Predicting height growth of sugar pine regeneration using stand and individual tree characteristics

Abstract

Concern exists among managers and researchers that sugar pine (Pinus lambertiana), a valuable, moderately shade-toleranttimberspecies, regenerationappearstobedeclining. Managementand restoration requireunderstandingfactorsleadingtosustainedsugarpineregenerationgrowthandoverstoreyrecruitment.Theprimaryresearchobjectivewastoidentifyfactorsinfluencingsugarpineregenerationheightgrowth.Datawerecollectedon sugarpineregeneration,includingheightgrowthandstandcharacteristicsacrosssixmanagedandeightunmanaged stands in the Lake Tahoe Basin, CA and NV, USA. Individual tree- and stand-level analyses were conducted using non-parametric statistical comparisons and regression. Results indicated low mean height growth rates and no relationship between canopy closure and either height growth or management history. Individual sugar pine seedlings grew significantly taller under unmanaged stand conditions with higher canopy closures while sapling growth did not differ statistically by management history. Individual tree-level height growth models neverexplained more than 35 percent of the variation. Stand-level models explained over 50 percent of the variationwithfewervariablesthantheindividual tree-levelmodels.Moreresearchshouldbeconductedtodetermine whethertheregenerationthatispersistingintheunderstoreywouldrespondpositivelytomoreaggressiveunevenaged silvicultural treatments designed for enhancing understorey pine growth.