Aspen Management Guidelines - Michigan Department of Natural

Paper birch Management Guidelines
1) Site Conditions. Paper birch grows reasonably well on a wide variety of sites but its best
development is on deep well-drained soils with good fertility, especially sandy loams (podzol or
gray-brown and brown podzolic soils), glacial tills and outwash (Burns et al 1990). Paper birch
stands in Michigan are commonly found on the habitat types listed in below Table 1. These habitat
types are on the lower end of the moisture and nutrient gradients.
Table 1. Common Habitat Types of Aspen in Michigan
site quality
1. NLP: Northern Lower Peninsula
2. EUP: Eastern Upper Peninsula
3. WUP: Western Upper Peninsula
2) Stand characteristics
a) Age/Size class. Age classes of paper birch in Michigan are displayed in Figure 1 below.
Figure 1. Paper birch age class distribution in Michigan State Forests, 2006.
Paper Birch
10 -99
11 0 9
12 1 9
Un 2 9
Paper birch acreage on State Forest lands is relatively minor totaling 35,463 acres, just under 1%
of the total State Forest. Most of the paper birch acreage (84%) is in the UP; with the majority in
the east half of the UP.
b) Species associations. Paper birch is recognized as the primary species in the Paper Birch cover
type (Society of American Foresters Type 18). Large, pure stands are uncommon. Birch is
commonly found in association with aspen, and northern hardwoods. Forest Inventory and
Analysis (FIA) data show that birch is also a common associate in the northern white cedar forest
type. Within the birch cover type, the most common associates are: northern white cedar (Thuja
occidentalis), red maple (Acer rubrum), balsam fir (Abies balsamea), and white spruce (Picea
glauca) (Burns and Honkala 1990, WI DNR 2002, FIA 2004).
3) Determining Management Objective. Paper birch is primarily managed on an even-age basis. Birch
does not thrive on sites with site indices below 55. These sites should be managed for objectives
other than paper birch. Where birch is mixed with aspen or northern hardwoods regenerating birch
as the primary cover type will be difficult. Where birch occurs on suitable sites in relatively pure
stands some form of shelterwood or seed tree harvest should be used. The following silvicultural
recommendations are excerpted or adapted from the Wisconsin DNR Silviculture and Aesthetics
Handbook (WI DNR, 2002).
4) Management Recommendations
a) Silvicultural System
i) Even-age management with regeneration through some form of clearcutting or by the
shelterwood system. General thinnings are only necessary to release crop trees for sawlogs
(on sites with site index of 70 or more) but can also be done on sites with site index less
than 70 if stocking exceeds the A-level (see Figure 2 below).
Figure 2. Stocking Guide for Paper Birch 1 (Marquis et al, 1969)
The area above the A-level represents overstocked conditions. The area between the A and B-levels represents
adequate stocking. The area between the B and C-levels should be considered as slightly understocked because the stand
will return to the B-level in 10 years or less. The area below the C-level is definitely understocked. Only trees in the
main crown canopy (dominants, co-dominants, and intermediates) should be included in stand measurements to be used
with this stocking guide.
Management Recommendations
i) Seedling/Sapling Stands (0-5" DBH). If the site index is less than 70, allow the stand to
develop naturally. When the site index is greater than 70, precommercial thinnings may be
done to remove brush and weeds to release crop trees but in most cases it is not
ii) Pole Timber Stands (5-11" DBH). If the stand is at site index rotation age (see Table 2
below), either regenerate to birch or if stand/site conditions are not favorable for birch
regeneration convert to another species. If the stand is within 10 years of rotation age or
stocking is below the A-level (see Figure 2), no action is required. If the stand is 10 years
or more below the rotation age and stocking is at or above the A-level, thin to the B-level.
Also when the site index is greater than 70, release crop trees during thinning.
iii) Sawtimber Stands (>11" DBH). If stand is at site index rotation age (see Table 2 below),
regenerate. When it is below rotation age, treat as recommended for pole stands.
iv) Regeneration.
(1) Seedbed preparation. Scarification or exposure of mineral soil is critical for successful
regeneration of paper birch. Disking that incorporates seed and coarse woody debris
(CWD) into mineral soil is the best seedbed. Disking should be disked within 2 years of
a good seed crop. Partial but not over-toping shade for new seedlings helps protect them
from drying without restricting the amount of precipitation that reaches the forest floor
(Perala and Alm, 1988).
(2) Shelterwood System. The initial cut should be from below to leave 20 to 40 percent
crown cover (Perala, 1988). Summer logging is recommended to improve seed bed by
scarification and to reduce the sprouting vigor of competing vegetation. Do not cut any
aspen during the initial cut to minimize sprouting competition. Remove the overstory two
to four years after the initial cut when seedlings are about waist height. This final cut
should be done in winter to minimize damage to paper birch seedlings and sprouts.
(3) Patch Clearcuts. Clearcutting small irregularly shaped patches of less than one acre is
especially useful on small tracts, roadsides, parks, or any area where consideration of
available space or potentially adverse aesthetic impact is important. Summer logging is
recommended and residual stems should be cut concurrently. Late summer or fall
scarification might be needed also.
(4) Clearcuts. This technique is recommended only when other regeneration techniques are
unfeasible for reasons such as terrain, geographic layout, merchantability, operability,
etc. Regeneration will be from stump sprouts and seed. Winter cutting, after fall seed
dispersal, may be desired. Three to five trees per acre should be left as a seed source if
cutting is done before seed dispersal. NOTE: In a clearcut, factors influencing
regeneration may favor species other than paper birch, thereby causing natural
Table 2. Expected rotation ages and sizes for paper birch stands (adapted from
Marquis et al, 1969)
Species and objective
Paper birch sawtimber
Paper birch, boltwood
Paper birch site index
Paper birch, aesthetics
Average diameter2
2. Average diameter of species shown, not of the entire stand
5) Wildlife considerations. A science-based, landscape level approach should be used to identify where
we want to manage for birch cover types, using tools such as: ecological classification systems like
habitat type (Burger and Kotar, 2003) or other systems, ecoregional plans, MI WILD, and stream
classification systems. Historic and current cover types should also be considered in the decision
making process.
Birch management requires both a “top down” (landscape) and “bottoms up” (stand level) approach
to management. Planning activities should focus on how much land is suitable for birch
management, and where that management should occur. Stand level decisions are also critical, as
these small units make up communities and landscapes. What is done at the stand level effects
wildlife habitat. Wildlife is impacted by both the composition and structural components of stands.
The more diverse the stand, the more diverse the array of wildlife species using the stand. Although
birch has a relatively limited distribution and its history is closely related to fire history it should be
managed on a variety of sites where possible. Harvest should replicate natural disturbance patterns
as much as possible, allowing for a variety of stand shapes, sizes, and amounts of variable retention.
Prescribed fire may be used to control competing vegetation and prepare a suitable seedbed for birch
establishment. On these sites, an array of age classes should exist representing everything from
newly regenerated to old and decadent. Rotation ages on this cover type should range from 45 to 80
years. Management specifications should vary from site to site. Pure birch stands are less likely in
the future in the absence of hot, catastrophic fire so birch will be found in mixtures with other
species like aspen, spruce-fir and northern hardwoods. Birch as a component of other timber types is
very important and should be retained as a minor associate as much as possible.
Birch is an important component of wildlife habitat affecting many species. All life stages are of
value to wildlife. It is generally believed that there is relatively low wildlife species diversity in pure
birch stands as opposed to more mixed stands. In Michigan, at least 60 species of birds and over 111
plant species are associated with birch.
Early developmental stages are important to a wide array of game animals (white-tailed deer,
american woodcock, snowshoe hare), and non-game species as well (chestnut-sided warbler,
morning warbler). Late developmental stages provide habitat for species such as the red-eyed vireo
and Connecticut warbler. Dead and down birch provides habitat to amphibian species.
Some areas of birch habitat should be set aside as “Special Conservation Areas” where natural
processes are allowed to occur with minimal interference. Ultimately, these areas will likely convert
to other cover types.
“Variable retention” harvests are useful in promoting wildlife values, as well as aesthetic values
when birch stands are treated. Specific site conditions dictate possible candidates for retention.
Promoting a conifer component enhances diversity, with common species including red pine, white
pine, balsam fir, northern white-cedar, and eastern hemlock. Deciduous species often include various
oaks, as well as white birch, red maple, sugar maple, and others. Leave trees occur as individual
trees or groups of trees. Even mature birch trees are beneficial when retained in “clumps” of other
trees species, around the edges of forest openings, and along stand edges. Mature birch legacy trees
ultimately provide snags that get used by woodpeckers and secondary nesters, and then eventually
become coarse woody debris. While legacy trees are not long lived, they are an essential attribute in
cover types that are predominately dominated by young age classes. The wildlife values associated
with variable retention are many. They vary from providing mast, to thermal cover for ungulates, to
perches for various species of birds that would not otherwise be found in these stands. Since birch is
most commonly managed on an “even-aged” basis, variable retention can go along way towards
alleviating public concern regarding clearcutting.
Finally, fisheries resources need to be considered in managing birch. This is particularly true of cold
water streams. Birch management in riparian zones can have a major impact on fisheries. Birch
management in riparian zones can increase available habitat for beaver, at the expense of trout
populations. Fisheries managers often prefer shade tolerant, long-lived forest cover in these areas to
provide shade to keep stream temperatures cooler and to attempt to discourage beaver. Effective
communication among resource managers is critical in these areas so that numerous conservation
values are given appropriate consideration.
Damage due to wildlife usage has been documented in this timber type. Ungulates, as well as beaver,
can have an impact on this resource.
6) Biodiversity considerations. When planning timber harvests in birch, consider designating 3 to 5%
of the total stocking as potential cavity trees and a source of future snags. Retain a minimum of four
secure cavity or snag trees per acre, with one exceeding 24” dbh and three exceeding 14” dbh. In
areas lacking cavity trees, retain live trees of these diameters with defects likely to lead to cavity
formation. Trees reserved for cavity trees and future snags can be seed trees or overstory trees left
for shelterwood purposes. In final harvest situations, consider leaving uncut patches within and
along the edges of the harvest area. These should utilize naturally occurring features of the stand
like conifer pockets, poorly drained swales and patches of mast producing species like oak, cherry or
beech. Patches may be left on the edges or within the harvest area. For harvest areas greater than 10
acres that are more than 5 chains wide some of the patches should be left within the harvest area.
Patches of at least ¼ ac (120 ft dia) should be left to equal at least 5% of the area. Use cavity trees
exceeding 18” dbh or active den trees as nuclei for uncut patches. During harvest, avoid damaging
existing downed woody material, especially large (16”+) hollow logs and stumps. Leave downed
woody material on site after harvest operations when possible. If snags and cavity trees pose safety
hazards they should be marked so that woods workers can avoid them. OSHA standards require that
“danger trees” are to be felled or marked so that no work is conducted within two tree lengths of
them. Therefore, it is often better to leave clumps or groups of trees for biodiversity and wildlife
purposes rather than individual trees. If snags must be felled for safety reasons they should be left
where they fall (adapted from Flatebo et al, 1999).
Several plants of special concern occur in these communities such as heart-leaved amica, sweet
cicely, fairy bells, and rayless mountain ragwort. Animal species of concern include red-shouldered
hawk, and northern goshawk. Consult MNFI conservation management guidelines:
 for plants:
 for animals:
[Keith, the preceding wildlife and biodiversity sections were adapted from Mike Koss’ aspen write
up and need to be revised to apply to birch. I did a search and replace to change “aspen” to
“birch” and added the bit about fire and shelterwood but the rest of it is pretty much untouched.
Please revise as needed.]
7) Regeneration standards. For purposes of MDNR’s regeneration survey, paper birch stands are
considered to be adequately stocked with 1,200 stems per acre over 1 ft tall at age 42.
8) Forest Health considerations. Paper birch is subject to many of the same insect and disease pests that
attack other shade-intolerant hardwoods in the Lake States, including gypsy moth (Lymantria
dispar), forest tent caterpillar (Malacasoma disstria), saddled prominent (Heterocampa
guttivitta), birch sawflies (Heterarthrus nemoratus) and birch leafminer (Fenusa pusilla). These
insects rarely cause mortality of otherwise healthy paper birch. Repeated attacks by birch leafminer
can predispose trees to attack by the bronze birch borer. Larval feeding by the bronze birch borer
interferes with transport of sugars and other photosynthates from leaves to roots. This leads to
smaller, less dense root systems that cannot provide adequate water to the crown. Top-down crown
dieback can eventually occur. Particularly in trees suffering from drought stress.
Paper birch is subject to a number of fungal organisms that enter through wounds and branch stubs
to cause discoloration and decay. Principal decay-causing fungi include Inonotus obliqua and
Phellinus igniarius. The root-rotting fungus Armillaria mellea infects paper birch, causing cracks at
the base of the stem (‘collar crack’).
Since the early 1930’s, widespread birch decline has occurred periodically across eastern Canada
and the northeast United States. Birch decline is the deterioration and mortality of white and yellow
birch usually following harvesting or other site disturbance, and is characterized by small, yellow
leaves in the upper crown, twig and branch dieback, bud failure and tree death within 3 to 6 years.
The problem is not fully understood, but predisposing stressors like drought, the birch
leafminer/bronze birch borer complex, root mortality and possibly viral agents play a role.
It is important to remember that paper birch is a shallow-rooted species and very susceptible to even
slight increases in soil temperature. Silvicultural activities should:
 Protect root systems of residual birch from damage and excessive sunlight
 Remove overmature and declining birch
 Remove shelterwood overstories as soon as understory birch is established.
Adapted from Cayuga Project Final Environmental Impact Statement, Chequamegon-Nicolet National Forest, 2003.
9) References
a) Burns, Russell M and Barbara H. Honkala. 1990. Silvics of North America. USDA For Serv Ag Handbook 654.
b) FIA 2004. Miles, Patrick D. Mar-20-2006. Forest inventory mapmaker web-application version 2.1. St. Paul, MN:
U.S. Department of Agriculture, Forest Service, North Central Research Station.
c) Marquis, D. A, Dale S. Solomon, John C. Bjorkbom, 1969. A Silvicultural Guide for Paper Birch in the Northeast.
USDA For Serv, NEFES Res paper NE-130.
d) Perala, D. A., and A. A. Alm. 1988. Regenerating paper birch in the Lake States with the shelterwood method.
Northern J. Applied Forestry., vol. 6, no. 4, p. 151-153.
e) WI DNR, 2002, Silviculture Handbook 2431.5, Ch 44.