Growth and mortality patterns before and after logging

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In the frame work of the STREK project, growth and mortality rates were analysed in both primary forest and after interventions such as logging or liberation thinning in logged-over forest. Dipterocarps, the dominant family in the upper storey and the major commercial species, were the particular focus. Before logging, the annual increment is a few millimetres per year and depends on the diameter class, linked to the social status in the stand. Dipterocarps grow faster than many other species and the stand density influences growth. The denser the stand, the higher the proportion of trees with negative or nil growth with an associated high probability of dying. After logging, growth and mortality were clearly influenced by the degree of canopy opening related to logging intensity. The data analysis therefore took into account different levels of logging intensity. A spatial approach using GIS showed that only a part of the stand suffered any harvesting impact. Two years after logging, the balance between growth, recruitment and mortality, showed no significant difference to the control plots. This suggests that the forest is not yet in a reconstitution phase but in a recovery process. Overall, the growth enhancement induced by canopy opening is balanced by a higher mortality. In the logged over areas, growth, after the silvicultural treatments, was enhanced by an average of 50%. The long-term effect of these treatments will have to be assessed over an extended period.

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