Trade-offs among establishment success,stem morphology and productivity of underplanted Toona ciliata: Effects of nurse-species and thinning density |
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| Authors: | Julia Dordel Suzanne W Simard Jürgen Bauhus Brad Seely Luciano J Pozas Cindy Prescott Hermann Hampel |
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| Institution: | 1. Department of Forest Sciences, 2424 Main Mall, University of British Columbia, Vancouver, BC, Canada V6T 1Z4;2. Silviculture Institute, University of Freiburg, Tennenbacher Str. 4, Germany;3. National University of Patagonia San Juan Bosco, Argentina;4. Danzer Forestación S.A., Argentina;1. Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada;2. Department of Medical Physics and Applied Radiation Sciences, McMaster University, Hamilton, Ontario, Canada;1. Earth Systems Research Center, University of New Hampshire, Durham, NH, 03833, USA;2. International Atomic Energy Agency, Vienna, Austria;3. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, 90183, Sweden;1. Research Center for Resource Economics and Environment Management, Northwest A&F University, Yangling, Shaanxi, China;2. Department of Medical Information Engineering, Zunyi Medical University, Zunyi, Guizhou, China;1. Sustainable Forest Management Research Institute, University of Valladolid, Avda. Madrid 44, 34071 Palencia, Spain;2. Central Ethiopia Environment and Forestry Research Center, P.O. Box 30708, Addis Ababa, Ethiopia |
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| Abstract: | Toona ciliata (Australian red cedar), a valuable hardwood species, requires a nurse-tree overstorey to prevent damage from frost and drought in some regions of north-eastern Argentina. Different nurse-species offer different degrees of protection, resource competition, and thinning revenues. In addition, choice of nurse-species will influence trade-offs between T. ciliata establishment success, stem quality and productivity as well as revenue from intermediate and final harvests. We tested the effects of overstorey species and planting density on underplanted T. ciliata survival, stem morphology and growth. Initial stand densities of nurse-species Pinus taeda (625 stems/ha), P. elliottii × P. caribaea (625 stems/ha), and Grevillea robusta (833 stems/ha) were thinned by 0%, 25%, 50%, and 75% in three experiments, each using a randomized block design. Initial mortality, light availability and growth of T. ciliata, as well as growth of its nurse-trees, were measured before and two years after thinning. In the third year, we characterized T. ciliata stem morphology (straightness and height-to-diameter-ratio) and destructively harvested a subsample of T. ciliata in order to investigate T. ciliata biomass production and allocation patterns in response to overstorey species, thinning density and light availability. T. ciliata mortality was lower when planted under G. robusta than the pines, and increased in plots with greater exposure to solar radiation. T. ciliata productivity was also greater under G. robusta than under the pines, and was generally greatest where any of the nurse-species were thinned by 75%. Stem form was best when growing under P. taeda and in stands thinned by 50%, regardless of nurse-species. With the exception of early mortality, light levels appeared to have limited effects on T. ciliata growth dynamics. Neither growth rate nor stem morphology was strongly correlated with light availability. Total overstorey basal-area was highest in P. taeda stands and individual overstorey tree growth generally increased with decreasing stand densities, except for slower height growth of G. robusta in more open stands. Thinning operations resulted in sawn-wood revenue for the pine species only. Because stand productivity and stem quality were optimized under different nurse-species and thinning treatments, we conclude that the choice of nurse-species and thinning intensity will depend on management objectives and will change with market preferences and conditions. |
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