Response of ponderosa pine plantations to competing vegetation control in Northern California, USA: a meta-analysis

Abstract

A meta-analysis was performed to determine response of stand basal area growth to competing vegetation control (CVC) in ponderosa pine (Pinus ponderosa) plantations grown at 29 sites across northern California. These studies were installed during the last 50 years on site indices from 11 to 35 m at 50 years and often included other treatments besides CVC. Our analyses showed, with considerable certainty, that magnitude of the CVC effect on overall basal area increase was 80% (40-105%). The 40% increase occurred 5 years and the 105% increase occurred 10 years after the treatment was applied. A 67-91% increase was found 15-30 years after CVC. Additional treatments such as fertilization and high stand density accelerated the CVC effect. The trends of the CVC effect not only varied with stand developmental stages, but also differed where CVC treatments were applied to seedlings or to older plantations. Results suggest that productivity response to vegetation control increases during the stand initiation stage and peaks when stands are in the stem exclusion stage. Thus, the magnitude of CVC effect depends on when it is applied relative to the stage of stand development. Any factors that increase stand development will accelerate this process. Therefore, to capture early growth gains, stands must be thinned soon after the onset of inter-tree competition. Timing depends on site productivity and previous silvicultural treatments.