Growth
Conspecific density. In both Q. macrocarpa and Q.
ellipsoidalis , growth was consistently negatively associated with
conspecific neighbor density (Figs. 4 and 5). Effects reached –0.5 to
-0.6, meaning that growth changed by half its standard deviation across
the range of neighbor density, although most effects had lower
magnitudes. The negative effect of conspecifics was consistent across
censuses in both species. In both species the impact of the nearest
conspecifics, those < 10 m away, was stronger than the impact
of neighbors 10-20 m away, though some significant negative effects
persisted at the greater distance (Figs. 4 and 5).
There were differences in detail between the two species, however. InQ. macrocarpa , the largest dbh category, trees ≥ 20 cm, was
unaffected by conspecific neighbors (Fig. 4); only smaller trees were
inhibited. In contrast, all dbh categories in Q. ellipsoidalissuffered lower growth near conspecifics (Fig. 5), though the 5-10 cm
class in Q. ellipsoidalis had small samples and erratic results.
Heterospecific density . The two species were quite distinct in
their response to heterospecific neighbors. Q. macrocarpa was
negatively impacted in all censuses and all dbh categories (Fig. 4). In
the largest dbh class (> 20 cm), this impact of
heterospecifics
contrasted
with the lack of impact of conspecifics. In contrast, Q.
ellipsoidalis was not affected by heterospecific neighbors (Fig. 5).
Effect sizes were positive more often than negative, but no effects were
significantly different from zero. The small sample sizes of the
smallest size class (2-5 cm dbh) made it difficult to discern a
relationship between neighbor density and growth, but where significant,
they were negative (reduced growth with more neighbors).
Elevation . Elevation had a significant negative effect on growth
in both species, meaning trees grew fastest at lower elevations. The
effect size was around –0.1 in most cases where it was significant,
though it reached –0.3 to –0.4 in the Q. ellipsoidalis trees
5-10 cm in diameter.
DISCUSSION