Jeffrey S. Fehmi

Short- and Long-Term Vegetation Change Related to Grazing Systems, Precipitation, and Mesquite Cover

Abstract Rangeland scientists struggle with how long rangeland experiments must continue in order to detect treatment effects, particularly in semiarid ecosystems characterized by slow responses and high spatiotemporal variability. We compared changes in eight grass and three shrub categories to grazing systems (yearlong vs. seasonal rotation with equivalent long-term stocking rates), and covariates (precipitation and mesquite [Prosopis velutina] gradients) over 12 yr (1972–1984) and 34 yr (1972–2006) on the Santa Rita Experimental Range, Arizona. We used split-plot analysis of variance, with year as the split, to make these comparisons. Grazing systems did not influence plant dynamics as shown by the lack of grazing system by year effect on all response variables in either time period. The absence of a detectable grazing effect on vegetation changes may be due to overriding influences of grazing intensity, pasture size, precipitation variability, and few replicates. Also, more time may be needed to detect the small accumulating and potentially temporary effects from grazing systems. The grazing system main effects present at the beginning and throughout the study suggest that pastures assigned to each grazing system had different potentials to support vegetation. Nearly twice the number of response variables were related to the precipitation covariate than to mesquite cover, but only about half of all the relationships were consistent between time periods. The struggle to know how long to observe before detecting a grazing system effect was not resolved with the additional 22 yr of observation because we cannot definitively reject that either more time is needed to detect small but cumulative effects or that the two grazing systems are not different.

DETECTING CHANNEL MORPHOLOGY CHANGE IN CALIFORNIA'S HARDWOOD RANGELAND SPRING ECOSYSTEMS

Permanent channel cross-sectional transects perpendicular to flow were used to estimate changes in spring and resultant creek channel morphology. Three cattle grazing treatments (none, light, and moderate) were applied to 2-5 ha pastures containing a perennial spring and resultant creek cohort for 5 years. Grazing effects on the total change in channel morphology were not detected, nor did our method detect channel morphology change over the 5 year study period. Ungrazed springs and creeks were observed to change more than grazed springs and creeks although these differences were not statistically significant. Observed, but not significant, change over time appears related to rainfall patterns. Permanent channel cross-sections, one of the currently recommended methods for monitoring livestock grazing impacts on stream channek

Competitive Effect of Two Nonnative Grasses on a Native Grass in Southern Arizona

may not be adequate for detecting channel changes in low-flow spring/creek systems.

A note on using a laser-based technique for recording of behaviour and location of free-ranging animals

Abstract Invasive buffelgrass, potentially invasive natalgrass, and the native grass Arizona cottontop were evaluated for their competitive response to one another in southern Arizona. Targets and neighbors were transplanted in a full-factorial randomized complete-block design consisting of nine pairwise combinations and each species alone (n  =  120). Plant pairs were separated by 5 cm and allowed to grow during the 2007 monsoon season (101 d). Aboveground biomass, reproduction, and Arizona cottontop water-potential data were collected. Buffelgrass neighbors reduced aboveground biomass production and reproductive output significantly more than did intraspecific neighbors (P < 0.05), whereas natalgrass neighbors did not significantly affect Arizona cottontop biomass production or reproductive output (P > 0.05). Cottontop and buffelgrass had no significant effect on natalgrass biomass. Similarly, cottontop and natalgrass neighbors had no neighbor effect on the biomass of buffelgrass. Arizona cottontop plants that neighbored buffelgrass averaged a significantly lower water-potential value of −3.18 MPa (P < 0.05), compared with −1.17, −0.93, and −1.32 MPa for control plants (i.e., those with no neighbor), intraspecific neighbors, and natalgrass neighbors, respectively. Although buffelgrass competitive ability is consistent with its invasiveness when grown with native Arizona cottontop, natalgrass was an intermediate competitor. This suggests that natalgrass is less of a competitive threat to native perennial grasses than buffelgrass, but that it may be more tolerant to resource depletion (i.e., the presence of buffelgrass) relative to Arizona cottontop. Nomenclature: Arizona cottontop, Digitaria californica (Benth.) Henr.; Buffelgrass, Pennisetum ciliare (L.) Link; Natalgrass, Melinis repens (Wild.) Zizka.

Cattle grazing behavior with season-long free-choice access to four forage types

We developed a precise, remote (up to 300m) observation system to record animal location and behaviour that requires no animal handling or disruption of the normal environment. Our system, combining a survey laser and a laptop, also allows recording of observed animal behaviour from seconds to hours, with accuracy of 1m or better. Up to one individual per second can be located, which supports data collection of large numbers of animals not possible with other methods. The laser system was used to track a halter-broken heifer led in an arc beginning and ending about 50m from the laser with a maximum distance of about 150m. We recorded the location of the heifer at 35 points along the arc using the laser, a global positioning system (GPS), and a nylon tape. There was an average linear difference of 1.16m (S.D. 0.63) between the laser data and the GPS data. The laser was potentially more accurate than GPS for this application because the laser averaged only 0.21m (S.D. 0.24) linear difference from the tape. Tests of the laser to relocate points in the field to within 0.20m and 0.1 degrees, averaged 0.42m (S.D. 0.29) from the original points. Our technique allows precise location of behaviour and navigation to grazed sites, potentially revealing how animals interact with the resources they exploit and showing the effect of landscape spatial heterogeneity on foraging and habitat use patterns.

A grid‐based method for sampling and analysing spatially ambiguous plants

This experiment investigated how season-long, free-choice grazing affected weekly cattle grazing behavior and resource use. Our objectives were to determine if known forage preferences change through the season, if feedbacks from previous grazing intensity affect current use, and if resources such as water and salt in combination with a shorter forage base increase grazing time compared to previously rested pasture. Two replicate 24.4-ha grazing enclosures contained four forage types: smooth bromegrass (Bromus inermis), crested wheatgrass (Agropyron desertorum), western wheatgrass (Pascopyrum smithii) and native range. Each forage type was divided into three sub-areas containing either: a water source, a salt block, or forage deferred from use before the experiment (rested). Resource use was tracked with analysis of aerial photos of the pastures before and after the 3-year study and with weekly direct observation of animal use of each area of the pastures. As each season progressed, use of smooth bromegrass declined and use of crested wheatgrass and western wheatgrass increased. Use of native range remained relatively constant and low throughout the study. The previously rested sub-areas of the replicate pastures had significantly and substantially more grazing than those with salt or water. Significant auto-correlation in the data was well described by an auto-regressive parameter comprised of the sum of the previous 2 weeks grazing time, which showed gradual shifts in forage preference from 1 week to the next. Aerial photo analysis supported the findings of the behavioral data; preference between forage types changed over time, and grazing use within pastures was uneven and negatively correlated with salt and water sites. Cattle can rotate themselves among various pasture types if given free-choice; and season-long grazing may be an effective system if a variety of forage types are available.

The Effects of Livestock on California Ground Squirrels (Spermophilus beecheyii)

Spatial data can provide much information about the interrelations of plants and the relationship between indi- viduals and the environment. Spatially ambiguous plants, i.e. plants without readily identifiable loci, and plants that are profusely abundant, present non-trivial impediments to the collection and analysis of vegetation data derived from stan- dard spatial sampling techniques. Sampling with grids of presence/absence quadrats can ameliorate much of this diffi- culty. Our analysis of 10 fully-mapped grassland plots demon- strates the applicability of the grid-based approach which revealed spatial dependence at a much lower sampling effort than mapping each plant. Ripleys K-function, a test com- monly used for point patterns, was effective for pattern analy- sis on the grids and the gridded quadrat technique was an effective tool for quantifying spatial patterns. The addition of spatial pattern measures should allow for better comparisons of vegetation structure between sites, instead of sole reliance on species composition data.

Uprooted buffelgrass thatch reduces buffelgrass seedling establishment

Abstract Understanding the impacts of livestock grazing on wildlands is important for making appropriate ecosystem management decisions. Using livestock exclosures, we examined the effects of moderate cattle grazing on the abundance of California ground squirrels (Spermophilus beecheyii Richardson) and the spatial distribution of active burrows within their colonies in grassland and blue oak (Quercus douglasii Hook. & Arn.) savanna habitats in the coastal range of California over a 3-year period (1991–1994). Overall, relative population densities of California ground squirrels declined significantly throughout the experiment, but did not differ between grazed and ungrazed colonies or between habitats. There was also no significant interaction between these 2 factors. The spatial distribution of burrows, as measured by the mean nearest neighbor distance of active entrances within a colony, did not differ significantly between grazed and ungrazed colonies or between habitats, nor was the interaction significant. Thus, low to moderate levels of cattle grazing did not appear to have a strong effect on the population dynamics of California ground squirrels, and grazing may be compatible with maintenance of ground squirrel populations. Based on multivariate analysis of variance of 1994 data, live plant cover, native plant cover, and standing biomass were lower where the number of burrows was higher on grazed colonies but were little affected on ungrazed colonies. Ground squirrels may increase the impact of livestock grazing and thus reduce the capacity of the land to support other activities. However, it is clear that the effects of livestock grazing are complex and that detailed studies of potential mechanisms by which grazing impacts California ground squirrel populations are necessary.

Assessing Emergence of a Long-Lived Monocarpic Succulent in Disturbed, Arid Environments: Evaluating Abiotic Factors in Effective Agave Restoration by Seed

ABSTRACT Buffelgrass (Pennisetum ciliare (L.) Link), a non-native perennial bunchgrass, invades ecologically intact areas of the Sonoran Desert. It competitively excludes native plants and increases fire frequency and intensity. Since the 1990s, whole buffelgrass plants have been manually uprooted and removed to control the invasion in southern Arizona. Uprooting plants results in bare, disturbed soil which promotes buffelgrass seed germination. This study examined whether leaving entire uprooted buffelgrass plants (thatch) on a field site reduces future buffelgrass establishment compared to removing uprooted plants from the site. A secondary goal was to determine whether light reduction and autoallelopathy were major factors in the negative effect of thatch on buffelgrass seedling density. Field plots with an average of 8,095 kg/ha thatch had 1.9 buffelgrass seedlings/m2 which was significantly fewer than the 2.9 seedlings/m2 in plots without thatch. Thatched portions of thatch plots (50% of their total area) had only 0.7 seedlings/m2. In the greenhouse, which reduced outdoor light intensity by 35.2%, buffelgrass seeds sown in bare soil resulted in significantly higher seedling density than beneath buffelgrass thatch. Potential autoallelopathic chemicals leached from partially decomposed buffelgrass thatch and leached thatch had an intermediate but not significant (p = 0.09) effect on seedling numbers. Results suggest that leaving uprooted buffelgrass plants has the benefit of reducing seedling establishment in the area disturbed by uprooting.

Research Note: Alignment of elongated Nassella pulchra plants with hill-slope contours

Agave palmeri Engelmann is a semelparous perennial succulent thought to provide a critical food source for the endangered species, Leptonycteris curasoae Miller. Concern over impacts to existing A. palmeri populations has accelerated interest into reestablishing populations after disturbance. Little is known about its early life history and potential for restoration by seed in its arid habitat. In a greenhouse we measured emergence for 5.5 months across treatments with four variables: simulated precipitation (low: 170 mm, average: 285 mm, high: 390 mm), shade (present, absent), surface mulch (straw, gravel, bare soil), and soil type (sand, sandy loam, loamy sand). The highest emergence was associated with high simulated precipitation (33%), straw mulch (42%), shade (38%), and the loamy soils (mean: 30%). High simulated precipitation on shaded, straw mulched treatments had the highest overall emergence (63%). Lowest emergence involved low simulated precipitation (11%), bare soil (9%), absence of shade (10%), and sandy soil (10%). Low levels of simulated precipitation, combined with unshaded, bare soil treatments—conditions common in heavily disturbed arid environments—had zero seedling emergence. Our results indicate that microsite conditions play a crucial role in the emergence of this species, and manipulation of these conditions may significantly increase emergence, even when water availability is low. This is critical information for land managers attempting to recover populations, as duration and frequency of rainfall are characteristically variable in regions A. palmeri inhabits. Thus, the use of surface mulches and shade may effectively facilitate restoration in large-scale disturbances when unfavorable conditions cannot be controlled.