Estimation of stand density index has been based on the assumption that the only cause of mortality in fully stocked stands is diameter growth. For example, when average diameter increases by 1 percent, a fixed proportion (1.6 percent) of trees must die, regardless of age, average tree size, and other factors. This balance between growth and mortality entails the maximum limit of density index; for loblolly pine it is 1,140. We found a 10-year-old loblolly pine stand with density that is up to 59 percent greater than the maximum. The decisive factor of this exceptional density is the abundance of seeds shed by a row of mature pines. This finding requires reconsidering our understanding of stand dynamics. It is likely that, in addition to diameter growth, some internal factors contribute to mortality of trees. The proportion of mortality is not fixed but may change with age. Besides theoretical implications, further analysis of the reported finding can produce better methods of density estimation.
Zeide, Boris; Stephens, John. 2010. The densest loblolly pine stand and its silvicultural implications. In: Stanturf, John A., ed. 2010. Proceedings of the 14th biennial southern silvicultural research conference. Gen. Tech. Rep. SRS 121. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 339-342.