Soil Water Dynamics and Growth of Street and Park Trees

Abstract

Soil water dynamics were studied in 100 street tree planting pits and in the soil surrounding five park trees. Volumetric soil water content and stem cross-sectional area increment were measured on both park and street trees. Different levels of irrigation were implemented on the 100 street trees. Winter assessments of soil wetness at field capacity showed that the water retention capacity was lower in street planting pits than in the park soil attributable to the rather coarse substrate used in the planting pits. High variability among street tree planting pits in regard to water retention capacity was determined and may be related to poor standardization of the substrates, but may also be affected by varying drainage conditions. The rate of water loss in the street tree planting pits was very high immediately after rainfall or irrigation and decreased exponentially during the first 10 days after water input. This was attributed to rapid drainage. The water loss rate in the park soil was on average slightly higher than in the nonirrigated control street pits but showed a more linear decrease over time. We concluded that the water loss in the park soil during summer was primarily driven by transpiration of trees (above 10 L/day [2.6 gal/day]), which complies with common Danish forest experience. The relationship between water loss and tree growth was reversed in the street tree planting pits. The street trees did consume water for growth, but growth and transpiration of the street trees were not a noticeably driving mechanism in the planting pit hydrology. The large variation in street tree increment is attributed to the variation among street planting pits in their ability to retain water. The faster the water loss rate, the slower the tree growth. Irrigation did not prevent final depletion of the soil water resource in planting pits, but irrigation elevated the water content for limited periods during the growing season and thereby enhanced tree growth. Besides the obvious possibilities for improved water balance by horizontal and vertical expansion of the rooting zone, we also suggest improving the water retention capacity of planting pit soil by adding clay nodules. Options for continuous monitoring of tree vitality and soil water content to optimize maintenance are discussed.

Different Responses of Evapotranspiration Rates of Urban Lawn and Tree to Meteorological Factors and Soil Water in Hot Summer in a Subtropical Megacity

“…Trees with limited root system space will face more frequent and severe water pressure, resulting in decreased stomatal conductance and transpiration levels [92]. Increasing the water permeability of the surrounding underlying surface and improving the soil looseness in the planting area of trees can significantly increase the water available to the roots of trees [93,94].…”

Water Availability Determines Tree Growth and Physiological Response to Biotic and Abiotic Stress in a Temperate North American Urban Forest

“…Urban trees often face water stress because temperatures are high and impervious surfaces and poor soils can reduce water infiltration [57][58][59]. Water stress causes xylem embolism and cavitation, which becomes damaging in A. rubrum at −3.9 MPa [48].…”

Street Tree Structure, Function, and Value: A Review of Scholarly Research (1997–2020)

“…Other research isolated specific biophysical contributors to establishment and growth, such as overall site conditions [22], pavement material [85], soil compaction [86], aeration [87], and different forms of soil amendments like biochar [88], compost [89], or engineered soils [90]. Additionally, the persistence of certain hydro-logic conditions, like water retention [91] or drought [92], as well as the presence of fungal colonies [93] have been subject to research.…”