Tuesday, May 19, 2009
300

Organic matter inputs to northern Minnesota headwater streams following riparian timber harvesting

Susan L. Eggert1, Brian J. Palik2, Doug N. Kastendick2, Josh J. Kragthorpe2, Randy K. Kolka2, and J. Nick Baldauf3. (1) USDA Forest Service North Central Research Station, 1831 Hwy 169 East, Grand Rapids, MN 55744, (2) Northern Research Station, USDA Forest Service, 1831 Hwy 169 E., Grand Rapids, MN 55744, (3) Water Resources Science, University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108

Timber harvesting within riparian management zones (RMZs) may affect the quantity and quality of organic matter (OM) inputs to stream food webs. We measured annual OM inputs to northern low-gradient streams in two studies.  In the first study, RMZs were either unharvested (control), or harvested within 45 m to low (5.7 m2/ha) or medium (11.5 m2/ha) residual basal area (RBA).  In the second study, RMZs were unharvested, or harvested within 30 m using whole-tree grapple skidding (WT) or cut-to-length (CTL) methods to a RBA of 15-16 m2/ha.  Total OM inputs to streams were lower immediately after riparian harvesting in the low RBA treatment of the first study.  After years 4 and 5, we found no significant differences in annual inputs between control and low or medium RBA treatments for any litter type (leaves, wood, seeds).  Eleven years after harvest within the second study, leaf inputs to low-gradient streams were significantly lower in the WT treatment compared to streams with unharvested RMZs (no difference in CTL treatment when compared to WT or control treatments).  Additional examination of instream OM standing crops and macroinvertebrate community composition will reveal whether these methods and levels of riparian harvesting alter other aspects of headwater stream function.


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