Doubts cast on ri­par­ian buf­fers

New Zealand Logger - - Forest Growers Research -

RI­PAR­IAN BUF­FER ZONES ARE SEEN AS THE AN­SWER TO pre­vent­ing sed­i­ment end­ing up in our wa­ter ways, but doubts are be­ing cast on their ef­fec­tive­ness.

Scion re­searchers have been study­ing ri­par­ian buf­fers in forests and dis­cov­ered that many of them are “in­ef­fec­tive”.

One of the Scion team mem­bers, Chris Phillips, told the For­est Grow­ers Re­search Con­fer­ence in Christchurch that sed­i­ment will often go through the buf­fer to a stream via con­cen­trated flow paths, even though the area is densely planted.

He says the steep­ness of the slopes is the over-rid­ing fac­tor in sed­i­ment flows and wa­ter will al­ways find a way through, car­ry­ing sed­i­ment with it, if the slope is steep enough. Trees and shrubs may trap some of the sed­i­ment, but not all of it.

Steep land sites that have just been har­vested con­tinue to be the most vul­ner­a­ble to sed­i­ment flows, as there is even less planted ma­te­rial to in­hibit wa­ter and de­bris flows.

Dr Phillips says buf­fer zones cre­ated on flat, or gen­tly slop­ing land ap­pear to be more ef­fec­tive in trap­ping sed­i­ment than those cre­ated on steep land. He says there is a need for more in-depth re­search to de­ter­mine how to bet­ter manage sed­i­ment flows.

NZL

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