Environmental Engineering Reference
In-Depth Information
and even any temporarily unstocked land that is expected to regenerate! As for the
specii c composition, bamboo and palms are included if their groves meet the basic
criteria, as are those plantations whose trees are used primarily for forestry or pro-
tection: as a result, both rubber and cork oak “forests” are in. Moreover, the total
also subsumes forest roads, i rebreaks, and “other small open areas.” Obviously,
increasing the canopy cover requirement to more forestlike rates of 25%-35%
makes a large difference, and the closed-canopy forest (100% coverage when seen
from above) becomes an even smaller fraction of that total. In addition, some his-
torical reconstructions and modern statistics combine a wide range of ecosystems
with trees under a sweeping category of “forest and woodland.”
The FAO's latest Global Forest Resources Assessment put the total forested are
at just over 4 G ha, or 31% of all continental surfaces (FAO 2011g). National
coverage varies widely, ranging from ten countries with no forest and 54 with for-
ested areas smaller than 10% of their territory to forest-rich Brazil, Canada, and
Russia. Primary forests (composed of native species with no obvious signs of human
activities) make up 36% of the global total, 57% are other naturally regenerated
forests, and 7% are tree plantations; the total phytomass storage was estimated at
289 Gt C. Comparisons with the end-of-the-century assessment indicate a relatively
small but absolutely appreciable gain of nearly 150 Mha (FAO 2001, 2011g).
In contrast, the 2000 total of 3.96 Gha (95% natural growth and 5% forest
plantations) was more than 500 Mha higher than the aggregate of 3.442 Gha
reported in 1990 (FAO 2001). An increase of just over 15% in ten years is unthink-
able, and indeed, it did not take place: the higher total is mostly the result of a new
uniform forest dei nition. The FAO had previously used canopy thresholds of 10%
for forests in low-income nations and 20% for those in industrialized nations, while
the 2000 assessment used only a single 10% threshold. This change made the great-
est difference in Kenya, where the increase was from 1.305 Mha to 18.027 Mha (a
nearly 14-fold jump) and Australia: the continent's forested area nearly quadrupled,
from about 40 Mha in 1990 to more than 157 Mha in the year 2000. The two
earlier FAO assessments had totals only slightly different from the 1990 value of
3.442 Gha: 3.779 Gha in 1963 and 3.650 Gha in 1947, while the i rst attempt at
assessing global forest resources, prepared by the U.S. Forest Service, ended up with
3.031 Gha for the early 1920s (Zon and Sparhawk 1923).
These comparisons would indicate that the global extent of forests was roughly
a third larger in 2010 than in 1920, a counterintuitive i nding given the intervening
decades of large-scale deforestation. But such a conclusion would be wrong. As
Mather (2005) stresses, it remains impossible to compile any reliable historical series
