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Context

Douglas fir (Pseudotsuga menziesii Mirb Franco) is the most productive non-native tree species in France. Its covers about 450 000 ha and produces 15 m3 per year as a mean.
Since the 1950's, this tree species was massively planted all over France, because of its production potential, the durability of its wood, its tolerance to relatively poor soils, and the limited impacts of pests and diseases. Douglas fir was thought to have moderate impact on the environment. But recent works showed that it nevertheless could have some negative impacts on soil quality through its N-cycle (Zeller et al, 2007). Several studies tend to show that Douglas fir controls Norg mineralisation and could lead through this process to rapid soil acidification when nitrates cannot be immobilized in the soil. Other field trials showed that liming was helpful to mitigate this acidification process, improving all the forest plantation services, including production.

It was then necessary to validate these findings in a large set of Douglas fir stands, in order to propose adapted management according to soil fertility level.

Objectives

i. To test, in soils ranging from acid to more or less saturated ones, the impact of Douglas-fir on soil biogeochemistry, more particularly on:
  - Soil organic-N mineralisation and nitrification
  - Soil solution composition and drainage losses, out of the rooting zone.
ii. To verify if a threshold of soil fertility could be find above which nitrates were all immobilized, thus avoiding drainage losses
iii. To test the impact of soil improvement by liming and fertilisation

Network description:

Twenty-two sites were selected in the entire Douglas fir plantation forests in France for investigations on vegetation, soil, and N_org mineralisation. Half of them were equipped for medium term monitoring of nutrient cycling.
Experimental design for monitoring nutrient cycling: each plot (about 0.25 ha) was equipped between July 2012 and March 2013 for monthly solution collection (throughfall, stemflow, soil solutions at 15 and 60 cm depth) and litter-fall (4 x 0.5m2 traps per stand). Soil moisture probes were installed in 2014 (5 replicates at 15 and 60 cm depth) (hourly measurements). Monitoring began in 2013 for solutions. All the information on methods & results are stored in a database managed by Pascal BONNAUD.

Project investigators

Arnaud LEGOUT, Bernd ZELLER (INRA- BEF); Jacques RANGER Engineer in charge of the sites Pascal BONNAUD (INRA-BEF) Technical staff : Séverine BIENAIME, Pascal BONNAUD, Jérôme DEMAISON, Gilles NOURRISSON , PhD Bruno GRATIA.
CONTACTS: name.surname@inra.fr

Publications:

Zeller et al 2007 ASF ; Zeller et al. Rdvt 2016.

Contributors:

Private forest owners on 9 sites and ONF on 2 sites.

Funding:

ONF, LHOIST Society, Parc Régional Morvan