Perennial Species Richness Research Articles

Consequences of Buffelgrass Pasture Development for Primary Productivity, Perennial Plant Richness, and Vegetation Structure in the Drylands of Sonora, Mexico

In large parts of northern Mexico native plant communities are being converted to non-native buffelgrass (Pennisetum ciliare) pastures, and this conversion could fundamentally alter primary productivity and species richness. In Sonora, Mexico land conversion is occurring at a regional scale along a rainfall-driven gradient of primary productivity, across which native plant communities transition from desert scrub to thorn scrub. We used a paired sampling design to compare a satellite-derived index of primary productivity, richness of perennial plant species, and canopy-height profiles of native plant communities with buffelgrass pastures. We sampled species richness across a gradient of primary productivity in desert scrub and thorn scrub vegetation to examine the influence of site productivity on the outcomes of land conversion. We also examined the influence of pasture age on species richness of perennial plants. Index values of primary productivity were lower in buffelgrass pastures than in native vegetation, which suggests a reduction in primary productivity. Land conversion reduced species richness by approximately 50% at local and regional scales, reduced tree and shrub cover by 78%, and reduced canopy height. Land conversion disproportionately reduced shrub species richness, which reflects the common practice among Sonoran ranchers of conserving certain tree and cactus species. Site productivity did not affect the outcomes of land conversion. The age of a buffelgrass pasture was unrelated to species richness within the pasture, which suggests that passive recovery of species richness to preconversion levels is unlikely. Our findings demonstrate that land conversion can result in large losses of plant species richness at local and regional scales and in substantial changes to primary productivity and vegetation structure, which casts doubt on the feasibility of restoring native plant communities without active intervention on the part of land managers.

Native Perennial Forb Variation Between Mountain Big Sagebrush and Wyoming Big Sagebrush Plant Communities

Big sagebrush (Artemisia tridentata Nutt.) occupies large portions of the western United States and provides valuable wildlife habitat. However, information is lacking quantifying differences in native perennial forb characteristics between mountain big sagebrush [A. tridentata spp. vaseyana (Rydb.) Beetle] and Wyoming big sagebrush [A. tridentata spp. wyomingensis (Beetle & A. Young) S.L. Welsh] plant communities. This information is critical to accurately evaluate the quality of habitat and forage that these communities can produce because many wildlife species consume large quantities of native perennial forbs and depend on them for hiding cover. To compare native perennial forb characteristics on sites dominated by these two subspecies of big sagebrush, we sampled 106 intact big sagebrush plant communities. Mountain big sagebrush plant communities produced almost 4.5-fold more native perennial forb biomass and had greater native perennial forb species richness and diversity compared to Wyoming big sagebrush plant communities (P < 0.001). Nonmetric multidimensional scaling (NMS) and the multiple-response permutation procedure (MRPP) demonstrated that native perennial forb composition varied between these plant communities (P < 0.001). Native perennial forb composition was more similar within plant communities grouped by big sagebrush subspecies than expected by chance (A = 0.112) and composition varied between community groups (P < 0.001). Indicator analysis did not identify any perennial forbs that were completely exclusive and faithful, but did identify several perennial forbs that were relatively good indicators of either mountain big sagebrush or Wyoming big sagebrush plant communities. Our results suggest that management plans and habitat guidelines should recognize differences in native perennial forb characteristics between mountain and Wyoming big sagebrush plant communities.

Plant diversity and flowering displays on old fields in the arid Namaqua National Park, South Africa

National Park and to investigate whether the time since abandonment has impacted on the diversity and mass flowering displays. Sixty-two old field sample sites were surveyed using the Braun-Blanquet method. Floristic data were analysed to produce a hierarchical classification, while a principal coordinates analysis was used to establish whether the ordination supported the classification. Species richness (total number of taxa), as well as the Shannon-Wiener diversity index, was calculated per vegetation unit for the different life forms. Four old field communities were identified, each containing a unique complement of species, which differed in their potential to produce a mass flowering display. On the Skilpad section of the park, Ursinia cakilefolia dominated the spectacular mass floral displays for which the park has become well known. Old fields in other parts of the park did not produce the same spectacular displays. Although total and perennial species richness did not differ significantly with time since abandonment, the richness of annual species, in particular of the showy annual species, decreased with time since abandonment. The relative contribution of the perennial species to vegetation cover increased with time since abandonment, whereas the relative contribution made by showy annual species to vegetation cover declined with time since abandonment. Although species composition and the potential to produce mass flowering displays of the four communities differed, diversity parameters were similar. However, to maintain a flower display for tourists on the Skilpad section, a degree of disturbance is essential. Conservation implication: Although deliberate disturbance is not desirable in a national park, we find that some disturbance is essential to maintain a spectacular flowering display. However, these intentionally disturbed old fields cover only a small proportion of the total area of the park. All other old fields in the park should not be disturbed, and should be allowed to recover naturally.

Community-level consequences of invasion: impacts of exotic clonal plants on riparian vegetation

Biological invasions by exotic species are occurring at exceptional rates and spatial scales worldwide and are increasingly recognized as key forms of global environmental change. Despite this growing prominence, surprisingly few ecological studies have quantified the impacts of exotic taxa on the plant communities they invade, and this is especially evident in riparian ecosystems. Along the Russian River in northern California, we used both comparative and experimental studies to investigate the influence of two exotic clonal plant species—giant reed (Arundo donax) and blue periwinkle (Vinca major)—on the composition of riparian plant communities. Our results indicate that Arundo invasion was associated with significantly lower richness of native perennial plant species on stream banks and floodplains, whereas there was no relationship on gravel bars. Additional research showed that plots invaded by Arundo and Vinca, both individually and collectively, exhibited significantly lower native and exotic species richness and abundance of both established plants and seedlings than uninvaded plots. Finally, after 2 years, experimental reductions of Arundo biomass via cutting and herbicide resulted in significantly increased native plant species richness and abundances of both established plants and seedlings, while having no effects on other exotics. In summary, our results indicate that Arundo and Vinca have strongly negative effects on diverse components of a riparian plant community, which must be addressed via effective control and restoration efforts.

Forb responses to grazing and rest management in a critically endangered Australian native grassland ecosystem

Worldwide, temperate grasslands have been extensively cleared for agriculture and urban expansion and the ‘Natural Temperate Grassland of the Victorian Volcanic Plain’ in south-eastern Australia has recently been listed as critically endangered. Because of land clearing, these grasslands now occupy &lt;1% of their original distribution and much of the remaining grassland continues to be grazed by livestock. Although forbs (wildflowers) constitute most of the floristic richness in natural grasslands, few experimental studies have focused on their responses to strategic livestock grazing and rest. This paper reports on the outcomes of five grazing and rest management regimes imposed for 4 years at three sites on the Victorian Volcanic Plain. Seasonal grazing and rest management regimes resulted in significantly different native and exotic forb frequencies, but not richness. Native perennial and exotic annual forb frequency was higher when management incorporated grazing and rest periods (14 and 16% deviance explained), particularly with spring rest from grazing. However, the most important influence on native perennial and exotic annual and perennial forb frequency (46, 58 and 41% deviance explained) and native perennial and exotic annual species richness (62 and 35% deviance explained) was site. Differences among the three sites included soil, rainfall, size of remnant, presence of small burrowing mammals, management history and consequent species assemblages. Despite differences among sites, the results indicate that native perennial forb frequency may be increased using management regimes that incorporate both grazing and rest. However, targeted management may be necessary to reduce exotic annual forbs, also promoted by grazing with seasonal rest.

Experimental study of the effect of hydrology and mechanical soil disturbance on plant communities in Mediterranean temporary pools in Western Morocco

Physical soil disturbance and the hydrology of temporary pools affect the biomass, species composition and richness of plant communities. Disturbance liberates sites for the random recruitment of new individuals. The addition of seeds modifies the structure of the communities. In order to verify these hypotheses concerning the vegetation of temporary pools, an experiment was carried out using 72 soil samples collected from a pool in Western Morocco and placed in containers. Three types of laboratory treatments were applied, each combined with control treatments: soil disturbance (control/disturbed), hydrology (flooded, saturated and dry) and seed addition (sowing/no sowing). The total biomass, the annual and perennial species richness were calculated for each sample to test the effects of disturbance, hydrology and seed addition on the biomass and species richness of the various plant communities. The results show that disturbance reduces the total biomass, especially of perennials, but without significantly increasing the richness of annuals. Seed addition does not affect the total biomass and reduces total richness only in saturated soil, where biomass production is high. The most extreme stress conditions (drought and flooding) limit the abundance of species and therefore competition.

Effects of camel grazing on density and species diversity of seedling emergence in the Dubai (UAE) inland desert

Germination in the arid rangelands of the UAE occurs as an ‘event’ following a mid-winter to spring rainfall. A fence line study of germination events was conducted in 2005 and 2006 to identify the response to differential grazing regimes. Fifty-six 1 m 2 seedling plots were destructively sampled each season. Heavy grazing reduced species richness and diversity without significantly reducing seedling density. Both annual and perennial species were impacted, though the reduction in richness of annual species was less pronounced than the natural variation among locations. Direct grazing of seedlings is limited to a few weeks, due to the short annual plant life span. Reduction of perennial seedling density and species richness was likely caused by the reduced size of adult plants under grazing. Recruitment of perennial species could be affected by heavy grazing, leading to loss of habitat, though under moderate grazing levels this could easily be compensated by greater survival.

Linking the spatial patterns of organisms and abiotic factors to ecosystem function and management: insights from semi-arid environments

Abstract. Numerous theoretical and modeling studies have demonstrated the ecological significance of the spatial patterning of organisms on ecosystem functioning and dynamics. However, there is a paucity of empirical evidence that quantitatively shows how changes in the spatial patterns of the organisms forming biotic communities are directly related to ecosystem structure and functioning. In this article, I review a series of experiments and observational studies conducted in semi-arid environments from Spain (degraded calcareous shrubland, steppes dominated by Stipa tenacissima, and gypsum shrublands) to: 1) evaluate whether the spatial patterns of the dominant biotic elements in the community are linked to ecosystem structure and functioning, and 2) test if these patterns, and those of abiotic factors, can be used to improve ecosystem restoration. In the semiarid steppes we found a significant positive relationship between the spatial pattern of the perennial plant community and: i) the water status of S. tenacissima and ii) perennial species richness and diversity. Experimental plantings conducted in these steppes showed that S. tenacissima facilitated the establishment of shrub seedlings, albeit the magnitude and direction of this effect was dependent on rainfall conditions during the first yr after planting. In the gypsum shrubland, a significant, direct relationship between the spatial pattern of the biological soil crusts and surrogates of ecosystem functioning (soil bulk density and respiration) was found. In a degraded shrubland with very low vegetation cover, the survival of an introduced population of the shrub Pistacia lentiscus showed marked spatial patterns, which were related to the spatial patterns of soil properties such as soil compaction and sand content. These results provide empirical evidence on the importance of spatial patterns for maintaining ecosystem structure and functioning in semi-arid ecosystems. Furthermore, they show how taking into consideration the small-scale spatial patterns of organisms and abiotic factors, their restoration can be improved.

An objective and quantitative methodology for constructing an index of stand structural complexity

In this paper, we demonstrate an objective and quantitative methodology for developing a stand scale index of structural complexity. While we use data from particular woodland and dry sclerophyll forests communities in south-eastern Australia to do this, our methodology has generic value. Our approach involves: (1) establishing a comprehensive suite of stand structural attributes; (2) quantifying attributes in the comprehensive suite, by collecting data from a set of stands representing the range of condition occurring in the vegetation communities in which the index is intended to operate; (3) identifying a core set of structural attributes from an analysis of these data; and (4) combining the core attributes in a simple additive index, in which attributes are scored relative to their observed levels in each vegetation community. To apply this approach, data were collected from 48 study sites representing the range of condition in a 15,000 km 2 study area located in the South-eastern Highlands Bioregion of Australia. The following 13 core attributes were identified from these data: vegetation cover <0.5 m; vegetation cover 0.5–6.0 m; perennial species richness; lifeform richness; stand basal area of live trees; quadratic mean diameter of live stems; ln(number of regenerating stems ha −1 + 1); ln(number of hollow-bearing trees ha −1 + 1); ln(number of dead trees ha −1 + 1); √(number of live stems ha −1 >40 cm dbh); √(total log length ha −1); √(total large log length ha −1); and litter dry weight ha −1. These core attributes were combined in a simple additive index, in which, each attribute accounted for 10 points in a total index value of 130. Attributes were rescaled as a score from 0 to 10, using equations that modelled attribute score as a function of the raw attribute data ( r 2 > 0.95, p < 0.0001). The index was not sensitive to attribute weightings and, on this basis, attributes carried equal weight. In this form, the index was straightforward to apply, and differentiated between study sites.

Wide Ecological Amplitude of a Diversity-Reducing Invasive Grass

The goals of this study were to identify habitats occupied by the Eurasian grass Bothriochloa ischaemum (King Ranch bluestem) on the eastern Edwards Plateau of central Texas, USA, and to measure the effects of this invasive species on plant diversity. A set of descriptive field studies were conducted to determine the relationships between habitat characteristics (woody cover, slope, presence of roads and trails, history of prescribed burning, and presence of grazing) and the presence and abundance of this species. Species richness and diversity of perennial herbaceous species were compared between plots in which B. ischaemum was absent and plots that it dominated.

Arbuscular mycorrhizal fungi associated with Populus–Salix stands in a semiarid riparian ecosystem

This study examined the activity, species richness, and species composition of the arbuscular mycorrhizal fungal (AMF) community of Populus-Salix stands on the Verde River (Arizona, USA), quantified patterns of AMF richness and colonization along complex floodplain gradients, and identified environmental variables responsible for structuring the AMF community. Samples from 61 Populus-Salix stands were analyzed for AMF and herbaceous composition, AMF colonization, gravimetric soil moisture, soil texture, per cent organic matter, pH, and concentrations of nitrate, bicarbonate phosphorus and exchangeable potassium. AMF species richness declined with stand age and distance from and elevation above the channel and was positively related to perennial species cover and richness and gravimetric soil moisture. Distance from and elevation above the active channel, forest age, annual species cover, perennial species richness, and exchangeable potassium concentration all played a role in structuring the AMF community in this riparian area. Most AMF species were found across a wide range of soil conditions, but a subset of species tended to occur more often in hydric areas. This group of riparian affiliate AMF species includes several not previously encountered in the surrounding Sonoran desert.

Effects of livestock watering sites on alien and native plants in the Mojave Desert, USA

Increased livestock densities near artificial watering sites create disturbance gradients called piospheres. We studied responses of alien and native annual plants and native perennial plants within 9 piospheres in the Mojave Desert of North America. Absolute and proportional cover of alien annual plants increased with proximity to watering sites, whereas cover and species richness of native annual plants decreased. Not all alien species responded the same, as the alien forb Erodium cicutarium and the alien grass Schismus spp. increased with proximity to watering sites, and the alien annual grass Bromus madritensis ssp. rubens decreased. Perennial plant cover and species richness also declined with proximity to watering sites, as did the structural diversity of perennial plant cover classes. Significant effects were focused within 200 m of the watering sites, suggesting that control efforts for alien annual plants and restoration efforts for native plants should optimally be focused within this central part of the piosphere gradient.

CHANGES IN SPECIES ASSEMBLAGES WITHIN THE ADELAIDE METROPOLITAN AREA, AUSTRALIA, 1836–2002

Currently, slightly less than half the world's population lives in dense urban areas, principally cities. In Australia, nearly 85% of people live in towns with 1000 or more residents. Although individual species of urban flora and fauna have often been well studied, little is known of the long-term temporal patterns associated with changes in both the abiotic and biotic environments as urban systems expand. Using historical and current information, the changes in species richness (defined as the native and introduced vertebrates and vascular plants) in Adelaide, South Australia, are described from its founding in 1836 until 2002. Adelaide is an isolated city of over a million inhabitants, bordered by a range of hills and the South Australian coastline. With a Mediterranean climate, a culture that places high importance on private residential gardens, and the presence of extensive public parklands, the metropolitan area has a significant diversity of both native and introduced flora and fauna. Using only the presence or absence of a species, the changes to plant and vertebrate species richness were quantified by analyzing the observed patterns of change at a functional group level. Powerful correlative evidence is provided to explain the development and establishment of patterns in urban ecology. There has been a dramatic change in species composition, with an increase in total species numbers of ∼30%. At least 132 native species of plants and animals have become locally extinct, and a minimum of 648 introduced species have arrived (mostly plants). The plants increased in species richness by 46%. Fifty percent of the native mammal species were lost, and overall, the birds declined by one species, representing 21 extinctions and 20 successful introductions. Amphibians and reptiles showed no net change. The herbaceous perennial and annual plant species richness showed a substantial increase. This temporal approach to urban ecology demonstrates new ways to identify individual species or groups at risk of extinction and provides some long-term management goals for large urban areas.

Remnant shrubs in Mediterranean semi-arid steppes: effects of shrub size, abiotic factors and species identity on understorey richness and occurrence

Isolated shrub patches are a key element for community structure and dynamics in semi-arid ecosystems, and may act as “hot spots” of understorey species diversity. Despite its importance, the relationships between shrub patch characteristics and understorey species richness, and the relative importance of these characteristics against other factors driving understorey species richness, are still poorly understood. We studied perennial species richness under the canopy of late-successional shrubs in semi-arid Stipa tenacissima steppes of SE Spain. The main aim of this study was to evaluate the relationship between shrub size and understorey richness, and to test if this relationship is modified by species identity. We also aimed to know the relative importance of shrub patch characteristics and abiotic factors as predictors of the distribution of understorey species under shrub canopies. Altitude and geographical co-ordinates were able to significantly explain the patterns of shrub occurrence and abundance in the study area. Understorey species richness was significantly related to the size of individual shrubs according to a simple power relationship for all evaluated species. Slope values of linear regressions with log-transformed data, ranging between 0.22 and 0.37, did not differ between species. Site characteristics, patch characteristics and patch species identity significantly explained the occurrence of species on patches. However, the relative importance of site characteristics was higher than that of patch characteristics and species identity in explaining these patterns. Our results agree with the general expectations of the theory of island biogeography and complement previous studies that emphasise the importance of late-successional shrubs in semi-arid Stipa steppes. Environmental management activities within these steppes should promote the conservation of remnant shrubs, as well as its introduction with restoration activities.

Life-history Habitat Matching in Invading Non-native Plant Species

We briefly reviewed the literature on habitat matching in invading non-native plant species. Then we hypothesized that the richness and cover of native annual and perennial plant species integrate complex local information of vegetation and soils that would help to predict invasion success by similarly adapted non-native plant species. We tested these ‘life-history habitat matching’ relationships in 603 0.1-ha plots, including 294 plots in Colorado, which were relatively high for the cover of native perennial plant species, and for 309 0.1-ha plots in southern Utah, which were relatively high in the cover of native annual plant species. We found strong positive relationships between the richness and foliar cover for both native and non-native species, whether they were annual or perennial species (0.34 > r 2 < 0.53; P < 0.0001). We also found significant positive relationships between the cover of native annual species at a site and the richness (r 2 = 0.13; P < 0.0001) and the foliar cover (r 2 = 0.06; P < 0.0001) of non-native annual species. The proportion of non-native annual species in the flora of a plot also increased significantly with the foliar cover of native annual species. Conversely, the richness and cover of non-native annual species were significantly negatively associated with the foliar cover of native perennial species (r 2 = 0.05 and 0.06, respectively; P < 0.0001). The cover of non-native annual or perennial species was not significantly correlated with soil texture variables, %N, or %C. We conclude that there may be a high degree of life-history habitat matching by non-native annual species in these study sites. Information on native annual and perennial species richness and cover may help characterize the complex soils, climate, and disturbance environment in which similarly adapted non-native plant species establish and gain foliar cover.

On the importance of patch attributes, environmental factors and past human impacts as determinants of perennial plant species richness and diversity in Mediterranean semiarid steppes

ABSTRACTRichness and diversity of perennial plant species were evaluated in 17Stipa tenacissimasteppes along a degradation gradient in semiarid SE Spain. The main objective of the study was to evaluate the relative importance of historical human impacts, small‐scale patch attributes and environmental factors as determinants of perennial plant species richness and diversity inS. tenacissimasteppes, where vegetation is arranged as discrete plant patches inserted on a bare ground matrix. Partial least squares regression was used to determine the amount of variation in species richness and diversity that could be significantly explained by historical human impacts, patch attributes, and environmental factors together and separately. They explained up to 89% and 69% of the variation in species richness and diversity, respectively. In both cases, the predictive power of patch attributes models was higher than that of models consisting of abiotic characteristics and variables related to human impact, suggesting that patch attributes are the major determinants of species richness and diversity in semiaridS. tenacissimasteppes. However, patch attributes alone are not enough to explain the observed variation in species richness and diversity. The area covered by late‐successional sprouting shrubs and the distance between consecutive patches were the most influencing individual variables on species richness and diversity, respectively. The implications of these results for the management ofS. tenacissimasteppes are discussed.

Predicting Plant Community Response to Picloram

Effective rangeland weed programs require the ability to predict plant community responses to management. Our objective was to develop regression equations to predict the plant community after control with picloram using the pre-treatment plant community. Five transects were established from dense spotted knapweed (Centaurea maculosa Lam.) in the center of each patch to an area of low or no spotted knapweed occurrence on the outside of the patch. Transects ended in areas dominated by Idaho fescue (Festuca idahoensis Elmer). Twenty permanent plots (20 x 50 cm, spacing along the transect ranged from 1/2 to 2 m) were placed along this gradient. Pre-treatment density and cover of all species were sampled in each plot. Biomass of all species was harvested in plots adjacent to the transect. Picloram (4-amino-3,5,6-trichloropicolinic acid) was applied along each transect at a rate of 0.28 kg a.i. ha-1 in October 1996 to each plot. Density, cover, and biomass of all species were re-sampled in August 1998. Regression models were fit using perennial grasses, Idaho fescue, forbs, species richness, and species diversity after treatment as predicted variables. All predicted variables were indigenous species. Regressor variables used were site, transect, and spotted knapweed, a spotted knapweed quadratic component, indigenous perennial grasses, Idaho fescue, indigenous forbs, species richness, and species diversity sampled in the first year (1996) prior to treatment. The best predictive models for assessing post-management indigenous perennial grass, Idaho fescue, and species richness were based on density. The best models predicting post-management forbs and species diversity were based on cover and biomass, respectively. In 4 out of the 5 models, for a given post-management parameter, an important predictor in the model was its pre-management regressor variable. Additionally, pre-management spotted knapweed was a relatively unimportant preditar in most models. The model predicting species diversity based on density (pre-treatment) predicted an increase in species diveristy 2 years after management. This study indicated that it may be feasible to use pre-management spotted knapweed was a relatively unimportant predictor in most models. The model predicting species diversity based on density (pre-treatment) predicted an increase in species diversity 2 years after management. This study indicated that it may be feasible to use pre-management plant community data to predict post-management plant community response for spotted knapweed-infested rangeland using picloram. DOI:10.2458/azu_jrm_v55i6_kedzie-webb

Vegetation and climate characteristics of arid and semi-arid grasslands in North America and their biome transition zone

The objective of this study was to investigate the relationship among species richness, functional group composition, and climate for three sites representing the shortgrass steppe, the Chihuahuan desert grasslands and their biome transition zone. We found that perennial species richness increased as the climate became more favorable for plant growth. The biome transition zone was more similar to the Chihuahuan desert grassland site in most climate and vegetation characteristics, partly because of the shorter biogeographic distance between the two sites. This study clarified the ecological position of the biome transition zone site with respect to the adjacent biomes.

Predicting plant community response to picloram

Effective rangeland weed programs require the ability to predict plant community responses to management. Our objective was to develop regression equations to predict the plant community after control with picloram using the pre-treatment plant community. Five transects were established from dense spotted knapweed (Centaurea maculosa Lam.) in the center of each patch to an area of low or no spotted knapweed occurrence on the outside of the patch. Transects ended in areas dominated by Idaho fescue (Festuca idahoensis Elmer). Twenty permanent plots (20 x 50 cm, spacing along the transect ranged from 1/2 to 2 m) were placed along this gradient. Pre-treatment density and cover of all species were sampled in each plot. Biomass of all species was harvested in plots adjacent to the transect. Picloram (4-amino-3,5,6-trichloropicolinic acid) was applied along each transect at a rate of 0.28 kg a.iha-1 in October 1996 to each plot. Density, cover, and biomass of all species were re-sampled in August 1998. Regression models were fit using perennial grasses, Idaho fescue, forbs, species richness, and species diversity after treatment as predicted variables. All predicted variables were indigenous species. Regressor variables used were site, transect, and spotted knapweed, a spotted knapweed quadratic component, indigenous perennial grasses, Idaho fescue, indigenous forbs, species richness, and species diversity sampled in the first year (1996) prior to treatment. The best predictive models for assessing post-management indigenous perennial grass, Idaho fescue, and species richness were based on density. The best models predicting post-management forbs and species diversity were based on cover and biomass, respectively. In 4 out of the 5 models, for a given post-management parameter, an important predictor in the model was its pre-management regressor variable. Additionally, pre-management spotted knapweed was a relatively unimportant preditar in most models. The model predicting species diversity based on density (pre-treatment) predicted an increase in species diveristy 2 years after management. This study indicated that it may be feasible to use pre-management spotted knapweed was a relatively unimportant predictor in most models. The model predicting species diversity based on density (pre-treatment) predicted an increase in species diversity 2 years after management. This study indicated that it may be feasible to use pre-management plant community data to predict post-management plant community response for spotted knapweed-infested rangeland using picloram.

Assessing and Monitoring the Health of Western Rangeland Watersheds

The most important function of watersheds in the western U.S. is the capacity to retain soil and water, thereby providing stability in hydrologic head and minimizing stream sediment loads. Long-term soil and water retention varies directly with vegetation cover. Data on ground cover and plant species composition were collected from 129 sites in the Rio Grande drainage of south-central New Mexico. This area was previously assessed by classification of Advanced Very High Resolution Radiometry (AVHRR) imagery. The classification of irreversibly degraded sites failed to identify most of the severely degraded sites based on size of bare patches and 35% of the sites classified as degraded were healthy based on mean bare patch size and vegetation cover. Previous research showed that an index of unvegetated soil (bare patch size and percent of ground without vegetative cover) was the most robust indicator of the soil and water retention function. Although the regression of mean bare patch size on percent bare ground was significant (p < 0.001), percent bare ground accounted for only 11% of the variability in bare patch size. Therefore bare patch size cannot be estimated from data on percent bare ground derived from remote sensing. At sites with less than 25% grass cover, and on sites with more than 15% shrub cover, there were significant relationships between percent bare soil and mean bare patch size (p < 0.05). Several other indicators of ecosystem health were related to mean bare patch size: perennial plant species richness (r = 0.6, p < 0.0001), percent cover of increaser species (r = 0.5, p < 0.0001) and percent cover of forage useable by livestock (r = 0.62, p < 0.0001). There was no relationship between bare patch size and cover of species that are toxic to livestock. In order to assess the ability of western rangeland watersheds to retain soil and water using remote sensing, it will be necessary to detect and estimate sizes of bare patches ranging between at least 0.5 m in diameter to several meters in diameter.