Shrub Component Research Articles

Spatial partitioning of the soil water resource between grass and shrub components in a West African humid savanna.

Most savanna water balance models assume water partitioning between grasses and shrubs in a two-layer hypothesis, but this hypothesis has not been tested for humid savanna environments. Spatial partitioning of soil water between grasses and shrubs was investigated in a West African humid savanna by comparing the isotopic composition (oxygen-18 and deuterium) of soil water and plant stem water during rainy and dry conditions. Both grass and shrub species acquire most of their water from the top soil layer during both rainy and dry periods. A shift of water uptake pattern towards deeper horizons was observed only at the end of the dry season after shrub defoliation. The mean depth of water uptake, as determined by the isotopic signature of stem water, was consistent with grass and shrub root profiles and with changes in soil water content profiles as surveyed by a neutron probe. This provides evidence for potentially strong competition between shrubs and grasses for soil water in these humid savannas. Limited nutrient availability may explain these competitive interactions. These results enhance our understanding of shrub-grass interactions, and will contribute to models of ecosystem functioning in humid savannas.

Measurements of transpiration from savannah shrubs using sap flow gauges

Sap flow gauges were used to measure transpiration from the shrub component of a 7-year-old agricultural fallow in Niger, West Africa. The aim of the study was to provide the data necessary to develop and validate multi-source models of evaporation from semi-arid land surfaces by measuring transpiration from a single component of the vegetation. The vegetation at the study site was a type of savannah, consisting of scattered shrubs, with an understorey of annual grasses and herbs. Sap flow measurements were restricted to Guiera senegalensis J.F. Gmel., the dominant shrub species. Sap flows were measured throughout the wet season of 1990 (June–September), using sap flow gauges operating on a constant power heat balance principle. Sap flow rates measured in individual stems were strongly related to leaf area and net radiation. Strong positive correlations were observed between the hourly mean flow rates measured in different stems. Daily transpiration, T, averaged across a 0.25 ha sample plot was compared with daily total evaporation (measured by eddy correlation), E. T was calculated by scaling up from sap flow measurements in a sample of stems to the whole plot by using the frequency distribution of stem diameter in the plot, and assuming that sap flow in each stem was proportional to its basal cross-sectional area. E varied from about 2 mm day −1 at the start of the wet season to 4–6 mm day −1 during August and September, when maximum leaf area and soil profile water content were observed. E, a measure of evaporation from all plant and soil sources, always exceeded T. At the end of two dry periods in June and July, when soil evaporation and transpiration from the herb understorey probably totalled about 0.5 mm day −1, E was only 0.7–0.9 mm day −1 greater than T, suggesting that the scaling procedure adopted gave reasonable estimates of bush transpiration. Over the whole wet season, transpiration from G. senegalensis accounted for 35% of the total wet season rainfall of 454 mm.

Recruitment and survival in Atriplex vesicaria populations in semi‐arid western New South Wales, 1977–1987

AbstractThe recruitment and survival of small and large shrubs of Atriplex vesicaria were examined for 21 periods from 1977 to 1987. Recruitment occurred in all seasons, including summer, and survival was independent of the size of the recruitment event. Recruitment was not related to the density of the large shrubs, suggesting that the available seed pool at this site was not limiting. Survival of both shrub components was only weakly correlated with rainfall (measured at a location between 6 and 30 km from the study transects) and with a ratio of rainfall and evaporation. Survival of small shrubs was constant over all cohorts, with half‐lives of only 7–8 months. Turnover of the population was substantial — an average of 60% of the individuals present at any one time were less than 24 months old.

Assessment of a Double-Sampling Technique for Estimating Browse Biomass

We assessed the potential for determining current annual growth (CAG) of browse with visual estimates of shrub canopy volume, combined with double sampling for clip-and-weigh measurements of biomass. This sampling approach permits direct assessment of CAG per unit area without estimates of shrub density. Ratio estimates based on double sampling provided suitable CAG estimates, assuming 80% confidence, for total production when browse species were combined. This double-sampling approach for individual browse species is likely possible only when shrub taxa are abundant or uniformly distributed, or when the sample site has been stratified according to the distribution of CAG values of specific browse species. J. WILDL. MANAGE. 54(2):342-348 Inventory programs to estimate browse production available for use by wildlife and livestock pose complex problems because of highly variable plant physiognomy, life history, and spatial distribution of browse species (Telfer 1981). Sampling methods range from visual estimates to detailed clip-and-weigh determinations of CAG or standing crop; each method has inherent strengths and weaknesses (Rutherford 1979, Pitt and Schwab 1988). Visual estimates offer an inexpensive and relatively easy method to assess shrub CAG, but are hindered by observer and statistical bias (Pechanec and Pickford 1937, Jolly 1954) and often fail to provide management agencies with verifiable levels of statistical confidence and precision (Pitt and Schwab 1988). Shrub CAG may be determined directly by clipping within randomly or systematically selected plots. Plant material is then oven-dried to obtain biomass, CAG, or availability per unit area (Mannetje 1978). Clip-and-weigh techniques are typically expensive and tedious and are more appropriate for intensive research than for extensive browse inventory programs (Pitt and Schwab 1988). Regression and ratio estimates reduce the arduous, expensive aspects of direct measurements by predicting CAG from more easily measured shrub components. Biomass of leaves, twigs, or entire shrubs have been associated with stems per unit area (Wolff 1978); twig diameter (Telfer 1969, Provenza and Urness 1981); stem diameter (Felker et al. 1982); shrub height (Ohmann et al. 1976); crown volume (Guy 1981); crown diameter, depth, and density (Dean et al. 1981); crown width (Rittenhouse and Sneva 1977); crown area, or cover (Anderson and Kothmann 1982); height and stem diameter products (Stone and Crawford 1981); twig lengths (Schuster 1965); twigs per plant (Peek 1970); and shrub ring widths (Davis et al. 1972). Despite the abundant literature describing methodology, extensive shrub inventories remain prohibitively costly, perhaps because most regression techniques provide CAG per stem or shrub. Such CAG estimates must be combined with stem or shrub density estimates to yield CAG per unit area. Appropriate techniques for estimating density vary according to physiognomy and spatial distribution of shrub species. Many density estimates are laborious or contain statistical bias (Pitt and Schwab 1988). The most appropriate shrub inventory method, therefore, is a regression or ratio estimate of CAG predicted from shrub components measured on a unit-area basis, such as canopy volume. These predictions estimate CAG per unit area directly, without density estimates. Shrub canopy volume also correlates well with biomass and CAG and has generally lower coefficients of variation compared to other predictor variables (Bryant and Kothmann 1979, Murray and Jacobson 1982). Direct predictions of CAG per unit area are feasible for browse inventory when double-sampling programs are used (Cochran 1977:327, Nichols 1979). We assessed a double-sampling approach for predicting shrub CAG using visual volume estimates recorded during first-phase sampling and actual CAG clipped and weighed during second-phase sampling. Feasibility for browse inventory programs was also evaluated relative to field sampling costs and statistical precision. M. L. Beets, C. A. Easthope, R. C. Gordon,

Twentieth-century climate change, fire suppression, and forest production and decomposition in northwestern Minnesota

Long-term fire, climate, and vegetation data were used together with simulation models to estimate the effects of 20th century climate change and fire suppression on fire regime and organic-matter accumulation in mixed-conifer stands of Itasca State Park, northwestern Minnesota. Spatial and temporal patterns of fire occurrence and forest composition over the last 150 years determined by stratigraphic charcoal, fire-scar, tree-ring, and pollen analyses in separate studies provide evidence for vegetation and fire relationships. Water balances constructed from temperature and precipitation data collected since 1840 were used to model fire probability and intensity of burn before fire suppression which began in 1910. Existing patterns of biomass accumulation in forest-floor, herb, shrub, and tree components were compared with fire history and topographic variability to provide a spatial perspective on fire effects. Simulation models used these relationships to estimate (i) how accumulation of organic matter had changed through the past under the different fire regimes that prevailed on different topographic aspects, (ii) the changes brought about by fire suppression in 1910, and (iii) the fire regimes and their effects that would have prevailed since fire suppression with the warm–dry climate of the 20th century. Humus, litter, shrubs, and herb cover were less abundant and more variable spatially and temporally before fire suppression. Spatial variability in forest-floor organic matter, which resulted from different fire frequencies in different vegetation and topographic settings before fire suppression, was largely gone by 1920 as a result of fire suppression. Had fire suppression not been instituted in 1910, fire frequency would have increased by 20–40% in the 20th century because of warmer and drier conditions. Forest-floor oganic matter would have been largely depleted by frequent and severe fires exposing mineral soils, particularly during the drought years of the 1930s. Herb biomass would have increased, shrubs would have been more variable, and tree seedling establishment would have been substantially altered. Time required for buildup of fuels limits the extent to which increased moisture deficits increase fire frequency.

Diurnal Radiance and Shadow Fluntuations in a Cold Desert Shrub Plant C Community

Remote sensing data can be acquired during different times of the year and different times of the day using satellite or aircraft systems. Radiance values of pixels vary with ground target, latitude, time of year, and the time of day for both aerial and ground-measured data. An understanding of the resulting fluctuations in spectra provides information necessary to improve the interpretation of airborne and satellite data. Aerial and field measured spectra v vary for a typical desert shrub plant community with low vegetation cover (27%) and considerable shade differences and bare ground. Low shadow percentages were found from 1000 to 1650 h Pacific Daylight Time (PDT) in July and between 1100 and 1500 PDT in September. Both ground-measured and 5 × 5 m aerial pixels had low radiance values (corrected for a 45° sun-angle) at 0800 PDT and higher radiance values throughout the day until solar zenith. September data had a greater range of values compared to July data. MSS7 / MSS5 and MSS6 / MSS5 ratiobased indices were higher in July than September, indicating a higher photosynthetically active biomass in the shrub component in July. Vegetation index measurements varied throughout the day and from season to season and were influenced by solar altitude and the amount of bare soil, plant biomass, and shadow present.

Biomass relations of shrub components and their generality

Biomass relations for six components of five tall shrubs: ( Acer spicatum Lam., Alnus crispa (Ait.) Pursh., Alnus rugosa (Du Roi) Spreng., Amelanchier spp. Medic., and Corylus cornuta Marsh.) were analyzed to assess the extent to which species- and site-specific models were better than generalized regression models. With few exceptions, species- and site-specific models significantly improved goodness of fit, especially for annual production-related components such as current annual twig production. Where specific models are not available, generalized models fit reasonably well, especially for components dealing with cumulative biomass. However, if high precision or estimates of annual production-related components are desired, generalized models may not be adequate.

Multiple goal feasibility of forage shrub plantations in a semi-arid mediterranean-type agropastoral system

This study is an ex ante analysis of multiple goal feasibility of forage shrub plantations in the context of a sheep and wheat agropastoral system. The goals imposed on the system were ‘farmer's income’ represented by gross margin, ‘regional balance of payments's represented by added foreign currency value per unit area and local currency cost of the added value, and ‘employment’ represented by size of farm unit. The socio-economic scenario is appropriate for a semi-arid Mediterranean environment where rural areas are close to urban centres of population and industry. Under such conditions, multiple goal feasibility of shrub plantations was limited by added foreign currency value and farm size in extensive systems, and by gross margin and cost of the added value in intensive systems. Improved ewe productivity improved overall feasibility. Feed substitution per se could not justify forage shrub plantations, but even a small improvement in the weaning rate consequent on the addition of a forage shrub component would greatly increase multiple goal feasibility, particularly in more intensive systems. However, it needs to be shown that such improvement can indeed be achieved in practice.

Beaver Habitat Use and Impact in Truckee River Basin, California

Stepwise logistic regression was used to identify factors important for habitat use by beavers (Castor canadensis) on streams. Increasing stream width and depth and decreasing gradient had the strongest positive effects on habitat use; food availability variables added little explanatory power. Some abandoned colony sites appeared to have been located on physically unsuitable habitat, whereas others appeared to be physically suitable sites abandoned due to resource depletion. The fact that few unused or uncolonized reaches were misclassified as suitable habitat suggests that suitable habitat has been saturated. Impact of beaver on woody plants was assessed for 8 forage species. Local extinction of quaking aspen (Populus tremuloides) and black cottonwood (P. trichocarpa) occurred on 4-5% of stream reaches. Willow (Salix spp.) showed good vigor despite heavy use in most reaches. J. WILDL. MANAGE. 51(4):794-799 Multivariate wildlife-habitat relationships models are often used to identify actually or potentially suitable habitat for various species, or to identify those factors that are important in habitat selection (Shugart 1981). Retzer (1955), Slough and Sadlier (1977), and Howard and Larson (1985) have used quantitative techniques to relate beaver occurrence, persistence, and density to various physical and vegetative characteristics. Wildlife managers have long been concerned with the loss of aesthetic value and impacts on stream channels due to destruction of riparian vegetation by beaver (Bump 1941, Munther 1981). Hall (1960) reported that beaver will deplete aspen in the immediate vicinity of a colony. However, there has been little quantitative documentation of the role of these animals in the loss of riparian vegetation (Kindschy 1985). Our objectives were to: (1) develop a model to identify the physical and vegetative characteristics of habitat colonized by beavers, and validate the model on a set of stream reaches not used in model development; (2) use the model results to suggest causes for colony abandonment, and evaluate whether beaver have saturated suitable habitat during the 40 years since introduction; and (3) describe the impact of beavers on woody vegetation. This research was supported by the Calif. Dep. Fish and Game and the Calif. Agric. Exp. Stn. Proj. 4326-MS. J. S. Slaymaker assisted in most of the fieldwork. M. L. Morrison, R. A. Lancia, S. H. Jenkins, and W. M. Block provided helpful criticisms of the manuscript. STUDY AREA The Truckee River Basin lies within Sierra, Nevada, Placer, and El Dorado counties, California, and Washoe County, Nevada. Our study covered the Truckee River and its tributaries from the confluence with Deer Creek downstream to Verdi, Nevada. This encompassed an area of approximately 600 km2, with 153 km of streams ranging from 1,485 to 2,750 m in elevation. Beavers were introduced into the area during 1938-46 and have since established colonies throughout the basin (P. Beier and R. H. Barrett, unpubl. data). The dominant vegetation of the area is mixed conifer forest with an overstory of white fir (Abies concolor); Jeffrey (Pinus jeffreyi), ponderosa (P. ponderosa), Washoe (P. washoensis), and lodgepole (P. contorta) pine; and a shrub component including greenleaf (Arctostaphylos patula) and whiteleaf (A. viscida) manzanita, snowbrush (Ceanothus velutinus) and squawcarpet ceanothus (C. prostratus), pale serviceberry (Amelanchier pallida), rose (Rosa spp.), and Sierra gooseberry (Ribes roezlii). The mixed conifer forest is replaced in higher elevations by a forest dominated by Shasta red fir (Abies magnifica), western white pine (P. monticola), and lodgepole pine, with squawcarpet as a dominant shrub; and in lower elevations by open stands of Jeffrey pine and an understory including big sagebrush (Artemisia tridentata), antelope bitterbrush (Purshia tridentata), and herbaceous plants. Stream banks were characterized by deciduous riparian vegetation consisting of aspen, cottonwood, willow, mountain alder (Alnus in-

Nutrient Concentrations in Foliage of Species Within a New South Wales Sub-Tropical Rainforest

Sub-tropical rainforests in New South Wales are complex, often with more than 30 tree species ha−1. Estimation of nutrient contents involves obtaining information on the range of nutrient concentrations both in different species and in different forest strata. The foliage from the tree and shrub components of an undisturbed forest were analyzed chemically together with the small tree and shrub component of an area logged two years previously. The site had high nutrient availability. All nutrients analyzed (nitrogen, phosphorus, calcium, magnesium, potassium, manganese, aluminium, sodium, zinc, iron, boron and chloride) varied between species. Some individuals accumulated high concentrations of specific nutrients, but an accumulator of one nutrient was not necessarily an accumulator of any other. Assessment of nutrient concentrations on the basis of forest strata showed major differences. Nutrients were accumulated in higher concentrations on a disturbed site than on an undisturbed site. This has been discussed in relation to nutrient conservation mechanisms after disturbance. Within the undisturbed stand, the large shrub stratum had the highest concentrations of nitrogen, phosphorus, potassium and boron. Mean concentrations of aluminium, sodium and chloride were highest in the small shrub stratum, mainly because several species accumulate these elements.

Velvet Mesquite Seedling Development in Three Southwestern Soils

Knowledge of the effects of saturated soils and flooding on Wyoming big sagebrush (Artemisia tridentata wyomingensis), green rabbitbrush (Chrysothamnus viscidiflorus), and black greasewood (Sarcobatus vermiculatus) can enhance our understanding of their distribution. The responses of these 3 species to elevated water tables were studied on 4 contours bordering an expanding lake in southeast Oregon during the 1983 and 1984 growing seasons. When plants were initially selected for study, contours were 0, 10, 20, and 40 cm above the lake surface. Continued expansion of the lake flooded the lower contours and elevated the water tables under the upper contours. Wyoming big sagebrush rapidly succumbed to surface flooding and elevated water tables within 10 cm of the surface. Green rabbitbrush behaved similarly, but responses lagged about 1 week behind sagebrush. Black greasewood tolerated surface flooding for 40 days before effects were apparent. Water tables within 25 to 30 cm of the surface had no effect on greasewood. Given adequate topography and water supplies, water spreading techniques could be used to control Wyoming big sagebrush and green rabbitbrush. Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle and Young) and black greasewood (Sarcobatus vermiculatus (Hook.) Torr.) are dominant or codomninant shrubs on large expanses of western rangelands (Tisdale and Hironaka 1981, Franklin and Dyrness 1973, Romo 1985). Green rabbitbrush (Chrysothamnus viscidiflorus (Hook.) Nutt.), typically a minor shrub component in climax communities, may also dominate areas where fire, overgrazing, or other disturbances have reduced the competitive ability of the accompanying vegetation (Young and Evans 1974). These 3 species, either singularly or collectively, shape the character and competitively control large areas within the Great Basin. Due to the importance of these shrubs in the region, land manAuthor is range scientist, United States Department of Agriculture-Agricultural Research Service, Eastern Oregon Agricultural Research Center, Squaw Butte Station, Burns, Oregon 97720. This article is Technical Paper No. 7592. Oregon Agricultural Experiment Station. Manuscript accepted 21 October 1985. agers must consider the biotic and abiotic factors affecting their establishment, health, or distribution. Water relations play a particularly prominent role in influencing the distribution of plants in this arid region, and abundances of water are typically not a concern. Several workers have noted, however, that excessive soil moisture is detrimental to big sagebrush (Artemisia tridentata) (U.S. Dept. Agr., Forest Serv. 1937, Branson 1956, Vallentine 1971) and speculated that anaerobic conditions in some soils prevent successful colonization of big sagebrush (Fosberg and Hironaka 1964). Lunt et al. (1973) found root growth of big sagebrush hindered by oxygen concentrations of 5% or less and observed low rates of recovery of big sagebrush after weakened plants were returned to ambient oxygen concentrations. These same workers speculated big sagebrush was excluded from fine textured and poorly drained soils by its high oxygen requirements. Greasewood has been classified as a phreatophyte (Robinson 1958), and Romo (1985) found water tables ranging from 3.5 to 15 m below greasewood dominated communities in Oregon. No information was found, however, regarding tolerances of greasewood or green rabbitbrush to saturated soils or low oxygen concentrations in the rooting zone. Given this lack of information, the objective of this study was to evaluate the relative tolerances of Wyoming big sagebrush, greasewood, and green rabbitbrush to elevated water tables and surface flooding. Study Area and Methods Studies were conducted on 6 locations bordering Malheur Lake in Harney County, Oregon. Elevations were approximately 1,245 meters. Harney Basin is internally drained and annually receives between 20 and 30 cm of precipitation. The historic meander of Malheur Lake encompasses approximately 25,000 ha; however, above-normal precipitation between 1978 and 1984 expanded the lake to 68,000 ha, inundating large areas of shrub-steppe vegetation in the process. Three study sites, approximately 2 km apart, were evaluated during the 1983 growing season. Rapid expansion of the lake in 1984 blocked access to the original study areas and 3 334 JOURNAL OF RANGE MANAGEMENT 39(4), July 1986 This content downloaded from 40.77.167.124 on Mon, 17 Jul 2017 15:35:13 UTC All use subject to http://about.jstor.org/terms

Tolerances of Sagebrush, Rabbitbrush, and Greasewood to Elevated Water Tables

Knowledge of the effects of saturated soils and flooding on Wyoming big sagebrush (Artem& tridkntata wyomingensis), green rabbitbrusb fChry~&~~~~us viscid#for~~), and black gmsewood (Sarcobatus vem&ulat~@ an enhance our understanding of their distribution. Tbe responses of these 3 species to elevated water tables were studied on 4 contours bordering an expanding lake in southeast Oregon during the 1983 and 1984 growing seasons. When plants were initially selected for study, contours were 0, 10,20, and 40 cm above the iake surface. Continued expansion of the lake flooded the lower contours and elevated the water tables under the upper contours. Wyoming big sagebrush rapidly succumbed to surface flooding and elevated water tables within 10 cm of the surface. Green rabbitbrush behaved similarly, but responses lagged about 1 week behind sagebrush. Biack greasewood toierated surface flooding for 40 days before effects were apparent. Water tables within 25 to 30 cm of the surface had no effect on greasewood. Given adequate topography and water supplies, water spreading techniques could be used to control Wyoming big sagebrush and green rabbitbrush. Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle and Young) and black greasewood (Sarcobatus vermiculatus (Hook.) Torr.) are dominant or codominanb shrubs on large expanses of western rangelands (Tisdale and’ Hironaka 1981, Franklin and Dyrness 1973, Romo 1985). Green rabbitbrush (Chrysothamnus viscidiforus (Hook.) Nutt.), typically a minor shrub component in climax communities, may also dominate areas where fire, overgrazing, or other disturbances have reduced the competitive ability of the accompanying vegetation (Young and Evans 1974). These 3 species, either singularly or collectively, shape the character and competitively control large areas within the Great Basin. Due to the importance of these shrubs in the region, land man

Late quaternary vegetational change in the Kotzebue sound area, northwestern Alaska

Two sediment cores from Kaiyak and Squirrel lakes in northwestern Alaska yielded pollen records that date to ca. 39,000 and 27,000 yr B.P., respectively. Between 39,000 and 14,000 yr B.P., the vegetation around these lakes was dominated by Gramineae and Cyperaceae with some Salix and possibly Betula nana/glandulosa forming a local, shrub component of the vegetation. Betula pollen percentages increased about 14,000 yr B.P., indicating the presence of a birchdominated shrub tundra. Alnus pollen appeared at both sites between 9000 and 8000yr B.P., and Picea pollen (mostly P. mariana) arrived at Squirrel Lake about 5000 yr B.P. The current foresttundra mosaic around Squirrel Lake was established at this time, whereas shrub tundra existed near Kaiyak Lake throughout the Holocene. When compared to other pollen records from north-western North America, these cores (1) represent a meadow component of lowland. Beringian tundra between 39,000 and 14,000 yr B.P., (2) demonstrate an early Holocene arrival of Alnus in northwestern Alaska that predates most other Alnus horizons in northern Alaska or northwestern Canada, and (3) show an east-to-west migration of Picea across northern Alaska from 9000 to 5000 yr B.P.

Estimating Twig and Foliage Biomass of Sagebrush, Bitterbrush, and Rabbitbrush in the Great Basin

Shrub crown characteristics useful in regression equations for predicting two biomass components (annual production and fine fuels) were identified for six shrubs common to the Great Basin. Shrub characteristics most useful in these equations were maximum and minimum crown diameter, and crown denseness and depth. Prediction equations were developed for each species or subspecies included in this study. Additionally, biomass equations were developed for combined species or subspecies of morphological similarity within the Artemisiu genus. As early as 1958, Evans and Jones addressed the practical importance of a method for determining forage production in which clipping or mowing was not necessary. Since then, much attention has been directed toward developing methods for predicting shrub production from easily measured crown dimensions. Volumetric or crown area relationships based on crown height and diameters have been described for serviceberry (Amelanchier alnifolia) by Lyon (1968), for eight Chihuahuan desert shrubs by Ludwig et al. (1973, and for big sagebrush (Artemisia tridentata wyomingensis) by Rittenhouse and Sneva (1977). Brown and Marsden (1976) and Alexander (1978) developed equations for predicting fuel loadings from height and percent crown cover measurements. Various stem diameter measurements were used as biomass predictors by Ohmann et al. (1976), Brown (1976), and Grigal and Ohmann (1977). Davis et al. (1972) related forage production to ring widths for several salt desert shrub species. Thus, the value and practicality of such methods has been well documented. The sagebrush taxon, Artemisia, constitutes the most abundant and widespread shrub component of ecosystems in the Great Basin and provides a source of food and cover for livestock and wildlife. Taxonomic difficulties exist within this genus at the species, subspecies, and variety levels. Although ecological differences have been described (Winward and Tisdale 1977), field identification of sagebrush species is often difficuh to determine. This is especially true between low and black sagebrush (A. arbuscula and A. nova) and the subspecies differentiations for big sagebrush (A. tridentata ssp. tridentata, A. tridentata spp. vaseyana, and A. tridentata spp. wyomingensis). A reliable dimension analysis technique for determining canopy biomass components in which species differences were not necessary would expedite field data collection and data analysis procedures. The primary objective of this study was to identify shrub crown characteristics which could be used to predict two shrub biomass components (annual production and fine fuels) and to formulate reliable prediction equations from these characteristics. The seconAuthors are research assistant and assistant professor, Renewable Natural Resources Division, University of Nevada Reno, 1000 Valley Road, Reno, Nevada 8951% and research forester, Intermountain Forest and Range Experiment Station, Renewable Natural Resources Center, 920 Valley Road, Rena, Nevada 89512. This research represents the contributions of the Nevada Agricultural Experiment Station Journal Series Number 446. Financial support from the IntermOUntain Forest and Range Experiment Station is acknowledged. dary objective was to evaluate the reliability of the prediction equations when shrub species of similar form were grouped together. Methods and Procedures Fifty-nine study sites were selected to represent the major shrub communities associated with the pinyon-juniper vegetation in the Great Basin. The study included the following taxa and number of sample shrubs: Artemisia tridentata tridentata (n=lO) ARTRTR Basin big sagebrush Artemisia tridentata vaseyana (n=54) ARTRVA Mountain big sagebrush Artemisia tridentata wyomingensis (n=50) ARTRWY Wyoming big sagebrush

Forage Selection by Mule Deer on Winter Range Grazed by Sheep in Spring

Late spring grazing by sheep altered the amount of several forage categories available to deer the subsequent autumn and winter. Total herbaceous plant material was much reduced by spring-time sheep grazing, but regrowth following fall precipitation increased the proportion of green herbaceous material available. Current year's growth of bitterbrush was also increased relative to the nongrazed situation due to the release of moisture and nutrients accompanying the removal of herbaceous plants by sheep. Subsequently winter diets of mule deer on the sheep-grazed area were higher in herbaceous components but lower in shrub components than on the adjacent area where sheep had not been previously grazed. Implications of these findings are that quality of deer diets was not detrimentally affected where sheep had grazed during the preceding spring and a much greater animal yield is possible through dual use. A deficit of winter forage apparently limits mule deer (Odocoileus hemionus hemionus) population over much of their range (Aldous 1945; Doman and Rasmussen 1944). This can be viewed in terms of both extent of winter rangeland and quantity of forage (principally shrubs) produced there. The Utah Division of Wildlife Resources estimates that there are approximately 7,424,000 ha of mule deer winter range in Utah, including some 1,149,000 ha dominated by the sagebrush complex, primarily big sagebrush (Artemisia tridentata). However, big sagebrush is viewed as only moderate quality winter forage for deer because of its low acceptability (Smith and Hubbard 1954). This is a particular problem where sagebrush exists in stands devoid of more palatable shrub species. Winter deer losses in Utah appear to be inversely related to the amount of palatable browse species available (Robinette et al. 1952). The grazing of deer winter ranges by domestic livestock is common throughout the Intermountain West. Such ranges are grazed in spring when forage is typically in short supply for the livestock industry. Hence, the generally low state of productivity of these ranges is viewed as a limitation to livestock production (Cook and Harris 1968) as well as to deer production. Recent research indicates that with properly designed grazing strategies, livestock-big game competition can probably be minimized (Jensen et al. 1972; Jensen et al. 1976). Moreover, these same studies suggest that livestock may be used to manipulate vegetation on deer winter ranges to effectively Authors were research assistant, associate professor, and research assistant, respectively., Department of Range Science, Utah State University, Logan 84322. Smith and Fulgham are now, respectively, assistant professor of animal science, Angelo State University, San Angelo, Texas 76901, and assistant professor of animal and range sciences, New Mexico State University, Las Cruces 88003. This report is Journal Paper No. 2249 of the Utah Agricultural Experiment Station, the supporting institution for this research. Authors also acknowledge the Utah Division of Wildlife Resources (UDWR) for providing the study site, the experimental animals, and logistic support. Charles H. Jensen, game biologist, UDWR, assisted in site selection and study design. -Dr. Charles Romesburg and Mr. Kim Marshall, US/IBP Desert Biome Project, were both especially helpful in the data analysis phase of the project. Manuscript received November 14, 1977. increase quantities of browse available to wintering deer. However, the specific responses of mule deer to such grazing systems have not been well established. Thus, the study reported in this paper was designed to determine: (1) the plant species present and available to wintering mule deer following spring-time sheep grazing and (2) the relative proportions of the various plant species in the diets of mule deer during the winter following the spring sheep grazing treatment.

The use of quadrat and plotless methods in the analysis of the tree and shrub component of woodland vegetation

Abstract Few attempts have been made to test plotless methods of botanical analysis in the field. Therefore eight such methods and the quadrat method of estimating the density and species composition of trees and shrubs were tested on the vegetation in the semi‐arid, south‐eastern lowveld of Rhodesia. These methods are compared and evaluated in terms of accuracy and efficiency. Methods using distance to third nearest plant were found to be less biased than the other plotless methods, but the quadrat method was found to be superior in all respects for this type of vegetation.

A note on the effects of browsing by feral goats on a Belah (Casuarina Cristata) - Rosewood (Heterodendrum Oleifolium) woodland.

In a Belah - Rosewood woodland in western New South Wales, stocking with feral goats over a four year period effected changes in the composition of the tree and shrub component. The most readily browsed tree was Rosewood and mature trees of this species were stripped of foliage to a height of 2 m. At an early stage Desert broombush (Templetonia egena) and young Warrior bush (Apophyllum anomalum) were severely damaged and young Yarran (Acacia homalophylla) and Belah defoliated. Most defoliated Yarran died within the observation period. Two shrubs regarded as weed species, Punty bush (Cassia eremophila var. platypoda) and Desert cassia (C. eremophila var. coriacea) were heavily browsed in the third year and subsequently eliminated. The weed shrub Turpentine (Eremophila sturtizl was not browsed at any time.

3. The role of the browser in the bushveld of the Eastern Cape

Abstract The role of the goat in the development and utilization of the optimum production potential of the bushveld regions of the Eastern Cape is discussed. It is important to distinguish between two types of bushveld: (1) Valley Bushveld and (2) dry thornveld. In the Valley Bush he emphasis lies primarily on preservation but at the same time achieving effective utilization of the valuable shrub component of the vegetation. These objectives are achieved by employing goat farming as the primary enterprise. In the dry thornveld the main objectives are the effective utilization of the grass component and the control of encroaching Acacia karroo. The full production potential of the thornveld areas can be achieved with cattle farming as the primary enterprise and with goats playing a secondary role.

Population Structure and Social Organization of Southwestern Riparian Birds

Breeding bird populations were studied on seven riparian woodland study plots in north-central Arizona. The densities of breeding birds varied from 193 to 847 pairs per 40 hectares. These differences were, in part, related to the vegetative structure of the habitat. Bird species diversity (BSD) was not correlated with foliage height diversity (FHD) in riparian habitats consisting of one major vegetational component (the cottonwood tree Populus fremontii ) where these habitats are bordered by agricultural fields. These areas supported the largest breeding bird populations (847, 612, 512, and 425 pairs per 40 hectares) while areas consisting of a mixed deciduous tree and shrub component ( Populus, Platanus, Salix, Acer, Fraxinus, Prosopis, etc. ) had smaller populations of breeding birds (322, 312, and 193 pairs per 40 hectares). On the mixed deciduous woodland areas the correlation between BSD and FHD was similar to what others have found in Eastern deciduous forests. The average weights of individual birds were significantly greater on the homogeneous cottonwood areas ( X ¯ = 46.4 g) than on the mixed deciduous areas ( X ¯ = 22.9 g). Data gathered indicate that two systems of social organization are being maintained. In areas of relatively low population density (mixed deciduous) 57% of the pairs maintained “class A” territories. On areas of relatively high population density (homogeneous cottonwood) only 22% of the pairs exhibited this form of spacing; here, most birds forage freely outside of the riparian habitat. We suggest that the differences in population density and average weights of birds found in the two habitat types are a result of the following: (i) relative productivity of areas adjacent to the riparian habitat, and (ii) degree of intra- and interspecific competition effected by avian populations found breeding in areas adjacent to the riparian habitat.

Dynamics of Black Cherry (Prunus serotina Erhr.) in Southern Wisconsin Oak Forests

Black cherry occupies a key position in the dynamics of oak (Quercus spp.) forests in southern Wisconsin. Its relative importance in sapling and small—tree sizes averaged over 50%, and in some stands it was the only species in these strata. Age analysis of 854 cores showed that 58% of all black cherry stems were established between 1931 and 1941. The appearance of large amounts of black cherry in the 1930 decade was the result of drought and livestock—feed shortages. The latter were especially severe in 1934 and 1936 and resulted in large—scale disturbance of forests through grazing and possibly extensive cutting of forests for foliage. The presence of a strong shrub component exerted a major influence on the dynamics of the oak forest. An inverse relationship existed between overstory tree basal area and the importance of shrubs. Although density and cover of tree seedlings were independent of tree basal area and shrub cover, seedling numbers were insufficient for adequate restocking of most stands. In clear—cut forests the shrub layer was extensive, and regrowth of trees was largely confined to stump sprouts. Shrubs in disturbed forests averaged 38,635 stems/acre, 4,535 square inches basal area/acre, and 145.8% cover. In undisturbed forests, shrub competition (average 16,231 stems/acre, 1,036 square inches basal area/acre, and 51.4% cover) largely precluded seedling establishment by tree species, and maximum basal area levels in these forests were not maintained. Growth and survival of black cherry in the understory depended on the complex interaction of environmental factors. Tree overstory basal area and soil available water were the most significant factors controlling its vigor. Suppressed stems of cherry were as old as 60 years. Growth patterns in stem cores showed that stems responded to release after 39 years of suppression. The capacity of black cherry to develop basal sprouts and the occurrence of light intensities greater than 1,200 ft—c in the understory greatly aided its survival in this stratum. The important role of black cherry in the dynamics of the oak forests was based on opportunistic characteristics including widespread dispersal, delayed germination of seeds, and flexible seedbed requirements. Forest conditions, such as the isolation of forests as woodlots, pioneer environmental conditions, and widespread disturbance, predisposed invasion by opportunistic species. Dynamic processes were characterized by general rather than gradient compositional changes. Patterns of replacement were not orderly and predictable, but irregular as a result of chance dispersal and local catastrophe. Although not uncommon in oak forests in the northeastern United States, invasion by Acer saccharum is not occurring in southern Wisconsin. Succession to Acer—Tilia is confined to specific sites. The overall existing pattern is one of increasing diversity typical of many pioneer communities in an early phase of colonization.