Abstract
Managed forests are subjected to wide variety of silvicultural treatments. These treatments or the lack thereof can influence the height growth of young stands. There is no standard approach to evaluating or quantifying the differences between silvicultural treatments. This is especially true with regard to forest models. We utilized a two-point height intercept method at 6 meters as an approach to quantify the treatment response of site preparation and planted versus naturally regenerated on ponderosa pine (Pinus Ponderosa) and western larch (Larix occidentalis) within the Inland Northwest, USA. Sampling was performed utilizing a balanced orthogonal matrix to ensure that sampling was collected across the entire range of climatic and environmental conditions present in the study area. Three geospatially derived variables: Mean Annual Precipitation (MAP), Soil Depth to Restrictive Layer (SDEP), and Annual Growing Season Days (GDAY) greater than 10 degrees Celsius were used to develop the sample matrix. Stand histories were researched and validated with site preparation and planting records.
A site-treatment linear regression model was developed for each species after performing step wise model reduction techniques from a larger full multiple regression model. Adjusted R2 for the western larch model was 0.4029, while the adjusted R2 for ponderosa pine was 0.6052. The addition of site preparation treatment before planting did not increase the growth rates of planted western larch. There was a significant increase in growth rates between planted and naturally regenerated western larch and ponderosa pine (P<.001). Untreated, planted western larch showed a significant increase in height growth compared to treated western larch (P=0.0159). A two-point height intercept method at 6 meters can be used to quantify and differentiate the silvicultural treatment response in height growth for young stands taller than 6 meters, particularly in non-pioneer species.