Aim Tree-line conifers are believed to be limited by temperature worldwide, and thus may serve as important indicators of climate change. The purpose of this study was to examine the potential shifts in spatial distribution of three tree-line conifer species in the Greater Yellowstone Ecosystem under three future climatechange scenarios and to assess their potential sensitivity to changes in both temperature and precipitation.Location This study was performed using data from 275 sites within the boundaries of Yellowstone and Grand Teton national parks, primarily located in Wyoming, USA.Methods We used data on tree-line conifer presence from the US Forest Service Forest Inventory and Analysis Program. Climatic and edaphic variables were derived from spatially interpolated maps and approximated for each of the sites. We used the random-forest prediction method to build a model of predicted current and future distributions of each of the species under various climatechange scenarios. ResultsWe had good success in predicting the distribution of tree-line conifer species currently and under future climate scenarios. Temperature and temperature-related variables appeared to be most influential in the distribution of whitebark pine (Pinus albicaulis), whereas precipitation and soil variables dominated the models for subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii). The model for whitebark pine substantially overpredicted absences (as compared with the other models), which is probably a result of the importance of biological factors in the distribution of this species.Main conclusions These models demonstrate the complex response of conifer distributions to changing climate scenarios. Whitebark pine is considered a 'keystone' species in the subalpine forests of western North America; however, it is believed to be nearly extinct throughout a substantial portion of its range owing to the combined effects of an introduced pathogen, outbreaks of the native mountain pine beetle (Dendroctonus ponderosae), and changing fire regimes. Given predicted changes in climate, it is reasonable to predict an overall decrease in pinedominated subalpine forests in the Greater Yellowstone Ecosystem. In order to manage these forests effectively with respect to future climate, it may be important to focus attention on monitoring dry mid-and high-elevation forests as harbingers of long-term change.

Summary 1We explored the role of the seed bank in population dynamics of the summer annual Helianthus annuus . First, we determined seed survival under field conditions. Secondly, we conducted an experiment in which a dispersal treatment (plants allowed/not allowed to disperse seeds) was crossed with a soil disturbance treatment that was predicted to increase seed bank recruitment. Our goal was to evaluate the relative importance of the previous year's seed production vs. the remainder of the seed bank to numbers of plants. 2 Yearly seed survival was variable, ranging from 46 to 83% when seeds were buried in mesh packets and from 12 to 76% for seeds placed on the soil surface. Survival was higher for plots established in 1999 than in 2000. Survival was often higher in later years but was unaffected by the presence of litter.3 By comparing seedling establishment between dispersal treatments, we inferred that approximately 10-23% of the seedlings were from the seed bank, independent of soil disturbance. 4 Although seed dispersal the previous year led to increased numbers of seedlings by at least 4.5 times, the number of adults only increased 2.5 times and head production only increased 1.5 times because of density-dependent processes. 5 Patches of seedlings emerging only from the seed bank (often at low densities) may have a disproportionate contribution to the next generation. Average head production/ seedling was 3.6 for such seedlings vs. 0.8 for seedlings from both the previous year's seed set and the seed bank. Emergence of seeds from the seed bank in high-density seedling areas may, however, have little effect on patch reproduction as reproductive output was asymptotically related to the number of seedlings initially present. Studies of seed survival and seedling biology should therefore be done with consideration of the entire life cycle.

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Greater sage-grouse (Centrocercus urophasianus) are threatened by loss of sagebrush habitat and the spread of West Nile virus throughout much of their range in North America; yet, future impacts of climate change on these potential stressors have not been addressed. Here, we aim to quantify the potential impacts of climate change on the distribution of climatically suitable habitat for sagebrush and on transmission risk for West Nile virus in the eastern portion of the species' range. We used Maxent to model the current and future climatically suitable habitat for two dominant sagebrush species in the study area, and we used a degree-day model to predict future West Nile virus transmission risk under likely climatechange scenarios. Our models suggest that areas with the highest future suitability for sagebrush habitat will be found in southwestern Wyoming and north-central Montana. The degree-day model suggests that greater sage-grouse in western portions of the study area, which are generally higher in elevation than where West Nile virus currently occurs, will see increasing risk of transmission in the future. We developed a spatially explicit map of suggested management actions based on our predictions that will aid in conservation of the species into the coming decades.

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