Can we set a global threshold age to define mature forests?

, , , , ,
1 Centre for Conservation Ecology and Environmental Science, Bournemouth University, Bournemouth, United Kingdom
2 Center for Macroecology and Evolution, University of Copenhagen, Copenhagen, Denmark
3 School of Life Science, University of Sussex, Brighton, United Kingdom
4 School of Science and the Environment, Manchester Metropolitan University, Manchester, United Kingdom
5 School of Environment, Natural Resources and Geography, Bangor University, Bangor, United Kingdom
6 School of Geography, Queen Mary University of London, London, United Kingdom
7 Department of Geography, University of Victoria, Victoria, British Columbia, Canada
DOI
10.7287/peerj.preprints.1474v1
Published
Accepted
Subject Areas
Biodiversity, Conservation Biology, Ecology, Ecosystem Science
Keywords
biomass, forest, succession, climate, mature forest, carbon, sucession, secondary forest
Copyright
© 2015 Martin et al.
Licence
This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ PrePrints) and either DOI or URL of the article must be cited.
Cite this article
Martin P, Jung M, Brearley FQ, Ribbons R, Lines ER, Jacob AL. 2015. Can we set a global threshold age to define mature forests? PeerJ PrePrints 3:e1474v1

Abstract

Globally mature forests appear to be increasing in biomass density. There is disagreement whether these increases are the result of increases in CO2 concentrations or a legacy effect of previous land-use. Recently, it was suggested that a threshold of 450 years should be used to define mature forests and that many forests increasing in biomass may be younger than this. However, the study making these suggestions failed to account for interactions between forest age and climate. Here we revisit the issue to identify: (1) how climate and forest age control global forest biomass density and (2) whether we can set a threshold age for mature forests. Using data from previously published studies we modelled the impacts of forest age and climate on biomass density using linear mixed effects models. We examined the potential biases in the dataset by comparing how representative it was of global mature forests in terms of its distribution, the climate space it occupied and the ages of the forests used. Biomass density increased with forest age, mean annual temperature and annual precipitation. Importantly the effect of forest age increased with increasing temperature, but the effect of precipitation decreased with increasing temperatures. The dataset was biased towards Northern hemisphere forests in relatively dry, cold climates. The dataset was also clearly biased towards forests <250 years of age. Our analysis suggests that there is not a single threshold age for forest maturity. Since climate interacts with forest age to determine biomass density a threshold age at which they reach equilibrium can only be determined locally. We caution against using biomass as the only determinant of forest maturity since this ignores forest biodiversity which often takes longer to recover. Future study of the influence of climate on forest biomass should aim to use the data currently being generated by long-term monitoring networks and satellite based observations.

Author Comment

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Supplemental Information

Data used for analyses

Biomass data used for analyses in this manuscript

DOI: 10.7287/peerj.preprints.1474v1/supp-1