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This paper deals with the issue of segmentation methods in hemispherical photography determining diffuse site factor (DIFFSF) and leaf inclination angle distribution in forest stands simultaneously. Field inclination angle distributions were sampled in pure stands of European beech, hornbeam, sessile oak and silver birch on sites where towers facilitated crown access. In the same stands leaf litter traps were placed from which LAI values were derived after autumn leaf fall. Analogue hemispherical photographs were taken in summer before leaf fall. We combined the ellipsoidal G-function and Markov–Poisson model to invert leaf inclination angle functions (LIDF). Field leaf inclination angle distributions were planophile for three species and plagiophile for birch. The planophile distributions were well represented by ellipsoidal as well as beta distribution while plagiophile distribution of birch was exclusively represented by beta distribution. When segmentation methods were varied, LIDF parameter predictions were more in correspondence with field values by using sub-pixel methods than by using binary methods. When integrating vignetting properties into the segmentation algorithm or when accounting for standard sky luminance distribution, the accuracy of LIDF predictions varied; it is assumed that this is due to variation in sky properties during photography. Thus, different segmentation techniques in hemispherical photography did not yield constancy in deriving different required variables, i.e. DIFFSF and LIDF. Rather, method of segmentation affects leaf inclination angle estimation.

In the tropics, old-growth forests are converted to other land cover types at a high rate and young secondary forest may gain in importance. Information on associated changes in leaf gas exchange and other leaf traits can be valuable for modelling biogeochemical fluxes under altered land-use patterns. We studied in situ photosynthetic parameters and stomatal conductance for water vapour in eight abundant tree species of young secondary forest and eight tree species of natural old-growth forest in Central Sulawesi, Indonesia. In sun leaves, the average maximal stomatal conductance (g smax) in the secondary forest (SF) species was 2.1 times higher than in the old-growth forest (OGF) species. Species with a high g smax reduced g s sharply when vapour pressure deficit of the air increased, whereas species with a low g smax were much less sensitive to air humidity. For area-based photosynthetic capacity (A max-area), the SF species had a 2.3 times higher average than the OGF species. For both, g smax and A max-area the variation among species was higher in the OGF than in the SF. When all tree species (n=16) are considered, species means of specific leaf area (SLA), leaf N concentration and leaf P concentration were significantly correlated with g smax and A max-area. The strong correlation between A max-area and foliar P (r 2=0.8) is remarkable as the alluvial soils in the study region are rich in nutrients. If the eight OGF species are analysed separately, the only significant correlation was observed between SLA and mass-based A max; in the SF species strong correlations were found between leaf size and A max-area and g smax. These results show that the conversion of old-growth forest to young secondary forest in Sulawesi significantly alters tree leaf gas exchange characteristics and that chemical and structural leaf traits can be used for the prediction of these changes. The best correlations between leaf gas exchange parameters and leaf traits were obtained by different traits in the SF species, the OGF species and the entire pool of studied species.