Long-Term Stand Growth of Interior Ponderosa Pine Stands in Response to Structural Modifications and Burning Treatments in Northeastern California

The Blacks Mountain Experimental Research Project created two distinct overstory structural classes (high-structural diversity [HiD]; low-structural diversity [LoD]) across 12 stands and subsequently burned half of each stand. We analyzed stand-level growth 10 years after treatment and then modeled individual tree growth to forecast stand-level growth 10-20 years after treatment. Net stand growth was compared between treatments and with adjacent Research Natural Areas (RNAs). An analysis of variance of growth in total aboveground tree biomass suggested that growth was greatest in unburned stands (P = 0.001) and in LoD stands (P = 0.039). We formed iteratively annualized nonlinear models to forecast individual tree growth. Modeled diameter growth, height growth, and mortality were used exclusively for forecasting and highlighting growth and mortality trends in the data (i.e., not testing effects). Forecasts of stand board foot volume suggested that HiD and LoD stands may be no different in net growth in the second decade since treatment (P = 0.355). Differences between logged and unlogged stands appeared to be much greater: we predict that RNA stands will net 136 board feet ac(-1) in the forecast period, whereas HiD and LoD stands are expected to net 627 and 485 board feet of volume per acre. We also tracked the large tree (dbh >23.5 in.) component stand density index (SDI) over the measurement and forecast periods. We found that the unburned HiD treatment had a net positive effect (13% increase over 20 years) on relative density, whereas the burned HiD was not expected to change (P = 0.803), and unlogged stands tended to exhibit a declining SDI over time (-16%).