Landscape restoration of a forest with a historically mixed-severity fire regime: What was the historical landscape pattern of forest and openings?

• Small openings (<50 m long) have declined but large openings remain (>50 m long).
• Forest patches are approximately 3× longer currently than prior to settlement.
• Restoration should recreate small openings but vary with local site conditions.

Forest management of dry forests in the western US that historically experienced mixed-severity fire regimes is increasingly focused on landscape-scale restoration. However, this restoration effort is constrained by historic range of variation (HRV) reference conditions that lack information concerning the spatial configuration of these forests at intermediate scales (approximately 0.01–100 ha). I used reconstruction methods to map historical (1860) pattern of ponderosa pine-Douglas-fir forests along twenty 1 km long transects on Colorado’s Front Range and compared pre-settlement opening and forest patch lengths to current forest configurations to inform restoration reference conditions. Historically, openings were prevalent on south-and east-facing aspects, at lower elevations, and on gentler slopes. Generally, mean forest cover rose from 57% prior to settlement to 83% currently, and the current condition of any one location is 3.7 times more likely to be forested now than prior to settlement. In addition, the mean forest patch length increased from 35 to 118 m long. However, the mean opening length has changed little, increasing from 26 to 27 m long. Changes in the distribution of forest opening lengths suggest that there has been a loss of small openings (<50 m long) producing the small increase in mean patch length; however, the abundance of larger openings (>50 m) across the landscape has been relatively stable. In addition, there has been an increase in large forest patches (>50 m) at the expense of small forest patches (<50 m). Results from this study suggest that forest restoration treatments should focus on recreating small openings (<50 m long) by breaking up large contiguous forest canopy patches within the context of local site conditions.