Southwestern ponderosa pine forest patterns following wildland fires managed for resource benefit differ from reference landscapes

Abstract

Context. Managers aiming to utilize wildland fire to restore southwestern ponderosa pine landscapes require better understanding of forest cover patterns produced at multiple scales. Restoration effectiveness of wildland fires managed for resource benefit can be evaluated against natural ranges of variation.Objectives. We describe landscape patterns within reference landscapes, including restored and functioning ponderosa pine forests of northern Arizona, and compare them to wildland fires managed for resource benefit. We make comparisons along a gradient of extents and assess the effects of scale on landscape differences.Methods. Using Sentinel-2 imagery, we classified ponderosa pine forest cover and calculated landscape metrics across a gradient of landscape extent within reference and managed landscapes. We used non-parametric tests to assess differences. We used random forest models to assess and explore which landscape metrics were most importance in differentiating landscape patterns.Results. Managed wildfire landscapes were significantly different from reference landscapes for most metrics and extents (15 ha to 840 ha). Landscape type (managed vs. reference) became increasingly differentiable with scale, with area and aggregation metrics being the most informative. Classification models increased in accuracy despite fewer observations with increasing scale.Conclusions. Wildland fires managed for resource benefit in ponderosa pine forests of northern Arizona are not producing landscape patterns consistent with reference landscapes likely due to predominance of low-severity burning and minimal resulting changes in overstory structure. Differences become more pronounced with increasing landscape size and suggest small-scale heterogeneity and mid - and large-scale homogeneity within each landscape type.