Stand development and tree growth response to sugar pine mortality in sierran mixed-conifer forests

Sugar pine (Pinus lambertiana) is a major component of the mixed-conifer forests found in the Sierra Nevada Mountains of California, USA. In the past several decades, sugar pine mortality has increased due to an introduced pathogen, white pine blister rust (caused by Cronartium ribicola). This study described stand development patterns in the mixed-conifer forests and quantified stand and tree growth response to the loss of sugar pine. Stratification patterns tended to follow patterns of shade tolerance with the more shade tolerant species found in lower canopy positions. Growth response was analyzed following the initial entry of blister rust and after more recent sugar pine mortality. Following the initial wave of mortality induced by blister rust, overstory trees and most individual species increased overall basal area growth. Although most species also responded to recent sugar pine mortality (occurring within the past ten years) by increasing basal area growth, the increase was only significant for white fir. Mortality of sugar pine has favored other conifer species, leading to changes in species dominance and negative effects on understory growth of sugar pine; release of these trees could improve overstory recruitment of sugar pine. However, due to the increased growth of white fir, any management strategies aimed at restoring sugar pine must also consider white fir management.