Effect of artificial canopy gaps on native regeneration in mature Pinus radiata forest in New Zealand. (2020)
Type of ContentTheses / Dissertations
Degree NameBachelor of Forestry Science
PublisherUniversity of Canterbury
Gap creation is what drives succession in natural forests. This research explored the effect of artificial canopy gaps in a mature single-aged Pinus radiata forest on understorey native regeneration, and what potential role artificial canopy gaps could have in transitioning a pine forest to a native forest. Species and abundance by cover class was recorded at 22 plots beneath a 22-year-old P. radiata forest, in the Marlborough Sounds. The plots included three treatments comprising (1) a closed canopy control, (2) a small gap with trees within a 2.3 m radius felled, and (3) a large gap with trees within a 5.6 m radius felled. The gaps were established in 2014, allowing six years for species to regenerate before they were measured.
The effect of treatment and gap ratio on native species importance value was found to be highly significant (p<0.01). Whereas only the effect of gap ratio, and not treatment, was found to be significant on native species richness (p<0.05). Native species importance value was found to be significantly different between the small gap and the control, and the large gap and the control. However, there was no significant difference between the small and large gap treatments. The composition of understorey species was also found to be significantly different between treatments (p<0.05).
The growth and abundance of regenerating understorey species was strongly influenced by the creation of canopy gaps. Gap creation also caused an increase in species richness; however, this effect was not as strong as the effect on growth and abundance. The presence of gaps was found to be more important than the size of the individual gap as there were only minor differences in understorey regeneration between small and large canopy gaps. This suggests that artificial canopy gap creation can be used to facilitate native regeneration beneath a mature pine canopy.
There was a distinct lack of later successional species in the forest understorey. This is likely due to both a lack of nearby mature forest to act as a seed source and effective seed dispersal mechanisms. Enrichment planting is likely to be necessary in many restorations to bring later successional species into ecosystems from which they have been lost. Herbivore exclusion and control of other mammalian pests is also likely to be necessary to allow for species to regenerate freely in the understorey without browsing pressure. Artificial canopy gap creation in single-aged plantation monocultures creates light environments and structural heterogeneity which can accelerate succession to a natural indigenous forest. However, long- term management and monitoring will be essential for successful ecosystem restoration.
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