Silviculture for a Climate of Change

Climatic changes within the life span of a tree may lead to species extinctions from their present environments. Withdrawal of silviculture from native forests follows from the assumption that natural processes will achieve the desired conditions. Benign neglect will not ensure success in a changed environment. The nature and extent of physical changes and the biological attributes of species must be understood in order to apply adaptive measures. Most plant species will grow satisfactorily beyond their natural distribution ranges provided various growth stages are facilitated and physical factors and competition are managed appropriately. Silviculture can and should be used to maintain species in desired locations and to introduce them to suitable new locations. Native forest silviculture is complex and our understanding of most species is limited, but we must attempt to overcome the effects of past disturbances and realise the many benefits that forests can provide

Stand density management in rainforest plantations

Trees in plantations established for timber production are usually grown at a sufficiently high density that canopy closure occurs within a relatively short time after planting. The trees then shade and outcompete most herbs, shrubs or grasses growing at the site. The closer the spacing (i.e. the greater the density) the faster this will occur. Subsequently, as the trees grow larger, this between-species competition is replaced by within-species competition. If unmanaged, this competition can reduce the commercial productivity of the plantation. Thus, there are two management dilemmas. One is knowing the best initial planting density. The second is knowing how to management the subsequent between-tree competition in order to optimize overall plantation timber productivity. In this chapter we consider initial spacing and thinning for high value timber trees grown in single and mixed species plantations. From growth studies in stands of different ages recommendations are proposed for managing both types of plantations where the primary objective is timber production. It seems that many rainforest species will require more space to achieve optimal growth than most eucalypts and conifers. On the other hand many rainforest species do not have strong apical dominance. Care will be needed to balance these two attributes

Subtropical-tropical urban tree water relations and drought stress response strategies

Understanding native habitats of species successful as subtropical and tropical urban trees yield insights into how to minimize urban tree water deficit stress experienced during monsoonal dry periods. Equatorial and montane wet forest species rarely subject to drought are generally absent in subtropical and tropical cities with pronounced monsoonal dry seasons. Species native to monsoonal dry forests appear to have wide environmental tolerances, and are successful as urban trees in many tropical cities. Monsoonal dry forest species have a tendency to be deep rooted to avoid drought, with leaf habits falling along an avoidance to tolerance spectrum. Dry deciduous species, typically found on more fertile soils, maximize growth during the monsoonal wet season with high photosynthesis and transpiration rates, then defoliate to avoid stress during the dry season. Evergreen tree species, typically found on less fertile soils, have a higher carbon investment in leaves that photosynthesize and transpire less year-round than do dry deciduous species. Dry deciduous tree species are more common urban trees than dry evergreen species explicitly due to more ornamental floral displays, but also implicitly due to their ability to adjust timing and duration of defoliation in response to drought. An empirical study of three tropical species exhibiting a range of leaf habits showed isohydric behavior that moderates transpiration and conserves soil water during drying. However, dry evergreen species may be less adaptable to tropical urban conditions of pronounced drought, intense heat, and limited rooting volumes than dry deciduous species with malleable leaf habit