Regional differences in aspen ( Populus tremuloides Michx.) seedling response to an established nursery protocol

In seedling-based reforestation operations, seed source is known to be an influential variable affecting outplanting success. Adaptive variation among seed sources may also be an important factor in the effectiveness of standardized nursery protocols for seedling production. Particularly for wide-ranging species, regional optimizations of nursery protocols may be necessary to ensure consistent production of quality seedling stock. Quaking aspen ( Populus tremuloides Michx.) is one such species, possessing the broadest distribution of any tree in North America. However, research on nursery protocols specific to aspen has focused on seed sources from a limited region in western boreal Canada. A well-established protocol shown to be effective for these boreal aspen uses a shoot growth inhibitor designed to maximize desirable seedling quality traits for outplanting success. We used this protocol on seeds sourced from two different regions in the southwestern portion of the species range (Utah and New Mexico, USA) and compared their response in the same nursery environment to that of a seedlot from Alberta, Canada to determine whether this protocol is also applicable for these very different regions. Seedlings from Utah and New Mexico differed significantly in their response to the protocol from the Alberta source, developing smaller root-to-stem ratios and sequestering less carbohydrate and nutrient reserves. Seedlings from Utah and New Mexico sources also differed from each other, with New Mexico seedlings growing larger according to all metrics. These results indicate that aspen nursery protocols will benefit from regional modification in order to optimize seedling stock quality and trait consistency.