Environmental Engineering Reference
In-Depth Information
remote sensing lumps natural forests with the plantations of introduced species
(eucalyptus, acacia, teak, rubber trees, pines), whose area has been expanding since
the early 1990s.
Too many countries are still clearing their forests at an unacceptable pace, but
the worldwide numbers have been improving. Global rates of deforestation rose
from 12 Mha/year between 1950 and 1980 to 15 Mha/year during the 1980s and
to about 16 Mha/year during the 1990s before they declined to around 13 Mha/
year between 2000 and 2010 (FAO 2011g). During that decade primary forests
decreased by 40 Mha, but thanks to the expanding reforestation the net annual
global loss fell from 8.3 Mha/year during the 1990s to 5.2 Mha/year between 2000
and 2010 (FAO 2011g). An important factor contributing to these diminishing losses
has been the growing protection of forests. Nearly 8% of all (FAO-dei ned) forests
now falls within the more strictly protected areas (the International Union for Con-
servation of Nature management categories I-IV), and the total rises to 13.5% when
the less strictly protected categories are included (Schmitt et al. 2009). Protected
shares range from about 3% of all temperate freshwater swamp forests to 28% for
temperate broadleaf evergreens, and 9%-18% for most tropical forests.
What these countervailing deforestation-reforestation trends mean in terms of
forests as sources or sinks of carbon remains uncertain. Between 1990 and 2005
the U.S. forest sector sequestered annually about 160 Mt C, about half of it in living
and dead trees and a quarter in wood products in landi lls (Woodbury, Smith, and
Heath 2007). Better management and expansion of European and Russian forests
have made them net sinks on the order of 300-600 Mt C/year (Nabuurs et al. 2003;
Potter et al. 2005; Beer et al. 2006). The latest value for the European forests as a
sink is about 75 g C/m
2
a year, with about 30% of that total sequestered in forest
soils and the rest added to phytomass increments (Luyssaert et al. 2009). Chinese
and Japanese forests have been also net sinks (Pan et al. 2004; Fang et al. 2005).
Piao et al. (2009) concluded that China's forests (above all in the south) store annu-
ally 190-260 Mt C.
Amazonia was seen as either a large net source of carbon (-3 Gt C/year) or a
major sink sequestering as much as 1.7 Gt C/year (Ometto et al. 2005), but a study
of vertical proi les of atmospheric CO
2
found that (after subtracting carbon emis-
sions from land use changes) tropical ecosystems may currently be strong carbon
sinks (Stephens et al. 2007). According to Lewis et al. (2009) during the recent
decades this sink averaged 1.3 Gt C/year. And Harris et al. (2012) concluded that
between 2000 and 2005 gross carbon emission from tropical deforestation averaged
about 0.8 Gt C, only 25-50% of previous estimates.
