Effect of a Spaced Thinning in Mature Lodgepole Pine on Within-Stand Microclimate and Fine Fuel Moisture Content

Thinning mature forest stands to wide spacing is prescribed to reduce crown bulk density and likelihood of severe crown fi re behaviour. However, it may adversely affect surface fuel load, moisture content and within-stand wind, which infl uence sur- face fi re behaviour and crowning potential. Comparison of a mature lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) stand in southeastern British Columbia to an adjacent stand with half the basal area removed by thinning to 4 m inter-tree spacing found a decrease in canopy interception of rainfall and increases in solar radiation, windspeed, and near-surface air temperature during peak fi re danger hours over 13 fi seasons. Moisture content of needle litter and fuel moisture sticks was measured in both stands in 2005. Between-treatment differences in moisture content of sticks and litter were greatest after rain, but decreased quickly as fuels dried, to very small at moderate fi re danger. Prediction of moisture content of lodgepole pine needle litter using the Canadian Fire Weather Index System also improved as fuels dried and worked well for both stands at moderate fi re danger. There was only one day at higher fi re danger during the study. Further studies should examine physical models of fuel moisture and microclimate under a wider range of stand densities, fuel types and climatic conditions.