Effets combinés de l’éclaircie et des feux prescrits sur les budgets de carbone et de nutriments

Abstract

-• Both burning and harvesting cause carbon and nutrient removals from forest ecosystems, but few studies have addressed the combination of these effects. For a Pinus jeffreyii forest in the Sierra Nevada Mountains of California, we posed the question: what are the relative impacts of thinning and subsequent burning on carbon and nutrient removals?• The thinning methods included whole-tree thinning (WT, where all aboveground biomass was removed) cut to length (CTL, where branches and foliage were left on site in a slash mat on top of skid trails) and no harvest (CONT). Total C and nutrient exports with thinning and burning were greater in the WT and CTL than in the CONT treatments. Total C and N removals were approximately equal for the WT and CTL treatments, although harvesting dominated exports in the WT treatment and burning dominated exports in the CTL treatment. Total removals of P, K, Ca, Mg and S were greatest in the WT treatments, where harvesting dominated removals.• Comparisons of nutrient removals with ecosystem capital and calculations of potential replenishment by atmospheric deposition suggested that N is the nutrient likely to be most depleted by harvesting and burning treatments.harvesting / prescribed fire / nutrients / Pinus jeffreyii / Sierra Nevada Mountains Résumé -Effets combinés de l'éclaircie et des feux prescrits sur les budgets de carbone et de nutriments.• L'un et l'autre, le brûlage et les récoltes, causent un enlèvement important de carbone et de nutriments dans les écosystèmes forestiers, mais peu de travaux se sont attelés à l'étude de la combinaison de ces effets. Pour une forêt de Pinus jeffreyii nous posons la question suivante : quels sont les impacts relatifs d'une éclaircie et d'un brûlage ultérieur sur l'enlèvement du carbone et des nutriments, dans les Montagnes de la Sierra Nevada en Californie ?• Les méthodes d'éclaircie comprennent : éclaircie totale des arbres (WT, toute la biomasse au-dessus du sol est enlevée), coupe à la dimension désirée (CTL, branches et feuillage ont été laissés sur site en andains) et pas de récolte (CONT). L'exportation totale de carbone et de nutriments avec éclaircie et brûlage dans les traitements WT et CTL a été plus importante que dans le traitement CONT. Les sommes totales de carbone et d'azote enlevées ont été approximativement les mêmes pour les traitements WT et CTL, bien que la récolte est été prédominante dans les exportations pour le traitement WT et que le brûlage soit prédominant dans les exportations pour le traitement CTL. Le total des enlèvements de P, K, Ca, Mg et S dans le traitement WT a été le plus grand dans les traitements WT où la récolte était plus importante que l'enlèvement.• La comparaison des nutriments enlevés par rapport au capital de l'écosystème et le calculs de réapprovisionnement par des apports atmosphériques suggère que l'azote (N) est le nutriment probablement le plus épuisé par les traitements de récolte et de brûlage.récolte / feux prescrits / nutriments / Pinus jeffreyii / montagnes de la Sierra ...

The Long-Term Effects of Wildfire and Post-Fire Vegetation on Sierra Nevada Forest Soils

“…Tree nutrient content was estimated from biomass estimates by component (foliage, branch, bole bark, bole wood) combined with previous analyses of nutrient concentrations within these tissues from nearby sites [12,17]. Understory nutrient content was estimated from biomass estimates combined with nutrient analyses of samples taken from the sites as described above for O horizon samples.…”

“…Short-term losses of N by volatilization are usually substantial [3,[8][9][10][11][12][13][14]. Wildfire typically burns components of forest ecosystem that have high N concentrations (forest floor and foliage), leaving low-N organic matter such as boles and large branches charred but not combusted [11,12,15]. Over the longer-term, N lost via volatilization during fires can be quickly replaced and even exceeded by inputs from N fixers after fire if they are present [16][17][18][19][20].…”

“…Fire has major and lasting effects on nutrient budgets of forests ecosystems, both in the short-and long-term. Short-term losses of N by volatilization are usually substantial [3,[8][9][10][11][12][13][14]. Wildfire typically burns components of forest ecosystem that have high N concentrations (forest floor and foliage), leaving low-N organic matter such as boles and large branches charred but not combusted [11,12,15].…”

Mercury concentrations and pools in four Sierra Nevada forest sites, and relationships to organic carbon and nitrogen

“…In the two adjacent Truckee sites, replicate circular plots of 0.04 ha in size were established in the intact and post-fire sites and four replicate plots each were estimation (per unit area) and for determination of soil properties (Johnson et al, 2008;Murphy et al, 2006). Tree diameter were measured at breast height (dbh) for all trees in all sampling plots and dry mass of foliage, branches, bole wood, and bole bark were estimated for each plot using established regressions of tree diameter and the respective biomass components (Gholz et al, 1979;Johnson et al, 2008). Forest floor (i.e.…”

“…After removal of the litter cover, soils at each point were sampled by depth (0-20 cm, 20-40 cm, and 40-60 cm) using a bucket auger. In order to estimate soil mass, quantitative pits were dug near the center of each plot and all soil and rock material was weighed (Johnson et al, 2008). Soil samples were oven dried at 55 • C until stable weight for calculation of bulk density to calculate areabased soil mass.…”