98
P. Goethals' A. Dedecker' W. Gabriels . N. De Pauw
Gammaridae also prefer more stony material, this means quickly running streams
where sediments do not settle. In cases of deeper waters without cavities (due to
artificial embankments) the Gammaridae are only present when the dissolved
oxygen percentage is sufficiently high. The pH value plays a role under specific
circumstances, but this classification is of the lowest importance in the tree.
6.3.1.2
Application of Predictive Classification Trees for River Management
waterlevel <= 10.5: 1
WATER
LEVEL
pH<~7,95: 0
waterlevel > 10.5
HOLLOW
RlVER BEDS
pH > 7,95: I
Fig. 6.4. Example of a classification tree model of Gammaridae in the Zwalm
river basin. The single bold frames contain the classification variables, while the
tripie frames contain the final prediction of the Gammaridae (0 = absent and 1 =
present). Hollbed is an ordinal categorical variable (six classes: 1= very good
hollow beds under trees; 2 = good hollow beds; 3 = hollow beds by erosion under
vegetation; 4 = moderate cavities; 5 = hollow beds not probable; 6 = no hollow
beds by artificial embankments).