Long-term changes in the plant ecology of an African savanna landscape and the implications for ecosystem theory and conservation management

Abstract

Background Studies of the African savannas have used national parks to test ecological theories of natural ecosystems, including equilibrium, non-equilibrium, complex adaptive systems, and the role of top-down and bottom-up physical and biotic forces. Most such studies have excluded the impact of pastoralists in shaping grassland ecosystems and, over the last half century, the growing human impact on the world’s rangelands. The mounting human impact calls for selecting indicators and integrated monitoring methods able to track ecosystem changes and the role of natural and human agencies. Our study draws on five decades of monitoring the Amboseli landscape in southern Kenya to document the declining role of natural agencies in shaping plant ecology with rising human impact. Results We show that plant diversity and productivity have declined, biomass turnover has increased in response to a downsizing of mean plant size, and that ecological resilience has declined with the rising probability of extreme shortfalls in pasture production. The signature of rainfall and physical agencies in driving ecosystem properties has decreased sharply with growing human impact. We compare the Amboseli findings to the long-term studies of Kruger and Serengeti national parks to show that the human influence, whether by design or default, is increasingly shaping the ecology of savanna ecosystems. We look at the findings in the larger perspective of human impact on African grasslands and the world rangelands, in general, and discuss the implications for ecosystem theory and conservation policy and management. Conclusions The Amboseli study shows the value of using long-term integrated ecological monitoring to track the spatial and temporal changes in the species composition, structure, and function of rangeland ecosystems and the role of natural and human agencies in the process of change. The study echoes the widespread changes underway across African savannas and world’s rangelands, concluding that some level of ecosystem management is needed to prevent land degradation and the erosion of ecological function, services, and resilience. Despite the weak application of ecological theory to conservation management, a plant trait-based approach is shown to be useful in explaining the macroecological changes underway.

Cascading effects of elephant-human interactions in a savanna ecosystem and the implications for ecology and conservation

“…The fever tree woodlands were supplanted by a Suaeda -dominated shrubland. The heterogeneity in woodland structure and species composition converged over the period from the 1970s to 2017, due largely to the woody mass declining across the Basin from 600 gm -2 to 200 gm -2 (72). The permanent swamps increased by two-fold, switching from tall to short sedges and banks of floating weed and large stretches of open water (88).…”

“…Based on the densitydependent responses of plant species richness, we deduce that protected area research and compressed populations mask the larger shifting patchwork effect of elephants as landscape agents (94). The impact of compression and curtailed movements on woody vegetation is analogous ecologically to the impact of heavy sustained grazing on grassland production in response to land subdivision and sedentarization of pastoral herds on the Kaputei group ranches north of Amboseli (69,72) Although Guldemond et al (2017) and Cook and Henley (2019) found high-density elephant populations do generally cause tree loss and habitat simplification, the ecological cascade effects can also be positive as in the case of the grazing success in wetlands. Skarpe and Ringrose (2014), in a detailed multispecies study of Chobe National Park in Botswana, added to the complex view in showing elephants to cause a wide range of cascade effects as a function of distance from water.…”

“…Based on the density-dependent responses of plant species richness, we deduce that protected area research and compressed populations mask the larger shifting patchwork effect of elephants as landscape agents (94). The impact of compression and curtailed movements on woody vegetation is analogous ecologically to the impact of heavy sustained grazing on grassland production in response to land subdivision and sedentarization of pastoral herds on the Kaputei group ranches north of Amboseli (69, 72)…”

An Integrated Method for Landscape Assessment: Application to Santiago de Cuba Bay, Cuba

“…An appropriate tool for the effective and sustainable management of landscape is required to preserve the beauty and functionality of natural areas [1]. This is a complex problem that must incorporate evolving ideas of how to value landscapes and landscape gaps (surrounding areas) in a way that encompasses a variety of stakeholder perspectives.…”

“…Delimitation of landscape units primarily using physical-geographical criteria does not consider the value of scenic and cultural attributes [12][13][14][15]. Some authors propose methodological frameworks for the study of visual landscapes [4,10,12,14,[16][17][18] or for the (1) What kind of research is required to characterise and value landscapes for sustainable management? (2) What set of factors, variables and sub-variables must be considered to characterize and value landscape for management?…”