Interactions of management and white pine blister rust on Pinus strobiformis regeneration abundance in southwestern USA

Abstract

Modelling natural regeneration is complex, and both natural and anthropogenic disturbances can alter forest trajectories. Pinus strobiformis (southwestern white pine, SWWP) is an important component of mixed conifer forests in the Southwest and management recommendations related to natural and planted regenerations are needed to guide conservation of SWWP in the face of an invasive disease (white pine blister rust, WPBR). Regeneration was surveyed across six mountain ranges, three silviculture treatments and two levels of disease severity in the Southwest US. Key findings were: (1) SWWP regeneration in stands with no recent management (<20 years) and high disease severity had unsustainable WPBR infection, (2) SWWP regeneration was less abundant but less likely to be infected in stands with recent management, (3) stands with high disease severity had fewer SWWP seedlings than stands with no or low disease severity and (4) SWWP regeneration densities were best predicted by other understory species abundance. We recommend silviculture treatments that reduce basal area to 9–10 m² ha⁻¹ and leave large canopy openings to enhance natural SWWP regeneration. Without creating conditions for disease-free regeneration to reach reproductive maturity, some stands may lose SWWP as an overstory component. Results may help refine SWWP management guidelines and expand conservation efforts in forests threatened by WPBR.