Assessment of tree layer biomass and structure using aerial photos in lake catchments of the Šumava Mts.

The combination of georeferenced colour aerial photos and limited field measurements of individual trees was used to determine tree stand biomass in forests of prevailing Norway spruce. The technique was carried out in two localities – small catchments of natural lakes in the Bohemian Forest (56 and 76 ha in size, respectively). This method is not so expansive as the inventory based on sample plots, namely in the terrain of high dynamics in the mountains. Tree crown diameters were determined semi-automatically on the basis of orthophotos. The catchment of Plesne jezero Lake can be described by these average values: crown diameter 4.5 ± 1.35 m, mean tree height varying between 19.6 and 30.2 m depending on altitude (tree average and standard deviation are 25.5 ± 3.9 m), tree density 154 ± 67.7 ha and stand biomass 197 t/ha. The Certovo jezero Lake catchment shows somewhat different values: crown diameter 4.9 ± 1.35 m, mean tree height varying between 20.9 and 25.1 m (dependence on altitude is weak; tree average and standard deviation are 25.6 ± 2.0 m), tree density 200 ± 65.7 ha (all parameters for Norway spruce only), and stand biomass 156 t/ha (Norway spruce) + 17 t/ha (European beech). Some features are common to both catchments: a regular to random tree pattern prevails. Tree clumping is typical of the most extreme stands. Minimum tree density occurs in the zone of the altitudes 1,200–1,250 m a.s.l. The crown diameter to dbh ratio is independent of altitude. Tree height decreases linearly with altitude. The distribution of trees according to crown diameter is skewed to higher values.