Abstract
Most North American forests are at some stage of post-disturbance regrowth, subject to a changing climate, and exhibit growth and mortality patterns that may not be closely coupled to annual environmental conditions. Distinguishing the possibly interacting effects of these processes is necessary to put short-term studies in a longer term context, and particularly important for the carbon-dense, fire-prone boreal forest. The goals of this study were to combine dendrochronological sampling, inventory records, and machine-learning algorithms to understand how tree growth and death have changed at one highly studied site (Northern Old Black Spruce, NOBS) in the central Canadian boreal forest. Over the 1999-2012 inventory period, mean tree diameter increased even as stand density and basal area declined significantly. Tree mortality averaged 1.4 ± 0.6% yr-(1), with most mortality occurring in medium-sized trees; new recruitment was minimal. There have been at least two, and probably three, significant influxes of new trees since stand initiation, but none in recent decades. A combined tree ring chronology constructed from sampling in 2001, 2004, and 2012 showed several periods of extreme growth depression, with increased mortality lagging depressed growth by ~5 years. Higher minimum and maximum air temperatures exerted a negative influence on tree growth, while precipitation and climate moisture index had a positive effect; both current- and previous-year data exerted significant effects. Models based on these variables explained 23-44% of the ring-width variability. We suggest that past climate extremes led to significant mortality still visible in the current forest structure, with decadal dynamics superimposed on slower patterns of fire and succession. These results have significant implications for our understanding of previous work at NOBS, the carbon sequestration capability of old-growth stands in a disturbance-prone landscape, and the sustainable management of regional forests in a changing climate.
Highlights
The interaction between ecosystem disturbance, vegetative succession, and carbon balance has been the subject of research for many decades (Odum, 1969; Pastor & Post, 1988; Heimann & Reichstein, 2008)
Net ecosystem production (NEP) in the ~100-year-old Harvard Forest has more than doubled in the last 18 years (Keenan et al, 2012); a similar trend was observed in the 150+ year Canadian boreal forest studied here (Dunn et al, 2006)
Recent syntheses of North American forests found no evidence for a decline in net ecosystem production (NEP) with age (Amiro et al, 2010)
Summary
The interaction between ecosystem disturbance, vegetative succession, and carbon balance has been the subject of research for many decades (Odum, 1969; Pastor & Post, 1988; Heimann & Reichstein, 2008). Analyses of global data such as atmospheric CO2 have provided further constraints on biome-level responses to climate (Randerson et al, 1999). These data have in turn been invaluable in drawing larger scale inferences about. Recent syntheses of North American forests found no evidence for a decline in NEP with age (Amiro et al, 2010). Such results suggest that old-growth forests could be global carbon sinks (Zhou et al, 2006; Luyssaert et al, 2008). The implications are significant, as forests sequester on the order of 10% of current fossil fuel emissions in the northern hemisphere alone (Goodale et al, 2002), and play a central role in the global carbon cycle (Pan et al, 2011a)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
