Vital Forest Graphics

Forests are a key source

Forests provide numerous ecological services. They regulate hydrological cycles, stabilize natural landscapes and protect soils and water courses. The level of these services depends on the location, type and use of forests

would result, according to projections, in regional decreases of precipitation and evaporation, potentially leading to sustained desertification. Already deforestation is causing fundamental changes in the Amazon climate and hydrology cycle, with possible implica- tions for regional ecosystem dynamics and the global climate (Chagnon and Bras 2005). Forests can regulate groundwater lev- els and increase drainage of soils where the water table is close to the surface. If there are salts in the upper soil lay- ers, then removal of forests can result in raised groundwater levels and the movement of salts into the rooting zone of plants (FAO 2008c). In the Murray- Darling Basin in Australia, deforestation and irrigation are the main causes of land salinization affecting some 300 000 hectares (Kabat et al. 2004). Forests can also increase water yields, particularly in tropical cloud forests occurring at relatively high elevations

where humidity levels can reach 100 per cent. Large amounts of water are deposited directly onto the vegetation, and excess water is more or less con- stantly dripping from the leaves to the ground below. The year-round supply of unpol- luted water from cloud forests is a vital resource in many regions. For example, the cloud forests of La Tigra National Park in Honduras provide more than 40 per cent of the water supply for the capital city, Tegucigalpa and its 850 000 people. Other capitals where cloud for- ests augment water supplies include Quito in Ecuador – a city of 1.3 million people – and Mexico City with its 20 million people (Bubb et al. 2004). Forests also contribute to the mainte- nance of good water quality. They mini- mize soil erosionandmitigateflashwater flows that cause erosion downstream. In turn this reduces levels of sediment in water bodies such as wetlands, ponds and lakes, streams and rivers. Forests also trap or filter some water pollutants. As water quality levels around the world deteriorate and the cost of filtration facilities remains high, several munici- palities have decided to invest resources in the conservation of water catchment areas, including protected forests. Approximately 9 million people in New York City and nearby areas enjoy access to clean, inexpensive drinking water. About 90 per cent of that water is drawn from the Catskill/Delaware watershed where the abundant for- est reserves, as well as soil with ade- quate carbon levels, provides excel- lent conditions for natural filtration (WRI 2008a).

< orests interact closely with the water cycle. Trees act like pumps. They help water percolate into the soil, the storehouse of water, during rainy periods and pump out water into the atmosphere, through evapo-transpir- ation, in dry periods. In the process forests help keep the hydrological cycle “alive”. Deforestation of the entire Ama- zon basin – a catastrophic scenario –

The world is losing its mangroves

A r c t i c Oc e a n

Asia

North and Central America

P a c i fi c Oc e a n

Africa

A t l a n t i c Oc e a n

South America

I nd i a n Oc e a n

P a c i fi c Oc e a n

1980

Oceania

Million ha

2005

0 2 4 6 8

Loss

Sources: UNEP World Conservation Monitoring Centre; FAO 2007.

32 VITAL FOREST GRAPHICS