ESTIMATION OF MECHANICAL RESISTANCE OF LAKESIDE PHRAGMITES STANDS

The power of resistance of reed stands against mechanical impact by wa ves and drifting matter is assessed using the mechanical properties of the stem wall (modulus of elasticity, breaking stress), the dimension s of the stem's cross section (diameter, momentum of inertia), and the culm density. The power of resistance of an individual stem (pmr) was found to be proportional to the bending stiffness (M(E)) and to the b reaking strength (M(S)) in the internode position where maximum deflec tion or breaking occurs. The power of mechanical resistance of reed st ands (PMR) was found to be proportional to the sum of individual M(E) values (or M(S) values, respectively) per unit surface (1 m(2)). Two p redictive models, based on the pmr and the PMR values were tested usin g mechanically damaged stands in the field; the pmr model fits observe d values in 70-90% of all cases (damaged culms), the PMR model explain s 53-67% of the variability in percentage of damaged biomass.