Fine root mass, distribution and regeneration in disturbed primary forests and secondary forests of the moist tropics

Abstract

In most tropical countries, rainforests are encroached by the local population and converted into agricultural land or pasture at constantly high rates. An increasing portion of this new agricultural land is abandoned within a few years and left for succession by woody plants. In many regions, already a considerable fraction of the forested area is covered by secondary forests formed by rapidly growing, short-lived pioneer tree species. In the Lore Lindu National Park on Sulawesi (Indonesia), like in other tropical countries, many of the remaining patches of protected primary forest are also offended at their margins by neighbouring villagers, who practise selective logging or local planting of crops inside the forest. Thus, disturbed old-growth forest and regrowing secondary forest after clearcut represent woody vegetation types, which are of rapidly growing importance throughout the tropics. Considerable research has focused on the effects of disturbance — natural as well as human-induced — on above-ground vegetation in primary forests, and on leaf and canopy characteristics of secondary as compared to primary forest trees. Only a few studies, however, have addressed the effects of disturbance and forest conversion on the below-ground compartment in wet tropical forests. This review surveys the literature on fine root biomass (roots < 2 mm) and its distribution and activity in disturbed old-growth and secondary tropical moist forests and compares the results with non-disturbed old-growth forests. Particular attention is being paid to the relationship between disturbance intensity, above-ground forest structure and fine root system size and structure. Secondly, we focus on the age-dependence of fine root biomass in regrowing secondary forests and the time required for fine root biomass recovery after clearcut. The results are interpreted with respect to carbon storage in the root system of tropical moist forests and its response to disturbance and conversion.