Rangeland Ecology & Management, Volume 69, Number 1 (January 2016)

The Dilemma of Improving Native Grasslands by Overseeding Legumes: Production Intensification or Diversity Conservation

Fri, 01 Jan 2016 00:00:00 GMT

The Dilemma of Improving Native Grasslands by Overseeding Legumes: Production Intensification or Diversity Conservation Jaurena, M.; Lezama, F.; Salvo, L.; Cardozo, G.; Ayala, W.; Terra, J.; Nabinger, C. In native campos of Uruguay, overseeding legumes coupled with phosphorus (P) fertilization is a technology used to increase animal production. Short-term improvements in both forage productivity and quality are repeatedly reported. However, some evidence suggests that this management may at times lead to the collapse of the native community and invasions by exotic species. Indeed, it is yet unclear to what extent overseeding legumes into native grasslands affects its long-term integrity. This study uses data from a long-term experiment to assess whether increased P fertilizer rates-typically used to encourage legume establishment and growth-are associated with reduced species diversity. In 1996 a grazed native grassland in eastern Uruguay was either left untouched (control) or overseeded with a mix of Trifolium repens and Lotus corniculatus and then fertilized at either a moderate or high rate of P (197 or 394 kg · ha-1 over 13 years, respectively). The three treatments were arranged in a randomized block design with four replicates of 2 hectares each. In 2005 the experiment was exhaustively sampled: 11 georeferenced sampling points per replicate, each encompassing∼20 m2. Extractable P was measured in the 0-5-and 5-15-cm soil layers. In 2009, species presence and cover were measured at the same points. Across treatments, wherever legumes were introduced, extractable soil P was negatively related to species richness and diversity (P < 0.01) and native grass cover was reduced. This effect became asymptotic once soil P exceeded 27 and 36 mg · kg-1 of P (0-5 cm), respectively. Therefore the documented reduction in species richness and diversity suggests a trade-off between increased pasture production and decreased vegetation stability may be operating in response to P fertilization of overseeded grasslands. The underlying ecophysiological mechanisms, as well as grazing management options to mitigate species diversity decline, should be further studied. © 2016 Society for Range Management. Published by Elsevier Inc. All rights reserved.

Targeted Grazing in Southern Arizona: Using Cattle to Reduce Fine Fuel Loads

Fri, 01 Jan 2016 00:00:00 GMT

Targeted Grazing in Southern Arizona: Using Cattle to Reduce Fine Fuel Loads Bruegger, R.A.; Varelas, L.A.; Howery, L.D.; Torell, L.A.; Stephenson, M.B.; Bailey, D.W. Managing the risk of wildfires is a growing concern in the western United States. Targeted grazing, or managing livestock grazing to achieve specific vegetation goals, is one possible tool to treat fuels, but few studies have evaluated its efficacy. The goal of this study was to test the effect of targeted grazing on herbaceous fuel loads and fire behavior by 1) implementing targeted grazing in a field experiment and 2) using a fire model (BehavePlus) to evaluate changes in fire behavior resulting from treatments. We applied targeted cattle grazing using low-stress herding and strategic placement of low-moisture block supplement on rugged rangelands in southwestern Arizona using a herd of 58 Red Angus cows and two bulls. Six of the cows were initially fitted with global positioning system collars. We tested two grazing treatments: 1) herding and supplement versus 2) no herding and no supplement on two pairs of study sites and replicated this for 2 years. Herding and supplement affected both the distribution of cattle and herbaceous fuel loads. Despite light utilization (26%) in treated sites, the BehavePlus fire model predicted that herding and supplement reduced fire rate of spread by more than 60% in grass communities and by more than 50% in grass/shrub communities. Fuel treatments dropped flame lengths below a 1.2-m critical threshold under the moderate fuel moisture scenario in grass communities and below a 2.4-m critical threshold in grass/shrub communities under both moderate and extreme fuel moisture scenarios. These results suggest that targeted grazing could reduce the potential cost of fighting fires in conditions similar to this study site. However, implementing this type of treatment on other sites will require careful calibration of animal numbers, supplement amounts, and length of herding periods relative to the specific context and goals. © 2016 Society for Range Management. Published by Elsevier Inc. All rights reserved.

Rangeland Monitoring Reveals Long-Term Plant Responses to Precipitation and Grazing at the Landscape Scale

Fri, 01 Jan 2016 00:00:00 GMT

Rangeland Monitoring Reveals Long-Term Plant Responses to Precipitation and Grazing at the Landscape Scale Munson, S.M.; Duniway, M.C.; Johanson, J.K. Managers of rangeland ecosystems require methods to track the condition of natural resources over large areas and long periods of time as they confront climate change and land use intensification. We demonstrate how rangeland monitoring results can be synthesized using ecological site concepts to understand how climate, site factors, and management actions affect long-term vegetation dynamics at the landscape-scale. Forty-six years of rangeland monitoring conducted by the Bureau of Land Management (BLM) on the Colorado Plateau reveals variable responses of plant species cover to cool-season precipitation, land type (ecological site groups), and grazing intensity. Dominant C3 perennial grasses (Achnatherum hymenoides, Hesperostipa comata), which are essential to support wildlife and livestock on the Colorado Plateau, had responses to cool-season precipitation that were at least twice as large as the dominant C4 perennial grass (Pleuraphis jamesii) and woody vegetation. However, these C3 perennial grass responses to precipitation were reduced by nearly one-third on grassland ecological sites with fine-rather than coarse-textured soils, and there were no detectable C3 perennial grass responses to precipitation on ecological sites dominated by a dense-growing shrub, Coleogyne ramosissima. Heavy grazing intensity further reduced the responses of C3 perennial grasses to cool-season precipitation on ecological sites with coarse-textured soils and surprisingly reduced the responses of shrubs as well. By using ecological site groups to assess rangeland condition, we were able to improve our understanding of the long-term relationships between vegetation change and climate, land use, and site characteristics, which has important implications for developing landscape-scale monitoring strategies. © 2016 Society for Range Management. Published by Elsevier Inc. All rights reserved.

Rangeland Ecology & Management Table of Contents Volume 69, Number 1 (2016)

Fri, 01 Jan 2016 00:00:00 GMT

Rangeland Ecology & Management Table of Contents Volume 69, Number 1 (2016)