Journal Article

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

Poska, Anneli, Avel, Eve, Veski, Siim, Reitalu, Triin, Sugita, Shinya, Hammarlund, Dan, Heikkilä, Maija, Seppä, Heikki, Saarse, Leili, Vassiljev, Jüri, Kihno, Kersti, Koff, Tiiu, Renssen, Hans, Kangur, Mihkel

2013

Overview

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-CLIOVECODE climate model provided summer and winter temperature data. The modelled data were supported by sedimentary stable oxygen isotope (δ 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.

• Publisher: Blackwell Publishing Ltd,Blackwell Publishing,Blackwell,Wiley Subscription Services, Inc
• Subject: Agricultural land / Alnus / Animal and plant ecology / Animal, plant and microbial ecology / Anthropogenic impact / Betula / Biological and medical sciences / Boreal forests / Charcoal / Climate change / Climate models / Climatic data / Climatology / community history / Corylus / Deciduous forests / Earth and Related Environmental Sciences / Earth sciences / Earth, ocean, space / Estonia / Exact sciences and technology / forest composition / Forest ecology / Forestry / Forests / Fraxinus / Fundamental and applied biological sciences. Psychology / General aspects / General forest ecology / Generalities. Production, biomass. Quality of wood and forest products. General forest ecology / Geologi / Geology / Geovetenskap och relaterad miljövetenskap / Holocene / Human-environment relationship / Influences on — inferences from — composition / meta-analysis / millennial time-scale / Natural Sciences / Naturvetenskap / Oxygen isotopes / palaeoecology / Paleoclimatology / Paleontology / Paleontology: general / Permaculture / Picea / Pinus / Pollen / pollen data / Quercus / Relative abundance / Salix / Soil fertility / Statistical analysis / Synecology / Taxa / Tilia / Ulmus / variation partitioning / Vegetation