Using DNA to trace the pre-European planting of karaka

Using DNA to trace the pre-European planting of karaka

Karaka, with its large shiny leaves and bright orange fruit, is one of New Zealand’s most distinctive trees. But in pre-European New Zealand, karaka was much more than just a handsome tree – the kernels of its fruit provided an important food source for Māori. This was despite the poisonous kernels requiring considerable treatment before they could be eaten. Karaka was so significant that Māori planted it outside its natural range of northern North Island and as far afield as Bank’s Peninsula and the Kermadec and Chatham Islands.

I was recently involved in a study that used DNA to try to trace the origins of these planted trees of karaka (Corynocarpus laevigatus).

Robin Atherton with the distinctive fruit of karaka. Robin studied karaka genetics for her PhD at Massey University and is a co-author on the new study. Photo credit: Robin Atherton
Robin Atherton with the distinctive fruit of karaka. Robin studied karaka genetics for her PhD at Massey University and is a co-author on the new study. Photo credit: Robin Atherton

Discovering the origins of planted trees can also tell us about the people that moved them. For example, finding the source of karaka on the Chatham Islands/Rekohu, where it is known as kōpi, may show the New Zealand departure point of the Chatham Island Moriori.

Our DNA results showed that karaka from the Three Kings Islands is distinct from karaka from the rest of New Zealand. Our dating using a DNA molecular clock showed that the karaka on the Three Kings Islands became isolated around a million years ago. This result is not surprising as the Three Kings Islands are home to a number of unique plants and animals. These endemic species indicate that these islands have long been isolated, despite being only 56 km from the northern tip of the North Island.

Karaka trees are often found growing in rows in the southern part of their range, indicating they have been planted. These trees were growing on a farm at Akitio, south of Napier. Photo credit: Lara Shepherd
Karaka trees are often found growing in rows in the southern part of their range, indicating they have been planted. These trees were growing on a farm at Akitio, south of Napier. Photo credit: Lara Shepherd

But what do these results mean for the origins of planted karaka trees? We can now exclude the Three Kings Islands as the source of karaka planted in southern New Zealand and the Chatham and Kermadec Islands. However, our current DNA analyses could not distinguish populations through a large area of the northern North Island, and the planted trees could have come from anywhere in there. We are now planning more detailed DNA analyses to try to tell apart karaka from different parts of northern North Island.

Science is often a slow process with many small steps towards a final goal.

6 Comments

  1. I see this threads pretty old however I’ll ask anyhow.
    I’ve long wondered about theses trees and my question is have the trees just simply been the result of discarded seeds rather than deliberate planting?
    Further to that are there other species also likely to have been carried by travelers appearing in unexpected locations along known routes of travel?
    I see in modern times wherever people go the weeds follow, humans are annoying like that.

    1. Author

      Thanks for your comment Dwayne. That is an interesting idea but given that the seeds were the part that was eaten it seems unlikely that southern karaka trees result from discarded seeds (unlike an apple were the fruit is eaten but the seeds in the core discarded). Also the observation that in some groves the trees are in rows further suggests deliberate planting.

      Yes there are many other species that seem to have been moved. Deliberate movements of plants include flax/harakeke and rengarenga. Accidental movements are likely to include plants like hook grass and bidibid, whose seeds can hitch a ride.

  2. I was recently watching a kererū busily dining on karaka berries in a tree growing in a bay in the Marlborough sounds when it suddenly occurred to me that it is possible… even likely?… that more so than planting karaka trees near pā and kāinga to have a nearby source of berries for human consumption it could be to attract pigeons for easy capture and eating. Regards Jan Worrall.

    1. Author

      Thanks for your comment Jan, I have heard this suggested before and it makes sense to me.

  3. The Karaka tree is interesting. I’ve got one in my front garden, and I’d be interested in trying to make something from the fleshy fruit (avoiding the kernels which apparently need robust detoxification). However, I can’t seem to find any recipes on how the fruit could be used other than drying it or eating it raw. How is it best to separate the fruit from the kernel and then use the fleshy fruit for, say, making a jam? Is there anything in indigenous texts that could shed light on this?

    1. Author

      Thanks for your comments Heef. I’ve only come across recipes for the (treated) kernels, not the fruit. I remember reading somewhere that karaka fruit were mostly eaten by children. I imagine that taking the fruit off the kernel would be a bit of a time consuming task so maybe there were other species used that were easier to prepare (I’ve read that poroporo was made into jam). Maybe another reader will be able to comment.

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