Shrub Canopy Cover Research Articles

Effects of habitat complexity on forest beetle diversity: do functional groups respond consistently?

ABSTRACTWe examined the responses of a beetle assemblage to habitat complexity differences within a single habitat type, Sydney sandstone ridgetop woodland, using pitfall and flight‐intercept trapping. Six habitat characters (tree canopy cover, shrub canopy cover, ground herb cover, soil moisture, amount of leaf litter, and amount of logs, rocks and debris) were scored between 0 and 3 using ordinal scales to reflect habitat complexity at survey sites. Pitfall trapped beetles were more species rich and of different composition in high complexity sites, compared with low complexity sites. Species from the Staphylinidae (Aleocharinae sp. 1 and sp. 2), Carabidae (Pamborus alternans Latreille), Corticariidae (Cartodere Thomson sp. 1) and Anobiidae (Mysticephala Ford sp. 1) were most clearly responsible for the compositional differences, preferring high complexity habitat. Affinities between general functional groupings of pitfall‐trapped beetles and habitat variables were not clear at a low taxonomic resolution (family level). The composition and species richness of flight‐intercept‐trapped beetles were similar in high and low complexity sites. Our study demonstrates that discrete responses of the various functional groups of beetles are strongly associated with their feeding habits, indicated by differing habitat components from within overall composite habitat complexity measures. Although habitat preferences by beetle species may often reflect their foraging habits, clarification of the causal mechanisms underpinning the relationships between habitat complexity and beetles are critical for the development of general principles linking habitat, functional roles and diversity.

Occupied and unoccupied sage grouse habitat in Strawberry Valley, Utah

This study evaluated multiple aspects of spring/summer sage grouse (Centrocercus urophasianus) habitat in Strawberry Valley, Utah by measuring vegetation associated with nest, brood and adult use sites. In addition, 3 types of random habitats were measured including available habitat within core use areas, random sagebrush (Artemisia spp.)/grass habitat outside core use areas, and random sagebrush/grass habitat sites that had been converted to an understory of smooth brome (Bromus inermis Leyss) by past range management practices. Logistic regression was used to identify those habitat variables that discriminated between site types. Variables that discriminated adult habitat from brood rearing habitat included: 1) sagebrush height (P ≤ 0.01) and 2) forb diversity (P = 0.12) with sagebrush height being greater at adult sites and forb diversity greater at brood sites Variables that significantly discriminated occupied adult habitat from random habitat outside of core use areas included: 1) percent grass cover (P ≤ 0.01) and 2) area of sagebrush canopy (P = 0.03) with both variables having grater values in adult habitat. Variables that significantly discriminated occupied adult habitat from random habitat with a smooth brome understory included: 1) percent forb cover (P ≤ 0.01), 2) shrub canopy cover (P = 0.02), and 3) area of sagebrush canopy (P = 0.08) with all variables being greater in adult habitat. In addition, this study identified sagebrush age, sagebrush canopy area, and forb diversity as potentially important aspects of sage grouse habitat that have not been previously reported.

Occupied and unoccupied sage grouse habitat in Strawberry Valley, Utah

This study evaluated multiple aspects of spring/summer sage grouse (Centrocercus urophasianus) habitat in Strawberry Valley, Utah by measuring vegetation associated with nest, brood and adult use sites. In addition, 3 types of random habitats were measured including available habitat within core use areas, random sagebrush (Artemisia spp.)/grass habitat outside core use areas, and random sagebrush/grass habitat sites that had been converted to an understory of smooth brome (Bromus inermis Leyss) by past range management practices. Logistic regression was used to identify those habitat variables that discriminated between site types. Variables that discriminated adult habitat from brood rearing habitat included: 1) sagebrush height (P ≤ 0.01) and 2) forb diversity (P = 0.12) with sagebrush height being greater at adult sites and forb diversity greater at brood sites Variables that significantly discriminated occupied adult habitat from random habitat outside of core use areas included: 1) percent grass cover (P ≤ 0.01) and 2) area of sagebrush canopy (P = 0.03) with both variables having grater values in adult habitat. Variables that significantly discriminated occupied adult habitat from random habitat with a smooth brome understory included: 1) percent forb cover (P ≤ 0.01), 2) shrub canopy cover (P = 0.02), and 3) area of sagebrush canopy (P = 0.08) with all variables being greater in adult habitat. In addition, this study identified sagebrush age, sagebrush canopy area, and forb diversity as potentially important aspects of sage grouse habitat that have not been previously reported.

Ecology and management of sage-grouse and sage-grouse habitat

Sage-grouse (Centrocercus urophasianus and C. minimus) historically inhabited much of the sagebrush-dominated habitat of North America. Today, sage-grouse populations are declining throughout most of their range. Population dynamics of sage-grouse are marked by strong cyclic behavior. Adult survival is high, but is offset by low juvenile survival, resulting in low productivity. Habitat for sage-grouse varies strongly by life-history stage. Critical habitat components include adequate canopy cover of tall grasses (≥ 18 cm) and medium height shrubs (40-80 cm) for nesting, abundant forbs and insects for brood rearing, and availability of herbaceous riparian species for late-growing season foraging. Fire ecology of sage-grouse habitat changed dramatically with European settlement. In high elevation sagebrush habitat, fire return intervals have increased (from 12-24 to > 50 years) resulting in invasion of conifers and a consequent loss of understory herbaceous and shrub canopy cover. In lower elevation sagebrush habitat, fire return intervals have decreased dramatically (from 50-100 to < 10 years) due to invasion by annual grasses, causing loss of perennial bunchgrasses and shrubs. Livestock grazing can have negative or positive impacts on sage-grouse habitat depending on the timing and intensity of grazing, and which habitat element is being considered. Early season light to moderate grazing can promote forb abundance/availability in both upland and riparian habitats. Heavier levels of utilization decrease herbaceous cover, and may promote invasion by undesirable species. At rates intended to produce high sagebrush kill, herbicide-based control of big sagebrush may result in decreased habitat quality for sage-grouse. Light applications of tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea) can decrease canopy cover of sagebrush and increase grass and forb production which may be locally important to nesting and foraging activities. The ability of resource managers to address sage-grouse habitat concerns at large scales is aided greatly by geomatics technology and advances in landscape ecology. These tools allow unprecedented linkage of habitat and population dynamics data over space and time and can be used to retroactively assess such relationships using archived imagery. The present sage-grouse decline is a complex issue that is likely associated with multiple causative factors. Solving management issues associated with the decline will require unprecedented cooperation among wildlife biology, range science, and other professional disciplines.

Ecology and management of sage-grouse and sage-grouse habitat

Abstract Sage-grouse (Centrocercus urophasianus and C. minimus) historically inhabited much of the sagebrush-dominated habitat of North America. Today, sage-grouse populations are declining throughout most of their range. Population dynamics of sage-grouse are marked by strong cyclic behavior. Adult survival is high, but is offset by low juvenile survival, resulting in low productivity. Habitat for sage-grouse varies strongly by life-history stage. Critical habitat components include adequate canopy cover of tall grasses (≥ 18 cm) and medium height shrubs (40–80 cm) for nesting, abundant forbs and insects for brood rearing, and availability of herbaceous riparian species for late-growing season foraging. Fire ecology of sage-grouse habitat changed dramatically with European settlement. In high elevation sagebrush habitat, fire return intervals have increased (from 12–24 to > 50 years) resulting in invasion of conifers and a consequent loss of understory herbaceous and shrub canopy cover. In lower elevatio...

Occupied and unoccupied sage grouse habitat in Strawberry Valley, Utah

This study evaluated multiple aspects of spring/summer sage grouse (Centrocercus urophasianus) habitat in Strawberry Valley, Utah by measuring vegetation associated with nest, brood and adult use sites. In addition, 3 types of random habitats were measured including available habitat within core use areas, random sagebrush (Artemisia spp.)/grass habitat outside core use areas, and random sagebrush/grass habitat sites that had been converted to an understory of smooth brome (Bromus inermis Leyss) by past range management practices. Logistic regression was used to identify those habitat variables that discriminated between site types. Variables that discriminated adult habitat from brood rearing habitat included: 1) sagebrush height (P ≤ 0.01) and 2) forb diversity (P = 0.12) with sagebrush height being greater at adult sites and forb diversity greater at brood sites Variables that significantly discriminated occupied adult habitat from random habitat outside of core use areas included: 1) percent grass cover (P ≤ 0.01) and 2) area of sagebrush canopy (P = 0.03) with both variables having grater values in adult habitat. Variables that significantly discriminated occupied adult habitat from random habitat with a smooth brome understory included: 1) percent forb cover (P ≤ 0.01), 2) shrub canopy cover (P = 0.02), and 3) area of sagebrush canopy (P = 0.08) with all variables being greater in adult habitat. In addition, this study identified sagebrush age, sagebrush canopy area, and forb diversity as potentially important aspects of sage grouse habitat that have not been previously reported.

Upland habitat use by Pyrenean grey partridges Perdix perdix hispaniensis during the breeding season

Whereas in most of Europe the decline of the grey partridge Perdix perdix is due primarily to agricultural intensification, the Pyrenean grey partridge P. p. hispaniensis is believed to suffer from the opposite effect, namely the abandonment of agricultural practices which allows the encroachment of dense shrublands. We investigated habitat use by the Pyrenean grey partridge during the breeding season and its relationship with reproductive success and survival. The study was based on 22 radio‐tagged grey partridges in a 5,800‐ha upland area of the eastern Pyrenees. Habitat use was non‐random, and shrubland with a shrub canopy cover higher than 40% was the most important requirement during the breeding season. In the spring, pairs that successfully reared a brood used shrublands (20–60% cover) twice as frequently as unsuccessful breeders, then in the summer halved their use of open habitats (montane grassland and shrubland with <40% cover), whereas failed breeders increased it sevenfold. Consequently, a good mixture of different cover types in the spring and summer is likely to provide the most suitable breeding habitat. There was no evidence linking the spring/summer survival of adult partridges to a particular habitat use. Current grazing practices, especially with the use of controlled burning to clear shrubby vegetation, reduce the amount of mature shrublands used by Pyrenean grey partridges. However, grazing management also delays the natural vegetation succession and hence contributes to the long‐term persistence of partridge habitat. Grazing practices that prevent reafforestation and maintain a mosaic of dense and open shrublands should be encouraged in the Pyrenean uplands.

Environmental factors influencing spatial patterns of shrub diversity in chaparral, Santa Ynez Mountains, California

We examined patterns of shrub species diversity relative to landscape‐scale variability in environmental factors within two watersheds on the coastal flank of the Santa Ynez Mountains, California. Shrub species richness and dominance was sampled at a hierarchy of spatial units using a high‐powered telescope from remote vantage points. Explanatory variables included field estimates of total canopy cover and percentage rock cover, and modeled distributions of slope, elevation, photosynthetically active radiation, topographic moisture index, and local topographic variability. Correlation, multiple regression, and regression tree analyses showed consistent relationships between field‐based measurements of species richness and dominance, and topographically‐mediated environmental variables. In general, higher richness and lower dominance occurred where environmental conditions indicated greater levels of resource limitation with respect to soil moisture and substrate availability. Maximum richness in shrub species occurred on high elevation sites with low topographic moisture index, rocky substrate, and steep slopes. Maximum dominance occurred at low elevation sites with low topographic variability, high potential solar insolation, and high total shrub canopy cover. The observed patterns are evaluated with respect to studies on species‐environment relations, resource use, and regeneration of shrubs in chaparral and coastal sage scrub. The results are discussed in the context of existing species‐diversity hypotheses that hinge on reduced competitive dominance and increased resource heterogeneity under conditions of resource limitation.

Vegetation Change and Surface Erosion in Desert Grasslands of Otero Mesa, Southern New Mexico: 1982 to 1995

Desert grasslands that skirt mountain ranges in northern Mexico and the southwestern United States were once common. These grasslands have largely been replaced by shrublands and their soils have become eroded. The most frequently cited causes of these changes are livestock overgrazing, fire and increasing aridity. Studies have not separated grazing and fire from climate effects. Our aim was to determine whether desert grasses are being replaced by shrubs and how rapidly soil surfaces are eroding on unburnt Otero Mesa desert grasslands, where livestock overgrazing has not been a significant factor in historic or recent times. In this article we describe how vegetation and soil surface levels changed from 1982 to 1995 on six permanent transects. Vegetation was measured by charting canopy cover and stem bases of perennial plants in quadrats. Soil surface levels were surveyed in reference to benchmarks placed in nearby bedrock. Vegetation quadrats and surface levels were remeasured in 1995. From 1982–1983 to 1995 the canopy cover of the desert shrubs, Larrea tridentata and Gutierrezia microcephala, declined by 1.5% and 5.8%, respectively. Canopy cover of the C4 xeric grass Bouteloua eriopoda declined by 5.3%. This decline in xeric grass cover was offset by a 1.2% increase in the C4 mesic grass Bouteloua curtipendula and a 4.0% increase in the C3 mesic grass Stipa neomexicana. From 1983–1984 to 1995 soil surfaces along transects eroded an average of 0.4 mm·y−1. Thus, desert shrubs were not replacing desert grasses, but mesic grass species were replacing xeric species. These changes were associated with a 15-y period of relatively wet cool-seasons and moist warm-seasons from 1981 through 1995. These results document that, even in the absence of livestock grazing and fire, desert grassland vegetation is very responsive to precipitation change over relatively short time periods.

MAMMAL MOUNDS STIMULATE MICROBIAL ACTIVITY IN A SEMIARID SHRUBLAND

This study was conducted to determine the influence of animal disturbance, in the form of banner-tailed kangaroo rat (Dipodomys spectabilis) mounds, on soil microbial abundance and activities in a Chihuahuan Desert shrubland. Total organic carbon (TOC), microbial biomass C (Cmic), and basal respiration were quantified in soils from beneath and between creosote bush (Larrea tridentata) in three zones: directly on the mounds, immediately surrounding the mounds, and between mounds. TOC, Cmic, and respiration were enhanced both in soils beneath the canopies of the shrubs and on the mammal mounds. Thus, mammals as well as shrubs contribute to spatial heterogeneity. Ratios of respiration to Cmic (metabolic quotient) were highest on the mammal mounds; however, the ratio of Cmic : TOC was not affected by shrub canopy cover or location relative to mammal mounds. The higher metabolic quotients in the vicinities of the mounds reflect physical disturbance by mammals and suggest higher proportions of relatively easily metabolized organic carbon than in soils more distant from mounds.

Mammal Mounds Stimulate Microbial Activity in a Semiarid Shrubland

This study was conducted to determine the influence of animal disturbance, in the form of banner-tailed kangaroo rat (Dipodomys spectabilis) mounds, on soil microbial abundance and activities in a Chihuahuan Desert shrubland. Total organic carbon (TOC), microbial biomass C (Cmic), and basal respiration were quantified in soils from beneath and between creosote bush (Larrea tridentata) in three zones: directly on the mounds, immediately surrounding the mounds, and between mounds. TOC, Cmic, and respiration were enhanced both in soils beneath the canopies of the shrubs and on the mammal mounds. Thus, mammals as well as shrubs contribute to spatial heterogeneity. Ratios of respiration to Cmic (metabolic quotient) were highest on the mammal mounds; however, the ratio of Cmic : TOC was not affected by shrub canopy cover or location relative to mammal mounds. The higher metabolic quotients in the vicinities of the mounds reflect physical disturbance by mammals and suggest higher proportions of relatively easily metabolized organic carbon than in soils more distant from mounds.

Mound Characteristics and Behaviour of the Orange-footed Scrubfowl in the Seasonal Tropics of Australia

SummarySeventeen site characteristics associated with the location of incubation mounds of the Orange-footed Scrubfowl Megapodius reinwardt were measured for three habitat types: monsoon forest, regeneration forest and a sandy coastal vine thicket adjacent to an intertidal zone. The three habitats differed with respect to shrub cover, litter cover, canopy cover and several tree measurements. Mound sites differed from random sites with respect to several variables, and these differences can be attributed to the litter-collecting activities of the birds, which disrupt the vegetation on and near the mounds. Internal mound temperatures were recorded over a 12 month period in 10 active mounds, two disused mounds and at two control sites. Active mound temperatures in all three habitats were similar despite significant mound site differences, particularly with respect to canopy cover and incident solar radiation. Whereas the decomposition of litter was the primary source of heat for the mounds in the monsoon and regeneration forests, both solar radiation and microbial decomposition contributed to the heat of the mounds in the sandy coastal vine thicket. Soil temperatures in disused mounds and at control sites decreased with the onset of monsoonal rains, but active mound temperatures remained stable during this period. Behavioural observations were recorded over a 19-week period for a pair of Orange-footed Scrubfowl at an active mound. The collection and incorporation of leaf litter into the mound increased significantly as monsoonal rains intensified. The birds were most active during the early morning period. Hatchlings and juvenile birds were observed in the study area throughout the eight months of field work and one colour banded bird was observed defending two mounds on several occassions.

Modeling Habitat Suitability for Small Mammals in Chihuahuan Desert Foothills of New Mexico

Desert arroyos make up only 2-4% of the desert landscape but may be unique habitat for some wildlife species. Habitat suitability models for small mammals could indicate habitat condition in these uncommon areas and, through monitoring, provide a tool for arid lands wildlife management. During 1993 and 1994, we modeled habitat associations for 18 species of small mammals in 6 habitats associated with desert foothills in the Sacramento Mountains, New Mexico. Habitat associations of small mammals remained relatively consistent through time, although community abundance decreased 34% from spring 1993 to fall 1994. These habitat associations allowed us to use discriminant analysis to model habitat associations based upon designation of habitat as capable of supporting high, moderate, or low relative abundance. The procedure successfully classified 80-93% of habitats as supporting high, moderate, or low abundance of 13 species of heteromyid and murid rodents. Murid rodents (Peromyscus, Reithrodontomys, Neotoma, Sigmodon) were found primarily within arroyos where shrub diversity, canopy cover, and height were greatest compared to surrounding habitats. The modeling approach described herein should be useful to managers because stochastic temporal change in the relative abundance of small mammals is effectively removed from consideration.

Biotic and abiotic correlates of small mammal community structure in the Groendal Wilderness Area, Eastern Cape, South Africa

We investigated the relations between environmental features (biotic and abiotic) and small mammal communities in the Groendal Wilderness Area, South Africa. Habitat architecture (expressed as both horizontal and vertical foliage density) and total plant canopy cover (especially shrub canopy cover) are the most important correlates of small mammal community structure at this site. The mechanisms for these relationships are complex, probably involving physiological, social and anti-predator effects as well as reflecting nutritional resources. Furthermore, man and fire influence small mammal community structure. These effects are as a result of altered plant community composition and structure by plantation and pasture establishment and burning. In order to maintain a diversity of small mammal communities, management should ensure a mosaic of diverse vegetation communities.

Ungulate Grazing in Sagebrush Grassland: Mechanisms of Resource Competition

In many areas of western North America, populations of Rocky Mountain elk (Cervus elaphus canadensis) avoid snow at high elevations during winter by migrating to sagebrush grassland communities in mountain valleys, communities that are used by cattle in the spring and early summer. As a result of these patterns of habitat use, the impact of elk on forage supplies for cattle has emerged as an important issue in range and wildlife management throughout the West. We examined effects of variation in population density of elk on the availability and use of forage resources by cattle in a randomized complete block experiment conducted in sagebrush grassland during four years. We manipulated elk numbers to achieve four levels of population density (0, 9, 15, and 31 elk/km2), replicated each level three times, and observed responses of vegetation and cattle to these manipulations. At high densities (31 animals/km2), elk annually removed 57% of the standing crop of dead perennial grass and 12% of the total annual production of live perennial grass. Standing crops of dead perennial grass in early spring declined in direct proportion to increasing elk density (linear effect F1,6 = 10.0, P = 0.02) from a mean of 8.7 g/m2 in the controls (0 elk/km2) to 3.3 g/m2 in the high density (31 elk/km2) treatment. Early spring standing crops of live perennial grass also declined as elk population density increased, but these trends only approached significance (linear effect F1.6 = 3.4, P = 0.12). Effects of elk grazing on herbaceous aboveground net primary production were not significant (minimum P > 0.38), but the total supply of herbaceous dry matter available to cattle (standing dead + primary production) declined in linear relation to elk density (linear effect F1.6 = 7.7, P = 0.03). Canopy cover of shrubs was least and canopy cover of grass was greatest at intermediate levels of elk density (quadratic effect F1.6 = 9.4, P = 0.03). We found weak enhancing effects of elk populations on nutritional quality of spring forage. Elk grazing caused linear increases in the digestibility (F1.6 = 5.0, P. = 0.07) and nitrogen content (F1.6 = 15.1, P = 0.008) of perennial grass available to cattle. Nitrogen content of cattle diets increased in the moderately grazed treatments (control vs. 15 elk/km2, F1.6 = 4.3, P = 0.06), but dietary digestibility and fiber content did not change significantly with treatment. Daily forage intake by cattle (kilograms of dry matter per cow per day) declined in direct relation to elk density (F1.6 = 5.2, P = 0.06), primarily as a result of reductions in intake of standing dead grass. Consequently, cattle daily intake of digestible energy (linear effect F1.6 = 5.1, P = 0.06) and nitrogen (control vs. others F1.6 = 5.4, P = 0.06) declined as elk population density increased. The mechanism responsible for this decline was a Type II functional response of cattle to forage biomass. We conclude that effects of elk on cattle represent a composite of facilitative and competitive effects. When forage production is low and cattle density is high, competition is a much stronger force than facilitation.

Climate-vegetation Relationships between the Great Plains and Great Basin

-Conditions responsible for vegetative differences between the Great Basin and Great Plains are poorly understood. Two hypotheses for the differences are (1) the geophysical barrier of the Rocky Mountains and a slow rate of dispersal of taxa restrict interchange of taxa between the Great Basin and Great Plains, even where gaps in the mountains occur; and (2) differences in climate between the two regions limit floristic intermixing. We examined relationships for both hypotheses using vegetative data from 14 study sites in Idaho, Colorado, Wyoming and Montana. Canopy cover of graminoids, forbs and shrubs was regressed against selected climatic variables and distance of each study site from the Rocky Mountains. Shrub cover diminished, graminoid cover increased and forb cover remained roughly constant on a west-to-east gradient. Graminoid cover increased and forb cover remained roughly constant on a west-to-east gradient. Graminoid cover was positively correlated with summer precipitation, and shrub cover was positively correlated with winter precipitation and negatively correlated with summer precipitation. These vegetative variables were more highly correlated with climatic data than with distance from a broad gap in the Rocky Mountain chain. Current distributions of Great Plains and Great Basin taxa suggest that the Rocky Mountains have not been an effective barrier to plant dispersal in Wyoming. Our data suggest that seasonality of precipitation restricts dispersal of taxa between the Great Basin and Great Plains.

Birth and Fawn Bed Site Selection by Pronghorns in a Sagebrush-Steppe Community

In a sagebrush-steppe community in southcentral Wyoming, we measured shrub canopy cover and height at 13 pronghorn (Antilocapra americana) fawn birth sites and 50 fawn bedding sites and compared them to measurements we made at 47 random points in areas infrequently used by parturient pronghorn. Birth sites and bed sites were similar (P=0.96) in shrub cover but differed from random points (P=0.015 and P=0.002, respectively). Plant height was not significantly different between birth sites, bedding sites, or random points measured in low use areas. In a second study, we fitted 7 pronghorn fawns (3-5 days old) with solar-powered radio transmitters and relocated them daily for 3 weeks

Differences in Riparian Vegetation Structure between Grazed Areas and Exclosures

The valuable role that healthy riparian ecosystems play in regional diversity of plant and wildlife communities is just beginning to be recognized. Resource managers need to know how degraded riparian areas respond to changes in management, such as reduction and elimination of grazing. Differences in vegetation structure were examined in a montane riparian zone in northcentral Colorado after 30 years of cattle exclusion and continued, but reduced, grazing pressure. In order to assess the changes in the riparian community, canopy coverage, density, and standing crop of important riparian species were measured in 1985 and 1986. Total vascular vegetation, shrub, and graminoid canopy cover was greater (P?0.05) in the exclosures as compared to grazed areas, while forb canopy cover was similar (P>0.05) between treatments. Exclosures had nearly 2 times the litter cover, while grazed areas had 4 times more bare ground. Willow canopy coverage was 8 1/2 times greater in protected areas than in grazed areas. Kentucky bluegrass (Poa pratensis L.) cover was 4 times greater in grazed areas than exclosures, while the cover of fowl bluegrass (Poa palustris L.) was 6 times greater in the protected sites. Canopy cover of other important riparian species, such as tufted hairgrass (Deschampsia caespitosa (L.) Beauv.), Nebraska sedge (Carex nebraskensis Dewey), and beaked sedge (C. rostrata Stokes), was similar (F>0.05) between treatments. Mean peak standing crop over the 2 years of the study ws 2,410 kg/ha in the exclosures and 1,217 kg/ha in caged plots within grazed areas. Cattle utilized approximately 65% of the current year's growth of vegetation during the 1985 and 1986 grazing seasons. Riparian areas provide habitat for wildlife and fish species, while providing forage for domestic livestock. These areas provide a diversity of foraging and breeding sites that permit coexistence of many wildlife species. Intact aquatic ecosystems with abundant streamside vegetation insure healthy fish populations (Kauffman and Kreuger 1984). Improper livestock use of riparian areas can increase erosion and reduce plant vigor, resulting in lowered forage production and altered plant age structure and species composition (Knopf and Cannon 1982, Kauffman and Krueger 1984, Skov

Assessment of permanence and stability in the territories of Kirk's dikdik (Rhynchotragus kirki) in Tanzania

ABSTRACTThe permanence and stability of 20 territories of the dikdik Rhynchotragus kirki, were studied at Arusha National Park Tanzania. Response criteria included the structure, size and vegetation attributes of territories, density of dikdik, and spatial distances between neighbouring territories. Fourteen of the territories studied were spatially fixed and stable while six were unstable. Two of the unstable territories were completely abandoned. Mean territory size was 0.11 and 0.13 ha during the rainy and dry seasons, respectively. 14.2% of circular territories and 42.9% of elliptical and kidney-shaped territories were stable. The figure of 55 dikdik km−2 sighted during morning censuses was lower than that for evening censuses by 13.5%. Spatial distance between territories ranged from 4.5 m to 100 m, an indication that population density might be a function of the size of suitable habitat. Although shrub canopy cover within stable territories decreased by 44.6% between 1982 and 1987, and some territories were realigned with changes in rainfall pattern, pair-bond was maintained by dikdik in 70% of the territories studied.

Mechanical Shrub Control on Flatwoods Range in South Florida

Relative plant abundance, canopy cover, and aerial biomass of shrubs on a poor condition, flatwoods range in south Florida were measured before, 1, and 3 yr after a single pass of a roller chopper or web plow when soils were dry (May 1981) and when soils were saturated (September 1981). Aerial biomass of herbaceous species was measured at the post-treatment sample dates. Abundance of saw-palmetto (Serenoa repens (Bartr.) Small) plants, the dominant shrub, was reduced 70%o by web plowing compared to 25% by roller chopping. Reductions of saw-palmetto canopy cover and aerial biomass also were greater on web-plowed than on roller-chopped plots. Runner oak (Quercus minima (Sarg.) Small) was the only other shrub which had more than 5% canopy cover before treatment. Both types of mechanical treatments controlled runner oak by approximately 50%o. However, responses of runner oak abundance, canopy cover, and aerial biomass were not significantly different between roller chop and web plow treatments.