Predicting site index with a physiologically based growth model across Oregon, USA

Abstract

With expanded interests in sustaining productivity under changing climate, management, and disturbance regimes, we sought a means of mapping the potential productivity of forests across the state of Oregon in the Pacific Northwest, USA. We chose the mapping tool 3-PG, a simplified physiologically based process model that can be driven with monthly averaged climatic data (DAYMET) and estimates of soil fertility based on soil nitrogen content. Maximum periodic mean increment (MAI, m3·ha–1·year–1), a measure of the forest's productive potential, was generated by the 3-PG spatial model and mapped at 1-km2 resolution for the most widely distributed tree species, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Maximum MAI is linearly correlated with yield table site indices and therefore comparable with field-derived estimates of site indices obtained from measurement of tree heights and ages at 5263 federal forest survey points. The model predicted 100-year site index (SI) reasonably well (R2 = 0.55; RMSE = 9.1), considering the difference in spatial resolution between the modeled (1 km2) and field-measured SI (<0.1 ha) and that field plots were offset for confidentiality by 1–3 km. We created a map of the differences between modeled and field-measured SI and found that the 3000 points within ±6 m error were relatively evenly distributed across Oregon. Improving the accuracy in modeling and mapping forest productivity using 3-PG will likely require refinements in soil surveys, the quality of climatic data, the location of field plots, and the model functions and species parameters.

Development of Site Index Equation and Curves for Site Quality Assessment of Pinus caribea Monoculture Plantations in Southwestern Nigeria

“…However, Wang et al (2008) reported that the tendency for a predictor age being derived, the closer be the base age among the plantation species, the higher the accuracy that would likely be obtained when he studied pine plantation of Taiwan using base age of 25 years. This site index curves produced for this study was on similar threshold of base age of 25 years, and was in consonant with the previous studies (Johansson 1995;1996;2012;Wang et al 2008;Swenson et al 2005).…”

Process-Based Modeling to Assess the Effects of Recent Climatic Variation on Site Productivity and Forest Function across Western North America

“…With even moderate refinement in the mapping of soil properties, we achieved closer agreement between predicted and measured growth than previously reported for parts of the US Pacific Northwest [80].…”

A process-based approach to estimate lodgepole pine (Pinus contorta Dougl.) distribution in the Pacific Northwest under climate change

“…Although we recognize that soil fertility and soil water storage capacity vary considerably across the region (Swenson et al 2005), in this paper, we chose to keep soil properties constant to simplify the analysis of the effects of climatic variation on tree distribution. We did this by setting the maximum available soil water storage capacity at 200 mm and assigning a moderately high rank to a soil fertility index (0.7), which generates a maximum photosynthetic quantum efficiency of 0.05 mol C mol photon −1 (2.75 g C MJ −1 of absorbed photosynthetically active radiation).…”