Impact of season, stem diameter and intensity of debarking on survival and bark re-growth pattern of medicinal tree species, Benin, West Africa

Abstract

Bark is a greatly coveted non-timber forest product (NTFP). Its overexploitation from medicinal tree species threatens an essential source of medication for rural populations. Despite the relevance of bark, not much information is available on the ecological impact of bark harvesting. In Benin, West Africa, we investigated how various harvesting techniques affect the bark re-growth of 12 tree species and the survival of debarked trees. Trees were debarked following a combination of three factors: (i) season of bark harvesting (dry or rainy season), (ii) size class of the tree (three stem diameter classes) and (iii) intensity of debarking (seven different percentages of trunk circumference debarked). Measurements of edge growth and survival were taken every 6 months during 2 years. Ring-barking (100% of trunk circumference debarked) did not allow the sustainable exploitation of any species, while all trees with 75% of debarked circumference remained alive and produced edge growth. Whatever the bark harvesting technique, 5 out of the 12 species had a bark recovery rate below 1 cm/year, rendering the wound closure very unlikely. On the other hand, five species showed good to very good bark recovery rates (>7 cm/year) and for these species the combination of debarking factors (season, dbh and intensity) allowing the highest edge growth was determined. This experimental bark stripping revealed the complexities involved in decision-making for sustainable tree management. Studying the patterns of bark recovery rates provides a relevant tool to assess for each species the delay for achieving closure of a specific wound area.