In each park, a 50 m transect was established, located essentially at random but covering all representative structures. Vegetation structure and composition were recorded at 25 points (spaced at 2 m intervals) along the line. The presence or absence of vegetation within a circle of 0.60 m diameter was recorded at each point, at thirteen different heights: 0, 0.12, 0.37, 0.75, 1.5, 3.0, 4.5, 6, 9, 12, 18, 24 and > 32 m (cf., Erdelen 1984). In this way, 25 recordings (presence or absence) were obtained for each of the 13 heights per urban park. In all recordings with vegetation present, the respective plant species were also determined.
The following variables were defined for each park:
• PB00 to PB12: plant-body amount = for each of the 13 layers, the number of positive recordings (i. e., vegetation present) along the transect (maximum = 25 points per layer). The term “layer” does not imply the presence of a distinct and recognizable structural element of vegetation, but simply refers to the levels at which recordings were taken.
• PBSUM: total plant-body amount = sum of PB values (from PB00 to PB12) over all layers.
• SPBSUM: shrub plant-body amount = sum of shrub layer PB values (from PB01 to PB05).
• TPBSUM: tree plant-body amount = sum of tree layer PB values (from PB08 to PB12).
• PBHD: plant-body height diversity, calculated with the Shannon- Weaver formula, with Pi = the PB value of the i-th layer divided by PBSUM.
PBHD = -£ Pi • ln Pi