Prickly Pear Cactus Responses to Summer and Winter Fires

Prescribed fire is used to reduce size and density of prickly pear cactus (Opuntia spp.) in many rangeland ecosystems. However, effects of dormant season fires (i.e., winter fires) are inconsistent. Thus, there is increasing interest in use of growing season (summer) fires. Our objective was to evaluate effects of fire season and fire intensity on mortality and individual plant (i.e., “motte”) structure (area per motte, cladodes per motte, motte height) of brownspine prickly pear (O. phaeacantha Engelm.). The study had 4 treatments: no fire, low-intensity winter fire, high-intensity winter fire, and summer fire. Three sizes of prickly pear mottes were evaluated: small (0–20 cladodes per motte), medium (21–100), and large (101–500). At 3 years postfire, prickly pear mortality in the summer fire treatment was 100% in small mottes, 90% in medium mottes, and 80% in large mottes. Motte mortality increased in this treatment over time, especially in large mottes. Mortality from high-intensity winter fires was 29% and 19% in small and medium mottes, respectively, but no large mottes were killed. Motte mortality was < 10% in low-intensity winter fire and no-fire treatments. Summer fires reduced all motte structural variables to 0 in small mottes and nearly 0 in other motte size classes. High-intensity winter fires reduced some structural variables of medium and large mottes, but had no long-term negative effects on area per motte or cladodes per motte in surviving small mottes. Low-intensity winter fires had no long-term negative effects on motte structure in any size class. Rapid growth of mottes, and especially small mottes, in the no-fire treatment suggested that resistance to winter fires can occur rapidly.     

Mesquite,Tobosagrass, and Common Broomweed Responses to Fire Season and Intensity

There has been increasing interest in the use of summer fires to limit woody plant encroachment on grasslands, but information regarding effects of such fires on perennial grass recovery and annual forb production is also needed. Our objective was to examine effects of fire seasonality and intensity on the woody legume honey mesquite (Prosopis glandulosa Torr.), the C₄ midgrass tobosagrass (Pleuraphis mutica Buckl.), and the annual forb common broomweed (Amphiachyris dracunculoides [DC.] Nutt.). Treatments included summer fires, high-intensity winter fires, low-intensity winter fires, and no burn in replicated plots. None of the fire treatments caused whole-plant mortality (root kill) in mesquite. Mesquite aboveground mortality (top kill) was much greater after summer and high-intensity winter fires than low-intensity winter fires. Tobosagrass total yield (live + dead) was lower following summer fires and was not enhanced by any of the fire treatments for two growing seasons postfire when compared to the no-burn condition. However, tobosagrass live yield was 40% greater in the high-intensity winter fire treatment than the no-burn condition the first summer postfire and recovered in the other fire treatments by the end of the first growing season postfire. Tobosagrass percentage of live tissue was greatest in the summer fire treatment at the end of each of the two growing seasons postfire. Common broomweed cover increased in the summer fire treatment and decreased in both winter fire treatments relative to the no-burn condition by the end of the first growing season postfire. Summer fire offered no clear advantage over high-intensity winter fire with respect to mesquite suppression. However, the increase in late-season tobosagrass percentage live tissue caused by summer fire may be advantageous for forage quality. In addition, patch burning summer fires to increase broomweed cover in selected areas may be useful for wildlife habitat.     

Summer and Winter Defoliation Impacts on Mixed-Grass Rangeland

Combined growing- and dormant-season pasture use has potential to increase herbage harvest without causing the undesirable shift in species composition that occurs with excessive utilization. The objective of this study was to determine the effect of summer clipping on winter pastures and winter clipping on summer pastures regarding standing crop, plant community composition, and forage quality. The study was conducted from 2003–2006 at the Antelope and Cottonwood Research Stations located in the mixed-grass prairie of western South Dakota. At each location, the experimental design was a randomized complete block with three replications that included 18 clipping treatments arranged as a split-split plot. Whole plots consisted of four summer clipping dates (May–August). Subplot treatments were two clipping intensities (clipped to residual height to achieve 25% or 50% utilization). Sub-subplots consisted of two winter clipping intensities (unharvested or clipped to a residual height to achieve a total utilization of 65%). Two winter control treatments were arranged in the subplot and split into two clipping intensities of 50% and 65% utilization. Winter biomass for the May 25% clipping treatment was similar to winter biomass for winter-only clipping. No increase in forage quality resulted from summer clipping compared with winter clipping. Three consecutive yr of combined growing-season and dormant-season defoliation to 65% utilization resulted in no change in functional group composition compared with ≤ 50% utilization treatments. Clipping in June resulted in reduced midgrass biomass at both stations and increased shortgrass biomass at Cottonwood. Results suggest that producers could combine growing and dormant-season grazing to increase the harvest of herbage on mixed-grass prairie, but should change season of use periodically to avoid an undesirable shift in plant composition.     

Effects of Fire Exclusion on Previously Fire-Managed Semiarid Savanna Ecosystem

Long-term (> 100 yr) fire exclusion is associated with numerous ecological consequences in grasslands and savannas, including transitions into shrub- or tree-dominated systems. Several studies have reported differences in woody vegetation after multiple fires among burned and unburned rangelands, but none have reported the impacts of fire exclusion after a period of fire management. We evaluated effects of fire exclusion on herbaceous and woody canopy cover and herbaceous biomass in semiarid savanna of southwest Texas in pastures with known burn histories. Pastures were burned in summer and winter in 1994, 2000, and 2006, followed by 11 yr of fire exclusion. Between 2006 and 2017, woody subcanopy increased (5–21%) in all treatments while overstory canopy remained unchanged. Herbaceous cover decreased (5–18%) in all treatments but remained higher in burned treatments. From 2006 to 2017, herbaceous biomass declined in all treatments by > 650 kg·ha⁻¹ and was not statistically different among treatments. These trends support other research demonstrating the importance of historical mean fire return interval in maintaining grasslands and savannas.     

Spring Clipping,Fire, and Simulated Increased Atmospheric Nitrogen Deposition Effects on Tallgrass Prairie Vegetation

Defoliation aimed at introduced cool-season grasses, which uses similar resources of native grasses, could substantially reduce their competitiveness and improve the quality of the northern tallgrass prairie. The objective was to evaluate the use of early season clipping and fire in conjunction with simulated increased levels of atmospheric nitrogen deposition on foliar canopy cover of tallgrass prairie vegetation. This study was conducted from 2009 to 2012 at two locations in eastern South Dakota. Small plots arranged in a split-plot treatment design were randomized in four complete blocks on a warm-season grass interseeded and a native prairie site in east-central South Dakota. The whole plot consisted of seven treatments: annual clip, biennial clip, triennial clip, annual fire, biennial fire, triennial fire, and undefoliated control. The clip plots consisted of weekly clipping in May to simulate heavy grazing. Fire was applied in late April or early May. The subplot consisted of nitrogen applied at 0 or 15 kg N · ha^?1 in early June. All treatments were initially applied in 2009. Biennial and triennial treatments were reapplied in 2011 and 2012, respectively. Canopy cover of species/major plant functional groups was estimated in late August/early September. Annual clipping was just as effective as annual fire in increasing native warm-season grass and decreasing introduced cool-season grass cover. Annual defoliation resulted in greater native warm-season grass cover, less introduced cool-season grass cover, and less native cool-season grass cover than biennial or triennial defoliation applications. Low levels of nitrogen did not affect native warm-season grass or introduced cool-season cover for any of the defoliation treatments, but it increased introduced cool-season grass cover in the undefoliated control at the native prairie site. This study supports the hypothesis that appropriately applied management results in consistent desired outcomes regardless of increased simulated atmospheric nitrogen depositions.     

Examination of Fire-Related Succession Within the Dry Mixed-Grass Subregion of Alberta With the Use of MODIS and Landsat

Fire is an important disturbance process historically present across the northern Great Plains. Previous research from northern dry mixed-grass prairie suggests that C4 (warm season) grasses replace C3 (cool season) climax species with increasing fire, particularly in the spring. This hypothesis was tested at a landscape scale at Canadian Forces Base Suffield Alberta, by exploring the relationship between ecosystem states (C3 dominant, C3/C4 codominant, C4 dominant) inferred from a MODIS multitemporal plant functional type classification (pseudo R²: 0.598, overall accuracy: 0.74) and interyear fire history digitized from the Landsat archive (1972–2007). Probit regression showed that succession processes were different between range sites, where C4-dominant pixels were positively related to fire (P < 0.001, pseudo R² = 1) and completely replaced C3-dominant pixels on loamy range sites after 14 fires in 36 yr. In contrast, C3- and C3/C4-codominant pixels were related with fire on Blowouts range sites (P < 0.001, pseudo R² = 1), where C3/C4-codominant pixels replaced C3-dominant pixels with increasing fire. Finally, there were no statistically significant relationships between ecosystem states and fire for Sands range sites. Analysis of recovery showed that after loamy pixels experienced three to six fires in 18 yr followed by 18 yr of rest, C3-dominant pixels were reduced by over 30% compared to unburned pixels. Finally, intrayear fire timing (2001–2009) was explored with the use of Wilcoxon signed-rank tests between the spatial extent of spring and summer fires, with the use of MODIS burned-area data. Results indicate that fires are not limited to the spring season (P < 0.05), but occur across the entire growing season. Although fire timing does not appear to play a role in driving succession, this ecosystem is generally sensitive to repeated fire, with recovery of C3 climax species taking decades.     

Seasonal Timing of Fire Alters Biomass and Species Composition of Northern Mixed Prairie

Fire plays a central role in influencing ecosystem patterns and processes. However, documentation of fire seasonality and plant community response is limited in semiarid grasslands. We evaluated aboveground biomass, cover, and frequency response to summer, fall, and spring fires and no fire on silty and clayey sites in semiarid, C₃-dominated grassland. The magnitude of change in biomass between years was greater than any differences among fire treatments. Still, differences existed among seasons of fire. Summer fire reduced non-native annual forb frequency (3% vs. 10% ± 2%) and Hesperostipa comata, reduced native annual forbs the first year, increased Poa secunda and bare ground, and increased Vulpia octoflora the second year. Fall fire increased grass biomass (1224 vs. 1058 ± 56 kg ? ha^? 1), but fall fire effects were generally similar to those of summer fire. Spring fire effects tended to be intermediate between no fire and summer and fall fire with the exception that spring fire was most detrimental to H. comata the first growing season and did not increase bare ground. All seasons of fire reduced litter, forb biomass, and frequency of Bromus japonicus and Artemisia spp., and they reduced H. comata, V. octoflora, and native annual forbs the first year, but increased basal cover of C₃ perennial grasses (2.2% vs. 0.6% ± 0.4%). Fire during any season increased dominance of native species compared with no fire (6.6% vs. 2.0% ± 1.0% basal cover) and maintained productivity. Seasonal timing of fire manipulated species composition, but increased C₃ perennial grass cover and native species dominance with fire during any season indicated that using fire was more important than the season in which it occurred. In addition, fire effects on the vegetation components tended to be counter to previously observed effects of grazing, suggesting fire and grazing may be complementary.     

Long-Term Effects of Fire,Livestock Herbivory Removal,and Weather Variability in Texas Semiarid Savanna

We examined how the occurrence and structure of grasses and woody plants changed after 12 yr of a fire season manipulation and removal of livestock herbivores. Applying high intensity fires in the summer preserved the structural integrity of this semiarid live oak (Quercus virginiana Mill.) savanna while decreasing or eliminating numerous problematic plants in the understory and overstory, such as prickly pear cactus (Opuntia spp.), sacahuista (Nolina texana S. Watson), Ashe juniper (Juniperus ashei J. Buchholz), Pinchot's juniper (J. pinchotii Sudw.), and honey mesquite (Prosopis glandulosa Torr.). In the less intense repeat winter burning treatments, undesirable woody plants were generally maintained at pretreatment levels in the overstory but all woody plants except Ashe juniper increased in the understory. Alternatively, areas excluded from fire in the control treatment rapidly transitioned from a grass-tree codominated savanna environment to one that is heavily dominated by woody plants. In the grass community, the most frequently occurring grass species in the winter burn treatment differed from summer burn and control treatments, whereas the summer burn treatment was not different from the control. Of the herbaceous plants, only little bluestem (Schizachyrium scoparium &lsqb;Michx.] Nash) responded to fire treatments. Little bluestem increased in the winter burn treatment, remained fairly constant in the summer burn treatment, and decreased in the control. Other grasses varied largely as a function of annual weather variability, the removal of livestock, and legacy effects resulting from pre-existing variability. These findings suggest that fire can reduce or eliminate woody plant species that threaten the stability of live oak savannas while having little long-term effect on grasses desired by rangeland managers.     

Effects of season and distance moved during loading on transport losses of market-weight pigs in two commercially available types of trailer

This study evaluated effects of trailer design and season on physical indicators of stress during loading and unloading and transport losses (dead and nonambulatory pigs) in market-weight pigs (BW = 129.6 +/- 0.40 kg). A total of 109 trailer loads of pigs (n = 17,256 pigs) from 1 farm were used in a randomized complete block design with a 2 x 4 factorial arrangement of treatments: 1) trailer design (potbelly vs. straight-deck) and 2) season (spring vs. summer vs. fall vs. winter). A subset of loads (n = 42) was used to examine effect of distance pigs were moved during loading [short (<24 m) vs. long (47 to 67 m)] on physical indicators of stress and transport losses. This study was conducted on 7 d per season at 1 farm with 4 loads (2 on potbelly and 2 on straight-deck trailers) being transported each day to 1 commercial packing plant. Pigs from different farm groups were mixed on the trailer and provided with 0.45 m(2)/pig floor space during an approximately 4-h journey to the plant. The percentage of pigs exhibiting open-mouth breathing, skin discoloration, and muscle tremors was recorded during loading and unloading. Additionally, dead pigs on arrival at the plant and nonambulatory pigs at the farm and at the plant were recorded. Effects of trailer design on open-mouth breathing and skin discoloration during unloading were dependent on season (trailer design x season interaction; P < 0.05). Pigs unloaded from potbelly trailers had a greater (P < or = 0.05) incidence of open-mouth breathing in the spring and summer and a greater (P < 0.05) incidence of skin discoloration in the spring, summer, and winter than pigs unloaded from straight-deck trailers. The incidence of total nonambulatory pigs at the plant was greater (P < 0.05) in the winter than in the spring and summer. The long compared with short distance moved treatment resulted in a greater (P = 0.001) incidence of open-mouth breathing and skin discoloration during loading and tended (P = 0.06) to increase the incidence of nonambulatory pigs at the farm. However, there was no effect of trailer design, season, or loading distance on total losses at the plant. In summary, physical indicators of stress (open-mouth breathing and skin discoloration) were increased with the long distance moved during loading treatment and were greater during unloading for potbelly than straight-deck trailers; however, trailer design, season, and loading distance had minimal effects on total transport losses.     

Effect of season of burning on grass recovery in the false thornveld of the eastern cape

Abstract

Season of burning is one of the most controversial questions concerning the use of fire in veld management. In the summer rainfall areas of South Africa the generally accepted rule of burning only after the first spring rains has proven ineffectual when using fire to control bush encroachment because the fires are too cool when burnt at this time. It was therefore decided to investigate the effect of burning on the regrowth of grass when applied during mid‐winter, spring, late spring and early summer. The results showed that burning when the grass was dormant (mid‐winter) had no deleterious effect on the recovery of grass when compared with burning after the first spring rains (spring). Conversely burning when the grass was actively growing (early summer) seriously retarded its regrowth.     

An analysis of canine hair re-growth after clipping for a surgical procedure

Hair growth and replacement have been studied extensively in humans, sheep and laboratory rodents, but in dogs and other mammalian species few studies have been published. The objectives of this study were: (1) to determine the time required for the hair to re-grow in dogs after clipping for a surgical procedure; (2) to define whether the season of the year influenced the period of time required for re-growth and; (3) to determine if season might influence the telogen: anagen ratio. Eleven Labrador retrievers were recruited during spring, 10 during summer, six during autumn and 10 during winter. Hairs re-grew to their preclipped length in 14.6 weeks, 14.5 weeks, 13.6 weeks and 15.4 weeks when shaved in the spring, summer, autumn and winter, respectively. The differences in these values were not significant suggesting that season has no effect on the rate of hair re-growth in Labrador retrievers housed indoors (P = 0.12). The mean values for the telogen: anagen ratio in each season were: 5.2 (spring), 6.1 (summer), 9.5 (autumn), and 5.3 (winter). The differences in these values also were not significant (P = 0.89). The percentage of hairs in telogen was over 80% in all four seasons.     

Veld burning in giant's castle game reserve,natal Drakensberg

A basic aim in the management of a wildlife reserve is to maintain ecological diversity. In the Giant's Castle Game Reserve the vegetation is largely composed of fire sub‐climax grasslands. Under the natural fire‐regime, before man influenced the system much, fires probably occurred at any time of the year, but mostly in summer. At present there are acute problems in controlling wildfires which occur mostly in late winter when there is an extreme fire hazard. Most of the Natal Drakensberg is now burnt by wildfires in late winter and deliberate fires in early spring. The ecological effect of the natural and present fire regimes are discussed, and a burning plan for Giant's Castle is outlined.     

Grazing Deferment Effects on Forage Diet Quality and Ewe Performance Following Summer Rangeland Fire

Complete rest or grazing deferment is a general recommendation to encourage vegetative recovery following fire in the western United States. However, effects of grazing deferments on animal performance have not been determined. Prescribed fires were individually applied to nine separate, 1.5-ha pastures each year (2006 and 2007) for a total of 18 pastures. Grazing was deferred until spring (16 May), early summer (19 June), or late summer (1 August) the growing season after fire. At the end of each deferment, a 70-d (2007) or 41-d (2008) grazing period was initiated. Stocking rates were consistent between treatments within year, but were adjusted between years to achieve the targeted residual biomass of approximately 300 kg · ha^?1. Diet quality was assessed approximately every 15 d throughout each grazing period (three pastures · period^?1) via collection of rumen extrusa throughout the 2-yr study. Ewe body weight was measured on and off-test for each grazing period. Diet extrusa samples for in vitro organic matter disappearance was less (P = 0.03) for late summer than early summer grazing periods and equal to the spring period (62.9, 64.6, and 61.0 ± 0.90%, respectively for spring, early summer, and late summer grazing periods). In vitro neutral detergent fiber disappearance decreased (P = 0.01) by 10.6 percentage units from early grazing to late grazing period in 2007, whereas no differences were observed in 2008. Ewe average daily gain did not differ between spring and early summer grazing periods and were greater (P = 0.03) than the negligible body weight gains of the late summer grazing period. Total gain was 10.9 kg · ha^?1 greater in 2008, and a quadratic response was measured for grazing period in 2007. Results indicate that deferment until early summer may be preferable so that stocking rates can be more accurately determined and animal performance is not diminished.     

Models for Predicting Fuel Consumption in Sagebrush-Dominated Ecosystems

Fuel consumption predictions are necessary to accurately estimate or model fire effects, including pollutant emissions during wildland fires. Fuel and environmental measurements on a series of operational prescribed fires were used to develop empirical models for predicting fuel consumption in big sagebrush (Artemisia tridentata Nutt.) ecosystems. Models are proposed for predicting fuel consumption during prescribed fires in the fall and the spring. Total prefire fuel loading ranged from 5.3–23.6 Mg · ha^?1; between 32% and 92% of the total loading was composed of live and dead big sagebrush. Fuel consumption ranged from 0.8–22.3 Mg · ha^?1, which equates to 11–99% of prefire loading (mean = 59%). Model predictors include prefire shrub loading, proportion of area burned, and season of burn for shrub fuels (R² = 0.91). Models for predicting proportion of area burned for spring and fall fires were also developed (R² = 0.64 and 0.77 for spring and fall fire models, respectively). Proportion of area burned, an indicator of the patchiness of the fire, was best predicted from the coverage of the herbaceous vegetation layer, wind speed, and slope; for spring fires, day-of-burn 10-h woody fuel moisture content was also an important predictor variable. Models predicted independent shrub consumption measurements within 8.1% (fall) and 12.6% (spring) for sagebrush fires.     

阿坝牧区草地不同利用方式与程度对植被碳含量的影响

为探讨不同利用方式与程度对草地植被碳含量的影响,对阿坝牧区不同利用方式草地(封育天然割草地、人工栽培、放牧草地)和植物生长季不同利用程度草地植被的地上部分、地下根系和枯落物的碳含量进行调研。结果表明,1)草地地上植被碳含量在不同利用方式上表现为封育天然割草地、冬春放牧草地和人工栽培草地显著高于夏秋放牧草地(P<0.05);生长季不同利用程度上冬春和夏秋轻度放牧草地显著高于重度和中度放牧草地(P<0.05)。2)草地枯落物碳含量在不同利用方式与程度上差异均不显著。3)从根系总碳含量来看,不同利用方式上夏秋放牧草地和封育天然割草地显著高于冬春放牧草地和人工栽培草地 (P<0.05);生长季不同利用程度上夏秋中度和轻度放牧草地显著高于夏秋重度和冬春放牧草地(P<0.05),且各种利用方式与程度草地地下根系总碳含量均从表层向下依次显著的递减(P<0.05),0~10 cm 的根系碳含量占总量的65%以上,10~30 cm各草地根系碳含量差异不显著(P<0.05)。通过数量关系得出,草地植被碳含量在利用方式上表现为封育天然割草地(356.509 g/m²)>冬春放牧草地(297.780 g/m²)>人工栽培草地(164.953 g/m²)>夏秋放牧草地(137.577 g/m²),地上植被碳含量分别为地下根系碳含量的15.334,17.130,9.167和5.146倍;在生长季不同利用程度上表现为冬春放牧草地(297.780 g/m²)>夏秋轻度放牧草地(217.002 g/m²)>夏秋重度放牧草地(113.849 g/m²)>夏秋中度放牧草地(81.882 g/m²),地上植被碳含量分别为地下根系碳含量的17.130,8.636,4.412和2.430倍。利用方式和放牧强度是影响草地植被碳含量的重要因素。     

Chihuahuan Desert Grassland Responds Similarly to Fall,Spring, and Summer Fires During Prolonged Drought

Land managers frequently use prescribed burning to help maintain grassland communities. Semiarid grassland dynamics following fire are linked to precipitation, with increasing soil moisture accelerating the rate of recovery. Prescribed fires are typically scheduled to follow natural fire regimes, but burning outside the natural fire season could be equally effective and more convenient for managers, depending on their management objectives. We conducted a field experiment in desert grassland to determine if fire seasonality influenced plant community recovery. Experimental burn treatments occurred in fall, spring, and summer in replicate 0.24-ha plots to determine if fire seasonality affected the rate of recovery of an ungrazed Chihuahuan Desert grassland in central New Mexico. Plant communities were surveyed seasonally for 5 yr after the burns. Grassland community structure responded to fire but not fire seasonality. Grass cover in all burned treatments remained lower than unburned controls for 3 yr after the burns. Community change through time was largely influenced by low rainfall, as grass cover in burned and unburned communities converged during a year with severe drought. In conclusion, fire seasonality did not influence rate of community recovery, but extended drought was possibly more influential than fire on grassland dynamics.     

Fire Return Interval and Season of Fire Alter Bud Banks

Despite the importance of vegetative reproduction in annual tiller replacement, little is known about the patterns and timing of tiller recruitment from the bud bank, especially regarding fire return intervals and seasons of fire. We examined aboveground plant density, temporal patterns of tiller production, and belowground bud bank dynamics for Bouteloua gracilis (Willd ex. Kunth) Lag. ex Griffiths), Pascopyrum smithii (Rydb.) A. Löve, and Hesperostipa comata (Trin. & Rupr.) Barkworth following summer, fall, and spring prescribed fires at 2-yr, 3-yr, and 6-yr fire return intervals, and their interactions. Fire treatments were initiated in 2006, and buds were assessed July 2011 through July 2013. Density and number of reproductive B. gracilis tillers increased in 2013 following drought during 2012, unlike H. comata, which decreased reproductive tiller production. Irrespective of fire treatments, B. gracilis produced the most buds (8 ? 10 buds ? tiller^? 1) and H. comata produced the least (2 ? 3 buds ? tiller^? 1), with P. smithii producing an intermediate amount (6 ? 8 buds ? tiller^? 1). Immediate B. gracilis and P. smithii bud mortality did not occur for all season and fire return interval treatments. However, H. comata bud mortality increased immediately following summer and fall prescribed fires. Three-yr fire return intervals increased active buds throughout the 2013 winter and growing season for B. gracilis and P. smithii relative to control plots and 2- and 6-yr fire return intervals. Fire stimulated bud activity of B. gracilis and P. smithii relative to nonburned plots. The aboveground and belowground response of H. comata indicated meristem limitations following fire treatments, illustrating greater vulnerability to fire for that species than B. gracilis and P. smithii.     

野牛草雌雄株对不同形态氮素的生理响应差异

为揭示野牛草雌雄株对氮素形态的偏好及生理响应差异,以野牛草克隆分株为材料,采用温室砂培盆栽方法,分析了硝态氮(N₁)、铵态氮(N₂)、铵硝混合态氮(N₃)和对照(CK)处理对野牛草雌、雄株生长性状、生物量、叶绿素含量、叶片氮含量及氮代谢相关酶活性的影响。结果表明,雌株在N₂处理时其生长性状、各部位生物量及地上生物量和总生物量均显著小于N₁和CK,且还小于N₃处理,表明铵态氮处理可能抑制野牛草雌株生长。N₁处理下的雄株间隔子长度、间隔子直径与CK无显著差异但显著大于N₂和N₃,同时其匍匐茎节数、匍匐茎长度、根生物量、地上生物量及总生物量显著大于其他处理。野牛草雌、雄株的叶绿素a含量和叶绿素总含量均在N₁处理时显著高于对照,但雌株在3种N形态处理之间没有显著差异、而雄株在N₁时与N₂或N₃处理差异显著。野牛草...     

Semiarid Rangeland Is Resilient to Summer Fire and Postfire Grazing Utilization

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.