Two decades of change in Ghanaian forests

Understanding the impacts and synergies of the many threats facing tropical forests is a key research challenge. Here, three potential threats are addressed: drought, fire and
lianas. Using a network of 31 plots, changes attributed to these threats are addressed over two decades in Ghanaian forests.

Ghana experienced a multi-decade drought beginning in the early 1970s. The impact of this drought on functional composition and forest structure was tested. The results show clear shifts in functional composition. Despite this, biomass increased during the study period. This suggests that shifting species composition in favour of drought-tolerant species increases the resilience of tropical forests to long-term drought.

A strong El Niño event in 1983 led to widespread wildfires in the Ghanaian forest zone. To test the long-term impacts of these fires the structure and composition of seven burnt
plots and three control plots were compared. 27 years after initial fires, stem density and biomass were reduced in burnt plots, and composition was characteristic of disturbed
forest. Over the twenty year study period, forest structure showed evidence of regeneration, but no recovery of floristic composition was observed.

In contrast to the large increase in lianas observed in the Neotropics, there was only a very slight increase in the percentage of infested trees over the study period. Forest
structure was found to be the main driver of liana spatial distribution. Importantly, large lianas showed different spatial patterns, as forest turnover was the strongest predictor of large liana distribution.

Overall, fire was found to be the strongest threat, having a large and long-term impact on forest structure and composition. The results highlight that the prevention of fire occurrence should be a priority in tropical forest regions, as should the maintenance of biodiversity to maximise the resilience of forest to external changes.