New Zealand Journal of Marine and Freshwater Research abstracts
Effects of forest harvesting and woody debris removal on two Northland
streams, New Zealand
Brenda R. Baillie
Forest Research
Private Bag 3020
Rotorua, New Zealand
email: brenda.baillie@forestresearch.co.nz
Kevin J. Collier
John Nagels
National Institute of Water and Atmospheric
Research Limited
P.O. Box 11 115
Hamilton, New Zealand
Abstract The short-term effects of Pinus radiata
forest harvesting to the stream edge followed by stream-cleaning (removal
of woody debris from the stream channel), on instream light levels, stream
temperature, dissolved oxygen concentrations, and aquatic invertebrates were
assessed in streams draining partly (25% clear-cut) and totally (100% clear-cut)
harvested catchments, compared with nearby indigenous forest and mature pine
plantation reference sites. There were marked increases in in-stream light
levels and water temperatures following forest harvest and stream-cleaning
at both sites. In-stream light levels increased from 8–13% to 60-90% and
maximum monthly water temperatures increased on average by 5.6°C in the
partly harvested and 3.6°C in the fully harvested catchment. Dissolved
oxygen levels decreased at both sites shortly after harvest (94%–71% saturation
in the partly harvested catchment; 72%–37% saturation in the totally harvested
catchment), increasing to 75% and 81%, respectively, 1 year later. Although
aquatic invertebrate mean density and taxa richness increased at both sites
following harvest, the relative abundance of sensitive mayfly, caddisfly,
and stonefly species decreased and community composition changed to one dominated
by Chironomidae (midges) or Mollusca. Impacts relative to pre-harvest conditions
were not as marked in the totally harvested catchment, possibly because of
pre-existing elevated stream temperatures and high levels of sand and silt.
Any downstream protection provided by the forested headwaters of the partly
harvested catchment was soon lost after the stream entered the clear-cut
area, although these forested headwaters may provide a potential source of
aquatic invertebrates for re-colonisation in the future as water quality
and habitat recover. Our results suggest that: (1) pre-existing constraints
on habitat quality can influence the magnitude of harvesting impacts; and
(2) length of stream edge harvested may be a better indicator of impact on
some aspects of stream ecology, such as lighting, stream temperature, dissolved
oxygen, and aquatic invertebrate community composition, than percentage of
catchment harvested. This study also highlights the importance of considering
the hydrological and landscape context for mitigating harvesting and wood
management impacts on stream ecosystems.
Keywords harvesting; forestry; stream; aquatic invertebrates;
temperature; dissolved oxygen; light levels; substrate; woody debris; New
Zealand
M03084; Online publication date 18 February 2005
Received 17 November 2003; accepted 28 October 2004
New Zealand Journal of Marine and Freshwater Research, 2005, Vol. 39:
1–15
0028-8330/05/3901–0001 © The Royal Society of New Zealand 2005
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