Study finds riparian areas can restore themselves

A study in Oregon wildlife refuge finds ‘passive restoration’ 
can have a dramatic impact after cattle removed

This photo taken in 1990, shows eroded banks, channel width, and many areas of bare soil.
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Simply removing cattle may be all that is required to restore many degraded riverside areas.

An Oregon State University study found removal of cattle from Hart Mountain National Antelope Refuge in eastern Oregon helped to rehabilitate the natural environment.

Riparian, or riverside, vegetation is particularly susceptible to the effects of grazing because cattle tend to congregate around rivers and streams for easy access to water, lush forage and favourable terrain. Their presence can cause woody plants to decrease, riverbanks to erode, streams to become shallower and wider, and change the quality and temperature of the water.

This photo taken in 2013 shows an increase in willow along with a decease in the amount of bare soil.
This photo taken in 2013 shows an increase in willow along with a decease in the amount of bare soil. photo: Jonathan Batchelor

The researchers, whose work is published in the journal Environmental Management, compared 64 pairs of repeat photographs taken in 2013 and 2014 with those taken before cattle were removed in 1991 on Hart Mountain. They found promising results showing that passive restoration works as a way to rehabilitate a landscape after decades of cattle grazing. There was an increase in woody riparian vegetation, and most notably a fourfold increase in willow and rushes. Patches of bare soil decreased to a 10th of what they were while livestock were still kept in the area. Exposed stream channels decreased dramatically in 63 per cent of the cases, as did channel widths (64 per cent) and the number of eroding banks (73 per cent).

The resurgence of riparian vegetation was not ascribed to climate changes, given that the years prior to 1991 were generally less drought stressed than the years following the removal of the cattle.

“The study at Hart Mountain National Antelope Refuge shows just how much a system can change within only two decades of cattle removal,” said researcher William Ripple.

“The removal of cattle can result in dramatic changes in riparian vegetation, even in semi-arid landscapes and without active restoration treatments,” added colleague Jonathan Batchelor.

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