Age-related changes in leaf area index of young Scots pine stands

Abstract

We studied the chronosequence of six Scots pine (Pinus sylvestris L.) plantations (6-, 9-, 11-, 15-, 17-, and 20-years-old) to examine the changes in leaf area index (LAI) over stand age. The study site was lo- cated on a mine spoil heap (outer dumping ground) in the Belchatow lignite open-cast mining district (cen- tral Poland). The main goal of the study was to analyze LAI changes over stand age in a chronosequence of young Scots pine stands and to test the relationship between LAI estimates derived from a LAI-2000 Plant Canopy Analyzer and site-specific allometric equations. In addition, we tried to determine whether LAI esti- matedby a LAI-2000 PCA can be usedto accurately estimate forest biomass. We hypothesizedthat LAI-2000 PCA underestimates LAI of the stands, andthat standage (andlinkedstandparameters) may influence the range of the hypothetical underestimation due to changes in biomass allocation. Our study revealed that LAI was highly dependent upon stand age and tree density (p<0.0001) regardless of the way how LAI was deter- mined. Moreover, we found that LAI estimated by LAI-2000 PCA significantly correlates with stand biomass per area; the highest coefficients of determination were found for total aboveground biomass, aboveground woody biomass, and stem biomass. This means that data obtained by LAI-2000 PCA are good predictors of standbiomass in the young stages of standd evelopment. In contrast to our prior assumption, the results showed that LAI-2000 PCA overestimates leaf area index. The relative differences between the values ob- tainedwith LAI-2000 andthose calculatedon the basis of the site-specific allometric equations increase with age. This may reflect changes in crown architecture over age causedby enlarging tree dimensions andover - crowding of trees leading to deterioration of light conditions inside the canopy.