Arboriculture & Urban Forestry 42(3): May 2016 Arboriculture & Urban Forestry 2016. 42(3): 133–145 133 Testing a New Approach to Quantify Growth Responses to Pruning Among Three Temperate Tree Species Matt Follett, Charles A. Nock, Christian Buteau, and Christian Messier Abstract. In settled areas, electrical line safety is maintained by pruning encroaching trees. Identifying key predictors of branch elon- gation growth rate following pruning would assist in developing predictive models and optimizing pruning cycles. However, measur- ing branches in trees near electrical lines is complex and challenging. This paper describes an innovative approach using a handheld laser rangefinder to safely and accurately estimate growth from the ground. In-tree and ground-based laser measurements were highly correlated. This was followed by testing for correlations between branch growth response over a number of years aſter pruning and many biotic and abiotic factors for Fraxinus pennsylvanica, Acer platanoides, and Acer saccharinum, in the city of Montréal, Canada. In a sample of 59 trees, A. saccharinum had the greatest branch growth, followed by F. pennsylvanica, and finally A. platanoides. Branch growth increased following pruning and subsequently strongly declined, with A. platanoides declining the fastest. Branch inclination angle was positively correlated with growth rate for two species, but not for A. saccharinum. Among the types of pruning used, direc- tional pruning techniques resulted in the least branch regrowth rate. Tree diameter was weakly related to branch growth rates. These results suggest that while growth conditions for street trees may be perceived as homogenous, there is substantial variation in branch growth response. This variation may be related to pruning history, or unmeasured abiotic or biotic variables. Estimating pruning cycle duration is a complex task and further work is needed to develop a predictive model for more accurate estimation of return times. Key Words. Acer platanoides; Acer saccharinum; Branch Growth; Canada; Fraxinus pennsylvanica; Growth Modeling; Laser Range- finder; Pruning; Québec; Urban Forestry; Utility Pruning; Vegetation Management. Urban trees play an important role in the infrastruc- ture of cities by providing numerous ecosystem ser- vices (Dwyer et al. 1992; Bolund and Hunhammar 1999; Kuo and Sullivan 2001; Nowak et al. 2008). However, trees must also coexist with other ele- ments of city infrastructure due to the compact na- ture of urban development. Where electrical utility line vegetation clearance is maintained by pruning encroaching trees, periodic returns are required to maintain adequate clearance from electrical conduc- tors. Estimating return time for vegetation manage- ment is an overarching concern for managers (Rees et al. 1994; Christian Buteau, pers. comm. 2012). Return time for vegetation management could be optimally planned using the clearance distance at the last pruning cycle and rates of regrowth of shoots that will likely be the first to intercept electrical lines. A number of factors will likely influence this rate of regrowth, including climate, species, site factors, and genetic and phenotypic variation. However, there is little published information on specific branch regrowth rates following prun- ing. While rates of gap closure as a result of lateral branch extension has been studied in managed for- ests (Heichel and Turner 1984; Runkle and Yetter 1987), such studies are difficult to extrapolate to urban tree branch regrowth in response to pruning for a number of reasons. First, urban tree spe- cies composition is oſten dissimilar to managed forests. Second, research on tree canopy growth response to gap creation, documenting branch elongation to altered environmental conditions in and near the crown (Canham 1988; Springmann et al. 2011), is difficult to extrapolate to urban tree responses to pruning. Finally, urban tree growth rates oſten differ from neighboring forests due to differences in environmental conditions (Close et al. 1996; Gregg et al. 2003; Searle et al. 2012). ©2016 International Society of Arboriculture
May 2016
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