The purpose of our study is to re-measure the continued recovery of the subalpine forest at two study areas following the 1988 Yellowstone fires: 1) Henderson Mountain in Gallatin-Custer National Forest, MT; and 2) Mt. Washburn in Yellowstone National Park, WY. The fires were the largest burn event in recorded history of the national park and consumed >600,000 hectares within the Greater Yellowstone Ecosystem. Specifically, we will determine: 1) the density and health of whitebark pine regeneration as well as regenerating conifer composition; 2) the life table demographics for regenerating whitebark pine and associated conifers; 3) the understory plant community (here defined as woody and herbaceous vegetation) composition and the changes in understory community development over time; 4) genetic diversity of recovering whitebark pine populations as compared to mature, unburned stands; and 5) the status of the soil microbial community and soil nutrient composition in burned and unburned treatments. We will also survey unburned stands in the nearest whitebark pine communities to examine the percent whitebark pine trees killed by mountain pine beetle and infected by white pine blister rust. Collectively, the conifer, understory, microbial, and chemistry data will be used to construct a predictive, multivariate model to understand upper subalpine community recovery and regeneration over time.
METHODS
1. Whitebark pine and conifer regeneration. We will track the fate of each whitebark pine stem that germinated in 2001 or earlier; measure and characterize current microsites for survivors; map, age, and measure all whitebark pine that germinated subsequent to 2001, including cotyledon seedlings, and describe their microsites. Other conifer regeneration will be identified to species, height measured, age approximated (from our own data), and condition noted (good, fair, poor), including cotyledon seedlings. 2. Understory composition. Remeasurement of the understory plant community involves determining cover by counting stems and listing species on four 1 m2 subplots, and keying out new/unknown species. Leaf Area Index (LAI) for each plot will be determined with a Go-Pro/selfie stick overhead photograph.
3. New unburned plots. We will set up 25 new plots in unburned forest contiguous with the moist, burned treatment on Mt. Washburn and measure conifer, understory, and microbial communities in these plots.
4. Microclimate data. We will deploy 20 Onset Computer Micro-climate weather stations from July through early September, stratified by aspect among treatments, including the unburned plots. We will measure PAR, air temperature, soil temperature, and soil moisture to determine differences within and among treatments.
5. Rapidly assess whitebark pine within 1 km of perimeter of study sites. Using random points, we will examine the unburned whitebark pine seed source nearest our plots for incidence of white pine blister rust and mortality of trees from MPB.
6. Sample soil nutrients and characterize microbial communities. Soil cores from plots will be taken to 10cm from a randomly selected subset of plots in the burned and unburned treatments. Soil dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and dissolved inorganic nitrogen (nitrate, nitrite, and ammonium) will be measured at the University of Colorado Denver Analytical Laboratory. Microbial DNA will be extracted from soil samples and sequenced using an Illumina MiSeq instrument housed in the University of Colorado Denver Genomics Core Facility or sent to an outside lab. Microbial sequences will be analyzed to determine community structure, phylogeny, and functional potential.
7. Demographic tables for whitebark pine and other conifers. The age class distributions will be constructed for whitebark pine and the other conifers. Our 1990-1995 measurements and tracking of individual whitebark pine will enable us to determine establishment and mortality rates earlier in the study for comparison with current rates.
8. Other analyses. Whitebark pine survival vs. micro-site type, understory community composition as of 2017 with successional trajectories, life tables for each conifer species and successional trajectories; and multivariate model using GLMM (R package) examining the influences of conifer, understory, soil nutrients, and microbial communities on whitebark pine regeneration.