The ecology, plant functional composition and ecosystem services across a range of the Afromontane and Afroalpine palustrine wetlands in Lesotho.

Abstract

Although wetlands are among the most socio-economically and ecologically valuable ecosystems worldwide, global coverage and condition of wetlands is declining, both to the detriment of ecosystem service delivery. Classification and description of wetland vegetation provide an understanding of how wetland vegetation is related to its environment, as well as the associated spatial variation and information for biodiversity conservation and water resource management. Furthermore, understanding the distribution of wetland ecosystem services across landscapes is essential for planning the conservation of the wetlands for a sustainable provision of the services. This study aimed to achieve four main objectives:(1) to classify and describe the Afromontane wetland vegetation in Lesotho, (2) to classify and describe the montane palustrine wetland vegetation of the Maloti-Drakensberg and the surrounding areas, (3) to assess the plant functional composition of the Afromontane palustrine wetlands of Lesotho and link this to environmental variables, and (4) to assess the Afromontane palustrine wetland ecosystem services in Lesotho and link them to environmental factors and functional traits, as well as to assess the level of threat to the delivery of the services. For the first objective, data on vegetation and different environmental variables were collected from the Afromontane wetland vegetation in Lesotho using the Braun-Blanquet method and a recommended protocol developed for environmental information of wetlands in South Africa, respectively. Regarding the second objective, the montane subset of the National Wetland Vegetation Database of South Africa (also collected using the same methods) was selected and coupled with the new data collected from the Lesotho part of the Maloti-Drakensberg. To achieve the third objective, in addition to the data collected for the first objective, plant functional trait data were also collected from the Afromontane wetlands of Lesotho using methods recommended in literature. For the purposes of the fourth objective, the WETEcoServices tool was used to collect data on wetland ecosystem services and this was coupled with the data collected for the first and third objectives. For all the objectives, the data were analysed mainly by means of clustering, indicator species analysis and ordination techniques. The study distinguished 22 Afromontane wetland plant communities in Lesotho and these displayed a high level of diversity in terms of species richness. With respect to species composition and diversity, the communities at higher altitudes were more diverse and were quite different from those at lower altitudes. While the higher-altitude communities mainly exhibited the dominance of C3 plants, those at lower altitudes were mainly dominated by C4 species. As revealed by the ordination, variation in the wetland vegetation in the country was mainly related to altitude, longitude (directly correlated with rainfall in the context of Lesotho), slope, inundation, soil parent material, landscape, potassium content, total organic carbon, soil texture, nitrogen, electrical conductivity and latitude. In terms of distribution, the occurrence of some plant communities was limited to either the Lowlands or Highlands, while others were widely distributed along the altitudinal gradient, occurring in both regions. For the Maloti- Drakensberg montane palustrine wetlands, the classification produced 42 wetland plant communities, which were summarised into 16 major vegetation types. These major vegetation types were rich in species and also displayed remarkable variation along the altitudinal gradient. This variation was mainly attributed to changes in the conditions of the environment that include the amount of precipitation, temperature and the underlying parent material. The ordination indicated that the variation in the vegetation types could more specifically and mainly be ascribed to variation in altitude, longitude, latitude, nitrogen content, soil depth, inundation depth and electrical conductivity. However, slope, pH, total organic carbon, sodium content, soil texture and degree of wetness were also important factors. Furthermore, with respect to species composition, significant variation was also observed between higher-altitude and lower-altitude plant communities. In terms of distribution, the montane wetland vegetation was more concentrated in the Maloti-Drakensberg than the other parts of the region, although some vegetation types also occurred in the lower altitudes of Lesotho and in all of the South Africa provinces. In terms of plant functional composition, eight plant functional types were obtained from the functional classification of the plant species in the Afromontane wetlands in Lesotho. The functional types were dominated by plants with C3 photosynthetic pathway, particularly in the high-altitude wetlands. Plant communities in the Lesotho exhibit the coexistence of species from different plant functional types, which highlights functional differentiation to exploit microhabitat heterogeneity. Both functional traits and functional composition of the communities were mainly and broadly influenced by altitude, longitude and slope, and more finely by edaphic factors that include electrical conductivity, total organic carbon, nitrogen, clay percentage, potassium, magnesium and calcium. Thus, functional differentiation of wetland vegetation along environmental gradients was demonstrated in this study. Furthermore, the study highlights the possibility of alterations in plant functional traits, types and functional composition in the face of environmental alterations, including climate change. Although the wetlands were all important for ecosystem service delivery, higher-altitude wetlands differed distinctively from the lower-altitude wetlands in the services they deliver most. The highest scoring ecosystem services for the higher-altitude wetlands were carbon storage, provision of natural resources, streamflow regulation, maintenance of biodiversity and erosion control, while natural resources, cultivated foods, nitrate removal, phosphate trapping and streamflow regulation scored highest for the lower-altitude wetlands. The most important environmental factors influencing the delivery of wetland ecosystem services in this study were altitude, longitude, landscape, soil parent material, slope and soil depth. The delivery of ecosystem services was also correlated with the functional traits of the dominant plant species in each wetland type where specific leaf area, total dry mass, shoot mass, root mass, rooting depth and plant height were the most important traits influencing ecosystem service delivery. For example, carbon storage and maintenance of biodiversity were positively correlated with plant shoot mass, total plant biomass and rooting depth, while specific leaf area and root/shoot mass ratio had a positive and strong correlation with supply of natural resources, cultivated foods and cultural significance. The ecosystem services provided by a given wetland are thus dependent on the location and environmental characteristics of the wetland within a catchment and the functional characteristics of the dominant wetland plant species. However, the supply of ecosystem services in Lesotho is threatened, with the level of threat higher in the loweraltitude than in higher-altitude wetlands. The threats, which are largely anthropogenic, are mainly associated with crop cultivation, overgrazing and trampling by livestock and economic development. The diversity exhibited by the wetlands in Lesotho and the Maloti-Drakensberg, coupled with their restricted habitat and distribution at high altitudes, capacity to support endemic species, their role in water resources and supply of other ecosystem services, points to the high conservation value of these ecosystems, particularly in the face of biodiversity loss and climate change. Thus, given the reported threats, the conservation of these montane palustrine wetlands is indispensable and should be set as a priority. Based on these findings that can contribute the information needed for biodiversity conservation planning and sustainable provision of wetland ecosystem services in Lesotho and beyond, the study recommends urgent attention and up-scaling of the conservation efforts to protect these Afromontane palustrine wetlands and theservices they provide.