Influences of silvicultural manipulations on above- and belowground biomass accumulations and leaf area in young Pinus radiata plantations, at three contrasting sites in Chile

There is a limited understanding of how resource availability (water+nutrients) interacts with soil physical properties in determining above- and belowground biomass allocation in radiata pine (Pinus radiata D.Don) plantations. We studied total above- and belowground biomass accumulation, and belowground biomass allocation (coarse and fine roots) in response to three contrasting silvicultural treatments (soil tillage, weed control and fertilization) applied to three sites of contrasting climate and soil textures in the Central Valley of Chile. At each site, tree growth (aboveground, belowground and total biomass), aboveground:belowground biomass ratio and leaf area index (LAI) were significantly increased by weed control. Weed control produced larger and more consistent responses in growth than subsoiling or fertilization. Weed control appears to ameliorate both water and nutrient limitations. The large differences in growth and biomass accumulation by weed control within sites, were mainly attributed to large differences in soil water availability, and among sites also due to atmospheric water demand differences. A linear relationship was established between LAI and stand growth across sites. The slope of the relationship, stemwood growth efficiency, was different among sites and was related to water and nutrient limitations. Stemwood growth efficiency varied from 2.9 m3 ha−1 year−1 to 7.1 m3 ha−1 year−1 per unit of leaf area, with lower growth efficiencies found on sites with greater water constraints.