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Forests 2018, 9(9), 555; https://doi.org/10.3390/f9090555

Generalized Nonlinear Mixed-Effects Individual Tree Crown Ratio Models for Norway Spruce and European Beech

Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Suchdol, Kamýcká 129, 165 21 Prague 6, Czech Republic
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Received: 13 August 2018 / Revised: 3 September 2018 / Accepted: 7 September 2018 / Published: 10 September 2018
(This article belongs to the Section Forest Ecology and Management)
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Abstract

Tree crowns are commonly measured to understand tree growth and stand dynamics. Crown ratio (CR—crown depth-to-total height ratio) is significantly affected by a number of tree- and stand-level characteristics and other factors as well. Generalized mixed-effects CR models were developed using a large dataset (measurements from 14,669 trees of Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica (L.)) acquired from permanent research plots in various parts of the Czech Republic. Among several tree- and stand-level variables evaluated, diameter at breast height, height to crown base, dominant height, basal area of trees larger in diameter than a focal tree, relative spacing index, and variables describing the effects of species mixture and canopy height differentiation significantly contributed to CR variation. We included sample-plot-level variations caused by randomness in the data and other stochastic factors into the CR models using the mixed-effects modeling approach. The logistic function, which predicts the values between 0 and 1, was chosen to develop the generalized CR mixed-effects model. A large proportion of the CR variation (R2adj ≈ 0.63 (Norway spruce); 0.72 (European beech)) was described by generalized mixed-effects model without significant residual trends. Testing the CR model against a part of the model fitting dataset confirmed its high prediction precision. Our CR model can be useful for growth simulation using inventory databases that lack crown measures. Other potential implications of our CR models in forest management are mentioned in the article. View Full-Text
Keywords: dominant height; logistic function; species mixing effect; random effect; relative spacing index; stand development stage dominant height; logistic function; species mixing effect; random effect; relative spacing index; stand development stage
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Sharma, R.P.; Vacek, Z.; Vacek, S. Generalized Nonlinear Mixed-Effects Individual Tree Crown Ratio Models for Norway Spruce and European Beech. Forests 2018, 9, 555.

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