PATCH DYNAMICS OF THE STREAM MACROPHYTE, CALLITRICHE-COPHOCARPA

1. We examined changes in position and growth of Callitriche cophocarpa patches in a shallow section of a small Danish stream during the main expansion of plant cover between April and June. Mean upstream growth of patches was only 7.5% of downstream growth. The mean growth rate was 1.02 cm day-1 in length and 0.55 cm day-1 in width and the growth rates were not significantly dependent on patch size. For patches with an area (A) above 100 cm2, the growth rates in patch area (dA/dt) was proportional to patch circumference and thus square-root A and the relative growth rate (dA/dt A-1) was inversely proportional to square-root A. The smallest patches (< 100 cm2), however, expanded less than expected because of their combined tendency to grow more slowly in patch length and width than larger patches. 2. The expansion of plant cover will be much more rapid in many medium-sized patches compared to few large patches of a similar combined area, because internal self-limitation by light and space is partially relieved in smaller patches. We anticipate that recruitment and mortality of new-formed patches are critical steps preceding areal expansion. Quantification of these processes are needed fully to evaluate patch dynamics and space occupation.