Kansas State University
Kansas State University
Interactive effects of drought + fire in encroached grassland communities
Konza Prairie Biological Station; Northeastern KS, USA
The goal of this project is to assess the impacts of combined drivers (drought + fire) on the growth and survival of encroaching woody shrubs in a temperate grassland. Passive rainout shelters (50% rainfall exclusion) were built over intact Cornus drummondii shrub islands in the field in 2017 on neighboring watersheds with different burn frequencies (1-yr vs. 4-yr fire return interval). Leaf-level physiology, growth and biomass production, and depth of water uptake has been tracked for C. drummondii and Andropogon gerardii (dominant C4 grass) since 2019.
PIs and collaborators for this project include Jesse Nippert (KSU), Kevin Wilcox (UNGC), Kate McCulloh (University of Wisconsin-Madison), Lydia Zeglin (KSU), and Kimberly O'Keefe (St. Edwards University).
Impacts of changing climate and land-cover on grassland ecohydrology
Konza Prairie Biological Station; Northeastern KS, USA
Related Publications:
Keen, R.M., Nippert, J.B., Sullivan, P.L., Ratajczak, Z., Ritchey, B., O’Keefe,
K. and Dodds, W.K., 2022. Impacts of Riparian and Non-riparian
Woody Encroachment on Tallgrass Prairie Ecohydrology. Ecosystems,
pp.1-12.
Dodds, W.K., Ratajczak, R., Keen, R.M., Nippert, J.B., Grudzinski, B., Veach,
A., Taylor, J., and Kuhl, A., 2023. Trajectories and state changes of a
grassland stream and riparian zone after a decade of woody
vegetation removal. Ecological Applications, e2830.
This research focuses on the impacts of land-cover change (specifically woody encroachment in temperate grasslands) on key water fluxes over time. Vegetation forms a pipeline for water movement from the atmosphere to the subsurface, and vice-versa. Large-scale changes in vegetation composition, particularly when a shift in dominant functional type (i.e., grasses to woody shrubs) occurs, can have substantial impacts on how water cycles through the system. Differences in water-use strategies, root system architecture, and functional rooting depth between functional types result in unique impacts on evapotranspiration, infiltration of water through the soil, and canopy/litter interception of precipitation. These projects largely focus on the contribution of woody encroachment to observed declines in water yield in a mesic grassland in northeastern Kansas.
PIs and collaborators for these projects include Pam Sullivan (OSU), Jesse Nippert (KSU), Li Li (Penn State), Matt Kirk (KSU), and Walter Dodds (KSU).
Belowground impacts of grassland-to-plantation conversion on the Great Escarpment
Mariepskop; South Africa
In this project, we assess the belowground impacts of roughly a century of pine (Pinus patula) and eucalypt (Eucalyptus grandis) plantation cover at Mariepskop (1,947 m) -- one of the highest peaks in the Northern Drakensbergs on the Great Escarpment in South Africa. Historically, this region was dominated by montane grassland and native forest or savanna cover, but grassland areas have almost entirely been converted to plantations or lost to native forest expansion over the last century. We are assessing changes in soil texture, chemistry, and stable carbon isotopes by soil depth to determine how pine and eucalypt cover has altered belowground dynamics through time.
Collaborators for this project include Tony Swemmer (SAEON, Ndlovu Node), and Jesse Nippert (Kansas State University).
Woody root systems in the prairie: Impacts of woody encroachment on carbon storage, biogeochemical cycling, and water fluxes
Konza Prairie Biological Station; Northeastern KS, USA
Woody encroachment results in drastic and obvious changes aboveground, but the changes belowground are often overlooked. The root systems of woody shrubs and trees are typically larger, deeper, and coarser than herbaceous rooting systems. Grasses, in particular, have root systems primarily composed of fine roots in shallow surface soil layers (top 20-30 cm), where they extract the vast majority of their water and nutrients. As woody shrubs and trees spread into historically grassy areas, the shift in depth, diameter, and density of roots impacts carbon storage, biogeochemical cycling, and water fluxes through the soil. We are interested in understanding how the proliferation of woody root systems in grasslands impacts ecosystem-scale cycling of carbon, water, and nutrients.
PIs and collaborators for this project include Jesse Nippert (KSU), Pam Sullivan (OSU), Lydia Zeglin (KSU), and Kimberly O'Keefe (St. Edwards University), Greg Tooley (CSU), and Seton Bachle (LiCOR)
Related Publications:
O'Keefe, K., Bachle, S., Keen, R.M., Tooley, E.G. and Nippert, J.B., 2022. Root traits reveal safety and efficiency differences in grasses and shrubs exposed to different fire regimes. Functional Ecology, 36(2), pp.368-379.
Early warning signals for drought-related mortality in the Sierra Nevada Mountains
Soaproot Saddle SSCZO; Central CA, USA
This project took place in the southern Sierra Nevada Mountains in central California, and centers around the 2012-2015 drought event. This severe, multi-year drought was punctuated by an epidemic-scale outbreak of western pine beetle (Dendroctonus brevicomis), and resulted in widespread mortality of ponderosa pines (Pinus ponderosa), among other dominant canopy tree species. In these studies, we assessed severity of drought stress in surviving trees vs. trees killed by bark beetles during the drought, and found that mortality during this drought event was preceded by decades of increasing sensitivity of tree growth and carbon isotope discrimination (∆13C) to Palmer Drought Severity Index (PDSI) and other hydroclimate variables. We propose that these shifts in sensitivity can serve as early warning signals for future drought-related mortality events in forests of the western United States.
PIs and collaborators for these projects include Steve Voelker (MTU), Barbara Bentz (USDA), and Simon Wang (USU).
Related Publications:
Keen, R.M., Voelker, S.L., Wang, S.Y.S., Bentz, B.J., Goulden, M.L., Dangerfield, C.R., Reed,
C.C., Hood, S.M., Csank, A.Z., Dawson, T.E. and Merschel, A.G., 2022. Changes in
tree drought sensitivity provided early warning signals to the California drought and
forest mortality event. Global Change Biology, 28(3), pp.1119-1132.
Keen, R.M., Voelker, S.L., Bentz, B.J., Wang, S.Y.S. and Ferrell, R., 2020. Stronger influence
of growth rate than severity of drought stress on mortality of large ponderosa pines
during the 2012–2015 California drought. Oecologia, 194(3), pp.359-370.