Assessment of crown base recession in uneven-aged ponderosa pine forest of Colorado and Arizona

Abstract

The structure of forest canopies from the individual tree crown to the stand canopy level informs a range of ecologically significant factors from photosynthetic capacity and tree vigor to wildlife habitat quality and crown fire potential. However, the data needed for characterizing the crown length/crown ratio is often, at best, subsampled during forest inventories. Therefore, it is important for forest growth and yield models to estimate these missing forest inventory values and to project future changes in crown structure. However, the wide range of tree and stand attributes impacting crown length and its temporal changes have proven to make this difficult in many forest systems. The work used two long-term research stem maps in Colorado (Manitou) and Arizona (Kaibab) ponderosa pine forests to evaluate the reliability of the Forest Vegetation Simulator Central Rockies (FVS-CR) variant for predicting missing crown lengths and projected changes in crown length. Additionally, we provide preliminary thoughts on alternative modeling strategies. FVS-CR prediction accuracy of missing crown lengths at the start of a simulation differed for the two sites (fig. 1), with mean absolute errors of 1.57 and 3.29 m for the Kaibab and Manitou stands, respectively. These differences might be attributed to the two sites being recommended to use different sub-models from FVS-CR. The fitting of a new model to predict missing crown lengths suggests modifying to a slightly simpler model form that includes height and the interaction of height and plot basal area as predictors, although accuracies were only mildly improved. The projection of future crown lengths by FVS-CR seemed to capture most crown change dynamics (fig. 2). However, initiating simulations without inventoried crown length data reduced the range of future predicted crown lengths. There were notable increases in mean error through time for both study sites, with these errors seeming to be worst when simulated without the inventoried crown ratio to begin with (fig. 3).

Parent Publication

• Sixth Forest Vegetation Simulator Conference; 2023 March 7-9; Fort Collins, CO

Citation

Tinkham, Wade T.; Battaglia, Mike A.; Asherin, Lance. 2024. Assessment of crown base recession in uneven-aged ponderosa pine forest of Colorado and Arizona. In: Shaw, John D; Battaglia, Mike A.; Castle, Mark, [comps.]. Sixth Forest Vegetation Simulator Conference; 2023 March 7-9; Fort Collins, CO. Proceedings RMRS-P-81. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 71-74.