Experimental Canopy Nitrogen Deposition Effects in Temperate Forests: The case of Quercus petraea L. and Fagus sylvatica L. Ring Width and Wood Density

As an essential nutrient, Nitrogen (N) availability is fundamental in monitoring forest productivity, and as such, understanding the effects of changing atmospheric N inputs in forest ecosystems is of high significance. While most field experiments have been employing ground fertilization to simulate Nitrogen deposition, two experimental forest sites in Italy have adopted the more advanced canopy N application approach.
Here we present findings from a case study of wood core analyses of predominantly pure, even aged, Sessile Oak (Quercus petraea L.) and European Beech (Fagus sylvatica L.) forest stands, under two treatments of below and above canopy Nitrogen application, comparing between the two methods. The potential effect of elevated N availability on total ring width, mean ring density, and their corresponding earlywood and latewood fractions are examined.
Our results indicate inconclusive effects of the treatments on the ring widths of either Q. petraea or F. sylvatica, although basal area increment patterns appeared to be affected divergently between the species and treatments. Mean and earlywood, but not latewood, densities exhibited a decrease in certain years of treatment in Q. petraea following the above canopy N application only, whereas F. sylvatica wood density showed no clear response to any of the treatments.
Thus, we describe distinct responses of these broadleaved species to the different treatment approaches, discussing potential growth patterns under increased N availability, and emphasizing the importance of considering wood density in tree biomass accumulation and Carbon storage capacity assessments.