Abstract
Contrary to expectations, some human-modified landscapes are considered to sustain both human activities and biodiversity over the long-term. Agroforestry systems are among these landscapes where crops are planted under native shade trees. In this context, ancient agroforestry systems can provide insight into how farmers managed the landscape over time. Such insight can help to quantify the extent to which tropical forests (especially habitat-specialist trees) are responding to local and landscape-level management. Here, we extracted fossil pollen (indicator of past vegetation changes) and macroscopic charcoal (indicator of biomass burning) from four forest hollows’ sedimentary sequences in an ancient agroforestry system in Western Ghats, India. We used a mixed-modelling approach and a principal components analysis (PCA) to determine past trajectories of forest change and species composition dynamics for the last 900 years. In addition, we reconstructed the long-term forest canopy dynamics and examined the persistence of habitat-specialist trees over time. Our results show that the four sites diverged to a surprising degree in both taxa composition and dynamics. However, despite these differences, forest has persisted over 900 years under agricultural activities within agroforestry systems. This long-term analysis highlights the importance of different land-use legacies as a framework to increase the effectiveness of management across tropical agricultural lands.
Highlights
In many tropical countries, agroforestry is an important strategy for forest management (McNeely and Schroth 2006; Bhagwat and others 2008)
Further progress is required to determine a consistent global trend across tropical agroforestry systems, our results suggest that the divergent trajectories of change might have promoted the maintenance of biodiversity within the landscape scale (Penne and others 2010; Ewers and others 2013)
A limitation encountered in this study is that we found a negative relation between forest and charcoal which shows the negative effect of burning related to agricultural activities on forest (Table 2), our analysis does not capture other landclearing mechanisms
Summary
Agroforestry (that is, the practice of planting crops under shade trees) is an important strategy for forest management (McNeely and Schroth 2006; Bhagwat and others 2008). Given that recent results suggest that tropical forest systems seem to be recovering faster following larger infrequent events such as cyclones and earthquakes than following small-scale human-induced impacts such as burning (Cole and others 2014). These findings are relevant in the old tropics where agricultural activities are thought to have started approximately 11,000 years ago and potentially leaving a historical legacy of past human impacts There is evidence that retention of tree cover under lowintensity land-use change can maintain forests in human-modified landscapes over hundreds of years (Ranganathan and others 2008)
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