Radial growth responses of singleleaf pinyon (Pinus monophylla) to wildfire

Dendroecological methods for quantifying and dating historical canopy disturbance events have been widely applied for temperate forests, but may not be useful for semi-arid woodlands, where growth is more strongly influenced by drought cycles. Our study focuses on the potential utility of dendroecological methods for reconstructing historical fire in woodlands of the Nevada Great Basin, USA, which are dominated by singleleaf pinyon pine (Pinus monophylla Torr. and Frem.). We assess growth responses to a historical fire of known date, and compare different analytical methods involving radial-growth averaging approaches.Despite the strong influence of climate on radial growth of trees growing in semi-arid woodlands, most pinyon pines sampled in this study exhibited profound growth releases in response to fire. The growth releases could be detected using radial-growth averaging criteria, even given thresholds of percent growth change that effectively eliminated responses to climatic variability. The most conservative dendroecological method was radial-growth averaging with a 10 yr moving window and a percent growth change (PGC) threshold of at least 125%. This method detected the known fire for nearly one in three surviving trees, with very minimal occurrence of false positives in control trees or in the historical record. Results suggest that such approaches may be useful for identifying and approximately dating historical fires that burned adjacent to living pinyon trees. However, these methods will likely not be able to separate historical wildfire from other disturbance types, such as pinyon ips (Ips confusus) or root rot fungi, which could be expected to cause growth releases in surviving trees. Also, the year of growth release following the known burn was delayed until years of good precipitation, resulting in a lagged response that can confound the ability of growth release methods to accurately pinpoint the year of disturbance.