Multiple factors constrain Ponderosa Pine regeneration 9 years after a mixed severity wildfire in Central Arizona

Abstract

Abstract Background: Long lasting drought, climate change and sub-optimal forest conditions are creating more frequent and severe fires in southwestern ponderosa pine (Pinus ponderosa) forests. These same conditions make ponderosa pine regeneration difficult as these trees are poorly adapted to establishing and surviving in sustained drought and in large treeless areas. The 2013 Doce fire in the Prescott National Forest burned three quarters of the Granite Mountain Wilderness in Arizona USA, and much of its ponderosa pine forests. Here we report the current state of pine regeneration on Granite Mountain and the conditions of the surviving stands, as well as climate factors relevant to their ability to facilitate regeneration. With unfavorable climate conditions predicted to continue, ponderosa pine regeneration in Xeric Southwestern Pine forests is likely to fail when stand conditions are also unfavorable. Results: Pine regeneration within the burned area was largely absent. Tree density and basal area were reduced in most fire severity classes. Significant differences in mean annual temperature, maximum vapor pressure deficit, and annual precipitation were identified since the 2000s drought began at the site. The average distance of high severity burn plots to a seed tree is beyond the suggested maximum distance of seed dispersal for ponderosa pine. Calculated establishment rates of ponderosa pine are below required levels for reforestation. Conclusions: A combination of climate factors and remaining stand structure characteristics is constraining ponderosa pine regeneration in the Granite Mountain Wilderness. With a hotter and drier future predicted, xeric ponderosa pine forests face harsh conditions, especially considering the likelihood of severe wildfires. Appropriate management actions should be taken before wildfires occur to ensure that these xeric forests are given optimal conditions to survive wildfire.