Water use by shrubs as affected by energy exchange with building walls

Abstract

Landscape plants in urban areas are routinely grown next to buildings which are sources of sensible heat and radiation. An experimental study was conducted to explore how building walls affect water use by adjacent landscape plants. Instantaneous rates of sap flow were measured using heat-balance, stem-flow gauges attached to wax leaf ligustrum shrubs growing adjacent to all four walls of a building shell. For comparison, sap flow was also measured on shrubs grown away from the influence of the building. Peak flow in plants adjacent to each wall occurred when direct beam irradiance on the wall and wall temperature were at their maxima. Peak flow was highest in plants adjacent to east and west walls, and lowest in plants adjacent to the north wall. Longwave radiation emitted by the walls appeared to be a major factor affecting flow while reflected radiation from walls was of secondary importance because of the low albedo of the walls. Cumulative flow was greatest in the shrubs grown away from the influence of the building, probably due to the absence of any shading by walls during the day, and to wind speeds that were higher than those adjacent to the building.