Net ecosystem productivity of boreal jack pine stands regenerating from clearcutting under current and future climates

Abstract

Life cycle analysis of climate and disturbance effects on forest net ecosystem productivity (NEP) is necessary to assess changes in forest carbon (C) stocks under current or future climates. Ecosystem models used in such assessments need to undergo well-constrained tests of their hypotheses for climate and disturbance effects on the processes that determine CO 2 exchange between forests and the atmosphere. We tested the ability of the model ecosys to simulate diurnal changes in CO 2 fluxes under changing air temperatures (T a ) and soil water contents during forest regeneration with eddy covariance measurements over boreal jack pine (Pinus banksiana) stands along a postclearcut chronosequence. Model hypotheses for hydraulic and nutrient constraints on CO 2 fixation allowed ecosys to simulate the recovery of C cycling during the transition of boreal jack pine stands from C sources following clearcutting (NEP from À150 to À200 g C m À2 yr À1 ) to C sinks at maturity (NEP from 20 to 80 g C m À2 yr À1 ) with large interannual variability. Over a 126-year logging cycle, annualized NEP, C harvest, and net biome productivity (NBP 5 NEP-harvest removals) of boreal jack pine averaged 47, 33 and 14 g C m À2 yr À1 . Under an IPCC SRES climate change scenario, rising T a exacerbated hydraulic constraints that adversely affected NEP of boreal jack pine after 75 years. These adverse effects were avoided in the model by replacing the boreal jack pine ecotype with one adapted to warmer T a . This replacement raised annualized NEP, C harvest, and NBP to 81, 56 and 25 g C m À2 yr À1 during a 126-year logging cycle under the same climate change scenario.

Simulating the Potential Effects of a Changing Climate on Black Spruce and Jack Pine Plantation Productivity by Site Quality and Locale through Model Adaptation

“…Additionally, temperature-induced increased rates of evapotranspiration and tree respiration [25] during the growing season may divert some of the photosynthate away from the production of new plant tissue. Inferences derived from physiological-based tree models have reported adverse climate change effects on jack pine arising from hydraulic limitations generated from temperature-induced vapour pressure deficits [26]. Similar site-specific effects were reported by Loustau et al [27] who found that climate effects on the productivity of forests in western Europe were greatest on the higher fertility sites.…”

“…These include the increased occurrence and severity of biotic (e.g., insect and disease [37]) and abiotic (e.g., wildfire [38]) impacts, increased rates of decomposition, unknown interactions between hydrological and biochemical cycles, and the CO 2 fertilization effect (e.g., [39]). Given the unknown impact of these effects on forest productivity and limitations of the statistical quasi-causal modeling approach [26], caution must be exercised when interpreting the predicted consequences of climate change.…”

Impact of forest harvesting on water quality and fluorescence characteristics of dissolved organic matter in eastern Canadian Boreal Shield lakes in summer

“…Many studies suggested that the most important processes to explain increases in DOC after forest harvesting was the rise in organic matter leaching from logging slash; the increase decomposition of organic logging residues and organic matter in the surface soils due to increased forest floor temperature and moisture; and a reduction in evapotranspiration causing an increase in runoff quantity leading to a higher water table favorable to the exportation of DOM from the surface and riparian soils (Qualls et al, 2000;Bishop et al, 2004;Kreutzweiser et al, 2008;Schelker et al, 2013b). However, the largest Cefflux from a forest floor is soil respiration, which has been shown to change as a result of forest disturbance (Grant et al, 2007). Leaching from logging slash or foliage and woody debris mixed to surface soils after forest harvesting could enrich water soil surface in organic components (Qualls et al, 2000).…”

Spatio-temporal patterns of forest carbon dioxide exchange based on global eddy covariance measurements

“…Nevertheless, patterns of inter-biome [15,18,25,26] or inter-annual [19,27,28] exchange of CO 2 between forest ecosystems and the atmosphere are not clear. Considerable uncertainties remain regarding C sink dynamics during forest succession [29,30] . Here, we synthesized published EC CO 2 flux measurements at various forest sites in the global network of eddy flux tower sites (FLUXNET) and regional flux networks.…”