EFFECTS OF OZONE AND CLIMATE ON PONDEROSA PINE (PINUS-PONDEROSA) GROWTH IN THE COLORADO ROCKY-MOUNTAINS

Long-term radial growth trends of ponderosa pine (Pinus ponderosa var. scopulorum) were studied in second-growth stands in the Front Range o f the Colorado Rocky Mountains to determine if there has been any impa ct from oxidant air pollution. Although ozone concentrations are relat ively high at some locations, visible pollutant injury was not found i n any trees. Time series of basal area increments are generally homoge neous within stands. Concurrent periods of increasing and decreasing g rowth can be found in stands throughout the Front Range, which indicat es that there are temporal growth trends at the regional level. Most o f these trends appear to be related to the effects of stand dynamics a nd climate. Correlation analysis with climatic variables indicates tha t soil moisture supply is the dominant factor controlling interannual variation of basal area growth. Palmer hydrological drought index is h ighly correlated (positively) with growth during the summer months; to tal precipitation in spring is positively correlated with growth, and mean temperature in spring is negatively correlated with growth. There are no recent changes in growth trends that might be associated with elevated levels of ambient ozone in the Front Range.