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Name : Nicholas B. Lanzer Organization : UNH Thompson School Email : - PowerPoint PPT Presentation

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Name : Nicholas B. Lanzer Organization : UNH Thompson School Email :
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  1. The Effect of Crown Thinning on Residual Stand Growth: a Dendroecological Approach Nicholas B. Lanzer and Michael J. Simmons University of New Hampshire – Thompson School of Applied Science University of New Hampshire INTRODUCTION OBJECTIVES and METHODS RESULTS and DISCUSSION • A forest stand has a finite amount of resources (e.g. sunlight, soil nutrients, water, space, etc.) for which trees often compete. Many forest management regimes prescribe silviculturalthinnings to allocate available resources to future crop trees • The objective of this study was to test for differences in radial growth of white pine (Pinusstrobus) trees between thinned and unthinned stands at the 277-acre UNH Saddleback Mountain property in Deerfield and Northwood, NH, using dendroecology, the analysis of annual wood rings • Hypothesis: Trees released from competition (i.e. those in the thinned stand) utilize additional resources provided by thinning and will demonstrate an increase in radial growth comparable to the control • Site (Saddleback Mountain) was selected due to a crown thinning operation performed in late fall/early winter of 2004 • Samples of ten dominant and/or co-dominant white pine trees from both the control and thinned stands were systematically selected for tree-ring analysis • An increment borer was used to extract one core per sample tree in each treatment; each core was subsequently dried, glued to a wooden mount, sanded with progressively finer grades of sandpaper (up to 400 grit) to produce a flat surface, and measured using a Velmexmeasurement system (accurate to 0.001 mm) and Measure J2X software • Tree-ring data were cross-dated by creating scatterplots in Microsoft Excel; growth patterns across series were identified and cross-referenced visually • The program COFECHA was used to test cross-dated core data for measurement errors; flagged cores were re-measured as necessary • A dimensionless ring width index (RWI) was constructed for each tree to remove age-related growth trends by fitting a negative exponential growth curve to the raw ring widths of each series and dividing the raw ring width by the predicted value of the exponential curve using the DplR package in the R programing environment. An RWI of 1.0 equals average growth • Repeated-measures analysis was used to test for statistical differences between control and thinned groups • One-tailed t-tests (α = 0.05) were performed a posteriori to test for significant differences in annual RWI between treatments in which the RWI of the thinned treatment was greater than the control • Tree core evidence indicated thinned group was slightly younger than the control group (Table 1) • The level of crown closure (percentage of sky obscured by crown foliage) was much higher in the control group, showing the effect of thinning operation on tree spacing. Consequently, trees in the thinned group receive much higher levels of sunlight than those in the control • Though the thinned group is younger than the control, the mean diameters of both groups are nearly equal. This suggests that the radial growth expressed by the thinned group may have accelerated after the thinning was performed • The large difference between each group’s mean live crown ratio (ratio of length of crown to total tree height) attests to the growth response of the residual stand post-thinning • Growth patterns for the two groups align closely for years 1980–2005 and begin to diverge in 2006 (Figure 3) • Repeated-measures analysis revealed a significant interaction between treatment and time (p = 0.0179) • p-values for years 2007, 2008, 2010, 2011 and 2012 were less than 0.05; it is therefore statistically improbable that the divergence in growth trends between the thinned and control stands would have occurred by chance (Figure 3) • Although the thinning treatment was performed in 2004, the thinned group did not express a significant radial growth response until 2006. The residual stand, exposed to additional crown space and sunlight, likely responded to this increase in resources by first expanding tree crowns in the first post-harvest growing season. Larger tree crowns and the associated increase in foliage then allowed the trees to produce additional photosynthate, a product of photosynthesis necessary for radial growth, in years 2006 and beyond. The difference in live crown ratio between the two groups (Table 1) supports this theory Table 1 – Mean age, height, live crown ratio, crown closure, and diameter for control and thinned groups at Saddleback Mountain, NH (SE = standard error) Figure 3 – RWI values for control and thinned groups from 1980 to 2012 Figure 1a – an example of an unthinned stand. Image credit: David J. Moorhead, University of Georgia, Acknowledgements We thank Tom Lee (UNH-NREN) for intellectual support and for the use of measuring equipment, and Steve Eisenhaure (UNH Woodlands Office) for access to site and forest management information. This work is part of a Spring 2013 undergraduate research project for INCO-590 (Student Research Experience). Figure 1b – an example of a thinned stand. Image credit: David J. Moorhead, University of Georgia, CONTACT Name: Nicholas B. Lanzer Organization: UNH Thompson School Email: Figure 2c – coring a white pine tree Figure 2a – Saddleback Mountain area Figure 2b – Saddleback Mountain detail