Seed fall and field germination of needlerush, Juncus effusus L.

Juncus effusus seed fall during one growing season was determined by use of seed traps in a freshwater emergent wetland. These observations provided i n situ seed fall estimates of similar to4.0 million seeds per square m with in the growing season, only 5% of which germinated during the 3-month field study, presumably because of unfavorable environmental conditions. Estimat ed biomass of seeds collected during this study (29 g ash-free dry mass/m(2 )) represents only 0.27% of J. effusus annual net production, despite the l arge numbers of seeds produced. (C) 2001 Elsevier Science B.V. All rights r eserved.