relascope

A relascope is a handheld optical instrument used in forestry for rapid, non-destructive estimation of stand density and basal area. It is designed to assist field crews in forest inventories by providing a quick method to translate visible tree trunks into a measure of how much wood occupies a given area.

The device typically consists of a small telescope or sighting tube with a reticle and a scale calibrated in basal area factors (BAF). By looking through the relascope at trees from a fixed line or distance, the user assesses whether a tree’s trunk image fills or exceeds a defined portion of the reticle. Each counted tree represents a fixed unit of basal area, determined by the instrument’s BAF setting. The total basal area for the surveyed stand can then be calculated by multiplying the number of trees counted by the corresponding BAF and adjusting for plot dimensions.

In practice, the relascope is commonly used on sampling lines as part of a cruise or inventory to estimate stand density, thinning requirements, or timber value. It offers a fast, economical alternative to direct diameter measurements, especially in even-aged stands or when a quick overview of site density is needed. Limitations include reliance on observer judgment, sensitivity to distance estimation, and reduced accuracy in uneven-aged or very dense stands. Modern field methods often supplement or replace it with prism-based devices or laser rangefinders, but the relascope remains a recognized tool in historical and some contemporary forest mensuration practices.