The upside of the flood
Woody weeds ( mainly lupins, gorse and broom) are becoming a major problem on the local Ashley river, where native birds require expanses of open, clean shingle on which to breed. The recent floods have changed the situation, but only temporarily.
Prior to this year, the last good flood was in May, 2014 (480m3 ). ’’We had to wait 3 years for the next one – a 240m 3 event on April 6 this year.’’ said AshleyRakahuri Rivercare Group member and mapping expert, Grant Davey. ’’The invasion of weeds shrunk the area of clean shingle in the core bird breeding stretch from around 200ha down to just 30ha. The April flood increased it up to 75ha.’’
Much more recently we had the July 22 flood of 572m 3 which was a 1-in- 10 year event. Without a doubt, the floods have cleared away significant areas of weeds, but they will also have brought in heaps of new seed.
‘‘So much so,’’ Davey said, ‘‘that without more such floods, the riverbed will be back to its former weed-infested state within 2-3 years. Elsewhere there is plenty of evidence of this’’.
Birds such as the wrybill, which are about to arrive for their riverbed breeding season will find plenty of new sites for breeding. The problem is that there is abso- lutely no guarantee about regular floods in the future, so those breeding locations are unlikely to remain weed-free.
‘‘Hence we have spent some time formulating a plan to counter this, Group Chairman, Nick Ledgard, said.
‘‘From our long-term monitoring records we know the stretches of the river most favoured for bird breeding, so we have obtained resource consents and funding to artificially clear around 50ha at these locations and then to maintain them as weed-free sites for the long-term. This work will begin within the next 6 weeks. The floods have been of enormous help, but there is plenty of manicuring and remnant weed clearing still needed.’’
‘‘At this time of the year we have 140 predator traps in the riverbed,’’ Group trapper, Geoff Swailes said.
‘‘We lost 8 traps in the April flood, with a number of others clogged up with silt. The July event will mean more swept down river or buried under silt and shingle, but experience has taught us how to minimise such losses.’’