PARENT SESSION
Oral Session # 4: Forest Ecology I: Diversity, Suppression, and Release.
Presiding: B Schamp
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.
Ontogeny of herb layer suppression by Acer saccharum regeneration thickets.
Schulz, Kurt*,1, Burleyson, Travis 1, Albrecht, Stephanie1, Zasada, John 2, Buckley, David 3, Crow, Thomas2, 1 Southern Illinois University Edwardsville, Edwardsville, IL, USA2 North Central Forest Experiment Station, Grand Rapids, MN, USA3 University of Tennessee, Knoxville, TN, USA
ABSTRACT- Sugar maple (Acer saccharum) dominated forests of Upper Michigan, USA experience a natural regime of canopy gap formation at a rate of ca. 2% per year. Selective harvest systems in the region employ multiple tree selection distributed over ca. 20-25% of stand area on a 20 year rotation. Observations of natural forest understories following gap formation suggest that understory herb communities lose species and decline in density in response to thickets of regenerating maple. Regeneration thickets are commonplace in managed stands, and may imperil most of the understory in the course of several harvest cycles. This study examined natural herb populations across a gradient of regeneration thicket age. In general herb cover and richness decline with time, showing the greatest depression in plots containing large numbers of large saplings 5-10 cm dbh. Data distributions are "triangular", with wide ranges in cover and richness at low density, and narrower ranges (and means) at high density. Light environments beneath thickets were compared across four developmental stages: seedling/small sapling phase, large sapling phase, small tree phase, mature phase. Both direct beam and diffuse light penetration are markedly lower in the large sapling phase; the other phases are comparable. Reduced light in the large sapling phase corresponds with particularly dense canopies at zenith angles that obstruct midmorning and midafternoon sun.
Key words: species richness, canopy gap, forest herb, forest management