DETERMINING FIELD PERFORMANCE POTENTIAL WITH THE USE OF LIMITING ENVIRONMENTAL-CONDITIONS

An operational assessment of stock quality, prior to field planting, u sually includes measures of morphology and a test for root growth capa city (RGC) conducted under optimum conditions. When measured under opt imum conditions and interpreted with regard to seedling phenology, per formance attributes, such as RGC, provide valuable information about t he ''functional integrity'' of stock at the time of measurement. Howev er, reforestation sites are rarely associated with optimum growing con ditions, and performance attributes measured under optimum conditions provide limited information about field performance potential. Due to these limitations, testing programs at the Forest Biotechnology Centre (BCRI) have used limiting environmental conditions to represent the p lanting site. This concept is based on the philosophy that tests under limiting environmental conditions will define seedling tolerance and/ or resistance to conditions that prevail on the planting site, and hen ce, better forecast field performance potential. Evidence supporting t his concept is presented in three case studies and other cited studies , where performance attributes were measured under a range of limiting environmental test conditions. A performance attribute response model is then presented to define the relationship between testing conditio ns and field performance potential forecasting. Applicability of this testing approach to operational reforestation programs is discussed.