Brown world forests: increased ungulate browsing keeps temperate trees in recruitment bottlenecks in resource hotspots

Abstract

Plant biomass consumers (mammalian herbivory and fire) are increasingly seen as major drivers of ecosystem structure and function but the prevailing paradigm in temperate forest ecology is still that their dynamics are mainly bottom-up resource-controlled. Using conceptual advances from savanna ecology, particularly the demographic bottleneck model, we present a novel view on temperate forest dynamics that integrates consumer and resource control. We used a fully factorial experiment, with varying levels of ungulate herbivory and resource (light) availability, to investigate how these factors shape recruitment of five temperate tree species. We ran simulations to project how inter- and intraspecific differences in height increment under the different experimental scenarios influence long-term recruitment of tree species. Strong herbivore-driven demographic bottlenecks occurred in our temperate forest system, and bottlenecks were as strong under resource-rich as under resource-poor conditions. Increased browsing by herbivores in resource-rich patches strongly counteracted the increased escape strength of saplings in these patches. This finding is a crucial extension of the demographic bottleneck model which assumes that increased resource availability allows plants to more easily escape consumer-driven bottlenecks. Our study demonstrates that a more dynamic understanding of consumer-resource interactions is necessary, where consumers and plants both respond to resource availability.

Influence of canopy openness, ungulate exclosure, and low‐intensity fire for improved oak regeneration in temperate Europe

“…Though oaks are preferentially browsed by ungulates (Bergqvist, Wallgren, Jernelid, & Bergström, ), they are considered browsing tolerant because they can survive moderate browsing for extended periods (Harmer, ). However, browsing can severely limit height growth and high browsing pressure can prevent oak and other palatable tree species from advancing to the overstory (Churski, Bubnicki, Jedrzejewska, Kuijper, & Cromsigt, ; Rooney & Waller, ). We observed a trend indicating that protection from wild ungulate browsers positively affected oak recruit survival and RGR H .…”

Mesophication in temperate Europe: A dendrochronological reconstruction of tree succession and fires in a mixed deciduous stand in Białowieża Forest

“…Thus, we cannot out rule also other factors having impact on tree regeneration, including for example other plant consumers (i.e., browsing ungulates), as it has been proposed by earlier studies in BF (Churski, Bubnicki, Jędrzejewska, Kuijper, & Cromsigt, 2017;Kuijper, Jędrzejewska, et al, 2010b; see also the following discussion). Thus, we cannot out rule also other factors having impact on tree regeneration, including for example other plant consumers (i.e., browsing ungulates), as it has been proposed by earlier studies in BF (Churski, Bubnicki, Jędrzejewska, Kuijper, & Cromsigt, 2017;Kuijper, Jędrzejewska, et al, 2010b; see also the following discussion).…”

“…Besides fire, mammalian herbivory has been proven to be of crucial importance in shaping tree regeneration and hence forest composition, both in BF (Churski et al, 2017;Kuijper, Cromsigt, et al, 2010;Kuijper, Jędrzejewska, et al, 2010b) and worldwide (Côté, Rooney, Tremblay, Dussault, & Waller, 2004;Forrester, Lorimer, Dyer, Gower, & Mladenoff, 2014). The possible interacting effect of those two main consumers of plant biomass (Bond & Keeley, 2005) should be considered as well (cf.…”

“…Nowacki & Abrams, 2008). Hornbeam and lime can tolerate high levels of browsing due to their adaptive traits (Churski et al, 2017;Kuijper, Cromsigt, et al, 2010). Even though the palatability does not differ considerably among these species, oak and pine are more sensitive to browsing by ungulates than the latter species.…”

Land surface greening suggests vigorous woody regrowth throughout European semi‐natural vegetation

“…The relationship between temporal Leaf Area Index (LAI) change and time-series complexity. Herbivore suppression of woody plant growth(Churski, Bubnicki, Jedrzejewska, Kuijper, & Cromsigt, 2017) may also be responsible for LAI declines in northern Scandinavia, where intense reindeer grazing has been A single segment is a standard linear regression, while two linear segments indicate one abrupt break point in the LAI time-series.…”