< Back  ||  Home > Reports

Forage Management

The Walker Basin Allotment (WBA) grazing system in central Arizona is designed to allocate resource use under elk (Cervus elaphus L.) and cattle (Bos taurus L.) grazing. The grazing system combines elements of rest-rotation and deferment to promote biologically acceptable levels of forage use by both elk and cattle. Seasonal cattle grazing is used to increase palatable regrowth, which is hypothesized to attract elk to recently grazed pastures, thereby resting part of the allotment from cattle and elk herbivory.

In phase one, detailed seasonal habitat maps were developed to predict population distribution and density using Landsat 7 data and NOAA-AVHRR satellite imagery. The relationship between spatial and temporal indices derived from remote-sensing data and actual forage consumption and use by both species is still in question, however. If indices derived using Landsat 7 data and NOAA-AVHRR satellite imagery and on-the-ground measures of forage quantity and quality are related, resource managers would have a science-based, economical method for evaluating rangeland conditions and for developing both short- and long-term land-use plans. The objectives of study are

1. to determine the relationship between on-the-ground measurements of forage use and indices developed during phase one, and
2. to determine whether the WBA grazing system is having the desired effect of balancing cattle and elk herbivory at 3 elevations where elk and cattle use may conflict (i.e., low-, mid-, and high-elevation).

Methods

Utilization And Stubble Height Methodology. We will use the paired-plot, height-weight, and stubble height techniques (Interagency Technical Reference 1996) to quantify production and use of several key forage species that grow in pastures at low-, mid-, and high-elevation zones where the potential for elk and cattle to interact occurs on the WBA.

Six, randomly-selected 3-ha sampling areas will be located in each elevation zone. Each sampling area will contain 6 paired-plot units consisting of 1 protected macroplot (1.7-m2 grazing exclosure), and two, 1.7-m2 unprotected macroplots, for a total of 108 protected and 216 unprotected plots across the 3 elevations. Unprotected and protected macroplots will be matched based on similar ocular estimates of key plant phytomass.

We will estimate forage use and stubble height in each pasture during 3 sampling periods: 1) immediately-before-cattle enter grazed pastures, 2) immediately-after-cattle exit grazed pastures, and 3) at the end of the growing season. Measurements made before cattle grazing will estimate relative elk use in all pastures. Measurements made immediately after cattle grazing will estimate relative cattle and/or elk use, while measurements made at the end of the growing season (mid-October) will estimate total forage use and production for the entire growing season (cattle and/or elk).

For each sampling period, 2 paired-plot units will be selected from each sampling area, and at least 1 key forage species will be clipped to ground level. Percentage use for a paired-plot unit will be the ratio of the mean unprotected and protected weights. We will also measure forage use and stubble height at 3-m intervals along the 400-m transects as described in the Interagency Technical Reference (1996: pg. 90). Mean forage use and stubble height for each from the 400-m transect will be calculated, and mean forage use and stubble height for each elevation will be calculated.

Fecal Collection And Analyses. On each occasion that forage use and stubble heights are measured, elk fecal pellet group data will be collected. In addition,10-20 current-year fecal samples will be gathered (10 pellets for elk and 10 ml from 18 beef cows) within each sampling area (Miller et al., 1994; Howery and Pfister 1990), and analyzed for fecal nitrogen and fecal phosphorus. Finally, microhistological analysis will be used to approximate relative diet composition for both cattle and elk.

Fecal microhistological analysis will be used to partition relative diet composition by forage class (e.g., grasses, forbs, and browse. Diet composition data will help us interpret fecal nutrient levels because secondary plant metabolites (e.g., phenolics) can elevate fecal nitrogen levels (Mould and Robbins, 1981).