Journal
FOREST ECOLOGY AND MANAGEMENT
Volume 459, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.foreco.2019.117823
Keywords
Stem diameter growth; Basal area increment; Two-stage potential-modifier approach; Realized diameter increment; Mixed effect modeling; Mixed species forests; Forest growth and yield modeling
Categories
Funding
- National Science Foundation Center for Advanced Forestry Systems (CAFS)
- USDA National Institute of Food and Agriculture, McIntire-Stennis Project through the Maine Agricultural and Forest Experimental Station [ME-041516]
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Tree diameter increment (Delta DBH) is a key component of a forest growth and yield model as predictions are passed to other submodels and tree-level estimates are scaled up to represent plot- and stand-level measures. A common problem faced in mixed-species stands is that Delta DBH needs to be characterized for numerous species, each with varying growth rates, shade tolerances, and competitive abilities. In addition, a variety of approaches have been used to model Delta DBH with unclear implications for general suitability for each species and overall prediction accuracy. This analysis used remeasurement data comprising 2,656,354 observations from 16,204 permanent sample plots across the Acadian Forest region of North America to develop and compare alternative approaches to estimating Delta DBH as well as stem basal area increment (Delta BA). Sixty-one species or genera including several with N < 10 were represented where observed mean growth rates ranged from 0 to 1.08 cm yr(-1) , depending on species. Analyzing several modeling approaches to project Delta DBH of the 15 most abundant species using various evaluation statistics to quantify prediction performance, this study showed that i) modeling Delta DBH was generally superior compared to approaches that estimated Delta BA, ii) a two-stage modeling procedure predicting potential growth and a corresponding multiplicative modifier to derive ultimate increment was mostly inferior compared to strategies predicting realized Delta DBH or Delta BA in a unified model form, and iii) species-specific, realized increment models exhibited similar behavior and accuracy compared to models fitted with modeling species as random effect. These key findings became even more evident when projection lengths increased ( >= 30 years). Our study thus showed the efficiency and flexibility of diameter predictions by including tree species as a random effect to account for Delta DBH differences of trees in mixed-species stands, including infrequent species. However, curves for rare species derived with the mixed effects modeling approach still need to be evaluated for biological plausibility as unbalanced or biased data can lead to uncharacteristic and potentially illogical behavior. Overall, the study highlights the challenges of accurately predicting Delta DBH across a range of species and conditions, but offers a general framework for future analyses in mixed species forests.
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