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Combining High-Resolution Aerial Photography with Gradient-Directed Transects to Guide Field Sampling and Forest Mapping in Mountainous Terrain

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Abstract:



Forest inventory and management relies on accurate maps of vegetation structure and composition. Creating such maps typically proceeds in two main stages: delineating stand boundaries on midscale aerial photography (≈1:15,000) followed by collection of reference data in field plots. Technical and logistical limitations arise with respect to the resolution of photography, the allocation of field plots, and the sequence of the stages. Here we present a novel approach for forest mapping that (1) places the mapping process as the last rather than the first stage; (2) concentrates sampling in areas with strong environmental gradients; and (3) uses large-scale, high-resolution aerial photography (≈1:2,000) to supplement field data and midscale airphotos. Our design builds on observations that plant communities in mountainous areas often exhibit strong correlations with environmental variables and that digital or hardcopy maps of these variables are becoming more widely available. In the first stage, 1:2,000 aerial photography is obtained via helicopter-mounted small-format cameras along flight lines that are located subjectively to follow significant environmental gradients. In the second stage, field plots are placed within airphoto transects to provide reference data of forest conditions. An integrated analysis of plot data and high-resolution photography provides the empirical basis for the development and calibration of an interpretation key. In the third stage, this key is applied to the delineation and classification of forested area on stereoscopic 1:15,000 aerial photography across the landscape of interest. We demonstrate this approach using a watershed in southwestern British Columbia and compare four probability-sampling designs with the gradient-directed approach proposed here using computer simulations. The results indicate that sampling along topographic gradients leads to a loss of accuracy with respect to estimation of distributional parameters. However, gradient-directed sampling is as likely as probability sampling to capture the full range of variability in forest conditions, with greatly improved logistics and cost-effectiveness. We conclude that our sampling design is a practical alternative for mapping projects in topographically complex landscapes. FOR. SCI. 49(3):429–443.

Keywords: Small-format aerial photography; dry montane forests; environmental management; forest; forest management; forest resources; forest structure; forestry; forestry research; forestry science; gradsects; natural resource management; natural resources; sampling design

Document Type: Miscellaneous

Affiliations: 1: Ph.D. Candidate School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia, Canada, V5A 1S6, Phone: (604) 291-5775; Fax: (604) 291-4968 hsandman@sfu.ca 2: Associate Professor School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia, Canada, V5A 1S6, Phone: (604) 291-3069 lertzman@sfu.ca

Publication date: 2003-06-01

More about this publication?
  • Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
    Forest Science is published bimonthly in February, April, June, August, October, and December.

    2015 Impact Factor: 1.702
    Ranking: 16 of 66 in forestry

    Average time from submission to first decision: 62.5 days*
    June 1, 2016 to Feb. 28, 2017

    Also published by SAF:
    Journal of Forestry
    Other SAF Publications
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