Insects gather, and now our watch begins

Above: Dacrycarpus dacrydioides, Lowland Kahikatea in the Riccarton Bush forest remnant. Jon Sullivan (CC BY-NC 2.0)

With the final season of Game of Thrones recently completed, it is only fitting for this blog post to be inspired by the greatest TV show of all time (no bias intended). Although attempting to squeeze in a few Game of Thrones phrases will be one of my goals here, the main goal is to share some awesome research undertaken at Lincoln University. Differences between invertebrate composition and biodiversity across a variety of habitats in Christchurch, New Zealand have recently been released in the New Zealand Journal of Ecology.

Consider this. New Zealand and Westeros, the continent made famous in George R R Martins “A Game Of Thrones” are, believe it or not fairly similar to each other. Well… apart from the dragons, zombies, giants, ice walls, and highly questionable environmental conditions (for earthlike plants to survive 10 year summers and possibly even longer winters is almost going a step too far for any self-respecting ecologist!). Westeros’s erratic climate, although interesting, is not our topic of conversation for today. It certainly deserves a blog all of its own though. Any takers? 

To show you some stark similarities between our two world’s, lets first jump into some Game of Thrones lore:

The Godswood of Winterfell is one of the last bastions of old growth forest in Westeros; containing weirwood trees that are thousands of years old. The whole continent was once covered in forest, but when the first men arrived they began the process of deforestation. Now protected by castle walls, this forest will certainly not be chopped down. Sound familiar? You’d be forgiven for mistaking the Godswood for Christchurch and Riccarton Bush. We equally have a history of deforestation and burning of forest to make way for pasture; however, Riccarton Bush was saved from that fate, and a fantastic example of 600 year old floodplain forest and towering kahikateas still remain. There aren’t castle walls surrounding it, but its predator-proof fence is the next best thing.

Convinced of our similarities yet? I thought so.

“dark and full of native insects” – Riccarton Bush. Image from Adrian Paterson.

Insect diversity, although not explained by George R R Martin must be just as important in Westeros as it is here in New Zealand. Native insect diversity has declined steadily since human settlement. A lot of that has to do with the fact that less disturbed habitats have higher native diversity and abundance; and we humans are as excellent at disturbing habitats as the Game of Thrones dragons.

A survey of the changes in insects across Christchurch’s landscape was done by Richard Toft during his time at Manaaki Whenua – Landcare Research. This survey work was analysed and repeated by Masters student Denise Ford. Beetles, butterflies, moths, and little flies called fungus gnats were sampled using Malaise traps (a tent-like structure to capture insects flying through the forest). It was expected that less disturbed habitats would have higher levels of native diversity and richness, so the following hypotheses were tested:

  1. Native insect richness would be higher in the old growth forest, followed by the restoration sites, followed by the suburban gardens.
  2. Native insect diversity would be lowest in the suburban gardens, and exotic insect diversity would be highest in the suburban gardens.
  3. The types of insects at the restoration sites would be different to the ones found at the remnant forest.
  4. The types of insects found at the edge of the remnant forest would be different to the insects found in the centre of the forest.

The sites used to research the differences in insects across Christchurch include Christchurch city’s urban old growth forest, forest restoration sites, and suburban gardens. Riccarton Bush was one of the study sites used to research insect diversity and abundance; chosen because it is the last remaining example of native floodplain forest present before human settlement.

The two forest restoration sites used were part of Nga Puna Wai and Canterbury Agricultural Park which are all part of the wider Wigram Retention Basin. Before people, these sites were mostly covered in forest, but by the time Europeans arrived, the forests had been burned off and the sites were made up of a mix of tussock grassland, shrubland, and swampland. “A New Zealander always pays his ancestors debts” however, so in the early 1990’s when the Christchurch City Council was developing a flood retention basin, a variety of local native forest plant species were planted, creating these restoration sites. Seven suburban gardens were also chosen as sample sites. Some gardens were less disturbed, while others tended to be covered in exotic species with well-kept lawns and pruned plantings that would give even House Tyrell a run for its money.

“bright and full of exotic insects” Image from Adrian Paterson.

What the researchers Richard Toft, Denise Ford, Jon Sullivan and Glenn Stewart found were that insects have yet to catch on to the fact that we are making some fantastic new homes for them, in the form of restoration sites across Christchurch.

A total of 4822 moths, 2992 beetles, and 4359 fungus gnats were collected across all of the sites. The restoration sites and suburban gardens were found to be sharing many native and exotic species. Suburban gardens did contain the majority of exotic insect species (100% of the fungus ngats), as well as a surprisingly high level of native moths (41% of the total native species sampled). The old growth forest had mostly native species in its interior. Interestingly, on the edge of the forest, there were a few more exotic species collected, making it an intermediate space between old growth and other habitats.

The results from this study suggest that our native invertebrates are as stuck in remnant forests as the White Walkers were behind the ice wall (spoiler alert). The remnant forest tended to be dark and full of native insects, sheltered from wind and light, whereas surrounding gardens and parks are as exposed as Rickon Stark running from Ramsay’s arrows. No wonder insects don’t want to take the leap, and spread out! What can be done to help our native insects is to plant native species in home gardens around Riccarton Bush, as well as around restoration sites to extend the reach of the forest, helping insects disperse easier across the landscape.

Questions that still need answers

Like George R R Martin who hasn’t concluded his story, we are yet to understand the reasons behind why so many of Christchurch’s native insects do not tolerate conditions outside their old growth forest home. Without a full understanding of the needs of our native insects it makes it difficult to include their needs into restoration management plans. Like the Night’s Watch waiting on the wall, we are waiting for insects to disperse, and occupy new habitats. There are still questions that need to be answered though: Why isn’t there more native species dispersal between habitats? How well can they disperse? And should action be taken to speed up the process? These are important questions that still need answering. Just as important as “who will sit on the iron throne?”

Karina Haddon is a postgraduate student in the Master of Natural Resources and Ecological Engineering. She wrote this article as part of her assessment for ECOL 608 Research Methods in Ecology.

The full article is available online via the New Zealand Journal of Ecology.

Invertebrates from an urban old growth forest are different from forest restoration and garden communities (2018).

Check out these ways to help our native insects:

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