• Semiarid rangeland is resilient to summer fire and postfire grazing utilization

      Vermeire, L. T.; Crowder, J. L.; Wester, D. B. (Society for Range Management, 2014-01)
      Most wildfires occur during summer in the northern hemisphere, the area burned annually is increasing, and fire effects during this season are least understood. Understanding plant response to grazing following summer fire is required to reduce ecological and financial risks associated with wildfire. Forty 0.75-ha plots were assigned to summer fire then 0, 17, 34 or 50% biomass removal by grazing the following growing season, or no fire and no grazing. Root, litter, and aboveground biomass were measured before fire, immediately after grazing, and 1 yr after grazing with the experiment repeated during 2 yr to evaluate weather effects. Fire years were followed by the second driest and fifth wettest springs in 70 yr. Biomass was more responsive to weather than fire and grazing, with a 452% increase from a dry to wet year and 31% reduction from a wet to average spring. Fire reduced litter 53% and had no first-year effect on productivity for any biomass component. Grazing after fire reduced postgrazing grass biomass along the prescribed utilization gradient. Fire and grazing had no effect on total aboveground productivity the year after grazing compared to nonburned, nongrazed sites (1 327 vs. 1 249 ± 65 kg · ha-1). Fire and grazing increased grass productivity 16%, particularly for Pascopyrum smithii. The combined disturbances reduced forbs (51%), annual grasses (49%), and litter (46%). Results indicate grazing with up to 50% biomass removal the first growing season after summer fire was not detrimental to productivity of semiarid rangeland plant communities. Livestock exclusion the year after summer fire did not increase productivity or shift species composition compared to grazed sites. Reduction of previous years' standing dead material was the only indication that fire may temporarily reduce forage availability. The consistent responses among dry, wet, and near-average years suggest plant response is species-specific rather than climatically controlled. © 2014 The Society for Range Management.
    • Short-and long-term influence of brush canopy cover on northern bobwhite demography in southern Texas

      Demaso, S. J.; Hernández, F.; Brennan, L. A.; Silvy, N. J.; Grant, W. E.; Ben, Wu, X.; Bryant, F. C. (Society for Range Management, 2014-01)
      Extensive research has been devoted to quantifying the habitat needs and selection of many wildlife species. However, how habitat selection affects the long-term demographic performance of a species largely has been ignored. We used northern bobwhite (Colinus virginianus) and brush canopy coverage-an important habitat component for quail-to evaluate the influence of habitat on short-and long-term demographic performance of this species. We used data from a 5-yr (2001-2005) radiotelemetry study of northern bobwhite in southern Texas to obtain estimates of bobwhite density, survival, and production on three study areas with 5%, 11%, and 32% brush canopy cover. Our objectives were to compare these demographic variables individually among brush canopy cover classes and then simulate their cumulative effect on demographic performance using a simulation model. All demographic parameters were similar among the three brush canopy cover classes. However, simulation modeling indicated that long-term demographic performance was greater on the 11% and 32% brush canopy cover classes. Simulated bobwhite populations were 2-3 times higher in these two cover classes than the 5% brush canopy cover class. In addition, the probability of population persistence was greater in the 11% (0.91) and 32% (1.00) brush canopy cover classes than the 5% cover class (0.54) using a quasi-extinction criterion of ≤ 40 birds (≤ 0.05 birds · ha-1). Our study highlights the shortcoming of considering only short-term effects when comparing habitat given that short-and long-term effects of habitat on demographic performance can differ. © 2014 The Society for Range Management.
    • Spatial and temporal variability in aboveground net primary production of uruguayan grasslands

      Guido, A.; Varela, R. D.; Baldassini, P.; Paruelo, J. (Society for Range Management, 2014-01)
      Aboveground net primary production (ANPP) is a variable that integrates many aspects of ecosystem functioning. Variability in ANPP is a key control for carbon input and accumulation in grasslands systems. In this study, we analyzed the spatial and temporal variability of ANPP of Uruguayan grasslands during 2000-2010. We used enhanced vegetation index (EVI) data provided by the MODIS-Terra sensor to estimate ANPP according to Monteith's (1972) model as the product of total incident photosynthetically active radiation, the fraction of the radiation absorbed by green vegetation, and the radiation use efficiency. Results showed that ANPP varied spatially among geomorphological units, increasing from the north and midwest of Uruguay to the east and southeast. Hence, Cuesta Basáltica grasslands were the least productive (399 g DM · m-2 · yr-1), while grasslands of the Sierras del Este and Colinas y Lomas del Este displayed the highest productivity (463 and 465 g DM · m-2 · yr-1, respectively). This pattern is likely related to differences in soil depth and associated variation in water availability among geomorphological units. Seasonal variability in ANPP indicated peak productivity in the spring in all units, but differences in annual trends over the 10-yr study period suggested that ANPP drivers are operating spatially distinct. Understanding the spatial and temporal variability of ANPP of grasslands are prerequisites for sustainable management of grazing systems. © 2014 The Society for Range Management.
    • Yield response of needle-and-thread and threadleaf sedge to moisture regime and spring and fall defoliation

      Koehler, A. E.; Whisenhunt, W. D.; Volesky, J. D.; Reece, P. E.; Holman, T. L.; Moser, L. E. (Society for Range Management, 2014-01)
      Little information is available to help managers of cool-season dominated semiarid rangelands determine when to begin and end grazing in the spring and fall. Therefore, we evaluated the effects of clipping spring and fall growth on subsequent-year yield of needle-and-thread (Hesperostipa comata [Trin. & Rupr.] Barkworth) and threadleaf sedge (Carex filifolia Nutt.) (USDA-NRCS 2012) using a randomized complete block, split-plot experimental design with fall moisture regimes (ambient or supplemental water) applied to main plots and defoliation treatments applied to subplots. Two combinations of spring defoliation, one for each fall moisture regime, were composed of a factorial array of three spring clipping dates (early May, late May, mid-June) and three levels of defoliation (0%, 40%, 80%). A third combination of treatments was composed of the supplemental water regime and an array of a single spring clipping date (late May), a single fall clipping date (late September, after regrowth), and three levels of defoliation (0%, 40%, 80%) in the same year. Ambient fall moisture was low, leading to continued senescence of needle-and-thread and threadleaf sedge, whereas the application of 10 cm of supplemental water in mid-August stimulated fall growth. The study was replicated with two sets of main plots at four sites in consecutive years, 2002 and 2003. Yield data were collected in mid-June of the year following treatment. Subsequent-year yield of needle-and-thread was not affected by defoliation under average plant-year precipitation conditions (2003) (P > 0.05); however, it was reduced following heavy (80%) late spring (late May or June) defoliation during a drought year (2002) (P > 0.05). Subsequent-year yield of threadleaf sedge was not affected by defoliation in either year (P > 0.05). Because it is difficult to predict when drought will occur, avoiding heavy late-spring grazing in needle-and-thread-dominated pastures in consecutive years would be prudent. © 2014 The Society for Range Management.