Extracting environmentally driven growth trends from diameter increment series based on a multiplicative decomposition model

Abstract

The study developed a conceptual framework for partitioning the components of diameter increment to potentially detect the influence of environmental changes. This process consisted of two steps. First, a multiplicative decomposition diameter increment model was introduced to evaluate the influence of ageing, site quality, competition status, and thinning effects on individual tree growth. Second, generalized additive models were applied to identify the nonlinear dynamic of growth trends caused by environmental changes. The conceptual framework was then applied to Norway spruce ( Picea abies (L.) Karst.) growing in southwest Germany. The database consisted primarily of tree ring series collected from trees cut from long-term experimental stands. Also, stand-level data were available from periodical remeasurements of these plots. The developed analytical technique effectively removed non-environment-related effects (ageing, site quality, and stand dynamic) from the growth signal provided in the diameter increment series. Growth trends deducted from estimates based on either nonlinear least squares, generalized nonlinear least squares, or nonlinear mixed-effects approaches displayed quite similar patterns. In general, the trend in diameter increment showed a long-term increase from the 1920s into the 1990s with a midterm depression in the 1940s that was followed by a significant decrease in the recent past.