Groundcovers, Organic and Inorganic Mulches, and Masonry Surfaces Differentially Affect Establishment and Root Zone Characteristics of Urban Trees

Abstract

Three experiments investigated the effects of various groundcovers on establishment of redbuds [Cercis canadensis L. var. texensis (S. Watson) M. Hopkins ‘Alba’] and baldcypress [Taxodium distichum (L.) Rich.]. The first experiment involved eight surface treatments. Controls were bare soil. Remaining treatments were pine bark mulch; Asian jasmine [Trachelospermum asiaticum (Siebold & Zucc.) Nakai]; St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze]; decorative gravel; recycled paper mulch; decorative brick pavers; or seasonal rotations of herbaceous annuals. Other experiments compared brick-on-sand treatments ranging in color from light blonde to dark charcoal with bare soil on establishment of redbuds or baldcypress. Most organic and living soil surface covers were preferable to bare soils, however, some inorganic surface covers were detrimental to tree growth. Paving surfaces adversely affected survival, shoot or root growth, but differences were species dependent. Soil moisture, pH, and bulk density did not appear to be limiting under pavers, but substantial seasonal fluctuations in soil temperatures were observed. Light and medium bricks reflected more photosynthetically active radiation than dark bricks or bare soil. Atmospheric temperatures were greatest above dark and medium bricks. Root growth decreased as darkness of brick color increased. Redbud survival and growth were more adversely affected than with baldcypress