Response of aquatic hyphomycete communities to enhanced stream retention in areas impacted by commercial forestry

Abstract

1. Aquatic hyphomycetes are an important component of detritus processing in streams. Their response to enhanced stream retentiveness was tested by manipulating three streams located in Kielder Forest (northern England), a large plantation of exotic conifers, and two streams in Montagne Noire (south‐west France) dominated by native broadleaf woodland. Treatment was by placement of logs or plastic litter traps into a 10–20 m stream section. Fungal spores were collected from stream water upstream and downstream of the treated sections over 1–2 years. 2. The average concentration of fungal spores in reference sections was nearly 10× greater in the French streams than in the English streams. The number of hyphomycete species was also higher in the French streams. These differences between regions were probably a consequence of the much lower standing stock and diversity of leaf litter in the English streams. 3. Despite these large regional differences, the treatment had a clear effect in all streams. Detrital standing stocks were enhanced in treated sections by up to 90% in French streams and 70% in English streams. 4. Mean spore density below treated sections increased by 1.8–14.8% in French streams and 10.2–28.9% in the naturally less retentive English streams. The number of fungal species increased significantly below the treated sections of the English streams, although not the French ones. 5. In biologically impoverished plantation streams, input of woody debris can increase detritus retention and enhance hyphomycete diversity and productivity. This may have consequent benefits for detritus processing and macroinvertebrate production.

Wood placement in river restoration: fact, fiction, and future direction

“…In fact, many studies report large (>50%) and significant increases in pool frequency, pool depth, woody debris, habitat heterogeneity, complexity, spawning gravel, or sediment and organic matter retention following placement of instream structures, particularly in mountain streams and rivers (e.g., Binns 1999; Brooks et al 2004;Cederholm et al 1997;Gerhard and Reich 2000;Pierce et al 2013;Reeves et al 1997;Roni and Quinn 2001a). Studies in low-gradient (<1.5%) streams such as those in the US Midwest or western Europe have demonstrated physical habitat changes, including increased depth, cover, narrower channels, and increased organic matter retention, as a result of wood placement projects (e.g., Gerhard and Reich 2000;Hunt 1988;Laitung et al 2002;Zika and Peter 2002). Other projects designed to aggrade incised stream channels have produced increases in water depth, width, pool area, and bed elevation (reduced incision) (Newbury and Gaboury 1988;Shields et al 2004Shields et al , 2006.…”

Processing of pine (Pinus sylvestris) and birch (Betula pubescens) leaf material in a small river system in the northern Cairngorms, Scotland

“…Hydrology and substrate related features are important factors affecting retention and riparian vegetation can be a major determinant of retentive properties of streams (Speaker et al, 1984). The retentive qualities of streams are an important factor influencing biological productivity and the introduction of features, particularly woody debris, to enhance litter retention has been recommended for stream restoration programmes (Laasonen et al, 1998;Laitung et al, 2002;Muotka and Laasonen, 2002) The processing rate of pine needles was very slow at all sites in the river Nethy and limited evidence from two of the sites indicates that a significant amount of a needle may remain even after it has been in the stream for 500 days. Such lengthy processing periods may not necessarily adversely affect stream productivity if sufficient needles are retained within the stream.…”

Aquatic Hyphomycete Species Are Screened by the Hyporheic Zone of Woodland Streams

“…Two first-order (Béal and Bergnassonne) and one second-order (Orbiel) permanent streams with similar physical and chemical characteristics were selected in forested areas, situated between 02°09=E and 02°20=E longitude and 43°21=N and 43°27=N latitude (8). In all catchments, forestry was the only anthropogenic disturbance, although limited within the study area (32).…”