Biodiversity and Ecosystem Functions Across an Afro-Tropical Forest Biodiversity Hotspot

Abstract

Ecosystem functions are important for the resilience of ecosystems and for human livelihood quality. Intact habitats and heterogeneous environments are known to provide a large variety of ecosystem functions. Natural and near natural ecosystems surrounding agroecosystems may positively support crop growing conditions and thus facilitate crop yields. In contrast, monocultures of crops and trees as well as degraded landscapes are known to provide less ecosystem functions. The Taita Hills in southern Kenya are part of the Eastern Afromontane biodiversity hotspot, and represent a habitat mosaic consisting of largely intact cloud forests, agroecosystems and plantations of exotic trees. In this region, subsistence farmers rely on ecosystem functions provided by natural ecosystems. In this study, we analyze three proxies of biodiversity and ecosystem functions, namely pollination activity, predation rates, and arthropod diversity in tree canopies. We set study plots along forest-agroecosystem-gradients, covering cloud forest, forest edge and agricultural fields, as well as plantations of exotic trees. We assessed environmental conditions, to evaluate the extent to which local environmental factors influence ecosystem functions. Based on these data we investigate potential spill over of ecosystem functions from forest into adjoining agroecosystems. For predation rates we found trends of spill over effects from forest interior into the agroecosystem. The expression of ecosystem functions differed among habitat types, with comparatively high predation rates in the forest, high pollinator activity in the open agricultural areas, and highest arthropod diversity along the forest edge. Eucalyptus plantations showed reduced ecosystem functions and lowest arthropod diversity. Local factors such as vegetation cover and flower supply positively influence pollinator activity. Our study show that natural ecosystems may positively contribute ecosystem functions such as predation, while the homogenization of biota through planting of invasive exotic tree species significantly reduce biodiversity and ecosystem functions. Transition habitats such as forest margins, and small-scale ecological enhancement positively influences biodiversity and ecosystem functions.

Green deserts, but not always: A global synthesis of native woody species regeneration under tropical tree monocultures

“…The view that tree monocultures are necessarily detrimental to the environment can be partially based on their direct comparison with native forests, as the conversion of forest remnants to tree monocultures has been an important driver of biodiversity loss across the tropics (Barlow et al., 2007; Iezzi et al., 2018; Seifert et al., 2022). However, when tree monoculture plantations are compared with other anthropogenic land uses, such as pasturelands and croplands, they may have considerably higher native species diversity, as plantations may attract more seed dispersers and their understory may have much better microsite conditions for woody seedling regeneration than open, intensively managed agricultural systems (Feyera et al., 2002; Schlaepfer et al., 2011).…”

Kaya forests: nucleus of cultural and biological diversity and functionality

“…They have played a central role in performing rituals, and they have restricted and managed access to the forests. However, the breakdown in traditional beliefs and the increased influence of Christianity and Islam along with the increasing demand for forest products made forest protection less and less efficient (Goldammer 1992, Sayer et al 1992. Today, the elders represent a rather marginal group than the centre of cultural and social cohesion, and in parallel, the pressure on the resources of Kaya forests increasedfor private use and for selling on the local market (Peltorinne 2004).…”

“…But also on a local level, such small forest fragments have a supportive effect on the surrounding landscape. Studies along the Arabuko Sokoke coastal forest and on forest fragments of the Taita Hills showed that pest infestations in agricultural areas are reduced by increased predation rates from the adjacent forest (Habel & Ulrich 2020, Seifert et al 2022. It is very important to communicate the relevance of kayas as a source of ecosystem services, for example, in schools.…”

Lack of benefit sharing undermines support for nature conservation in an Eastern Afromontane biodiversity hotspot

“…The remaining forest fragments still host many endemic and endangered plant and animal species (Githiru and Lens 2007) and are important for carbon sequestration (Njeru 2016, Njeru et al 2017. The cloud forests act as water catchments (Kivivouri et al 2013, Mkaya 2013) and provide indigenous seed banks and medicinal plants, among other ecosystem services (Seifert et al 2022). On the other hand, insecure land tenure (Maeda et al 2010) and rapidly declining plot sizes per capita (Nzau et al 2018) contribute to mismanagement of natural resources across the Taita Hills.…”