Recruitment of Phalaris aquatica within existing swards 1. Effects of biomass manipulation, seed level modification and site preparation

A successful recruitment event in perennial grasslands is infrequent and when it occurs, the rate of recruitment and survival is low, <1% in most occasions. This paper reports on two field experiments that investigated the effects of biomass manipulation, seed level modification and site preparation on the recruitment of Phalaris aquatica seedlings. The experiments were done through drier than average years, where P. aquatica achieved successful recruitment of seedlings. Recruitment rates proportional to total seed set were 1.3-13.3% in experiment 1 and 0.5-4.2% in experiment 2. The control treatment, on average, resulted in 352 seedlings/ m2 in experiment 1 and 16/m2 in experiment 2 compared to the best treatments which had 500/m2 and 38/m2 respectively, on average. There was poor seed set in experiment 2 before the recruitment event. Presence of existing biomass compared to either removing or leaving the plant material on the ground had greater success on seedling emergence, whereas seed addition had little effect suggesting that microsites may be more important than seed availability for P. aquatica seedling emergence. Soil scarification in general failed to have significant effects in both experiments. Seedlings survived until the following summer, but few then remained through the ensuing drought. This research showed that minimal intervention was needed to encourage emergence and early survival, and provides data on the mechanisms involved for recruitment of a perennial grass species in existing swards.