Climate Change and Forest Growth
Forests contain the majority of the earth's terrestrial carbon stocks. Changes in patterns of tree growth can have a huge impact on atmospheric cycles, biogeochemical cycles, climate change and biodiversity.
Recent studies have shown increases in biomass across many forest types. Although this increase has been attributed to climate change, without knowing the disturbance history of the forest (which is difficult in the commonly studied tropical primary forest stands or any stand with unknown age), growth could also be due to normal recovery from unknown disturbances. Using a unique data set of tree biomass collected over the past 22 years from 55 temperate forest plots with known land-use histories and stand ages ranging from five to 250 years, we estimated the background or ensemble rate of forest regeneration (Figure 1).
Soon after disturbance, the forest grows quickly before levelling off. 37 of these stands also had multiple censuses taken over varying intervals. When these rates of growth were estimated (Figure 2a), we found that recent biomass accumulation greatly exceeded the expected growth due to natural recovery (Figure 2b).
As our sites also have over a century of local weather measurements and 17 years of on-site atmospheric CO2, both showing consistent increases in line with globally observed climate change patterns, we can confidently attribute this recent rate change to shifts in local climate. Here we demonstrate that the changes in local temperature and CO2 that have been observed worldwide are fundamentally altering the rate of critical natural processes, as predicted by biogeochemical models. These results signal a pressing need to better understand the changes in growth rates in natural systems that will influence our understanding of current and future states of our atmosphere and biosphere.