The Project of enhancing
National Forest Resources Inventory System
contributing to Sustainable Forest Management
Field survey
Field surveys constitute the most difficult part of the work required to estimate Gabon’s forest resources, but are critical toward fully understanding the state of forests in Gabon.
An entire survey of all forests in Gabon would be ideal, but doing so is physically impossible. Thus, a sample survey of a finite number of samples was conducted to make estimates about all forests.
The sample survey was designed according to the following procedure.
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Conduct a pre-inventory of each type of forest classified through remote sensing, and gather field survey data.
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Determine survey plot shapes and areas in light of factors such as the amount of time taken and cost of field surveys, the priority of the field data to be gathered, and the human resources tasked with the field surveys.
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Use pre-inventory data to calculate the number of survey points required for each type of forest in Gabon, and place them throughout the country.
Survey Plot Design
Plot areas are 0.5 ha, and each plot comprises five 0.1 ha circular plots, each with a radius of 17.84 m.
The following provides the reasoning for using circular plots.
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The judgment of whether a tree lies inside or outside a plot is an extremely important decision because it has a substantial effect on the estimation of timber volume within that plot.
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The perimeter of a given circular plot is smaller than that of a rectangular plot of the same area, thereby decreasing the probability of errant judgments of whether trees near the perimeter are inside or outside the plot.
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Reliable judgments as to whether trees are inside or outside plots can be made from the centers of circular plots using Vertex ultrasonic measurement instruments, as they enable the measurement of horizontal distances from the center of circular plot to trees near plot perimeters.
688 field survey plots
Using ground surveys designed according to these procedures, 688 field survey points were placed throughout Gabon.
Field surveys were launched in 2013 after one field survey team in each of the nine provinces was trained based on the survey manual jointly developed by Japanese experts and MINEF officers.
As of the end of September 2016, surveys have been completed at 277 points.
Field survey data, gathered by the field survey teams from each province, are compiled and stored in the database at the Project Implementation Office in the Gabonese capital of Libreville.
