Abstract
Nursery-grown tree seedlings are a vital component of successful restoration and reforestation programs, useful when calls for increased planting for industrial forest management are made, and a tool for climate change mitigation. One of the most extensively planted and studied trees in Western North America is Douglas-fir. Building on that body of work, this review was conducted to identify if the root-to-shoot ratio (root:shoot, R:S), a commonly referred-to metric in reforestation planning, yields meaningful guidance for producing seedlings that are better able to establish across a variety of field conditions. The results indicated that there is wide variability in R:S of nursery-grown seedlings. The relationship between R:S and subsequent root growth and seedling survival varies depending on Douglas-fir variety, seedling stocktypes, and site conditions. The biological and physiological basis for using R:S remains, and likely could be used to enhance seedling quality; however, there is an ongoing need for planning and collaboration between researchers and practitioners to identify how to best deploy this evaluation tool.
Highlights
IntroductionThe Target Plant Concept was developed as a framework to guide the successful establishment of nursery-grown seedlings [5]
Planted seedlings are a key part of many reforestation plans, including environmental restoration and efforts to address climate change [1]
There is a strong impetus to ensure the performance of planted seedlings, given that there are over a billion seedlings being grown in forest nurseries in the United States for reforestation and restoration [3] and global commitments to restore and expand forest cover [4]
Summary
The Target Plant Concept was developed as a framework to guide the successful establishment of nursery-grown seedlings [5]. One aspect of the Target Plant Concept is to identify quantifiable morphological and physiological seedling attributes which ensure establishment success. Nursery professionals look for specific morphological metrics to guide seedling production, with species and outplanting context in mind. Nursery production regimes manipulate seedling growth and physiology using environmental conditions and the timing of production cycles [7,8]. Silvicultural treatments, vegetation management, microenvironments, planting quality, and seedling size and structure at planting (i.e., stocktype) impact seedling survival and growth [15,16]. It is challenging to define quantifiable morphological attributes with enough specificity to be useful to nursery professionals, while allowing for the variability in attributes necessary to accommodate different outplanting environments
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