STEMWOOD PRODUCTION PATTERNS IN PONDEROSA PINE - EFFECTS OF STAND DYNAMICS AND OTHER FACTORS

Growth patterns of vertical stems in nine ponderosa pines from a stand in the southern Sierra Nevada were analyzed for recent changes due to stand dominance position, age, climate, and ozone exposure. Increment s in gross bole volume and changes in growth rate were calculated for each tree. Large positive correlations were found between increments i n volume growth and basal area at d.b.h. Increments in gross bole volu me indicated that some trees declined in growth despite a large releas e of growth in 1965. Patterns of stemwood distribution along the bole were analyzed by comparing Growth Layer Profiles (GLP's) of ring width and basal area increment series. Spearman correlations were calculate d between basal area increments along the bole and normalized bole vol ume increments. The results indicated that patterns of wood distributi on along the bole were associated with age, competitive position, and release from competition. Young trees showed a trend of increasing woo d production in the upper bole after release from competition. Older d ominant/codominant trees had a similar response, although they previou sly had had more equal wood distribution along the bole. The opposite pattern was observed for canopy intermediates and suppressed trees. Th ese trees produced more wood in the upper bole area both before and af ter release from competition. Changes in relationships between seasona l climate variables and annual increments of basal area and volume wer e also examined. A multiple regression model using winter and spring p recipitation adequately explained short-term growth fluctuations durin g 1920-1955 and predicted growth during 1956-1985 for the trees as a g roup. A prominent feature of all volume, basal area, and ring width se ries was a growth response to a selective harvest in 1965. Increments in gross volume increased throughout the bole of all trees after thinn ing. This increasing trend continued for young and dominant trees but declined for older nondominant trees. It was difficult to determine wh ether ozone has contributed to these growth declines because the decli ne pattern was also consistent with competitive suppression. There is no conclusive evidence that growth changes vertically along the bole o r through time are due to ozone exposure. This study illustrates the d ifficulty of assigning causal factors to observed growth patterns, and the need to use several measures of growth response to determine the effect of different environmental factors.