Prescribed fire effects on resource selection by cattle in mesic sagebrush steppe. Part 2: Mid-summer grazing
Highlights
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- Beef cows were tracked with GPS for 2 yrs prefire and up to 5 yrs postfire on sagebrush steppe.
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- A resource selection function accurately predicted prefire and postfire cattle use.
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- Elevation, slope, NDVI standard deviation, and distance to upland water sources were the primary drivers of prefire cattle use.
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- Prefire cattle selectivity was neutral towards areas later burned.
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- Cattle selected for burned areas during 3 of the 4 postfire years evaluated.
Abstract
Prescribed
fire can release herbaceous forages from woody plant competition thus
promoting increased forage plant production, vigor, and accessibility.
Prescribe fire also consumes standing litter thereby improving forage
quality and palatability. Consequently, prescribed fire is commonly
considered an effective tool for manipulating livestock distribution on
rangelands. Efficacy of this tool on mesic sagebrush steppe, however,
has received little research attention. Beginning in 2001, resource
selection by beef cows under a mid-summer (July) grazing regime was
evaluated using global positioning system (GPS) collars for 2 years
prior to and for up to 5 years after a fall prescribed fire was
conducted on mesic sagebrush steppe in the Owyhee Mountains of
southwestern Idaho, USA. Cattle selected for burned areas during the
first, second, and fifth postfire years. Cattle had exhibited neutral
selectivity towards these areas, during one of the two prefire years.
Burning in the uplands reduced cattle use of near-stream habitats but
only during the second postfire year. Differences in phenological timing
of grazing may account for differences in cattle response to burning
noted between this study and one conducted nearby under a spring (May)
grazing regime. This is a case study and caution should be taken in
extrapolating these results.
Keywords
- Burning;
- GPS tracking;
- Livestock distribution;
- Modeling;
- Rangeland improvement;
- Riparian use
1. Introduction
Fire plays an important ecological role as a disturbance agent which promotes successional cycling (Christensen, 1985, Keane et al., 2004 and Turner et al., 1997). Many woody plant species are killed or reduced by fire. Western juniper (Juniperus occidentalis
Hook.) is one such species and fire serves to control the extent of
this invasive native plant and its encroachment into sagebrush steppe
rangelands ( Burkhardt and Tisdale, 1976 and Miller and Rose, 1999). Burning of shrubs and/or trees also releases associated herbaceous plants from woody competition ( Bates et al., 2011, Miller et al., 2000 and Wrobleski and Kauffman, 2003). Fire consumes standing litter accumulations in herbaceous plants, often without unduly compromising plant vigor ( Willms et al., 1980a).
Removal of standing litter from forage species like bunchgrasses can
increase nutritional quality and palatability to grazing wildlife and
livestock ( Cook et al., 1994, Hobbs and Spowart, 1984, Willms et al., 1980a, Willms et al., 1980b, Willms et al., 1981 and Young and Miller, 1985).
Exotic plant invasions, poorly-managed livestock grazing, and wildfire
suppression, however, have drastically altered the historic fire regimes
on many rangelands of the world ( Brooks et al., 2004 and D'Antonio and Vitousek, 1992). While some systems, like those converted to exotic annual grasslands, now have too much fire ( Brooks et al., 2004), others often have too little (e.g., higher-elevation, mesic sagebrush steppe; Miller and Rose, 1999).
In the later case, in the absence of fire, fuels have accumulated to
excessive and hazardous levels. Stands of shrubs and trees have become
exceptionally dense and decadent. Competition from these woody plants
and physical obstruction by their canopies have depressed the presence,
vigor, and/or production of herbaceous forage plants and reduced forage
accessibility to wildlife grazers and livestock ( Miller et al., 2000).
Consequently, there is a critical need on many rangelands, where fire
has been wrongly excluded, to re-establish an appropriate fire cycle.
Hazardous fuel accumulations and proximity to human settlement,
infrastructure, or valuable commodities (e.g., flammable crops or
timber); however, commonly prohibit the use of “let-burn” wildfire
management policies on these rangelands. Fortunately, it is often
possible to use carefully-managed, prescribed fire as a safe and
effective means of re-initiating and/or maintaining an appropriate fire
cycle.
Prescribe fire can
promote increased forage production, quality, and palatability while
also opening up new foraging areas where wildlife and livestock grazing
was previously excluded by dense shrub canopy (Cook et al., 1994, Davies et al., 2012, Hobbs and Spowart, 1984, Willms et al., 1980a, Willms et al., 1981 and Young and Miller, 1985).
Research in a number of rangeland ecosystems; including montane and
prairie grasslands, shrub steppe, and savanna, have demonstrated
prescribed burns are highly attractive to grazing animals and, in some
cases, can be used to manipulate animal distribution (Augustine et al., 2010, Bates et al., 2009, Hobbs and Spowart, 1984, Klop et al., 2007, Peek et al., 1979, Van Dyke and Darragh, 2007 and Vermeire et al., 2004).
As such, it is reasonable to hypothesize prescribed burning could be
used to manage cattle resource-selection patterns on sagebrush-steppe
rangelands.
The
sagebrush-steppe ecosystem occurs on about 44.4 million ha of western
North America. A higher-elevation, more mesic portion of this ecosystem
is dominated by mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyanna Beetle), with antelope bitterbrush (Purshia tridentata [Pursh] DC) and/or mountain snowberry (Symphoricarpos oreophilus
A. Gray) often occurring as co-dominants. The mesic sagebrush steppe
represents a considerable proportion of the sagebrush-steppe ecosystem
and is a principal habitat of many wildlife species, some of which are
threatened or endangered (e.g., greater sage-grouse [Centrocercus urophasianus
Bonaparte]. Mesic sagebrush steppe is also important livestock grazing
land in several western regions. The ability of exotic annual grasses,
such as cheatgrass (Bromus tectorum L.) and medusahead (Taeniatherum caput-medusae
[L.] Nevski) to invade and, through repeated burning, convert sagebrush
steppe into annual grassland is a considerable threat in the drier,
lower-elevation portions of the sagebrush-steppe ecosystem ( Brooks et al., 2004; Chambers et al., 2007).
Mesic sagebrush-steppe rangelands, however, are currently much less
susceptible to exotic annual grass conversion. Mesic sagebrush steppe is
susceptible, however, to invasion by native woody plants like western
juniper ( Burkhardt and Tisdale, 1976, Miller and Rose, 1999 and Miller and Wigand, 1994).
Long-term absence of fire can promote conversion from mesic sagebrush
steppe to juniper woodland which can often have adverse consequences to
rangeland hydrology, soil stability, wildlife habitat, and livestock
grazing ( Noson et al., 2006, Pierson et al., 2010, Pierson et al., 2013 and Wall et al., 2001).
While
prescribed fire is widely considered to be an effective tool for
controlling western juniper encroachment in the mesic sagebrush steppe,
claims about its efficacy for also managing livestock distribution have
received comparatively little research attention. It has been found;
however, under a spring (May) grazing regime, that fall prescribed fire
in mesic sagebrush steppe can promote increased use of burned areas by
cattle for up to 5 years postfire (Clark et al., 2014).
The longevity of this cattle resource-selection response to fire is
quite unprecedented even in other rangeland types. The phenological
timing of grazing, however, may influence both, the efficacy of
prescribed fire for manipulating cattle distribution and the longevity
of this effect. In addition, site factors including slope, distance to
water, and vegetation composition and structure affect cattle
distribution and may interact with or cancel out fire-related effects (Bailey, 1995, Bailey, 2005, Cook, 1966, Ganskopp, 2001, Ganskopp and Vavra, 1987, Howery et al., 1996, Howery et al., 1998, Loza et al., 1992, Mueggler, 1965, Pinchak et al., 1991, Roath and Krueger, 1982 and Senft et al., 1985).
As such, additional research was required to investigate the efficacy
of fall prescribed fire for manipulating cattle resource-selection
patterns under different site conditions and grazing regimes (e.g.,
mid-summer [July] grazing) than those used by Clark et al. (2014).
Objectives
of this study were to: i) Evaluate whether fall prescribed fire
affected cattle resource-selection patterns under a mid-summer (July)
grazing regime; ii) if fire effects on cattle resource selection were
detected, determine how long these effects persisted postfire; and iii)
compare and contrast findings with those obtained by Clark et al. (2014).
This study was conducted within the scope of a larger research project
intended to evaluate spatiotemporal effects of prescribed fire on
resource selection, activity budgets, and movement path characteristics
of beef cattle in mesic sagebrush-steppe rangelands. A series of 3
papers was the intended product from this project with Clark et al. (2014)
being the first paper in the series, the present paper on mid-summer
resource selection as the second, and a third paper on cattle activity
budget and movement path responses to prescribed fire is in preparation.
2. Methods
2.1. Study area
The
study was conducted at the Breaks study area (176 ha), a fenced
rangeland pasture within the Reynolds Creek Experimental Watershed (43°
6′ 29″ N, 116° 46′ 37″ W) located 80 km south of Boise in southwestern
Idaho (Fig. 1).
Climate is continental with maritime influences. Winters are cold and
wet while summers are warm and dry. Long-term (1966–1975, 2002–2013)
mean annual precipitation at the Breaks gauges (145) was 588 mm (NWRC, 2014) with typically about 1/3 of the precipitation occurring as snow (Hanson, 2001).
Annual precipitation during the study (2001–2007) varied from a low of
421 mm in 2002, 463 mm in 2007, 542 mm in 2003, 543 mm in 2004, 655 mm
in 2006, and a high of 773 mm in 2005. Precipitation data from the
Breaks gauges was not available for 2001, but data from the nearby
Tollgate gauges (116c) indicated precipitation in 2001 was below the
long-term mean (1962–2013) for Tollgate (NWRC, 2014).
The growing season is about 100 days in length but frost can occur
during any month of the year. Long-term (1967–2010) mean daily maximum,
minimum and mean air temperatures at the nearby Lower Sheep Creek
weather station (127 × 07) were 12.7, 3.8, and 8.3 °C, respectively (Hanson et al., 2001 and NWRC, 2014).
Mean daily air temperature varied during the study from a low of 8.3 °C
in 2002, 8.6 °C in 2005, 8.7 °C in 2001, 8.8 °C in 2004 and 2006;
9.4 °C in 2003, and a high of 9.6 °C in 2007. Note that mean annual air
temperatures for all study years, except 2002, were warmer than
long-term mean.
- Fig. 1.A map (left) illustrating the dominant prefire vegetation (6 types) which occurred at the Breaks prescribed fire study area (176 ha) in the Owyhee Mountains of southwestern Idaho. This map (left) also includes an overlay of elevation contours (5-m intervals) illustrating study area topography. A second map (right) displaying Normalized Difference Vegetation Index (NDVI) or vegetation greenness values throughout the study area. The map on the right also illustrates the distribution of fire severity (4 classes) which occurred as a result of the Breaks prescribed fire (34 ha) on 24 September 2002.
Topography
of the study area is an east-facing hillslope ranging from 1547 to
1761 m in elevation. Slope ranges from flat to very steep (107.5% or
47.1° maximum) with aspects in all four cardinal directions well
represented. Soils are primarily derived from granitic parent materials
and composed of a complex of Takeuchi (coarse, loamy, mixed, frigid
Typic Haploxerolls) and Kanlee (fine, loamy, mixed, frigid Typic
Argixerolls) soil series (Seyfried et al., 2001).
Three
vegetation cover types; including mountain big sagebrush – mountain
snowberry, antelope bitterbrush – mountain big sagebrush, and native
bunchgrass types, dominate the study area as they do in the mid- and
higher-elevation portions of the sagebrush steppe throughout much of the
Intermountain West (Fig. 1).
Besides the 2 dominant species, the mountain big sagebrush-mountain
snowberry type includes western juniper, yellow rabbitbrush (Chrysothamnus viscidiflorus [Hook.] Nutt.), Saskatoon serviceberry (Amelanchier alnifolia [Nutt.] Nutt. ex M. Roem. alnifolia), bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. L
ve), Sandberg bluegrass (Poa secunda J. Presl.), squirreltail (Elymus elymoides [Raf.] Swezey), Idaho fescue (Festuca idahoensis Elmer), basin wildrye (Leymus cinereus [Scribn. & Merr.] A. Love), mountain brome (Bromus marginatus Nees ex Steud.), tapertip hawksbeard (Crepis acuminata Nutt.) and western aster (Symphyotrichum ascendens
[Lindl.] Nesom). Other components of the antelope bitterbrush-mountain
big sagebrush type include western juniper, native bunchgrasses, and
biscuitroots (Lomatium spp. Raf.). When contrasted,
the mountain big sagebrush-mountain snowberry type generally had the
more herbaceous cover, both in the interspaces and under the shrub
canopy than the antelope bitterbrush-mountain big sagebrush type (Clark
unpublished data). Bluebunch wheatgrass, Sandberg bluegrass,
squirreltail, Idaho fescue, and needlegrasses (Achnatherum spp.
Beauv.) dominate the native bunchgrass cover type. Cheatgrass has a
minor to common presence in all three of these dominant vegetation
types.
ve), Sandberg bluegrass (Poa secunda J. Presl.), squirreltail (Elymus elymoides [Raf.] Swezey), Idaho fescue (Festuca idahoensis Elmer), basin wildrye (Leymus cinereus [Scribn. & Merr.] A. Love), mountain brome (Bromus marginatus Nees ex Steud.), tapertip hawksbeard (Crepis acuminata Nutt.) and western aster (Symphyotrichum ascendens
[Lindl.] Nesom). Other components of the antelope bitterbrush-mountain
big sagebrush type include western juniper, native bunchgrasses, and
biscuitroots (Lomatium spp. Raf.). When contrasted,
the mountain big sagebrush-mountain snowberry type generally had the
more herbaceous cover, both in the interspaces and under the shrub
canopy than the antelope bitterbrush-mountain big sagebrush type (Clark
unpublished data). Bluebunch wheatgrass, Sandberg bluegrass,
squirreltail, Idaho fescue, and needlegrasses (Achnatherum spp.
Beauv.) dominate the native bunchgrass cover type. Cheatgrass has a
minor to common presence in all three of these dominant vegetation
types.
Cattle had access to
two perennial streams, Reynolds Creek and Dobson Creek, while in the
study area. The riparian zones of both streams were dominated by a black
cottonwood (Populus balsamifera L. ssp. trichocarpa [Torr. & A. Gray ex Hook.] Brayshaw) overstory, a peachleaf willow (Salix amygdaloides Andersson), redosier dogwood (Cornus sericea L. ssp. sericea), and rose (Rosa woodsii Lindl.) shrub layer, and a sedge (Carex spp.) and Kentucky bluegrass (Poa pratensis L.) understory. Small, dry meadows typically less than 0.25 ha in size and dominated by Kentucky bluegrass and rushes (Junus spp.) where located on the stream terrace and in upland swales. Willow (Salix spp.), quaking aspen (Populus tremuloides
Michx.), and black cottonwood occurred as occasional, small clumps or
groves (0.001–1 ha) near upland surface-water sources and in other
upland areas where the water table was shallow. Occasional, small groves
(1–2 ha) of Douglas-fir trees (Pseudotsuga menziesii [Mirb.] Franco) occurred in the southern end of the study area where the elevation was highest.
