Arboriculture & Urban Forestry 45(4): July 2019 Arboriculture & Urban Forestry 2019. 45(4):109–119 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & A Comparison of Indirect Watering Devices for Benefiting Newly Transplanted Urban Trees By Shaik M.Y. Hossain, H. Christoph Stuhlinger, Matthew Olson, and Benjamin A. Babst Abstract. Three types of indirect watering devices were compared to evaluate their performance and to determine their benefits to newly trans- planted river birch (Betula nigra) trees grown in containers with well drained compost in a controlled greenhouse experiment. Two examples of each device type were used to water trees in this study: upright bags, ring bags, and open tubs. Watering device characteristics, including pur- chase cost, weight, capacity, and drainage times, were measured prior to installing the devices around the trees. Tree stem heights and calipers, along with leaf coverage and leaf water potential, were measured to determine any growth or water stress differences associated with watering treatments. There was substantial variation in costs and drainage times among watering devices, with ring bags being the least expensive and draining water completely during the drainage test. However, there was no evidence that watering devices benefited tree growth, leaf rating, or water stress in comparison with direct watering, with the possible exception of Treegator ring bags, which may have reduced water stress mar- ginally. Although water release from some of the indirect watering devices was much slower than direct watering, water release from all of the devices was completed within ten hours, which is too rapid to reduce the frequency of watering in our experiment. The major benefits of these devices are slower release of water to the soil, with reduced operator time required, and more infiltration into the soil and root zone, which avoids the surface runoff caused by quick hose (direct) watering. Key Words. Betula nigra; Greenhouse; Indirect Watering Device; Leaf Water Potential; River Birch; Slow-Release Watering Device; Transplanting; Tree Growth; Urban Landscape; Water Stress. Newly transplanted trees in the urban landscape (e.g., university campus, community park, city street) undergo significant stress during and after transplant- ing from the tree nursery to the planting site. One source of transplant shock for field-grown trees is reduced root surface area resulting from lifting trees out of the ground and the acclimation to the new site (Watson 1996). However, a more significant transplant - related stress is limited water availability in the plant- ing site (Kramer 1987), a problem exacerbated by reduced root surface area. Usually, a tree receives an adequate supply of water when growing in the nurs- ery. When a tree is transplanted, however, it is subject to a new soil environment that is commonly water limited. As such, it must grow enough new roots at the new planting site to access a limited water supply (Clark and Kjelgren 1990; Ferrini and Fini 2011). Transplanted trees that were grown in nursery con- tainers can also suffer from transplant and drought stress because water tends to drain more quickly from the soilless media (Watson 1996). Limited water availability hinders physiological functions in newly planted trees (Fichot et al. 2010). When adequate water is available, as in nurseries, transpiration allows water to move through the xylem conduits under tension (negative water potential). In contrast, when water becomes limited, as in the urban landscape, xylem tension increases to maintain its hydraulic conductivity. As xylem tension reaches a critical maximum threshold, cavitation may occur and disrupt water movement through xylem conduits (Tyree and Sperry 1989). To prevent cavitation, sto- matal closure occurs in the leaves (Sperry et al. 2002), but this process comes at the cost of lower CO2 avail- ability in the photosynthetic apparatus, causing reduced carbon assimilation and hence reduced photosynthate for tissue maintenance and growth (Ryan et al. 2006). Water stress can also cause growth declines in plants indirectly via reduced cell enlargement associated with loss of turgor pressure (Ranney et al. 1991). One way to reduce water stress associated with transplanting is to use supplemental watering during ©2019 International Society of Arboriculture 109
July 2019
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