Twenty five years long survival analysis of an individual shortleaf pine trees.
Abstract
A growth study of natural stands of shortleaf pine (Pinus echinata) that was measured 6 times from 1985 to 2014 provided an opportunity to investigate the influence of time dependent covariates on the survival of individual trees. Over 200 permanent plots located in naturally occurring shortleaf pine forests on the Ozark and Ouachita National Forests were measured every 4 to 7 years. Results showed that the position of a tree (RAQD), and site productivity (SIND) were important prognostic variables in determining survival of an individual shortleaf pine. The variable crown ratio (CRT) behaved as significant protective variable, and had marginally increasing influence in survival probability. The influence of RAQD in mortality increases over the time. Though average dominant plot height (PLTHT) was a prognostic variable, its influence decreases over time. An individual tree with greater than 50% crown loss has higher mortality risk than a tree with less than or equal to 50% crown loss.