The Rift Valley highlands are subject to high evaporation rates; freshwater resources are scarce, and their occurrence is closely linked to precipitation. Mountain forests, vegetated stream corridors and wetlands provide regulatory mechanisms for the maintenance of essential regulating ecosystem services that contribute to the well-being of local communities. Through deforestation, grazing, and farming, human activities undermine the capacity of natural ecosystems to oppose climatic variability, and river basins are over-exposed to floods and droughts. To discuss the impact of local land use, we conducted a detailed survey of the longitudinal succession of riparian plant communities along the River Gilgil, a tributary of Lake Naivasha. The distribution of upstream and downstream vegetation groups correlated with changes in lithology and soils. Riverine and native trees, but not saplings, tended to increase downstream, while forest trees preferred sites at higher altitude. Potential vegetation maps indicated that Afromontane vegetation found refuge in the riparian corridor and extended its distribution towards lower altitudes. In upstream sites, riparian vegetation merged with the remains of the surrounding forest, while lower sites were characterised by large trees belonging to a distinctive riverine community not found anywhere else in the catchment. Lack of regeneration of these riverine trees indicated that this community is progressively fading away while the floodplain is shrinking. This evidence is accompanied by deforestation and catchment degradation in the upper slopes. Studies conducted in the nearby Mau Forest indicated that recent deforestation has reduced evapotranspiration and increased temperature more significantly than what would be predicted by global climate change models, with impairment of ecosystem services’ fluxes and a weakening of the biotic regulation of the local water cycle.
Chapter 6: Linking Hydrology to Biodiversity, Ecosystem Services and Climate within the Lake Naivasha Catchment
Nic Pacini
Writing – Original Draft Preparation
;
2024-01-01
Abstract
The Rift Valley highlands are subject to high evaporation rates; freshwater resources are scarce, and their occurrence is closely linked to precipitation. Mountain forests, vegetated stream corridors and wetlands provide regulatory mechanisms for the maintenance of essential regulating ecosystem services that contribute to the well-being of local communities. Through deforestation, grazing, and farming, human activities undermine the capacity of natural ecosystems to oppose climatic variability, and river basins are over-exposed to floods and droughts. To discuss the impact of local land use, we conducted a detailed survey of the longitudinal succession of riparian plant communities along the River Gilgil, a tributary of Lake Naivasha. The distribution of upstream and downstream vegetation groups correlated with changes in lithology and soils. Riverine and native trees, but not saplings, tended to increase downstream, while forest trees preferred sites at higher altitude. Potential vegetation maps indicated that Afromontane vegetation found refuge in the riparian corridor and extended its distribution towards lower altitudes. In upstream sites, riparian vegetation merged with the remains of the surrounding forest, while lower sites were characterised by large trees belonging to a distinctive riverine community not found anywhere else in the catchment. Lack of regeneration of these riverine trees indicated that this community is progressively fading away while the floodplain is shrinking. This evidence is accompanied by deforestation and catchment degradation in the upper slopes. Studies conducted in the nearby Mau Forest indicated that recent deforestation has reduced evapotranspiration and increased temperature more significantly than what would be predicted by global climate change models, with impairment of ecosystem services’ fluxes and a weakening of the biotic regulation of the local water cycle.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
