COS 129-4 - Patch characteristics interact with abiotic features to modify conifer seed dispersal patterns and regeneration outcomes after high-severity fire
University of New Mexico Albuquerque, New Mexico, United States
Abstract: Unnaturally large high-severity burn patches are increasingly common in southwestern US dry conifer forests in recent decades. The heavy seeds of seed-obligate conifers rarely travel the distances required to reach core patch area in the largest patches. Patch characteristics and abiotic features may interact to alter the distance seeds can and must travel to regenerate a patch, which could change expected regeneration patterns after fire. We used ponderosa pine regeneration density as a proxy for seed dispersal to quantify the effect of patch attributes on seed dispersal patterns into high-severity patches. We measured regeneration density in 46 transects that varied by slope, aspect, and prevailing wind direction relative to intact forest. To determine how these factors would influence post-fire establishment, we modeled abiotic feature effects on regeneration density and compared model extrapolations across high-severity patches against estimates from a distance-only model. Regeneration densities were highest on north-facing patch locations that were downwind and downslope of intact forest, which decreased as slope position and wind direction became less favorable for dispersal. The abiotic features model predicted greater regeneration density than the distance-only out to 160 m from the intact forest for all aspects when the severely burned patch was either downwind and downslope or downwind and upslope of the intact forest. Regeneration density was also higher on north aspects with the abiotic features model when the burned patch was upwind and upslope or upwind and downslope from the intact forest. Although, the increases in density over the distance-only model were smaller than for the other location conditions. The distance-only model overpredicted regeneration density on east, south, and west aspects when the burned patch was upwind and upslope from the intact forest and model predictions were similar between the two for these aspects when the burned patch was upwind and downslope. Our findings suggest that in more complex high-severity patch shapes, more of the severely burned area is likely to have higher regeneration density than we would expect with the distance-only model. But, in large and simple patches, the differences between the two models is likely to have less of an overall effect on regeneration density because a large proportion of the burned area will be beyond the dispersal distance of ponderosa pine.