Effects of the clear-cutting of a Douglas-fir plantation (Pseudotsuga menziesii F.) on the chemical composition of soil solutions and on the leaching of DOC and ions in drainage waters

Abstract

-The effects of the clear-cutting of a 70-year-old Douglas-fir plantation on the chemical composition of soil solutions and on leaching of nutrients in drainage waters were observed by a continuous monitoring, six years before and three years after the cutting. Forest harvesting was made with very limited soil disturbances. Results showed that the concentration of weakly fixed solutions did not change but that the concentration of gravitational solutions of the upper soil layers drastically fell down after the cutting. The limited increase in nutrients leached with drainage waters was only due to the increase in the water flux, which is difficult to quantify because of the presence of ground vegetation. The monitoring of numerous fluxes before and after the clear-cutting could explain the specific behaviour of the soil solutions. The limited losses of nutrients the after clear-cutting in a potentially responsive ecosystem were unexpected. The initial hypothesis was that the decrease in the mineralization and nitrification rates observed after the cutting was related to a stimulating effect of Douglas-fir on the activity of soil nitrifyers.Douglas-fir / clear-cutting / soil solutions / nutrients / leaching Résumé -Effet de la coupe à blanc d'un peuplement de Douglas (Pseudotsuga menziesii F.) sur la composition chimique des solutions du sol et sur le flux d'éléments drainés. Les effets de la coupe à blanc d'une plantation de Douglas de 70 ans ont été observés sur la composition chimique des solutions du sol et les pertes d'éléments par drainage, par un suivi mensuel pendant 6 ans avant, et 3 ans après la coupe. L'exploitation du peuplement a été réalisée avec une perturbation minimum du sol. Les résultats montrent que les solutions liées ont peu évolué après la coupe, alors que le changement des solutions libres a été drastique dans les horizons de surface du sol. Malgré des incertitudes sur le rôle de la végétation spontanée, le drainage d'éléments n'a pas fortement augmenté après la coupe. La prise en compte de l'ensemble des flux mesurés dans cette étude semble pouvoir expliquer les observations. Les pertes limitées après la coupe d'une plantation où l'activité nitrifiante était élevée avant la coupe étaient inattendues. L'hypothèse avancée est l'arrêt du contrôle stimulateur des populations nitrifiantes du sol après la coupe du Douglas. Douglas / coupe-à-blanc / solutions du sol / éléments nutritifs / lixiviation

Effets de la coupe à blanc d’un peuplement de Douglas (Pseudotsuga menziesii (Mirb.) Franco) sur la fertilité chimique du sol

“…In the present situation, losses by drainage did not greatly increase after clear-cutting and are therefore not able to completely explain the soil changes [39].…”

Effects of storm Lothar (1999) on the chemical composition of soil solutions and on herbaceous cover, humus and soils (Fougères, France)

“…The acceleration of the mineralization of organic matter due to changes in the soil climate is a well known phenomenon (Vitousek and Melillo, 1979;Attiwill and Adams, 1993;Dahlgren and Driscoll, 1994; Ranger et al, 2007) following forest ecosystem disturbance and may partly explain the disappearance of the humus layers. In fact, several factors influencing the mineralization rate changed rapidly after the storm: we noticed a slight increase in the soil moisture ( Fig.…”

“…Even if a large amount of literature is available, it is difficult to predict what will occur at a specific site, due to the methodology used, the scales investigated and the specific site conditions, such as soil and vegetation type (Ranger et al, 2007). The plot or the stand scale seems to be relevant for observing changes in soil quality, humus and vegetation.…”

“…) or natural (storm) disturbances. These disturbances could have potentially serious effects on the ecosystem and especially could cause great damage to the soil, which is not an entirely renewable resource (Ranger et al, 2007). This damage results in constraints to the physical, chemical and biological properties.…”

“…The sequence of mechanisms which lead to these losses is a quite well known phenomenon. In fact, mineralization of organic matter and nitrification rates generally increase after a disturbance (Vitousek and Melillo, 1979;Attiwill and Adams, 1993;Dahlgren and Driscoll, 1994;Ranger et al, 2007) due to changes in the soil climate. Moreover, the rate of soil organic matter mineralization and, more specifically, the rate of nitrification are recognized as driving processes, which explain nutrient losses by drainage after disturbances (Dahlgren and Driscoll, 1994).…”