MECHANISMS UNDERLYING PRODUCTION STABILITY IN TEMPERATE DECIDUOUS FORESTS

A persistent and reliable future terrestrial carbon (C) sink will depend on how stable forest production is under more variable climate conditions. We examined how age, forest structure, and disturbance history relate to the interannual variability of above-ground wood net primary production (NPPw). Our site in northern Michigan spans two experimental forest chronosequences and three late successional stands; the chronosequences have distinct disturbance histories, originating following either clear cut harvesting (“Cut Only”) or clear cut harvesting and fire (“Cut and Burn”), and range from 21 to 108 years old. Annual NPPw was estimated using dendrochronology and site specific allometric equations. We used a portable canopy LiDAR (PCL) system to derive canopy rugosity, a measure of the variability and heterogeneity of vertical and horizontal leaf arrangement, to quantify plot level canopy complexity. Counter to our hypothesis, we found that NPPw stability was greatest in the most frequently disturbed, Cut and Burn stands and lowest in less recently disturbed, late successional forest communities. Opposing trends in chronosequence interannual variation of NPPw indicated that stand age and canopy complexity are not consistently related to production stability. Furthermore, sub-canopy leaf trait properties and breadth were not, as hypothesized, correlated with canopy complexity or NPPw stability. Our mixed findings suggest that multiple factors, including stand age and disturbance history, interact to influence NPPw stability, but also highlight an unexpected dichotomy in which disturbance legacies at our site negatively impact the long-term trajectory of annual forest NPPw, but enhance its interannual stability