United States

Department of

Agriculture

Forest Service

Northeastern

Research Station

Research Paper NE-714

Laura S. Kenefic

Ralph D. Nyland

Habitat Diversity in Uneven-aged

Northern Hardwood Stands:

A Case Study
Published by: For additional copies:

USDA FOREST SERVICE USDA Forest Service

11 CAMPUS BLVD SUITE 200 Publications Distribution

NEWTOWN SQUARE PA 19073-3294 359 Main Road

Delaware, OH 43015-8640

June 2000 Fax: (740)368-0152

Visit our homepage at: http://www.fs.fed.us/ne

The Authors

LAURA S. KENEFIC received a B.A. in environmental studies from the State

University of New York at Binghamton in 1992, and an M.S. in forest resource

management from the State University of New York College of Environmental

Science and Forestry in 1995. She joined the Northeastern Research Station in

1994 and is a Cooperative Education Graduate Student and Research Forester

(in training) with the Ecology and Management of Northern Forest Ecosystems

unit. She is stationed at the Penobscot Experimental Forest in Bradley, Maine,

and is completing a Ph.D. in forest resources at the University of Maine, Orono.

RALPH D. NYLAND received B.S. and M.S. degrees in forestry and silviculture

from the State University of New York College of Environmental Science and

Forestry in 1958 and 1959, and a Ph.D. in forest management and silviculture

from Michigan State University in 1966. He joined the faculty of the State

University of New York College of Environmental Science and Forestry in 1967,

and serves as Distinguished Service Professor of Silviculture within the Faculty

of Forestry.

Manuscript received for publication 16 February 2000

Abstract

Habitat characteristics were quantified in an empirically balanced uneven-aged

northern hardwood stand in central New York. Canopy structure, wildlife trees,

downed woody material, low cover, and richness and abundance of understory

vegetation were assessed. High vertical structural diversity and low horizontal

patchiness were associated with the single-tree selection system. Downed logs

and wildlife trees were spatially well distributed, and cavities at a range of

heights and sizes were documented. Application of a selection cutting

decreased total canopy closure, but maintained high vertical structural diversity

and an even distribution of foliage among canopy strata. Cutting reduced the

number of wildlife trees, but increased low cover, shade-intolerant understory

vegetation, and the abundance and complexity of downed woody material. This

study provides quantifiable evidence of the diversity of habitat characteristics

associated with a balanced stand structure and uniform spatial arrangement of

different sized trees in uneven-aged northern hardwood stands.
1

Introduction

The objective of our research is to quantify habitat

characteristics of uneven-aged northern hardwood stands.

The structural complexity of uneven-aged communities

has been a deterrent to habitat assessment in the past.

Furthermore, the selection system is not often applied in

northern hardwoods, making it difficult to locate potential

research areas. Although irregular uneven-aged stands

commonly result from different forms of partial cutting,

“true” selection cutting resulting in empirically balanced

stands is rare.

The selection system enables forest managers to sustain

long-term growth and production in uneven-aged stands

(Nyland 1996). A target structure is defined in terms of

basal area, diameter distribution, and maximum diameter.

Cuttings are then made on a fixed cycle to remove mature

trees individually or in small groups, tend immature age

classes, and regenerate a new cohort. Removals are

prioritized within the limits of residual spacing, structure,

and density goals. Noncommercial and disease-prone

species, unacceptable growing stock (poor form, low

vigor, defective, or low-quality trees), and trees beyond

the maximum diameter are removed where possible.

Marking diminishes structural excesses and makes

provisions to rebuild deficit size classes. Adequate

growing space is allocated to vigorous trees, and

acceptable growing stock (trees with demonstrated

potential for future growth) is released. Once a balanced

condition has been attained, it is believed that managed

stands will prove sustainable in terms of both structure

and production (Nyland 1996).

The deliberate attempt to define, create, and maintain an

empirically balanced uneven-aged condition differentiates

selection system from other partial cuttings, which often

have a disruptive effect on stand structural conditions

(Nyland et al. 1993). For this reason, we describe the

habitat characteristics of a balanced stand, to serve as

an example of the type of conditions associated with

selection cutting. This study is comprehensive, and we

have presented only selected highlights of our findings

here.

Materials and Methods

Study Area

The Cuyler Hill State Forest in Cortland County, New York,

is a northern hardwood forest dominated by Acer

saccharum Marsh. (60% of basal area) with

representations of Fraxinus americana L. (12%), Prunus

serotina Ehrh. (8%), Fagus grandifolia Ehrh. (7%), Betula

alleghaniensis Britton (3%), Tsuga canadensis (L.) Carr.

(3%), Acer rubrum L. (2%), Tilia americana L. (2%),

Ostrya virginiana (Miller) K. Koch (1%), Acer

pensylvanicum L. (1%), and miscellaneous (1%).

Topography is hilly, and soils are well to somewhat poorly

drained channery and medium-textured loams and silt

loams (Nyland et al. 1976).

The stand was treated with single-tree selection cuttings

in 1973 and 1993. These treatments removed the

poorest trees and maintained a measurably uniform spatial

distribution of growing stock. The harvesting operation

was done by chainsaw felling and tree-length skidding

with rubber-tired tractors. Directional felling was used to

minimize residual stand damage, and logs were skidded on

designated trails to a landing outside the stand. Residual

structure closely resembled the Arbogast (1957)

distribution both times (Fig. 1). This structure, proposed

by Eyre and Zillgitt (1953) and presented as a

management guide by Arbogast (1957), represents an

empirically balanced distribution of trees by size class.

Residual basal area in the Cuyler stand, computed for all

trees 2.54 cm in diameter at breast height (d.b.h.) and

larger, was 16.5 m2/ha in 1973 and 16.6 m2/ha in 1993.

Data Collection and Analyses

A 30.5-m systematic grid with a nested plot design was

used to sample structure and vegetation in the 12-ha

study stand before and after the 1993 cutting.

Cavity trees, snags, and downed logs were measured on

8.03-m radius plots at 45 grid points (every other point

on the grid). Cavity trees were defined as live trees and

snags at least 2.0 m in height and 10 cm in d.b.h. with a

nest cavity, den, or hollow that might shelter a holenesting species (Healy et al. 1989). No attempt was

made to differentiate between inactive and active cavities,

or between “natural cavities” (Evans and Conner 1979)

and excavated holes. Potential cavity trees with decay but

no actual hollow were not included in the sample.

Diameter at breast height, species, cavity height, and size

of the cavity entrance were recorded. Multiple cavities

were recorded if present. Diameter and length were

recorded for downed logs greater than 10 cm at the small

end. Logs in decomposition class 5 (Maser et al. 1979)

were not included in the sample.

Number of stems by species of all herbaceous and shrub

vegetation regardless of size, and seedlings less than 0.3

m in height were recorded on 1.01-m2

 plots at all 87 grid

points. Percentage of cover by species was also

determined on these plots using the “cramming” method

(Hays et al. 1981). Ranges, rather than absolute values,

were used for estimating percentage of cover.

Canopy structure was quantified at 1.52-m intervals on

four 9.14-m transects in cardinal directions at 45 grid

points. A right angle penta-prism was used to determine

presence or absence of foliage in each of three canopy

strata: understory (1.5 to 5.0 m), midstory (5.0 to 12.0

m), and overstory (12.0 m and above). Total canopy

closure (percentage of sample points with foliage in at

least one canopy layer) was used as an index of withinstand horizontal structural diversity. Vertical structural

diversity, or the degree of stratification, was the

percentage of points with foliage in two or more strata

simultaneously. Vertical structural consistency, or the

degree to which foliage is evenly distributed through the
2

three defined canopy layers, was determined by comparing

closure in different strata.

Point samples of ground cover were also obtained every

1.52 m on the transects. Categories included downed

woody material (including logging slash), litter, exposed

organic soil, and exposed mineral soil. Additional

measurements of understory vegetation were taken by

dropping a plumb bob and recording all species intersected.

The 24 samples of ground cover and canopy closure at each

grid point were treated as subsamples for statistical

analyses. Percentage of ground cover and canopy closure

were determined using the mean number of observation

points at which a given condition was present within each

plot. Pre-cut and post-cut values were compared using a

paired t-test for means (α= 0.05).

In addition to the above measurements, tops of 20 A.

saccharum trees felled in 1993 were measured. Diameter

at the base of the top, number of forks, and length and

diameter of all bole and branch pieces were recorded down

to a 10-cm minimum diameter.

Results

Cavity Trees and Snags

In the 1993 pre-cut stand, cavity trees (n= 25) occurred at

a density of 27.45 ± 4.57/ha, with a mean of 1.04 ± 0.04

cavities/cavity tree. Mean d.b.h. of cavity trees was 38.8 ±

2.8 cm (range 12.5 to 61.4 cm). Cavities were unevenly

distributed by tree species with a disproportionate number

occurring in F. grandifolia, although d.b.h. ranges and

means were similar among species. Of the measured

cavities, 27 percent were smaller than 8 cm, 32 percent

between 8 and 15 cm, and 41 percent larger than 15 cm.

These were distributed at a range of heights, with 42

percent below 1.5 m, 19 percent between 1.5 and 5 m, and

38 percent between 5 and 12 m. No cavities were detected

above 12 m.

Snags (n= 10) occurred at a density of 10.97 ± 3.83/ha in

the 1993 pre-cut stand. Mean snag d.b.h. was 18.6 ± 3.9

cm, but both mean d.b.h. and range in diameter differed by

species. Notably, F. grandifolia had a higher mean diameter

(35.6 ± 11.7 cm) and a far greater range of values (19.1 to

52.0 cm) than those for other species, though a small

sample size precluded meaningful statistical evaluation.

Furthermore, even though 92 percent of cavity trees were

live, 8 percent were dead F. grandifolia. This suggests a

link to the beech bark disease, which is known to

predispose trees to decay in the sawtimber classes of

hardwood stands (Filip 1978; Houston and O’Brien 1983).

A projection of post-cut conditions from a tally of trees

marked for removal suggests that the abundance of cavity

trees and snags decreased and the distribution by size and

tree species was altered. Large diameter F. grandifolia, for

example, were heavily marked due to the beech bark

disease.

Canopy Structure

Horizontal structural diversity, vertical structural diversity,

and vertical structural consistency were all high in the precut stand (Table 1). These structural characteristics are

indicative of the widespread intermingling of trees of

different sizes and ages that is related to a balanced

diameter distribution and even spacing (Kenefic and

Nyland 1996). The link between diameter distribution and

canopy structure is further strengthened by a study of tree

and crown characteristics in this stand, that established

significant relationships between tree diameter and height,

crown length, and crown projection area (Kenefic 1995;

Kenefic and Nyland 1999).

Although foliage in the residual stand remained distributed

evenly between the midstory and overstory, percentage of

canopy closure in all categories decreased significantly

(Table 1). Lower percentage of closure in the understory

(and thus lower occurrence of all three strata

simultaneously) is most likely the result of sapling losses

during logging rather than silvicultural treatment because

few understory trees were of merchantable size.

Figure 1.—Diameter distribution of an empirically

balanced uneven-aged stand on the Cuyler Hill State

Forest, in relationship to the Arbogast (1957) guide.
3

Low Structure

Downed logs greater than 10 cm in diameter at the small

end (n= 128) occurred in the pre-cut stand at a density of

140.35 ± 16.43/ha. These had a mean length of 5.82 ±

0.30 m and 7 percent forked at least once. Selection cutting

resulted in an influx of downed woody material. Logging

slash in the form of hardwood tops, in particular, greatly

increased the complexity of low structure. The A.

saccharum tops sampled following the 1993 entry were

highly complex, with a mean of 3.72 ± 0.80 forks/top and a

mean accumulated branch length (sum of all branch and

bole pieces in a given top) of 20.53 ± 4.36 m. Percentage

of ground cover by woody slash increased significantly (p=

0.0001) from 3 percent to 11 percent post-cut, and foliage

on branches and tops from felled trees covered 20 percent

of the post-cut ground surface. This represents a

potentially important but temporary source of woody

material and browse.

Understory Vegetation

Thirty-eight plant species were detected in the understory

sample of the study stand. Herbaceous vegetation

contributed the most in terms of ground cover (23%),

followed by shrubs (10%) and seedlings (8%). Importance

values based on percentage of cover, stem density, and

frequency show that the five most important species were:

A. saccharum, Viburnum alnifolium Marshall, Dryopteris

spp., Viola papilionacea Willd., and Arisaema triphyllum (L.)

Schott. Overall, the understory community consisted

primarily of shade-tolerant species, with minimal

components of early successional, light-demanding

species. Percentage of cover of herbaceous, shrub, and

seedling vegetation decreased significantly following

logging, while exposed mineral soil, organic matter, and

logging slash increased significantly (Table 2). Although

time since cutting was insufficient to detect changes in

species composition, sampling in another selection stand

suggests that a short-term increase in the component of

shade-intolerant understory vegetation will occur in

response to lower residual canopy closure (Kenefic 1995).

Conclusions

These measurements of stand structural diversity and

species composition represent the first attempt at

comprehensive habitat quantification in a managed

uneven-aged stand. The findings clearly demonstrate the

diversity of features associated with the selection system in

northern hardwoods, and should serve as a source of

baseline data for future research on this and similar sites.

The diversity of habitat characteristics associated with an

empirically balanced structure provides a noncommodity

incentive to practice the selection system. High canopy

closure, predominance of shade-tolerant understory

vegetation, and a wide range of cavity heights and sizes

were documented in our study and may prove

characteristic of uneven-aged stands. Most notably, the

stand had a high vertical structural diversity and an even

distribution of foliage among canopy strata both before and

after selection cutting. This consistency of structure is

evidence of the previously unquantified link between

habitat diversity and maintenance of a balanced stand

structure and uniform spatial arrangement of different-sized

trees in uneven-aged northern hardwood stands managed

under the selection system.

Table 1.—Canopy closure percentages and stratification in an empirically balanced selection stand on the Cuyler

Hill State Forest, 1993 (Kenefic and Nyland 1996). Results of paired t-tests for means (α = 0.05) are shown

Pre-cut Post-cut Paired t-test

Canopy stratification (n = 45) (n = 45) (p-values)

Canopy 97 ± 0.7 85 ± 2 < 0.0001

- foliage in any stratum

Understory 67 ± 3 37 ± 3 < 0.0001

- foliage 1.5 to 5.0 m

Midstory 68 ± 3 59 ± 3 0.0050

- foliage 5.0 to 12.0 m

Overstory 76 ± 3 59 ± 3 < 0.0001

- foliage above 12.0 m

Both understory and midstory 46 ± 3 27 ± 3 < 0.0001

- foliage 1.5 to 5.0 m and 5.0 to 12.0 m

Both midstory and overstory 50 ± 2 38 ± 3 < 0.0001

- foliage 5.0 to 12.0 m and over 12.0 m

All three strata simultaneously 35 ± 2 18 ± 3 < 0.0001

- foliage 1.5 to 5.0 m, 5.0 to 12.0 m, and above 12.0 m
4

Literature Cited

Arbogast, Carl, Jr. 1957. Marking guides for northern

hardwoods under selection system. Stn. Pap. 56. St.

Paul, MN: U.S. Department of Agriculture, Forest

Service, Lake States Forest Experiment Station. 20 p.

Evans, K.E.; Conner, R.M. 1979. Snag management. In:

Management of north central and northeastern forests

for nongame birds. Workshop proceedings. Gen. Tech.

Rep. NC-51. St. Paul, MN: U.S. Department of

Agriculture, Forest Service, North Central Forest

Experiment Station: 214-225.

Eyre, F.H.; Zillgitt, W.M. 1953. Partial cuttings in northern

hardwoods of the Lake States. Tech. Bull. 1076.

Washington, DC: U.S. Department of Agriculture, Forest

Service. 124 p.

Filip, Stanley M. 1978. Impact of beech bark disease on

uneven-age management of a northern hardwood

forest (1952 to 1976). Gen. Tech. Rep. NE-45.

Broomall, PA: U.S. Department of Agriculture, Forest

Service, Northeastern Forest Experiment Station. 7 p.

Hays, R.L.; Summers, C.; Seitz, W. 1981. Estimating

wildlife habitat variables. FWS/OBS-81/47. U.S.

Department of Agriculture, Fish and Wildlife Service,

Biological Service Program. 111 p.

Healy, W.M.; Brooks, R.T.; DeGraaf, R.M. 1989. Cavity

trees in sawtimber-size oak stands in central

Massachusetts. Northern Journal of Applied Forestry.

6:61-65.

Houston, David R.; O’Brien, James T. 1983. Beech bark

disease. U.S. Department of Agriculture, For. Insect and

Dis. Leafl. 75. Washington, DC: Forest Service. 8 p.

Kenefic, L.S. 1995. Quantitative assessment of wildlife

habitat in uneven-aged northern hardwood stands.

Syracuse, NY: SUNY College of Environmental Science

and Forestry. M.S. thesis. 202 p.

Kenefic, Laura S.; Nyland, Ralph D. 1996. Structural

development and consistency in uneven-aged

northern hardwood stands. In: Proceedings of the

1995 Society of American Foresters convention; 1995

28 October-1 November; Portland, ME. Bethesda, MD:

Society of American Foresters. 441-442.

Kenefic, L.S.; Nyland, R.D. 1999. Sugar maple heightdiameter and age-diameter relationships in an

uneven-aged northern hardwood stand. Northern

Journal of Applied Forestry. 16:43-47.

Maser, Chris; Anderson, Ralph G.; Cromack, Kernait, Jr.;

Williams, Jerry T.; Martin, Robert E. 1979. Dead and

down woody material. In: Thomas, Jack Ward. Wildlife

habitats in managed forests: the Blue Mountains of

Oregon and Washington. Agric. Handb. 553.

Washington, DC: U.S. Department of Agriculture:

78-95.

Nyland, R.D. 1996. Silviculture: concepts and

applications. New York: The McGraw-Hill Companies,

Inc. 576 p.

Nyland, R.D.; Alban, L.M.; Nissen, R.L. 1993. Greed or

sustention: silviculture or not. In: Nurturing the

northeastern forest. Proceedings of a joint meeting of

the New England Society of American Foresters and

Maine chapter of the Wildlife Society. Misc. Rep. 382;

Publ. 93-05. Orono, ME: Maine Agricultural and Forest

Experiment Station: 37-52.

Nyland, R.D.; Craul, P.J.; Behrend, D.F.; Echelberger, H.E.;

Gabriel, W.J.; Nissen, R.L.; Uebler, R.; Zarnetske, J.

1976. Logging and its effects in northern hardwoods.

Res. Pap. 31. Syracuse, NY: Applied Forest Research

Institute, SUNY College of Environmental Science and

Forestry. 134 p.

Table 2.—Ground cover percentages in an empirically balanced selection stand on the

Cuyler Hill State Forest, 1993. Results of paired t-tests for means (α = 0.05) are shown

Pre-cut Post-cut Paired t-test

Ground cover (n = 45) (n = 45) (p-values)

Herbaceous vegetation 25 ± 2 14 ± 1 0.0001

Shrubs 11 ± 2 7 ± 2 0.0143

Seedlings 21 ± 2 12 ± 1 0.0001

Litter 95 ± 0.8 77 ± 3 0.0001

Exposed mineral soil 1 ± 0.5 13 ± 1 0.0001

Exposed organic soil 0 ± 0 5 ± 3 n/a

Logging slash 3 ± 0.6 11 ± 2 0.0001
Printed on Recycled Paper

Kenefic, Laura S.; Nyland, Ralph D. 2000. Habitat diversity in uneven-aged

northern hardwood stands: a case study. Res. Pap. NE-714. Newtown Square,

PA: U.S. Department of Agriculture, Forest Service, Northeastern Research

Station. 4 p.

Habitat characteristics were quantified in an empirically balanced uneven-aged

northern hardwood stand in central New York. Canopy structure, wildlife trees,

downed woody material, low cover, and richness and abundance of understory

vegetation were assessed. High vertical structural diversity and low horizontal

patchiness were associated with the single-tree selection system. Downed logs

and wildlife trees were spatially well distributed, and cavities at a range of

heights and sizes were documented. Application of a selection cutting

decreased total canopy closure, but maintained high vertical structural diversity

and an even distribution of foliage among canopy strata. Cutting reduced the

number of wildlife trees, but increased low cover, shade-intolerant understory

vegetation, and the abundance and complexity of downed woody material. This

study provides quantifiable evidence of the diversity of habitat characteristics

associated with a balanced stand structure and uniform spatial arrangement of

different sized trees in uneven-aged northern hardwood stands.

Acknowledgments

This research was funded in part by the McIntire-Stennis Cooperative Forestry

Research Program. The authors would like to thank Roger Nissen, Steven

Stedman, Craig Davis, Dudley Raynal, and William Porter of SUNY-CESF for

their assistance and advice. Reviews of an earlier version of this manuscript

were provided by William Ostrofsky, formerly of the Cooperative Forestry Research

Unit, University of Maine; and Alan White and Michael Greenwood, Department

of Forest Ecosystem Science, University of Maine.
Headquarters of the Northeastern Research Station is in Newtown Square,

Pennsylvania. Field laboratories are maintained at:

Amherst, Massachusetts, in cooperation with the University of Massachusetts

Burlington, Vermont, in cooperation with the University of Vermont

Delaware, Ohio

Durham, New Hampshire, in cooperation with the University of New Hampshire

Hamden, Connecticut, in cooperation with Yale University

Morgantown, West Virginia, in cooperation with West Virginia University

Parsons, West Virginia

Princeton, West Virginia

Syracuse, New York, in cooperation with the State University of New York,

College of Environmental Sciences and Forestry at Syracuse University

Warren, Pennsylvania

The U. S. Department of Agriculture (USDA) prohibits discrimination in all its programs and

activities on the basis of race, color, national origin, gender, religion, age, disability, political

beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all

programs.) Persons with disabilities who require alternative means for communication of

program information (Braille, large print, audiotape, etc.) should contact the USDA's TARGET

Center at (202)720-2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room

326-W, Whitten Building, 14th and Independence Avenue SW, Washington, DC 20250-

9410, or call (202)720-5964 (voice and TDD). USDA is an equal opportunity provider and

employer.

“Caring for the Land and Serving People Thr ving People Through Research”