The effects of climate change on plant communities at Mt. Rainier

How will climate change influence the distribution of species? To answer this question, we need to know what controls range limits, and how those controls differ by species. Climate is thought to determine where species can survive given their physiological tolerances, with biotic interactions such as competition acting to fCensusing seedlingsurther restrict those distributions. Despite the long acceptance of these ideas by ecologists, we still lack a complete understanding of the forces that constrain species’ distributions. First, few studies have quantified how both climate and competitive interactions affect species performance across ranges – key for assessing the relative importance of fundamental vs. realized niches. Second, most range limit studies ignore the possibility of historical legacies – when the distributions of long-lived and/or locally-dispersing species reflect past rather than current conditions. Finally, we generally lack the data and analytical approaches to estimate how rapidly species distributions will respond to changing conditions.  Addressing these shortcomings is essential, given rapid rates of climate change that have already resulted in the upwards or polewards movement of many species, with continued range shifts expected.

To explore these questions, we are combining observational monitoring, common garden experiments and statistical modeling to assess the controls over current and future altitudinal range limits of tree species on Mt. Rainier, Washington. Because Mt. Rainier covers large climatic gradients, it is an ideal natural laboratory for studying climate change and altitudinal range limits. Using field observations, experiments and statistical modeling, we are 1) determining what climatic factors limit performance at range limits, and how these vary among species; 2) assessing the relative importance of climate relative to other factors (e.g. competitive interactions, edaphic conditions); building population growth models (IPM's) to assess the net effects of climate change on population dynamics; and 4) revisiting legacy vegetation plots (censused in the late 70's) to determine how and whether overstory and understory plant communities have changed with recent warming. Ongoing data collection includes monitoring of tree growth, survival, seed production (4-30 years data), seed dispersal and microclimate (temperature, snow depth, soil moisture, date of meltout - 4 years data) in 18 stands located across Mt. Rainier National Park. These 18 stands are part of a large scale network of permanent vegetation plots located across the Pacific Northwest (established by Jerry Franklin and colleagues). We have also conducted several common garden experiments - planting seeds and seedlings at and beyond range limits to assess climatic controls on seedling recruitment. In addition to ongoing monitoring and experiments, we make use of extensive spatial data on the distribution of focal conifers (collected by the National Park Service in the early eighties and early nineties) and spatial climate models, allowing us to ask whether species current distributions on Mt. Rainier can be predicted by relationships between climate and population growth (from demographic measurements). Coniferous forests in the Pacific Northwest are among the most productive ecosystems in the continental U.S, provide valuable ecosystem services (water supply, timber, carbon sequestration), and are the home to many endangered species (e.g. the Northern Spotted Owl). Thus, understanding how climate change will affect this biome is critical. 

What controls the wildflower phenology in high mountain meadows?
The timing of key life events like reproduction (i.e. phenology) is tightly linked to climate. For example, alpine wildflowers emerge and flower within a few weeks of snow disappearance, and complete their life-cycles before the frost in early autumn. Because annual variability in snow disappearance is large, the timing of seasonal wildflower displays also varies annually, influencing visitation and staffing needs within parks. Additionally, as climate change causes earlier snow disappearance, wildflowers that cannot shift their phenology to match this altered “climate window” may decline. Thus, resource managers and conservation biologists need the ability to seasonally forecast snow disappearance and wildflower phenology as well as monitor their long-term annual trends to better conserve and manage high mountain wildflower meadows.

In collaboration with Mt. Rainier National Park, Jessica Lundquist and Regina Rochefort, wwildflower bloominge are building decision making tools to support natural resource and recreation management and inventory and monitoring. These tools will enable provide resource managers and visitors to Mt. Rainier National Park with 1) live-updating seasonal forecasts of snow disappearance and peak wildflower displays; 2) long-range forecasts of changes in these processes with climate change; and 3) automated tools for summarizing and archiving annual spatio-temporal estimates of snow disappearance date and peak wildflower phenology (the former from NASA satellite images, the latter from citizen science efforts).  Please see our preliminary forecasting tool (Beta version). Observations used to validate and build phenological forecasts are in part collected through the phenology citizen science project MeadoWatch, which was launched in summer of 2013.

Funding: NSF (Career), NICCR (Department of Energy), NASA, University of Washington Royalty Research Fund

Niches and neutrality in diverse serpentine annual communities

Are niches critical for the biodiversity of California's wildflowers?
It’s safe to say that Steve Hubbell shook up the ecological world when he introduced community ecologists to the idea that diverse communities need not necessarily result from species that are niche differentiated, but may simply occur because speciation balances extinction over long time scales. Traditionally, community ecologists had focused their research on niches, those which lead to more negative intra-specific interactions than inter-specific interactions (e.g. resource niches, density-dependent natural enemies, storage effects). Such interactions provide species with an advantage when rare, thus buffering them from extinction when they are rare. Niche differences are critical for maintaining diversity when competitive differences among species are large (otherwise rapid competitive exclusion would occur). Given that highly diverse communities are the norm, ecological debate today centers on whether diversity results from strong niche differences overcoming large differences among species in competitive ability, or whether species are roughly equivalent in their competitive ability, requiring little (or no, in the special case of the neutral model) niche differences for diversity maintenance.

I am collaborating with Jonathan Levine to experimentally determine the importance of niches for the coexistence of California serpentine annuals. We are quantifying the relationship between frequency and per-capita growth rates for ten serpentine annual plants in experimental gardens. This is key, because frequency-dependent negative population growth is the signature of all stabilizing niche processes. We are also calculating population growth rates in the absence of stabilization to predict the magnitude of competitive ability differences in the absence of niches. Finally, we are manipulating seed production to remove negative frequency dependence and compare diversity and extinction dynamics in finite stochastic communities in the presence and absence of niche differences. Although maExperimental Plant Communitiesny theoretical and empirical studies demonstrate that particular diversity-promoting mechanisms operate in natural communities, few studies attempt to determine the importance of niches for maintaining diversity, and none (that we are aware of) have attempted an experimental approach. Results thus far indicate that without frequency-dependent processes (i.e. niches), diversity plummets and a single species would dominate our experiment within 20 years.

Funding: NSF

Nutnet: top-down and bottom-up controls over herbaceous productivity and diversity

What controls the biodiversity and productivity of rare Washington Prairie habitats?  NutNet (i.e. the Nutrient Network) is a large-scale, grassroots collaborative research effort initiated in 2006 by Peter Adler, Elizabeth Borer, Dan Gruner, Stan Harpole, John Orrock, Eric Seabloom and Melinda Smith. Nutnet is designed to quantify how resource limitation vs. herbivory limits plant productivity and diversity in herbaceous dominated communities. This is of ecological relevance for the following reasons; i) the generality of multiple resource limitation in plant communities is unknown and debated; as is ii) the relative importance of top-down (i.e. herbivory) vs. bottom-up (i.e. soil resources) controls on plant productivity and diversity.  Instead of performing a large experiment at one field site, Nutnet comprises a series of small, identical experiments run by a multi-collaborator network in a large number of sites.  There are currently over 60 sites (scattered across North and South America, Europe, Africa, Asia and Australia) and many more PIs involved.  Treatments include nutrient additions (N,P,K) and herbivore exclosures, with 10 treatments and 30 plots per site.  The large number of replicate sitesCamas blooming at Smith Prairie participating offers the unique possibility of generalizing these results to multiple regions.

I work with Jon Bakker (College of Forest Resources, University of Washington) on a regional NutNet site at Smith Prairie. Besides the broader Nutnet goals of understanding the relative importance of top down vs. bottom up constraints on productivity and effects on diversity, these sites will also offer valuable regional insights. Many of western Washington’s prairies have been converted to agriculture or are close to urban centers. Both these landuse changes generally come with increased inputs of soil nutrients (particularly nitrogen and phosphorus). Herbivores are probably much more abundant now than they were historically in western Washington, due to the extirpation of their major predators (wolves, bears, lynxes). Western Washington grasslands are also being exposed to novel kinds and levels of herbivory, with the introduction of nonnative herbivores like rabbits and Canada Geese. Finally, exotic plant species represent one of the biggest threats to native diversity within these systems. Thus, understanding how plant diversity and the success of exotic plant species, like Canada thistle and Tansy ragwort, are influenced by nutrient addition and herbivore exclosures might aid conservation and restoration efforts in these rare Washington habitats.

The Implications of bird loss for forest community dynamics

I collaborate with Haldre RogersJosh Tewksbury, Ross Miller, and Amy Dunham on the Ecology of Bird Loss Project in Guam and the Mariana Islands. We are taking advantage of a conservation tragedy on Guam - the virtual elimination of the native avifauna due to the introduction of the Brown Tree Snake - to examine the effects birds have on forest dynamics. Please see the project website for the most up-to-date news and progress. 

Funding: NSF, USDA

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Biology Department
University of Washington
Seattle WA, 98195-1800
jhrl@uw.edu, 206-543-7389