Geographic Resource Solutions

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A thematic study to assess the scientific accuracy and cost efficiency of different
field methods for gathering data to promote forest management for protection of soil
and water, aimed at identifying a method to recommend to developing countries.

To identify the most scientifically valid and least expensive method for collecting data on
the soil and water protective function of forest in developing countries, FAO carried out a
comparative study of four methods: visual forest floor cover assessment; forest canopy and
floor cover assessment; line-point transect forest cover assessment; and forest floor cover
biomass assessment. In collaboration with partner organizations in three pilot countries –
Mexico, Nepal and Viet Nam – the methods were field tested during the summer of 2014. An
international workshop with the pilot country counterparts in October 2014 then evaluated the
methods for the accuracy of the forest cover and erosion data obtained, time required, costs of
gathering data and ease of use in the field. The results of the study are presented here.

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This paper addresses the differences between canopy cover and canopy closure, as well as different estimation techniques that are suitable for making accurate estimates of the two different canopy measurements.

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This paper reviews and compares/contrasts some of the different canopy cover estimation techniques.  Included in the paper is a reviewof the different concepts of canopy cover and canopy closure and how the methods are either appropriate or inappropriate for estimation of these canopy characteristics.

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The California Department of Forestry and Fire Protection(CDF) investigated seven methods for estimating overstory crown canopy. Subjective ocular estimates were compared with the more objective sampling tools; vertical sighting tubes and spherical densiometers. Intensive and controlled measurements allowed us to compare accuracy. We also present the time required to complete the different methods. Ocular estimates based on a walk-through of the riparian area proved sufficient for most pre-harvest evaluations. These estimates were always underestimates, which is conservative from a public trust resource perspective. Estimates that are more accurate require the use of a vertical sighting tube. We recommend the use of the vertical sighting tube to sample canopy along transects rather than plots, as the former are more efficient.

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This is a USFS Technical Note that involves a comparison of cover estimation using a vertical sighting tube and densitometer.

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A scientifically sound, cost effective and easy-to-apply method for collecting overstory and understory cover and disturbance data to promote forest management for protection of soil and water.

This publication presents a method for collecting reliable data on forest protective functions for soil and water. This method – the line-point transect forest cover and erosion assessment method – records forest canopy, floor cover and erosion evidence. The method was designed through an FAO study designed to identify the most scientifically valid and least expensive method for collection of these data in developing countries. The instrument used in this method, the GRS DensitometerTM, is small, light and easy to carry and comparatively cost efficient.

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Master's Thesis by Sarah Moore of Texas A&M University at Kingsville, 2010.  This paper involves an evaluation of Northern Bobwhite habitat and includes  the use of the GRS Densitometer for sampling horizontal cover, which was be used to estimate visual obstruction/cover of a site.  Visual obstruction was related to nesting success and used to evaluate different types of habitat.