The plant canopy is a site of physical and biochemical processes associated with the terrestrial biosphere. The functional and structural attributes of plant canopies are dependant on species composition, microclimatic conditions, nutrient dynamics, herbivore activities, and many other activities like management. The amount of foliage in a plant canopy is one of the basic ecological characteristics reflecting the integrated effects of these factors in an ecosystem. In turn, canopy leaf area is the dominant driving force of primary production, water and nutrient use, energy exchange, and other physiological functions of a range of ecosystem processes. Understanding the organization and function of plant canopies is of central importance when conducting many types of comparative ecological studies or when developing biophysical Earth system models involving water and carbon balances. Yet, characterizing plant canopies presents many challenges, largely because of their complex geometry, and because of the difficulties of obtaining meaningful quantitative indices that relate back to fundamental processes such as light interception, transpiration, and photosynthesis. Ecophysiologists, managers (farmers and foresters), ecologists, climate and weather forecast modelers, ecosystem modelers, and atmosphere-ecosystem interaction modelers, request information about canopy leaf area index (LAI), one of the most widely used descriptors of the canopy.
LAI is a measure of canopy foliage content commonly used in studies of vegetation and ecosystems. LAI is the total area of one side of the leaf tissue per unit area of ground surface. According to this definition, LAI is a dimensionless quantity characterizing the canopy of an ecosystem. One unit of LAI is equivalent to 10 000 m of leaves per hectare. LAI has been recognized as the most important attribute of vegetation structure for characterizing canopies from the stand to large areas at broad spatial scales. In defining ecology as the study of the structure and function of ecosystems, LAI is one of the core parameters in ecology, as it links canopy structure and ecosystem function.
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