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South African Indigenous Forest: Its Response to Late 20th-Century Environmental Change
Midgley, J.J. and Seydack, A. 2006. No adverse signs of the effect of environmental change on tree biomass in the Knysna forest during the 1990s. South African Journal of Science 102: 96-97.

The authors note that "present and predicted future impacts of global environmental change on intact forests are both alarming and contentious," and that "some local models have predicted the demise [our italics] of South Africa's only significant extent of indigenous forest, the Knysna forest, by 2050," as reported by Midgley et al. (2001).

What was done
In a study designed to see how bad things had become by the end of the 20th century, Midgley and Seydack measured and analyzed the growth of all trees greater than 10 cm in diameter at breast height in 108 0.04-ha plots distributed throughout an unharvested nature reserve within the Knysna forest over the period 1991-2001.

What was learned
Following a protocol that provided what they say is "probably an under-estimate," the two researchers determined that "net basal area and aboveground biomass increased over the 10-year study period by 2% and there was a 1.2% increase in stem numbers, distributed almost equally amongst all size-classes."

What it means
Because of the particular nature of the Knysna forest, Midgley and Seydack say that "over relatively short periods such as our decade, the aboveground biomass of this forest is more sensitive to negative/stressful conditions that would increase mortality, than to factors which may increase growth." Despite this, however, and as reported above, they found that "biomass increased." And because "precipitation over the period 1991-2001 was some 5% less than the long-term average," they concluded that the observed increase in growth rate "may have been the effect of the increase in global atmospheric carbon dioxide."

Midgley, G.F., Rutherford, M. and Bond, W.J. 2001. The Heat is On: Impacts of Global Change on Plant Diversity in South Africa. National Botanical Institute, Cape Town, South Africa.

Reviewed 24 January 2007