Arboriculture & Urban Forestry 35(5): September 2009 Arboriculture & Urban Forestry 2009. 35(5): 221–231 221 A Meta-analysis of Studies Published in Arboriculture & Urban Forestry Relating to Organic Materials and Impacts on Soil, Tree, and Environmental Properties Bryant C. Scharenbroch Abstract. Organic materials are commonly used in urban landscapes to improve soil quality and tree health. Literature reviews suggest that the effects of organic materials are beneficial, but these impacts have yet to be evaluated using meta-analytical approach. This work pres- ents a literature summary of 176 articles published in Arboriculture & Urban Forestry (AUF) and evaluates 33 of these papers using a meta-analysis. Research relevant to this topic is not published solely in AUF, but the meta-analysis is limited to AUF in an attempt to specif- ically focus on the information provided to AUF readers. This meta-analysis provides evidence of the mostly positive impacts organic ma- terials have on shoot growth, root growth, tree physiology, and soil physical properties. It also identifies specific gaps in AUF literature for the effects organic materials have on soil chemical, soil biological, and environmental (e.g., climate, competition) properties. Further, this me- ta-analysis suggests the type of organic material and the mode of application have differential effects on tree, soil, and environmental properties. Key Words. Environment; Meta-Analysis; Organic Materials; Soil Organic Matter; Soil Biological Properties; Soil Chemical Properties; Soil Physi- cal Properties; Tree Health. Soil organic matter (SOM) is derived from the decay of once liv- ing organisms and is composed of organic (C-based) compounds (Brady and Weil 2008). Organic matter is the most complex, dy- namic, and reactive soil component (Tabatabai 1996). It positively contributes to tree and environmental health, through effects on soil physical, chemical, and biological properties (Magdoff et al. 1996). In urban landscapes, natural tree restitution avenues (e.g., leaf-litter fall) are often interrupted and as a result SOM dynamics altered (Craul 1985; Craul 1999). Consequently, organic materials are commonly applied as mulches and soil amendments to restore SOM inputs. A recent review by Chalker-Scott (2007) identified organic mulches consistently rated as the best or second best mulches for overall plant performance in comparative field trials. Arboriculture & Urban Forestry (AUF), formerly Journal of Arboriculture, is a primary source for the exchange of scientific knowledge in the profession of arboriculture and urban forestry. This meta-analysis was limited to results published in AUF in or- der to assess information provided by AUF. Arboriculture & Ur- ban Forestry has a wide circulation among professional arborists and urban foresters, and these practitioners rely on the scientific journal as a main source of scientific information for the care and management of urban trees. Furthermore, most arborists and urban foresters do not subscribe to technical soil science journals, such as Soil Science Society of America Journal, Journal of Environ- mental Quality, or Soil Science, and it is likely they acquire most of their soil-related technical knowledge through AUF. Consequent- ly, a meta-analysis limited to AUF will assess the information that urban tree care professionals have been exposed to pertaining to organic materials. A recognized shortcoming of limiting a meta- analysis to studies published in AUF is that it does omit key papers published in other journals; but, by doing so the meta-analysis more accurately represents information available to the arboricul- ture profession. Because the meta-analysis was limited to AUF, it is a comprehensive examination of literature in this journal. A meta-analysis (i.e., an analysis of analyses) provides an al- ternative analytical framework for the synthesis of results from separate studies (Cooper and Hedges 1994; Curtis 1996). Meta- analytical approaches have been used to synthesize research and examine ecological questions relating to competition (Gurevitch and Hedges 1993), elevated CO2 (Curtis 1996), and animal ecolo- gy (e.g., Jarvinen 1991; Poulin 1994). A meta-analytical review in- volves a literature search to identify appropriate and relevant stud- ies to answer a particular question. Treatment responses (i.e., % change relative to control or effect size) are calculated across inde- pendent studies for standardization, and then statistically evaluated to provide information for the question of interest (Curtis 1996). The goal of the study was to assess information in the journal Arboriculture & Urban Forestry pertaining to the effects of organ- ic materials on trees, soil, and environmental properties. The spe- cific objectives of this study were: 1) perform a literature search and summary of AUF literature relating to organic materials; 2) identify studies meeting the specific criteria for inclusion in a me- ta-analysis; 3) compile parameter response data for those studies; and, 4) perform a meta-analysis to examine the impacts of organic materials on trees, soils, and the environment as presented in AUF. METHODS Every article of Arboriculture & Urban Forestry (1975 to 2008) was surveyed to address the question of how organic materials impact trees, soil, and the environment. Organic treatments were defined as C-based materials (e.g., organic mulch and compost), ©2009 International Society of Arboriculture
September 2009
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