Forest productivity and associated soil ecosystem services remain altered 15years after mechanized site preparation for reforestation with Pinus radiata

Abstract

The projected increase in the worldwide demand for forest products over the coming decades may lead to more intensive forest management. This will involve extension of the area of planted forests, increased mechanization and greater pressure to extract timber from sensitive zones such as steep slopes, wet and heavy soils. However, such intensification may place soil protection and ecosystem services provided by forests at risk. In this study, the impacts of mechanized forest site preparation (shearing and ripping) and manual site preparation were evaluated during the first 2.5 years and 15 years after plantation establishment in a soil susceptible to erosion and compaction in a temperate humid climate. Site productivity, soil carbon storage, soil fertility, soil hydrological properties and protection against erosion and run-off were evaluated as ecosystem services provided by forest soils. Soil loss due to manual site preparation was 25 g m−2 yr-1, while annual soil loss ranged from 98 to 3128 g m−2 in sheared sites and from 345 to 4652 g m−2 in ripped sites. However, soil loss was negligible 2.5 years after site preparation. By contrast, soil compaction persisted during 15 years and was significantly higher in mechanically prepared plots than in manually prepared plots. The changes in soil water holding capacity persisted 15 years after site preparation. The available water content was significantly lower in mechanically prepared plots (by shearing and ripping) than in manually prepared plots. During the period 2002–2004, tree height was between 13 and 52 % higher in manually prepared sites than in sheared sites, while in ripped sites tree height was between 91 % higher and 62 % lower than in the manually prepared plots. However, no significant differences in tree height were observed 15 years after site preparation. By contrast, significant differences in the quadratic mean diameter of trees were observed 15 years after site preparation, with tree volumes being highest in manually prepared plots. The findings show that manual site preparation preserves forest ecosystem services such as site productivity and water regulation and can be considered a means of conserving soil and water and a “climate smart” approach in plantation forestry.