Stronger influence of anthropogenic disturbance than climate change on century-scale compositional changes in northern forests

Abstract

Predicting future ecosystem dynamics depends critically on an improved understanding of how disturbances and climate change have driven long-term ecological changes in the past. Here we assembled a dataset of >100,000 tree species lists from the 19th century across a broad region (>130,000km2) in temperate eastern Canada, as well as recent forest inventories, to test the effects of changes in anthropogenic disturbance, temperature and moisture on forest dynamics. We evaluate changes in forest composition using four indices quantifying the affinities of co-occurring tree species with temperature, drought, light and disturbance. Land-use driven shifts favouring more disturbance-adapted tree species are far stronger than any effects ascribable to climate change, although the responses of species to disturbance are correlated with their expected responses to climate change. As such, anthropogenic and natural disturbances are expected to have large direct effects on forests and also indirect effects via altered responses to future climate change.

Disturbances amplify tree community responses to climate change in the temperate–boreal ecotone

“…This suggests that the pattern we uncovered might be caused primarily by an increase in abundance of species already present rather than by new colonization. Danneyrolles et al () also found that forest compositional changes over the last centuries (between 1790–1900 and 1980–2010) in deciduous forests of southern Québec were largely driven by changes in land use, favouring more disturbance‐adapted tree species, but did not find any signs of thermophilization. In contrast to our study, which covers a period of pronounced climate warming, Danneyrolles et al () investigated a period dominated by changes in land use and population, which might explain the absence of thermophilization signal in their results.…”

“…Danneyrolles et al () also found that forest compositional changes over the last centuries (between 1790–1900 and 1980–2010) in deciduous forests of southern Québec were largely driven by changes in land use, favouring more disturbance‐adapted tree species, but did not find any signs of thermophilization. In contrast to our study, which covers a period of pronounced climate warming, Danneyrolles et al () investigated a period dominated by changes in land use and population, which might explain the absence of thermophilization signal in their results. In light of their results, we hypothesize that some of the thermophilization we reported here in the sugar maple domains is, in fact, the result of secondary succession after historical disturbances.…”

“…The interaction between climate and disturbances is likely to promote generalist tree species adapted to disturbances, with high dispersal abilities (Aubin et al, ). For instance, generalist species such as Acer spp., especially Acer rubrum , have been expanding in eastern North America since the pre‐industrial period (Boucher et al, ; Danneyrolles et al, ; Thompson, Carpenter, Cogbill, & Foster, ) and recently established themselves in boreal forests (Leithead et al, ; Sittaro et al, ) because they quickly take advantage from disturbances and thrive in a wide variety of ecological conditions. In contrast, some species limited by dispersal, such as Carya spp.…”

“…Leithead et al () also observed that the establishment of southern temperate species in the temperate–boreal ecotone of northern Ontario increased with the size and age of canopy gaps. Although Boisvert‐Marsh et al () found that climate change outweighs disturbances in explaining latitudinal shifts of tree saplings in Québec in the last decades, Danneyrolles et al () found larger impacts of anthropogenic disturbances than climate warming on forest compositional changes in southern Québec over the last centuries. Hence, to anticipate and adapt to future forest changes, large‐scale empirical studies are required in order to unravel individual and aggregated impacts of multiple stressors on forest composition.…”

Trait-based responses to land use and canopy dynamics modify long-term diversity changes in forest understories

“…1). Since the changes experienced by the field layer are further buffered by the canopy layer (De Frenne et al, 2019;Lembrechts et al, 2020) , and both canopies and understories have been shown to have small responses to climate change compared to land-use at decadal timescales (Danneyrolles et al, 2019;Tonteri et al, 2016) , the direct effect of climate change was left out of the models.…”