Describing the Structural Complexity of Old-Growth

Eric Zenner, Dave Hibbs, Steve Acker, Bill Emmingham

How do you characterize the structural complexity of a forested stand?  One approach is to evaluate the relationship of a tree to its neighboring trees and determine the degree of difference (the gradient) in the magnitude of the diameter or height.

Zenner, E.K.  2004.  Does old-growth condition imply high live-tree structural complexity?  Forest Ecology and Management 195:243-258.

Zenner, E.K. and D.E. Hibbs.  2000.  A new method for modeling the heterogeneity of forest structure.  Forest Ecology and Management 129:75-87.

Zenner, E.K., S.A. Acker, and W.H. Emmingham.  1998.  Growth reduction in harvest-age coniferous forests with residual trees in the western central Cascade Range of Oregon.  Forest Ecology and Management  102:75-88.

Acker, S.A., E.K. Zenner, and W.H. Emmingham.  1998.  Structure and yield of two-aged stands on the Willamette National Forest, Oregon:  Implications for green-tree retention.  Canadian Journal of Forest Research  28:749-758.

Promoting the Natural Regeneration of White Pine

Eric Zenner, Jerry Krueger, Klaus Puettmann

What's the recipe for white pine regeneration and growth?  Two parts receptive seedbed, one part overstory cover to provide moisture yet discourage rust, and one part aspen competition control.

Zenner, E.K.  2008.  Short-term changes in Pinus strobus sapling height-to-diameter ratios following partial release:  testing the acclimative stem-form development hypothesis.  Canadian Journal of Forest Research, in press.

Krueger, J.A., E.K. Zenner, and K.J. Puettmann.  2007.  Development of eastern white pine (Pinus strobus L.) regeneration under a reserve shelterwood following intermediate removals and windthrow. Northern Journal of Applied Forestry 24(2):134-137.

Zenner, E.K. and J.A. Krueger.  2006.  Understory and overstory growth responses to structural retention of mature eastern white pine (Pinus strobus L.).  Journal of the Torrey Botanical Society, 133(4):585-592.

Zenner, E.K., K. Puettmann, and J. Krueger.  2005.  Early growth responses of naturally regenerated eastern white pine (Pinus Strobus L.) to partial release from juvenile aspen and pathological pruning.  Northern Journal of Applied Forestry 22:27-34.

Characterizing the Impacts of Riparian Silviculture on Soil Nutrients

Doug Kastendick, Eric Zenner, Brian Palik

Riparian forests are often managed differently from upland forests to protect important hydrologic function and stream habitat, but little work has been done to determine the impacts of different approaches to riparian management on these, or other, important ecological conditions.  This project documents impacts of alternative management practices on subsurface flows.

Impacts of Riparian Silviculture on the Diversity and Species Composition of Understory Vegetation

Michelle Martin, Eric Zenner, Brian Palik

This project documents impacts of alternative management practices in riparian areas on coarse woody debris and the composition, abundance, and diversity of understory vegetation.

Characterizing the Impacts of Riparian Silviculture on Woody Vegetation

Stacey Olszewski, Eric Zenner, Brian Palik

This project documents impacts of alternative management practices in riparian areas on understory light levels and the abundance of woody vegetation, including competition.

Evaluating the Development of Forest Heterogeneity

Eric Zenner

How you characterize forest stand structure has a lot to do with where you are standing and what indices you use.  Because many tools are dependent on spatial scale, using a "moving window" lets us determine an optimal plot size to accurately characterize structure.  These structures then provide clues as to the development of forests subjected to various fire intensities, and now to fire suppression.

Zenner, E.K.  2005.  Investigating scale-dependent stand heterogeneity with structure area curves.  Forest Ecology and Management 209:87-100.

Zenner, E.K.  2005.  Development of tree size distributions in Douglas-fir forests under differing disturbance regimes.  Ecological Applications 15:701-714.

Zenner, E.K.  2000.  Do residual trees increase structural heterogeneity in Pacific Northwest coniferous forests?  Ecological Applications 10(3):800-810.

Evaluating the Effects of Deer Browse and Prescribed Fire on the Development of Red Pine Forests

Eric Zenner, Jeri Peck

Lacking natural predators, deer populations have been rising for years.  These hungry ungulates don't hunker down for the winter--they're out there eating up a storm, including millions of tasty tree seedlings.  By munching white pine seedlings in preference to shrubs and hardwood species, deer browse has shifted understory and midstory diameter distributions, species compositions, and rates of succession.

Testing the Response of Young Birch to Early Thinning

Eric Zenner, Klaus Puettmann

We often hear the call to thin "early, light, and often," but how heavy is light?  A range of residual thinning densities (3663-6692 trees/ha, 1800, 1200, and 600 trees/ha) were tested in a 5 m tall aspen-paper birch stand.  After 6 years, paper birch was overtopped by aspen in the control plots and accounted for only 14% of the basal area.  In thinned plots, paper birch occupied all diameter classes and accounted for 77-87% of the basal area.  While some thinning was necessary to maintain paper birch dominance, no residual density was the clear winner.

Zenner, E.K. and K.J. Puettmann.  2008.  Contrasting release approaches for a mixed paper birch (Betula papyrifera) / quaking aspen (Populus tremuloides) stand.  Northern Journal of Applied Forestry, in press.

Investigating Alternative Silvicultural Approaches in Northern Hardwoods

Julia Burton, Eric Zenner, Lee Frelich

How can silviculture be used to create old-growth structure in northern hardwoods forests?  Old-growth characteristics were evaluated in several stands in and near the Crosby-Manitou State Park along the north shore of Lake Superior in Minnesota and used to develop prescriptions for cutting nearby younger stands.  Natural disturbances create small gaps, which can be silviculturally recreated in younger forests to achieve management goals such as enhanced wildlife habitat and higher stem quality.

Burton, J.I., E.K. Zenner, and L.E. Frelich.  2008.  Frost crack incidence in primary and mature to old second-growth hardwood forests of the southern boreal – northern temperate transition zone.  North. J. Appl. For., in press.

Evaluating the Impacts of Harvest Operations on Regeneration

Jeremy Fauskee, Eric Zenner, Alaina Berger, Klaus Puettmann

You hear a lot of talk about how you have to be careful about compaction when you harvest with heavy equipment, but what impact does it really have?  Re-vegetation following harvest was correlated with the number of times equipment was driven over a given spot (precisely recorded using GPS) and soil compaction.  Sure enough, it doesn't take too many passes to compact the soil.  But suckering species like aspen don't seem to mind.

Zenner, E.K., J. T. Fauskee, A.L. Berger, and K.J. Puettmann.  2007.  Impacts of skidding traffic intensity on soil disturbance, soil recovery, and aspen regeneration in north-central
Minnesota.  Northern Journal of Applied Forestry 24(3):177-183.

Overstory Structure of Mature Red Pine Forests:  Characterizing the Range of Natural Variability and the Impacts of Alternative Silvicultural Prescriptions

Eric Zenner, Jeri Peck

To restore the landscape mosaic, we need structural targets for mature stands as well as old-growth.  This project provides the first data on the natural range of variation in mature red pine stands and poses the question, What affect on overstory structure do silvicultural prescriptions intended to transition mature stands toward "old growth condition" have?

Ecological Land Types as Clues to Oak Regeneration

John Kabrick, Eric Zenner, Dan Day, D. Gwaze, Randy Jensen

From an oak's point of view, what's the best way to characterize the "good spots" for regeneration?  Turns out topography, soils, hydrology, and the local plant community are pretty helpful.

Kabrick, J.M., E.K. Zenner, D.C. Dey, D. Gwaze, and R.G. Jensen.  2008.  Using ecological land types to examine landscape-scale oak regeneration dynamics.  Forest Ecology and Management, in press.

Contrasting Seedling Survival and Growth among Thinning, Small Gap, and Large Gap Harvest Treatments

Eric Zenner, Jeri Peck

What are the differences among stands that receive different silvicultural treatments from a pine seedling's point of view?  This study evaluates the regeneration success of underplanted red pine, white pine, and jack pine seedlings under three alternative silvicultural prescriptions (thinning, 1/4 acre gaps, and 3/4 acre gaps) in the vicinity of Lake Winnibigoshish.