New paper: legacy effects of land use change on tree diversity

By Girma Shumi Dugo

I am Girma, one of Joern’s PhD students working on his ERC-project that aims to identify social-ecological system properties benefiting food security and biodiversity. My background is in forestry and plant ecology – with a focus on sustainable use and conservation of woody plants. I’ve worked on participatory forest management (PFM) in coffee forests of SW Ethiopia; ecological indicators for Chilimo PFM of Ethiopia; and contributed to various research projects in forestry, agroforestry and ecosystem services in rural landscapes of Ethiopia.

ethiopia.pngIn the current project, I am working on the empirical case study conducted in the rural landscapes of southwestern Ethiopia. In my research, I am assessing the effects of historical and current land use, site level forest management (e.g., disturbances, management for coffee production) and forest landscape history (e.g., primary vs secondary forest – time lag effects, edge effects) on biodiversity, more specifically on woody vegetation in both agricultural and forest landscapes. Furthermore, to better understand the link between conservation and human well-being, I am investigating local people’s woody plant use, conservation and their perception of their property rights, particularly, with respect to tenure security and the rights to withdraw or wood, which may hinder both the use and conservation of woody plants in the landscapes.

The main purpose of this post is to share with you the findings of a new paper we’ve just published where we’ve looked into land use legacy effects on woody vegetation in agricultural landscapes of southwestern Ethiopia.

In our study landscape, some plant species respond to land use changes immediately while others show a time delayed response. In this regard, past land use legacy effects – extinction debts and immigration credits – might be particularly pronounced in regions characterized by complex and gradual landscape change. In order to examine the existence of such land use legacy effects, we surveyed woody plants in 72 randomly selected 1 ha sites in farmland, and grouped them into forest specialist, generalist and pioneer species. We examined their composition and distribution using non-metric multidimensional scaling; modelled their richness in response to historical and current distance from the forest edge; and examined tree diameter class distributions in recently converted versus permanent farmland sites.

Overall, we found 110 species of trees, shrubs and subshrubs, representing 48 families. Historical distance to the forest edge was a primary driver of woody plant composition and distribution. However, somewhat surprisingly, we found no extinction debt for forest specialist species, suggesting that this debt was rapidly paid off in the farming landscape (i.e. forest specialists disappeared quite quickly). In contrast, and again surprisingly, we found immigration credits in farmland for generalist and pioneer species. This might suggest that long established cultural landscapes in Africa might have unrecognized conservation value – not for forest specialist species, but for a rich array of other species. In conclusion, our results indicate that conservation measures in southwestern Ethiopia should recognize not only forests, but also the complementary value of the agricultural mosaic – similarly to the case of European cultural landscapes. A possible future priority could be to also better maintain forest specialist species in the farmland mosaic.

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