Art. XXXVIII.—Notes on the Napier—Greenmeadows Road.
[Read before the Hawke's Bay Philosophical Institute, 10th June, 1901.]
The following rough notes on the natural history of one of our main roads are given not from any scientific value that they may have at the present time, but from a possible historic interest, as the area through which the road runs is changing rapidly from swamp and mud-flat to dry land, with a corresponding and most striking change in its living inhabitants, both plant and animal. This change is from causes both natural and artificial. The natural causes may all be summed up practically in one word—floods. From the smallest up-country freshet that just tinges the river-channel with yellow to the wild outpourings of April, 1897, each and every manifestation of the power of rain helps the spread of the dry land seaward.
It is to the work of that wild Easter-tide on this road that we may turn for a vivid illustration of reclamation, change, and renewal. Before 1897 the first section of this road that is clear of the town—that between the railway-crossing and the Tutaekuri Bridge—was bordered on each side by mudflats covered daily by the tide. Tenanted by countless crabs and estuarine shells, a feeding-ground for gulls and curlews, its only plant-growth mats of sea-grass—Zostera marina—this area looked as if its time as habitable dry land was very far off. But the great flood buried the mud-flats and their denizens deep in silt, so deep that the area rose above the influence of the tide and stretched on either side a sweep of featureless sand for the rest of the winter. With the spring, however, the salt-weed, Salicornia indica, began to creep in from the landward edges, and a small green rush-like plant sprang up in great quantities. This latter plant was Triglochin triandrum. Till this visitation of 1897 it was somewhat uncommon here. Mr. Colenso, in a delightful paper on the flora of the Napier Swamp in the old days, speaks, if I remember
rightly, of finding it only along the banks of a certain creek near Clive. Another well-known botanist told the writer to look out for it under the description of “a plant like a rush, but with a fruiting-spike like a loose-headed plantain.” This fits the plant exactly, and it was found shortly afterwards on the banks of the creek by the Petane Hotel. It must have been plentiful enough in some part of the region swept over by the flood, for upon large areas of flood silt it sprang up thickly, and is now almost as common a feature on the swamp and harbour shores as the salt-weed.
These two plants, Triglochin and Salicornia, are both natives: it seems fitting that these pioneers of the silt should be of our native flora. They are followed very closely by an introduction from Europe, the buckhorn plantain (Plantago coronopus). Like the Triglochin, it showed up but little till after this flood, but has since increased enormously, and is doing very good work here, being the first plant to take hold of the swamp that is useful from a stock-raiser's point of view.
The area raised above tide-level, and all its molluscan and crustacean life buried deep in silt, the gulls and curlews left it for better feeding-grounds. and it was not till a strong square-stemmed sedge sprang up thickly in the damper parts that it could boast of any bird-life save an occasional groundlark. But now that a few species of Mollusca (Potamopyrgus antipodarum) in great numbers, and an occasional specimen of Amphibola avellana, have worked up the channels again, and there are pools in places deep enough for eels, one may sometimes see a bittern here, mostly on the seaward side of the road, which is much the lowest and wettest portion. Towards the New Cut, where salt-weed is the largest growth, it is very barren of higher life. But, if the crabs have vanished, their place is taken in point of numbers by land-loving relatives—the common “slater” or woodlouse, an introduced species, and a smaller native species of a marbled brown and white colour, the introduced outnumbering the native by a hundred to one. The vanished shells are represented, too, by a land species—the common grey slug of our gardens. Besides slugs and slaters, spiders and a small hymenopterous insect are fairly plentiful—a poor list after the rich water-life that lies buried under them.
We can hardly think that it ever crossed the minds of the builders of this road that their embankment would in time act as a boundary between two distinct zoological provinces Yet from the Tutaekuri Bridge to the Wharerangi turn-off this road has been for some years practically the boundary between sea-birds, sea-shells, and sea-plants, and land-birds, fresh- and brackish-water shells, and land-plants: the sea
groups on the mud-flats and shallows of the Inner Harbour side; the land groups in the scrub and reeds and weed-choked channels that stretch away into the swamp on the other.
The mud-flats are the resort of black swan, gulls, terns, curlews, and stilts, the last four often within a short distance of the roadway; but the swan, except in the wildest weather, keeps far out of gunshot in the harbour shallows. In the low scrub of the opposite side blackbirds and thrushes chatter and whistle, starlings and mynahs wheel in flocks, with sparrows, linnets, and yellow-hammers. Besides these introduced species natives are fairly common; bitterns may often be seen during the season, hawks figure largely, with more rarely pukeko and weka, and, still more rarely, the swamp-crake.
It is interesting to note some of the typical land-birds simulating the habits of waders and fishers. I pulled up the other day to watch a large black-brown bird wading far out in the sluggish channel by the roadside, thinking it must be a rail, but it was only a hen blackbird; and I have watched larks busy in the same manner, thigh deep on the trailing strands of the weed that chokes the channel, picking off, I presume, the small shells and water-folk that swarm upon it.
The contrast between the molluscan life of either side is as marked as in the birds; in fact, from their slow mode of locomotion, still more so. Land-birds and sea-birds trespass to a certain extent on each other's ground, but the fresh- and brackish-water molluscs of the sluggish landward channel would perish as surely in the salt water of the seaward side as would the sea-shells of the tidal channel in the fresh water. It is the roadway, acting as a dam between the outgoing fresh and the incoming salt water, that has caused this sharp distinction between the inhabitants of these channels, a distinction which would be sharper still were it not for the culverts allowing a certain amount of salt water to mix with the fresh and make it brackish. This mixing adds to the interest of the landward channel, for brackish water has its own peculiar fauna and flora. The Mollusca of the landward channel are: Potamopyrgus antipodarum (common alike in fresh and brackish water); P. cumingiani (in Hawke's Bay found only in brackish water, but reported a fresh-water shell in some localities); and P. pupoides (found only in brackish water). The Crustacea consist of great numbers of sandhoppers (Gammarus,?), both in and about the water, with slaters (Oniscus) equally abundant on the dry land. The channels and mud-flats on the harbour side have a population that must be in or about more or less pure salt water. The Mollusca are: Potamides nigra and bicarinata, Cominella maculata and funerea, Monodonta œthiops, Amphibola avel-
lana, Tralia costellaris, Chione stutchburyi, and Mesodesma novœ-zelandiœ. The Crustacea are: Crabs, shrimps, and sandhoppers.
These sea and salt-marsh shells are being driven gradually seaward year by year by the encroaching flood deposits. Tralia costellaris, a curious little member of the family Auriculidœ, was, before 1897, very plentiful in the salt-weed on the harbour side of the Wharerangi Road. But that flood practically exterminated it from this area; it is now very scarce, and is only found on the highest banks of the sea-creeks that run up to the road. It is plentiful enough still at the Petane end of the harbour, where I have found it climbing high on the rush-bushes after rain, reminding one that some tropical species of this family have taken to an inland and forest life as true land-shells.
The flora of the seaward side of this road is interesting only from its contrast to the opposite side. Once past the shooting-butts point, the tide swirls up almost to the roadway, leaving naked on its retreat mats of sea-grass (Zostera); then these harbour shallows shrink to evernarrowing channels, which lose themselves towards the Wharerangi turn-off in silt-flats given over solely to Salicornia and Triglochin.
On the landward, or rather the swamp, side there is much more variety. We get here the typical sea-marsh flora, flourishing on the neck of comparatively dry land that divides the road from a large lagoon. The pioneers of the silt-flats nearer town, Salicornia and Triglochin, are here in abundance, with wild celery (Apium australe), Samolus littoralis, Selliera radicans, and Mimulus repens. The weed that chokes the channel is a brackish-water plant, Ruppia maritima.
Apium australe is the wild celery, so common alike on our coastal cliffs and sea-marshes. It is said that Cook's seamen used this plant as an antidote to scurvy. Samolus littoralis is of interest from being the one and only representative of the primrose family native to New Zealand. Its pale-pink flowers, which it bears in great profusion, relieves the somewhat sombre colouring of this roadside during the early months of summer. Mimulus repens, a curious little creeping ally of the snapdragon, is only to be seen at one place by the roadside, and that nearly opposite the Wharerangi turn-off; but it is very plentiful in other parts of the swamp, notably round the wetter portions of the paddocks of the North British Freezing-works.
The work of the flood of 1897 has been given as an example of natural reclamation. Turning to the artificial, it is interesting to watch the inroads made by man by means of draining
and cultivation. A few years ago an enterprising person fenced in a section of sea-marsh bordering the Wharerangi Road. It consisted of a desolate stretch of salt-weed bordered by pools, tenanted by just such a population as described from the seaward side of the road. It was then ploughed (it must have been wet work in many places for the horses), harrowed, and sown down in oats. These came up strong and green on the higher portions of the paddock, then reddening, lessened and failed altogether over the lower portions, nearly three-quarters of the area. Here the salt-weed sprung up refreshed, and the crabs returned to bore again in the sodden furrows. But in spite of apparent relapse the ploughing had acted beneficially for land-plants. Cotula repens, the “bachelor's button,” sprang up thickly in the salt-weed: then on the unbroken furrows a clover (the black medick, Medicago lupulina) got a grip, and that pioneer of the silt the buckhorn plantain. Then it was ploughed again and sown with mangold-wurzels, with about the same result as with the oats—a fair crop inland, but dwindling outward to little yellow bulbs no larger than a radish. The second ploughing strengthened the land-plants; a sward of plantain and a feather-topped grass all but ousted the salt-weed. A third ploughing was followed by maize, which still left the outer edges to the plantain and grass, but brought in with it a wonderful collection of foreign weeds—fat-hen, Prince of Wales' feather, and others—which, now the maize is cut for green fodder, have taken full possession. The some-time marsh is now a paddock, waiting only the plough to fall into the same state as the monotonous grassy levels inland.
Beyond the Wharerangi turn-off the sea-marsh fauna and flora are soon lost in paddocks, whose alien weeds and grasses are encroaching yearly upon them. It is curious to note that here and there an ill-drained portion has, in spite of cultivation, gone back to its original salt-weed; and Samolus littoralis and Selliera radicans follow the drain-sides right up to Greenmeadows Township. But these drains have quite lost their sea-marsh fauna; crabs and sand-hoppers have given place to woodlice again, and of all the shells only Potamopyrgus antipodarum has survived the change to pure fresh water. It is here with its relative P. corolla and the limneids Amphipeplea ampulla and Planorbis corinna. These last three species are emphatically denizens of fresh water. If careful notes were taken year by year of their habitats, I think they would be found to be encroaching on the sea-marsh by water, just as the snails, slugs, woodlice, weeds, and grasses are by land. At present they are down as far as the Napier Park Racecourse, on the Greenmeadows side; at Napier they are in the swamp channel opposite the
gasworks; and they are in the Tutaekuri as low down as the mouth of the New Cut.
These rough notes are taken mainly from the point of view of a lover of shells and plants; but it would seem that this area would afford a most interesting harvest to those interested in crustacean and insect life, the crustacean life of the salt and brackish water giving place to the insect-life of the fresh, and of the insects themselves the littoral giving place to the inland species. The fauna of the New Cut gives a fair illustration of this. Where this canal joins the channel just below the recreation - ground the hand-net brings up small crabs, shrimps, sand-hoppers, and a crustacean very like a woodlouse with swimming-lobes to its tail-segments. Following up the Cut with the net, the crabs soon disappear, then the water-slater; sand-hoppers and shrimps become scarce; and as one nears the Tutaekuri the larval forms of insects come up in the net—the hideous masked nymphs of a dragon-fly, and lesser relatives, the sand and horny tubes of caddis-worms, with fresh - water shells and drowned land-shells, and the seeds of many inland plants, just such a haul as one may take from a mat of watercress in one of our upland streams.