Physiological processes in plantation establishment and the development of specifications for forest planting stock

Abstract

Both the morphological and physiological characteristics of forest planting stock vary widely with nursery culture and environment. Through the control of environmentally determined variation in phenotype, stock can be adapted to both the stress of transplanting from nursery to forest site and the particular environmental conditions of the forest site. Evidence is discussed that indicates that the stress of transplanting is primarily water stress, resulting from (i) the confinement of roots to the planting hole, (ii) poor root–soil contact, and (iii) low root permeability. These deficiencies are overcome by root growth, which is thus a central process in plantation establishment. Root growth depends largely on current photosynthesis. Photosynthesis depends on the assimilation of carbon dioxide at the expense of lost water in transpiration. Transpiration is limited by water uptake and hence depends on root growth. Root growth and photosynthesis in newly planted trees are thus mutually dependent. Because of this relationship, plant water status immediately after planting, or as soon as conditions favorable to root growth occur, is a crucial factor in determining plantation establishment success. High plant tissue water status immediately after planting, or as soon as environmental conditions permit root growth, allows the onset of a positive cycle of root growth supported by photosynthesis and photosynthesis supported by root growth; whereas low tissue water potential immediately after planting can lead to the inhibition or root growth by a lack of photosynthesis and the inhibition of photosynthesis by a lack of root growth. Stock characteristics that enhance plant water status immediately after planting are reviewed and the scope for their control considered. Stock characteristics affecting adaptation to particular planting site conditions, or capable of affecting postestablishment plantation performance, are also discussed.