Most of our posts have been about the giant mammals of the Pleistocene – creatures of legend, and folklore which people have wondered at for thousands of years. Yet we can’t forget they existed in landscapes very different from our own. Many times these creatures and their predecessors had existed and evolved in regions, which had known no anthropogenic influences whatsoever – and it has been shown, unfortunately, humans have had a pretty negative influence when they decide to take over environments.
This blog is a bit different from our others. It’s still an Ice Age beast of sorts, and it’s most certainly a living thing, but it’s not a mammal, bird or reptile. It’s the super-sized Agathis australis tree, often now known as the kauri, a living fossil from the most ancient of times. It had (and still has) a special place in the balance of nature in the southern hemisphere, and as such, it’s a vital factor to consider in Pleistocene landscapes, which were home to so many weird and wonderful creatures of that epoch.
They are stunning trees, by their sheer size alone. These native New Zealanders regularly attain girths of over 20meters, grow to almost 50m tall and live for well over 1000 years. Older specimens are not unheard of. It is perhaps not surprising that individual trees are named, just as people are, for they are, in many ways, the age-old spirits of the ancient forest systems of New Zealand. One of the oldest was known as the ‘Father of the Forest’, and was felled in the mid 19th century. The oldest we know of today is “Tane Mahuta” or “Te Mahuta” (the king of the forest) in the Waipoua protected woodland. This tree is 1500 years old and over 51 meters tall.
Humans have depredated the forests quite severely, due to the sheer beauty of the wood. And it is indeed beautiful – golden, with shimmering, ‘white bait’ patterns and whorls in their growth rings. I have a guitar which has inserts of this wood, and you would seldom hear such a sweet thing (if played properly – not by me!). But being the incurable romantic that I am, I love the fact I have a tiny piece of a primeval forest in my hands, although I am also glad it is a wood which is increasingly protected from being used for such frivolous things.
Kauri trees thrive in temperate, slightly humid climates, and are often classified as a species which defines a forests soil structure. The ample amounts of litter it produces is unusual in that the leaves don’t decompose terribly fast like the sludgy leaves of the deciduous forests so many of us are familiar with in the northern hemisphere. It can also be up to 2m deep! The result is, it doesn’t release nitrogen back into the earth very quickly and produces a dry, leached soil which is gritty and lacking in the nutrients needed for agricultural use (known in the farming business as podsol). This is pretty acidic and not very fertile. It’s an ingenious environmental response, as A. australis basically starves out any competitors for space and light, only allowing smaller plants in its shade.
The relationship of forest floor plants and the taller trees whose shade they live in are part of a complex dance of nature, which influences the kinds of creatures – think of the specialized diet of the panda and bamboos, or the koala and the euclayptus. The low fertility of A. australis tends to allow only more exotic varieties of Ericaceae like the spiderwood (Dracophyllum latifolium) to flourish. These plants are sometimes known as ‘Dr Seuss trees’, because they look like the rather wacky trees illustrated in those great kids books! Humans have used these plants to weave baskets and occasionally clothes with, while the seeds are eaten by birds and the leaves much loved by ungulates such as goats and deer. You can imagine the graceful early Pleistocene forests of kauri, dappled sunlight filtering through the canopy of leaves far above, and long-extinct grazing creatures sheltering from heat of the southern sun. The soil may be infertile, but dispersal still happens because of the animals the vegetation attracts!
Some have theorized that the plants which tolerate the soils created by the massive kauri adapted to become almost indestructible, be it from grazing Moa birds or the climate fluctuations of the Ice Age – which remember, affected the southern hemisphere too!
Unlike the forest floor plants with which it shared a peculiar symbiotic relationship with, A. australis could not – and cannot – survive temperatures dipping much lower than 17oC. This makes the tree into a powerful and accurate climate proxy, and increases our understanding of the inexorable southwards spread of the great glaciers of the Ice Age. It’s believed that the mighty trees were widespread across New Zealand before the big chill of the Ice Age. As the cold spread, the trees retreated to small, isolated refugial zones.
Terrible and unknown cataclysmic events, between 60,000 and 10,000 years ago felled many of these trees which slumped into wetlands and were preserved there, in a similar manner to the bog oak of the northern hemisphere. We have no real way of knowing if these deposits, which run for a line of about 300km in northern New Zealand, were the result of a sudden biting cold killing off the trees, huge storms and hurricanes, or sea level changes, but as the trees have been analysed, a dramatic use has been found for these wetland subfossils.
Like all trees, the kauri produces tree rings, which tell their own stories of deep time and climate, year by year. Each year, a tree ring tells of what affected its growth – rainfall, drought, lack of sunlight from perhaps a volcanic cloud. It’s all there, year by year, natures own diary. This dating method is known as dendrochronology. In archaeology, the dendrochronological record of oak trees in Ireland has been pioneered by Professor Mike Baillie and David Brown, both of QUB Belfast (my university, of course, and by the way, they are both the coolest dudes you’d ever want to meet). This tree-ring record extends back the better part of 8000 years and link up with the German oak record, offering absolute dates for certain climate events.
Despite the antiquity of these European oak records, the potential of the bog kauri is even more spectacular. I’ve mentioned the girth of these trees, and their preference for warmer climate conditions, which offers a pretty good marker of when the last glacial event gripped the southern hemisphere. These ancient bog kauri were old even when they were destroyed and cast into the wetlands. Now, think of the story those tree rings could tell of what happened before the Ice Age….
The potential for a long, and very ancient chronological template is a bit of a palaeoenvironmental Holy Grail, so the new developments on this project of analyzing kauri tree rings can open so many exciting possibilities in absolute dating!
Research has been carried out by the University of Exeter and it’s expected it’s only the start of a long and fascinating journey back to the most ancient landscapes of the southern hemisphere, to understand the landscape and climate of the Twilight Beasts themselves.
Written by Rena Maguire (@JustRena)
More on indigenous peoples use of plants here.
For more info on preserved forests in New Zealand click here.
Ahmed, M. & Ogden, J. (1987). ‘Population dynamics of the emergent conifer Agathis australis (D. Don) Lindl. (kauri) in New Zealand. 1. Population structures and tree growth rates in mature stands’. New Zealand Journal of Botany. 25. pp 217–229. [Full article]
Allan H. H. (1961). Flora of New Zealand. R.E. Owen: Wellington. [Book]
Baillie, M.G. (2009). ‘The radiocarbon calibration from an Irish oak perspective.’ Radiocarbon. 51.1. pp 361-371. [Full article]
Barbier S., Gosselin F. & Balandier P. (2008). ‘Influence of tree species on understory vegetation diversity and mechanisms involved – a critical review for temperate and boreal forests’. Forest. Ecology Management. 254. pp1-51. [Abstract only]
Biffin, E., Hill, R. S., & Lowe, A. J. (2010). ‘Did kauri (Agathis: Araucariaceae) really survive the Oligocene drowning of New Zealand?’ Systematic Biology. 59.5. pp 594-602. [Abstract only]
D’Costa, D. M., et al. (2009). ‘Stratigraphy, pollen and 14C dating of Johnston’s Gum Hole, a late Quaternary fossil kauri (Agathis australis) site, Northland, New Zealand’. Journal of Quaternary Science. 24.1. pp47-59. [Abstract only]
Hogg, A. G., et al. (2013). ‘The New Zealand kauri (Agathis australis) research project: a radiocarbon dating intercomparison of Younger Dryas wood and implications for IntCal13’. Radiocarbon. 55 (4). [Full article]
Jongkind, A. G., Velthorst, E. & Buurman, P. (2007). ‘Soil chemical properties under kauri (Agathis australis) in The Waitakere Ranges, New Zealand’. Geoderma 141. pp. 320–331. [Abstract only]
Ogden, J., et al. (1992). ‘The late Quaternary history of kauri (Agathis australis) in New Zealand and its climatic significance.’ Journal of Biogeography. pp. 611-622. [Abstract only]
Palmer, J. G., et al. (2015). ‘Progress in refining the global radiocarbon calibration curve using New Zealand kauri (Agathis australis) tree-ring series from Oxygen Isotope Stage 3’. Quaternary Geochronology. 27. Pp. 158-163. [Abstract only]
Thorsen, M. J. Dickinson, K. J. M., & Seddon, P. J. 2009. ‘Seed dispersal systems in the New Zealand flora’. Perspectives in Plant Ecology, Evolution and Systematics 11. pp. 285-309. [Full article]
Turney, C. S.,et al. (2010). ‘The potential of New Zealand kauri (Agathis australis) for testing the synchronicity of abrupt climate change during the Last Glacial Interval (60,000–11,700 years ago)’. Quaternary Science Reviews. 29.27. pp 3677-3682. [Full article]
Wardle P. (1991). Vegetation of New Zealand. Cambridge: Cambridge University Press. [Book]
Wyse, S. V., et al. (2014). ‘Distinctive vegetation communities are associated with the long‐lived conifer Agathis australis (New Zealand kauri, Araucariaceae) in New Zealand rainforests’. Australian Ecology. 39.4. pp. 388-400. [Abstract only]
Wyse, S. V., & Burns, B. R. (2013). ‘Effects of Agathis australis (New Zealand kauri) leaf litter on germination and seedling growth differs among plant species. New Zealand Journal of Ecology. pp 178-183. [Full article]