Balnacarn Forest - Location possibly Glen Moriston area
One of a series of maps and drawings found in old ex military map cases stored in the loft of the Fort August Forest office and recovered by Grant Macintosh.
A map of Balnacarn Forest (possibly part of Glenurquhart Forest area - but see comment below) showing the windthrow hazard classification zones for the area ranging from a reasonable 2 up to a high of 5. These important numbers guided the forester in the subsequent management of the forest the main guides being whether to carry out thinning operations in the main crop or follow a non thin regime and also at what age/height the forest crop should be felled to avoid the onset of severe wind damage. Up to a score of 3 foresters were fairly confident of thinning and growing tree crops for longer rotations. Scores of 4 and 5 presented major limitations on thinning and generally not carried out plus clear felling generally started when trees were reaching 20-25 meter top heights. A score of 6 presented a severe challenge to growing and harvesting timber crop trees.
Topex scores were major component of wind hazard calculation and arrived at by adding the elevation angles from the site to the horizon for each of the eight cardinal compass points. Some site specific topex scores are noted on the map and the higher the score the more sheltered the site.
Note that the surveys and calculations were done by Forest Surveyors George Caird and Jim Davidson.
Any clarification and corrections very welcome.