When humans arrived in New Zealand, a bit over 700 years ago (Wilmshurst et al., 2008; Jacomb et al., 2014), it seems some of the driest parts of the country, in Central Otago, were under low forest, dominated by kowhai (Pole, 2022). Specifically, this was on the lower slopes of the gorges and slopes of ranges like the Obelisk/Old Man, below around 400 m above sea level. Conifers appear to have been absent, or at least vanishingly rare in this vegetation. However, they were likely prominent at higher altitudes, where they continued up to the tree line. In this zone, based on both relict living specimens, and ancient logs, trees like totara were common.
But how ‘natural’ was that kowhai-dominated forest? Two places really make me wonder, and they are at either end of the Pisa Range.
Left: a tree just visible (arrow) on the skyline of Criffel Peak, from Mount Barker, Wanaka. Right: Enlargement of left image. Closer investigation showed this to be an iolated, relict, but dead, kowhai. The proximity to relict patches of beech forest on Mount Roy, and elsewhere on the Pisa Range, suggests this post-dates a general beech forest cover. Image: the author (Mike Pole).
The first is a tree, when viewed from down on the Mt Barker lowlands, is silhouetted right on the Criffel Peak skyline. It intrigued me, but I couldn’t identify at that distance. Eventually I got permission to hike up for a close look, and it turned out to be a large ‘relict’ kowhai – one that likely predates Europeans. Unfortunately, though, it’s dead (see the Featured Image). The slightly better news, is that there is one young living kowhai a few meters away. But I saw no others.
That one big, old kowhai, suggests to me that the kowhai-dominated forest of Central Otago, may have extended to here. But here’s the rub – this kowhai is growing in line of sight across the Cadrona Valley to Mount Roy (I’ve grown up saying ‘Mount Roy’, and the ‘official’ ‘Roy’s Mount’ sort of irritates me). On Mount Roy there are highly relictual patches of beech forest – remaining only in spots were they have managed to evade fire. They are clearly relicts of when extensive beech forest cloaked Mt Roy, from near the base of the range, up to the natural tree line.
But if Mt Roy had beech forest, surely the Criffel Range, at the north end of the Pisas, would have as well? Kowhai was probably not a usual part of beech forest, though it does happen in some situations.
The second place is opposite the ‘Roaring Meg’, at the other end of the Pisa Range. On the other side of the Kawarau River from main road (the Mount Difficulty side) is a typical ‘moa shelter’ with the usual compliment of dried kowhai remains below the surface. This shelter is one of over a hundred that I used (pole, 2022) to argue that the lower gorges were once covered in a kowhai forest. But just up the Roaring Meg, is a relict patch of beech forest. Like those on Mt Roy, as well as in the Albert Burn, they are prima facie evidence that the Pisa Range had beech forest up to the tree line.
Once gain, if the Pisa Range had beech forest – then surely it could have grown on the other side of the Kawarau River, on the slopes of Mount Difficulty. But in that case, where do the kowhai forests ‘fit in’?
Researcher Jamie Wood and co-authors (Wood et al., 2008) made a curious observation – that so far, most carbon dates of the ‘moa shelter’ material, date to younger than about 3,500 years (a remarkable exception is an early Holocene site at Gibraltar Rock: McGlone and Wood, 2019). Wood drew a link from that to evidence that southern New Zealand had dried out round about that time (McGlone and Moar, 1998; Wilmshurst et al., 2002). If that was the case, the Wood group argued, Central Otago may have dried out enough, such that plant material in the rock shelters began to accumulate, rather than decay.
But if southern New Zealand dried around 3,500 years ago, and a ‘dry’ kowhai-dominated forest grew, then perhaps a ‘wetter’ forest existed before? Being damper, the leaves and fruits that fell from this forest, and found their way into rock shelters, just rotted, instead of ‘mummifying’.
Both the relict kowhai at the north end of the Pisa Range, and the Roaring Meg shelter at the other, are in locations strongly suggesting that they may post-date an earlier beech forest on their sites. Extrapolating from this – perhaps all the kowhai forest that covered the lower slopes of the Kawarau, Cromwell, and Roxburgh Gorges, as well as the lower slopes of the Old Man Range, may have replaced an earlier, wetter forest – although not necessarily of beech.
Is there any evidence for this?
A peat swamp in the Ida Valley sheds some interesting light. McGlone and Moar (1998) found that the peat levels dated to c.7500 -4000 BP, sometimes contains over 20 % matai pollen. While the pollen researchers were somewhat hesitant to believe this pollen came from matai growing near the peat swamp, to me it suggests matai on the surrounding slopes. Wood and Walker (2008) later named this ‘Arthur Swamp’, and looked at the seed and wood content. They found remains of Olearia and the herb Colobanthus, but no remains of matai, or any other forest plants. That certainly seems to indicate the actual swamp was unlikely to have been matai forest, but still doesn’t rule out that it was on the slopes. Incidentally, the pollen record from Earnscleugh Cave, above Alexandra, only extends back to about 2176 years BP (Clark et al., 1996). So although matai was the most prominent of the conifer pollen, it’s still one of those <4,000 year old sites.
Matai is one of trees more tolerant of drier conditions in New Zealand. If Central Otago once had a forest slightly ‘wetter’ than a ‘dry’ kowhai forest – then perhaps it was matai-dominated. Beyond some intriguingly-high pollen proportions, there is no positive evidence for this – yet. I suspect if any does turn up, it may be in some of the wetter schist country to the east, the Maniatoto.
References
Clark, G.R., Petchey, P., McGlone, M.S., and Bristow, P. 1996. Faunal and floral remains from Earnscleugh Cave, Central Otago, New Zealand. Journal of the Royal Society of New Zealand, 26:363-380. https://doi.org/10.1080/03014223.1996.9517515
Jacomb, C., Holdaway, R.N., Allentoft, M.E., Bunce, M., Oskam, C.L., Walter R., and Brooks, E. 2014. High-precision dating and ancient DNA profiling of moa (Aves: Dinornithiformes) eggshell documents a complex feature at Wairau Bar and refines the chronology of New Zealand settlement by Polynesians. Journal of Archaeological Science, 50:24-30
McGlone, M.S., and Moar, N.T. 1998. Dryland Holocene vegetation history, Central Otago and the Mackenzie Basin, South Island, New Zealand. New Zealand Journal of Botany, 36: 91-111.
McGlone, M.S., and Wood, J.R. 2019. Early Holocene plant remains from the Cromwell Gorge, Central Otago, New Zealand. New Zealand Journal of Ecology, 43, DOI: 10.20417/nzjecol.20443.20413.
Pole, M. 2022. A vanished ecosystem: Sophora microphylla (Kōwhai) dominated forest recorded in mid-late Holocene rock shelters in Central Otago, New Zealand. Palaeontologia Electronica, 25(1):a1. https://doi.org/10.26879/1169 palaeo-electronica.org/content/2022/3503-vanished-ecosystem.
Wilmshurst, J.M., McGlone, M.S., and Charman, D.J. 2002. Holocene vegetation and climate change in southern New Zealand: linkages between forest composition and quantitative surface moisture reconstructions from an ombrogenous bog. Journal of Quaternary Science, 17: 653–666.
Wilmshurst, J.M., Anderson, A.J., Higham, T.F.G., and Worthy, T.H. 2008. Dating the late prehistoric dispersal of Polynesians to New Zealand using the commensal Pacific rat. Proceedings of the National Academy of Sciences of the United States of America, 105:7676-7680. https://doi.org/10.1073/pnas.0801507105
Wood, J.R., Rawlence, N.J., Rogers, G.M., Austin, J.J., Worthy, T.H., and Cooper, A. 2008. Coprolite deposits reveal the diet and ecology of the extinct New Zealand megaherbivore moa (Aves, Dinornithiformes). Quaternary Science Reviews, 27:2593-2602. https://doi.org/10.1016/j.quascirev.2008.09.019
