Long-term influence of stand thinning and repeated fertilization on forage production in young lodgepole pine forests

Abstract

Integration of trees with forage and livestock production as silvopastoralism is another potential component of intensive forest management. Stand thinning and fertilization may enhance growth of crop trees and understory forage for livestock. We tested the hypothesis that large-scale precommercial thinning (PCT) (particularly heavy thinning to ≤1000 stems·ha−1) and repeated fertilization, up to 20 years after the onset of treatments, would enhance production of graminoids, forbs, and shrubs as cattle (Bos taurus L.) forage. Results are from two long-term studies: (1) PCT (1988–2013) and (2) PCT with fertilization (PCT–FERT) (1993–2013) of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stands in south-central British Columbia, Canada. Mean biomass estimates of graminoids, forbs, total herbs, and shrubs were not affected by stand density. However, fertilization enhanced mean biomass estimates of graminoids, forbs, and total herbs, but not shrubs. Thus, the density part of our hypothesis was not supported, but the nutrient addition part was supported at least for the herbaceous components. Biomass of the herbaceous understory was maintained as a silvopasture component for up to 20 years (stand age 13 to 33 years) in fertilized heavily thinned stands prior to canopy closure.

Influence of nitrogen fertilization on abundance and diversity of plants and animals in temperate and boreal forests

“…Longevity of effects of repeated fertilization on abundance and diversity of herbs and shrubs were reported from a long-term study in the interior of BC. At 6 and11 years after the last of five repeated fertilizer applications, mean abundance and mean species diversity of herbs and shrubs in fertilized stands had returned to levels recorded in unfertilized stands (Lindgren and Sullivan 2013b;Lindgren et al 2017). The persistence of a fertilization effect was not noted in this study as was reported for post-clearcut stands, that had been previously fertilized, in the boreal forest of Scandinavia (Olsson and Kellner 2006;Strengbom and Nordin 2008).…”

“…Resilience of vegetation is likely slower in boreal than temperate forests, as indicated by the longterm repeated fertilization study in the interior of BC. At 6 and11 years after the last of five repeated fertilizer applications, mean abundance and mean species diversity of herbs and shrubs in fertilized stands had returned to levels recorded in unfertilized stands (Lindgren and Sullivan 2017).…”

“…Declines in these food D r a f t sources were likely owing to changes in soil nutrients (mushrooms) and dramatic increases in abundance of grasses and fireweed (legumes). The common pattern of a shift in vegetation from dwarf shrubs and mosses-lichens to grasses and dominant herbs provided excellent habitat for voles of the genus Microtus (Boonstra et al 2001b;Sullivan et al 2012a;Sullivan and Sullivan 2014) in Canada and also Scandinavia (Ball et al 2000;Huitu et al 2012) (Table 5) This difference in numbers of red-backed voles between fertilized and unfertilized stands tended to disappear at years 15 (Sullivan et al 2013) and 20 (Sullivan and Sullivan 2017), 6 and 11 years, respectively, after the final treatment was conducted in 2002. Overall for small mammals, there were 6 positive, 15 neutral, and 6 negative responses to fertilization (Fig.…”

Over-yielding in temperate silvopastures: a meta-analysis

“…Twenty-two articles were included in the quantitative synthesis. Of the full-text articles assessed for eligibility, two were excluded because they did not include an open pasture control (Oswald et al 2017;Pearson and Baldwin 1993), a forest or timber plantation control (Silva-Pando et al 2002), or both (Debruyne et al 2011;Ares et al 2006;Lopez-Diaz et al 2009;Morris and Clason 1997;Perry et al 2009;Devkota et al 2009;Fernandez-Nunez et al 2014;Folkard et al 2012;Houx et al 2012;Lehmkuhler et al 1999;Lewis 1989;Lindgren and Sullivan 2014;Lindgren et al 2017) and no reasonable assumptions about the productivity of such controls were provided by the authors.…”