Great Cranberry Island Heath Focus Area Description, MNAP October 2003 
Great Cranberry Island Heath 
Cranberry Isles 
Description: 
This focus area, located on the southwestern portion of Great Cranberry Island, consists 
chiefly of a 175-acre Coastal Plateau Bog Ecosystem in outstanding condition. Although it is not 
as large or dramatic as some other coastal bog systems in Downeast Maine, the location of Great 
Cranberry Island Heath at the southern geographic limit of this ecosystem type, coupled with its 
excellent condition, make it one of the best examples of this ecosystem type in Maine. 
Information on it was obtained by University of Maine researchers in the 1980s; it is a current 
priority to revisit the site and update this information. 
The peatland occupies a shallow sand- and gravel-surfaced basin and is bordered by 
small hills. It appears to drain westerly and southwesterly to the sea via two low corridors 
between hills. The bog exhibits characteristic zonation that includes a well-developed black 
crowberry (Empetrum nigrum) community with abundant baked apple-berry (Rubus 
chamaemorus) and lawns of deer-hair sedge (Trichophorum cespitosum). Black crowberry, 
baked apple-berry, and deer hair sedge are all characteristic plants of coastal bogs in Downeast 
Maine. Interestingly, these truly boreal plants also occur in alpine areas of Western Maine and 
New Hampshire – the common feature being the cool summer climate. Common juniper 
(Juniperus communis) and islands of black spruce (Picea mariana) are locally abundant in the 
bog. Only a relatively small central area of the bog is raised and it lacks the steep marginal slopes 
characteristic of some coastal bogs. The raised area consists of shrub-heath and wooded shrubheath 
dominated by black spruce, dwarf huckleberry (Gaylussacia dumosa), and peat moss 
(Sphagnum fuscum). On its northern slope the raised plateau is more heavily wooded with black 
spruce and on its other sides it slopes down to moss-lawn/sedge/shrub-heath fen. The south side 
of the western drainage corridor consists of a very wet open fen with abundant white beak-rush 
(Rhyncopsora alba). A different peat moss, Sphagnum pulchrum, is the dominant moss in this 
wet fen. The peripheral margins of the peatland are sparsely wooded with black spruce. Peat 
depths range from 5.5 meters in the raised plateau area to 2-3 meters in the open fen areas and 
shallower in the peripheral wooded fens. 
The coastal shores adjacent to Great Cranberry Island Heath have been mapped as tidal 
waterfowl and wading bird habitat. 
Rare Species and Exemplary Natural Community Table for Great Cranberry Island Heath 
Common Name 
Latin Name 
S-RANK 
G-RANK 
State 
Status 
Exemplary Natural Communities 
Coastal Plateau Bog Ecosystem S3 N/A N/A 
Other Habitats Mapped by MDIFW: 
Tidal Waterfowl / Wading Bird Habitat 
Conservation Considerations: 
• In general, threats to peatlands include peat mining, hydrologic alteration, timber harvest 
around the forested perimeters, and inappropriate adjacent development. 
• Invasive plant species such as common reed (Phragmites australis) and purple loosestrife 
(Lythrum salicaria) may pose future threats to this wetland. 

Great Cranberry Island Heath Focus Area Description, MNAP October 2003 
• Peatland systems benefit from establishing and/or maintaining vegetative buffers around 
their perimeter wherever possible. A buffer of 250 feet or more will serve to limit 
impacts from adjacent development, help prevent erosion, limit colonization of invasive 
species, and prevent unnecessary impacts from off road vehicle use. 
Protection Status: 
The focus area is currently in private ownership.