Restoring Old-Growth Forest Tree Species Through Enrichment Planting

Our paper makes the following key points:

1. Old-growth trees species have been lost from many of New Zealand's lowland environments,
2. Reincorporating old-growth species into secondary native vegetation, exotic vegetation, or restoration plantings requires deliberate and careful interventions by either seeding or planting,
3. Methods of incorporating old-growth species requires further research to increase certainty over this restoration treatment,
4. Restoration of old-growth species is crucial from cultural, ecological and economic perspectives,
5. Government policy (e.g., afforestation grants and carbon sink initiatives) needs to enable enrichment planting to help ensure forests reach their full ecological potential and provide much needed ecosystem services (e.g., carbon sequestration).

Most of New Zealand’s formerly extensive lowland native forests have been cleared or modified and large areas of secondary-growth vegetation have subsequently established. The old-growth tree species (i.e., those representing the mature-phase of the forest regeneration cycle) are often missing from these forests, and this impacts on long-term biodiversity conservation and provision of ecosystem services (e.g., sequestering atmospheric carbon to help respond to climate change).

Old-growth forest remnant and regenerating scrub. In many areas of New Zealand seed sources are much more distant than this example and old-growth tree species struggle to establish themselves

To restore secondary forests, depauperate remnant forests and create new forests that have complex structure, high biomass, and natural canopy tree diversity, old-growth tree species should be reintroduced through enrichment planting.

A naturally established thin-barked totara seedling

Native conifers planted into a degraded exotic conifer plantation

Re-establishing old-growth tree species in a range of existing vegetation types is not straightforward, and we need to conduct further restoration research to refine techniques so that this aspect of forest restoration can be more widely appreciated and applied.  

Without enrichment planting, many planted native forests will lack old-growth tree species

While there is currently much political focus on establishing new forest (e.g. through Te Uru Rakaū’s One Billion Trees grants) and sequestering carbon with young secondary forest (e.g., the Emissions Trading Scheme), such policy needs to better enable and incorporate enrichment planting to ensure the ecological and ecosystem service benefits provided by old-growth tree species in existing vegetation are achieved widely.

Read more about this topic in this paper published in the New Zealand Journal of Ecology: https://newzealandecology.org/nzje/3404