Abstract
ContextManagers 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.ObjectivesWe 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.MethodsUsing 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.ResultsRestored forests exhibited landscapes patterns consistent with those of ecologically intact forest landscapes. Managed wildfire landscape patterns differed significantly when compared to reference landscape patterns among nearly all landscape metrics considered and became increasingly different with increasing landscape extent (15–840 ha), tending towards both denser and larger patch areas.ConclusionsLandscape patterns from wildland fires managed for resource benefit we examined differ from those of reference landscapes. Differences become more pronounced with increasing landscape size. Landscape patterns among large managed forest landscapes suggest that the predominately single-entry, low-severity disturbance regime from these managed fires is failing to reduce tree densities and break up large contiguous areas of canopy cover.
Highlights
In northern Arizona, USA, an extensive history of fire exclusion and the subsequent densification of ponderosa pine
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
We focused on three specific objectives: 1) quantify and test differences in landscape metrics calculated across a gradient of landscape extents among managed and reference landscapes, including restored and functioning landscapes 2) determine which landscape metrics are most important for distinguishing landscapes and identify how this relationship changes with landscape extent, and 3) interpret the management implications of multi-scale landscape metric differences among landscape types
Summary
In northern Arizona, USA, an extensive history of fire exclusion and the subsequent densification of ponderosa pine It is well accepted that restoration of structure and ecological function is needed across large swaths of southwestern ponderosa pine forests (Allen et al 2002; Churchill et al 2013). Silvicultural prescriptions for mechanized restoration approaches are often guided by reference information, or descriptions of intact forest structure and processes (Fulé et al 1997), but these treatments are prohibitively expensive across large scales. Such reference information is commonly used as a baseline against which effectiveness of various restoration approaches are evaluated (Morgan et al 1994, White and Walker 1997, Landres et al 1999). An approach moving beyond typical plot-based comparisons is needed to capture the variability of landscape patterns across such a gradient of landscape scales and examine the current state of forest structure across the region
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