Within Icelandic State Park is the Gunlogson State Nature Preserve. The preserve provides an excellent opportunity to view and study segments of natural communities marginally influenced by man. An extensive self-guided trail system has been established along the Tongue River, with access beginning at the Gunlogson Homestead site. Foot bridges provide easy crossing of the Tongue River and the area's many natural springs.
Gunlogson Nature Preserve is a link to earlier eras of different climatic conditions, and to the vast bounty that greeted North Dakota's first settlers. It is an island of intact habitat within an extensively modified landscape, and a refuge in its cool, moist conditions. Its significant biological features are the forest and wetland habitats themselves, and the array of rare plants and animals that depend on them.
Lowland Woodland. Lowland woodland is the prevailing community type in the Preserve occupying all but the wettest areas of the valley bottom. As such, it is the biological fabric which is to be maintained intact on behalf of all other Preserve features and in its own right. It is predominantly made up of eastern deciduous forest species. American elm, basswood, and ironwood dominate the mature forest canopy and subcanopy; basswood and ironwood co-dominance is relatively uncommon in the state. North of the river many of the stately canopy elm and basswood are over twenty inches in diameter. South of the river where there has been some selective logging and a small clearing, the overall dimensions of the trees are smaller. The recent spread of Dutch elm disease has resulted in the death of most elms and creation of a snaggle-toothed canopy with many standing dead and brushy openings. Beyond the immediate loss, the long-term effects on forest composition and structure are unknown and are among the major questions to be resolved by monitoring, as discussed under Preserve management. Canopy trees have also died along the River with riverbank slumping.
Beneath the forest canopy is a shrub layer of beaked hazel, which is particularly developed under canopy openings on well-drained soils. The forest floor is dominated by a variety of native sedges and forbs. A regional description and analysis of this community type is provided in Wanek (1967).
Oak Woodland. Bur oak lines the upper margins of the Tongue River Valley on both sides in bands of oak woodland. On the steep north-facing valley slope, the woods take on a decidedly boreal flavor with aspen, paper birch, and northern shrubs and herbs present. It is an admixture of eastern deciduous forest species as well as boreal and grassland species. The relatively lush woods here may also be influenced by groundwater near the surface. Almost all of the gentle south-facing valley slope on the opposite side with oak woodland is outside the Preserve boundaries and has a long history of grazing. It is drier and has more stunted trees. The oak woodland community is not particularly well-developed or intact here but, as with the opposite valley slope, is necessary for maintenance of the valley-bottom forest and its features. It fits into plans for buffering the Preserve, as well as expanding the Park trail system.
River - Creek. The Tongue River is identified as a riverine system of biological significance at state, regional, and local levels (ND Parks and Recreation Department 1987). It came out high in terms of its state - significant botanical and forest resources. These features are basically outside of the river channel itself, though the river may be considered the lifeline of the larger riverine system. Two features of this Tongue River segment are particularly pronounced. First, it is a spring-fed river segment. It often has a low flow, but it does not run dry and is a stable aquatic community in this regard.
Second, it is a "hungry" river segment because its sediment load is dumped upstream in Renwick Reservoir. This is not its natural characteristic but resulted from dam construction. The unnatural scouring quality of the river has promoted river incisement, slump banks, decline in forest canopy along the river corridor, and bare shore habitat for weed invasion. The Tongue River remains a vital component to the Preserve setting and system, and ties Renwick Reservoir management to Gunlogson Arboretum management.
Wetland Thicket. The four major scattered wetland thicket basins in and around the Preserve harbor the highest local concentrations of rare species. This habitat is known by other names as well: swamp, shrub carr, and alder thicket. It is spring-fed, remaining saturated year-round, hummocky, and dominated by dense shrubs of alder with or without red-osier dogwood. The tall shrub growth may or may not represent an overgrown, unnatural condition. Both eastern deciduous and boreal aquatic species are present, many at the outer limits of their range. It is thought to represent a "relict community" dating back to the time when the climate was cooler and moister, and forest plants and animals were spreading out in the wake of glaciers and subsequent retreat of Lake Agassiz. This habitat depends on stable groundwater flow to the surface, a topic for subsequent management discussion.