Fire-caused tree mortality in thinned Douglas-fir stands in Patagonia, Argentina

Abstract

In 2003 in a municipal park near Esquel, Patagonia, Argentina, plots within a 21-year-old Douglas-fir (Pseudotsuga menziesii) afforested area were subjected to three silvicultural treatments (thinning to Reineke's Stand Density Index (SDI) of 900, 700, 500). In March 2007 all plots were burned by a wildfire that presented extreme fire behaviour. Three weeks after the wildfire we assessed mortality, height of scorch and percentage of crown scorch, and during three subsequent growing seasons we measured mortality and growth parameters. At the end of the study, mortality differed significantly among treatments and an untreated control, and ranged from 100% in the untreated control to 25, 10 and 5% in the SDI 900, 700 and 500 treatments. The highest growth parameters and lower mortality rates were achieved at SDI indices of 700 or 500 (i.e. in the least dense plots). Trees thinned to these densities not only appear to withstand extreme fires, at least under the conditions presented, but also to achieve the highest growth rates.