Whitebark Pine Prevalence and Ecological Function in Treeline Communities of the Greater Yellowstone Ecosystem, U.S.A.: Potential Disruption by White Pine Blister Rust

Abstract

In the northern Rocky Mountains of the U.S. and Canada, whitebark pine (Pinus albicaulis Engelm.) is a functionally important species in treeline communities. The introduced fungal pathogen Cronartium ribicola, which causes white pine blister rust, has led to extensive whitebark pine mortality nearly rangewide. We examined four treeline communities within the Greater Yellowstone Ecosystem (GYE) to assess structure and composition, whitebark pine prevalence and functional role, differences in growing season mesoclimate among study areas, and blister rust infection incidence. We found that (1) whitebark pine frequently serves as the majority overall, solitary, and leeward tree island conifer; (2) the prevalence of different tree species in the windward position in tree islands, and thus their potential as tree island initiators, may be predicted from their relative abundance as solitary trees; and (3) white pine blister rust infection incidence ranged from 0.6% to 18.0% across study areas. White pine blister rust poses a threat to treeline development and structure and the provision of ecosystem services in the GYE. Increasing blister rust resistance in nearby subalpine whitebark pine communities through seedling planting or direct seeding projects should eventually result in higher levels of blister rust resistance in whitebark pine in treeline communities.

Survival of Whitebark Pine Seedlings Grown from Direct Seeding: Implications for Regeneration and Restoration under Climate Change

“…We included nurse object because seedling survival can be influenced by the presence and type of nurse object, and seedlings are often planted near nurse objects to improve restoration outcomes [45,74,75]. These observed patterns may persist through tree maturity, given that mature whitebark pine are not uniformly distributed among microsite types [52,76,77]. We did not include age as a covariate, despite expectations that seedling survival increases with age, because seeds within the same cache may have germinated in different years [45,62,78].…”

“…Elevations within the study area range from 2980 to 3240 m and encompass both upper subalpine and treeline forest. A detailed description of the study area including the plant community composition is presented in [32,45,52]. Figure created using the ggmap [55] and ggplot2 [56] packages in R [57].…”

Dynamics of Abies nephrolepis Seedlings in Relation to Environmental Factors in Seorak Mountain, South Korea

“…In general, alpine plants adapted to dry conditions can use water very sparingly [27][28][29]. Wind conditions have the greatest influence on physiological change and damage of plants at the treeline, and rocks can provide shelter to tree seedlings from wind during the germination and early growth stages [30][31][32][33]. The influence of canopy gaps on forest processes such as stand structure, regeneration, and understory dynamics is important [34][35][36].…”

Seedling Survival at Timberline Is Critical to Conifer Mountain Forest Elevation and Extent

“…More specifically, emergent seedling survival at the alpine timberline appears constrained to favorable microsites facilitated by microtopography (e.g., depressions), existing vegetation (Wheeler et al, 2011), or inanimate structures such as boulders, rocks, and fallen logs (Smith et al, 2003;Körner, 2012;Wagner et al, 2018). These structures within the environment serve multiple roles such as accumulating leeward snow and snowmelt water that is available later in summer, buffering seedlings from extreme maximum and minimum temperature fluctuations, and protecting seedlings from high winds that often carry abrasive ice crystals that can damage the waxy needle cuticle and lead to desiccation death (Hadley and Smith, 1986;Renard et al, 2016).…”