Recommendations on tree harvesting at Spirit Mountain

Gary B. Walton                                                                                                                                                    
July 5, 1999

1) Summary of the 1998 Rare Plant Survey on Spirit Mountain

In May and June of 1998 I conducted a rare plant survey at spirit Mountain in Duluth, Minnesota.  The purpose of the survey was to locate and identify populations of Minnesota Department of Natural Resources (MN-DNR) listed rare plant species.  Ultimately, information collected from the survey would become part of an environmental assessment for a proposed golf course at Spirit Mountain.

The chosen site of the golf course is largely forested by an ecosystem known as the “northern hardwoods association”.  The northern hardwoods association is transitional between the eastern temperate forests and boreal forests.  This forest type shows its best development and is particularly species-rich on moist fertile soils that are seldom burned or otherwise disturbed.  The fundamental tree species of the northern hardwoods association is sugar maple and depending on latitude, soil moisture, and mean annual temperature may include American basswood, yellow birch, beech, red maple, and sometimes oaks, in the overstory with ironwood in the understory.  Variations in soil moisture, soil fertility, and frequency of disturbance may create conditions suitable for boreal forest species such as quaking aspen, paper birch, balsam fir, and spruce.  Long-lived conifers such as white pine, white cedar, and Canada hemlock may also occur in northern hardwoods associations.

A large number of rare plant species are known to occur in St. Louis County including Duluth.  Of these, the MN-DNR considered at least three Special Concern status species very likely to occur at the proposed golf course site.  These were Canada hemlock tree (Tsuga canadensis), Carolina spring-beauty (Claytonia caroliniana), and moschatel (Adoxa moschatellina).  Old records report these species from similar forest stands between Duluth and Jay Cooke State Park.

A rare plant survey limited to the flora of the early spring was conducted between May 8, 1998 and June 18, 1998. Proposed golf links, cart paths, and adjacent areas were searched by walking through them several times in closely spaced parallel lines to insure complete coverage.  A total of 106 vascular plant species, most native to this area, were identified during the survey.  Included in this inventory are three state listed and one tracked species:

1)  Claytonia caroliniana Michx. (Carolina spring-beauty, Fam. Portulaceae, Special Concern)

2)  Sparganium glomeratum Laest. (clustered bur-reed, Fam. Sparganiaceae, Special Concern)

3)  Adoxa moschatellina L. (moschatel, Fam. Adoxaceae, Special Concern)

4)  Actaea pachypoda Ell. (white baneberry, Fam. Ranunculaceae, Tracked)

Thirty populations of Carolina spring-beauty were located, several of which are extensive densely covering thousands of square feet.  Seven populations of clustered bur-reed, one of moschatel, and four of white baneberry were discovered.  Canada hemlock was not found during the survey nor were any other rare plant species.

Because the survey was limited to the spring flora, certain species with later appearance times could not be targeted for searching.  Conditions in the sugar maple forest on Spirit Mountain are such that three rare moonwort ferns (Botrychium mormo, B. minganense, and B. lanceolatum var. angustisegmentum) and one rare grapefern (B. oneidense) may be present.  B. lanceolatum var. angustisegmentum (triangle moonwort, Threatened species) was found in Duluth last year near Amity Creek.  B. minganense (Mingan moonwort, Threatened species) was also found in Duluth last year near Spirit Mountain.  B. mormo (goblin fern, Special Concern species) is known almost exclusively from sugar maple forests in Minnesota.  One population site is in northern St. Louis County.  B. oneidense (blunt-leaf grapefern, Threatened species) also favors hardwood forest habitat.  I would recommend that a survey be undertaken for these and other Botrychium ferns known to occur in hardwood forests.  This survey should be conducted in tandem with a general floristic survey and other biotic surveys.

2) The Northern Hardwoods Association and Spirit Mountain’s Forests

In Minnesota the northern hardwoods association approaches its northern limits along the shore of Lake Superior starting in Duluth and ending in Cook County.  Scattered stands occur further inland along the Iron Range to Cass County.  On Spirit Mountain the northern hardwoods association is composed of sugar maple and American basswood with red oak, quaking aspen, black ash, and some conifers such as white pine, white cedar, and white spruce.  In Duluth’s remaining northern hardwoods stands species diversity is particularly high in all vegetation layers and it is possible to find plants such as maidenhair fern, blue cohosh, white baneberry, Dutchman’s breeches, and trout lily.  Elsewhere in Duluth, fragments of northern hardwoods stands can be found in the Piedmont, Woodland, and Kenwood neighborhoods but these are under pressure from development and have experienced severe human perturbation. 

Farther north in Minnesota in the Lake Superior Highlands the northern hardwoods association is represented by smaller stands and a gradual decrease in species diversity.  Many of these stands have been logged, some have been clear-cut and replaced with conifer plantations.  At its extreme northern periphery, certain herbaceous and woody species typical of northern hardwoods association become less common, rare, or drop out altogether.  In many of these peripheral forests, the only tree species present is sugar maple and species in the groundlayer are few and scattered.  Fewer than 50 native vascular plant species compose these extreme northern stands (by comparison at least 80 native vascular plant species are known from uplands sugar maple on Spirit Mountain).  For some rare herbaceous plant species at the edge of the northern hardwoods association populations are small and isolated.  Eventually the northern hardwoods association grades into boreal forest.  The boreal forest typically is composed of quaking aspen, paper birch, balsam fir, and spruce in the overstory and mountain maple, alder, and beaked hazel in the shrub layer.  Ground layer species in the boreal forest include plants such as Canada Mayflower, bluebead lily, goldthread, twinflower, and bristly clubmoss.  Very often the forest floor is carpeted by feather mosses.  In the northern hardwoods association mosses are restricted to tree trunks, rocks, and wetlands.

The terrain of Spirit Mountain is steep in most places.  Elevation in the survey area ranged between 1000 and 1300 feet.  Bedrock exposures create micro-habitats [for] ferns and mosses.  Troughs, ravines, depressions, and swales are terrain features only vaguely seen in topographic maps and these too create micro-habitats within the larger sugar maple forest. 

As discussed above, Spirit Mountain is largely forested by sugar maple with American basswood.  Red oak and other tree species are also present.  Most of the trees and forested areas appear to be mature and some parts may be remnant old growth.  The structure of the forest is composed of mature maples in the overstory with young maple trees and seedling maples in lower layers.  In places, ironwood (Ostrya virginiana) is common in the understory.  Drier sites tended to have more red oak.  Some areas have been recently logged.  These are mostly on the Midway Township side of the site.  Tree cover is sparser in these places and aspen more common than maple.

There are also numerous wetland areas ranging from seeps to black ash swamps, alder thickets, and vernal pools.  Small streams flow from some of these wetlands.  Many wetlands are found on the uneven top of Spirit Mountain which is poorly drained.  The most common type of wetland on Spirit Mountain is the black ash swamp.  These forested wetlands are found in troughs and shallow depressions and at the base of steep hills.  Most appear to have some ground water discharge supplying them.  Vegetation tends to be very lush and species rich.  The unique hydrology and the soils, which develop consequently, make these black ash swamps impossible to replace.

Several vernal forest pools were seen during the survey.  Vernal forest pools are wetlands that are temporarily flooded in the spring but often dry later in the summer.  They are important breeding habitat for several frog and salamander species because predatory fish are unable to live in these temporary ponds.  A number of other species also favor vernal forest pools such as the fairy shrimp, a sort of fresh water version of the brine shrimp.  No golf course pond can match one of these pools for diversity and beauty that results from a combination of a huge number of unrepeatable historical events that began centuries ago.

3) Logging the Northern Hardwoods Association on Spirit Mountain

The hardwood forest and forested wetland types on Spirit Mountain cannot be logged and still be expected to function as before.  Northern hardwoods association forests seldom burn and disturbance is usually limited to occasional deadfalls and tree tip-ups.  It is doubtful this area was ever cleared of trees before European settlement.  Some high grading occurred early in the century on Spirit Mountain when white pines were cut and recently logging for hardwoods has taken place on privately owned parcels.  Logging on such steep land presents problems, too.  Erosion of topsoil will occur, streams and pools will be silted in, and serious, possibly irreparable, damage will happen to the various components of natural systems on Spirit Mountain if it is logged.

Once tree cover is removed, vernal pools will quickly become dehydrated.  Water temperatures will also go up without the shade of trees making them less suitable for the species that now live there.  Logged black ash swamps will convert to alder thickets and it may be decades before trees come back.  Logging of the sugar maple forests to clear land for golf links or any other reason is not recommended.  Although patches of forest may be saved for visual enhancement, these patches are not truly representative of the sugar maple forest.  The dense shade and cool temperatures of the intact forest will be gone.  Warm air from open areas can penetrate the remaining stands to a distance about three times the height of the trees.  So, if most trees are 50 feet tall the influence of the cleared areas will be felt 150 feet inside the patch.  The smaller the patch the greater the warming and drying influence.  Species composition can be expected [to change] over time as herbs adapted to shade and cool temperatures die out.  These will be replaced by species tolerant of sun and dry, warm air.  In time one could reasonably expect see grasses, tansy, hawkweed, valerian, and dandelion becoming common species in the forest patches.  Wildflowers will become scarce or disappear.  Grading and filling associated with golf course construction will affect existing drainage patterns.  These may have negative effects on remaining maple and black ash stands, drowning one, draining another.

The Spirit Mountain sugar maple forest is contiguous with the sugar maple forest of Magney-Snively Park.  Sugar maple forests of such high quality are scarce in St. Louis County and nearly gone in Duluth.  Where are the maple forests on Maple Grove Road?  The sugar maple forest with its associated wetlands at Spirit Mountain is nearly 1.75 square miles.  For the most part, it is “roadless” except for the ski trails and some intrusions along Skyline Drive.  It probably contains the largest population of spring beauty plants anywhere in St. Louis County.  It is my opinion that no more changes should be made to the forests and wetlands on Spirit Mountain.  I believe that the ski trails and other trails are damage enough.  It is obvious that these were placed with no regard for existing populations of rare plant species or to wetlands and natural drainage patterns.  I would recommend continued floristic and rare plant surveys on Spirit Mountain.  If a commercial use must be made of this forest, I would suggest an eco-tourism approach, which would leave the forest intact for this and future generations to enjoy, appreciate, and find renewal and inspiration.  The entire parcel should be merged with Magney-Snively and this should be considered for designation as a state natural area in perpetuity.