Limber pine regeneration and white pine blister rust in the central and southern rocky mountains

Abstract

Mountain pine beetle (MPB) and white pine blister rust (WPBR) cause mortality in limber pine and limber pine seedlings in Colorado, Wyoming, and Montana, USA. Seedlings can be killed rapidly by WPBR, and WPBR and bark beetles reduce cone and seed availability. In 2011 and 2012, we assessed occurrence, abundance, recent growth, and health status of limber pine seedlings in stands affected by WPBR and MPB. We determined biotic and abiotic factors influencing limber pine seedling density and terminal growth, and proportion of limber pine seedlings with WPBR. Live seedling density averaged 141 stems ha-1 and ranged from 0 to 1,935 stems ha-1. Blister rust was the primary damage agent with 0 to 100% incidence. Diseased seedlings occurred on 30% of all plots. Seedling density was predicted by limber pine tree density, total tree density, percent ground cover as grass, and seedling height. The proportion of limber pine seedlings with WPBR was related to limber pine seedling height, cankers ha-1, percent crown dieback of overstory, and density of trees with WPBR. Monitoring and restoration of stands, including planting on sites with adequate moisture and near objects with some overstory cover, are needed to ensure limber pine regeneration on some sites.