In wet savannas fire can be beneficial, but only when the timing is correct. If a fire occurs before the start of the rainy season, the trees are protected (see above) and safe sprouting of grasses is obtained. The centers of tussocks of grasses supporting the meristems for regrowth are protected from the heat of the fire by an insulat-
ing layer of old leaves. If burning occurs too early in the dry season, subsequent new growth uses up water reserves and dies before the rainy season sets in, and the whole plant may dry out totally. If burning is done too late in the dry season, new
Table 10.16 Comparison of adjacent hectares of low-tree and scrub cerrado of central Brazil periodically burned each 2-3 years and not burned for over 20 years, respectively. (Density of stems is larger than density of individuals since some individuals produce more than one stem.) (G. Eiten and R. H. R. Sambuichi, pers. comm.)
Not burned Burned
Stems (number ha-1) 6677 1765
Individuals (number ha-1) 5788 1663
Species 92 57
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.