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We evaluated the relationship between annual forage production and annual and seasonal precipitation and temperature at a shortgrass steppe site in north-central Colorado using a long-term data set (52 yr). We also constructed a relationship between forage production and aboveground net primary production (ANPP). Precipitation fluctuated randomly, but temperature had clear warming and cooling trends including a 17-yr warming trend from 1974 to 1990. Forage production was significantly related to both annual and seasonal precipitation but not temperature. Precipitation events between 15 and 30 mm accounted for most of the variability in production because they accounted for most of the variability in precipitation...
Bare-soil evaporation is an important component of the water balance in semiarid systems. However, little is known quantitatively about the influence of soil texture on bare-soil evaporation. We hypothesized that soil texture would have a great influence on both the temporal dynamics of bare-soil evaporation as well as on the depth ?to which evaporation-influenced soil water content throughout a 51-d simulated drought period. We measured soil water in lysimeters filled with three different soils. We measured daily evaporation gravi metrically and estimated evaporation rates using the energy balance method of Ben-Asher et al. We estimated soil water content at depths of 3.8 cm, 11.4 cm, 19.0 cm, 26.6 cm, and 34.2...
A potentially important organizing principle in arid and semi-arid systems is the inverse-texture hypothesis which predicts that plant communities on coarse-textured soils should have higher above-ground net primary productivity (ANPP) than communities on fine-textured soils; the reverse is predicted to occur in humid regions. Our objectives were: (1) to test predictions from the inverse-texture hypothesis across a regional precipitation gradient, and (2) to evaluate changes in community composition and basal cover on coarse- and fine-textured soils across this gradient to determine how these structural parameters may affect ANPP. Sites were located along a precipitation gradient through the Central Grassland region...
Small precipitation events account for a large proportion of the precipitation received in semiarid regions, and their potential ecological importance has previously been ignored. We investigated the effect of a small rainfall event (5 mm) upon Bouteloua gracilis, the dominant grass species of the central and southern Great Plains of North America. An effect of a small event on leaf water potential and leaf conductance to water vapor was observed in less than 12 h and lasted for up to two days. The remarkable short response time of Bouteloua gracilis to a rainfall stimulus enables this species to utilize small events and, therefore, may influence its persistence as a dominant species in the steppe region. We proposed...
1 The ability of drought-stressed Bouteloua gracilis H.B.K. Lag. ex Steud. to respond rapidly to a small rainfall event with increases in leaf water potential and leaf conductance directed our attention to the role of the roots in these responses. Our first objective was to determine whether new root growth was required to restore the water status to that of a non-stressed plant, following a small rainfall event. The results indicated that surviving roots were able to absorb water at approximately 40% of the rate of new roots, which was sufficient to restore non-stressed leaf water potentials within one day of watering. 2 The second objective was to estimate the rate and amount of new root growth following simulated...
The effects of soil texture and grazing by cattle on the production of seeds of Bouteloua gracilis were evaluated for a semiarid grassland in northeastern Colorado. Ten locations were chosen to represent the range in soil textures and grazing intensities found at the Central Plains Experimental Range research site. Number of flowering culms, inflorescences and seeds, length of each flowering culm, total biomass of reproductive structures (culms, inflorescences, and seeds), and basal area were assessed for 96 B. gracilis plants at each location. Community-level estimates of density of flowering culms and density of viable seeds were made for each location. Both soil texture and grazing by cattle were important to...
Pulses of water availability characterize semiarid and arid ecosystems. Most precipitation events in these ecosystems are small (?10 mm), but can stimulate carbon flux. The large proportion of carbon stored belowground and small carbon inputs create the potential for these small precipitation events to have large effects on carbon cycling. Land-use change can modify these effects through alteration of the biota and soil resources. The goal of our research was to determine how small precipitation events (2, 5, and 10 mm) affected the dynamics of soil carbon flux and water loss in previously cultivated Conservation Reserve Program (CRP) fields and undisturbed shortgrass steppe. Total carbon loss and duration of elevated...
Hector et al. (1) reported on BIODEPTH, a major international experiment on the response of plant productivity to variation in the number of plant species. They found ?an overall log-linear reduction of average aboveground biomass with loss of species,? leading to what the accompanying Perspective (2) described as ?a rule of thumb?that each halving of diversity leads to a 10 to 20% reduction in productivity.? These conclusions, if true, imply that the continuing high rate of plant extinction threatens the future productivity of Earth's natural and managed ecosystems and could impair their ability to produce resources essential for human survival and to regulate the concentration of atmospheric CO2. Published in...
Categories: Publication; Types: Citation, Journal Citation; Tags: Science
1 We examined the effects of patch disturbance leading to removal of conspecific neighbours, and of microsite type on the emergence, survival, and performance of seedlings of Bouteloua gracilis at a shortgrass steppe site. Our hypothesis was that the death and/or removal of a full-size B. gracilis plant, would result in increased availability of below-ground resources and thus promote the establishment of conspecific seedlings. 2 In 1990 and 1991, experimental plots were treated to mimic the effects of some common patch disturbance types. Caryopses were then planted into both plant microsites (i.e. located in the hummock formed by adult plants of B. gracilis) and bare soil. Seedlings were watered until they were...
Bromus tectorum, a successful and damaging exotic annual grass throughout the western U.S., has also been a successful invader of C3-C4 perennial grasslands located within the low elevation, open ponderosa pine forests of Colorado's Front Range. Successful invasion can result in replacing a perennial grassland, which is active throughout most of the growing season, with an annual grassland, which is active only from early fall through early summer of the following year. To date, the results of studies that attempt to document how B. tectorum invasion into perennial grasslands changes soil nutrient and carbon (C) pools have been mixed, perhaps because most studies do not control for (1) daily and/or seasonal variation...
Categories: Publication; Types: Citation, Journal Citation
The positive effect of disturbance on plant community invasibility is one of the more consistent results in invasion ecology. It is generally attributed to a coincident increase in available resources (due to the disturbance) that allows non-resident plant species to establish (Davis MA, Grime JP Thompson K, J Ecol 88:528?534, 2000). However, most research addressing this issue has been in artificial or highly modified plant communities. Our goal in this study was to investigate the interactive effects of resource availability and plant mortality disturbance on the invasion of natural plant communities. We conducted a series of experiments that examined the response of Bromus tectorum L., a highly invasive annual...
Question: What are the plant population- and community-level effects of removal of dominant plant species in the shortgrass steppe? Location: The Shortgrass Steppe Long-Term Ecological Research site in northern Colorado, USA. Methods: We annually measured plant cover and density by species for 10 years after a one-time aboveground removal of the dominant perennial grass, Bouteloua gracilis. Removal and control plots (3 m � 3 m) were within grazed and ungrazed locations to assess the influence of grazing on recovery dynamics. Our analyses examined plant species, functional type, and community responses to removal, paying special attention to the dynamics of subdominant and rare species. Results: Basal cover of B....