Here’s the illuminating quote about secondary forests on page 5 of State of the World’s Forests 2005, from the UN Food and Agriculture Association (FAO):
Areas of secondary forest throughout the
tropics are increasing dramatically, and in many
tropical countries they now exceed areas covered
by primary forest. Most of these secondary
forests develop following the disturbance or
elimination of natural forests by slash-and-burn
practices, conversion to agricultural activities and
subsequent abandonment of lands or following
excessive logging operations that have reduced
the original forest to a non-commercial resource.
In both cases, seeds from surrounding trees have
led to eventual regeneration of the forest.
Although figures vary according to the
definition used, the extent of degraded forests
and secondary forests in tropical Africa,
America and Asia in 2002 was estimated at 245
million, 335 million and 270 million hectares,
respectively, for a total 850 million hectares
(ITTO, 2002). According to FAO (2001), the
reported loss of natural forests in the tropics
during the 1990s was approximately 15.2
million hectares annually, of which 90 percent
or more was converted to other land uses. These
estimates indicate that the potential future area
of secondary forests could be considerable.
That 850 million hectares of secondary and degraded tropical forest translates to 2.1 billion acres or 3.3 million square miles.
The 15.2 million hectares of primary tropical forest lost annually equals 37.3 million acres or 58,300 square miles.
The ratio is 55 to 1. For every acre of primary tropical forest being cleared, logged, or burned, some 55 acres of secondary tropical forest is growing back or can be nurtured back. How climate change is affecting those numbers remains to be seen.
The two citations are:
ITTO (International Tropical Timber Organization).
2002. ITTO guidelines for the restoration, management
and rehabilitation of degraded and secondary forests.
ITTO Policy Development Series No. 13. Yokohama,
Japan.
page 5:
The extent of forest degradation in the tropics is vast. According to estimates given in these
guidelines, some 350 million hectares of tropical forest land have been so severely damaged that
forests won’t grow back spontaneously, while a further 500 million hectares have forest cover that is
either degraded or has regrown after initial deforestation.
Such large areas of damaged forest and land are cause for concern, but they also represent a potential
resource of immense value. The ITTO guidelines for the restoration, management and rehabilitation of
degraded and secondary forests have been formulated to help communities realize that potential.
FAO. 2001. Global Forest Resources Assessment
2000 – Main report. FAO Forestry Paper No. 140.
Rome
While the FAO’s State of the World’s Forests 2005 emphasized secondary forests, the latest edition—State of the World’s Forests 2009—mentions secondary forests not at all.