Predicting annual canopy litterfall production for Norway spruce (Picea abies (L.) Karst.) stands

Canopy annual litterfall production in 18 Norway spruce stands in Finland was studied and predictive models developed. The stands ranged in age from 32 to 163 years old and located at latitudes from 60 to 68°N. Stand litterfall had been continuously collected using 6–12 traps per stand for periods of 1–43 years. Dry weight annual total litterfall production (LFtotal) values ranged from 44 to 677 g m−2 and needle litterfall production (LFneedle) values from 27 to 465 g m−2. Stand characteristics (stocking density, height, breast height diameter, stem volume and basal area) were measured and canopy needle biomass estimated using an allometric function. Both mean LFtotal and LFneedle were significantly and negatively correlated with latitude, which was considered to reflect the effects of climate. Of the stand characteristics, mean height was the most important. More detailed analysis revealed that observed inter-annular variability in both LFtotal and LFneedle was related to the effective temperature sum, July temperature and annual precipitation amount, and that significant lag effects for up to 3 years occurred. Multiple linear regression (MLR) models could explain 88% and 82% of the variation respectively in mean LFtotal and LFneedle when only stand and site variables were allowed to enter the model. Corresponding S.E.est values, reflecting model precision, were 33 and 23 g m−2. Interestingly, latitude did not enter the model. MLR models to predict LFtotal and LFneedle for any specific year (by allowing specific weather variables to enter) explained 80% of LFtotal variability and nearly 70% of LFneedle variability. After testing the models with an independent data set from Sweden, we concluded that the models can be used to predict annual canopy litterfall of mature Norway spruce stands for sites in the boreal zone.