Leaf area index and canopy stratification in Scots pine (Pinus sylvestris L.) stands

In order to assess the contribution of each layer to effective leaf area index (LAI) in stratified forest canopies, two Scots pine stands were selected in Haguenau forest, Alsace, France. One stand, 80 years old, had a sparse tree layer and a dense herb layer. The other stand, 50 years old, had a closed tree layer and dense herb and shrub layers. Hemispherical photographs, taken at 10-metre intervals along transects beneath each layer, were digitized and analysed. In the two-layered stand, mean LAI was 0.9 for herbs and 1.5 for trees, contributing 37% and 63%, respectively, to total LAI. A positive and significant correlation was found between layers, suggesting that the herb layer had not yet adjusted to the recent thinning of the stand. In the three-layered stand, mean LAI was 1.1 for herbs, 0.4 for shrubs and 2.1 for trees, a contribution of 31%, 11% and 58%, respectively, to total LAI. The positive and significant correlation for LAI among layers may be explained by the presence of a mixture of light demanding and shade-tolerant species in the undergrowth. Horizontal spatial auto-covariance of estimates was not significant, denoting adequate sampling interval for statistically independent measurements. Such in situ assessments of LAI, differentiating vegetation strata, are useful from the perspective of remote sensing of forests, since undergrowth plays an important role in the integrated spectral response of whole canopies.