Species relative abundance and aboveground biomass production driven by climate change and stand ageing

Abstract

Understanding forest communities’ responses to climate change is central to global change ecology research. Access to large data sets from government sources has enabled extensive examinations of the effects of climate change on the boreal forest of Canada. Despite the recent proliferation of studies on boreal forests’ responses to climate change, two major facets remain unexamined. First, although it is known that traits and species respond distinctly to climate change, whether these different responses have caused a compositional shift in tree communities is unknown. Second, whether the effects of local soil drainage properties alter the responses to climate change is unknown. A network of 1,711 permanent sample plots (PSPs) from across Alberta, Saskatchewan, and Manitoba, Canada, was used to determine whether tree community composition has shifted as a result of climate change, while controlling for the effect of endogenous processes related to stand ageing. Over the course of the last half-century, communities have shifted towards a higher prevalence of deciduous broadleaf and early-successional conifers at the expense of late-successional conifers. This shift to more productive species that are less susceptible to climate change has a negative feedback on anthropogenically-induced increases in atmospheric carbon dioxide. The increase in deciduous broadleaf species provides another negative feedback on climate warming through higher albedos and evapotranspiration. A similar network of 1,324 PSPs from across the three provinces was used to determine if local soil drainage altered the effect of climate change on net aboveground biomass change. Over the course of the study period, the effects of climate change on net aboveground biomass change were more pronouncedly negative for late-successional conifers, and to a lesser extent for deciduous broadleaf species on well drained than poorly drained sites. However, for drought-tolerant early-successional conifers, the negative effects of climate change were felt stronger on poorly drained than well drained sites. In summary, climate change has altered community composition in the boreal forest as the responses to climate change have differed with life-history traits and by species. The negative effects of climate change are most detrimental to late-successional conifers on well drained soils. The boreal forest has shifted towards more heavily populated by early-successional conifers on well drained sites, and a mixture of deciduous broadleaf and early-successional conifers on other sites, at the expense of late-successional conifers.