Identifying changes in tree form for harvested ponderosa pine in the Black Hills

Recent underestimates of total volume for timber sales in the Black Hills National Forest prompted analysis of two felled ponderosa pine (Pinus ponderosa Laws.) data sets that were collected approximately 10 years apart. Though neither data set collected was a representative sample of the Black Hills, both were similar in terms of diameter at breast height and total height. We investigated several methods for assessing differences in tree form and applied them to these two data sets. Under the assumption that these two data sets were representative of harvested trees in the Black Hills (which may be incorrect), we concluded that the average tree form of harvested ponderosa pine has changed significantly in the last 10 years. This conclusion highlights the importance of using representative data in model building.