NWT Accession Number: NWT2014
Understanding the factors that influence above-ground biomass (AGB) in subalpine forests is important for predicting the vulnerability of these ecosystems to variations in climate. Utilizing ten permanent forest plots containing >5000 tagged trees, we examined changes in tree diameter distribution, mortality, and AGB estimates from 1982 to 2016, to address the following questions: 1) How is change in stand-level tree biomass influenced by stand age, species composition, and initial stand structure? 2) How is change in stand-level tree biomass influenced by site-level differences in topoclimatic conditions which influence moisture availability? 3) How do changes in stand-level tree biomass reflect climate variability? In addition to a total 6.5% AGB gain across all permanent plots over the period of study, we found all stands were able to accrue biomass had they not been affected by disturbance. Sites not limited by moisture obtained the highest increases in AGB. The lack of annual census data made it difficult to interpret the response each variable had to climate. However, differentiating between expected successional trajectories of each variable and trends coinciding with climate variability allowed for ecologically meaningful interpretations. Overall, we found measures of tree population structures in all stands to be sensitive to climate variations. This was evident in the increase and subsequent decrease in tree mortality rates that coincided with increases and decreases in precipitation deficits. Hence, mortality rates increased in each successive mortality census (1982-1994, 1995-2007, 2008-2013) until the latest census period (2014-2016) when mortality rates show a decline in nearly all permanent plots, which corresponds with the increasing moisture deficits that lasted until 2011 followed by periods of higher precipitation.
sub alpine forest, biomass, species composition, topoclimate
This material is based upon work supported by the National Science Foundation under Cooperative Agreement #DEB-1637686. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necesarily reflect the views of the National Science Foundation.
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