02410nas a2200205   4500008004100000245012000041210006900161300001500230490000700245520171400252653002401966653002701990653001802017653001802035653002502053653001802078100001802096700002402114856006602138       2013                        eng d00aSmall-scale patch structure in North American and South African grasslands responds differently to grazing and fire0 aSmallscale patch structure in North American and South African g  a1293 -13060 v283 a<p>Fire and grazing significantly impact small-scale patch structure and dynamics in savanna grasslands. We assessed small-scale grass-forb associations in long-term fire and grazing experiments in North America (NA) and Southern Africa (SA). Transects of 128 0.25 m2 contiguous quadrats were sampled in areas with different combinations of grazing (ungrazed, single grazer, or multiple grazers) and fire frequency (unburned or annually burned). We predicted that (1) the patch structure of each of the dominant grasses in NA and SA would respond similarly to fire and grazing, and (2) that forb richness would be correlated to grass patch structure. Semi-variance analysis was used to determine patch structure of dominant grasses and forb cover. Community structure responded similarly in NA and SA to fire, grazing, and fire-grazing interactions. Species richness, diversity, and community heterogeneity were significantly higher in unburned-grazed sites. Grazing significantly increased forb cover and decreased cover of the dominant grasses, and the effects of fire on community structure depended on the grazing regime. Contrary to our prediction, we found that small-scale patch structure of the dominant grass species in NA and SA responded differently to grazing and fire. We found strong grass patch structure in unburned-ungrazed grasslands in both sites; however, grazing and fire reduced patch structure in NA but not SA, and in no instance did grass patch structure influence forb community structure. We conclude that fire and grazing have larger impacts on small-scale patch structure in NA than they do in SA even though overall community structure responded similarly on both continents.</p>10aDominance-diversity10aGrass-forb interaction10aheterogeneity10aKonza Prairie10aKruger National Park10aSemi-variance1 aKoerner, S.E.1 aCollins, Scott., L.  uhttps://link.springer.com/article/10.1007%2Fs10980-013-9866-002573nas a2200205   4500008004100000245010900041210006900150300001300219490000800232520185800240653001702098653001202115653001802127653002102145653002202166100001502188700002002203700002002223856012402243       2003                        eng d00aA comparative assessment of potential mechanisms influencing plant species richness in grazed grasslands0 acomparative assessment of potential mechanisms influencing plant  a385 -3910 v1373 aGrazing by large ungulates often increases plant species richness in grasslands of moderate to high productivity. In a mesic North American grassland with and without the presence of bison (Bos bison), a native ungulate grazer, three non-exclusive hypotheses for increased plant species richness in grazed grasslands were evaluated: (1) bison grazing enhances levels of resource (light and N) availability, enabling species that depend on higher resource availability to co-occur; (2) spatial heterogeneity in resource availability is enhanced by bison, enabling coexistence of a greater number of plant species; (3) increased species turnover (i.e. increased species colonization and establishment) in grazed grassland is associated with enhanced plant species richness. We measured availability and spatial heterogeneity in light, water and N, and calculated species turnover from long-term data in grazed and ungrazed sites in a North American tallgrass prairie. Both regression and path analyses were performed to evaluate the potential of the three hypothesized mechanisms to explain observed patterns of plant species richness under field conditions. Experimental grazing by bison increased plant species richness by 25% over an 8-year period. Neither heterogeneity nor absolute levels of soil water or available N were related to patterns of species richness in grazed and ungrazed sites. However, high spatial heterogeneity in light and higher rates of species turnover were both strongly related to increases in plant species richness in grazed areas. This suggests that creation of a mosaic of patches with high and low biomass (the primary determinant of light availability in mesic grasslands) and promotion of a dynamic species pool are the most important mechanisms by which grazers affect species richness in high productivity grasslands.10acolonization10aGrazing10aheterogeneity10aSpecies richness10atallgrass prairie1 aBakker, C.1 aBlair, John, M.1 aKnapp, Alan, K.  uhttp://lter.konza.ksu.edu/content/comparative-assessment-potential-mechanisms-influencing-plant-species-richness-grazed01822nas a2200241   4500008004100000245010000041210006900141300001100210490000700221520104700228653002001275653000901295653001801304653001401322653001001336100001701346700002401363700001501387700001901402700001501421700001801436856012601454       2003                        eng d00aDisturbance dynamics and ecological response: the contribution of long-term ecological research0 aDisturbance dynamics and ecological response the contribution of  a46 -560 v533 aLong-term ecological research is particularly valuable for understanding disturbance dynamics over long time periods and placing those dynamics in a regional context. We highlighted three case studies from Long Term Ecological Research (LTER) Network sites that have contributed to understanding the causes and consequences of disturbance in ecological systems. The LTER Network significantly enhances the ability to study disturbance by (a) encompassing ecosystems subject to a wide range of disturbances, (b) providing a long-term baseline against which to detect change and measure ecosystem responses to disturbance, (c) permitting observation of slow or infrequent events, (d) facilitating the use of multiple research approaches, (e) providing a focus for modeling disturbance dynamics, and (f) contributing to land and resource management. Long-term research is crucial to understanding past, present, and future disturbance dynamics, and the LTER Network is poised to make continuing contributions to the understanding of disturbance.10abiotic invasion10afire10aheterogeneity10ahurricane10ascale1 aTurner, M.G.1 aCollins, Scott., L.1 aLugo, A.L.1 aMagnuson, J.J.1 aRupp, T.S.1 aSwanson, F.J.  uhttp://lter.konza.ksu.edu/content/disturbance-dynamics-and-ecological-response-contribution-long-term-ecological-research01497nas a2200217   4500008004100000245013400041210006900175260003600244300001100280520071700291653001401008653001201022653001801034653001601052100001801068700001601086700001501102700002201117700001801139856012201157       1978                        eng d00aThe use of beta attenuation to measure productivity, foliage height diversity and vegetational heterogeneity in tallgrass prairie0 ause of beta attenuation to measure productivity foliage height d  aAmes, IAbIowa State University  a74 -773 a<p>The attenuation of beta radiation by prairie standing crop was measured in quadrats which were also harvested. Attentuation and harvest measurements were made at weekly intervals and at five sites differing in soil type and/or burning treatment. Attenuation measurements were made within each quadrat accross both the vertical and horizontal dimensions. Living and dead biomass were separated at harvest for dry weight determinations. Attenuation measurements are excellent predictors of standing crop. The vertical profile of measurements may be used to determine foliage height diversity. Patterns of temporal and spatial heterogeneity in vegetation are also shown by this particular set of measurements</p>10adiversity10afoliage10aheterogeneity10ameasurement1 aJohnson, M.P.1 aOksanen, L.1 aFinney, C.1 aGlenn-Lewin, D.C.1 aLanders, R.Q.  uhttp://lter.konza.ksu.edu/content/use-beta-attenuation-measure-productivity-foliage-height-diversity-and-vegetational