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