Artificial canopy gaps accelerate restoration within an exoticPinus radiataplantation

Abstract

We created small‐scale artificial canopy gaps to accelerate the growth of mature indigenous forest canopy species for restoration of an 18‐year‐old exoticPinus radiataplantation 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) andBeilschmiedia 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. BothP. totaraandB. tawadiffered significantly in height growth and in animal browse occurrence among artificial gap treatments. Growth of the light‐demandingP. totarawas better under large canopy gaps, whereas growth of the shade‐tolerantB. tawaincreased under gaps of any size but was most consistent under small gaps. ForP. totara, any significant restoration benefit of gap formation on height growth was lost when browsed seedlings were taken into account. Animal browse significantly limitedB. tawaheight 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.