The Inter – Annual Dynamics of Basal Area Increment Derived from Permanent Girth Band Measurements in Intensive Forest Monitoring Network

Abstract

Knowledge of intra-annual tree growth dynamics allows a better understanding of tree reaction to short-term climate variation. The main objective of our study was modeling intra-annual dynamics of basal area increment (BAI) in four-level II plots in Romania, composed of pedunculate oak (Quercus robur L.), sessile oak (Q. Petraea [Matt.] Liebl.), Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.), which are placed in representative forest ecosystems, as well as in climatic and altitudinal conditions. Between 2010 and 2014, for a number of 60 trees (15 for each plot and species), the growth variations of the selected trees were recorded bimonthly using permanent girth bands. Seasonal dynamics of radial increment were modeled using Gompertz functions. Results confirm that each year the growing season period is different for each location. For pedunculate and sessile oak a common onset of the growth was observed during the whole period, except 2012. The same situation was emphasized for European beech (situated at 1300 m altitude) and Norway spruce. For these species located in mountainous regions, the maximum growth rate is recorded in the same period (late June). In general, in all studied plots, the values recorded on permanent girth bands regarding the onset and maximum growth rate are confirmed by the data recorded on continuous point dendrometers.