24 Tree Planters’ Notes Abstract Assessment of forest seedling quality has many components beyond the usual height and stem-diameter specifications found in growing contracts. Various measurements can aid in making decisions about culturing, lifting, storing, and planting. Several common morphological and physiological measurements of forest seedlings and their interpretation are described. Introduction The demand for bigger, better, faster-growing seedlings has been ever-growing. As a result, forest seedling produc- tion is a continually evolving technology in reforestation. Evaluating seedling quality is crucial for understanding seedling development in the nursery, as well as subsequent field growth and survival. Stock quality, however, often is assessed inconsistently and on only a limited basis. Some nurseries and reforestation managers assess their stock thoroughly each year, while others do few assessments unless a problem arises. Although seedlings are relatively pampered in the nursery, they can have a rather perilous journey from their safe growing environment to their outplanting destination. During lifting, grading, storing, handling, and planting, opportunities for seedlings to be subject to moisture stress, temperature stress, or physical stress are numerous. These stresses are cumulative and can lead to poor field performance. When this occurs, there can sometimes be a dispute between the nursery and the landowner over what caused the poor growth, survival, or both after outplanting. Seedling quality data can assist in determining whether seedling performance issues are due to something that occurred in the nursery, improper planting practices, or environmental conditions after outplant. Seedling quality evaluation can be used to establish bench- marks at specific points, such as time of lift or delivery, so that the nursery and the customer have a quantitative Understanding Forest Seedling Quality: Measurements and Interpretation Diane L. Haase Associate Director, Nursery Technology Cooperative, Department of Forest Science, Oregon State University, Corvallis, OR Figure 1. Measurement of height and stem diameter are the most common morphological assessments of seedling quality. appraisal of a particular seedling lot. In addition, seedling quality data can help seedling growers and users to better understand seasonal patterns among species, stocktypes, seed lots, and cultural treatments. Seedling Quality Assessment There are two categories of seedling quality assessment: morphological and physiological (Mattson 1997). Morphological quality is based on the physical attributes of the seedling (table 1), whereas physiological quality is based on the seedling’s internal functions (table 2). Of course, the two categories are not mutually exclusive. A seedling’s morphological characteristics can be considered a physical manifestation of its physiological activities. Morphological Quality. Morphology is used far more often than physiology to evaluate seedling quality. Height and stem diameter are the two characteristics most com- monly examined on forest seedling stock (figure 1). The growing contract usually specifies a target for these two parameters, along with acceptable minimum and maximum ranges. Oddly, height is usually designated in English inches (in) but stem diameter (also known as caliper or Tree Planters’ Notes 2008, 52(2): 24-30.