ARTICLE : Eco-sourcing - it’s in the genes (Otari-Wilton’s Bush)

Eco-sourcing - it’s in the genes (Otari-Wilton’s Bush)

One of the biggest challenges of managing the forest reserve at Otari-Wilton’s Bush is protecting and maintaining its natural character in the face of a variety of external influences.

Vegetation is a key part of this character, and revegetation efforts at Otari have resulted in some real success stories where areas have been restored to a vegetation cover more in keeping with what was once there.

Part of this work involves considering how the genetic make-up of the existing vegetation shapes the forest’s character.   We think carefully about where we source our plants and seed, and we ensure our sources are from local populations of our unique vegetation - commonly known as eco-sourcing.

A plant’s physical appearance and chemical make-up are determined by its genes, passed on through successive generations, and by the changing environments in which those generations grow and reproduce.

There can be a variety of forms of a single gene (called alleles) that correspond to a variety of plant traits or characters.   These characters may be visible, such as slightly smaller or larger leaves, greater or lesser amounts of pollen production, and variable timing of seasonal events such as flowering and fruiting.   Alternatively, they may be cryptic and require detailed analysis, such as differing palatability of leaves to predators.

This variety of forms of a single gene means that the genes of a local species can differ slightly from that of any other population of the same species.   That is, a population of a species from Gisborne is likely to differ genetically from a population of the same species from Nelson.

Eco-sourcing - sourcing local plants for local plantings - is becoming the norm for revegetation projects.   This is generally considered the best way to alleviate concerns that revegetation might change the genetic character of local populations.   Because we cannot be sure how the introduction of a plant from outside the Wellington region will affect the genetic character of the same species naturally occurring in Otari, all plants used for revegetation within the forest reserve at Otari are eco-sourced.

The introduction of non-local plants could introduce undesirable forms of a gene into the existing population - called genetic pollution - with the resulting change in genetic character termed genetic erosion.

Of course, changes in genetic character do occur naturally, and genetic material is dispersed as far as pollen and seed is carried across the New Zealand landscape.   This can be a considerable distance for some species, possibly as far as Australia!

Movements such as this are termed gene flow, and the overall effect is to decrease naturally the differences between populations.   The potential for this gene flow diminishes as the distance between populations becomes greater, and varies between pollination mechanisms and seed-dispersal mechanisms - commonly achieved by birds and the wind.

The further apart populations become, the less likely they are to be influenced by natural gene flow and the more likely they are to begin to separate from the prevailing gene pool.   This is termed genetic drift and is considered to be one of the factors that can result in the evolution of a new species over time.

So despite restrictions on the source of Otari’s revegetation plants, we do not want to disrupt the natural introduction of new forms of genes.   In the future, corridors of restored vegetation may link important areas of vegetation in Wellington and help this important gene flow to occur.

When we engage in revegetation at Otari, we want to be considerate and thoughtful, to the best of our abilities and knowledge, about representing the uniqueness and character that we are trying to protect and maintain.   Eco-sourcing is one of these measures.

Rewi Elliot, Curator / Manager, Otari-Wilton’s Bush.