Regional growth changes in ozone-stressed ponderosa pine (Pinus ponderosa) in the Sierra Nevada,California,USA

Basal area growth trends were determined for ponderosa pine (Pinus ponderosa) in the Sierra Nevada, California, USA, to: (1) evaluate long term growth patterns, and (2) determine if there has been any recent change in the frequency of growth changes outside the expected range of natural variability. Ponderosa pine was sampled in 56 stands with the sample divided equally between sites with and without documentation of symptomatic ozone injury. Basal area increment growth was calculated, temporal growth patterns were evaluated for each tree using time series analysis techniques, and changes in growth trends were summarized for each site by decade. There were several regional growth trends during this century, including a large number of growth decreases in the 1920s and a large number of increases in the 1930s. Many trends were synchronous within stands but were less frequently synchronous between stands. There were significant growth reductions since 1950 in some stands in the southern Sierra. These growth reductions occurred in areas with the highest levels of ozone exposure and needle injury. There was no evidence, however, of significant numbers of recent growth reductions for the entire Sierra Nevada region. Some sites had growth changes possibly associated with stand dynamics, management practices, and pathogens.