Relative Tolerance: A Test of Some Indirect Criteria
Foresters define relative tolerance as the capacity of plants to persist in the understory, enduring low light and high-root competition. Indirect relative tolerance criteria have been postulated to help foresters establish species' relative tolerance ratings. Nine of these criteria were chosen and tested for their ability to make tolerance classifications for Douglas-fir and juniper stands and for their ability to make a tolerance distinction between the two species. Stands of each species were predetermined to be either more or less tolerant. Data from eight of the criteria were used in cluster analysis. The results showed few groupings of the stands within species. The two species did form two distinct clusters. T-tests showed few significant differences between tolerant and intolerant stand data for either species. T-tests on averaged species' data for the two species indicated significant differences for all but one of the criteria. About half of the results supported the original criteria. Juvenile height growth rate, number and location of seedlings data were also analyzed. Number and location of seedlings seem to be poor indicators of tolerance. Juvenile height growth rate may not be a good criterion for relative tolerance, when measured under unregulated conditions. Most criteria tested appeared incapable of making conclusive tolerance classifications; however, a possible criterion for making such classifications is leaf area: sapwood cross-sectional area ratio.
Parker, Joy N. (1986). Relative tolerance: a test of some indirect criteria. MS. 33p.