Widespread Shrub Research Articles

Monepenepe (Cassia abbriviata): A Medicinal Plant in Botswana

Cassia abbrivata commonly known, as Monepenepe in Botswana is a widespread shrub or medium sized tree or shrub belonging to the Caesalpinaceae family. In Africa it grows from Somalia to South Africa. It is important medicine plant utilized by people living in rural and urban areas where it grows. The bark and roots of the plant have medicinal properties that treat different ailment in Botswana and other countries where it grows. Too much cutting of the bark and root digging for medicinal uses has left many trees dead in Botswana. It is therefore recommended that removal of the bark for medicine should be in small pieces and not around the trunk (ring barking) if the tree is to be preserved. This study reviews the characteristics and medicinal uses of Cassia abbriviata.

SEED GERMINATION OF SIERRA NEVADA POSTFIRE CHAPARRAL SPECIES

ABSTRACT The California chaparral community has a rich flora of species with different mechanisms for cuing germination to postfire conditions. Here we report further germination experiments that elucidate the response of several widespread shrub species whose germination response was not clear and include other species from the Sierra Nevada, which have not previously been included in germination studies. The shrubs Adenostoma fasciculatum and Eriodictyon crassifolium and the postfire annual Mentzelia dispersa exhibited highly significant germination in response to smoke treatments, with some enhanced germination in response to heating as well. The shrubs Fremontodendron californicum and Malacothamnus fremontii were stimulated only by heat-shock treatments. Seeds buried in the soil for one year exhibited substantially higher germination for controls and most treatments. In the case of two postfire annuals, Mimulus bolanderi and M. gracilipes, germination of fresh seed was significantly greater with smoke...

Allozyme diversity and genetic structure of marginal and central populations of Corylus avellana L. (Betulaceae) in Europe

Corylus avellana L. (hazel, Betulaceae) is a long-lived, widespread shrub in Europe, having its northern range margin in Fennoscandia and a postglacial history involving range-expansion from refugial areas in southern Europe. In this study, we tested for a relationship between marginality and low within-population genetic diversity by assessing patterns of variation at 14 putatively neutral allozyme loci (comprising 43 putative alleles) within and between 40 natural populations of C. avellana along a north-south transect in Europe. Geographically marginal populations (central Sweden) showed lower levels of within-population diversity than populations in more central regions, as indicated by significant negative correlations between latitude and the percentage of polymorphic loci (rS=–0.47, P < 0.001), the average number of alleles per locus (rS=–0.65, P < 0.001), the expected heterozygosity (rS=–0.19, P < 0.05), and the proportion of distinguishable genotypes (rS=–0.56, P < 0.001). These patterns, combined with the unusually high between-population component of gene diversity (GST=19.7%) and allelic richness (AST=24%) in the marginal region, can be attributed to historical bottlenecks during the species’ postglacial range-expansion, but may also reflect a history of genetic drift in the small, isolated populations occupying the marginal region. Information on the spatial distribution of genotypes provide further support for a role of vegetative reproduction (layering) in the structuring of genetic variation within populations.

Assembly of tropical plant diversity on a local scale: Cyrtandra (Gesneriaceae) on Mount Kerinci, Sumatra

At a regional scale, the high species numbers (gamma diversity) of tropical forests have been explained by either a gradual accumulation of species through time (museum hypothesis) or, by contrast, rapid recent speciation in large genera. However, the origins of local rain forest diversity (alpha diversity) have been given little attention. Cyrtandra (Gesneriaceae), an understorey genus in the highly species-rich Indo-Malayan rain forest, has considerable capacity for producing local endemics, making it particularly suitable for studying diversity on a local scale. We sampled Cyrtandra species from one community on Mount Kerinci, Sumatra, and phylogenetic analyses of ITS sequences suggest that this community is an assembly of three distinct phyletic lineages: (1) a group of herbaceous or subshrub plants of Bornean affinity, (2) one member of a group of widespread shrubs forming Cyrtandra section Dissimiles and (3) a second group of shrubs. The evolutionary origin of this community is therefore not a result of rapid and recent speciation: it is assembled from species resulting from a gradual accumulation of diversity through time (museum hypothesis), although one lineage shows evidence of more recent, continuing speciation than the other two. The community includes two distantly related, apparently endemic species, but there is no evidence for a local adaptive radiation. The protection of representative species from each lineage would allow the conservation of genetic diversity. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 49–62.

Effects of Historic Livestock Grazing on Vegetation at Chaco Culture National Historic Park, New Mexico

Abstract: Livestock grazing is the most ubiquitous land use in western North America, yet it rarely has been studied in a controlled manner because of the lack of large areas free of grazing. We compared the ecological effects of three grazing treatments—long‐term protection, short‐term protection, and currently grazed—at Chaco Culture National Historic Park in northern New Mexico. Chaco has a long history of human habitation and is now one of the largest grazing exclosures in the American West. We studied the effects of livestock grazing on the cover of plants, soil crusts, and plant species richness at six sites with different potential natural vegetation. Species richness was higher under long‐term protection than under current grazing at all six sites. Trends in shrub and grass response varied significantly across the six sites. Shrub cover increased with long‐term protection at four upland sites, and grass cover increased with protection at four sites. The response of Chaco vegetation to release from grazing varied significantly according to each site's ecological potential, determined in part by edaphic and topographic characteristics. These nuances in vegetation response represent natural ecological variation and contrast with the notions of widespread shrub “invasion” often inferred in the past.

Consequences of green alder expansion on vegetation changes and arthropod communities removal in the northern French Alps

Green alder is a widespread shrub species in the Alps. The intense grazing practices of the last centuries relegated it to avalanche tracks on wet and steep slopes. However, it is currently colonizing abandoned meadows and pastures on relatively wet and drained soils at the subalpine and the montane belts, creating a dense shrub cover. The aim of this study is to assess the biodiversity changes induced during alder expansion by taxonomic and functional traits, using two representative taxa, i.e. vegetation and arthropods. The results show that the alder expansion strongly affects the 0.5–1 m vegetation layer and the plant species richness as well as the biomass and composition of the arthropods active on the soil surface. Hymenoptera, Orthoptera and Coleoptera, which compose the major part of the arthropod biomass, decline significantly as the green alder canopy grows. Such changes in specific and functional diversity may have strong effects on the ecosystem functioning and particularly on the maintenance of the habitat of several endangered species such as the black grouse ( Tetrao tetrix L.). The impact of green alder on biodiversity must be taken into account as well as its functional role in the ecosystem before leading any management against its expansion.

High-temperature tolerance of Artemisia tridentata and Potentilla gracilis under a climate change manipulation.

Leaf tolerance to high temperatures, as determined by electrolyte leakage and chlorophyll a fluorescence, was compared for Artemisia tridentata (Asteraceae), a widespread shrub of the Great Basin, Colorado Plateau, and western slope of the Rocky Mountains, and Potentilla gracilis (Rosaceae), a herbaceous forb common to high-elevation meadows of the western United States. Species-specific and treatment-specific differences in leaf temperature, high-temperature tolerance and chlorophyll a fluorescence from photosystem II were compared, to test the hypothesis that plants at ecosystem borders will exhibit species-specific responses to climate change. Measurements were made for plants exposed to a climate change warming manipulation on a major ecosystem border at the Rocky Mountain Biological Laboratory, Colorado, United States, in July and August 1995. In July, daily maximal leaf temperatures were significantly higher for P. gracilis than for A. tridentata. Leaf temperatures were slightly lower in August than July for leaves of both species, on control and heated plots, despite the fact that daily maximum air temperatures were not significantly different for the two months. High-temperature tolerance was determined for leaves treated for 1 h at temperatures ranging from 15°C to 65°C. LT50 was approximately 46°C for both species on control plots, but was 43°C for leaves of both species from heated plots, contrary to the predictions of the hypothesis. No shift in LT50 (acclimation) was apparent between July and August. Changes in chlorophyll a fluorescence from photosystem II (F V /F M ) were used to characterize the photosynthetic response to high temperatures. For both A. tridentata and P. gracilis in July, F V /F M was about 0.7, but decreased for temperatures above 40°C. The results suggest that plant responses to global warming at ecosystem borders may be influenced by factors other than leaf-level physiological tolerance to elevated temperatures.

Seasonal Patterns of Leaf Growth and Loss, Flowering and Fruiting on a Subtropical Central Pacific Island

We studied the phenology of leaf production and loss, flowering, and fruiting on Henderson Island, a raised limestone island situated at 24?S in the Central South Pacific. The one-year study encompassed 19 of the 22 wide-spread indigenous tree and shrub species found in the plateau forest. Of 11 species showing significant annual variation in leaf production, all grew most new leaves immediately after the solar zenith between January and March, when temperatures were highest. Thirteen species showed significant annual variation in leaf loss, with peaks in October/ November or January/February. In most species, January-June saw net leaf gain, while the converse was true from July-December. Only one species, Premna serratifolia, was deciduous, shedding leaves and then remaining leafless for approximately two months until new shoots grew leaves. Flowering and fruiting were more evenly distributed through the year than leaf production. This could be related to the scarcity of pollinating insects and/or of fruit dispersers on this exceptionally remote island.

Contrasting Morphology and Ecophysiology of Cooccurring Broad and Terete Leaves in Hakea trifurcata (Proteaceae)

We studied the morphology, anatomy, phyllotaxy and daily seasonal ecophysiology of the two leaf types (broad and terete) of Hakea trifurcata (Smith) R.Br., a widespread shrub in south-western Australia. Both leaf types may be present on the same branchlet, with one or two broad leaves forming first during the annual growth period (late winter) followed by many terete leaves in spring. Terete leaves were more xeromorphic than broad leaves, including greater thickness, denser tissues and fewer veins. Broad leaves fixed more carbon and transpired more water per unit mass than terete leaves, in a well ventilated leaf chamber, and had lower (more negative) xylem pressure potentials. Broad leaf temperatures only exceeded those of terete leaves under hot, dry conditions, with no relationship between transpiration rates and leaf temperature. Terete leaves possessed many structural and physiological characteristics commonly associated with drought-tolerant leaves, whereas broad leaves were characteristic of leaves which keep their stomates open during periods of water and heat stress. Both leaf types appear to increase the fitness of this species in a mediterranean climate, with broad leaves having the potential to supply extra photosynthates and nutrients to the new season's growth.

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