Stress resistance and seedling quality are considered to be fully defined by the curve of future shoot growth. The factors controlling this curve's starting level, slope, and upper asymptote are analysed in terms of four major subsystems: substrate utilisation, photosynthesis, water, and information.
Published equations describing the first three of these subsystems are used to define a necessary and sufficient set of quality criteria. These include functional capabilities such as specific maintenance rate and photochemical efficiency, material properties such as elasticity and hydraulic conductances, environmental coefficients such as the temperature range for root growth, and lethal doses such as frost hardiness. In addition, they include variables describing the current state of the plant, such as leaf area, and water content.
The informational subsystem is considered to control the seasonal change, or "acclimation", in parameters of the other three subsystems, but is still too poorly understood for mechanistic description. Quality criteria arising from it include the extent to which chilling requirement has been fulfilled.
Applying such analyses to the business of reforestation consists of choosing a subset of the quality criteria according to past and future conditions in the crop and measuring them by methods such as those outlined here. Important methods include carbohydrate and infra-red gas analysis, porometry, the pressure-volume technique, and short-cut procedures derivable from these. Measurements of field-proven quality criteria can be compared with seasonal norms, or with values calculated from mechanistic models to be suitable for given site conditions. Practical decisions can then be made about nursery treatments, site preparation, planting, and genetic selections.