Biology of Poa annua in a temperate zone golf putting green (Agrostis stolonifera/Poa annua). I. The above-ground population.
Seasonal changes in the above-ground population of a temperate zone golf green were studied for 2 years by destructive sampling (coring and sorting). Five species were identified in the green. Only Poa annua and Agrostis stolonifera were numerically significant and they formed a mosaic of patches dominated by one species or the other. The P. annua population depended for its maintenance, at least in part, upon annual re-establishment from seeds, an event that overlapped with the senescing of flowering tillers in spring and early summer. Dense patches of A. stolonifera did not suppress P. annua germination but may have suppressed seedling establishment. By comparison with other populations of P. annua and other grasses, seed production rates and seedling and tiller densities were high (270 000 tillers m-2), but tiller life expectancy was short. Most tillers died without flowering. A. stolonifera was the dominant component in summer and P. annua was dominant in winter. Seasonal changes in composition appeared to be driven by the tillering capacity of one species relative to the other (i.e. by birth rates not death rates). Most greens were subject to random, patchy disturbances. Since A. stolonifera had limited ability to colonize open areas, it was probably in these patches that P. annua initially established. The balance finally achieved between the companion species in any particular green may reflect the probability of disturbances occurring in that green.