New Forest Restoration Paper Available: Opportunities and limitations of exotic Pinus radiata as a facilitative nurse for New Zealand indigenous forest restoration

There has never been a more urgent need to restore forest cover on deforested areas of New Zealand’s landscape. Restoring a permanent native forest cover provides multiple benefits, including boosting biodiversity and ecosystem services such as carbon storage and protecting soils and water quality. 

There are, however, numerous challenges in effectively restoring NZ’s temperate rainforest ecosystems. To mention just a few issues, light-demanding weeds are much more successful than shade-tolerant native tree species in establishing at sites lacking forest canopy cover. The microclimate provided by a forest canopy aids the natural establishment of shade-tolerant species which have the ability to form an independent forest canopy. Proximity to native seed sources is also important. With NZ being so heavily deforested, native seed sources are often some distance from restoration sites and this can limit the structure and composition of the forest that regenerates.

In this paper (click to access a free PDF copy), we examined the long-term role of exotic non-harvest/permanent radiata pine plantations for the facilitation of native forest regeneration. We studied radiata pine stands aged 2 to 89–years–old, and surveyed stand structural parameters, light-transmission, landscape context and response variables relating to forest regeneration. 

                                                           Ninety-year-old radiata pine stand

The exotic radiata pine stands accumulated shade-tolerant indigenous forest species richness with increasing age. The structure and composition of the plantation understories were strongly influenced by stand age and proximity to indigenous forest. Stand age was important from the perspective of creating shaded conditions for the establishment of shade-tolerant woody forest species. Our results suggest that proximal indigenous forest was required for the consistent natural establishment of larger-fruited, bird-dispersed mature forest canopy species, such as tawa and mangeao, in radiata pine plantations.

Thirty-year-old radiata pine stand

Overall, our study shows that radiata pine stands can provide conditions suitable for the establishment and growth of shade-tolerant temperate rainforest tree species. The paper provides important insights into limitiations on regeneration in radiata pine stands and aspects needing further research are highlighted. Related research has highlighted methods of optimising radiata pine stands for forest restoration, including breaking-up the even-aged canopy using artificial canopy gaps, managing understory competition, and directly introducing native canopy species through underplanting. Management of herbivory has also been highlighted to be of importance in some locations.

You can access our new paper for free here: http://nzjforestryscience.nz/index.php/nzjfs/article/view/45