The Sandstone Pavement Pine Barren of Northeastern New York: A Legacy of Fire and IceDavid Franzi
Continent: North America
State/Province: New York
UTM coordinates and datum: none
Climate Setting: Humid
Tectonic setting: Craton
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The sandstone pavement pine barren of northeastern New York are island ecosystems amidst the larger matrix of northern hardwood and mixed hardwood-conifer forests in the Champlain Lowland (Fig.1). Reschke (1990) describes sandstone pavement barren as open-canopy woodlands on very shallow soils over nearly level sandstone bedrock. The barren are marginal ecosystems in delicate balance with existing hydrogeologic and climatic conditions and vulnerable to extinction by natural processes or human activities. With fewer than 20 known sites worldwide, they are considered to be globally rare.
The sandstone pavements, known locally as "Flat Rocks", were created by the erosional effects of late-glacial catastrophic floods from the drainage of glacial Lake Iroquois and younger post-Iroquois proglacial lakes in the St. Lawrence Lowland (Chapman, 1937; Denny, 1974) approximately 13,438-12,793 calendar years before present (Rayburn et al., 2007) (Fig. 2). Ice recession from the Covey Hill threshold allowed Lake Iroquois to spill across the St. Lawrence-Champlain divide to Lake Vermont in the Champlain Lowland. The breakout lowered water level in the St. Lawrence Lowland by 14-15 meters and released an estimated 570 ± 85 km3 from storage in Lake Iroquois (Rayburn et al., 2005). The flood water was directed southeastward along the ice margin where it crossed the English, North Branch and Great Chazy watersheds before emptying into Lake Vermont. The pavements generally occur on the drainage divides between watersheds where flood scour was greatest and the exposed surfaces were not subsequently covered (Denny, 1974). Altona Flat Rock is the largest sandstone pavement in the region and lies at the southeastern end of the "Flat Rock" belt where flood water from the Iroquois breakout entered Lake Vermont (Rayburn et al., 2005; Franzi et al., 2007).
Large, coarse-boulder deposits were laid against the ice front at the mouth of the flood channel where it emptied into Lake Vermont, forming the Cobblestone Hill moraine (Franzi et al., 2007) (Fig.3). Flow velocity must have been in the range of 8.1-8.9 m sec-1 to transport the largest (2.5-3.0 m-diameter) boulders and from estimates of paleo-channel dimensions near Cobblestone Hill; flood discharge was probably in the range of 83,000-92,000 m3 sec-1. If this discharge is close to the average for the event, the duration of the Lake Iroquois breakout would have been approximately 2.5 months (Rayburn et al., 2005).
The sandstone pavements provide habitat for some of the largest jack pine (Pinus banksiana) barren in the eastern United States (Reschke, 1990). Jack pine is a relatively short-lived (<150 years), shade-intolerant, boreal species that maintains communities on the sandstone pavements because of its adaptations to fire and ability to survive in an area with thin (or absent), nutrient-poor soils and low seasonal water availability. The northeastern New York barren are near the southern limit of the present natural range of jack pine (Burns and Honkala, 1990). The relatively low-diversity pine barren community is dominated by a single tree species, jack pine, with virtually no subcanopy and few understory trees (Fig.4). The understory shrubs are predominantly late low blueberry (Vaccinium angustifolium), black huckleberry (Gaylussacia baccata), black chokeberry (Pyrus melanocarpa), sweetfern (Comptonia peregrina), and sheep laurel (Kalmia angustifolia). Three species of lichen comprise most of the ground cover (Cladonia uncialis, Cladina rangiferina, and Cladina mitis). Other ground cover plants include haircap moss (Polytrichum commune), bracken fern (Pteridium aquilinum), and Sphagnum spp. Jack pine requires periodic crown fires for successful regeneration to occur. Fire releases seeds from serotinous cones stored in the jack pine canopy, prepares a nutrient-rich ash seedbed, and reduces competition for the young seedlings (Fig. 4). Since these barren are fire-dependent ecosystems, fire exclusion may ultimately cause the local extinction of jack pine and the deterioration of the major heath plants, blueberry and huckleberry (Adams and Franzi, 1994).
The sandstone pavement pine barren in northeastern New York illustrate the impact of geologic and hydrologic processes on landscape development and contemporary ecosystem-level processes. The physical environment of the sandstone pavements strongly influences vegetation distribution and ecosystem processes; such as surface water runoff, organic matter decomposition and nutrient cycling; and the effects of ecological disturbances such as wildfires and ice storms. Recognition of these influences ensures better management and protection of the unique pine barren ecosystems.
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