214 Etemadi et al.: Post-transplant Shoot Growth is Affected by Site and Species According to the results, current-season shoot growth of eldarica pine and white mulberry trees in the second year was significantly reduced as compared to the first year (Figure 2). This reduction was more pronounced for white mulberry trees where the mean shoot length decreased from 22 cm in the first year to 8 cm in the second year. However, a strong increase (5.7 cm, 4.3 cm, and 9.7 cm for eldarica pine, white mul- berry, and smoothleaf elm trees, respectively) was observed in shoot growth of all three species during the third year. It is worth noting that unlike two other species, shoot growth of white mulberry trees in the third year was still statistically lower than that of untransplanted trees, suggesting that this species requires more time for post-transplant establishment. DISCUSSION Figure 1. Effect of transplanting method on relative growth rate for trunk diameter (RGRD ) of transplanted eldarica pine (Pinus eldarica), white mulberry (Morus alba), and smoothleaf elm (Ulmus carpinifolia) trees during first (a) and second (b) years after transplanting. Trunk diameter was measured 10 cm above soil surface. Means followed by the same letter are not signifi- cantly different (Duncan’s multiple-range test) at 5% level. Transplanting date had significant impact on survival of eldarica pine. The highest percent survival was observed for late-spring-transplanted trees (mean air temperature between 10°C–20°C). This result is in agreement with previous find- ings asserting one of the appropriate times for transplanting conifers is the early growing season when the temperature is warm enough to permit new root growth to begin immediately after planting (Iles 2001). Late-spring transplanting resulted in significant reduction in tree survival. Furthermore, none of the early-winter-transplanted trees were able to tolerate trans-planting (probably due to restricted root growth and continued transpira- tion demand from shoots and green leaves). However, this result differs from that of Aref and El-Juhany (2004), who showed that one-year-old Juniperus procera seedlings transplanted early in winter reached 98% survival after two years following trans- planting in temperate climate of southwest Saudi Arabia. Species type, larger size transplanted trees, and drier climate of present study may be reason for the poor results obtained. White mulberry trees had great capability to tolerate trans- planting operation when harvested and dug during the dormant season, since none of the early-winter-transplanted trees were lost by the end of experimental period. Transplanting in warmer ambient temperatures (early and late spring) significantly decreased survival rate. Several benefits have been considered for planting and transplanting deciduous trees during dor- mant seasons, including cooler temperatures and shorter days that decrease transpiration demand, lignified cells and ceased shoot extension which all reduce water stress (Good and Corell 1982; Richardson-Calfee and Harris 2005). Moreover, dormant- transplanted trees have more time to establish suitable root-to- soil contact before shoot growth in spring (Buckstrup and Bassuk 2000). Although tree species vary in their preferred trans- planting date, many deciduous trees have been demonstrated to respond better when transplanted in fall or winter such as Fraxinus pennsylvanica Marsh., Syringa reticulate (Harris and Bassuk 1994), Chionanthus virginicus L. (Harris et al. 1996), and Celtis occidentalis (Buckstrup and Bassuk 2000). In this study, smoothleaf elm showed a high rate of mortality. of Yet, Figure 2. Annual shoot growth of transplanted eldarica pine (Pinus eldarica), white mulberry (Morus alba), and smoothleaf elm (Ulmus carpinifolia) trees during three years following trans- planting. Means followed by the same letter are not significantly different (Duncan’s multiple-range test) at 5% level. ©2013 International Society of Arboriculture those survived, early-winter-transplanted trees had significantly greater percent survival than early-spring transplanted trees, suggesting that winter planting was advantageous compared to spring planting. The study authors assume that among contrib- uting factors for high mortality rate of smoothleaf elm trees, the pre-transplant status of these trees is probably the most influential factor, as in recent years, incidence of elm beetle pest (Galerucella
September 2013
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