Determining Reference Conditions for Ecosystem Management of Southwestern Ponderosa Pine Forests

Abstract

The fire disturbance regime and forest structure prior to Euro‐American settlement (AD 1883) of a southwestern ponderosa pine (Pinus ponderosa) landscape were quantified in order to establish reference conditions as a baseline for ecosystem management. The mean presettlement fire interval between 1637 and 1883 was 3.7 yr for all fires and 6.5 yr for widespread fires, but fire has been excluded from the study area since 1883. Forest density increased under fire exclusion from an average of 148 trees/ha in 1883 (65 pines, 80 oaks, three other species), an open forest dominated by relatively large ponderosa pines, to 1265 trees/ha in 1994/1995 (720 pines, 471 oaks, 74 others), a dense forest characterized by relatively small and young trees. Species composition has shifted toward greater dominance by Gambel oak (Quercus gambelii) and conifers less adapted to frequent fires: white fir (Abies concolor) and Douglas‐fir (Pseudotsuga menziesii). The reference presettlement conditions can be applied to management of this ecosystem in two ways. First, reference conditions are a benchmark against which to evaluate contemporary conditions and future alternatives. The comparison shows that the contemporary forest is well above the range of presettlement variability in forest density, and both live and dead fuel structures have developed that can support high‐intensity wildfire. Second, reference conditions can serve as a goal for ecological restoration treatments.

Carbon Stocks and Climate Change: Management Implications in Northern Arizona Ponderosa Pine Forests

“…Table 3 lists stand conditions, averaged by elevational grouping (low, mid, high), including trees-per-hectare (TPH), basal area (BA), and quadratic mean diameter (QMD). We compared our data with findings from Fulé et al 2007, who used tree-ring analysis to reconstruct historic conditions in northern Arizona ponderosa pine stands (2134 m elevation) [59]. That study found pre-settlement BA to range between 17 and 27 m 2 /ha (95% confidence interval), TPH to range between 51 and 79 (95% confidence interval), and QMD to range between 36 and 47 centimeters (95% confidence interval) [59].…”

“…However, we note that the silvicultural prescriptions proposed by the 4FRI team are much more complex than our design and are tailored toward multi-objective management [56,57]. A review of the literature also lent support for our management scenarios [31][32][33][59][60][61].…”

“…Management scenarios were implemented in Climate-FVS and were designed to mimic common and proposed management practices in the dense, over-stocked ponderosa pine forests of Northern Arizona. The management scenarios selected for this study were influenced by prescriptions developed by the US Forest Service's 4FRI team and a review of the literature [33,[56][57][58][59][60][61]. However, we note that the silvicultural prescriptions proposed by the 4FRI team are much more complex than our design and are tailored toward multi-objective management [56,57].…”

“…We compared our data with findings from Fulé et al 2007, who used tree-ring analysis to reconstruct historic conditions in northern Arizona ponderosa pine stands (2134 m elevation) [59]. That study found pre-settlement BA to range between 17 and 27 m 2 /ha (95% confidence interval), TPH to range between 51 and 79 (95% confidence interval), and QMD to range between 36 and 47 centimeters (95% confidence interval) [59]. Our results indicate that the average lower-elevation stand contains many small-diameter trees at the beginning of the simulation period and develops dense, dog-hair-thicket type conditions by the end of the century.…”

The “emulation of natural disturbance” (END) management approach in Canadian forestry: A critical evaluation

“…Indeed, the appropriate range of "natural variability" is often implicitly held to be before European colonization of the North American continent (Fulé et al 1997, Moore et al 1999, Betts and Loo 2002, Oliver et al 2002. In other words, the END reflects the perspective that the "natural order" is distinct from culture-at least European culture.…”