Forest Fragmentation

Forest fragmentation occurs when large continuous forests are divided into smaller blocks. Harvesting, road-building, construction of hydro corridors and other human disturbances can result in the creation of small isolated patches of forested land. These fragmented forests are subject to a number of risks related to patch size and patch isolation.
 

Aerial shot of fragmented forest near Geraldton

“The fragmentation of a forest may disrupt some ecological processes and wildlife habitat, and affect its capacity to maintain species and processes usually found in those habitats. Forest fragments may be too small to maintain viable breeding populations of species and excessive fragmentation can contribute to the loss of plant and animal species that are unable to adapt to fragmented forest conditions.” 
Ontario State of the Forest Report 2001 Section 1.1.4

 

  • Fragmentation changes habitat area and type. Reducing the amount of forest interior and increasing the amount of forest edge, favours species that prefer edge. 
  • Species may become trapped in fragments of forest. Many organisms e.g. salamanders, frogs, and turtles, find it difficult or impossible to disperse across inhospitable terrain. Even some bird species find it difficult to disperse across large clearcuts, and many plants, insects and other animals become increasingly confined to small ‘islands’. These islands support fewer species over time. 
  • Populations isolated in small patches are prone to decline due to inbreeding, and are prone to removal from the patch due to disturbances such as blow-down or changes in microclimate.
  • From an ecological perspective, forest fragmentation compounds the effects of habitat loss from clearcutting: interpreting surveys of forest wildlife data as indicators of the effects of fragmentation is challenging as it is difficult to distinguish between the effects of habitat loss and fragmentation.
  • There is a lack of empirical data and good fragmentation studies - the effects of forest fragmentation and connectedness of ecosystem components are difficult to assess

Wildlife indicators of fragmentation
A variety of forest species – salamanders, lynx, pine martin, caribou, and various plant species - are excellent indicator species.  Forest birds are excellent indicators of forestry effects at both the stand and landscape level. Many interior birds, including endangered or vulnerable species such as the Acadian Flycatcher and Louisiana Waterthrush, now occur in very low numbers due to lack of forest interior habitat. Other interior or area sensitive species of birds include Brown Creeper, Broad Winged Hawk, Barred Owl, Pine Warbler, Cerulean Warbler, Black and White Warbler, Winter Wren, Pileated Woodpecker, and the Ovenbird. Species that prefer open or forest edge areas include Blue Jay, Chickadee, Northern Flicker, Cowbirds, Ruffed Grouse, Grey Catbird, and Downy Woodpecker.
 
The Forest Management Planning Manual lists six indices of landscape fragmentation and connectedness:
  • forest composition and diversity,
  • forest edge, 
  • forest interior, 
  • forest fragmentation, 
  • forest isolation, and 
  • forest spatial pattern.
Ontario Forest Management Planning Tip:

See Table FMP 4 “Landscape Pattern or Forest Diversity Indices” for details and check Annual Reports and Reports of Past Forest Operations (RPFO) for indicators of fragmentation
 



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