J. E. Ellis

Stability of African pastoral ecosystems: alternate paradigms and implications for development

JIM ELLIS took undergraduate work in animal husbandry at the University of Missouri and also obtained his Master of Science degree there studying wildlife biology. In 1970, he received his Ph.D. in Zoology at the University of California at Davis, where he was a National Institute of Health trainee in systems ecology. Shortly thereafter, he held a National Science Foundation postdoctoral fellowship at the University of Bristol working on systems analysis of mammalian social systems. He joined the Natural Resource Ecology Laboratory of Colorado State University as a Research Ecologist in 1971. He is currently the Associate Director of the Laboratory. Jim has enjoyed immense success in developing research programs; during the last decade he directed or played a major role in 12 successful proposals, collectively exceeding three milliondollaninsuppott. He has publishedextensively, withmost of his work focussing on processes regulatinggrazing systems. Jim has served as a consultant to the U.S. Senate, as well as the govcmmcnt of Saudi Arabia and the Norwegian Agency for International Development. His must recent project uses a systems approach to understand the controls on stability and persistence of a pastoral ecosystem in East Africa.

Response of seasonal vegetation development to climatic variations in eastern central Asia

Abstract Meteorological records show that central Asia has experienced one of the strongest warming signals in the world over the last 30 years. The objective of this study was to examine the seasonal vegetation response to the recent climatic variation on the Mongolian steppes, the third largest grassland in the world. The onset date of green-up for central Asia was estimated using time-series analysis of advanced very high resolution radiometer (AVHRR) normalized difference vegetation index (NDVI) biweekly composite data collected between January 1982 and December 1991. Monthly precipitation and mean temperature data (1982–1990) were acquired from 19 meteorological stations throughout the grasslands of the eastern Mongolian steppes in China. Our results showed that while the taiga forest north of the Mongolian steppes (>50°N) experienced an earlier onset of green-up during the study period, a later onset was observed at the eastern and northern edges of the Gobi Desert (40°N–50°N). Responses of different vegetation types to climatic variability appeared to vary with vegetation characteristics and spring soil moisture availability of specific sites. Plant stress caused by drought was the most significant contributor to later vegetation green-up as observed from satellite imagery over the desert steppe. Areas with greater seasonal soil moisture greened up earlier in the growing season. Our results suggested that water budget limitations determine the pattern of vegetation responses to atmospheric warming.

Energy Extraction and Use in a Nomadic Pastoral Ecosystem

An analysis of annual energy flows in an arid tropical ecosystem inhabited by nomadic pastoralists provides insight into a subsistence life-style that has persisted in droughted environments for hundreds to thousands of years. Although a large fraction of the total energy consumed by the Ngisonyoka of Kenya followed a single pathway from plant to animal to human, they also harvested solar energy from a relatively diverse assemblage of energy flow channels. Energy utilization and conversion efficiencies were generally low, as the system is maintenance-rather than production-oriented. Energy flow to maintenance must be relatively high to support biotic responses that enable tolerance of abiotic variability and to stabilize energy flow under the stress of severe droughts. Energy utilization by the Ngisonyoka is therefore consistent with ecological patterns that promote rather than diminish ecological stability under stress.

Climate patterns and land-use practices in the dry zones of Africa

Comparative regional analysis of Africa provides insights into the effects of climatic variation on land use. This information can be used to predict effects of future climatic change. This article discusses the following two areas in depth: precipitation patterns and land use including temporal precipitation patterns, seasonality, interannual variability, and long term trends; Seasonality, interannual variability and land use including agriculture and range vegetation and pastoralism. Numerous examples are presented. The authors conclude by integrating the regional information with global predictions and the problems of interactions among climate, ecosystems, land use and human culture. 80 refs., 6 figs.

Evaluating vegetation phenological patterns in Inner Mongolia using NDVI time-series analysis

Interannual changes in temperature and precipitation can profoundly influence plant phenological status such as the date of onset of green-up, the rate of biomass accumulation, and the onset and rate of vegetation senescence. The objective of this study is to examine annual climatic variation, and its influence on plant phenology of the steppes of Inner Mongolia. Variation in the date of onset of green-up was studied using a 9-year dataset of biweekly composites of the maximum Normalized Difference Vegetation Index (NDVI) values (1982-1990). We found little or no change in date of onset of green-up over the 9-year period for forest and cultivated lands. The date of onset of green-up was progressively earlier or later for the typical and desert steppes, and highly variable for the Gobi Desert. Meteorological data (monthly mean temperature and monthly precipitation) indicated a correlation between date of onset of green-up and climate measurements.

Landscape and climatic control of woody vegetation in a dry tropical ecosystem: Turkana District, Kenya

The spatial organization of a dry woodland/ savanna/shrub-steppe ecosystem in a 9000 km2 region of arid Northern Kenya was explored by analysing the abundance and distribution of woody vegetation in relation to landscape gradients and gradients in rainfall. Woody species assemblages were clustered into four major groups. Three of these (and most of the sites) were dominated by species of Acacia. Acacia tortilis was the community dominant in riparian and riverine zones, A. senegal on hilly and rocky sites, and A. reficiens on non-riparian sites with fine soils. The fourth group, found at highest elevations, was distinguished by a very low abundance of Acacia. These soil/landform associations were systematically distributed along land system gradients (mountains, pediment, valley, bajada), thus relating woody species groups to large-scale landscape characteristics. Tree woody canopy cover ranged from < 1.0% to 100% over the region as a whole. Cover was directly related to precipitation when the effects of water concentration in riparian zones were removed. However, canopy cover was not greatly influenced by either species composition or landscape characteristics. Fire reduced woody canopy cover, however, fires appeared to affect a relatively small portion of the ecosystem. Recent anthropogenic disturbances such as wood-cutting and livestock corralling were encountered in patches, but the cumulative long-term effects of patch scale disturbances could not be discerned in vegetation patterns at the regional scale. Vegetation physiognomy (woodland, bush, bushed grassland, etc.) was controlled by both water availability and landscape pattern. Woodland and forest occurred almost exclusively in riparian and riverine situations while the driest parts of the region supported dwarf shrub grassland with few trees. Over the region as a whole, climate and landscape gradients converged in diverse ways, giving rise to structurally variable associations of woody plant species. Vegetation structure in tropical savannas and dry woodlands is often interpreted in terms of competition between woody and herbaceous life forms for soil moisture. The outcome of this competitive interaction is thought to be influenced by disturbances that shift the system from one stable state to another. However, our findings suggest that dry tropical ecosystem structure is hierarchically constrained by physical factors: by climate at regional to continental scales; by topographic effects on rainfall and landscape water redistribution, and geomorphic effects on soil and plant available water at the landscape to regional scales; and finally by water redistribution and disturbance at local and patch scales.

Immediate Effects Of Prescribed Burning On Mineral Soil Nitrogen In Ponderosa Pine Of New Mexico

Three 0.1-ha ponderosa pine (Pinus ponderosa Dougl. ex Laws) sites were burned in the fall of 1981. The burn was mainly a ground fire. Burn intensity was 980, 1760, and 2280 kJ s−1 m−1 on sites 1, 2, and 3, respectively. We analyzed the mineral soils on each of these sites for total N, NO2−+NO3−-N and NH4+-N prior to prescribed burning, 1 d postburn, and 30 d postburn. On the most intense burn, NH4+-N levels increased threefold from preburn (10 ppm) to 1 d postburn (32 ppm), but declined somewhat 30 d following the burn (24 ppm). Concentrations of NO2+NO3−-N on site 3 rose from 1 ppm preburn and 1 d postburn to 5 ppm 30 d postburn. There were no significant differences in soil total N after burning. Immediate postburn inorganic N values for ponderosa pine mineral soils have not been previously reported in the literature. It is important to investigate burned soils immediately after burning to better understand sequential processes involved in postfire inorganic N dynamics.

Interannual variations of the grassland boundaries bordering the eastern edges of the Gobi Desert in central Asia

The Mongolian Steppe that borders the northern and eastern edges of the Gobi Desert in central Asia is one of the worlds largest grasslands, extending across the nation of Mongolia and the Inner Mongolian Autonomous Region (IMAR) of China. Recent findings show that this region has one of the strongest warming signals on Earth since the late 1970s. The objective of this study was to evaluate the relationships between climate and interannual variation of the grassland boundaries in Mongolia and IMAR between 1982 and 1990. The remote sensing data used in this study were the 15–day maximum Normalized Difference Vegetation Index (NDVI) composites derived from the Global Area Coverage of the Advanced Very High Resolution Radiometer (AVHRR). Monthly precipitation, mean monthly temperature, and monthly actual evapotranspiration (AE) were derived from meteorological station records acquired during the study period across the eastern Mongolian Steppe. The occurrence of onset of green–up, as determined with time-series NDVI data, was used to identify vegetated and non-vegetated areas. Great interannual variation of the Gobi boundary position was observed over the study period. This boundary variation was largely controlled by the climate before the growing season (the ‘preseason’ climate). Along the eastern edge of the Gobi desert in central IMAR, preseason AE was the major climatic factor affecting the annual shift of the Gobi boundary, while further north in Mongolia, preseason temperature was the driving climatic factor. Our findings suggest that the response of vegetation communities to climate changes varied as a function of land-use intensity within the ecosystem.

Patterns of species and community distributions related to environmental gradients in an arid tropical ecosystem

The heterogeneous vegetation mosaic of the South Turkana region of north Kenya is associated with diversity in the regions physical environment. The abundance and distribution of the dominant species are related to gradients in those abiotic factors that influence water availability, including precipitation, soil texture, and topographic relief. Research focused on three Acacia species that are a major component of the Turkana vegetation; A. tortilis, A. senegal, and A. reficiens. These species each exhibit a different response to variations in abiotic factors. Consequently, species abundance varies independently across the landscape, creating a continuum of intergrading populations. Community types can be identified within the mosaic of intergrading populations. Although community borders are not discrete due to continual change in species abundance, types are identifiable and are repeated in areas with similar environmental conditions. The landscape patterns are representative of Whittakers (1953) climaxas-pattern, with communities created by individual patterns of populations responding to environmental gradients, creating a continuum of community change across the landscape.

Morphometric relationships and developmental patterns of Acacia tortilis and Acacia reficiens in Southern Turkana, Kenya'

ecosystem of northern Kenya. We found relationships for both multi-stemmed species between aboveground biomass and the aggregate of diameters of all stems. Relationships between aggregate stem diameter and crown diameter suggested that large individuals had smaller crown diameter increments per increment in aboveground biomass. Acacia tortilis displayed a pronounced developmental transition from low biomass-open crown to heavy trunk-dense crown morphology at sizes of 63-223 mm stem diameter. Stem diameter of A. tortilis increased by 2 mm for each tree ring among small trees. While rings may not be exactly annual, an average of one ring may be produced per year. Root systems of both species were a mixture of tap and lateral roots. There was a concentration of root biomass in the surface meter of soil and most root biomass was accounted for in the top 2.5 m of soil. A logarithmic relationship between root biomass and stem diameter applied to both small and large trees. Although large trees had tap roots with large diameters, these were not necessarily deep. Root: shoot ratios declined from 1.5 in small trees to 0.2 in mid and large trees.