The value of forest fragments in maintaining ecosystems for food security in Sub-Saharan Africa. (2019)
Type of ContentElectronic Thesis or Dissertation
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
AuthorsTela, Murnashow all
Historically, forest fragments in Afrotropical montane regions have supported a rich diversity of bird species. On the Mambilla Plateau in South East Nigeria, forest fragments have a long history of association with small subsistence farmlands, and it is likely that birds provided ecosystem services to farmers through pest control and possibly pollination. However, more recently, increased human populations have dramatically reduced fragment sizes, or totally cleared them. Anthropogenic fire, grazing and farming have been responsible for most of the more recent forest destruction. This must impact bird populations and the ecosystem services they provide. Understanding the distribution of bird species and their role in providing ecosystem services to subsistence farmers in this forest-farmland mosaic is critical for both farmers and conservation managers. In this study, based on the Mambilla Plateau, I documented in detail the bird community composition and identified the potential roles of birds in providing pest control services to subsistence farmlands. I explored how distance of farms from fragments affected pest control services. Firstly, I surveyed bird community composition in both farmlands and forest fragments, and classified all birds recorded based on two main ecological traits: habitat preference and trophic functional group (based on their feeding guild). Secondly, I investigated the pest control services birds may provide to maize (Zea mays) on farms at varying distances from native forest fragments. I explored how excluding birds influenced maize crop yield by comparing the crop productivity in two caged treatments i) birds excluded, ii) birds and insects excluded) versus open (control) plots on maize farms. Thirdly, I tested whether, and if so, to what extent, plasticine pest mimics on groundnut (Arachis hypogea) and Bambara nut (Vigna subterranea) crops were being attacked by insectivorous birds, and whether attack rates depended on the proximity of farmlands to forest fragments.
I found significant bird biodiversity within this forest-agricultural landscape. While as expected, bird diversity was higher in the forest fragments, the farmlands also supported high bird diversity, although a significant proportion of the farmland species depend on forest fragments for a part of their life cycle. My study did not demonstrate any significant relationship between bird pest control and maize crop productivity (exclosure experiments showed that insectivorous bird abundance was not an important predictor of crop productivity). I also found that crop yield was higher further from forest fragments, and insectivorous birds were more abundant farther away from the forest. However, I did show that it is likely that natural pest control occurs, and that it affects yield substantially, because I found a significant decrease in yield and increase in insect damage by excluding birds. This suggest that something must be controlling pests on maize (perhaps the key biocontrol insectivores in my study area are not birds, but bats). I also found a strong positive correlation between the abundance of insectivorous birds and mean number of missing mimics and/or bird attack marks on mimics. The positive effect of insect-eating bird abundance on prey mimics became less strong the farther they were from a forest fragment. Together, these findings suggest that pest predation may be a key ecosystem function provided by insectivorous birds on Nigerian subsistence farmlands, and farmlands that are closer to forest fragments may experience a higher rate of pest control than those further away.
Of note is that I had contradicting results regarding the role of birds in pest control from my maize exclosure experiment (Chapter 3) compared with the plasticine mimic experiment (Chapter 4). This suggests that birds, while providing important ecosystem services in some crops, may not necessarily be as important in others. This research highlights the need for further investigations into the role of birds, but also other taxa in biological pest control in rural West Africa.