Does fallen timber on floodplains influence distributions of nutrients, plants and seeds?

While much is conjectured about the ecological significance of fallen timber, there has been little work on the influence of logs on plants and nutrient distributions on periodically inundated floodplains. We compared distributions of seeds, germinated plants and a suite of soil properties around logs on (a) the floodplain proper, (b) in ‘flood runners’ (floodplain drainage channels) and (c) at randomly selected log-free locations on the floodplain. Sampling was conducted on logs oriented parallel to the river, so that we could compare the sides of logs closer to and further from the river. Numbers of exotic species germinating around flood-runner logs was much reduced compared with the other two locations. Native seeds accumulated to a greater extent on the river-side of floodplain logs compared to flood-runners logs. Densities of plants were lowest in the immediate proximity of logs, increasing up to two-fold 2 m away on both sides of logs. Gravel fraction was highest around flood-runner logs, while the fraction around floodplain logs was higher than at log-free locations. Extractable Na was higher around flood-runner logs (2.6%) than at log-free points (1.2%), but levels for floodplain logs were intermediate (2.1%). Soil samples taken near flood-runner logs were slightly more acidic than samples taken elsewhere. Our results generally were not consistent with expectations that floodplain logs would act as favourable areas for plant germination and survivorship. While certain sediment characteristics did appear to be influenced by the presence of logs (e.g., gravel fraction, pH and Na), effects were relatively small and most other measured characters were not affected by location.