Observations and assessment of forest carbon dynamics following disturbance in North America

Abstract

Disturbance processes of various types substantially modify ecosystem carbon dynamics both temporally and spatially, and constitute a fundamental part of larger landscape‐level dynamics. Forests typically lose carbon for several years to several decades following severe disturbance, but our understanding of the duration and dynamics of post‐disturbance forest carbon fluxes remains limited. Here we capitalize on a recent North American Carbon Program disturbance synthesis to discuss techniques and future work needed to better understand carbon dynamics after forest disturbance. Specifically, this paper addresses three topics: (1) the history, spatial distribution, and characteristics of different types of disturbance (in particular fire, insects, and harvest) in North America; (2) the integrated measurements and experimental designs required to quantify forest carbon dynamics in the years and decades after disturbance, as presented in a series of case studies; and (3) a synthesis of the greatest uncertainties spanning these studies, as well as the utility of multiple types of observations (independent but mutually constraining data) in understanding their dynamics. The case studies—in the southeast U.S., central boreal Canada, U.S. Rocky Mountains, and Pacific Northwest—explore how different measurements can be used to constrain and understand carbon dynamics in regrowing forests, with the most important measurements summarized for each disturbance type. We identify disturbance severity and history as key but highly uncertain factors driving post‐disturbance carbon source‐sink dynamics across all disturbance types. We suggest that imaginative, integrative analyses using multiple lines of evidence, increased measurement capabilities, shared models and online data sets, and innovative numerical algorithms hold promise for improved understanding and prediction of carbon dynamics in disturbance‐prone forests.

On linking an Earth system model to the equilibrium carbon representation of an economically optimizing land use model

“…Most notably, carbon stocks were much more sensitive to LUC than were carbon fluxes. This result matches both theory (Odum, 1969) and a wide variety of field studies (Amiro et al, 2010;Goetz et al, 2012): stocks are by their nature integrative and accumulate relatively slowly compared to C flux changes. In contrast, the C flux variables were highly sensitive to climate effects but exhibited low sensitivity to LUC.…”

“…These data may be more vulnerable to LUC effects than carbon flux data, however, as fluxes typically recover much faster from disturbance than do the slower pools (Amiro et al, 2010;Goetz et al, 2012). Short-term changes in C fluxes can be analytically related to steady-state C pools in models, even in the presence of ecosystem disturbances .…”

Moderate forest disturbance as a stringent test for gap and big-leaf models

“…Not all disturbances, even of the same severity, equally affect biogeochemical processes that support recovery -for example, slow versus immediate tree death have very different consequences (Franklin et al, 1987). Our results suggest that some ecosystem models, developed to simulate processes following stand-replacing disturbances, may not simulate gradual death scenarios well (McDowell et al, 2013), specifically nonlinear or threshold responses of the carbon cycle in disturbance intensity (Goodrich-Stuart et al, 2015) over short timescales. Their skill over longer (decadal) periods remains an open ques-tion.…”

“…Natural and anthropogenic disturbances have numerous effects on the carbon (C) and energy dynamics in forested ecosystems and result in a variety of feedbacks between terrestrial ecosystems and climate (Goetz et al, 2012). In particular, disturbance-induced tree mortality is a key factor regulating the forest C balance but a complicated one due to high temporal and spatial heterogeneity (Vanderwel et al, 2013).…”

Attribution of divergent northern vegetation growth responses to lengthening non-frozen seasons using satellite optical-NIR and microwave remote sensing

“…HNL vegetation growth is primarily constrained by seasonal cold temperatures (Nemani et al 2003;Friedlingstein et al 2006;Qian, Joseph, and Zeng 2010), but recent reports indicate that widespread drought and wildfire disturbances exacerbated by continued warming have resulted in the frequent occurrences of tree mortality and declines in boreal productivity (Girardin and Mudelsee 2008;Goetz et al 2005;Peng et al 2011). Spatially extensive patterns of drought-induced vegetation growth decline have also been reported across the HNL domain (Goetz et al 2012;Kim et al 2012;Schaphoff et al 2006;Zhang et al 2008), including interior Alaska (Baird, Verbyla, and Hollingsworth 2012;Verbyla 2008), Canada (Ma et al 2012;Peng et al 2011), and Eurasia (Park and Sohn 2010;Piao et al 2011).…”