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Abstract
This chapter reviews the complex history of conservation activities in the Lake Naivasha area from the onset of European colonial settlement to the present. Conservation in the region is not a recent activity spurred by the growth of horticulture. Over the last 125 years, residents, government authorities, and conservation advocates have raised the alarm over human-induced environmental changes caused by many forms of local development, including European settlement in the riparian area, tourism, commercial fishing, postcolonial relocation schemes for landless Kenyans, horticulture, and geothermal power. There have also been several attempts to create a coordinated plan for managing the lake and to bring local development decisions under a central authority. We examine the rhetoric and reality of environmental efforts centred on Lake Naivasha, the ecological and socio-political dynamics driving these conservation efforts and their actual outcomes. These efforts have not prevented the ongoing ecological degradation of the lake, but each has introduced new regulatory strategies and partnerships in governance that have resulted in some positive changes. If this lake and the many human and non-human communities it sustains are to continue to thrive, centralized control and management strategies that keep in mind the ecological limits to growth and development are still necessary.
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.
Abstract
Lake Naivasha has been vital to humans for freshwater and grazing for millennia – it was an essential and reliable all-season water hole for pastoralist Maasai, whose oral history for at least the past 700 years coincides with the paleolimnological record of high water (prosperity) and low water (hardship). The lake has only been known to the Western world for fewer than 130 years, passed by several European explorers on their way seeking to quash “preposterous” rumours such as “snow on the equator” and to find the source of the Nile, who left maps and comments. It has only been seriously studied for under a century; the first scientists from Cambridge University inventoried its limnology during an extensive visit to East African lakes in 1930. Even by that time however, humans had left their “fingerprints” on the lake directly by introducing 2 fish species in the 1920s, most notably the American large-mouthed bass. Indirectly, they started affecting the lake 20 years earlier, when the “Lunatic Express” passed by the eastern side of the lake with a railway station, which initiated the settlement that now supports over half a million people.
This chapter explains how the valuable natural and living resources of the lake came about, and discusses whether we humans value the resources adequately, our impacts upon them and their response, over the past 7 decades.
Caesalpinia echinata (pernambuco or pau-brasil), is recognized as the premier wood for manufacturing stringed instrument bows. Owing to limited supplies and concerns regarding species survival, interest exists in establishing pernambuco plantations to provide future bow-quality wood. For native forest- and plantationgrown woods we examined several wood properties considered important in determining bow quality including basic density, modulus of elasticity (MOE), modulus of rupture (MOR) measured using static bending samples, air-dry density, microfibril angle (MFA), and stiffness using SilviScan. Color, extractives content and loss tangent (tan δ) were measured for a subsample of the static bending samples. Finally, the samples were also ranked based on their potential for manufacturing high-quality bows (0 = poor, 1 = good and 2 = excellent) by an experienced bow maker. No evidence of differences between means for density, MOE and MOR for native, and 25- and 30-year-old plantation-grown pernambuco was observed; however, when sorted based on quality, the excellent group had higher density, MOE and MOR. MFA and tan δ were low, especially for native forest samples. Extractive contents were low for plantation samples; 5.7% and 12.7% respectively for the 25- and 30-year-old samples, compared to the native forest samples (set 1 = 23%, set 2 = 22.5 %) and few samples had heartwood. Overall, plantation-grown samples provided promising results in terms of their quality.
Summary
Brassica plants naturally produce glucosinolates as secondary metabolites hydrolysed to biocidal isothiocyanates (ITCs). As such, they have the potential for nematode management through a strategy known as biofumigation. Pratylenchus penetrans causes significant yield losses in many important crops. Understanding the relative impact of different ITCs on the motility and mortality of this nematode species could provide some insights into the selection of relevant brassica biofumigants. The effects of 3.125, 6.25, 12.5, 25, and 50 μg ml−1 of pure Allyl, 2-Phenylethyl and Benzyl ITCs on the motility and mortality of P. penetrans were evaluated in laboratory in vitro assays. Motility was assessed after incubating the nematodes in ITCs for 24, 48 and 72 h with distilled water as a negative control. Motile and non-motile nematodes were counted. After motility assessment at 72 h, nematodes were rinsed and incubated in water for 48 h, after which live and dead nematodes were counted. Nematodes were considered dead if they remained non-motile after probing with a picking needle. Nematode motility and mortality were significantly affected by the type of ITC, concentration and time of exposure. The number of non-motile nematodes increased with increasing concentration and time of exposure across all tested ITCs. The ED50 values (concentration required to cause 50% non-motility) of Allyl, 2-Phenylethyl and Benzyl were 37.4, 12.8 and 8.6 μg ml−1 after 24 h exposure. The ITC with potentially the greatest nematicidal effect was Benzyl (LD50 = 3.2 μg ml−1), followed by 2-Phenylethyl (LD50 = 5.2 μg ml−1), and Allyl (LD50 = 9.9 μg ml−1). The LD50 of all ITCs were not different from the ED50 after 72 h, meaning the effects of ITCs could be considered irreversible. This study suggests that brassica biofumigants that produce Benzyl, Allyl and 2-Phenylethyl ITCs are promising candidates for biofumigation of P. penetrans.