Forest degradation and recovery in a miombo woodland landscape in Zambia: 22 years of observations on permanent sample plots

Abstract

Because dry tropical forests cover 40% of tropical forest area and contain considerable biomass and carbon stocks, deforestation and forest degradation of these forests have global significance. However, in most developing countries with dry forests there is no quantitative information on past trends of forest degradation so that the development of historical reference levels is virtually impossible. This study assessed impacts of forest practices on forest degradation from 1990 to 2012 using data from destructive tree sampling and permanent sample plots in a miombo woodland landscape in central Zambia. Aboveground live wood biomass was estimated using allometric equations developed from 113 felled trees. Resprouting was a major source of regeneration on clear-cut subplots and the rate of aboveground wood biomass accumulation was much higher on re-growth sites than on old-growth sites. Changes in aboveground live wood biomass on uncut subplots were linked to biomass loss due to fire, harvesting and conversion to crop cultivation on the one hand and biomass increment due to growth of remaining trees on the other hand. Forest degradation was estimated to cause aboveground wood biomass loss of 0.3tha−1year−1 on the least impacted site to 4.0tha−1year−1 on the most impacted site. Control of fire and harvesting for charcoal production is recommended if miombo woodland is to be managed for biomass and carbon storage and sequestration. The study also found that negative trends in woody biomass accumulation rate and standing stocks are good indicators of forest degradation while positive trends in species diversity indices and standing wood biomass are useful indicators of forest recovery. However, the application of these indicators requires repeated inventories at permanent sample plots to establish reference levels against which changes in these indicator variables can be compared.