• Saw Palmetto (Serenoa repens) Flowering and Fruiting Response to Time Since Fire

      Carrington, Mary E.; Mullahey, J. Jeffrey (Society for Range Management, 2013-01-01)
      Saw palmetto (Serenoa repens [Bartr.] Small) is a shrubby palm common in southeastern US pine flatwoods ecosystems. Demand recently has increased for fruits for the herbal remedies market. Because only wild saw palmettos are harvested, management strategies are needed to promote flowering and fruiting. This study investigated effects of time since growing season (April-July) fires on flowering and fruiting of saw palmetto ramets 54 cm in height, in 18 pine flatwoods or dry prairie sites (six sites in three locations, burned in 1996, 1995, 1994, 1993, 1992, or before 1991) in central and southwest Florida from 1996 to 1999. We used repeated measures, linear mixed models to test for time since fire effects on proportion of ramets flowering, proportionof ramets fruiting, and fruit yield. Ranges of means among sites over all years of the study for proportion of ramets flowering, proportion of ramets fruiting, and fruit yield were 0 to 0.78, 0 to 0.72, and 0 kg ha-1 to 2 869 kg ha-1, respectively. Time since fire strongly influenced flowering; highest probability of flowering occurred 1 yr after burning, followed by an abrupt decrease 2 yr after burning, then a gradual increase from 3 to 5 yr after fires (polynomial regression, P<0.0001 for fixed effects). Probability of fruiting increased with increasing time since fire (quadratic regression, P<0.001 for fixed effects), but fruit yields showed no pattern in response to time since fire (P=0.916). The decrease in influence of fire from flowering through fruit maturity presumably was caused by mortality from factors such as caterpillar predation and fungal infection. To promote increased flowering and fruit yields, we recommend that growing season burns be conducted approximately every 5 yr. We suggest, however, that management strategy be modified as necessary to maintain ecosystem diversity and function.
    • Spatial Redistribution of Nitrogen by Cattle in Semiarid Rangeland

      Augustine, David J.; Milchunas, Daniel G.; Derner, Justin D. (Society for Range Management, 2013-01-01)
      Nitrogen (N) availability can strongly influence forage quality and the capacity for semiarid rangelands to respond to increasing atmospheric CO2. Although many pathways of nitrogen input and loss from rangelands have been carefully quantified, cattle-mediated N losses are often poorly understood. We used measurements of cattle N consumption rate, weight gains, and spatial distribution in shortgrass rangeland of northeastern Colorado to evaluate the influence of cattle on rangeland N balance. Specifically, we estimated annual rates of N loss via cattle weight gains and spatial redistribution of N into pasture corners and areas near water tanks, and used previous studies to calculate ammonia volatilization from urine patches. Using measurements of plant biomass and N content inside and outside grazing cages over 13 yr, we estimate that cattle stocked at 0.65 animal unit months (AUM) ha-1 consumed 3.34 kg N ha-1 yr-1. Using an independent animal-based method, we estimate that cattle consumed 3.58 kg N ha-1 yr-1 for the same stocking rate and years. A global positioning system tracking study revealed that cattle spent an average of 27% of their time in pasture corners or adjacent to water tanks, even though these areas represented only 2.5% of pasture area. Based on these measurements, we estimate that cattle stocked at 0.65 AUM ha-1 during the summer can remove 0.60 kg N ha-1 in cattle biomass gain and spatially redistribute 0.73 kg N ha-1 to areas near corners and watertanks. An additional 0.17 kg N ha-1 can be lost as NH3 volatilization from urine patches. Cumulatively, these cattle-mediated pathways (1.50 kg N ha-1) may explain the imbalance between current estimates of atmospheric inputs and trace gas losses. While NOx emission remains the largest pathway of N loss, spatial N redistribution by cattle and N removed in cattle biomass are the second and third largest losses, respectively. Management of cattle-mediated N fluxes should be recognized as one means to influence long-term sustainability of semiarid rangelands.
    • Understanding Variability in Adaptive Capacity on Rangelands

      Marshall, Nadine A.; Smajgl, Alex (Society for Range Management, 2013-01-01)
      The art and science of developing effective policies and practices to enhance sustainability and adapt to new climate conditions on rangelands and savannas are typically founded on addressing the ‘‘average’’ or ‘‘typical’’ resource user. However, this assumption is flawed since it does not appreciate the extent of diversity among resource users; it risks that strategies will be irrelevant for many people and ignored, and that the grazing resource itself will remain unprotected. Understanding social heterogeneity is vital for effective natural resource management. Our aim was to understand the extent to which graziers in the northern Australian rangelands varied in their capacity to adapt to climate variability and recommended practices. Adaptive capacity was assessed according to four dimensions: 1) the perception of risk, 2) skills in planning, learning and reorganising, 3) financial and emotional flexibility, and 4) interest in adapting. We conducted 100 face-to-face interviews with graziers in their homes obtaining a 97% response rate. Of the 16 possible combinations that the four dimensions represent, we observed that all combinations were present in the Burdekin. Any single initiative to address grazing land management practices in the region is unlikely to address the needs of all graziers. Rather, policies could be tailored to type-specific needs based on adaptive capacity.Efforts to shift graziers from very low, low, or moderate levels of adaptive capacity are urgently needed. We suggest some strategies.