Shrub Size Research Articles

Soil property variations in relation to topographic aspect and vegetation community in the south-eastern highlands of Ethiopia

Study of soil property variations resulting from topographic aspect and vegetation changes will have implication on the proper management of marginal and environmentally sensitive areas. This study addressed the effects of topographic aspect and vegetation community types on soil physical and chemical properties in the Bale Mountains, south-eastern highlands of Ethiopia. At each stratified vegetation community; Schefflera– Hagenia, Hypericum– Erica– Schefflera, and Erica arborea (shrub size), and in each of the four topographic aspects, four representative soil profiles giving a total of 3 × 4 × 4 = 48 were opened and described. Soil texture, bulk density, soil pH, plant available phosphorus, CEC, exchangeable base cations, and percent base saturations were analyzed and interpreted. Except in few cases, all considered soil properties showed significant differences among vegetation communities and topographic aspects. The differences may be attributed to leaching and differences in organic matter (carbon) contents within the soil profiles due to topographic aspect-induced microclimatic differences, reflecting the response of vegetation communities to the conditions. Soil textural fractions, mainly silt and clay, bulk density, pH, plant available phosphorus, percent base saturation, CEC, and exchangeable base cations generally increased in the Schefflera– Hagenia vegetation community zone. Further studies might be required to fully understand and clarify the influence of aspect, topography and vegetation types on soil properties for site-specific soil resource management practices in this mountainous area.

Soil organic carbon and total nitrogen stocks as affected by topographic aspect and vegetation in the Bale Mountains, Ethiopia

Soil organic carbon (SOC) and total nitrogen (total N) stocks in 0–0.3 and 0.3–1.0 m soil layers were estimated following the standard procedures for three vegetation communities; Schefflera-Hagenia, Hypericum-Erica-Schefflera, and Erica arborea (shrub size), at different topographic aspects (east-, west-, north- and south-facing) on the Bale Mountains in the south-eastern highlands of Ethiopia. The results showed that SOC and total N in the top 0.3 m depth varied significantly among vegetation communities ( p < 0.001) and aspects ( p = 0.003). At all aspects studied, the overall mean SOC and total N amounts to a depth of 1.0 m ranged from 32.67 to 46.03 kg C m − 2 and 2.89 to 3.61 kg N m − 2 among the vegetation communities. The overall mean SOC and total N stocks to a depth of 1.0 m varied from 35.13 to 44.97 kg C m − 2 and 2.90 to 3.75 kg N m − 2 among aspects. Topographic aspect induced microclimatic differences and vegetation community types were found to be important factors for the significant variations in SOC and total N stocks in the Bale Mountains. About 45% of the SOC stock in the 0–1.0 m layer of the mineral soil was held in the top 0.3 m of the soil, indicating the potentially large amount of CO 2 that can be released from the top surface soils when these vegetations are deforested and converted into grazing and cultivation.

Effect of conspecific adult plants on the spatial patterns of the soil seed bank of Calligonum rubicundum

Deterministic functions that aim at quantifying and modelling the spatial effects of shrubs on the soil seed bank of a Calligonum rubicundum stand are described. The procedure utilises data on the spatial location of 99 individual C. rubicundum plants and the number of seeds of this species in the soil at 169 grid-nodes. We developed a regression equation that quantified the effects of shrub size, shrub height and prevailing wind direction on seed dispersal. The deterministic models revealed a good fit between the measured and simulated data using parameters estimated from the data set of soil seed bank values. The results presented in this paper provide a way to examine, quantify and model the spatial effects of shrubs on soil seed banks at the stand level. The method presented here can be applied to examine and estimate the influence of dominant plants on other biotic or abiotic properties of an ecosystem.

A Test of the Utility of Exotic Tree Plantations for Understory Birds and Food Resources in the Colombian Andes1

ABSTRACTThe spatial distribution and abundance of animals are in part determined by the distribution and abundance of their resource base. In the Central Andes of Colombia, monospecific tree plantations have been used to recover vegetative cover in watershed protection programs, but these plantations differ from natural forests in structure, composition, and resources available to wildlife. To evaluate these plantations as habitat for wildlife, we compared the diversity and abundance of understory birds, flowers, and fruits between juxtaposed 40‐yr‐old patches of exotic Chinese ash (Fraxinus chinensis) plantations and naturally regenerated forest of the same age. We observed more fruiting species in the regenerated forest, but there were no differences in total flower and fruit availability between habitat types. We also observed differences between habitats in the size of some understory shrubs, but these differences did not lead to differences between habitats in the diversity and abundance of birds. Capture rates of nectarivores correlated with resource abundance at sampling plot scale, but no such correlation was found for frugivores. Understory frugivorous birds are apparently functioning at a larger spatial scale than the patchiness created by the two habitats. Nectarivorous birds are responding to small‐scale patchiness in resource availability, but not to the different habitats. These results indicate that at small scales, the ash plantation understory provides adequate habitat for birds.

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

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

Effects of wildfire season on the resprouting of kermes oak ( Quercus coccifera L.)

The resprouting growth of kermes oak ( Quercus coccifera L.) after wildfire, in relation to certain ecological parameters, has been studied. The effect of time of fire incident (beginning versus end of growth season) on growth (height and diameter) of new sprouts was examined. For each time of fire incidents, the influence of aspect (slope exposure), and pre-fire size of parental shrub, on resprouting ability and growth of kermes oak was also investigated. A total of 100 burned kermes oak shrubs were randomly selected on each burnt site: 25 per the main four aspects (north, east, south, west). The number of resprout influences their height and thickness. Three resprouts were kept per shrub, and their height and basal diameter were measured every 3 months for three vegetative periods. Statistical analysis of the data included standard procedures of comparison of means. Both sites comprised shrubs with similar pre-burn dimensions. Height growth showed no particular divergence between the two sites, following a typical sigmoidal tree growth curve, and reaching a maximum at the end of the second vegetative period. Height measurements showed highly significant differences between the two sites during the first two trimesters only, while differences in diameter were significant during the whole measurement period. Same-ages resprouts of Site 2 showed a faster initial height growth than those at Site 1. After the age of 12 months, however, height growth was more or less the same at both sites. Differences in aspects (orientation) were found only in plants of Site 2. Height and diameter of new resprouts were positively correlated to height of maternal sprout. Analysis of climatic data identified precipitation as the decisive factor in resprout development. The results of the present study conclude that the date of occurrence of wildfire does not affect the final dimensions of kermes oak shrubs, but it does affects initial growth rate. There are some differences in rate of growth after wildfires occurring at the end of the vegetative period especially relative to aspects. Moreover, after three vegetative periods, shrubs had regained a considerable part of their pre-burn height.

Annual, Local, and Individual Variation in the Inflorescence and Fruit Production of Eastern Leatherwood (Dirca palustris L. Thymelaeaceae)

through time when vegetative growth must also be supported from a limited pool of photosynthate. We compared reproductive performance characteristics among natural stands in Upper Michigan, USA across seven years. In addition, we inquired whether small or deeply shaded shrubs tended to be less consistent fruit producers. Fruit set fluctuated considerably over the period, but several conspicuously good and poor years did not correspond to temperature patterns. Flower production was largely stable at the stand level over the seven year period, with increases in years 2000 and 2001. Fruit production was a function of shrub size and did not differ between years or between stands. At an individual level, small and deeply shaded individuals tended to have one or two conspicuously good fruiting years against a background of low fruit production; sunlit and larger individuals were more consistent fruit producers. Fruit production was not related to the previous year's fruit crop. Shrub size and, secondarily, light availability were the important determinants of fruit production, implying that stand age and history govern the population recruitment of leatherwood.

Non‐destructive dry matter estimation of Alhagi sparsifolia vegetation in a desert oasis of Northwest China

Abstract:Question: Can above‐ground biomass of naturally growing Alhagi sparsifolia shrubs be estimated non‐destructively?Location: Qira oasis (37° 01′N, 80° 48′E, 1365 ma.s.l.) at the southern fringe of the Taklamakan desert, Xinjiang, NW China.Methods: Two methods were compared to estimate above‐ground biomass (AGB) of Alhagi. At first shrub AGB was estimated by manual ground measurements (called ‘allometric approach’) of length, width and height of 50 individuals. Subsequently regression equations were established between calculated shrub canopy volume and shrub AGB (r2= 0.96). These equations were used to calculate AGB from manual ground measurements in 20 sample plots within the Alhagi field. Secondly, kite‐based colour aerial photography coupled with the use of a Geographic Information System (called ‘GIS approach’) was tested. First and second order polynomial regressions between AGB data of the 50 individual shrubs and their respective canopy area allowed to automatically calculate the AGB of all remaining shrubs covered by the photograph (r2= 0.92 to 0.96). The use of non‐linear AGB regression equations required an automatised separation of shrubs growing solitary or in clumps. Separation criteria were the size and shape of shrub canopies.Results: The allometric approach was more reliable but also more time‐consuming than the GIS‐based approach. The latter led to an overestimation of Alhagi dry matter in densely vegetated areas. However, this systematic error decreased with increasing size of the surveyed area. Future research in this field should focus on improvements of AGB estimates in areas of high shrub density.

Facilitative interactions on coastal dunes in response to seasonal weather fluctuations and benefactor size

:We analyzed spatial plant-plant associations (during three seasons: nortes, dry, and rainy) and performed a field experiment on seedling survival, in order to test whether the occurrence of facilitation varied in response to seasonal weather fluctuations and to benefactor size. In a mobile dune system (central Gulf of Mexico) we focused on the endemic early colonizer shrub Chamaecrista chamaecristoides and two late colonizer bunch grasses. Total shrub cover and density were highest during the rainy period. Density of adult Trachypogon plumosus, but not that of adult Schizachyrium scoparium, was higher beneath the canopy of the shrub. No seasonal variations in spatial associations were observed. Density of grass seedlings decreased during the nortes beneath and beyond the canopy of C. chamaecristoides. Fitness parameters of both grasses improved beneath the benefactor plants, while sand accretion decreased. The number of grass individuals benefiting from facilitation increased with shrub size except for the largest shrubs, which had a reduced density of grasses. Temperature on the sand surface was lowest beneath the larger shrubs. Our results highlight the importance of different life stages at which facilitation may occur together with a varying effect of benefactor size in the overall role of facilitation in structuring communities.

True Mountain Mahogany Community and Shrub Size Responses to Browsing

True mountain mahogany (Cercocarpus montanus Raf.) provides nutritional winter forage for big game species in the mountain brush zone. To determine browsing effects, animal use, percent vegetation cover, and shrub dimensions were measured inside and outside exclosures up to 7 years old on 4 sites on the North Slope of the Unita Mountains, and at an exclosure > 50 years old in the Wasatch Mountains, Utah. Utilization was measured in an associated twig demography study. Winter big game use increased from 1997 to 1999 at the North Slope. Utilization of annual growth ranged from 21 to over 300%, depending on the site and year and did not necessarily parallel animal use. Greater than 100% utilization of annual growth resulted when previous years' wood was browsed. There was little difference in vegetation cover, species richness, and diversity inside and outside the exclosures, but mountain mahogany had lower cover and smaller size outside than inside the exclosures at 3 North Slope sites. Mahogany cover was similar, but width and breadth of shrubs were smaller outside than inside the > 50-year old exclosure in the Wasatch Mountains. Browsed shrubs maintained their size from 1995 to 1999 at the North Slope, despite over 100 % utilization of annual growth at 3 of the sites in at least 1 year. True mountain mahogany is highly tolerant of winter browsing, and can compensate for > 100% utilization of annual growth by increased growth during wet years. However, continued use of over 100 % of annual growth could reduce cover, shrub size, and forage production during years of lower resource availability. A practical management approach is to monitor cover and size of shrubs inside and outside well-placed exclosures across the winter range over time, and reduce herd numbers as appropriate to allow browsed shrubs to maintain or reach the size of unbrowsed shrubs when their growth has leveled off after a few years of exclusion. DOI:10.2458/azu_jrm_v56i6_turley2

Spatial and temporal variations in the timing of leaf replacement in a Quercus cornelius‐mulleri population

Abstract. The phenology of spring leaf replacement was studied in a population of 46 evergreen scrub oaks (Quercus cornelius‐mulleri) at the edge of the Mojave Desert in each of five years over the period 1990–2001. The oaks occupied a site that spanned rocky slopes to sandy bajadas. The site receives variable annual rainfall (estimated 12‐yr average 195 mm; range in study years 67–706 mm). The spatial coordinates of all individuals were recorded, and in April, when leaf replacement was underway, individual replacement phenologies were assessed. Shrub sizes were recorded in three separate years, and in 2001 water potentials were measured.Individuals vary greatly in their timing of leaf replacement within years, and also between years. Many individuals with an early phenology one year are significantly later in the following year, and vice versa. While we detected weak influences on leaf replacement phenology due to shrub size, position within the site, and a genetic component, stronger influences were attributable to the phenology of the shrub in prior years, and to the phenology of neighbours within years. Neighbouring individuals that are close and/or large are significantly disparate in phenology, with one early and the other late. A potential mechanism of local resource depletion associated with costs to an early phenology is discussed.

Spatial and temporal variations in the timing of leaf replacement in a Quercus cornelius-mulleri population

Abstract The phenology of spring leaf replacement was studied in a population of 46 evergreen scrub oaks (Quercus cornelius-mulleri) at the edge of the Mojave Desert in each of five years over the period 1990–2001. The oaks occupied a site that spanned rocky slopes to sandy bajadas. The site receives variable annual rainfall (estimated 12-yr average 195 mm; range in study years 67–706 mm). The spatial coordinates of all individuals were recorded, and in April, when leaf replacement was underway, individual replacement phenologies were assessed. Shrub sizes were recorded in three separate years, and in 2001 water potentials were measured. Individuals vary greatly in their timing of leaf replacement within years, and also between years. Many individuals with an early phenology one year are significantly later in the following year, and vice versa. While we detected weak influences on leaf replacement phenology due to shrub size, position within the site, and a genetic component, stronger influences were att...

The Bunker Hill Hillsides: A Case Study in the Use of Adaptive Management in Early Successional Restoration on the Nation's Largest Superfund Site

Active hillsides restoration included development and installation of site prescriptions using adaptive management and monitoring of results. Initial prescriptions for hillsides restoration and their implementation were based on a combination of site characterization and demonstration studies. Prescriptions were modified over time as the results of past activities became evident. Hillsides have responded well to prescriptions and successional processes appear to have been re-initiated. Adaptive management induced prescription modifications including changing liming materials to improve performance, increasing seeding rate to improve initial plant canopy cover, adjusting seed mix composition to remove poorly germinating species and adding herbaceous species with exceptional establishment and growth performance, increasing shrub sizes to improve establishment, and selecting tackifiers that reflected actual site performance of the products. Target plant covers were 50 percent or greater and overall plant canopy cover from 1998 and 1999 operational hydroseeding averaged over 61 percent after two growing seasons. Red top, bluegrass, sheep fescue, Idaho fescue, and timothy dominate the seeded communities. Plant and mulch cover is approximately 10 percent higher on east-facing slopes compared to west-facing slopes. Areas of low cover are often composed of rock pavement surfaces. New seedlings are emerging and volunteer plant species are appearing on the slopes. Turbidity of surface water emanating from the hillside watersheds has dropped substantially from past years. Instantaneous comparisons between background turbidity at the mouths of Government and Deadwood creeks indicate that State of Idaho water quality standards are being met in most cases. Early successional processes appear to be emerging on the hills with assistance provided by wildlife. Additional keywords: monitoring, surface water quality, plant cover, remediation

Microenvironmental and vegetational heterogeneity induced by phytogenic nebkhas in an arid coastal ecosystem

The nebkhas of woody plants represent distinct habitats in arid and semiarid ecosystems. Nebkhas are mounds composed of wind-borne sediment within or around shrub canopies. We studied the effects of widely spaced nebkhas of Retama raetam shrub on their microenvironment and associated herbaceous vegetation in the Mediterranean coast of Sinai Peninsula. Our measurements included nebkha size (height and width) and shrub size (canopy height and diameter). We identified four distinct microsites at each nebkha: crest, mid-slope, edge, and internebkha space. We measured soil temperature and moisture, photosynthetically active radiation (PAR), and soil properties. The plant species grown at each microsite were identified and their densities were measured. Average soil temperature and PAR were highest at internebkha space and lowest at nebkha crest. The maximum diurnal temperature and PAR of internebkhas exceeded that of nebkhas. Soil moisture and nutrient concentrations showed a gradient of spatial heterogeneity and were highest at the nebkha edge. Regression analysis indicated that total herbaceous plant density was significantly related to nebkha size, and to shrub canopy diameter and area. Detrended correspondence analysis indicated that patterns of species composition were correlated with the spatial variability in soil moisture and nutrient content along the gradient of increasing distance from the nebkha crest. It is assumed that shrub canopy and its nebkha interact in governing ecosystem functioning in this environment.

A Proposed Method for Determining Shrub Utilization Using (LA/LS) Imagery

Utilization of plant above ground biomass has continued to be a critical yet difficult assessment in rangeland monitoring. Shrub size and woody structure further compound the measurement of shrub biomass utilization. This study was designed to determine the potential utility of low altitude/large scale (LA/LS) imagery in assessing shrub utilization. A near monoculture of Ceriotoides lanata (Pursh) J.T. Howell (winterfat) located in the western desert shrubland of Utah was used to evaluate this technique. Four, 3.1 by 3.1 m plots were identified and the shrubs within the plots were defoliated by hand-picking at about 10% intervals with imagery of the plots obtained between pickings. Imagery was obtained using a radio controlled airplane (drone) fitted with a 35 mm camera. Images were evaluated using image processing software and the resulting reflectance data correlated with defoliation percentages (weight basis) for each plot. Reflectance data from images correlated highly with defoliation percentages (r2 > 0.9). This technique of using LA/LS imagery shows promise for a quick and accurate tool in assessing utilization of shrubs. DOI:10.2458/azu_jrm_v54i4_quilter

Snow–Shrub Interactions in Arctic Tundra: A Hypothesis with Climatic Implications

In the Arctic, where wind transport of snow is common, the depth and insulative properties of the snow cover can be determined as much by the wind as by spatial variations in precipitation. Where shrubs are more abundant and larger, greater amounts of drifting snow are trapped and suffer less loss due to sublimation. The snow in shrub patches is both thicker and a better thermal insulator per unit thickness than the snow outside of shrub patches. As a consequence, winter soil surface temperatures are substantially higher, a condition that can promote greater winter decomposition and nutrient release, thereby providing a positive feedback that could enhance shrub growth. If the abundance, size, and coverage of arctic shrubs increases in response to climate warming, as is expected, snow–shrub interactions could cause a widespread increase (estimated 10%–25%) in the winter snow depth. This would increase spring runoff, winter soil temperatures, and probably winter CO2 emissions. The balance between these winter effects and changes in the summer energy balance associated with the increase in shrubs probably depends on shrub density, with the threshold for winter snow trapping occurring at lower densities than the threshold for summer effects such as shading. It is suggested that snow–shrub interactions warrant further investigation as a possible factor contributing to the transition of the arctic land surface from moist graminoid tundra to shrub tundra in response to climatic warming.

A proposed method for determining shrub utilization using (LA/LS) imagery

Utilization of plant above ground biomass has continued to be a critical yet difficult assessment in rangeland monitoring. Shrub size and woody structure further compound the measurement of shrub biomass utilization. This study was designed to determine the potential utility of low altitude/large scale (LA/LS) imagery in assessing shrub utilization. A near monoculture of Ceriotoides lanata (Pursh) J.T. Howell (winterfat) located in the western desert shrubland of Utah was used to evaluate this technique. Four, 3.1 by 3.1 m plots were identified and the shrubs within the plots were defoliated by hand-picking at about 10% intervals with imagery of the plots obtained between pickings. Imagery was obtained using a radio controlled airplane (drone) fitted with a 35 mm camera. Images were evaluated using image processing software and the resulting reflectance data correlated with defoliation percentages (weight basis) for each plot. Reflectance data from images correlated highly with defoliation percentages (r2 &gt; 0.9). This technique of using LA/LS imagery shows promise for a quick and accurate tool in assessing utilization of shrubs.

Visual perception based quantitative measurement of crown size of shrub from digital camera image and factors affecting the size.

Visual perception based quantitative measurement of crown size of shrub from digital camera image and factors affecting the size.

Predictive Equations for Biomass and Fuel Characteristics of Argentine Shrubs

Predictive equations for estimating shrub biomass in semi-arid scrub ecosystems are essential for evaluating shrub encroachment, conducting ecosystem-level studies of net primary productivity (NPP) and nutrient cycling, and examining effects of different fire regimes. In this study, we developed predictive equations to estimate total aboveground biomass and biomass of foliage and stems of the 8 most common shrubs in the semi-arid scrub (Monte) of central Argentina. We also examined the relationship between shrub size and proportions of these components for the dominant species, Larrea divaricata Cavanilles (creosotebush), and determined fuel characteristics (dead-to-live ratio, bulk density) of the 8 shrub species. Regression analyses were used to examine the relationships between aboveground biomass and 5 field measurements (diameter of the longest stem, shrub height, maximum crown width, crown width at right angles to maximum crown width, and crown volume). A natural log-log model based on a single variable best described this relationship in most cases. The easiest field measurement for 6 of the 8 species was diameter of the longest stem, and this measure was often the best predictor of shrub biomass. As L. divaricata increased in size, the proportional biomass of large stems increased, and bio mass of foliage and small stems decreased. This pattern suggests pro ductivity may decrease with shrub age. The mass of dead material was low in most shrub species. Bulk densities were comparable to those of shrubs in other semi-arid ecosystems. Equations developed here will allow rapid and accurate estimation of shrub biomass in the Monte of Argentina.

Predictive equations for biomass and fuel characteristics of Argentine shrubs

Predictive equations for estimating shrub biomass in semi-arid scrub ecosystems are essential for evaluating shrub encroachment, conducting ecosystem-level studies of net primary productivity (NPP) and nutrient cycling, and examining effects of different fire regimes. In this study, we developed predictive equations to estimate total aboveground biomass and biomass of foliage and stems of the 8most common shrubs in the semi-arid scrub (Monte) of central Argentina. We also examined the relationship between shrub size and proportions of these components for the dominant species, Larrea divaricata Cavanilles (creosotebush), and determined fuel characteristics (dead-to-live ratio, bulk density) of the 8 shrub species. Regression analyses were used to examine the relationships between aboveground biomass and 5 field measurements (diameter of the longest stem, shrub height, maximum crown width, crown width at right angles to maximum crown width, and crown volume). A natural log-log model based on a single variable best described this relationship in most cases. The easiest field measurement for 6 of the 8 species was diameter of the longest stem, and this measure was often the best predictor of shrub biomass. As L. divaricata increased in size, the proportional biomass of large stems increased, and bio-mass of foliage and small stems decreased. This pattern suggests productivity may decrease with shrub age. The mass of dead materialwas low in most shrub species. Bulk densities were comparable to those of shrubs in other semi-arid ecosystems. Equations developed here will allow rapid and accurate estimation of shrub biomass in the Monte of Argentina.