30 Aug 2020

Restoring the forest: 'Negative interactions are really important'

7:28 pm on 30 August 2020

Restoring forest ecosystems need to include bringing back both the good and bad animal species and plants.

New Zealand forest. A fern sits in the center of frame.

Photo: RNZ / Cole Eastham-Farrelly

This is the finding of a study by Manaaki Whenua - Landcare Research.

Post-doctoral researcher Jo Carpenter said the loss of so-called negative interactions in the past, such as predation of both animals and seeds, had not been at the forefront of restoration.

When restoring forests, the Department of Conservation has a goal - known as ecological integrity - that makes sure all species that used to live in the area are present and all interactions and processes between species in that ecosystem are present again.

''It's a fantastic goal but frequently when we think of restoring those interactions between these species we tend to think about, kind of, happy, nice interactions, such as tui pollinating kowhai flowers, or kereru eating fruits and dispersing the seeds, really nice stuff we can understand is important, but I think actually the kind of negative interactions between species, like predation, parasitism or competition are really important too and actually building blocks in our ecosystem that we also should be trying to restore.

''If we focus on restoring species and bringing species back we kind of hope that by including those species we are going to include the interactions they carry out.''

Carpenter said not everyone was likely to be happy and gave the weka as an example.

''Weka are a very controversial species because they eat other threatened species and for that reason weka are often not included in restoration programmes."

Carpenter said it was a delicate balancing act, but hopefully in time it would happen.

She said the loss of mutually benefiting links between species, both positive and negative had lasting impacts for ecosystems.

Carpenter said in time it will become increasingly important.

Her study was based on seed perdition (species that destroy seeds).

''We showed seed predation was a really important process originally for structuring forests and changing what plants end up succeeding and which ones become rare.''

Carpenter said she was not suggesting the country return to a pre-human state because it was just not possible.

''People are part of New Zealand's ecosystems now and we have had so many species go extinct and so many new ones introduced that it is just impossible to go back to original pre-human conditions.''

She said when restoration of ecosystems is being thought of we also consider that these negative or antagonistic interactions are really important.

''Eventually if we want to say is that ecosystem in tack and is it healthy and working the way it should, then that will also include the restoration of these negative interactions between our native species.''

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