Effects of riparian manipulation on stream communities in small streams: Two case studies

Published source details Jowett I.G., Richardson J. & Boubée J.A.T. (2009) Effects of riparian manipulation on stream communities in small streams: Two case studies. New Zealand Journal of Marine and Freshwater Research, 43, 763-774.
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This study is summarised as evidence for the following.

	Action	Category
	Plant bankside vegetation Action Link
	Clear bankside vegetation Action Link
	Exclude livestock from riverbanks  Action Link

Plant bankside vegetation

A replicated, controlled, before-and-after study in 1995 and 2003–2005 in two streams in North Island, New Zealand (Jowett et al. 2009) found that planting bankside vegetation, along with building fences, bridges and troughs to exclude livestock, had no effect on shortfin Anguilla australis and longfin Anguilla dieffenbachii eel density. The study does not distinguish between the effects of planting vegetation and excluding livestock. Average density did not differ significantly before and 8–10 years after bankside vegetation was planted, and livestock excluded, for shortfin eels (before: 15 eels/100 m, after: 10–12 eels/100 m) or longfin eels (before: 9 eels/100 m, after: 10 eels/100 m). Average density also did not change significantly over the same time period at upstream sites in native forest for shortfin eels (‘before’: 3 eels/100 m, ‘after’: 1–2 eels/100 m) or longfin eels (‘before’: 21 eels/100 m, ‘after’: 5–11 eels/100 m). In 1995–1996, two streams (average 0.9–1.2 m wide) flowing through pasture were restored by planting bankside trees and shrubs, along with building 12 km of fences, five bridges and 12 water troughs to exclude livestock from the stream banks. One unrestored section of each stream located in native forest was sampled for comparison. Eels were surveyed by electrofishing along one unrestored and two restored sections per stream (each 35–50 m long) before restoration in 1995, and after restoration in 2003 and 2005.

(Summarised by: Vanessa Cutts)
Clear bankside vegetation

A replicated, controlled study in 2001–2002 in a stream in North Island, New Zealand (Jowett et al. 2009) found that clearing bankside vegetation, along with removing in-stream woody debris, led to higher elver density, lower longfin eel Anguilla dieffenbachii density, and similar numbers of shortfin eels Anguilla australis compared to uncleared stream sections. Results are not based on tests of statistical significance. After six months, cleared stream sections had higher average densities of elvers (1.7 elvers/m) and lower average densities of longfin eels (0 eels/m) than uncleared sections (0.8 elvers/m, 0.2 eels/m). Overall, similar numbers of shortfin eels were caught in cleared (total 11 eels) and uncleared sections (total 10 eels). In November 2001, bankside vegetation was cleared (including overhanging branches of larger trees/shrubs), and in-stream woody debris removed, from five 15-m-long stream sections. Immediately upstream of each cleared section, a second 15-m section was left uncleared and used as a comparison. Eels were surveyed monthly in each stream section from December 2001 to May 2002 by electrofishing. Stop nets were placed at the ends of each section to stop fish escaping. Eels <100 mm length (elvers) were not identified to species.

(Summarised by: Vanessa Cutts)
Exclude livestock from riverbanks 

A replicated, controlled, before-and-after study in 1995 and 2003–2005 in two streams in North Island, New Zealand (Jowet & Richardson 2009) found that installing fences and bridges to exclude livestock, along with planting vegetation, had no effect on shortfin Anguilla australis or longfin Anguilla dieffenbachii eel density. The study does not distinguish between the effects of excluding livestock and planting vegetation. Average density did not differ significantly before and 8–10 years after fences and bridges were installed, and vegetation was planted, for shortfin eels (before: 15 eels/100 m, after: 10–12 eels/100 m) or longfin eels (before: 9 eels/100 m, after: 10 eels/100 m). Average density also did not change significantly over the same period at upstream sites in native forest for shortfin eels (‘before’: 3 eels/100 m, ‘after’: 1–2 eels/100 m) or longfin eels (‘before’: 21 eels/100 m, ‘after’: 5–11 eels/100 m). In 1995–1996, two streams (average 0.9–1.2 m wide) flowing through pasture were restored by building 12 km of fences, five bridges and 12 water troughs to exclude livestock from the stream banks, along with planting of bankside trees and shrubs. One unrestored section of each stream located in native forest was sampled for comparison. Eels were surveyed by electrofishing along one unrestored and two restored sections per stream (each 35–50 m long) before restoration in 1995, and after restoration in 2003 and 2005.

(Summarised by: Vanessa Cutts)