The self-thinning rule and red alder management

The self-thinning rule (the —3/2 power rule) has been used frequently to describe the competition-regulated relationship between size and density in plant populations. Because the parameters of the self-thinning rule and principles are easily derived, the application of this rule to tree stands could simplify the development of stand density management guides. This paper briefly examines the structure and development of the few existing stand density management guides which are based on the self-thinning rule. The self-thinning rule is then applied to seven existing data sets to develop a guide for red alder (Alnus rubra Bong.). The self-thinning line for red alder has a slope of -1.5 and a (y-intercept (average stem volume) of 3.3 m³ (1.175 × 10² ft³). The density unit is stems ha⁻¹. The other two lines on the density management diagram, the line of imminent competition mortality and the lower thinning limit, are placed at relative densities of 55 and 30%. The relative-density values for crown closure, mortality and the lower thinning limit correspond to those for other species. It was not possible to use a seedling alder study to determine the intercept of the self-thinning line for trees.