Site- and Species-Specific Influences on Sub-Alpine Conifer Growth in Mt. Rainier National Park, USA

Janneke Hillerislambers,Myesa Legendre-Fixx,Leander Anderegg,Ailene Ettinger

doi:10.3390/f9010001

Abstract

Identifying the factors that influence the climate sensitivity of treeline species is critical to understanding carbon sequestration, forest dynamics, and conservation in high elevation forest/meadow ecotones. Using tree cores from four sub-alpine conifer species collected from three sides of Mt. Rainier, WA, USA, we investigated the influences of species identity and sites with different local climates on radial growth–climate relationships. We created chronologies for each species at each site, determined influential plant-relevant annual and seasonal climatic variables influencing growth, and investigated how the strength of climate sensitivity varied across species and location. Overall, similar climate variables constrained growth on all three sides of the mountain for each of the four study species. Summer warmth positively influenced radial growth, whereas snow, spring warmth, previous summer warmth, and spring humidity negatively influenced growth. We discovered only a few subtle differences in the climate sensitivity of co-occurring species at the same site and between the same species at different sites in pairwise comparisons. A model including species by climate interactions provided the best balance between parsimony and fit, but did not lead to substantially greater predictive power relative to a model without site or species interactions. Our results imply that at treeline in moist temperate regions like Mt. Rainier, the same climatic variables drive annual variation in growth across species and locations, despite species differences in physiology and site differences in mean climates.

Highlights

Climate change is expected to affect alpine and sub-alpine areas [1,2,3,4] and forecasting changes to these areas is critical for natural resource management and conservation
Our results demonstrate that tree growth of our four focal high elevation conifers on all three sides of the mountain responded to similar climate variables, and that climate sensitivities for each climate variable—regardless of the species or site—were similar in magnitude, with a few minor exceptions
Rainier), neither species identity nor mean climatic conditions has a major influence on high elevation conifer climate sensitivity

Summary

Introduction

Climate change is expected to affect alpine and sub-alpine areas [1,2,3,4] and forecasting changes to these areas is critical for natural resource management and conservation. On a warming planet where multiple aspects of climate are changing [5], climate sensitivities that differ among sub-alpine tree species could result in differing growth responses. Our results demonstrate that tree growth of our four focal high elevation conifers on all three sides of the mountain responded to similar climate variables, and that climate sensitivities for each climate variable—regardless of the species or site—were similar in magnitude, with a few minor exceptions. Our results imply that at treeline in moist temperate regions (like Mt. Rainier), neither species identity nor mean climatic conditions has a major influence on high elevation conifer climate sensitivity. Rainier), neither species identity nor mean climatic conditions has a major influence on high elevation conifer climate sensitivity.

Study Site and Species

Tree Growth Data

Closed-canopy

Climate Data

Results

Conclusions

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