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Artificial canopy gaps accelerate restoration within an exotic Pinus radiata plantation

Forbes, Adam S., Norton, David A., Carswell, Fiona E.
Restoration ecology 2016 v.24 no.3 pp. 336-345
Beilschmiedia, Pinus radiata, Podocarpus totara, animals, canopy gaps, felling, forest canopy, forest plantations, forest restoration, lighting, mortality, planting, seedling growth, seedlings, shade tolerance, tree growth, understory, New Zealand
We created small‐scale artificial canopy gaps to accelerate the growth of mature indigenous forest canopy species for restoration of an 18‐year‐old exotic Pinus radiata plantation forest, in the Marlborough Sounds, New Zealand. Small and large circular gaps were formed by felling. Seedlings of two indigenous forest canopy species, Podocarpus totara (Podocarpaceae) and Beilschmiedia tawa (Lauraceae), were planted within artificial gaps and undisturbed plantation canopy. Seedling height growth, mortality, and occurrence of animal browse were monitored at approximately 6‐month intervals over 17 months. Both P. totara and B. tawa differed significantly in height growth and in animal browse occurrence among artificial gap treatments. Growth of the light‐demanding P. totara was better under large canopy gaps, whereas growth of the shade‐tolerant B. tawa increased under gaps of any size but was most consistent under small gaps. For P. totara, any significant restoration benefit of gap formation on height growth was lost when browsed seedlings were taken into account. Animal browse significantly limited B. tawa height growth in large but not in small gaps. Small‐scale canopy gap creation is an effective method of modifying light transmission to the plantation understorey and accelerating seedling growth rates. Canopy gap size can be used to optimize understorey illumination according to species‐specific light requirements. The increased occurrence of animal browse in gaps requires consideration. Artificial canopy gaps within planted monocultures create structural heterogeneity that would otherwise take an extended period of time to develop. These results further support the role of plantations as indigenous forest restoration sites.