Research--Silviculture PSU

Our research interests are both applied and theoretical, our projects span a variety of temporal and spatial scales, and our products are shaped by the graduate students involved.

Overstory Structure of Mature Red Pine and Eastern Hardwoods Forests: Characterizing the Range of Natural Variability

Eric Zenner, Jeri Peck

To restore the landscape mosaic, we need structural targets for mature stands as well as old-growth. This project provides data on the natural range of variation in mature red pine (MN) and eastern hardwood (PA) stands and evaluates our ability to characterize structural variation in plots up to 1 ha in area.

Zenner, E.K. and J.E. Peck. 2009. Characterizing structural conditions in mature managed red pine: Spatial dependency of metrics and adequacy of plot size. Forest Ecology and Management 257:311-320.

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 10:800-810.

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.

Natural regeneration and stand dynamics

Linking Oak Regeneration, Productivity, and Quality to Site

Yvette Dickinson, Eric Zenner

Despite our love affair with oak, not all sites are suited to oak regeneration. Some just aren't worth the time and money it would take to get them/keep them in oak. But can we predict which sites those are based on soils, topography, and management history? This project attempts to do just that, at the landscape scale in central Pennsylvania.

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 38:181-189.

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 24:134-137.

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, 133:585-592.

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 Spatial Pattern of Natural White Pine Regeneration

Eric Zenner, Jeri Peck

When natural regeneration of white pine occurs, where does it occur? Patches of young white pine under red pine near Lake Winnibigoshish, MN are being evaluated for proximity to seed source, overstory composition, and growth to try to characterize under what conditions this species natural regenerates. The odds of white pine advance regeneration surviving a winter harvest with respect to distance to skid trails was also determined.

Peck, J.E. and E.K. Zenner. 2009. Field Note: Quantifying the risk of mortality and damage to advance regeneration within the path of harvesting equipment. Northern Journal of Applied Forestry 25:211-213.

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. Fortunately, that kind of information is often available in the GIS database and can be used to predict which areas will need the least help getting regenerated.

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 255:3051-3062.

Ecological responses to silvicultural treatments

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, MN.

Testing the Response of Young Birch to Early Thinning

Eric Zenner, Klaus Puettmann

How heavy should "early, light, and often" be? A range of residual thinning densities (600 to >6000 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 25:124-132.

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 Impacts of Harvest Operations on Regeneration

Jeremy Fauskee, Eric Zenner, Alaina Berger, Klaus Puettmann

How careful do you have to be about compaction when you harvest with heavy equipment? Re-vegetation following harvest was correlated with the number of times equipment was driven over a given spot (recorded using GPS). Sure enough, it doesn't take too many passes to compact the soil. Suckering species like aspen don't seem to mind, but herbs sure do.

Zenner, E.K. and A.L. Berger. 2008. Influence of skidder traffic and canopy removal intensities on the ground flora in a clearcut-with-reserves northern hardwood stand in Minnesota, USA. Forest Ecology and Management 256:1785-1794.

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 24:177-183.

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.

Impacts of Harvest Intensity on the Ground Flora

Eric Zenner, John Kabrick, Randy Jensen, Jeri Peck, Jennifer Grabner

The Missouri Ozarks Forest Ecosystem Project (MOFEP) is a multi-generational study on silvicultural impacts that demonstrates adaptive management in practice. This project looked at short-term changes in the ground flora from the first wave of harvest entries.

Zenner, E.K., J.M. Kabrick, R.G. Jensen, J.E. Peck, and J.K. Grabner. 2006. Responses of ground flora to a gradient of harvest intensity in the Missouri Ozarks. Forest Ecology and Management 222:326-334.

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. Northern Journal of Applied Forestry 25:133-138.