Restoration of Rivers Used for Timber Floating: Effects on Riparian Plant Diversity

Abstract

Abstract. Fluvial processes such as flooding and sediment deposition play a crucial role in structuring riparian plant communities. In rivers throughout the world, these processes have been altered by channelization and other anthropogenic stresses. Yet despite increasing awareness of the need to restore natural flow regimes for the preservation of riparian biodiversity, few studies have examined the effects of river restoration on riparian ecosystems. In this study, we examined the effects of restoration in the Ume River system, northern Sweden, where tributaries were channelized to facilitate timber floating in the 19th and early 20th centuries. Restoration at these sites involved the use of heavy machinery to replace instream boulders and remove floatway structures that had previously lined stream banks and cut off secondary channels. We compared riparian plant communities along channelized stream reaches with those along reaches that had been restored 3-10 years prior to observation. Species richness and evenness were significantly increased at restored sites, as were floodplain inundation frequencies. These findings demonstrate how river restoration and associated changes in fluvial disturbance regimes can enhance riparian biodiversity. Given that riparian ecosystems tend to support a disproportionate share of regional species pools, these findings have potentially broad implications for biodiversity conservation at regional or landscape scales.

Demonstration Restoration Measures in Tributaries of the Vindel River Catchment

“…In general, stream restoration has produced somewhat ambiguous results. For example, in some stream reaches, the current best-practice methods have been shown to enhance biodiversity (Helfield et al 2007), whereas in others there has been no effect (Lepori et al 2005). It may be that best-practice restoration does not produce the best possible result because the original channel material available to be placed back in the channels was broken up (boulders) or eliminated (large wood) as a result of channelization (Nilsson et al 2005a).…”

“…In 2010, 10 of these sites became the subject of demonstration restoration, where large boulders and large wood from upland areas were placed in the channels to compensate for the previous losses, following the recommendations of Helfield et al (2007). The tree species placed in the channel were Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L) H.…”

“…Trees were placed either diagonally or perpendicular to the flow direction, at a spacing of about one tree per 10 m of stream length. Most trees were placed with their root wads in the riparian zone, and were left unanchored to allow for restructuring and downstream movement following high flows (Helfield et al 2007). In deciding the number and location of large boulders to be added to the channel, the availability of boulders in the surrounding floodplain and hill slope was considered, along with the availability of locations to anchor them in the substrate where they would redirect the flow.…”

“…It would have been preferable to also include unmodified, pristine stream reaches in this study. However, as stressed by Helfield et al (2007), streams that were used for timber floating generally do not have unimpacted reaches and if they do, these reaches were typically bypassed by the log drivers because they were too narrow or steep and, therefore, are not comparable to impacted reaches.…”

Legacy effects of altered flooding regimes on decomposition in a boreal floodplain

“…Mean soil temperature was calculated per turf for the incubation periods of tea and the local litter separately. We determined flood duration by visual inspection of the temperature readings, as the number of days that lacked diurnal fluctuations (Helfield et al 2007). To determine soil abiotic properties we collected 16 composite soil samples from the top 5 cm of the soil (one at each incubation elevation of each treatment block).…”