Arboriculture & Urban Forestry 34(3): May 2008 Arboriculture & Urban Forestry 2008. 34(3):157–162. 157 Mulching of Ornamental Trees: Effects on Growth and Physiology Francesco Ferrini, Alessio Fini, Piero Frangi, and Gabriele Amoroso Abstract. Two organic mulching materials applied to newly planted Tilia × europaea and Aesculus × carnea trees were evaluated for effects on tree growth and physiology. Both mulches were efficient in maintaining a cleared area around newly planted trees, although pine bark was more durable than coarse compost from mixed green material. Trees mulched with compost generally had greater height, trunk diameter, and current-year shoot growth. Differences were more evident in the first year in Aesculus and in the second year in Tilia. Mulching with compost increased carbon assimilation of linden leaves in 2005 when compared with pine bark and chemical weeding. Both mulching materials increased transpiration of horsechestnut in 2005. Little effect on gas exchange was found in 2006 in both species. However, because mulched trees were larger with longer shoots, whole plant leaf gas exchange was probably greater. Mulching had very limited effects on chlorophyll fluorescence. Results of this project have shown that mulching materials applied around trees after planting can positively affect tree growth without significantly affecting tree physiology. Key Words. Aesculus × carnea; chlorophyll fluorescence; compost; leaf gas exchange; mulching; pine bark; Tilia × europaea. A key to success for new tree planting both in open-field nurs- eries and in the urban environment is the protection of young plants from noncrop plant species (including some hardwoods, shrubs, grasses, and forbs). These fast-growing plants often kill or greatly suppress desired trees by competing with them for light, water, and nutrients needed to grow. As a result, nursery- men, arborists, and urban forest managers generally use herbi- cides to suppress noncrop vegetation. However, the European Union’s Fifth Environmental Action Program (5EAP) set out a series of targets for the year 2000, including “the significant reduction in pesticide use per unit of land under production, and the conversion to methods of inte- grated pest control.” As a consequence, to protect young trees, environmentally sound, effective, cost-efficient, and socially acceptable tech- niques for managing noncrop vegetation are needed. In this scenario, we focused on the need for environmentally friendly establishment and low-cost management methods of the urban green areas. Mulching and its skilled use can contribute to such a development by improving organic matter content in the soils and by affecting other soil characteristics (Harris et al. 2004). Even if mulching is a worldwide practice in urban green areas and different materials can be used for this purpose (mainly shredded wood, chipped woods, pine bark, and, above all, com- posted materials) (Rakow 1989), little research has been done in Italy to determine the effectiveness of this practice. Positive effects after organic mulch application have been obtained by previous research, which has shown beneficial ef- fects on soil physical and chemical properties (Fraedrich and Ham 1982; Litzow and Pellett 1983; Watson 1988; Appleton et al. 1990; Himelick and Watson 1990; Smith and Rakow 1992; Iles and Dosmann 1999; Tiquina et al. 2007; Dahiya et al. 2007) and on plant growth and physiology (Watson 1988; Green and Watson 1989; Appleton et al. 1990; Himelick and Watson 1990). Also, the invertebrate diversity can be positively affected by mulching (Jordan and Jones 2007). However, sometimes the results from mulching are variable being affected by the different environmental conditions and by the different tree species (Whit- comb 1979; Iles and Dosmann 1999). Moreover, if the quality of the mulching materials supplied by the producers is not satisfac- tory, tree performances can be affected in a negative way. This can be related either to its quality or to its misuse, i.e., adding too much material, which can negatively affect soil oxygen content (Gilman and Grabosky 2004; Hanslin et al. 2005), although Wat- son and Kupkowski (1991) found no detrimental effect from the application of 0.45 m (1.5 ft) of wood chip mulch over the soil in which the roots of trees were growing. The application of bark mulch can sometimes decrease growth in the first year, but the effect on plant growth is positive when examined in the long term (Samyn and de Vos 2002). This can be caused by a tem- porary nitrogen depression until the microorganisms are able to decompose a sufficient amount of organic material to provide the needed nitrogen (Craul 1992). Composted materials need to be well characterized for nutri- ent values, stability, and other properties for the support of tree growth and effect against weeds. In a review of the use of com- posts for mulching and soil amendments, Sæbø and Ferrini (2006) suggest designing the composts to fit the specific effects that are wanted. For example, composts for mulching should consist of layers of compost of different particle sizes so that both nutrients can be supplied and weeds are not given good germination conditions. The purpose of this study was to investigate the use of mulch- ing materials and their possible influence on growth and physi- ology of two shade tree species widely grown in the urban en- vironment. MATERIALS AND METHODS Plant Material In 2004, before bud break, uniform, 2.5 to 3 m tall (8.3 to 9.9 ft), 3 to 4 cm (1.2 to 1.6 in) in diameter (measured at 1.3 m [4.3 ft] ©2008 International Society of Arboriculture
May 2008
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