David W. Hann

Analysis and comparison of nonlinear tree height prediction strategies for Douglas-fir forests

Using an extensive Douglas-fir data set from southwest Oregon, we examined the (1) performance and suitabil- ity of selected prediction strategies, (2) contribution of relative position and stand-density measures in improving tree height (h) prediction values, and (3) effect of different subsampling designs to fill in missing h values in a new stand using a regional nonlinear model. Nonlinear mixed-effects models (NMEM) substantially improved the accuracy and precision of height prediction over the conventional nonlinear fixed-effects model (NFEM) that assumes the observations are inde- pendent, particularly when a few trees are subsampled for height. The predictive performance of a correction factor on a NFEM with relative position and stand-density measures was comparable to that of a NMEM when four or more trees were subsampled for height. When two or more heights were randomly subsampled, the NMEM efficiently explained the differences in the height-diameter relationship because of the variations in relative position of trees and stand density without having to incorporate them into the model. When only one height was subsampled, selecting the largest diameter tree in the stand would result in a lower predicted root mean square error (RMSE) than randomly selecting the height, re- gardless of the model form or fitting strategy used.

Development of a tree height growth model for Douglas-fir

Abstract Using a sample of 866 Douglas-firs, a predictive model is presented which expresses 5-year height growth as a nonlinear function of potential height growth, crown ratio and height of the subject tree divided by dominant stand height. The adjusted coefficient of multiple determination ( R 2 ) of this model exceeded 0.70, which was superior to four alternative models derived from previous studies. The final model also fit well to the data from each crown class. A number of different techniques for expressing competitive effects were also studied. The most influential variables in the height growth analysis were related to tree position, crown competition factor in larger trees and height divided by dominant stand height. Crown ratio, considered an index of tree vigor, was statistically significant but only accounted for about 8% of the residual variation in height growth.

Evaluation of individual-tree and disaggregative prediction methods for Douglas-fir stands in western Oregon.

The efficiency of six disaggregative methods and two individual-tree methods was evaluated in terms of their ability to predict 5-year basal area increment for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands in western Oregon. Models were developed for predicting gross stand basal-area increment and individual-tree diameter increment. In addition, models were developed to disaggregate the active increment prediction methods to the tree level. Passive and active prediction schemes were evaluated for both the tree and stand levels. Generally, the individual-tree approach was superior to the disaggregative approach for prediction of both stand and tree growth. This was less evident, however, when crown ratio was eliminated from the individual-tree models. This suggests that at least some of the disparity between the two is due to the presence of crown ratio in an individual-tree passive aggregation approach. The additive disaggregation approach appeared to be best suited to young stands (less than 50 years of age). The linearity assumption required for this particular model appeared to be violated for older stands with larger trees. Generally, the two whole-stand, gross-growth models used in this study were inferior to the individual-tree method for predicting gross basal area growth for one period. Resume : Six modles qui dOcomposent la croissance du peuplement et deux modles de croissance diarbre sont OvaluOs pour leur capacitO ‡ prOdire liaccroissement quinquennal en surface terrire des peuplements de Douglas taxifoliO ( Pseudotsuga menziesii (Mirb.) Franco) dans liOuest de liOrOgon. Les modles diarbre prOdisent directement liaccroissement de liarbre en diamtre alors que les modles de croissance du peuplement prOdisent directement liaccroissement brut du peuplement en surface terri et len accriamtrarbre llemen de prsive et active sont OvaluOs pour le double niveau de liarbre et du peuplement. En gOnOral, liapproche par arbre est supOrieure ‡ celle du peuplement pour prOdire la croissance de liarbre et du peuplement. NOanmoins, cette supOrioritO siattOnue lorsque la longueur relative du houppier est OliminOe des modles diarbre. Ce rOsultat suggre que certaines disparitOs entre les deux approches sont dues ‡ la prOsence de la longueur relative du houppier dans les modles diarbre ‡ recomposition passive. Liapproche de dOcomposition additive semble la plus adOquate pour les peuplements juvOniles (‚gOs de moins de 50 ans). Lihypothse de linOaritO requise par cette approche de dOcomposition ne semble pas aussi valable dans les peuplements plus ‚gOs avec des arbres plus gros. Les deux modles de peuplement analysOs qui font appel ‡ la croissance brute sont infOrieurs au modle diarbre pour prOdire la croissance brute en surface terrire sur une pOriode de temps. (Traduit par la ROdaction)

The importance of forest stand-level inventory to sustain multiple forest values in the presence of endangered species.

The College of Forestry at Oregon State University (OSU) manages the 4600-hectare McDonald-Dunn teaching, demonstration, and research forest on the western edge of Oregon’s Willamette Valley. The College Forest sits near the city of Corvallis, a politically liberal town of 50,000 people and the home of OSU. Researchers and teachers throughout the University use the College Forest, and it receives at least 150,000 recreational visits each year. Timber harvest produces revenue to maintain and operate the forest, and to meet special College instructional and research needs.