Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 97

The annual removal is the net volume of growing stock trees removed from the inventory during a specified year by harvesting, cultural operations, such as, timber stand improvement, land clearing, and removal of trees killed or damaged by natural causes (natural losses), e.g. fire, wind blow, insects and diseases.

An example is clipping (i.e., harvesting aboveground plant biomass) which is common in agriculture and for bioenergy production.

Forest ecosystems contain large amounts of nutrients in woody biomass that may exist either as standing material, on the soil surface, or within the soil profile. Logs removed during timber harvesting remove considerable amounts of nutrients, and the disturbance caused by the process may sometime later, if not immediately, affect the amount of nutrients left on the site due to increased soil erosion, mineralization, and leaching. Thus, intensive harvesting, which removes a greater proportion of the forest biomass than conventional harvesting and the associated nutrients, may cause a decline in forest productivity.

Separately, warming and clipping alter soil and plant properties in either similar or contrasting fashions. For example, in grassland areas, both warming and clipping were observed to increase soil temperature and decrease soil moisture. In contrast, warming increased net primary productivity and plant carbon input to soil, but clipping reduced both. Moreover, warming led to an extended growing season length, while clipping caused compensatory root growth and stimulated exudation of carbon. The interactive effects of warming and clipping on these soil and plant properties rely on the mechanisms governing each single factor and the degree to which these factors interact. The responses of soil microbial communities to two or more factors are even less predictable than those of soil and plant properties, owing to their extremely high diversity.

See also: Biomass.