Reintroducing fire into a ponderosa pine forest with and without cattle grazing: understory vegetation response

Abstract

Abstract. Reestablishing historical fire regimes is a high priority for North American coniferous forests, particularly ponderosa pine (Pinus ponderosa) ecosystems. These forests are also used extensively for cattle (Bos spp.) grazing. Prescribed fires are being applied on or planned for millions of hectares of these forests to reduce fuel loads, alter forest structure, and maintain and enhance the productivity of native plant communities. However, cattle grazing is ubiquitous in ponderosa pine forests and the consequences of post-fire cattle grazing on plant communities are not well understood. We evaluated cattle grazing effects (grazing, no grazing) on upland bunchgrass and Carex geyeri dominated ponderosa pine plant communities over five growing seasons after prescribed fires (spring reburn, fall reburn, no burn). Vegetation was measured prior to a 5-year interval reburn and the subsequent exclusion of cattle, and in the second and fifth growing seasons thereafter. We found no interactions between reburning and grazing for the understory response variables. For all reburn treatments, including unburned areas, five growing seasons of cattle grazing exclusion significantly increased: (1) total vegetative cover, (2) native perennial forb cover, (3) grass stature, (4) grass flowering stem density, and (5) the cover of some shrub species and functional groups. Grazing exclusion did not strongly affect plant compositional patterns, although differences were detected. Compared to unburned areas, neither spring nor fall reburning increased perennial native species cover or richness, and reburning reduced sedge cover. Fall reburning increased cover of native colonizers, and exotic species cover and richness (largely Bromus tectorum and Cirsium vulgare), although overall exotic cover remains low (,1%). We document several potentially chronic impacts of cattle grazing in both burned and unburned areas, and show that the understory release from a long history of cattle grazing caused a greater degree of change than the initial reintroduction of fire. If a goal of ecological restoration in these forests is increased cover of native perennial plants, and the potential for increased native perennial grass reproduction, then cattle grazing exclusion, or a change in cattle management, could provide critically important options in restoration plans.

Increasing weight of evidence that thinning and burning treatments help restore understory plant communities in ponderosa pine forests

“…For example, unsatisfactory gains in cover and richness on more mesic sites might indicate further overstory manipulations are required to create openings and reach a basal area of $6 m 2 ha À1 , a threshold below which understory communities have been shown to respond (Sabo et al, 2008). Additionally this might suggest testing seeding as an additional treatment, or help managers decide whether grazing should be reduced or deferred for a period of time (Kerns et al, 2011).…”

Role of season and interval of prescribed burning on ponderosa pine growth in relation to soil inorganic N and P and moisture

“…Nitrogen mineralization rates may also be affected by higher soil moisture and temperature, which occurred on the fall burn treatments but not the spring burn treatments. There are at least two N fixing species at this site: L. caudatus and C. velutinus (Kerns et al, 2011). L. caudatus is a perennial forb which as a class accounted for less than 7% of the cover across all treatments (no significant differences among control, fall-5, or spring-5 treatments).…”

“…These initial burns had the highest severity compared to the second burn likely due to high fuel loading. As a result of the second fire, fuels were reduced 23-25% with significant reductions in the O horizon, 10-h, and 100-h fuels (Kerns et al, 2011). Both fall and spring prescribed burning had an effect on fuels on these sites.…”

Effect of season and interval of prescribed burn on ponderosa pine butterfly defoliation patterns

“…Ponderosa pine trees in the study area are approximately 80-100 years old with infrequent individuals of about 200 years old (Emigrant Creek Ranger District, unpublished data). Understory species composition varies among the sites (Kerns et al 2006(Kerns et al , 2011, but P. ponderosa/Pseudoroegneria spicatum (Pursh) Á. Löve and P. ponderosa/ Carex geyeri Boott are the major plant associations. Each stand was thinned in 1994 or 1995.…”

“…Each stand was thinned in 1994 or 1995. More extensive details on the study area and the experiment can be found in Thies et al (2005Thies et al ( , 2006; and Kerns et al (2006Kerns et al ( , 2011.…”