sup>−</sup><sup>1</sup> was among the largest carbon emission due to land use change [33].

potential food sources [23], tropical forests can provide enough food to maintain the human population of traditional habitants [24], reaching values up to US \$18.5 per hectare and year [25]. Fuelwood is also the main energy source for heating and cooking of millions of people in tropical countries. For example, in Mexico alone, 7 million of rural people depend on tropical forests [26]. Timber, usually of high quality and value, is among the most valued goods provided by tropical forests, sometimes being also the cause of the deforestation (often illegal) and land use change [27]. Similarly, traditional medicine from tropical communities is also providing new compounds for medicines, but at the same time can also cause local extinctions

4 Tropical Forests - The Challenges of Maintaining Ecosystem Services while Managing the Landscape

Among other goods, water is usually given from granted, but freshwater is a very valuable ecosystem service that comes mainly from higher elevation ecosystems. Ponette-González et al. [28] performed a meta-analysis of the effects of land use change on hydrological cycles of tropical high-elevation ecosystems. The types of land use change included the conversions from forest to grassland, agroforest to nonforest, nonforest to tree plantation, and recent glacier retreat. The deforestation did not lead to an expected substantial increase in downstream runoff in Latin America and the Caribbean and in Hawaii. On the other hand, Muñoz-Villers and McDonnell [29] compared the streamflow of three watersheds that have old-growth cloud forest, 20-year-old regenerated cloud forest, and heavily grazed pasture, respectively, in Mexico. The land use type of pasture produced 10% higher streamflow compared to the two forested catchments. Their results imply that a short period of 20 years of recovery from pasture to forest may be enough for the restoration of hydro-

Through plant-soil-atmosphere interactions, tropical forests have a major role in regulating atmospheric gases and therefore climate. Carbon emissions due to deforestation in the tropics were 810 Tg C year−<sup>1</sup> between 2000 and 2005 [30], in which Brazil and Indonesia were the first

carbon loss due to land use change in the tropical area was estimated to be 79 Pg CO2 during

Peat swamp forests in Southeast Asia are an important carbon stock due to their predominant wet soil condition. However, the need for more farmland has largely changed the peatlands into different agricultural uses such as rice fields and oil palm plantations. Hergoualc'h and Verchot [32] demonstrated a very clear change in greenhouse gases (CO2 + CH4 + N2O) budgets when original peatlands were converted to six different land use types including degraded forest, croplands and shrublands, rice fields, oil palm plantation, Acacia crassicarpa plantation, and Sago palm plantation. On average, the undisturbed peatlands are the strongest CH4 source, which, however, could be offset by the CO2 sink strength and thus remain the only net greenhouse gas sink of the magnitude of −1.3 ± 5.9 Mg CO2-Eq ha<sup>−</sup><sup>1</sup> year−<sup>1</sup>

conversion of peatland into Acacia crassicarpa plantation turns the sink into the largest source

, respectively. Soil

. The

two contributing countries with an emission rate of 340 and 105 Tg C year−<sup>1</sup>

the past 150 years (1860–2101, averaged from three different models) [31].

.

if their harvest is not controlled [25].

logical conditions.

4. Regulation services

of 72.0 ± 12.8 Mg CO2-Eq ha<sup>−</sup><sup>1</sup> year−<sup>1</sup>

Land use change in tropical forests can also have indirect effects of the capacity of the ecosystems to regulate processes in water ecosystems. For example, land use change in a tropical watershed could change the decomposition rate of organic matter in tropical rivers [34].

Tropical forests also mitigate extreme weather. Structural complexity [35], together with other factors such as microtopography and soil features, modulates the impacts of extreme events [36]. In a model simulation of the precipitation regime under combined factors of land use change (transformation of rain forests to pasture) and different levels of soil water availability in the Amazonian rain forests, Bagley et al. [37] showed a clear reduction in precipitation and increase in drought degree under deforestation scenarios.

Tropical forests can also regulate air quality. Changes in air quality and atmospheric chemistry often arise when land use type has changed because the land-atmosphere fluxes of material and energy are to a certain extent vegetation-specific processes (e.g., see [38]). For example, isoprene is a biogenic volatile organic compound that emits naturally from forest vegetation. By deforestation, the emission of isoprene will decrease and the subsequent photochemical process of ozone formation will also decrease, leading to a decreased ozone deposition in the Amazonian rainforests [39]. On the other hand, the agricultural use of the deforested area has been shown to emit more NOx to the atmosphere, mostly due to the higher N-fertilizer application.

In some tropical region, slash-and-burn is still a predominant method to create farmland [40]. The emissions from fires and smokes often cause regional problems of air quality. Marlier et al. [41] pointed out an important finding that ca. 80% of 2005–2009 fire emissions from Sumatra were related to degradation or land use maintenance. The fire emissions from land use conversion thus may have longer-term effect on the air quality.
