Contrasting pathways to ombrotrophy in three raised bogs from Ireland and Cumbria, England

The plant macrofossil records from three raised bogs from western and central Ireland and from Cumbria were compared to investigate variations in the character and timing of the fen-bog transition (FBT). Two modes of raised or ombrotrophic peat formation were recognized. In the first mode the transition develops through a sedge-fen stage directly to raised-bog lawn, maintaining a near surface water table throughout the FBT (Abbeyknockmoy Bog). The second mode is characterized by a switch from fen or reedswamp to a dry Eriophorum-dominated mire type, suggestive of low or unstable water tables (Mongan Bog and Bolton Fell Moss). Comparisons with the Holocene effective precipitation record suggest that the type of transition and its timing may be affected by the prevailing climate regime. All that is required for ombrotrophy is a separation of the growing peat surface from the influence of ground and surface waters. This separation may be achieved by rapid peat accumulation in a moist climate, the accumulation of decay-resistant Eriophorum vaginatum hummocks or by a lowering of the water table, leading to a 'perched peat bed'. In the latter two cases, a 'pseudo-raised bog' community often persists, laying down highly humified peat, until increased oceanicity enables Sphagnum to dominate

Dispersal phenology of hydrochorous plants in relation to discharge, seed release time and buoyancy of seeds: the flood pulse concept supported

Item does not contain fulltext1 Restored floodplains and backwaters lacking a viable propagule bank, may need flood pulses to facilitate inward dispersal of diaspores. Temporal patterns of hydrochorous plant dispersal are, however, not well known. 2 Diversity and abundance of diaspores dispersed in a water body over 12 months were quantified using a 200 mum net in order to: (i) test for a relationship between discharge and the number of species and diaspores dispersed; (ii) examine the effect of seed buoyancy and seed release period on the length of the dispersal period; and (iii) test whether diaspores of species that disperse during a similar period of the year are characterized by similar dispersal and dormancy traits. 3 A total 359 188 individuals of 174 vascular species developed from 144 samples, with most (90%) from vegetative diaspores and only 10% from seeds. Mean number of species and diaspores varied between months in parallel with discharge levels. Stepwise multiple regression analysis showed that both seed buoyancy and seed release influenced dispersal periods. 4 In general, species that dispersed most diaspores in spring and summer had non-dormant seeds, a shorter seed release period and a shorter seed dispersal period than species whose dormant seeds dispersed in autumn and winter. Vegetative diaspores were dispersed on average over 8 months, indicating their importance to long-distance dispersal. Several species dispersed both generative and vegetative diaspores, often in different seasons. 5 Our results may assist the planning of regenerative processes in riverine wetlands at landscape scales, as dispersal phenology, and discharge rates must be taken into consideration. Vegetative diaspores may be more important than seeds, although the latter may extend the species dispersal period into other seasons. Temporal heterogeneity in diaspore dispersal influences the identity of diaspores reaching restored habitats