Long-term survival, growth, and reproduction responses of Engelmann spruce provenances to climate

Abstract

As changes in climate accelerate, mature forests experience different local conditions than those that they were established under and are likely adapted to. Tree regeneration is highly constrained by climatic conditions and as these conditions continue to change, it is important to understand how reforestation choices will affect future forests. Provenance studies have been used for more than a century to understand the influence of genetics and the environment on traits, and can now additionally provide information on provenance performance under the rapidly changing climate. Here we compare survival, growth, reproduction, and growth-climate relationships among 20 provenances of Engelmann spruce (Picea engelmannii) trees over 45 years in a provenance study. We found that the best surviving provenances were climatically similar to the plantation with dry climates and short growing seasons, but this did not apply to overall growth. Seedlings from provenances with higher summer to spring precipitation ratios were faster to reproduce and were taller at outplanting, which was advantageous for all but the tallest seedlings. Annual growth rings of provenances responded similarly to climate, with most having both high resistance and resilience to drought. Growth was positively correlated with high temperatures year-round and wet summers. This study reveals that many Engelmann spruce provenances from varying climates can be successful at relatively cold and dry high elevation sites, boding well for assisted population migration efforts. However, differences exist between provenances in their growth, survival, and reproduction potential, which will continue to influence how they perform in the future.