Long-Term Responses to Competing Vegetation Management for Pinus radiata

Numerous studies have been carried out to quantify the response to competing vegetation control (CVC) in P. radiata plantations. Most of these publications have reported on the early response in tree growth; however, a knowledge gap exists regarding the growth responses throughout the rotation. In this study, we analyzed the long-term response of P. radiata plantations across a gradient of seven sites in central Chile. Treatments included a no-action control, two spot (circular) areas of competing vegetation control using herbicides around individual P. radiata seedlings (spot herbicide application of 0.75 and 1.5 m), and total competing vegetation control using herbicides. Additionally, three different timings for control regimes were included (0, 1, and 2 years after planting). Competing vegetation biomass abundance during the first growing season ranged from 0.6 to 5.7 Mg ha(-1) across all sites. The total competing vegetation control treatment maintained for 2 years (TotalY(012)) showed the largest gain in stem volume per hectare (VOL) in most of the sites. The sites included in this study showed contrasting values in productivity, having volume yields for the TotalY(012) treatment ranging from 238 m(3) ha(-1) at the site with the lowest annual rainfall (age 12 years) to 471 m(3) ha(-1) at the southern site (age 14 years). Across all sites, maximum gain in VOL ranged between 21 and 175 m(3) ha(-1) at age 11 to 14 years and was linearly correlated to the amount of competing biomass controlled during the first year after planting. At the southern, wetter site, plots with only pre-planting spot herbicide application achieved 87% of VOL of plots with TotalY(012). Our results suggest that CVC improved the availability of resources at the site for P. radiata seedlings, increasing volume production by reducing environmental constraints to tree growth differentially at each site.