Long‐term drivers of forest composition in a boreonemoral region: the relative importance of climate and human impact

Abstract

Aim To assess statistically the relative importance of climate and human impact on forest composition in the late Holocene.Location Estonia, boreonemoral Europe.Methods Data on forest composition (10 most abundant tree and shrub taxa) for the late Holocene (5100-50 calibrated years before 1950) were derived from 18 pollen records and then transformed into land-cover estimates using the REVEALS vegetation reconstruction model. Human impact was quantified with palaeoecological estimates of openness, frequencies of hemerophilous pollen types (taxa growing in habitats influenced by human activities) and microscopic charcoal particles. Climate data generated with the ECBilt-CLIO-VECODE climate model provided summer and winter temperature data. The modelled data were supported by sedimentary stable oxygen isotope (d 18 O) records. Redundancy analysis (RDA), variation partitioning and linear mixed effects (LME) models were applied for statistical analyses.Results Both climate and human impact were statistically significant predictors of forest compositional change during the late Holocene. While climate exerted a dominant influence on forest composition in the beginning of the study period, human impact was the strongest driver of forest composition change in the middle of the study period, c. 4000-2000 years ago, when permanent agriculture became established and expanded. The late Holocene cooling negatively affected populations of nemoral deciduous taxa (Tilia, Corylus, Ulmus, Quercus, Alnus and Fraxinus), allowing boreal taxa (Betula, Salix, Picea and Pinus) to succeed. Whereas human impact has favoured populations of early-successional taxa that colonize abandoned agricultural fields (Betula, Salix, Alnus) or that can grow on less fertile soils (Pinus), it has limited taxa such as Picea that tend to grow on more mesic and fertile soils.Main conclusions Combining palaeoecological and palaeoclimatological data from multiple sources facilitates quantitative characterization of factors driving forest composition dynamics on millennial time-scales. Our results suggest that in addition to the climatic influence on forest composition, the relative abundance of individual forest taxa has been significantly influenced by human impact over the last four millennia.

From broadleaves to spruce – the borealization of southern Sweden

“…This process of borealization has received significant attention in countries experiencing this transition, both with respect to the long-term underlying processes which span the majority of the Holocene (Berglund 1969;Tallantire 1977;Giesecke & Bennett 2004;Latalowa & van der Knaap 2006;Seppä et al 2009;Tallavaara & Seppä 2012;Reitalu et al 2013), as well as the shorter term anthropogenic drivers (Östlund et al 1997;Emmer et al 1998;Lagerås 2007;Niklasson et al 2010;Lindbladh et al 2011;Terauds et al 2011;Cui et al 2013).…”

Contrasting tree‐ring growth response of picea abies to climate variability in western and eastern estonia

“…This species is the latest of major arboreal taxa to immigrate to Estonia after the ice age, known to have spread from the southeast around 8000 years ago (Saarse et al 1999). These geographical patterns have been related both to calcareous and shallow soils (Laasimer 1965) and maritime climate in the coastal areas, envisaged less suitable for spruce, in comparison to southern areas characterised by deeper soils on sandstone and clay (Reitalu et al 2013). Since the spruce maximum around 4000 years ago, the forests in southern and eastern areas of the country have either remained spruce dominated or turned into dominance of pine, birch and willow.…”

“…The risk may materialise in Estonian forests where the growth processes of Norway spruce depend mostly on summer moisture conditions (Läänelaid and Eckstein 2012;Läänelaid et al 2015). We anticipate that delineating the spatial patterns in this response and portraying its relative strength in different parts of Estonia should guide the predictions of biomass production and forest damage, while also helping to bridge the gaps between the forestry, plant ecology and palaeoecology disciplines (Mandre et al 1996;Nilson et al 1999;Reitalu et al 2013Reitalu et al , 2014, thus addressing the questions of past and future spruce forests in this country. We anticipate that delineating the spatial patterns in this response and portraying its relative strength in different parts of Estonia should guide the predictions of biomass production and forest damage, while also helping to bridge the gaps between the forestry, plant ecology and palaeoecology disciplines (Mandre et al 1996;Nilson et al 1999;Reitalu et al 2013Reitalu et al , 2014, thus addressing the questions of past and future spruce forests in this country.…”

Holocene fire in Fennoscandia and Denmark

“…Prior to 3500 cal years BP, the human population was largely controlled by environmental factors (Tallavaara and Seppä 2012). The establishment and expansion of agriculture enabled population growth, and human influence is estimated as the strongest driver of forest compositional change (Reitalu et al 2013). The anthropogenic use of fire intensified in conjunction with slash-and-burn activity driven by swidden cultivation and animal husbandry (e.g.…”