Persistence of scarification effecs in a scots pine stand within the spanish central system mountains

Abstract

It is widely accepted that site preparation techniques such as scarification can improve seed-soil contact and reduce weed competition thus enhancing seedling establishment. Nevertheless the efficacy of the treatment relies on its persistence which is expected todepend strongly on site conditions (soil + climate) and treatment features (size + depth). This study aims at analyzing the ?useful life? of small-sized scarification effects in a Scots pine stand located in the Mediterranean mountain range where natural regeneration processes may become especially vulnerable to extra limiting factors, as growing season is itself constrained by both cold and drought. 198 1.5x1.5m plots were randomly selected within the study area and one out of four among them were manually scarified to a depth of 15cm. Two years after, vegetation coverture (% Grass cover, % Debris cover and % Shrub cover), soil compaction (Penetration Resistance at 0-10cm & 10-20cm depth), soil moisture and stand density (GAP fraction & surrounding Basal Area) were assessed in all plots. A significant mean reduction of vegetation cover was still noticeable in the scarified plots both in grass (-12,9%), shrub (-6,0%) and debris (-10,7%). On the contrary there were no significant differences between treated and non-treated plots compaction level. Regarding soil moisture, only a slight increase (+1,9%, p-value=0,08) was still detectable in the treated plots. Stand density significantly influenced restoration of both compaction levels (?2 0-10cm=-0.58, ?2 10-20cm=-0.44) and coverture of grass (?2=-0.40) and debris (?2=0.80). Nevertheless it didn?t seem to affect shrubs cover recovery. Those results confirm so far that, in this environment, pre-tillage soil conditions are quickly recovered after scarification when treatment is applied in plots this small (1,5x1,5m). It seems time available is too short for seedling to benefit from soil decompaction. Stand density should be considered when evaluating scarification effects.