Modeled Ecosystem Occurrences

This way of scaling ecosystems recognizes an explicit spatial hierarchy. For example, a large area dominated by lowland conifer forest (a matrix-forming system) may, on close examination, reveal a network of bogs, swamps and marshes (large patch systems) and even smaller settings of cliffs, outcrops and shores (small patch systems). Patch-forming ecosystems are often richer in species diversity than the matrix-forming ecosystems that surround them and are of great interest to conservationists as "special habitats" or "biotic hotspots." Regardless of scale, ecosystems are still coarse-filter targets as they are composed of many individual species populations and conservation activity is best directed at maintaining the entire system. 

Ecosystem Models 
Ecosystem models were created based on a landform/topographic feature data layer available for the entire ecoregion (Anderson, 1999). The landform coverage classified and mapped the ecoregion into 14 topographic settings that collectively covered 100% of the landscape. Data on wet flats and wetlands were supplemented and enhanced by detailed digital maps of wetlands delineated from airphoto analysis and compiled from several sources: National wetlands inventory, Maritime's wetland inventory and Quebec wetland mapping.

Relationships between the mapped landform units and the NVC/Natureserve community classification units were studied and made explicit through the overlay of over 8,000 ground inventory points for community types available in the U.S. and forest stand data points available in maritime Canada. Some relationships were directly synonymous (e.g. cliff and steep slope landform = Natureserve cliff and talus ecological system) others were more complex and we characterized them quantitatively (e.g. 80% of the rich northern hardwood forests occurred on bowl/ravine landforms, while 20% were on steep slopes). These relationships are discussed in detail in the individual ecosystem chapters.

After examining the relationships to the Heritage and CDC inventory points we simplified the landform models to encompass six key settings that were highly correlated with, and logical surrogates for, patch-forming ecosystems. When tested against the U.S. Heritage program ground inventory points that included natural community types, these six features collectively contained almost 81% of the 8554 compiled points although the systems themselves covered only 15% of the ecoregion. The final set included:

• Summits and hilltops
  
• Cliffs and steep slopes
  
• Bowls, hollows and ravine networks
  
• Freshwater wetlands
  
• Riparian and floodplains networks
  
• Coastal shores and wetlands

Other topographic settings, particularly side-slopes, gently sloping hills, dry flats and valley bottoms were associated with matrix-forming forest.

For more information please see The Nature Conservancy's The Northern Appalachian Ecoregional Plan.