PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Importance of site-specific characteristic regarding thinning effects on nutrient cycling in two contrasting Pinus sylvestris L. forests in the Pyrenees (Northern Spain).

Blanco, Juan¹, Imbert, J.¹, Castillo, Federico¹, Zavala, Miguel², ¹ Universidad Publica de Navarra, Pamplona, Navarra, Spain² Universidad de Alcala, Alcala de Henares, Madrid, Spain

ABSTRACT- Effects of thinning on nutrient cycling (N, P, Ca, Mg and K) in Pinus sylvestris L. forests were studied in two contrasting forests in the Western Pyrenees (Northern Spain): Aspurz (625 m, 7% slope, high productivity) and Garde (1335 m, 40% slope, low productivity). There were three types of plots (30 x 40 m) in both sites, with three replicates of each: PR or reference plot (not thinned), P20 (reduction of 20 % in basal area) and P30 (reduction of 30 %). Changes in above-ground biomass and nutrient pools were estimated after thinning. Monitoring of nutrient concentrations in litterfall, green needles and soil, and litterfall decomposition rates was carried out during 2-4 years after thinning. All these variables or processes were significantly influenced by site conditions and thinning. In addition, significant differences between sites were found for retranslocation rates, resorption proficiency and nutrient use efficiency (NUE), implying that both forests function differently. A PCA based on nutrient fluxes showed first order differences between sites and second order differences between thinning intensities. All data were integrated into a hybrid model of nutrient cycling simulating the thinning recommendations for forests in the region. The simulation showed that for P reserves application of these prescriptions may be above the sustainability threshold in the least productive site and on the verge of this threshold in the most productive site. These results imply that nutrient fluxes in these ecosystems are influenced by the specific geoclimatic conditions, which determine the ecosystem response to human activities, the sustainability of forest practices and the future evolution of these forests, suggesting the need for site-specific impact evaluations. It appears that in our heterogeneous region it is not appropriate to extrapolate thinning effects from site to site or to utilize general silvicultural recommendations based only on productivity criteria.

Key words: Forest management sustainability, Nutrient fluxes and cycles, Mediterranean forests, Hybrid model of nutrient cycling