Herbaceous Plant Diversity Research Articles

Piospheric influence on forage species composition and abundance in semi-arid Karamoja sub-region, Uganda

Piospheres in semi-arid areas are gradients of animal impacts around watering holes. Few studies have examined the impact dynamics of herbaceous and woody species composition and abundance in relation to piospheres in East Africa. In this study, we identified the trend in piosphere development, assessed piosphere use and change indicators, and identified herbaceous and woody plant structure in relation to piospheres in the Karamoja sub-region, Uganda. Results revealed that piosphere development has been reactionary to drought and/or insecurity events and increased rapidly in the last decade. A diversity of herbaceous and woody plants exists around the piospheres. Use and change indicators revealed high trampling and grazing intensity, high presence of erosion signs and low litter cover. Gradient distance had both positive and negative effects on trampling intensity, percent exposure and plant height, respectively. A negative and positive effect of gradient distance was also observed on different herbaceous and woody forage species leading to the identification of both increaser and decreaser species around the piospheres. Therefore, as concentrated use of the piospheres continues unabated, an outward ripple effect leading to loss and/or increase of undesirable herbaceous and woody species will be felt. This will have an impact on the composition and abundance dynamics of desirable forage species in the sub-region.

Have changing forests conditions contributed to pollinator decline in the southeastern United States?

Two conservation goals of the early 20th century, extensive reforestation and reduced wildfire through fire exclusion, may have contributed to declining pollinator abundance as forests became denser and shrub covered. To examine how forest structure affects bees we selected 5 stands in each of 7 forest types including: cleared forest; dense young pines; thinned young pines; mature open pine with extensive shrub/sapling cover; mature open pine with extensive herbaceous plant cover and little shrub cover; mature upland hardwood forest; and mature riparian hardwood forest. We sampled bees during the 2008 growing season using pan traps and measured overstory tree density, understory herbaceous plant and shrub diversity and cover, light penetration, and leaf area index. Numbers of bees and numbers of species per plot were highest in cleared forest and in mature pine stands with an herbaceous plant understory. Estimates of asymptotic species richness were highest in mature riparian hardwood forests, cleared forests and open pine forests with an herbaceous plant understory. Bee communities in the cleared forests and in the mature pine with an herbaceous plant understory were grouped together in ordination space which was consistent with perMANOVA results. The best predictor variable for bee species density was total tree basal area which was negatively correlated (r2=0.58), while the best model for predicting bee abundance (r2=0.62) included canopy openness, plant species density (both positively correlated) and shrub cover (negatively correlated). Our results combined with many others show that thinning forests combined with shrub control provides good bee habitat, is compatible with habitat restoration and management for other species, and the resulting forests will be healthier and less susceptible to old (e.g., southern pine beetle, Dendroctonus frontalis) and new (European woodwasp, Sirex noctilio) threats.

不同植被类型植物物种多样性研究

PDF HTML阅读 XML下载 导出引用 引用提醒 不同植被类型植物物种多样性 DOI: 10.5846/stxb201312032870 作者: 作者单位: 河南大学环境与规划学院,河南大学环境与规划学院,河南大学中药研究所,河南大学中药研究所,河南大学环境与规划学院; 作者简介: 通讯作者: 中图分类号: 基金项目: 中国博士后基金项目(2013M531668); 河南省教育厅自然科学重点项目(13A180057) Plant's diversity of different vegetation types Author: Affiliation: College of Environment and Planning, Henan University,,,,Henan University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了评价大面积人工种植杜仲对当地植物多样性的影响,以河南省汝阳县不同植被类型为研究对象,通过群落学调查,运用重要值、Shannon-Wiener物种多样性指数(H)、Simpson物种多样性指数(D)和均匀度指数(JH')等指标,统计分析杜仲人工林、温带落叶阔叶林(以下简称次生林)和撂荒地3 种不同植被类型的植物物种多样性,探讨杜仲种植对植物多样性的影响。调查发现,杜仲林样地中出现植物 82种,隶属39科63属,草本层为最发达的一层;次生林样地中出现植物70 种,隶属32科62 属,乔木层为最发达层;撂荒地样地中出现植物84种,隶属35科69属,无乔木层。杜仲林物种丰富度和多度均不亚于次生林和撂荒地,且杜仲林草本层物种丰富度和植株总数均高于次生林。统计分析显示,杜仲林乔木层、灌木层和草本层多样性指数H和D值、均匀度指数JH'值与其它两种植被类型相比无显著性差异(P>0.05)。因此,种植杜仲过程中采用合理密度,适当管理,不仅能提供叶、花、果等资源,而且能够丰富草本植物的种类和数量,增加植物物种多样性。 Abstract:Human-driven ecosystem simplification has highlighted questions about how the number of species in an ecosystem influences its functioning. Biodiversity is now known to affect ecosystem productivity and stability of the ecosystem. In this study, different vegetation types in Ruyang County, Henan Province, China, were examined to evaluate the impact of large-scale planting of Eucommia ulmoides on local species diversity. The species diversity was analyzed using Shannon-Wiener diversity (H), Simpson diversity (D), and evenness (JH') indices in three different vegetation types: Eucommia ulmoides plantation, temperate fallen broad-leaved forest (referred to as secondary forest), and abandoned land (old field). The results indicated that there were 82 species belonging to 39 families and 63 genera in the Eucommia ulmoides forest, in which the herbaceous layer was the most developed. The secondary forest contained 70 species belonging to 32 families and 62 genera, and the tree layer was more developed than more developed than the herbaceous and shrub layers. The old field included 84 species of 35 families and 69 genera but lacked a tree layer. The richness and abundance of species in the Eucommia ulmoides forest were similar to those in the secondary forest and old field, whereas the richness and abundance of species in the herbaceous layer of the Eucommia ulmoides forest were higher than those in the secondary forest. Our results showed that the H, D, and JH indices of the three layers of the Eucommia ulmoides forest were not significantly different from those of the secondary forest and old field (P> 0.05). Collectively, these results illustrate that, with a reasonable planting density and proper management, Eucommia ulmoides forests can not only provide us with leaves and fruit but can also enrich the amount and diversity of herbaceous plants, thereby increasing biological diversity. 参考文献 相似文献 引证文献

Species richness, diversity and density of understory vegetation along disturbance gradients in the Himalayan conifer forest

We investigated whether species richness, diversity and density of understory herbaceous plants differed along logging (gap) and grazing (primarily by cattle) disturbance gradients, and sought to identify drivers of richness, diversity and density of understory vegetation of logged sites. A factorial experiment was conducted in the mixed conifer forest of Gidakom in Western Bhutan. Levels of the logging treatment included small (0.15 – 0.24 ha), medium (0.25 – 0.35 ha) and large (0.36 – 1.31 ha) gaps. The grazing treatment included grazed (primarily by cattle) and ungrazed (where herbivores were excluded by a fence) plots nested within each gap. Data were collected from 12 gaps (4 replicates at each level of logging) using the point intercept method. Shannon Weaver Diversity and Margalef’s indices were used to estimate species diversity and describe species richness, respectively. Soil samples were analyzed for pH and nutrients. The interaction effect of logging and grazing was significant (p≤0.001) only on species diversity. Relative to ungrazed areas, species diversity was significantly higher (0.01≤p≤0.05) in medium grazed gaps. Under grazed conditions, soil P was negatively correlated with gap size and species diversity. While species diversity was positively correlated (0.01≤p≤0.05) with soil N in grazed plots species richness was positively correlated (0.001≤p≤0.01) with soil N in ungrazed plots. Relative density of Yushania microphylla and Carex nubigena were higher under ungrazed conditions. Our study suggests that the combined effect of cattle grazing and logging results in higher species diversity of understory vegetation in medium and grazed gaps in mixed conifer forests of Bhutan,whereas increase or decrease in relative density of major species is determined primarily by the independent effects of grazing and logging. From management perspective, forest managers must refrain from creating large gaps to avoid loss of nutrients (mainly P and N), which may eventually affect tree regeneration. Managers intending to maintain understory vegetation diversity must consider the combined effects of grazing and logging, ensuring low to moderate grazing pressure.

Relationships Among Anthropogenic Disturbances Representative Riparian and Non-Riparian Herbaceous Indicators (Biomass and Diversity), Land Use, and Lotic Water Quality: Implications on Rehabilitation of Lotic Waters

This study was carried out to evaluate the linkages among herbaceous plant biomass (i.e., aboveground and litter biomasses) and diversity (Shannon-Wiener index) in riparian and non-riparian areas, land use, and lotic water quality (which included first- and second-order natural streams, a canal, and a reach of a lowland river). Herb stands selected were free from anthropogenic disturbances such as farming and construction activities for a period of 3 years (this was the dominant and peak frequency of disturbances of the study area). The results suggested that herb indicators are good representatives of the land use. However, land use explanations for herb indicators were complex and not universal for all lotic waters. The correlations between herb indicators and water quality were strong for the low-order natural streams. In these streams, herb indicators explained >36 % of the total variation with several statistically significant herb indicators. However, the large river section showed weak correlations. Furthermore, the canal’s hydrology (connectivity to sea) seemed to be more influential in shaping its water quality. This study demonstrated that the rehabilitation works with a span of 3–4 years using herbs in riparian and/or non-riparian areas could significantly improve water quality of low-order streams with natural origin.

Effects of Biennial Fire and Clipping on Woody and Herbaceous Ground Layer Vegetation: Implications for Restoration and Management of Oak Barren Ecosystems

AbstractSavannas and oak barrens are threatened in North America, due, in part, to removal of natural disturbance regimes. However, the periodic prescribed fires used in savanna and oak barren management sometimes accelerate the formation of a shrub layer, which can displace herbaceous species. This may be because periodic low severity fires act much like clipping, topkilling shrubs, yet allowing them to accumulate reserves in intervals without fire for more vigorous sprouting. To test this, we compared biennial dormant season burn prescriptions to a fire surrogate (clipping) using three oak barrens sites in the Bluegrass Region of southern Ohio. Fire and clipping treatments did little to suppress the resprouting ability of shrubs (woody stems <2 cm dbh), which regrew rapidly and in equivalent densities following treatment. However, both treatments reduced shrub cover, resulting in a 35% decrease in shrub cover over the course of the study. In contrast, non‐manipulated plots experienced a 44% increase in shrub cover over the same time period. Despite this reduction in shrub cover, treatments had no effect on herbaceous plant cover, richness, diversity, or evenness. These results suggest that the use of biennial prescribed dormant season fire, as employed in this study, is equivalent to clipping, and although effective at temporarily reducing shrub cover, is not effective in reducing shrub densities or resprouting potential. Thus, burning during marginal conditions should be avoided for achieving a short‐term restoration goal of shrub removal, but can be effective for maintaining the current shrub layer.

Unpalatable weed Stellera chamaejasme L. provides biotic refuge for neighboring species and conserves plant diversity in overgrazing alpine meadows on the Tibetan Plateau in China

Steller chamaejasme L. (S. chamaejasme for short) is one of the most noxious unpalatable weeds in China, which has been frequently reported its negative interaction (i.e. competition and allelopathy) with other herbaceous species in grasslands. This study compared species diversity, biomass and sexual reproduction of herbaceous plants in meadows with S. chamaejasme and in open meadows without S. chamaejasme in overgrazing meadows on the Tibetan Plateau in China to determine whether positive facilitation exist between S. chamaejasme and other herbaceous species under livestock’s overgrazing. The results showed that there are more herbaceous species in meadows with S. chamaejasme than those in open meadows (35s and 30s, respectively). Diversity index and above-ground biomass were also significantly higher in meadows with S. chamaejasme. There were 39% (11/28) of all species with sexual reproduction found in meadows with S. chamaejasme, which was 7 times more than those in open meadows. Our study showed that S. chamaejasme could provide biotic refuge for neighboring plants and preserve plant diversity from livestock’s overgrazing in alpine meadows on the Tibetan Plateau. It also suggested that inter-specific facilitation between S. chamaejasme and other herbaceous species may play a key role in overgrazing alpine meadows.

Comparison of Trends in Habitat and Resource Selection by the Spanish Festoon,Zerynthia rumina, and the Whole Butterfly Community in a Semi-Arid Mediterranean Ecosystem

Butterfly community and single species based approaches were taken to establish conservation priorities within a nature reserve in Central Spain. In this study, patch type (sclerophyllous, halophilous, or disturbed), potential herbaceous nectar availability, potential woody plant nectar availability, total nectar availability, and two approximations to plant diversity (herbaceous and woody plant diversity) were evaluated as variables that account for adult butterfly density. Butterfly communities in the reserve, which consist mostly of generalist species, were denser in relatively wet areas dominated by halophilous vegetation. Diversity did not significantly vary between ecologically different transects. Total nectar availability correlated with higher butterfly densities within both undisturbed and disturbed areas, which could be primarily explained by the lack of water typical of semi-arid Mediterranean climates, where fresh, nectariferous vegetation is scarce. Woody plants were also found to be important sources of nectar and shelter. In the dryer sclerophyllous sites, adult butterfly density was best explained by herbaceous plant diversity, suggesting better quality of available resources. The endangered specialist Zerynthia rumina (L.) (Lepidoptera: Papilionidae) was only present at the sclerophyllous sites. Its density was very low in all sampled transects, excluding one relatively isolated transect with high larval host-plant density. In contrast to the community-based approach, density of Z. rumina adults is better explained by the density of its larval host-plant than by nectar availability, a trend previously described for other sedentary species. Management strategies for protecting insect-rich areas should consider the specific ecological requirements of endangered species.

The response of Mediterranean herbaceous community to soil disturbance by native wild boars

Native wild boar (Sus scrofa lybicus) populations in Israel increased in the last decades, and their rooting activity presents an apparent severe disturbance that may affect herbaceous plant communities. We studied the extent of wild boar rooting and its effect on herbaceous vegetation in an east Mediterranean garrigue. We compared the effects of rooting soil disturbance (RSD) between summer, winter, and RSD-free control plots on herbaceous plants. RSD affected four percent of the area covered by herbaceous vegetation in winter and spring, and only 2 % in summer. Summer RSD increased herbaceous species diversity in the following spring by decreasing the abundance of the dominant species, but it did not affect total herbaceous biomass. Winter RSD lowered herbaceous biomass but did not affect herbaceous plant abundance or diversity. We conclude that Mediterranean herbaceous plant community appears to be resilient to RSD, causing only minor changes in species composition and small decrease of their biomass. The contrast between the relatively large extent of wild boars RSD, and its limited impact on the herbaceous plant community, can be attributed to the long mutual evolutionary history of wild boars and these vegetation communities.

Loss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa

Large herbivore grazing is a widespread disturbance in mesic savanna grasslands which increases herbaceous plant community richness and diversity. However, humans are modifying the impacts of grazing on these ecosystems by removing grazers. A more general understanding of how grazer loss will impact these ecosystems is hampered by differences in the diversity of large herbivore assemblages among savanna grasslands, which can affect the way that grazing influences plant communities. To avoid this we used two unique enclosures each containing a single, functionally similar large herbivore species. Specifically, we studied a bison (Bos bison) enclosure at Konza Prairie Biological Station, USA and an African buffalo (Syncerus caffer) enclosure in Kruger National Park, South Africa. Within these enclosures we erected exclosures in annually burned and unburned sites to determine how grazer loss would impact herbaceous plant communities, while controlling for potential fire-grazing interactions. At both sites, removal of the only grazer decreased grass and forb richness, evenness and diversity, over time. However, in Kruger these changes only occurred with burning. At both sites, changes in plant communities were driven by increased dominance with herbivore exclusion. At Konza, this was caused by increased abundance of one grass species, Andropogon gerardii, while at Kruger, three grasses, Themeda triandra, Panicum coloratum, and Digitaria eriantha increased in abundance.

Comparison of trends in habitat and resource selection by the Spanish Festoon, Zerynthia rumina, and the whole butterfly community in a semiarid Mediterranean ecosystem.

Butterfly community and single species based approaches were taken to establish conservation priorities within a nature reserve in Central Spain. In this study, patch type (sclerophyllous, halophilous, or disturbed), potential herbaceous nectar availability, potential woody plant nectar availability, total nectar availability, and two approximations to plant diversity (herbaceous and woody plant diversity) were evaluated as variables that account for adult butterfly density. Butterfly communities in the reserve, which consist mostly of generalist species, were denser in relatively wet areas dominated by halophilous vegetation. Diversity did not significantly vary between ecologically different transects. Total nectar availability correlated with higher butterfly densities within both undisturbed and disturbed areas, which could be primarily explained by the lack of water typical of semiarid Mediterranean climates, where fresh, nectariferous vegetation is scarce. Woody plants were also found to be important sources of nectar and shelter. In the dryer sclerophyllous sites, adult butterfly density was best explained by herbaceous plant diversity, suggesting better quality of available resources. The endangered specialist Zerynthia rumina (L.) (Lepidoptera: Papilionidae) was only present at the sclerophyllous sites. Its density was very low in all sampled transects, excluding one relatively isolated transect with high larval hostplant density. In contrast to the community-based approach, density of Z. rumina adults is better explained by the density of its larval hostplant than by nectar availability, a trend previously described for other sedentary species. Management strategies for protecting insect-rich areas should consider the specific ecological requirements of endangered species.

Natural regeneration of the herbaceous community in a semiarid region in Northeastern Brazil

This study aimed to describe and compare the interannual changes in the diversity and population structure of herbaceous plants in an anthropogenic area that has been regenerating for 15years and to identify the similarities and differences in the biological attributes of the community compared with the characteristics of a regenerating conserved area. In total, 105 plots measuring 1m(2) were established. In each plot, the herbaceous plants were identified, and their height and stem diameter were measured for two consecutive years. The herbaceous flora of the anthropogenic area was represented by 86 species in 70 genera and 27 families, and there were no significant differences in the average richness between years. The conserved area was represented by 71 species in 63 genera and 35 families, and there was a significant difference in the total richness between areas and between years, except when comparing the richness between the conserved area and the anthropogenic area during the second year. Considering both the anthropogenic and conserved areas, 123 herbaceous species were listed, and the similarity between areas was 60%. For the anthropogenic area, the floristic similarity between years was 95%, and in the fragment of the conserved area, the similarity was 74%. The diversity and density were significantly different between years and between areas. Given these results, this study suggests that 15years of natural regeneration for the caatinga is not sufficient to reestablish its native flora with respect to its herbaceous component.

Herbaceous species diversity patterns across various treatments of herbivory and fire along the sodic zone of the Nkuhlu exclosures, Kruger National Park

Understanding relationships between large herbivores and plant species diversity in dynamic riparian zones is critical to biodiversity conservation. The Nkuhlu exclosures in the Kruger National Park (KNP) provided opportunity to investigate spatial heterogeneity patterns within riparian zones, as well as how these patterns are affected by fire and herbivory. A monitoring project was initiated to answer questions about the dynamics of the herbaceous layer and was aimed at determining, (1) whether there exists meaningful variance in herbaceous plant species richness and diversity across different treatments in the ecologically sensitive sodic zone and (2) whether an increase in herbaceous biomass, an artefact of herbivory and fire exclusion, suppresses herbaceous plant species diversity and richness. Herbaceous vegetation was sampled in two 1 m2 circular sub-plots in the eastern and western corners of 81 fixed plots. The biomass of each plot was estimated with a disc pasture meter (DPM) diagonally with the plot. DPM-readings were converted to kg/ha, according to the latest conversions for the Lowveld Savanna. Species richness and biomass showed significant variance across treatments, whereas no significant variation in herbaceous species diversity was perceived. Combined treatment of fire absence and herbivore presence contributed to higher forb species richness in the sodic zone. Biomass is significantly higher in fully fenced areas where herbivores are excluded, as opposed to the open and partially fenced areas. Although no significant variation was recorded for diversity across treatments, lowest diversity was recorded in the absence of all herbivores, especially in combination with fire treatment. Therefore herbivores are essential in sustaining herbaceous plant species richness in the sodic zone, whilst no significant results were found with regard to their effect on species diversity. Although statistically non-significant, fire seems to suppress species richness.Conservation implications: This study could be used as framework to advance and develop science-based management strategies for, at least, the sodic zones of the KNP. Research in these exclosures will create better understanding of these landscapes, benefit ecosystem conservation planning of national parks and also provide valuable long-term information on key ecological processes.

Herbaceous Plant Diversity and Identification of Indicator Species in Olive Groves in Central Greece

The present study is aimed at assessing the herbaceous plant diversity and determining the specific species related to different management systems in olive grove ecosystems [organic, conventional (unsprayed), and conventional (sprayed)] in two sites (Nies and Pteleos) of Magnesia Prefecture (central Greece). The sampling of herbaceous vegetation was carried out in randomly selected plots of 0.25 m2 (0.5 m × 0.5 m) each. The results showed that the organic system in Pteleos favored plant species richness and Shannon–Weiner, Simpson, Margalef, Brilluin, McIntosh, and Menhinick indexes more than the other management systems (P < 0.05). A Renyi diagram revealed the greatest plant diversity in the organic system in Pteleos site. According to cluster analysis results, the organic and the conventional (unsprayed) olive groves in Pteleos exhibited a strong similarity regarding plant diversity. The same was detected in the pairs: Nies conventional (unsprayed) and Nies organic, and in Nies conventional (sprayed) and Pteleos conventional (sprayed). IndVal analysis revealed three “characteristic” types of indices, Chenopodium album in the organic olive groves in Pteleos, Sinapis arvensis in the organic ones in Nies, and Aegilops geniculata in the conventional (unsprayed) olive groves in Nies.

Effects of Organic Farming on Winter Plant Composition, Cover and Diversity in Olive Grove Ecosystems in Central Greece

The present study aimed to assess the effects of organic farming in comparison with conventional on plant composition, plant cover (%), diversity [species richness, Shannon, Simpson, and evenness (Pielou's) indexes] and investigate and describe the relations among plant species richness, plant cover, indexes, and soil parameters (pH and temperature) in olive grove ecosystems during the winter. Organic olive groves had significantly greater values of cover, species richness, and Shannon and Simpson indexes than the conventional ones. Plant species richness was positively correlated to plant cover and Shannon and Simpson indexes but negatively correlated to evenness index for both farming system. Finally, plant cover was positively correlated to the Shannon and Simpson indexes for both farming systems. According to principal component analysis (PCA), for axis 1, positive correlation was detected among the plant species richness, soil temperature, and Shannon and Simpson diversity indexes, whereas for axis 2, negative correlation was detected between plant cover and soil pH. It can be concluded that the organic management system enhances herbaceous plant cover and diversity (species richness, Shannon and Simpson indexes) in olive grove ecosystems during the winter.

Response of herbaceous plant community diversity and composition to overstorey harvest within riparian management zones in Northern Hardwoods

Partial timber harvest within riparian management zones (RMZs) may permit active management of riparian forests while protecting stream ecosystems, but impacts on herbaceous communities are poorly understood. We compared herbaceous plant community abundance, diversity and composition in RMZs along small streams in northern Minnesota, USA, among four treatments before harvest and 1 year and 9 years following treatment. Treatments included a no-harvesting control and three different treatments of the RMZs where the adjacent upland forest was clearcut: (1) an RMZ control, with no harvesting in the RMZ; (2) RMZ TL, in which the RMZ was partially harvested (60 per cent removal of basal area) using tree-length harvesting and (3) RMZ cut-to-length (CTL), in which the RMZ was partially cut (also 60 per cent removal) using CTL harvesting. Herbaceous cover, richness, diversity and most synecological coordinate scores (reflecting tolerances for light, heat, moisture and nutrients) varied over time but not among riparian treatments, whereas composition varied over time and by treatment but not differentially among treatments over time. These results indicate a lack of herbaceous plant community response to partial timber harvesting within these RMZs, which is consistent with previous work suggesting that understorey communities may be resistant to change below thresholds of disturbance intensity.

Consequences of Treating Wyoming Big Sagebrush to Enhance Wildlife Habitats

Sagebrush (Artemisia L.) taxa historically functioned as the keystone species on 1 090 000 km2 of rangeland across the western United States, and Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young) is or was dominant on a substantial amount of this landscape. Wyoming big sagebrush provides habitat for numerous wildlife species. Nevertheless, Wyoming big sagebrush communities are commonly manipulated to decrease shrub cover and density and increase the productivity and diversity of herbaceous plants. We examined relationships between management-directed changes in Wyoming big sagebrush and greater sage-grouse (Centrocercus urophasianus), elk (Cervus elaphus), pronghorn (Antilocapra americana), and mule deer (Odocoileus hemionus), species commonly associated with these ecosystems. We focused on herbicide applications, mechanical treatments, and prescribed burning, because they are commonly applied to large areas in big sagebrush communities, often with the goal to improve wildlife habitats. Specifically, our objective was to identify treatments that either enhance or imperil sagebrush habitats for these wildlife species. The preponderance of literature indicates that habitat management programs that emphasize treating Wyoming big sagebrush are not supported with respect to positive responses by sage-grouse habitats or populations. There is less empirical information on ungulate habitat response to Wyoming big sagebrush treatments, but the value of sagebrush as cover and food to these species is clearly documented. A few studies suggest small-scale treatments (≤ 60-m width) in mountain big sagebrush (Artemisia tridentata ssp. vaseyana &lsqb;Rydb.] Beetle) may create attractive foraging conditions for brooding sage-grouse, but these may have little relevance to Wyoming big sagebrush. Recommendations or management programs that emphasize treatments to reduce Wyoming big sagebrush could lead to declines of wildlife species. More research is needed to evaluate the response of sagebrush wildlife habitats and populations to treatments, and until that time, managers should refrain from applying them in Wyoming big sagebrush communities. Sagebrush (Artemisia L.) históricamente ha funcionado como un especie clave en 1 090 000 km2 de pastizales a través del oeste de los Estados Unidos y Wyoming big sagebrush (A. tridentata Nutt. ssp. wyomingensis Beetle and Young) es o fue dominante en una gran área de este paisaje. En Wyoming big sagebrush provee hábitat para una gran cantidad de especies de fauna silvestre. Sin embargo, en Wyoming las comunidades de big sagebrush son comúnmente manipuladas para disminuir su cobertura y densidad para incrementar la productividad y diversidad de plantas herbáceas. Se examinó la relación entre los cambios debidos al manejo dirigido en Wyoming big sagebrush y las especies de sage-grouse (Centrocercus urophasianus), elk (Cervus elaphus), berrendo (Antilocapra americana) y venado mula (Odocoileus hemionus), comúnmente asociadas con estos ecosistemas. Nos enfocamos en la aplicación de herbicidas, tratamientos mecánicos, y fuego prescrito, ya que ellos son se aplican comúnmente en áreas extensas de comunidades de big sagebrush, frecuentemente con la meta de mejorar el hábitat para fauna silvestre. Específicamente, nuestro objetivo fue identificar los tratamientos que mejoran o ponen en riesgo los hábitats de sagebrush para estas especies silvestres. La preferencia de la literatura indica que los programas de manejo de hábitat que enfatizan el tratamiento de big sagebrush en Wyoming no están apoyados con respecto a las respuestas positivas por los hábitats o poblaciones de sage-grouse. Existe información menos empírica acerca de la respuesta del hábitat de ungulados a los tratamientos de Wyoming big sagebrush, pero el valor de sagebrush como fuente de cobertura y alimentación para estas especies está claramente documentada. Pocos estudios sugieren tratamientos a pequeña escala (≤ 60 m ancho) en mountain big sagebrush (A. t. ssp. vaseyana &lsqb;Rydb.] Beetle) podrían crear condiciones atractivas forrajeras para el anidamiento de sage-grouse, pero éstas podrían tener poca relevancia para Wyoming big sagebrush. Recomendaciones o programas de manejo que enfoquen sus tratamientos en la reducción de Wyoming big sagebrush podrían conducir a la reducción de especies silvestres. Más investigación es necesaria para evaluar en mejor manera la respuesta de los hábitats de sagebrush para fauna silvestre y sus poblaciones a estos tratamientos y hasta entonces, manejadores deben abstenerse de aplicarlas en las comunidades de big sagebrush en Wyoming.

Complex facilitation and competition in a temperate grassland: loss of plant diversity and elevated CO2 have divergent and opposite effects on oak establishment

Encroachment of woody vegetation into grasslands is a widespread phenomenon that alters plant community composition and ecosystem function. Woody encroachment is often the result of fire suppression, but it may also be related to changes in resource availability associated with global environmental change. We tested the relative strength of three important global change factors (CO(2) enrichment, nitrogen deposition, and loss of herbaceous plant diversity) on the first 3 years of bur oak (Quercus macrocarpa) seedling performance in a field experiment in central Minnesota, USA. We found that loss of plant diversity decreased initial oak survival but increased overall oak growth. Conversely, elevated CO(2) increased initial oak seedling survival and reduced overall growth, especially at low levels of diversity. Nitrogen deposition surprisingly had no net effect on survival or growth. The magnitude of these effects indicates that long-term woody encroachment trends may be most strongly associated with those few individuals that survive, but grow much larger in lower diversity patches. Further, while the CO(2) results and the species richness results appear to describe opposing trends, this is due only to the fact that the natural drivers are moving in opposite directions (decreasing species richness and increasing CO(2)). Interestingly, the mechanisms that underlie both patterns are very similar, increased CO(2) and increased species richness both increase herbaceous biomass which (1) increases belowground competition for resources and (2) increases facilitation of early plant survival under a more diverse plant canopy; in other words, both competition and facilitation help determine community composition in these grasslands.

Two decades of low-severity prescribed fire increases soil nutrient availability in a Midwestern, USA oak (Quercus) forest

For the last 23years, low-severity prescribed fire has been used to decrease shade and fire tolerant tree species, increase oak (Quercus spp.), and increase herbaceous plant diversity in the East Woods of The Morton Arboretum, Lisle, Illinois, USA. The impacts of these fires on the belowground ecosystem have yet to be measured. Soil (0 to 10cm) and litter samples were collected 12, 19, and 24months following the most recent fire on 40 plots in burned and un-burned control areas. Soil physical, chemical, and biological properties were measured and compared with vegetation composition and structure from these same plots. Compared to un-burned controls, burn plots had greater canopy openness, greater herbaceous richness, and a lower spring/summer herbaceous ratio. Burned plots had higher soil moisture content, pH, electrical conductivity, Ca2+, Mg2+, K+, Na+, NO3−, total N, particulate organic matter (POM), total organic C, and potential N mineralization. Soil microbial biomass and respiration, texture, color, aggregate stability, and hydrophobicity were not different in burned compared to un-burned plots. Indices of litter and soil invertebrate diversity were also not affected by prescribed fire. Three stepwise least squares models predicted woody richness, herbaceous richness, and spring/summer herbs with aspect, litter invertebrate richness, and soil factors (pH, potential N mineralization, C/N ratio, Mg2+, Bray P, and soil invertebrate Simpson index). These results confirm others showing prescribed fire to increase soil nutrient availability. Forest structural changes with fire appear correlated with soil nutrient availability. Decreased soil C, nutrient retention, invertebrate diversity, or increased hydrophobicity and the presence of exotic plants is often observed with high-severity fire; but, these negative impacts do not appear to be present with these long-term, low-severity fires.

Experimental tree removal in tallgrass prairie: variable responses of flora and fauna along a woody cover gradient

Woody plant encroachment is a worldwide phenomenon in grassland and savanna systems whose consequence is often the development of an alternate woodland state. Theoretically, an alternate state may be associated with changes in system state variables (e.g., species composition) or abiotic parameter shifts (e.g., nutrient availability). When state-variable changes are cumulative, such as in woody plant encroachment, the probability of parameter shifts increases as system feedbacks intensify over time. Using a Before-After Control-Impact (BACI) design, we studied eight pairs of grassland sites undergoing various levels of eastern redcedar (Juniperus virginiana) encroachment to determine whether responses of flora and fauna to experimental redcedar removal differed according to the level of pretreatment redcedar cover. In the first year after removal, herbaceous plant species diversity and evenness, woody plant evenness, and invertebrate family richness increased linearly with pretreatment redcedar cover, whereas increases in small-mammal diversity and evenness were described by logarithmic trends. In contrast, increases in woody plant diversity and total biomass of terrestrial invertebrates were accentuated at levels of higher pretreatment cover. Tree removal also shifted small-mammal species composition toward a more grassland-associated assemblage. During the second year postremoval, increases in herbaceous plant diversity followed a polynomial trend, but increases in most other metrics did not vary along the pretreatment cover gradient. These changes were accompanied by extremely high growing-season precipitation, which may have homogenized floral and faunal responses to removal. Our results demonstrate that tree removal increases important community metrics among grassland flora and fauna within two years, with some responses to removal being strongly influenced by the stage of initial encroachment and modulated by climatic variability. Our results underscore the importance of decisive management for reversing the effects of woody plant encroachment in imperiled grassland ecosystems.