ALLOMETRIC THEORY EXPLAINS SELF-THINNING RELATIONSHIPS OF MOUNTAIN BEECH AND RED PINE

Allometric theory on mechanisms of the self-thinning rule was tested f or Nothofagus solandri populations from the Craigieburn Range, New Zea land and for Pinus densiflora stands from northern Japan. The self-thi nning rule describes a consistent relationship of mean plant mass to t he approximately -3/2 power of plant density in even-aged monocultures . Although this rule has been described for various species, mechanism s that produce certain relationships have not been well understood. We tested an allometric theory of Long and Smith of the self-thinning ru le that assumes constant foliage mass density and allometry for mean d imensions of populations that represent densest conditions for given m ean plant sizes. Only stands at maximum crowding were selected for ana lysis. The self-thinning boundary of N. solandri showed an exponent -1 .13 with a 95% CI of -1.25 to -1.02 for mean stem mass. This was signi ficantly shallower than the conventional value of the exponent -3/2, b ut was identical to the predicted exponent from the allometric theory. The thinning coefficient was also explained numerically by this hypot hesis. In contrast, analysis of published data for P. densiflora indic ated that the thinning exponent did not differ from the proposed -3/2. Empirical thinning tines varied substantially depending on species an d plant parts considered; however, the allometric theory consistently provided predictions that agreed with the observed thinning relationsh ips. Implications for the geometry of self-thinning populations and ge nerality of the allometric theory are discussed.