Survival and early growth of mixed forest stands installed in a Mediterranean Region: Effects of site preparation intensity

Abstract

a b s t r a c tIn Mediterranean environments, availability of water and nutrients are the main factors limiting the success of afforestation. As part of a wider project, an experiment was established in Northeast Portugal, aiming at testing the effect of several site preparation techniques on plant survival and growth (height and diameter) in a newly installed mixed forest stand. Results presented regard plant response during 42 months after plantation. The experimental protocol consisted in seven treatments described by mechanical operations that rank soil disturbance intensity from none to high, set in plots of 375 m 2 , randomly distributed in three blocks, in different topographic positions (gentle slope plateau, moderate slope shoulder, and steep mid-slope). Pseudotsuga menziesii (PM) and Castanea sativa (CS) forest species were planted in a 4 m × 2 m scheme and in alternate rows with 12 plants on each row per plot, summing up 72 plant per specie and treatment at start of the experiment. The results show that: (i) the highest mortality was observed immediately after the plantation and before the dry season, on the lowest intensity treatments; (ii) after the dry season, the highest mortality was also observed in treatments with the lowest intensity of soil disturbance, while the lowest values were found on the intermediate intensity treatments; (iii) during the experimental period, the effect of treatments on plant growth (height and diameter) was statistically significant; however, experimental results do not lead yet to a clear quantitative relationship between soil disturbance intensity due to site preparation and plant response under the conditions tested.

European Mixed Forests: definition and research perspectives

“…Soil treatment influences survival rates in Mediterranean conditions although sapling growth is not affected (Fonseca et al, 2011) Size-density relationship has been long studied in pure and mixed-species forests as it has a notable impact on forest yield. In forestry practice, Reineke's stand density index (SDI, Reineke, 1933), an analogous relationship to Yoda's 3/2 self-thinning boundary, has been used to manage density in even-aged singlespecies forests.…”

Soil loss and run-off in young forest stands as affected by site preparation technique: a study in NE Portugal

“…A small part of the experimental field in a plateau is covered by soils derived from a shallow tertiary sedimentary deposit, resting over the schist basement. These soils have higher silt, clay and organic matter contents, are more acid and have lower P and K, than the ones previously described, as shown by data from samples collected on 48 profiles before site preparation operations, and differences found are statistically significant (P \ 0.05) (Fonseca 2005).…”

“…5, for the same index, correlation declines from the first to the fourth semester. Indexes involving rainfall intensity tended to better correlate with soil loss and run-off in treatments with soil disturbance, while for No_D (original soil), a better correlation was obtained with precipitation (Fonseca 2005).…”

“…Average annual temperature and precipitation are 12°C and 656 mm, respectively, with typically Mediterranean seasonal distribution (Agroconsultores e Coba 1991;INMG 1991). According to FAO/UNESCO (1988), soils are dystric Cambisols and dystric Leptosols developed on schist, in the area characterized as sandy-loam, with high stoniness (higher in the latter ones, which occur in steeper slopes), normally acid, moderate to poor in organic matter content, with low to very low P and low to moderate K contents (Agroconsultores e Coba 1991;Fonseca 2005). A small part of the experimental field in a plateau is covered by soils derived from a shallow tertiary sedimentary deposit, resting over the schist basement.…”

“…Mechanical operations associated with site preparation imply important disturbance due to heavy machinery normally used in forestry (Alcázar et al 2002). Disturbance means parent material breakdown by deep subsurface tillage, necessary to improve rooting depth in shallow soils (Fonseca et al 2011). As a consequence, it increases rock fragment content in the profile and eventually at surface if tillage reverses soil layers as it is also normally the case of surface tillage.…”