Survival
Neighbor density. In both Q. macrocarpa and Q.
ellipsoidalis , neighborhood density, both heterospecific and
conspecific, was positively associated with survival likelihood. Effects
were consistent across dbh classes and censuses (Figs. 2 and 3). The
effect of neighbors did not diminish with distance. Effect sizes were
often +0.5 up to +0.9. To reach effects > 0.8 means
survival would increase from 10% per 5 years without neighbors to 90%
with dense crowding.
The two species differed in detail. Indeed, both benefited most by
having Q. macrocarpa neighbors, that is, the conspecific effects
in Q. macrocarpa were stronger than the heterospecific, but just
the opposite in Q. ellipsoidalis (Figs. 2 and 3). Note: while
small sample sizes of the 2-5 cm dbh trees during the latter time
intervals made it impossible to model these trees throughout the study,
during the first two intervals, the survival effects of neighbors for
these trees were similarly consistently positive. As in the larger
trees, small Q. macrocarpa were best protected by conspecifics,
while small Q. ellipsoidalis were best protected by
heterospecifics.
While neighbor facilitation with respect to tree survival persisted
throughout the study, and in most cases remained strong after
twenty-five years, the data showed a slight but consistent downward
trend in the strength of this relationship (Figs. 2 and 3).
Elevation . Survival generally was not significantly associated
with elevation. Few tests were significant, and those that were
significant were inconsistent in direction, so we omit the effect sizes.