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

Censusing seedlingsHow will climate change influence the distribution of species? To answer this question, we need to know what controls range limits. Climate is thought to determine where species can survive given their physiological tolerances, with biotic interactions such as competition acting to further 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 trees on Mt. Rainier, Washington. Because Mt. Rainier covers large climatic gradients, it is an ideal natural laboratory for studying altitudinal range limits. For each focal species, we are 1) determining the relative importance of climate and competition for tree performance across their altitudinal ranges using observational monitoring and common garden experiments; 2) exploring the possibility of historical legacies by determining how observed altitudinal distributions compare to areas predicted to be climatically suitable from population growth modls; and 3) combining forecasts of climate change with dispersal and demographic data to estimate rates of range expansion and contraction.
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 are also planning 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. 

Wildflower phenology
How will the timing of wildflower phenology at Mt. Rainier National Park change in response to the warmer temperatures and lower snowpack forecast for the Pacific Northwest? Presumably, as snow melts earlier in the season, the timing of the peak wildflower season will come earlier, with implications for the functioning of these systems (e.g. through impacts on plant-pollinator dynamics) as well as the management of these diverse wildflower meadows. In collaboration with
Jessica Lundquist, Regina Rochefort, Elli J. Theobald, Anna Wilson, and Lou Whiteaker, we are developing tools to forecast the timing of snowmelt and wildflower phenology, using satellite images and on-the-ground observations of microclimate and wildflower phenology. Observations are in part collected through a phenology citizen science project at Mt. Rainier called 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 exExperimental gardens of Serpentine annuals at Sedgwick Reserve, Californiatinction dynamics in finite stochastic communities in the presence and absence of niche differences. Although many 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 is  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 (the general ecological MO), Nutnet comprises a series of small, identical experiments run by a multi-collaborator network in a large number of sites.  There are currently over 30 sites (most in the US, some in Europe, Africa and Australia) and 50 people involved - see the  NutNet project website for more details.  Treatments include nutrient additions (N,P,K) and herbivore exclosures, with 10 treatments and 30 plots per site.  The large number of replicate sites participating offers the unique possibility of generalizing these results to multiple regions.  The project is a brainchild of Peter Adler (Utah State University), Elizabeth Borer (University of Minnesota), Stan Harpole (Iowa State University), John Orrock (University of Wisconsin), Eric Seabloom (University of Minnesota), and Melinda Smith (Colorado State University).

Camas blooming close to the site on Whidby IslandJanneke Hille Ris Lambers and Jon Bakker (College of Forest Resources, University of Washington) are Washington regional PI's for the nutnet site at Smith Prairie, with Susan Waters, Karen Reagan (Tewksbury lab), Rachel Mitchell (Bakker Lab) and Ryan Haugo (Bakker lab) as participating graduate students. Besides the broader Nutnet goals, 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 inf
luenced 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 Rogers and Josh Tewksbury on the Ecology of Bird Loss Project in Guam and the Mariana Islands. See the following website for more details on this project.

back to top

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