Zeide, B. and Y. Zhang. 1998. Mortality of trees in loblolly pine
plantations. Canadian Journal of Forest Research. (submitted)
The annual probability of mortality for planted loblolly pine
(Pinus taeda L.) trees was estimated using a set of permanent
plots covering the entire native range of the species from the
Atlantic coast to eastern Texas. The recorded causes of death
were infestation by the southern pine beetle (Dendroctonus
frontalis Zimmermann) and other insects, lightning, and unknown
reasons. It was found that mortality from these causes does not
change much with age of trees, which allowed us to calculate an
overall mean annual mortality probability for each
density-independent factor. Two sets of these estimates are
provided: one for all plots and another for the plots that in the
past were affected by a given factor. A model was constructed to
separate analytically density-dependent from density-independent
factors of mortality recorded as "other causes." A model for
predicting density-dependent mortality was developed by
generalizing Reineke's equation. It explains 97% of variability
in predicted number of trees. The average annual probabilities
of mortality are 0.8% and 0.6% for density-independent and
density-dependent causes, respectively. Our analysis also covers
the events that wipe out entire plots such as flood, fire, and
catastrophic insect infestation. This neglected kind of
mortality, referred to as indiscriminate, eliminates four times
as many trees as density-dependent mortality and three times as
many as density-independent mortality. The difference between
the number of planting spots and the number of trees at the first
measurement makes it possible to estimate the initial mortality.
This study shows that on the average out of 100 planted trees
about two (2.2) die every year before the first inventory (mean
age is 15 years ) and four (3.8) afterwards.