ASSESSMENT OF WHITEBARK PINE SEEDLING SURVIVAL FOR ROCKY MOUNTAIN PLANTINGS

Whitebark pine (WBP) is a keystone species of Rocky Mountain alpine and subalpine areas. A pervasive non-native fungal disease (white pine blister rust), mountain pine beetle infestation, and successional replacement by shade-tolerant competitors following decades of fire exclusion have severely reduced whitebark pine and threaten these high-elevation ecosystems. Land managers are attempting to reverse whitebark pine’s decline by increasing regeneration of rust-resistant trees while restoring successional processes. Restoration efforts include the planting of whitebark pine seedlings and over 200,000 seedlings have been planted on National Forest, BLM and National Park service lands. In this Rocky Mountain (RM) study, select whitebark pine plantations were surveyed and seedling survival rates and ecological data collected. The purpose of this initial study was to determine overall survival rates for planted whitebark pine seedlings and to identify environmental conditions that have promoted high seedling survival. Data were analyzed at the site, plot and tree level. Microsites created by stumps, rocks and downed logs in close proximity to WBP seedlings greatly enhanced survival, seedling height and seedling growth during the first year after planting. Potential direct solar radiation was inversely related to WBP survival. Wet planting sites were detrimental to seedling survival. Results as to the effect of fire on seedling survival were inconclusive. However for 1st year seedlings it does appear that moderate, mixed or severe burning did result in much higher survival than unburned. To further understand the environmental conditions that affect seedling survival, an experimental planting was designed and monitored using the knowledge gained from the RM study. Seedling survival in this planting was statistically significantly associated with the presence of a microsite. And increased health of seedlings was associated with the presence of beneficial mycorrhizal associates. Only seedling located in burned or unburned whitebark pine communities were colonized with native fungi and colonization was higher for burned than for unburned sites. Whitebark pine seedlings are successfully being planted and it is possible to discern how different environmental conditions are affecting the survival, height, growth and health of planted seedlings

Pinus albicaulis Engelm. (Whitebark Pine) in Mixed-Species Stands throughout Its US Range: Broad-Scale Indicators of Extent and Recent Decline

We used data collected from >1400 plots by a national forest inventory to quantify population-level indicators for a tree species of concern. Whitebark pine (Pinus albicaulis) has recently experienced high mortality throughout its US range, where we assessed the area of land with whitebark pine present, size-class distribution of individual whitebark pine, growth rates, and mortality rates, all with respect to dominant forest type. As of 2016, 51% of all standing whitebark pine trees in the US were dead. Dead whitebark pines outnumbered live ones—and whitebark pine mortality outpaced growth—in all size classes ≥22.8 cm diameter at breast height (DBH), across all forest types. Although whitebark pine occurred across 4.1 million ha in the US, the vast majority of this area (85%) and of the total number of whitebark pine seedlings (72%) fell within forest types other than the whitebark pine type. Standardized growth of whitebark pines was most strongly correlated with the relative basal area of whitebark pine trees (rho = 0.67; p < 0.01), while both standardized growth and mortality were moderately correlated with relative whitebark pine stem density (rho = 0.39 and 0.40; p = 0.031 and p < 0.01, respectively). Neither growth nor mortality were well correlated with total stand basal area, total stem density, or stand mean diameter. The abundance, extent, and relative growth vs. mortality rates of whitebark pine in multiple forest types presents opportunities for management to encourage whitebark pine recruitment in mixed-species stands. The lodgepole pine forest type contained more whitebark pine seedlings (35%) than any other forest type, suggesting that this forest type represents a potential management target for silvicultural treatments that seek to facilitate the recruitment of whitebark pine seedlings into larger size classes. National forest inventories in other countries may use a similar approach to assess species of concern