Canopy Structure and Environment

Gases and Particles

For CO2, of course, canopies form a tremendous sink due to carbon uptake by leaves. Other gases and airborne particles, including potentially polluting aerosols such as SO4-2, NH4+, and NO3-, generally exhibit a slight depletion from canopy top to bottom (e.g., Wimen and Agren 1985, Lovett and Lindberg 1992). Models to predict the severity and effects airborne pollution on forest ecosystems have been generated, including models based on wind tunnel simulations (Ould-Dada 2002) and direct measurement of airborne particle concentrations (Kwiecien 1997; Figure 1).

 

Figure 1. Deposition of pollutants in the canopy of a mixed pine-oak forest in the Rybnik Coal Basin, Poland. Values indicate the quantity, in kg per hectare per growing season, of inorganic particulate aerosols. Inputs to the system (deposition) include inorganic dust (D) and aerosols trapped by the canopy (A). These are partitioned into the inorganic particles that remain on leaves (L), and those that fall through to the forest floor (F). From Kwiecien (1997).