Ecological correlates of small mammal community structure in the semi-arid Karoo, South Africa

The understanding of the determinants of small mammal community structure in arid and semiarid ecosystems is of importance, both in the light of the role that small mammals play, and the impact of livestock grazing on the flora of these systems. In a study aimed at identifying these determinants, small mammal assemblages and environmental features were quantified at six localities (a gradient of floristic structure, with constant annual rainfall) across the southern Karoo, South Africa. Stepwise variable regression indicated that small mammal diversity was correlated with plant and rock cover, as well as plant cover and horizontal foliage diversity at intermediate heights (40–60 cm). Initially, small mammal diversity increased with increasing plant cover, but decreased at cover levels greater than 30%. This relationship is similar to that found in other desert systems, although the peak in diversity found here is at higher levels of plant cover than found previously. I suggest that this higher peak may be owing to the lack of reliance on granivory by these animals, which are relatively omnivorous. This model may therefore explain the conflicting reports on the impact of livestock grazing on desert small mammals, with small mammal diversity decreasing with grazing below the peak, and increasing with grazing above the peak.     

Disturbances in semi-arid shrubland and arid grassland in the Karoo, South Africa: mammal diggings as germination sites

Mammals (mainly aardvark Orycteropus ufer , porcupine Hystrix austro-africanae , bat-eared fox Otocyon megalotis and Cape fox Vulpes chama ) which excavate holes in hard-capped soils in Karoo shrubland and inter-dune pans create microsites where seeds, detritus and water accumulate, and seeds germinate. Holes with seedlings were significantly deeper (6.7 ± 0.4 cm) than holes without seedlings (4.5 ± 0.3 cm). In open, inter-shrub sites, significantly more seedlings germinated in diggings than on the flat soil surface, but there was no difference in the proportion of seedlings germinating under shrubs and in diggings. In inter-dune pans, 96% of all seedlings found were growing in diggings.

Résumé

Les mammifères (surtout l'oryctérope Orycreropus afer , le porcépic Hystrix austro-ajricanae , l'otocyon Otocyion megalotis , et le renard du Cap Vulpes chama ) qui creusent des trous dans les régions buissonneuses du Karoo et dans les creux entre les dunes créent des microsites où les semences, les déchets et l'eau se rassemblent, et les semences germent. Les trous où elles germent sont significativement plus profonds (6,7 ± 0,4 cm) que ceux où elles ne germent pas (4,5± 0,3 cm). Aux endroits buissonneux ouverts, il pousse plus de jeunes plantes dans des creux qu'à la surface du sol, mais il n'y a pas de différence entre les proportions de celles qui poussent sous les buissons et dans les creux. Dans les creux entre les dunes, 96% des jeunes pousses croissent dans les excavations.     

Environmental History and the Desertification of the Karoo,South Africa

Abstract

This paper reviews the desertification debate in South Africa and emphasizes the methods that have been used to understand the environmental history of the semi–arid rangelands in the eastern Karoo during the last 500 years. These mixed grass/dwarf shrub rangelands, with mean annual rainfall totals typically between 300–400 mm, are described and the main driving variables discussed. A brief historical account of the European settlement of the region is also presented. The desertification debate has focussed on three main issues. Firstly, because arid and semi–arid lands appear to be heavily influenced by climate, the changing climatic regime during the Holocene and particularly during the last two hundred years has been the subject of intensive investigation. While all studies conclude that there is no evidence in the historical record to support the popular perception that rainfall totals have decreased this century, the question of changing rainfall seasonality has not been adequately explored. Although mean annual temperatures over the last 50 years have not changed there have been significant increases in mean monthly maximum temperatures and significant decreases in mean monthly minimum temperatures for some of the stations investigated. The second issue of great interest in the South African desertification literature is that of the nature of pre–colonial environments. A wide variety of archaeological, historical and ecological techniques have been used, including analyses of fossil mammal bones in owl pellets, fossil pollen in hyrax middens, notes from traveller's accounts of the region and stable carbon isotopes in soil as well as fossil mammal bones. While all authors agree that the eastern Karoo was more grassy at some stage in the past there is disagreement as to both the timing and cause of the changes to a more shrubby vegetation. The final issue of great concern to the desertification debate in South Africa concerns the rate of change during the last 100 years. Satellite imagery, matched ground and aerial photography, survey data and an analysis of historical stock records cannot agree as to whether the Karoo is degrading or not. Certainly, the classic view of an annually expanding desert margin has been replaced in recent years by a more realistic understanding of the seasonal dynamics of the vegetation. The recent trend to detailed modelling of the demographic process in key species holds much promise for our understanding of the degradation process. The vibrant community of researchers, employing a range of archaeological, historical and ecological techniques, will make important contributions to South Africa's National Action Plan to Combat Desertification.     

Live fast,die young: estimating size-age relations and mortality pattern of shrubs species in the semi-arid Karoo,South Africa

We present a technique for estimating size-age relations and size-dependent mortality patterns of long-lived plants. The technique requires two sets of size data of individual (non-marked) plants that should be collected with a time-lag of several years in the same area of a study site. The basic idea of our technique is to assume general (three parameter) families of size-dependent functions which describe growth and mortality that occurred between the two data gathering events. We apply these growth and mortality functions to the size data of the early data set and construct predicted size-class distributions to compare it, in a systematic way, to the size-class distribution of the later data set. In a next step we calculate the size-age relations from the resulting growth functions, which yield the smallest difference between observed and predicted size-class distribution. Applying this technique to size data of five dominant shrub species at the Tierberg study site in the semiarid Karoo, South Africa produced new insight into the biology of these species which otherwise cannot be obtained without frequent measurements of marked plants. We could relate characteristics of growth behavior and mortality, for certain subgroups of the five species, to the life-history attributes evergreen vs. deciduous, succulent vs. woody, and early reproductive vs. late reproductive. The results of our pilot-study suggest a broad applicability of our technique to other shrublands of the world. This requires at least one older record of (individual) shrub-size data and performance of resampling.     

Conservation value of road verges in the semi-arid Karoo, South Africa: ants (Hymenoptera: Formicidae) as bio-indicators

Ground-foraging ants (Hymenoptera: Formicidae) were used to assess the conservation value of road verges in a semi-arid region around Prince Albert, Western Cape Province, South Africa. Ant communities were sampled using pitfall traps on 50 sites along two roads. Four transects were sampled at each site, two in the road verge and two in adjacent rangeland. A total of 43,298 individual ants of 34 species were caught, with 31 and 32 species in the road verge and adjacent rangeland respectively, but on average road verges were the more species-rich. Road verges also contained relatively more rare species (i.e. those species that occurred in <10% of the traps. Ant species richness appeared to be influenced by food availability. Although ants appeared to be negatively impacted by higher grazing intensities in the rangeland, there was no difference in species richness between fenced and unfenced road verges. Species in the road verge may benefit directly from road kills, and indirectly from lower grazing pressure on plants, increased surface run-off and differences in soil surface temperatures. No alien ant species were observed or captured at any of the sites.     

Evaluation of Restoration Techniques for the Succulent Karoo, South Africa

Abstract Possible constraints on the passive recovery of bare areas in the Karoo, a semiarid region in South Africa, include inadequate supply of seed, availability of suitable microsites for plant establishment, altered soil properties, and the truncation of key soil biotic processes. Here we investigate the possibility of initiating the restoration of bare areas by soil surface treatments with gypsum (CaSO₄) and/or organic mulch. We also apply an exogenous seed source to test the hypothesis that seed availability limits autogenic recovery. Both gypsum and mulch improved rain water infiltration, gypsum more so than mulch, and both treatments resulted in significantly higher numbers of reseeded seedlings compared with controls. Gypsum also improved the survival of the cohorts of seedlings of the larger seeded Tripteris sinuata. Tripteris showed the highest number of seedlings (maximum count of 150 seedlings/1,000 viable seeds sown) and surviving plants of the three reseeded species, which included two small‐seeded species, Ruschia spinosa and Chaetobromus dregeanus. Throughout the study period significantly higher plant volumes of naturally seeded annuals and perennials were recorded in the gypsum and/or mulch treatments compared with the controls. Germination and emergence of reseeded and naturally seeded plants appears to be determined by the availability of cool season (autumn to spring ) soil moisture, whereas follow‐up rainfall during this time is important for plant survival. Mulching of bare areas in the Succulent Karoo has the potential to re‐create vegetated areas that will further capture and conserve water, soil, and nutrients. Gypsum also showed positive results but might not be a cost‐effective option because of transport costs to these remote arid areas.     

The distribution and biology of nomadic birds in the Karoo, South Africa

Dryland nomadic bird species, as a proportion of all bird species in a biome in southern Africa, are highest in the arid grassland and arid and semi-arid Karoo in South Africa. Nomadic birds, of which the most widespread species is the greybacked finchlark Eremopterix verticalis (Smith), are most frequently observed in the north-central and north western Nama Karoo. The species richness of nomadic species is inversely correlated with species richness of all bird species in the Karoo. Since the distribution of nomadic birds is in areas where rainfall is patchy, low (<250 mm per year) and aseasonal, this supports the idea that fewer species are able to cope with resources that are patchy in time and space, and that there has been selection for nomadism in the species that are able to use patchy environments. Species richness and abundance of nomadic birds is negatively correlated with rainfall amount but positively correlated with the coefficient of variation of the rainfall and with rainfall in autumn. The frequency of nomadic birds is inversely correlated with altitude range; nomadic species are most often recorded in structurally simple habitats (shrubland and grassland) on open plains. Most nomadic bird species in the Karoo are granivorous. Perennial desert grasses are important components of the habitat and diet of small nomadic granivores, and also provide nest sites and nest material. Nomadic birds can breed throughout the year, without a clearly defined ‘season’ in both the Succulent and Nama Karoo. Average clutch sizes do not differ significantly between resident and all nomadic species in the arid and semi-arid Karoo. Nomadism is an evolutionary stable strategy for individual species only when extremes in environmental conditions are frequent enough, and unpredictable enough, to maintain movements to high resource patches or to maintain dispersal away from low resource patches. If high rainfall years are too regular or infrequent, or peaks in fluctuations of resources in the environment too low, or rainfall patches are randomly distributed, nomadism would not be maintained as part of the individual behaviour pattern.     

Physiological characteristics of geophytes in semi-arid Namaqualand,South Africa

Namaqualand, a semi-arid winter rainfall region of South Africa, supports an exceptional diversity of geophytic species. The survey focused on gas exchange reactions and chlorophyll a fluorescence in geophytes with different leaf orientation in relation to environmental variability. Although the above ground life cycle of geophytes can be extremely short, unlike desert annuals, they are not characterized by a high photosynthetic CO₂ uptake. Maximum CO₂ uptake ranged from 4 to 20 mol CO₂ m^-2 s^-1. Temperature optima of photosynthetic CO₂ uptake were comparably low and ranged from 12 to 22°C for eleven species tested, with only one species above 19°C. The decrease of CO₂ uptake with rising temperatures was associated with a substantial increase of photorespiration. Net photosynthesis was saturated between 500 and 900 mol photons m^-2 s^-1 while electron transport through PSII was saturated at higher photon flux densities. At light intensities beyond saturation, a high variability of PSII efficiency occurred. It was highest for horizontal leaves and lowest for upright leaves. However, the maximum quantum yield of PSII (F_v/F_m)remained constant during the course of a day, regardless of leaf orientation. This indicates the absence of photoinhibitory effects and a well protected photosynthetic apparatus. Leaf orientation determined interception of solar radiation and thus leaf temperature which was highest for horizontal leaves. In conclusion, Namaqualand geophytes show photosynthetic characteristics that are well adapted to the mild and generally moist conditions during the growing season.     

Trophic cascading in an oligotrophic temperate estuary, South Africa

Trophic cascading resulting from the coupling between componentsof the microbial food comprising bacteria, phytoplankton andprotozooplankton [nano- (2–20 µm) and microzooplankton(20–200 µm)] and mesozooplankton (copepods) (200–2000µm) was investigated at three stations in the oligotrophictemperate Kariega estuary during the summer (February) and winter(May) 2001. Total chlorophyll a (Chl a) was dominated by picophytoplankton(<2 µm) throughout the study comprising between 55and 74% of the total pigment during summer and between 64 and78% of the total during winter. Among the heterotrophic componentsof the pelagic food web, nanozooplankton (HNAN) were identifiedas the most important consumers of bacteria and microzooplankton(MICRO) the primary consumers of Chl a. The low impact of themesozooplankton (MESO) on the Chl a appears to be related tothe size structure of the phytoplankton community in the estuarywhich is too small to be grazed efficiently by the larger zooplankton.In response to the unfavourable size structure of the phytoplanktoncommunity in the estuary, it is suggested that the MESO consumeHNAN, MICRO and/or detritus. The negative impact of the MESOon the net growth rates of the HNAN and MICRO resulted in adecrease in the feeding impact of these organisms on the Chla < 2 µm and bacteria. This result is consistent withthe expectations of predator–prey cascades.     

Life on high: the diversity of small mammals at high altitude in South Africa

The Great Escarpment is the major mountain system in South Africa, yet very few biological surveys have been conducted outside of the well-known Drakensberg section. This is surprising given the important role that mountains play in local and global biodiversity patterns. In this study, small mammal diversity and community composition were estimated at three high altitude (>1,700?m) sites within the Sneeuberg Mountain Complex (SMC) of the Great Escarpment, South Africa from June 2009 to May 2010. The influences of selected environmental variables on diversity were also tested. Of 423 live-captures, a total of 292 unique individuals of 12 small mammal species (one shrew, one elephant shrew and 10 rodents) were identified during 5,280 trap nights. No single environmental variable could account for the variation observed in diversity measurements but vegetation height appeared to be the most important factor to influence the number of individuals captured. It is hypothesised that the high species richness and diversity of small mammals observed in the SMC compared to other parts of the Great Escarpment is due to the SMC being located in a transition zone of the Grassland and Nama-Karoo biomes. Our results suggest that the SMC could be important in conserving small mammal species from western and eastern assemblages across South Africa.     

Community structure on unusual habitat islands: quartz-fields in the Succulent Karoo,South Africa

Quartz fields are edaphically arid, azonal habitats occurring under different macroclimatic conditions in several arid regions of southern Africa. They are the exclusive home of 142 plant species of which ca. 70% are local or regional endemics. This paper is an analysis of the quartz-field floras and growth form-soil relationships in two quartz field regions: the Knersvlakte in the Namaqualand-Namib Domain of the Succulent Karoo, and the western Little Karoo in the Southern Karoo Domain. The Knersvlakte supported 52 quartz-field specialists of which 39 were endemic to the region. Corresponding data for the Little Karoo were 11, and 10 species, respectively. In both regions, the average canopy cover on the quartz-field relevés was ca. 8%, and more than half of this comprised contracted, succulent nanochamaephytes. Cover and vegetation stature were markedly higher on adjacent zonal habitats. Quartz fields in both regions supported a similar array of compact, subglobose and subterranean nanochamaephytes, as evidenced by convergent patterns in two distantly related genera (Argyroderma N. E. Brown and Gibbaeum (Haworth) N. E. Brown, both Mesembryanthemaceae), endemic to the Knersvlakte and largely restricted to the Little Karoo, respectively. Analyses of vegetational and edaphic data of quartz fields and adjacent, zonal habitats were carried out using multivariate direct gradient analysis (Canonical Correspondence Analysis) in order to identify those factors that control the peculiar composition of growth forms on quartz fields. The results revealed highly similar patterns of growth form composition in relation to similar edaphic gradients in both regions. In general, the soils of quartz fields were shallower compared to those of adjacent zonal habitats. In both regions, two different groups of quartz-field edaphic habitats, representing extremes of a continuum, were identified. Group 1 was characterized by high salt content, neutral to slightly acid soil pH, and low stone content. Group 2 was characterized by low salt content, low soil pH, and high stone content. Group 1 quartz fields are the most edaphically arid habitats and support the highest relative cover and diversity of subglobose and subterranean chamaephytes. The combination of reduced competition from larger growth forms, shallow soils and high soil salinity, represents a regionally unusual selective regime. Some succulent lineages in the Mesembryanthemaceae have undergone diversification which has resulted in the fine-scale discrimination of subtle edaphic gradients within the saline quartz-patch habitats. Reliable seasonal rainfall and reduced thermal stress have also played a role in the evolution of quartz patch specialists.     

Reserve selection in the Succulent Karoo,South Africa: coping with high compositional turnover

The Succulent Karoo biome is home to the world's richest succulent flora. It has approximately 1954 endemic plant species, and is the only semi-arid region to qualify as a hotspot of global significance. Despite its importance, only 2% of the biome is currently protected. Based on its flora, the biome can be divided into 12 bioregions, reflecting its high compositional turnover in relation to environmental and geographical gradients. Only three of these bioregions (the Gariep Centre, the Namaqualand Rocky Hills and the Tanqua Karoo) contain National Parks, and three contain large (over 10000 ha) provincial reserves (the Gariep Centre, the Namaqualand Rocky Hills and the Little Karoo). The current reserve system does little to conserve biodiversity, with only one reserve significantly conserving Red Data Book (RDB) plant diversity. Using a RDB plant species database of 3874 records at a quarter degree scale (QDS = 15×15), we used hotspot analyses and iterative reserve selection algorithms to identify possible locations for future reserves. The hotspot analysis and iterative analyses yielded similar results for the top 11 QDS, mainly due to very high local endemism. Also because of the local endemism and the high species turnover within the biome, the real-world iterative algorithm (starting with the seven already reserved QDS) selected a very large total number of QDS (59% of the total in the biome) to conserve all RDB species. As a possible alternative to conservation planning based on QDS, we also assessed priorities at the scale of bioregions, but showed that representation at this geographic level misses important areas defined at a finer scale. We suggest that if the objective is to maximise the retention of RDB species in the landscape (to pre-empt extinction by scheduling the allocation of limited conservation resources), at least the top 5% of QDS (n=11) selected by the iterative procedure, and identified as the core conservation sequence by analysis of endemicity and threat, should be given priority for reservation. Less extensive and, in some cases, less formal conservation action can be applied to QDS later in the sequence, based on species-specific monitoring and action plans. Of the 11 core areas, four fall in a node centred on the Vanrhynsdorp Centre, two fall in a node centred on the Kamiesberg, and the remaining five are isolated. With existing reserves, the core areas capture 50% of the RDB flora in 8% of the biome.     

Effect of grazing on vegetation and soil of the heuweltjieveld in the Succulent Karoo,South Africa

We asked how historical and recent grazing intensity affect the patchy landscape of the heuweltjieveld in the semi-arid biodiversity hotspot Succulent Karoo. The study was carried out on a communal farmland 80 km south-west of Springbok, in Namaqualand. Heuweltjies are roughly circular earth mounds that are regularly distributed in this landscape. We sampled plant species and life-form composition, diversity measures, habitat and soil variables in 100 m² plots, placed in three visually distinguishable heuweltjie zones (centre, fringe, and matrix) and distributed across grazing camps with different recent and historic grazing intensities. Differences between heuweltjie zones were assessed with ANOVAs and multiple linear regressions. The effect of past and recent grazing intensity on soil and plant variables was analysed by Generalized Linear Models for each heuweltjie zone separately. The three zones constituted clearly distinguishable units in terms of vegetation and soil characteristics. Soil pH and cover of annual plants increased from matrix to centres, while total vegetation cover, species richness and perennial plant cover decreased in the same direction. Historic (pre-2000) grazing patterns had the strongest effects on fringes, showing the strongest soil and vegetation-related signs of overutilization with increased stocking density. Centres showed signs of overutilization irrespective of the stocking density. The much shorter exposure to recent grazing pattern (post-2000), which was nearly inverse to the historic grazing pattern, showed increase of vegetation cover (centres) and species richness (matrix) with recent grazing intensity. We interpret these effects as still visible responses of the lower grazing intensity in these camps during the historic period. No recovery under recent grazing was observed at any of the zones. We conclude that irrespective of their conducive growing conditions, once transformed to a disturbed state, heuweltjie centres recover slowly, whereas the less impacted soil and vegetation of fringes are more responsive than centres and matrix.     

Reproduction in the round-eared elephant shrew (Macroscelides proboscideus) in the southern Karoo, South Africa

Reproduction in round-eared elephant shrews occurred throughout the year. Male round-eared elephant shrews were spermatogenically active, with spermatozoa stored in the cauda epididymes, throughout the year. Pregnant females occurred in all months except March and May and there was a decline in the occurrence of pregnancies during early winter (March-July). This tendency towards seasonality of pregnancies was mirrored by the appearance of juveniles, with 77% of all young animals caught between September and February. Bone calcium concentrations were significantly lower during the dry winter than during summer. From October onwards (the beginning of the wet season), bone calcium concentrations increased, reaching high levels in December which were maintained until April. This increase in bone calcium concentrations coincided with the rainy season and with an increase in the intake of herbage, and during this period 60% of all pregnancies occurred. We conclude that the ability of the round-eared elephant shrew to vary its diet may allow some individuals to breed throughout the year. The reduction in the occurrence of pregnancies in early winter probably ensures that few births occur when bone calcium concentrations are low.     

Non-target grasshoppers as indicators of the side-effects of chemical locust control in the Karoo, South Africa

In most locust or grasshopper control programmes, the proximate aim is to suppress grasshopper numbers. However, in the semi-arid Karoo, South Africa, only the brown locust (Locustana pardalina) has significant pest status. Non-target grasshoppers form a conspicuous and important part of the Karoo ecosystem, many being endemic. Grasshopper diversity was monitored in treated and untreated plots (0.25 ha) to establish the impact of spraying. Grasshopper abundance was significantly reduced one day after treatment. Vagile species recovered by immigration from the surrounding areas following the breakdown of chemical residues. Endemic apterous bushhoppers with low vagility recovered the following season after rainfall triggered hatching. Grasshopper numbers hatching in treated plots were significantly lower than in untreated plots the following summer season because of a reduction in the number of individuals in the preceding generation. However, species composition was similar to untreated plots and this reduction is unlikely to have significant, long-term biological effects in such small treated areas (0.25 ha being usual for hopper band control). The rate of recovery of grasshoppers, particularly bushhoppers, was linked to rainfall indicating that the timing of control relative to rainfall is important. Grasshopper assemblages are potentially useful indicators of the effect of chemical locust control in the Karoo.     

Identification and quantification of edible plant foods in the Upper (Nama) Karoo,South Africa

More than 18 000 archaeological sites have been identified, and a dozen rock shelter sites investigated in the Zeekoe Valley, Upper Karoo, South Africa, but no work has been performed to date regarding edible plant remains. A baseline for understanding potential contribution of plants to the Zeekoe Valley diet is crucial for developing models of land use and mobility patterns for Late Stone Age (LSA) inhabitants, particularly since ethnographically known foragers in Botswana, some 800 km to the north, are as much as 80% dependent on plant foods for their survival. Since native foraging groups are long extinct in this semi-arid region with abundant natural springs, a rigorous investigation of botanical and ethnohistoric literature forms the groundwork for field investigations where direct ethnographic observation is no longer an option. First, edible species in the study area are identified in the literature. They are then sought on the ground with the aid of local informants whose families have resided in the valley for generations. It appears as though some knowledge of local plants gained from native foragers 150 years ago or more has remained in Afrikaans families passed down from landowning parent to child. On the ground, collection and middle range experimentation was followed by basic nutritional analysis. These measures were then used to compare foraging efficiency to measures from extant foraging groups. While dozens of edible species were identified, five plant species formed the focus of this study: Slymstock Uintjie (Albuca canadensis); Boesman Uintjie (Cyperus usitatus, Cyperus fulgens); Jakkalsbosberry (Diospyros austro-africana); Rooi wortel (Pelargorium sidoides); and Osbossie (Talinum caffrum). Results suggest native foraging groups, now extinct in the vicinity, may have been 60% or more dependent on plant food resources, despite abundance of game in the area and in the archaeological record.     

Trophic levels of small mammals: Multi-elemental composition and toxic load

The chemical compositions (25 elements) of the diet and carcass of two sympatric small mammal species (Clethrionomys glareolus and Sorex caecutiens) inhabiting near a large copper smelter and in unpolluted area (Middle Ural, Russia) have been analyzed and compared. The group of phytophages is shown to play a special role in the translocation of chemical elements over the trophic levels of mammals. Specific features of the diet and a barrier at the gastrointestinal level limit accumulation of chemical elements in the animal body. Under the same conditions, carnivores act in the mammal community as concentrators of several elements (Pb, Cd, Cr, and As), displaying increased their concentrations in the body as compared with the diet. On the other hand, the toxic load on the animal organism is independent of trophic specialization.     

Growth,flowering and recruitment of shrubs in grazed and in protected rangeland in the arid Karoo,South Africa

A three-year study involving 1300 marked shrubs of three species differing in palatability to sheep provided evidence that changes in the demographic structure of shrub populations in arid rangelands are a function of seed availability. Sheep reduced canopy size and flowering of their preferred forage species but had no effect on survivorship of seedlings or established plants during the study. Although annual turnover in all populations was low (<6%), abundant recent recruitment of non-forage species was observed on degraded rangeland. Natality of all three species was positively correlated with flower abundance. Mortality was correlated with natality because seedlings had a low probability of surviving their first year. Recruitment of both forage and non-forage species, appeared to be inhibited by competition and seedlings seldom survived near adult plants of the same growth form.