@article {KNZ001800, title = {Temporal variability in large grazer space use in an experimental landscape}, journal = {Ecosphere}, volume = {8}, year = {2017}, abstract = {Land use, climate change, and their interaction each have great potential to affect grazing systems. With anticipated more frequent and extensive future drought, a more complete understanding of the mechanisms that determine large grazer landscape-level distribution under varying climatic conditions is integral to ecosystem management. Using an experimental setting with contrasting fire treatments, we describe the inter-annual variability of the effect of landscape topography and disturbance from prescribed spring fire on large grazer space use in years of variable resource availability. Using GPS telemetry, we investigated space use of plains bison (Bison bison bison) as they moved among watersheds managed with variable experimental burn treatments (1-, 2-, 4-, and 20-year burn intervals) during a seven-year period spanning years of average-to-above average forage production and severe drought. At the landscape scale, bison more strongly favored high-elevation and recently burned watersheds with watersheds burned for the first time in 2 or 4 yr consistently showing higher use relative to annually burned watersheds. In particular, watersheds burned for the first time in 4 yr were avoided to lesser extent than other more frequently burned watersheds during the dormant season. This management type also maintained coupling between bison space use and post-fire regrowth across post-drought growing season months, whereas watersheds with more frequent fire-return intervals attracted bison in only the first month post-fire. Hence, fire frequency played a role in maintaining the coupling of grazer and post-fire regrowth, the fire{\textendash}grazer interaction, in response to drought-induced reduction in fuel loads. Moreover, bison avoided upland habitat in poor forage production years, when forage regrowth is less likely to occur in upland than in lowland habitats. Such quantified responses of bison to landscape features can aid future conservation management efforts and planning to sustain fire{\textendash}grazer interactions and resulting spatial heterogeneity in grassland ecosystems.}, keywords = {LTER-KNZ}, doi = {10.1002/ecs2.1674}, url = {https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecs2.1674}, author = {Raynor, E.J. and Anthony Joern and Skibbe, A.M. and Sowers, M. and J. M. Briggs and Laws, A.N. and Goodin, D.G.} } @article {KNZ001537, title = {Blazing and grazing: influences of fire and bison on tallgrass prairie stream water quality}, journal = {Freshwater Science}, volume = {32}, year = {2013}, pages = {779 -791}, abstract = {

Fire and grazers (such as Bison bison) were historically among the most important agents for maintaining and managing tallgrass prairie, but we know little about their influences on water-quality dynamics in streams. We analyzed 2 y of data on total suspended solids (TSS), total N (TN), and total P (TP) (3 samples per week per stream during flow) in 3 prairie streams with fire and bison grazing treatments at Konza Prairie Biological Station, Kansas (USA), to assess whether fire and bison increase the concentrations of these water-quality variables. We quantified the spatial and temporal locations of bison (\∼0.21 animal units/ha) with Global Positioning System collars and documented bison trails, paw patches, wallows, and naturally exposed sediment patches within riparian buffers. Three weeks post-fire, TN and TP decreased (t-test, p \< 0.001), but TSS did not change. Bison spent \<6\% of their time within 10 m of the streams, increased the amount of exposed sediment in the riparian areas, and avoided wooded mainstem branches of stream (χ2 test, p \< 0.001). Temporal trends suggest that low discharge or increased bison density in the stream may increase TSS and TP during the summer months. Our results indicate a weak connection between TSS and nutrients with bison access to streams over our 2-y study and indicate that low TSS and nutrients characterize tallgrass prairie streams with fire and moderate bison densities relative to surrounding land uses.

}, keywords = {LTER-KNZ, Bison bison, Bos bison, burning, Grasslands, grazers, prescribed fire, streams, tallgrass prairie, total nitrogen, total phosphorus, total suspended solids}, doi = {10.1899/12-118.1}, url = {https://www.journals.uchicago.edu/doi/10.1899/12-118.1}, author = {Larson, D.M. and Grudzinski, B.P. and W. K. Dodds and Daniels, M.D. and Skibbe, A.M. and Anthony Joern} } @article {KNZ001606, title = {Evidence of physiological decoupling from grassland ecosystem drivers by an encroaching woody shrub}, journal = {PLoS ONE}, volume = {8}, year = {2013}, pages = {81630 -}, abstract = {

Shrub encroachment of grasslands is a transformative ecological process by which native woody species increase in cover and frequency and replace the herbaceous community. Mechanisms of encroachment are typically assessed using temporal data or experimental manipulations, with few large spatial assessments of shrub physiology. In a mesic grassland in North America, we measured inter- and intra-annual variability in leaf δ13C in Cornus drummondii across a grassland landscape with varying fire frequency, presence of large grazers and topographic variability. This assessment of changes in individual shrub physiology is the largest spatial and temporal assessment recorded to date. Despite a doubling of annual rainfall (in 2008 versus 2011), leaf δ13C was statistically similar among and within years from 2008-11 (range of \−28 to \−27\‰). A topography*grazing interaction was present, with higher leaf δ13C in locations that typically have more bare soil and higher sensible heat in the growing season (upland topographic positions and grazed grasslands). Leaf δ13C from slopes varied among grazing contrasts, with upland and slope leaf δ13C more similar in ungrazed locations, while slopes and lowlands were more similar in grazed locations. In 2011, canopy greenness (normalized difference vegetation index \– NDVI) was assessed at the centroid of individual shrubs using high-resolution hyperspectral imagery. Canopy greenness was highest mid-summer, likely reflecting temporal periods when C assimilation rates were highest. Similar to patterns seen in leaf δ13C, NDVI was highest in locations that typically experience lowest sensible heat (lowlands and ungrazed). The ability of Cornus drummondii to decouple leaf physiological responses from climate variability and fire frequency is a likely contributor to the increase in cover and frequency of this shrub species in mesic grassland and may be generalizable to other grasslands undergoing woody encroachment.

}, keywords = {LTER-KNZ, Ecosystems, Grasslands, Grazing, Leaves, Plant physiology, Seasons, Shrubs, Water resources}, doi = {10.1371/journal.pone.0081630}, url = {https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0081630}, author = {Jesse B. Nippert and Ocheltree, T.W. and Orozco, G.L. and Z. Ratajczak and Ling, B. and Skibbe, A.M.} } @article {KNZ001488, title = {Global diversity of drought tolerance and grassland climate-change resilience}, journal = {Nature Climate Change}, volume = {3}, year = {2013}, pages = {63 -67}, abstract = {

Drought reduces plant productivity, induces widespread plant mortality and limits the geographic distribution of plant species1, 2, 3, 4, 5, 6, 7. As climates warm and precipitation patterns shift in the future8, 9, understanding the distribution of the diversity of plant drought tolerance is central to predicting future ecosystem function and resilience to climate change10, 11, 12. These questions are especially pressing for the world\’s 11,000 grass species13, which dominate a large fraction of the terrestrial biosphere14, yet are poorly characterized with respect to responses to drought. Here, we show that physiological drought tolerance, which varied tenfold among 426 grass species, is well distributed both climatically and phylogenetically, suggesting most native grasslands are likely to contain a high diversity of drought tolerance. Consequently, local species may help maintain ecosystem functioning in response to changing drought regimes without requiring long-distance migrations of grass species. Furthermore, physiologically drought-tolerant species had higher rates of water and carbon dioxide exchange than intolerant species, indicating that severe droughts may generate legacies for ecosystem functioning. In all, our findings suggest that diverse grasslands throughout the globe have the potential to be resilient to drought in the face of climate change through the local expansion of drought-tolerant species.

}, keywords = {LTER-KNZ, Climate-change ecology, Drought, Grassland ecology}, doi = {10.1038/nclimate1634}, url = {https://www.nature.com/articles/nclimate1634}, author = {Craine, J.M. and Ocheltree, T.W. and Jesse B. Nippert and Towne, E.G. and Skibbe, A.M. and Kembel, S.W. and Fargione, J.E.} } @article {KNZ001536, title = {Linking abundances of the dung fungus Sporormiella to the density of bison: implications for assessing grazing by megaherbivores in paleorecords}, journal = {Journal of Ecology}, volume = {101}, year = {2013}, pages = {1125 -1136}, abstract = {

Megaherbivores likely had important influences on past vegetation dynamics, just as they do in modern ecosystems. The exact nature of megaherbivores\&$\#$39; role can be studied using a relatively new suite of palaeoecological techniques, including the quantification of fossil spores from Sporormiella and other coprophilous fungi as indicators of megafaunal biomass in sediment records. However, a quantitative linkage of spore abundance with megaherbivore biomass or grazing intensity has been lacking. Konza Prairie Biological Station (Kansas, USA), located in the midcontinent of North America, contains native tallgrass prairie grazed by a herd of bison (Bison bison) in a 1000-ha enclosure, providing an excellent opportunity to test the effects of megaherbivores on grassland community composition and their potential signature in the palynological record. We collected pollen and spores during 2009 and 2010 from a network of 28 modified Tauber traps. The precise locations of the bison herd were recorded using GPS collars; we calculated bison grazing intensity (kg m\−2 year\−1) to high spatial precision within concentric circles around each trap (radii from 25 to 500 m). Both relative (per cent) and absolute (concentration) abundances of Sporormiella were significantly higher in traps inside the enclosure and were positively correlated with bison grazing intensity. The cut-off for distinguishing between bison-grazed and ungrazed traps was determined to be 2.8\% Sporormiella of the total pollen and spore sum, consistent with previous palaeoecological reconstructions. The relationship between Sporormiella abundances and available grazing area around each trap was strongest at short radii (25\–100 m), suggesting that spores do not disperse far from their source. Sporormiella should thus be considered a local-scale indicator of megaherbivore presence. Traps in the grazed area had significantly higher percentages of Ambrosia and lower percentages of Poaceae pollen than traps from ungrazed areas. This suggests that the pollen record has the potential to detect the ecological effects of bison grazing on grassland community composition. Synthesis. This study refines the use of Sporormiella as a proxy for local megaherbivore presence, especially in grassland systems. Multiproxy Sporormiella and pollen analyses may help elucidate the past drivers of grassland dynamics, including the possible role of bison in mediating grass\–forb interactions during the variable moisture regimes of the last 12,000 years.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2745.12130}, url = {https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.12130}, author = {Gill, J.L. and McLauchlan, K.K. and Skibbe, A.M. and Goring, S. and Zirbel, C.R. and Williams, J.W.} } @article {KNZ001464, title = {The timing of climate variability and grassland productivity}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, year = {2012}, pages = {3401 -3405}, abstract = {

Changes in precipitation amount and variability have the potential to alter the structure and function of grasslands, but we know little about how changes in the timing of precipitation might affect grasslands. Here, we analyze long-term records from a tallgrass prairie to show that shifts in the timing of precipitation during the growing season have little effect on primary productivity or grass reproduction, but can greatly affect grazer performance. While greater late-season precipitation increases the weight gain of adult and young bison, greater mid-season precipitation decreases their weight gain. In addition, calving rates are lower after years with greater mid-season precipitation and higher after years with greater late-season precipitation. As well-timed drought can actually increase grazer weight gain and reproduction, it will be necessary to generate predictions of within-season distribution of precipitation to successfully forecast future grazer performance.

}, keywords = {LTER-KNZ}, doi = {10.1111/j.1600-0706.2012.20400.x}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1600-0706.2012.20400.x}, author = {Craine, J.M. and Jesse B. Nippert and Elmore, A.J. and Skibbe, A.M. and Hutchinson, S.L. and N. Brunsell} } @article {KNZ001367, title = {Functional consequences of climate-change induced plant species loss in a tallgrass prairie}, journal = {Oecologia}, volume = {165}, year = {2011}, pages = {1109 -1117}, abstract = {

Future climate change is likely to reduce the floristic diversity of grasslands. Yet the potential consequences of climate-induced plant species losses for the functioning of these ecosystems are poorly understood. We investigated how climate change might alter the functional composition of grasslands for Konza Prairie, a diverse tallgrass prairie in central North America. With species-specific climate envelopes, we show that a reduction in mean annual precipitation would preferentially remove species that are more abundant in the more productive lowland positions at Konza. As such, decreases in precipitation could reduce productivity not only by reducing water availability but by also removing species that inhabit the most productive areas and respond the most to climate variability. In support of this prediction, data on species abundance at Konza over 16 years show that species that are more abundant in lowlands than uplands are preferentially reduced in years with low precipitation. Climate change is likely to also preferentially remove species from particular functional groups and clades. For example, warming is forecast to preferentially remove perennials over annuals as well as Cyperaceae species. Despite these predictions, climate change is unlikely to unilaterally alter the functional composition of the tallgrass prairie flora, as many functional traits such as physiological drought tolerance and maximum photosynthetic rates showed little relationship with climate envelope parameters. In all, although climatic drying would indirectly alter grassland productivity through species loss patterns, the insurance afforded by biodiversity to ecosystem function is likely to be sustained in the face of climate change.

}, keywords = {LTER-KNZ, biogeography, Climate change, Functional traits, Grasslands, Konza Prairie}, doi = {10.1007/s00442-011-1938-8}, url = {https://link.springer.com/article/10.1007\%2Fs00442-011-1938-8}, author = {Craine, J.M. and Jesse B. Nippert and Towne, E.G. and Tucker, S. and Kembel, S.W. and Skibbe, A.M. and McLauchlan, K.K.} } @article {KNZ001387, title = {Linking plant growth responses across topographic gradients in tallgrass prairie}, journal = {Oecologia}, volume = {166}, year = {2011}, pages = {1131 -1142}, abstract = {

Aboveground biomass in grasslands varies according to landscape gradients in resource availability and seasonal patterns of growth. Using a transect spanning a topographic gradient in annually burned ungrazed tallgrass prairie, we measured changes in the height of four abundant C4 grass species, LAI, biomass, and cumulative carbon flux using two closely located eddy flux towers. We hypothesized that seasonal patterns of plant growth would be similar across the gradient, but the magnitude of growth and biomass accumulation would vary by topographic position, reflecting spatial differences in microclimate, slope, elevation, and soil depth. Thus, identifying and measuring local growth responses according to topographic variability should significantly improve landscape predictions of aboveground biomass. For most of the growth variables measured, classifying topography into four positions best captured the inherent spatial variability. Biomass produced, seasonal LAI and species height increased from the upland and break positions to the slope and lowland. Similarly, cumulative carbon flux in 2008 was greater in lowland versus upland tower locations (difference of 64 g m\−2 by DOY 272). Differences in growth by topographic position reflected increased production of flowering culms by Andropogon gerardii and Sorghastrum nutans in lowland. Varying growth responses by these species may be a significant driver of biomass and carbon flux differences by topographic position, at least for wet years. Using a digital elevation model to classify the watershed into topographic positions, we performed a geographically weighted regression to predict landscape biomass. The minimum and maximum predictions of aboveground biomass for this watershed had a large range (86\–393 t per 40.4 ha), illustrating the drastic spatial variability in growth within this annually-burned grassland.

}, keywords = {LTER-KNZ, ANPP, Eddy covariance, Flux footprint, LAI, Mesic grassland, topography}, doi = {10.1007/s00442-011-1948-6}, url = {https://link.springer.com/article/10.1007\%2Fs00442-011-1948-6}, author = {Jesse B. Nippert and Ocheltree, T.W. and Skibbe, A.M. and Kangas, L.C. and J.M. Ham and Shonkwiler-Arnold, K.B. and N. Brunsell} }