Whitebark Pine Recruitment in Sierra Nevada Driven by Range Position and Disturbance History

Michèle R. Slaton,Carlos M. Ramirez,Martin MacKenzie,Tanya Kohler

doi:10.3390/f10050455

Michèle R. Slaton, Carlos M. Ramirez + Show 2 more

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https://doi.org/10.3390/f10050455

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Journal: Forests	Publication Date: May 25, 2019
Citations: 6	License type: CC BY 4.0

Affiliation: US Forest Service, Pacific Southwest Research Station

Abstract

Effective restoration of whitebark pine populations will require a solid understanding of factors affecting seedling recruitment success, which may vary by site and biogeographic region. We examined the relationship between whitebark pine seedling recruitment, disturbance history, and range position in three independent studies in the southern Sierra Nevada, California (CA), USA. In 66 plots broadly distributed across watersheds, we found that whitebark pine seedling density and proportion were greatest at upper elevations, and where canopy cover of whitebark pine was higher (density ranged 0–383 seedlings/ha; x ¯ = 4, σX = 1). Seedling density and proportion were also greater in plots that had recently experienced loss of canopy cover from insects, avalanche, windthrow, or other disturbance effects. In a second study conducted in popular recreational areas, including campgrounds and trailheads, the response of whitebark pine recruitment to disturbance was strongly dependent on the relative position of stands within the range, or proximity to other forest types. Both studies indicated that low to moderate levels of disturbance enhanced whitebark pine recruitment, especially at its range edge, a finding consistent with the early seral status of whitebark observed in previous studies conducted elsewhere in North America. In our third study, a case study at the June Mt. Ski Area, we demonstrate the potential for a downward shift in the whitebark-lodgepole pine ecotone as a result of insect-caused disturbance.

Highlights

Whitebark pine (Pinus albicaulis Engelm.) is endemic to western North America, and in California (CA) occurs in the Sierra Nevada, Great Basin, Cascade and Klamath Mts
We aimed to evaluate the abundance of whitebark pine recruitment and the relative success of whitebark compared to other tree species with respect to disturbance history, climate, and contextual range position
Whitebark pine recruitment was significantly correlated to the disturbance and range position, though relationships varied by metric and were in some cases weak (Figure 5, Table 1)

Summary

Introduction

Whitebark pine (Pinus albicaulis Engelm.) is endemic to western North America, and in California (CA) occurs in the Sierra Nevada, Great Basin, Cascade and Klamath Mts. Found mainly above 2500 m, and often dominating the upper treeline, whitebark pine forests receive a large proportion of mountain snowfall, and play an important role in regulating water supply [1]. Whitebark pine is a candidate species for listing under the US Endangered Species Act, with primary threats from white pine blister rust (Cronartium ribicola J.C. Fisch.), mountain pine beetle (Dendroctonus ponderosae Hopkins), warmer temperatures, loss of snow, and fire exclusion [2]. The fact that populations are in inaccessible terrain, and often within wilderness areas means that the management toolset for restoration is limited, underscoring the need for highly targeted restoration efforts [4,5,6]

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