Curator Interview: Ewen Cameron
Ewen Cameron is the museum’s Curator of Botany, looking after a collection of over 330,000 different botanical specimens from the foliage of giant trees to the tiny algae that grow in stagnant ponds.
Ewen has been the curator for 15 years and has been involved in botanical research and conservation in northern New Zealand for nearly 30 years.
One of the world’s most primitive kind of plants, the liverwort, is thoroughly at home in New Zealand where roughly 10% of the world’s total species can be found hanging on in niches they have occupied since the time of the dinosaurs.
What did New Zealand’s flora look like in the Cretaceous?
Flowering plants were evolving quite rapidly right through the Cretaceous and though by the end of the Cretaceous some of the more advanced groups like the grasses and orchids had not yet appeared, many of the main families were quite advanced, such as the proteas (Proteaceae). Today in New Zealand we only have two proteas, rewarewa and toru, but the fossil record tells us we used to have at least 14 genera of this distinctive primitive woody family.
Are the proteas of Gondwanan origin?
Yes they are. They flourished on Gondwana for over 90 million years, reaching their heyday in the Eocene-Oligocene. Today there are some 1700 species, mainly in Australia (>1100 spp.) and South Africa, but they are also present in New Caledonia and South America.
In fact, New Zealand used to have Embothrium (Cilean firebush) now found only in the Andes. That’s one of the big differences between the present-day New Zealand flora and the ones of Australian and New Caledonian - the huge element of the proteas reduced to two relic species in New Zealand but still flourishing in Australia and New Caledonia.
Why are there so many in Australia and New Caledonia and so few here?
The Oligocene bottleneck, or near drowning, would have had something to do with it, followed by the cooler times in the Pliocene when many warm-adapted organisms like the proteas became extinct. If we want to know what the New Zealand forests looked like before the ice-ages we need to look at New Caledonia where they still prominently have proteas, she-oaks, wattles, eucalypts, araucarias and large-leaved beech, which once also flourished in New Zealand.
At the beginning of the Cretaceous New Zealand was firmly attached to Gondwana and but by the end it had separated, hadn’t it?
Zealandia (which New Zealand was part of) did not just separate straight off in one go; we unzipped from around 80 million until 60 million years ago. During this unzipping there was a land bridge in the north and the date of that total separation is still questioned. This could explain why some fauna and flora could have still crossed maybe post-Cretaceous to Zealandia.
So New Zealand was much bigger at that time?
Yes, it was then part of Zealandia, the large land mass that New Zealand was part of, stretching from New Caledonia to the subantarctic islands. The undersea map in the Oceans gallery clearly shows the shallow continental shelf around New Zealand which represents the former limits of Zealandia.
How do we know what the flora was like then?
There are two types of data, the real data, which is the present geographical distributions, and the fossil record (macro and microfossils), and then the interpretive data and that’s from the DNA, both the constructed phylogenetic trees and the molecular clock, which is measured by an estimated mutation rate.
What have we got in terms of the plant fossil record?
Both micro- and macrofossils. Microfossils include pollen, spores, starch grains and phytoliths. We are very lucky in plants that most pollen is almost indestructible because it has an incredibly tough layer that you can boil in acid and it survives while everything else dissolves. The disadvantage of pollen is that for wind-pollinated plants it is mass produced and may blow for extremely long distances. Macrofossils (e.g. leaves, fruit, wood) on the other hand, are usually preserved close to the site where they grew.
Where would you find fossil pollen, inside rocks?
Yes, they can be extracted out of rocks, so that is a wonderful tool that has been well used for a long time. More modern pollen is extracted from peat bogs. And although pollen usually won’t provide species level differences it can usually can be identified at family level, and often down to generic level, when interpreted by experts in pollen morphology (palynologists). Palynologists can reconstruct vegetation patterns based on the pollen present and its abundance. It has been used for assisting in interpreting the arrival of Maori, as forest fires leave a carbon layer in the soil profile and directly above that carbon there is a thick layer of fern spores (bracken), being slowly displaced by the shrub and finally the tree species returning. It is estimated that pre-European Maori burnt nearly one-third of New Zealand forests.
What about ferns in the Cretaceous?
Ferns were already very common; they had evolved much earlier than the flowering plants. New Zealand still has a very diverse fern flora, of nearly 200 species and most of them are common. However, recent molecular studies show that many of these ferns arrived here in the last 5 million years or so – so an ancient group, but most are fairly recent arrivals. Their light spores are well-dispersed by wind, so most can easily cross the Tasman Sea.
Why so many ferns?
Ferns like water, they need water to establish and New Zealand has a high rainfall and I suppose partially it’s lack of competition from other plant groups. An island flora is always going to have gaps in it, due to the chance of some things making it and others not, as well as extinctions. For example, the proteas that used to be well represented here but dropped drastically down to two species, along with some other families we lack altogether, but which are well represented in Australia.
What are the gaps in the knowledge about what New Zealand looked like?
Well, you have got to find the right type of rocks of the right age, and this is one of the problems. Most of New Zealand is young, metamorphosed or volcanic. Recently an early Miocene bed of mudstone from shallow lake deposits has been discovered in Central Otago (Lake Manuherikia series) which has beautifully preserved the forest record for about 10 million years. The research here is far from complete but already scientists have discovered a rich eucalypt / she-oak assemblage, tropical leaves of unknown plants, and many animal bones (tuatara, crocodile, lizards, birds and bats). Future discoveries of the right rocks will unearth more treasures.
Is it correct that New Zealand was much further south then?
Yes, but it was warmer. There was beech forest then right across Antarctica. It was dark for a long winter periods just because of where it was. So it must have been very strange how some of these plants survived, there would have been a need for winter dormancy and probably the forests were quite open-canopied to allow more light onto the trees.
Given this pre-history I‘m surprised we have so few deciduous plants. However, some of our evergreen trees are almost deciduous. For example the new season’s leaves of New Zealand beech come out as they drop all their old leaves, so there is only an overlap of less than 4 weeks of old and new leaves. While they’re leafing out the trees can look almost leafless, so they are virtually deciduous, and you can see they probably evolved from a deciduous origin.
Was there a greater diversity of plants then compared to now?
In terms of the flowering plants we have lost many and probably gained fewer. Look at New Caledonia which had a similar Zealandia Gondwanan “starting flora”, however, New Caledonia is only the size of Northland but has greater than two times the flowering plant flora of New Zealand. The main difference is that it didn’t nearly drown and it didn’t suffer the ice-ages. However, in some plant groups we are still very rich by world standards, for example possessing nearly one-tenth of the worlds’ liverworts, ferns and lichens. Interestingly our liverworts are also very primitive – basal members of the whole group.
Does that mean the liverworts evolved in New Zealand first?
No. I suspect ours were isolated early, so did not have competition with higher evolved ones and therefore haven’t changed much.
Kauri and the podocarps, are theoretically not supposed to be as competitive as the angiosperms, the flowering plants, but they are still here, how is this so?
Just their sheer size and longevity give them some sort of advantage over the shorter-lived angiosperms. When they establish they are likely to hold the site for centuries. The podocarps (e.g. rimu) with their small fleshy fruit are well dispersed as is kauri with its wind-dispersed seed. Therefore these conifers can frequently establish on disturbed sites early and hold them for a long time. Kauri has a competitive edge in poor soils, e.g. it often grows on exposed ridges. This isn’t because kauri prefers poor soils, but because it has a competitive edge on these sites. Kauri can survive in these sites of adversity, but if planted in rich soil without competition they will grow much faster.