Landscape and organismal factors affecting sagebrush‐seedling transplant survival after megafire restoration

Larger and more frequent disturbances are motivating efforts to accelerate recovery of foundational perennial species by focusing efforts into establishing island patches to sustain keystone species and facilitate recovery of the surrounding plant community. Evaluating the variability in abiotic and biotic factors that contribute to differences in survival and establishment can provide useful insight into the relative importance of these factors. In the western United States, severe degradation of the sagebrush steppe has motivated substantial efforts to restore native perennial cover, but success has been mixed. In this study, we evaluated survival of more than 3,000 sagebrush seedlings transplanted on 12 patches totaling 650 ha within a 113,000 ha burn area, and related the survival to organismal and subtaxonomic traits, and to landscape variables. Big sagebrush has high intraspecific diversity attributed to subspecies and cytotypes identifiable through ultraviolet (UV)‐induced fluorescence, length:width of leaves, or genome size (ploidy). Of these organismal traits, survival was related only to UV fluorescence, and then only so when landscape variables were excluded from analyses. The most significant landscape variable affecting survival was soil taxonomic subgroup, with much lower survival where buried restrictive layers reduce deep water infiltration. Survival also decreased with greater slope steepness, exotic annual grass cover, and burn severity. Survival was optimal where perennial bunchgrasses comprised 8–14% of total cover. These soil, topographic, and community condition factors revealed through monitoring of landscape‐level treatments can be used to explain the success of plantings and to strategically plan future restoration projects.     

Reintroduction of Nassella pulchra to California coastal grasslands: Effects of topsoil removal,plant neighbour removal and grazing

Question: What is the most appropriate combination of treatments to reintroduce Nassella pulchra, a perennial bunchgrass, into degraded mediterranean coastal grasslands? Location: Central coast of California, USA. Methods: N. pulchra was sown from seeds and transplanted into a degraded grassland in a multi‐factorial experiment testing the effects of (1) two grazing intensities (lightly grazed by native mammal species or ungrazed); (2) topsoil removal and (3) reduction of plant neighbours. The experiment was carried out on two types of surrounding vegetation (exotic annual grasses and exotic forbs). Results: Topsoil removal greatly enhanced establishment from seeds and transplant survival, mainly because it reduced the exotic vegetation and thus reduced competition. While removing neighbours was essential when topsoil was left intact, it had a negative effect on N. pulchra when surrounding species included exotic forbs (Brassica spec, and Asteraceae) at low density (after topsoil removal). Moderate grazing by native mammals (deer, rabbits and gophers) did not affect N. pulchra. Conclusion: Our results suggest that seeding after topsoil has been removed is a promising method to reintroduce N. pulchra to highly degraded sites where there is little to no native seed bank.     

The influence of shade and clouds on soil water potential: The buffered behavior of hydraulic lift

In the sagebrush/bunchgrass steppe of the North American Great Basin soil water potential has been shown to exhibit diel fluctuations with water potential increasing during the night as a result of water loss from roots in relatively dry soil layers. We hypothesized that environmental conditions promoting low transpiration rates (shading, cloudiness) would cause a net increase in soil water potential as a result of reduced soil water depletion during the day and continuing water efflux from roots during the night. We examined the response of soil water potential to artificial shading in sagebrush/bunchgrass plantings and used a simple model to predict how soil water potential should respond to reduced transpiration. Field measurements of soil water potential indicated that shading reduced daytime soil water depletion, but that the magnitude of the soil water potential increase during the night was related to the magnitude of the soil water potential decline during the preceding day. As a result, shading had little net effect on soil water potential. This behavior was consistent with model results and appears to result from the fact that soil water depletion during the day is largely responsible for creating the water potential gradients that drive nocturnal recharge of the shallow soil layers. The overall effect of such behavior is to buffer the seasonal course of soil water depletion in the rooting zone against day-to-day fluctuations in evapotranspiration. Despite the buffered behavior of soil water potential change, reduced evapotranspiration during light summer rains, and resulting soil water redistribution in the rooting zone, may enhance plant water status to a greater extent that would be expected on the basis of the rainfall received.     

Burning and Grazing Management in a California Grassland: Growth, Mortality, and Recruitment of Nassella pulchra

Abstract Annual grasslands in California are often managed with seasonal grazing and prescribed burning on the assumption that such practices have long‐term benefits for native species. Mature native perennial bunchgrasses, particularly Nassella pulchra (purple needlegrass), are often the focal species, although very little is known about responses at different life history stages. Thus, important questions remain about long‐term population dynamics of both mature plants and seedling recruitment. In plots receiving repeated grazing and burning events over 7 years, mortality of mature plants was threefold higher on mounds than on intermounds and likely reflected increased competition intensity associated with increased resource availability in deeper soil. Burning and grazing treatments had strong positive effects on basal area of mature N. pulchra. However, plants in grazed plots that were not burned contained considerable standing dead biomass. Topographic location strongly influenced growth as intermound plants grew relatively more than mound plants, but the effects on growth of burning and grazing did not vary with topographic location. In mapped plots N. pulchra recruitment was very low, and overall density dropped an average of 31%. However, a significant time‐by‐burning effect indicated that survival was significantly higher in burned plots. After 7 years of repeated treatments, effects of burning and grazing management on mature N. pulchra were positive but not for all phenological stages. Understanding long‐term influence of management on bunchgrass populations may not be easy to determine because short‐term results may not reflect long‐term responses and some life cycle dynamics may be observed only over very long periods.     

Pocket Gophers and the Invasion and Restoration of Native Bunchgrass Communities

More than 7 million hectares of California native plant communities are now dominated by exotic annual species, a biological invasion that has made native bunchgrass ecosystems in this region one of the most endangered ecosystems in North America. Many land use and environmental factors have contributed to the conversion of bunchgrass areas to annual grassland, but the role of gopher disturbance remains understudied. Here I report observational evidence that suggests gopher foraging is nonrandomly concentrated in the open spaces between clumps of bunchgrass and as a result may inhibit the recruitment of bunchgrass into these areas. Understanding patterns of direct gopher impact and coincident soil disturbance in bunchgrass versus annual grassland is important for successful restoration of bunchgrass habitats. While the prospect of excluding gophers is daunting, even short-term reductions in gopher populations would help to promote a restored community structure with a mature native bunchgrass and annual forb association.     

内蒙古草原3种针茅属植物不同组织水平的生物量生殖分配

植物资源的生殖分配是链接进化生态学和功能生态学的纽带。该文从4个组织水平上研究了针茅属(Stipa) 3种植物克氏针茅(S. krylovii)、大针茅(S. grandis)和贝加尔针茅(S. baicalensis)的生物量生殖分配以及株丛和种群水平上可育散布体的数量和生物量。结果表明: 1) 3种针茅属植物在不同组织水平上的生物量生殖分配呈现明显分异。在株丛水平上, 克氏针茅和大针茅的株丛生物量分配到生殖枝的比例分别为44.3%和47.9%, 均显著高于贝加尔针茅的35.7%。在生殖枝水平, 克氏针茅的生殖枝生物量分配到穗器官的比例为30.3%, 显著低于大针茅的42.9%和贝加尔针茅的48.4%。在穗器官水平, 大针茅穗生物量分配到散布体的比例(63.9%)最高, 克氏针茅(49.9%)次之, 贝加尔针茅(39.1%)最低。在散布体水平, 贝加尔针茅的可育散布体生物量占散布体总生物量的比例为92.3%, 显著高于克氏针茅的67.2%和大针茅的71.3%。2) 尽管3种针茅属植物在不同组织水平上的生物量生殖分配存在显著差异, 但从最终可育散布体占株丛生物量的比例看, 克氏针茅为6.1%, 贝加尔针茅为6.3%, 大针茅为9.5%; 三者在生物量生殖分配上表现出明显的趋同效应。3) 3种针茅属植物生物量生殖分配的限制性环节存在显著差异。生殖枝向穗的生物量分配是克氏针茅和大针茅生殖分配的限制性环节, 株丛向生殖枝的生物量分配或穗器官向散布体的分配是贝加尔针茅生物量生殖分配的限制性环节。从可育散布体的数量和个体生物量看, 克氏针茅采取了倾向于拓展空间的增加散布体数量的策略, 而大针茅和贝加尔针茅逐步进化出了趋向于提高个体竞争能力的增加散布体个体生物量的策略。     

Structural Attributes of Schizachyrium scoparium in Restored Texas Blackland Prairies

Structural attributes of the C₄, perennial bunchgrass Schizachyrium scoparium in restored prairies may be affected by the time since restoration. One hundred plants each in 8‐, 17‐, and 23‐year‐old restored prairies and a native Texas Blackland prairie were assessed for the presence/absence and diameter of a hollow crown (i.e., dead center portion), degree of fragmentation, plant height, and tiller density. Structural attributes of S. scoparium plants were generally (1) different between recent (8 years) and older (17 and 23 years) restored prairies (2) similar between the 17‐ and 23‐year‐old restored prairies, and (3) more similar between the 8‐ and 17‐year restored prairies and the native, remnant prairie than between the 23‐year restored prairie and the native prairie. Plants were shorter in restored prairies, regardless of time since restoration, than in the native prairie. Mean basal area of plants was 80–163% greater in the 17‐ and 23‐year restored prairies compared with the native and 8‐year restored prairies. Percentage of hollow crowns and fragmentation was smallest in the 8‐year restored prairie, largest in the 17‐ and 23‐year restored prairies, and intermediate in the native prairie. Tiller density exhibited inverse second‐order polynomial decreases with increasing plant basal area for all prairies. In contrast to tiller density, diameter of hollow crowns increased logarithmically with increasing plant basal area. Structural attributes of S. scoparium in restored prairies changed predictably with age, despite growing in different communities.     

Arid grassland bee communities: associated environmental variables and responses to restoration

In recent years restoration project efforts in arid grasslands of the Pacific Northwest have increased; however, little is known about the bee communities in these areas or how restoration affects them. Native bees provide an essential ecosystem service through pollination of crops and native plants and understanding their response to restoration is a high priority. To address this issue, we conducted a three‐year study in an arid bunchgrass prairie with three objectives: (1) describe the bee community of this unique grassland type and its temporal variability; (2) investigate environmental variables influencing the community; and (3) examine effects of restoration on the community. We identified 62 bee species and found strong seasonal and inter‐annual variation in bee abundance, richness, diversity, and species composition. Unexpectedly, these temporal trends did not correspond with patterns in floral resources; however, several variables were associated with variation in bee abundance, richness, and diversity among sites. Sites with high levels of litter cover had more bees, while sites with taller vegetation or more blooming flowers had greater species richness but lower diversity. We found no detectable effect of restoration on bee abundance, richness, diversity, or composition. Species composition at native sites differed from those in actively and passively restored sites, which did not differ from each other. Restored sites also had fewer flowers and differing floral composition relative to native sites. These results suggest that if grassland restoration is to benefit bees, efforts should focus on both expanding floral resources and enhancing variables that influence nesting habitat.     

Fire Effects on Cover and Dietary Resources of Sage-Grouse Habitat

Abstract: We evaluated 6 years of vegetation response following prescribed fire in Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis) steppe on vegetation cover, productivity, and nutritional quality of forbs preferred by greater sage-grouse (Centrocercus urophasianus), and abundance of common arthropod orders. Habitat cover (shrubs and tall herbaceous cover [>18 cm ht]) was about 50% lower after burning compared to unburned controls because of the loss of sagebrush. Perennial grasses and an invasive annual forb, pale alyssum (Alyssum alyssoides), increased in cover or yield after fire. There were no increases in yield or nutritional quality of forb species important in diets of sage-grouse. Abundance of ants (Hymenoptera), a significant component in the diet of young sage-grouse, decreased after fire. These results suggest that prescribed fire will not improve habitat characteristics for sage-grouse in Wyoming big sagebrush steppe where the community consists of shrubs, native grasses, and native forbs.