Response of plant community abundance and diversity during 10 years of cattle exclusion within silvopasture systems

Abstract

The effects of cattle ( Bos taurus L.) grazing on upland plant communities in forested rangelands are poorly understood. Cattle interactions with plant communities were studied in intensively managed (precommercially thinned (PCT) and repeatedly fertilized) silvopasture systems in young lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forests. We investigated the response of plant community abundance and diversity to cattle grazing and how these responses were affected by PCT and repeated fertilization. The study was conducted inside and outside cattle exclosures over 10 years in two regional replicates in south-central British Columbia, Canada. PCT and repeated fertilization increased both the amount and quality of forage. Effects of cattle grazing on plant community abundance and diversity were variable and significantly influenced by the nutrient status of the site. In fertilized stands, cattle grazing increased species richness and diversity, particularly for the herb layer, although these treatment effects often took several years to be expressed. In unfertilized stands, cattle grazing did not significantly reduce herb or shrub volumes; however, species richness and, to a lesser extent, diversity of the shrub layer declined. In a landscape context, management strategies for silvopasture should promote heterogeneity for conservation of plant diversity through a variety of grazing pressures, as well as forest enhancement treatments such as PCT and repeated fertilization.

Influence of repeated fertilization and cattle grazing on forest ecosystems: Abundance and diversity of forest-floor small mammals

“…50-60 m 3 /0.01 ha appeared to trigger selection by cattle, which then resulted in the significant reduction in herb volume observed after 1996. As measured in this study and that of Lindgren and Sullivan (2012), cattle grazing did not significantly reduce volumes of herbs in unfertilized stands. Selection for fertilized stands was also suggested by cattle activity (inferred from abundance of fecal cowpies), which indicated that mean activity was 1.8 times higher in fertilized than unfertilized stands during the final five years of the study.…”

“…As forage opportunities were enhanced by fertilization treatments (i.e., increased abundance, palatability, and nutritive value), cattle grazing pressure also appeared to increase, which eventually lead to significant reductions in herb volume compared to exclosure plots. Lindgren and Sullivan (2012) suggested that stands with mean volumes of herbs greater than ca. 50-60 m 3 /0.01 ha appeared to trigger selection by cattle, which then resulted in the significant reduction in herb volume observed after 1996.…”

“…Stand thinning reduces shade and delays canopy closure, and hence may increase forage yields and prolong the silvopasture potential (Hall, 1988;Lindgren et al, 2006). In addition, the quality and quantity of forage produced within forest rangeland may be enhanced by fertilization (Freyman and van Ryswyk, 1969;Wikeem et al, 1993b;Lindgren and Sullivan, 2012). From a forest ecosystem perspective, positive biomass responses of understory vegetation have been reported for stand thinning (Crouch, 1986;Sullivan et al, 2001;Lindgren et al, 2006) and fertilization ( VanderSchaaf et al, 2000;Turkington et al, 2001).…”

“…This study is part of a large-scale and long-term project investigating the influence of PCT and repeated fertilization on timber and non-timber components of lodgepole pine ecosystems on the Okanagan Plateau in south-central British Columbia (BC), Canada (Sullivan et al, 2006b,c, 2010Lindgren et al, 2007;Lindgren and Sullivan, 2012). In addition, this region has a long history (1960s to present) of cattle grazing in early successional sites after forest harvesting.…”