Competition for water and nutrients in forests

Abstract

Competition for water and nutrients between trees and other vegetation is discussed using examples from the interactions between tree and weeds in production forests, and trees and pasture in agroforestry systems. Production and economic viability of plantation forests are dependent upon sound weed management practices. Competition for water and nutrients by a plant is registered as a water deficit or a nutrient deficit. Plant responses to competition are similar to those for coping with water and nutrient deficiency in the soil. One species may have a competitive advantage over another for water and nutrients by (i) acquiring a greater proportion of available soil water and (or) nutrients, (ii) using water and nutrients more efficiently in producing biomass, and (or) (iii) allocating assimilate in ways that maximize survival and growth. The benefits from managing weeds during establishment of a stand have been demonstrated, but the value of managing understory in older stands is unclear. It is not possible to have water stress (through competition) without some degree of nutrient stress, but the opposite may not be the case in some environments. Managing competition effectively requires a clearer understanding of the dynamics of water × nutrient interactions, as well as the dynamics of the interactions between trees and associated vegetation and how this is modified by silviculture. Experiments where variables are well controlled and supported by simultaneous and regular measurements of both water and nutrients are required.