Rangeland Ecology & Management, Volume 64, Number 4 (July 2011)

Long-Term Livestock Exclusion in an Arid Grassland Alters Vegetation and Soil

Fri, 01 Jul 2011 00:00:00 GMT

Long-Term Livestock Exclusion in an Arid Grassland Alters Vegetation and Soil Allington, Ginger R. H.; Valone, Thomas J. Changes in soil and vegetation due to livestock grazing are occurring in arid lands throughout the world. The most extreme cases result in desertification, which is seen as largely irreversible, because of altered soil properties. To understand better how long-term livestock removal affects soil properties and vegetation, we compared water-infiltration rates, soil bulk density, and perennial grass cover inside and outside a long-term livestock exclosure in an arid grassland site in southeastern Arizona, United States. The site had not been desertified at the time of this study. Exclusion of livestock for 40 yr was associated with lower bulk density and higher water infiltration in both the dry and wet seasons. Perennial grass cover was higher and two native grasses, Eragrostis intermedia and Bouteloua hirsuta were significantly more common (P < 0.05) in the ungrazed area. These findings parallel our results from a desertified site and suggest that changes in soil physical properties associated with long-term livestock removal are not an artifact of desertification and can take place in a system that has remained in a grassland state. Our data suggest that, although significant changes in species composition have occurred, this grassland is relatively resilient to substantial changes in soil physical properties.

Fire History of a Relict Oak Woodland in Northeast Texas

Fri, 01 Jul 2011 00:00:00 GMT

Fire History of a Relict Oak Woodland in Northeast Texas Stambaugh, Micheal C.; Sparks, Jeff; Guyette, Richard P.; Willson, Gary Empirical data generated from fire scars are a foundation for understanding fire regimes, designing land-management objectives, and addressing long-term land-use and climate-change effects. We derived precise dates of historic fires from fire-scar injuries occurring on trees growing in a relict post oak woodland in northeastern Texas. The fire-event chronology shows the last three centuries were marked with human influence, with an overall trend of decreasing fire occurrence through time. Thirty different fire events occurred between 1690 and 2007, of which 26 occurred prior to 1856. All fires occurred while trees were dormant. From 1690 to 1820, the mean fire interval was 6.7 yr. A 50-yr period without fire occurred in the latter 19th century (1855-1905) and coincided with the establishment of an oak cohort. A second extended period (80 yr) without fire characterized most of the 20th century. We hypothesize that the absence of fire during much of the last century has resulted in increased tree density and canopy closure, the establishment of fire-intolerant vines, shrubs, and trees, and likely the decline of fire-dependent plant species. Information describing long-term changes of fire regimes in oak woodlands in this region could aid in determining fire-management objectives with respect to prescribed fire implementation and community restoration.

Homogenization of the Soil Surface Following Fire in Semiarid Grasslands

Fri, 01 Jul 2011 00:00:00 GMT

Homogenization of the Soil Surface Following Fire in Semiarid Grasslands White, Carleton S. Semiarid grasslands accumulate soil beneath plant ‘‘islands’’ that are raised above bare interspaces. This fine-scale variation in microtopographic relief is plant-induced and is increased with shrub establishment. Research found that fire-induced water repellency enhanced local-scale soil erosion that reduced variation in microtopographic relief, suggesting that fire may counteract vegetation-driven, fine-scale spatial soil heterogeneity. This article analyzes longer-term measurements (up to 9 yr) of soil microtopography to evaluate the hypothesis that fire in semiarid grasslands results in more homogenous soil microtopographic relief. Changes in soil microtopographic relief were measured prior to and following a total of five fires at three semiarid grasslands within central New Mexico, United States. The fires included three cool-season prescribed fires, a warm-season prescribed fire, and a warm-season wildfire. Four of the five fires resulted in significantly lower soil microtopographic variation that persisted for up to 4 yr. The duration and magnitude of the soil leveling effect was lowest in the grassland with clay-rich soils, indicating a possible soil texture interaction. Although two grasslands had net soil loss following fires, no net erosion occurred at the third grassland, indicating that redistribution of soils can occur without net erosion. These results show that management with prescribed fire reduces biotic-driven variation in soil microtopographic relief in semiarid grasslands that may help limit the transition to shrubland ecosystems in this region.

Plains Prickly Pear Response to Fire: Effects of Fuel Load, Heat, Fire Weather, and Donor Site Soil

Fri, 01 Jul 2011 00:00:00 GMT

Plains Prickly Pear Response to Fire: Effects of Fuel Load, Heat, Fire Weather, and Donor Site Soil Vermeire, Lance T.; Roth, Aaron D. Plains prickly pear (Opuntia polyacantha Haw.) is common throughout the Great Plains and often becomes detrimental to agricultural production on noncultivated lands. We examined direct fire effects on plains prickly pear and mechanisms of tissue damage to facilitate development of fire prescriptions. Cladodes from clones on three soils (claypan, gravelly, silty) were subjected to fire with two weather conditions (moderate, severe) at four fuel loads (1 500, 3 000, 4 500, and 6 000 kg ha-1) and a nonburned control. Fire was simulated with field-collected grass, and heat was measured using thermocouples at the soil surface and 8 cm above. Plants were maintained in a greenhouse and monitored for cladode mortality or growth. Cactus response to fire was examined in a field experiment with four nonburned and four summer-burned 0.75-ha plots. Some plants from each treatment sprouted new cladodes. Donor site soil and fire weather effects were limited to mass of new sprouts as they interacted with fuel load. Fire under any condition reduced cactus mass and survival. Reduction in cactus mass increased from 42% with 1 500 kg ha-1 to 92% with fuel loads of 3 000 kg ha-1 or more. Fuel load, duration of heat, maximum temperature, and degree-seconds were each positively related to mortality, but duration of heat greater than 60 degreesC was the best predictor. Plant mortality was 15% in the field, but number of live cladodes was initially reduced 91%. After one year, number of live cladodes in burned plots was 43% of that in nonburned plots because burned plants sprouted more new cladodes than nonburned plants. Insect and browsing damage occurred on 83% of cladodes in burned plots and only 8% for nonburned plots. Lack of fire weather effects suggests prickly pear control can be achieved under broad fire prescriptions, given the amount of combustible fuel is adequate.