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The Vegetation of New Zealand

Chapter IV. — Sketch of the leading Physiographical Features of the Region

Chapter IV.
Sketch of the leading Physiographical Features of the Region.

1. General.

The New Zealand Botanical Region comprises those islands lying in the south-west Pacific between the parallels of 30° and 55° S. lat. and 158° 56' W and 176° W long. The archipelago, if may be so termed, consists of the following groups of islands, each far distant from the others — the Kermadecs, New Zealand proper the Chathams and the New Zealand Subantarctic Islands. The total land area of the Region is about 270,000 sq. km.

New Zealand proper consists of two large islands, North Island and South Island and the much smaller Stewart Island. The above, together with some small islands and islets, including the Three Kings m the north, lie between the 34° 6' and 47° 20' parallels S. lat. and the meridians 166° 30' W. and 178° 30' W. long.

North Island has an area of 114,740 sq. km., a length of 829 km and a maximum breadth of 458 km. (Cape Egmont to East Cape), and 324 km. from Tirua Point to Tolaga Bay, but north of lat. 38° and south of lat. 40° is quite narrow. The area of South Island is 151,120 sq. km., its length 845 km., and its greatest breadth 338 km. (Cape Saunders to Dusky Sound). Stewart Island has an area of 1721 sq. km. and is about 48 km. in length. Taking the land surface as a whole it is long and narrow, the most distant points from the sea being Tokaanu (North Island) 104 km., and 20 km. to the east of Kingston (South Island) 128 km.

The long isolation of New Zealand far from other land masses is a matter of profound significance with regard to the flora Tasmania, the nearest land of importance. is about 1540 km. distant. The actual Australian continent is somewhat further away (1640 km.). Norfolk Island is 650 km. from North Island, Lord Howe Island 1320 km. and the New Hebrides 1540 km. South America is distant 6900 km. from the Chathams and the latter 600 km. from New Zealand proper. Finally, Antarctica lies 1350 km. from Macquarie Island and 2250 km. from Stewart Island.

A consideration of the ocean-depths in the neighbourhood of the New page 43Zealand Archipelago both serves to emphasize the isolation of the region and to show how wide-spread would be the effect of a gener 1 considerable elevation of the ocean-bed. The 180 m. line follows rather closely the outline of the present main islands and includes the adjacen small islands together with the Three Kings, Stewart Island and the Snar s. The 900 m. line conforms closely to the above line on the eas, but westwards it extends a considerable distance from the land, while to the south it goes beyond the Lord Auckland Islands. The 1800 m 1 ne includes the whole archipelago except Macquarie and Kermadec Islands, and, extending far to the north-west, it reaches to within comparatively close proximity to the Queensland coast while Lord Howe Island and New Caledonia rise from this broad submarine ridge. Southwards to Antarctica the ocean bed lies between 1800 m. and 3600 m. below the surface, while between Australia on the west and South America on the east the depth is profound.

2. Physical Features of New Zealand proper.

a. North Island.

Mountains. As a rule the land-surface is much broken, hilly, and in parts mountainous. The main range extends from the east of Wellington Harbour to the East Cape. The highest peaks are in the Ruahine and Tararua Mountains, but none reach 1800 m. and few more than 1520 m. The rocks are chiefly mudstones, sandstones and greywacke.

The centre of the island is a volcanic plateau much of which is, at an altitude of more than 600 m., but, northwards, gradually becoming lower, it extends to the Bay of Plenty. This area, within recent geological times, has been exposed to powerful volcanic action. The eruptions have been largely explosive and the present surface-pumice is the result. Even yet there is much thermal activity1 in the shape of boiling springs, geysers, mud volcanoes, &c, especially on a line connecting White Island, a volcano in the solfatara stage, and Ruapehu. From the highest portion of the Plateau rise the semiactive volcanoes, Ruapehu (2803 m.), Ngauruhoe (2291 m.) and Tongariro (1968 m.). The crater of Ruapehu is filled with ice in which lies a lake of, sometimes, extremely hot water, while small glaciers extend over the crater-rim and descend to comparatively low levels in the gullies.

Mt. Egmont (2521 m.) in Taranaki is an extinct volcano standing far isolated from other mountains; its summit carries perpetual snow. The

1 1) In 1886, the supposed extinct volcano Tarawera, situated on the Volcanic Plateau burst forth forming a rent 19 km. long with a mean width of 108 m. and ejecting light scoria and volcanic dust over an area of 15,000 sq km.

page 44remaining mountains are not lofty enough to bear subalpine vegetation1, nevertheless some of them2 show distinct altitudinal belts.

The extreme north of the island consists of a small, narrow, much dissected tableland some 300 m. high, formed of hard igneous and sedimentary rocks. At one time this was disconnected from the mainland, but now is united by a narrow spit of recent and consolidated dunes.

Plains. An extensive plain of marine origin, the Wanganui, lies between the Ruahine Mountains and Mount Egmont extending to Ruapehu where it is over 600 m. altitude and bounded on the south by the coastline. The rock consists of marl enclosing beds of shells. This plain is deeply cut by numerous streams so that, in many places, there is a network of deep gorges, often extremely narrow. River-formed gravel plains, the upper soil of which is frequently extremely rich, occur east and west of the main range (Manawatu, Wairarapa and Hawkes Bay Plains). The Waikato Plain, formed of river-borne pumice, occupies much of southern Auckland; it extends from the Firth of Thames to the R. Waipa. Its surface, rarely more than 30 m. above sea-level, is extremely wet and swampy. Northwards from the Auckland Isthmus there is much low-lying ground.

Rivers. The land throughout is well watered, every gully containing tsi running stream. In many places, the rivers have cut deeply into the surface, so that gorges are a familiar feature. The rivers rising in the high mountains are of a torrential character, but this feature is much less marked than in South Island, while gently flowing streams are more common. Where the rivers have not cut deep beds the adjacent land is liable to be flooded and extensive swamps are so formed (Manawatu, Waikato, Bay of Plenty, Thames, Northern Wairoa, Awanui). The Rivers Waikato and Wanganui are the most important in point of size and drainage area.

Lakes. The largest lakes are on the Volcanic Plateau, the most important being L. Taupo. L. Waikaremoana in the East Cape district lies 600 m. above sea-level. So far as plant-life is concerned it is the natural ponds and shallow lakes met with in many places that are of most importance.

Sea-coast. The coast is about 2152 km. in length. The various outlying islands also fournish coastal conditions. A most important feature of the coast-line is the extensive dune-area of much of the west coast which extends inland in places for 12.8 km. Also, there are considerable dunes in the far north, and north-east on the coast of the Bay of Plenty, and at various places between Poverty Bay and Cape Turnagain.

1 1) Mount Te Moehau in the north of the Coromandel Peninsula, carries a few subalpine plants, but this in relation to frequent wind.

2 2) The Maungaraki Mts. (900 m.), extending northwards from C. Palliser; the Puketoi Hills (610 m.) in the east of Wellington; the volcanic Mt. Karioi and Mt. Pirongia near the coast of south-west Auckland; the Cape Colville Range; the high land culminating in Mt. Tutamoe (800 m.), south of Hokianga Harbour, and the high land north of the latter with Mt. Raetea (800 m.).

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The coast is frequently rocky. The south and south-east coast-line in its southern part consists of cliffs of slaty shale. Further north, low cliffs of soft marl and mudstone occur fronted by a narrow beach with the stony surface worn quite flat. The north-east coast consists at first of steep slaty cliffs, but from Opotiki onwards the land as a rule is low. The shore-line of the Coromandel Peninsula consists mostly of slate cliffs, but volcanic rock is not uncommon. From Auckland to North Cape the coast is much broken and presents a great diversity of stations for plant-life. Low cliffs fringed by a sandy or stony beach are common. There are bold rocky headlands. Many of the rivers have wide mouths, but these are shallow and mud-flats are exposed at low water. The short north coast is frequently precipitious through truncation of the tableland.

Where dunes are absent on the south-west and west coasts there are cliffs, some volcanic (Maunganui Bluff, &c.), others limestone (Kawhia, west of Taranaki &c), and others of slaty shale (Reef Point, South Waikato Head &c).

Many miles of coast are without inlets, estuaries &c. With the exception of Wellington and Porirua Harbours in the south, nearly all of any moment are to be found on the east and west coasts of Auckland.

b. South Island.

Mountains. The surface is extremely mountainous. Commencing in the south there are two chains, the one composed of gneisses and granulite on the west, and the other of schist extending from the shore at Dunedin and joining the former between Lakes Wakatipu and Wanaka. The latter is continued in an unbroken line as the Southern Alps to Cook Strait; and its eastern slopes are formed of slaty shales and greywackes. Below the shales &c. on the west the rock is schist, but at low levels occasionally gneiss. Granite occurs in a few places. The loftiest peaks are situated at about the centre of the chain. They vary from some 3000 m. to 3766 m. (Mt. Cook). Proceeding north and south, the range gradually decreases in height, but for a long distance few peaks are lower than 1800 m. Many lofty ranges and spurs extend eastwards for 48 km. or thereabouts from the main Divide. These eastern mountains are especially characterized by the vast masses of unstable debris covering their slopes, locally known as "Shingle-slips".

The snow-line in the Southern Alps is perhaps, on an average, at about 2200 m. altitude, but it is not uniform and varies according to latitude, while also it is lower on the west than on the east. The central part of the range is heavily glaciated, the size of the glaciers being correlated with the altitude of the peaks. The Great Tasman Glacier is about 29 km. long and its terminal face 918 m. above sea-level. On the west, the Fox and Franz Josef Glaciers descend to less than 210 m. altitude. page 46Glaciers are wanting to the south of lat. 45° and;n the north they cease at a little to the north of lat. 43°. The eastern valley glaciers are generally covered with an enormous amount of moraine. The central Southern Alps form an unbroken wall, but to the north and south there are numerous passes, the lowest being the Haast (570 m.).

Besides the Southern Alps there are other lofty ranges. The Kaikoura Mountains are the two parallel ranges in the north east with several peaks exceeding 2400 m. altitude but they carry neither glaciers nor perpetual snow, except in small patches; their debris fields are of enormous extent. To the west of the Southern Alps, in the north-west, lie several rugged ranges which extend from near Greymouth to the north coast with many peaks of 1500 m. altitude. Banks Peninsula, on the east of Canterbury, is formed of much-denuded volcanic rocks, and reaches a maximum height of some 900 m In addition to the great ranges, there is on the east much hilly land some undulating, and within the high mountain area several extensive mtermontane basins.

Plains. Gravel plains formed by glacial or snow rivers are a striking feature of South Island topography. The most importan are: — The Canterbury Plain (161 km. long by 48 km. wide at its widest); the long narrow Westland coastal plain (200 km. long by 10 km. wide) and the Southland Plain extending from near Lumsden to Foveaux Strait. Flat as the Canterbury Plain appears to the eye, the surface near the foothills of the Southern Alps is more than 457 m. above sea-level. Borings for artesian water shew by the peat-deposits at different depths that there have been several changes in the land-surface during the formation of the plain.

Rivers. The numerous rivers issuing f om the glaciers or fed by melting snows, or frequent downpours, are torrential at first, their beds full of huge rocks over which the waters leap and foam. By degrees, the valleys shaped by former glaciers widen and are filled from side to side, it may be, by a flat stony bed over which, in anastamosing streams, the river wanders. Lower down, as the valley widens still more, or when the plain is gained, the river may flow between high permanent terraces that it has built, and frequently there is a series of such at different levels with portions of the ancient flood-plains at their bases. River beds 1 km. or more wide with terraces on either side are a common feature of the valleys and gravel-plains (Fig. 1).

Where a tributary stream in a mountain-valley joins a river the shingle of its bed spreads out as a fan. Such are present at the mouth of almost every gully, sometimes naked and active, at other times plant-clad and passive.

Glaciation. At the height of the New Zealand glacial period great glaciers extended throughout most of the high lands of South Island even as far east as the uppermost part of the Canterbury Plain and, on the page 47west in no few places to the sea Remains of ice-action are to be seen throughout the Southern Alps, and m the western range ot Nelson, except where in the drier parts excessive denudation has taken place. Cirques, hanging-valleys, moraines large and small, transported morainic materi 1, roches moutonnees ice-shorn hillsides, truncated spurs and U-shaped valle s are abundant, and both testify to the exrent of the glaciation and prov de special growing-places for plants. Gla?ial lakes are frequen and range from small tarns on moraines to the lakes, many kilometres in length and frequently of great depth, of Canterbury and Otago. In North Island, glaciation, if it occurred at all was evidently trifling.

Sea-coast. The coast-line about 2740 km, in length in general is little broken Notable exceptions are the Marlborough Sounds and Otago Fiords, the former drowned river-valleys the latter of glacial origin. Banks Peninsula contains a number ot mle s, some much-eroded, submerged, volcanic craters. There are also a few shallow estuaries, more or less closed by sand or gravel spots, whose floors are in part bare at low-water.

In many places, the coast is low and the shore sandy, so that long stretches of dunes occur. Shingly shores are frequent in many parts and correlated with the great river-beds

Rocky shores and cliffs are frequent at many points n the coast. In this regard, the most noteworthy are the rocky walls of the Otago fiords formed by lofty mountains rising from the water's edge as precipices for 1000 m. or more. These fiords extend inland for many kilometres and some of them almost reach Lakes Te Anau and Manapouri — themselves to all intents and purposes fiords also. Facing Cook Strait, in the north of the island, are also long arms of the sea penetrating the land, but such are not of glacial origin but are submerged river valleys

Coastal islands are few. The most important are those to the north of Marlborough and in Foveaux Strait. The Open Bay Islands on the west are composed of limestone, and although mere islets possess a remarkable plant-covering.

c. Stewart Island.

Stewart Island lies about 25 km. from South Island from which it is separated by Foveaux Strait, this nowhere more than 48 m. deep.

In shape the island is irregularly triangular. The surface is hilly, much broken and in parts mountainous, the peaks varying in height from 676 m. to 975 m. There is but little truly flat ground. East of the central range the land is low, but broken. At the head of Paterson Inlet a narrow valley, the Freshwater, extends northwards to the Ruggedy Mts., while, westwards, an opening widening out into an ancient dune-area, connects the valley and the west coast. West of Port Pegasus there is some low boggy moorland. The coast is in general rocky. At Mason Bay on the west is an extensive dune-area.

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Perhaps the most striking features of the island are Paterson Inlet and Port Pegasus. The former, a broad expanse of lake-like water, irregular in shape, enclosed by hills and dotted with forest-clad rocky islets, extends westward for 17 km. putting forth three diverging arms. Port Pegasus, situated in the south, runs parallel with the south-east coast for about 12 km., its entrance blocked by three islands.

There are a number of outlying rocky islets especially to the east and south-west, while to the north-west is the fairly large Codfish Island. Thirty-two kilometres to the eastward is the flat island of Ruapuke 7.6 km. long by 3.4 km. wide.

3. Physical Features of the Outlying Islands.

The Kermadec Islands. These are four in number. They extend from 29° 15' S. lat. and 177° 59° W. long, to 31° 24' S. lat. and 178° 51' W. long., and are distant about 960 km. from New Zealand. The group is volcanic, but it stands on a submerged plateau, part of a ridge connecting New Zealand with Tonga. Outside the plateau the ocean is 2700 m. deep.

Sunday Island, the largest of the group, 10.3 km. long and 29.25 sq. km. in area, reaches a height of 524 m. It is composed chiefly of pumiceous and other tuffs; lava streams are few. The surface is hilly with many narrow spurs separating deep gullies. These spurs, truncated at the coast, drop as sheer precipices to the water for 200 to 300 m. The greater part of the island is a crater, its rim 55 m. above sea-level in the north but elsewhere averaging over 300 m. There are three small crater lakes. There is a small sandy beach and one of gravel.

Macauley Island, distant 109 km. from Sunday Island, is 2 km. long, 3 sq. km. in area, and its highest point 237 m. above sea-level. Cliffs everywhere fall to the sea.

Curtis Island, 35 km. from the last-named, are two rocky islets with an area of 0.6 sq. km. and the highest point 100 m. The crater-floor contains hot mud, boiling springs and sulphur. (All the above is taken from Oliver 1910).

The Chatham Islands. These consist of four islands and several detached islets and rocks, lying between the parallels of 43° 35' and 44° 25' S. lat., and the meridians of 176° and 176° 55' W. long, and distant 600 km. from New Zealand proper. Chatham Island, by far the largest of the group, is 967 sq. km. in area and is somewhat the shape of a horseshoe. Generally the land is low but undulating. Much of the interior is occupied by the Te Whanga lagoon which, roughly triangular extends from the north coast southwards for 25 km., and, at its greatest breadth, is nearly 15 km. wide. On the east, it is separated from the sea by a very narrow strip of land broken through at one point. South of the lagoon the island is a compact four-sided block, which, in comparison with the remaining land, looks quite hilly, but its highest part is only 286 m. and the culminating point of the page 49main ridge about 2 m. lower. From this ridge a tableland extends southwards terminating in abrupt cliffs 182 to 213 m. in depth irregularly cut by small streams. Here and there conical volcanic hills, 152 to 182 m. high, stand out from the flat, northern and central portions of the island.

The extensive coast-line varies from flat ground bordered by dunes or low rocks to the high cliffs of the south and south-west.

Besides the Whanga, there are many other lagoons and lakes, indeed, it is stated that one-third of the surface is occupied by water. Bogs of great extent and depth are a familiar feature both of high and low ground. Small, sluggish streams of peaty dark-brown water are. abundant.

Pitt Island, 13.6 km. long by 6 km. across, lies about 22 km. to the south of the main island. Its coast is rocky. The remaining islands (Mangere, South-East Island) are quite small, but the latter rises to 184 m.

The New Zealand Subantarctic Islands. These consist of several distant groups lying between the parallels of 45° 44' and 47° 43' S. lat. and 158° 56' and 179° W. long. The names, distance and direction of each group from the South Cape of Stewart Island are as follows: Snares, 113 km., S. S. W.; Lord Auckland Islands, 348 km., S. by W.; Campbell Islands, 608 km., S. by E; Macquarie Islands, 1049 km., S. W. by S.; Antipodes Island, 902 km., E. S. E.; Bounty Islands, 902 km., E.

All the islands, excepting the Bounties and the Snares, are chiefly of volcanic origin and, the Bounties excepted, the surface consists in general of a deep layer of peat.

The Snares consist of North-East Island, 1.6 km. long and 0.8 km. wide, which rises perpendicularly on its south side to 131 m. and of four other rocky islets lying to the south-west. The main island has a rocky precipitous coast-line except in one place on the east side where a small stream enters the sea. The island is formed of a pale moderately-coarse muscovite granite.

The Lord Auckland Islands consist of two fairly large islands, Lord Auckland Island, 40 km. long by 27 km. wide in its widest part and Adams Island 24 km. long and 8 km. wide in its widest part, together with a group of small islands to the north and the small precipitous Disappointment Island on the west. An elevation of 360 m. would connect the group with New Zealand proper.

Adams Island is separated from Lord Auckland Island by Carnley Harbour, the site of an old volcano. It is a fairly even ridge, 600 m. high, with a long slope northwards, but southwards descending to the sea in a sheer precipice.

Lord Auckland Island is also high and rises in more than one place to 600 m. Several arms from Carnley Harbour pierce it in the south. On the east are a number of small fiords the result of ice-action, but on the west there is a perpendicular wall of stupendous cliffs.

The islands in the north are separated from Lord Auckland Island by page 50Port Ross, a land-locked sheet of water. They are quite low but their coasts are rocky. On Enderby Island there is a sandy beach, 8 km. long backed by low dimes. Disappointment Island, some hundreds of metres high with cliffs on all sides is about 3 km. in length.

Rivers of considerable size for so small a land-area fill the valleys of the two larger islands. The watershed of Lord Auckland Island is close to the summit of the western cliffs. There are one or two small mountain lakes.

There is abundant evidence of glacial action, but according to Speight it is improbable that the islands have been completely covered by ice.

The Campbell Islands consist of a main island (Campbell Island) 48 km. in circumference, but the other members of the group are mere rocks. The northern end of the island rises as a whole to about 300 m., but in the south there are a number of isolated peaks, the highest being from 400 to 500 m. altitude. Two long inlets pierce the land on the east.

The rocks are in part volcanic and in part limestone containing fossils. According to Maeshall the surface-features are due to glacial action, but there is no evidence that the island was covered by an ice-sheet.

Macquarie Island, according to Scott (1883:486), is exceedingly hilly, the hills rising to perhaps 280 m., while numerous tarns lie amongst their hollows. The coast-line consists principally of cliffs with a few shingle beaches. Possibly the island is 30 km. long. The rocks, so far as known, are volcanic. Apparently the island is separated from the rest of the Subantarctic Group by the ocean's depth of no less than 3600 m.

The Antipodes Islands consist of Antipodes Island (8 km. long by 4.6 km. at its widest) and Bollons Island, quite small, but 150 m. high. The surface of the main island is an undulating plateau, Mt. Galloway, the highest point reaching 530 m. The coast consists of high, perpendicular cliffs. The rocks, so far as known, are basalts.

The Bounty Islands are a small group of rocky islets and rocks formed of a pale biotite granite. The largest island is 1 km. long by 0.8 km. wide and 88 m. high. The surface is without a true soil and is polished smooth as glass by thousands of penguins and other birds, which live for part of the year on the island and numerous fur seals. Quantities of guano collect during the breeding season of the birds, but the greater part is removed by the rains of winter.

4. The Soils of the New Zealand Botanical Region.

In what follows merely general and guarded statements are made, based for the most part on the experience of agriculture and horticulture and on rapid field observations. Also the distribution of the plant communities supplies some information — not always reliable — as to the relative fertility of the soil on which they grow.

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The soils which occupy the widest areas are pumice, clays of various kinds, loess (in a wide sense), loams, sand and stony debris. Peat, including-raw humus, mica-schist soils, calcareous soils, soils derived from basic volcanic rocks and rocks of various kinds are common enough but of more local distribution. Certain soils are purely local, e. g., scoria, sulphur &c, soils near hotsprings &c, salt soils, magnesian soils and soil heavily manured by sea-birds.

Loess soils occur over wide areas in South Island. They have arisen from silt blown from the glacial river-beds; such accumulation and transport still goes on. Loess is frequently mixed with clay derived from the underlying rock or of glacial origin. Loess is an important ingredient of soils to the east of the Divide in South Island.

Pumice soils play a large part in the centre of North Island and the land adjacent. When pure, unweathered and perhaps mixed with scoria, they provide, even in a wet climate merely steppe or desert conditions. When weathered and mixed with humus, pumice soil is "fertile" enough as the farms of the Waikato, and, in part, those of Hawkes Bay bear witness.

Clay soils of various kinds are common in North, South and Stewart. Islands. The extremely abundant greywacke readily weathers into clay. The low hills and undulating ground of lowland Auckland, known as the "gumlands", are covered with a great depth of specially impervious clay deficient in humus which though variable in quality is generally extremely poor. This is especially so with the white clays locally termed "pipeclay". The Stewart Island clays are formed from granite. Glacier clay occurs on mountain slopes and river-valleys. The "fertility" of these clay soils is governed by the drainage-conditions and the percentage of humus. Frequently clay becomes hard and dry during a period of drought and it then offers a most unfavourable station for plant-life.

Mica-schist soils occupy a wide area in the North and South Otago Botanical Districts. They are particularly fertile and contain, when apparently dry, a considerable amount of available moisture.

Calcareous soils are a feature of the Wanganui "coastal" plain. They also occur locally throughout the Region and frequently extend over considerable areas, but the fact that a soil overlies limestone by no means proves that it is truly calcareous.

Sandy soils are frequent on and near the coast, and arise either as blown sand from the shore or from the disintegration of soft sandstone. They are also frequent on the gravel plains.

Alluvial loams form the bulk of the soil of lowland valleys in both Islands.

Humus soils are of widespread distribution. They occur at all altitudes and vary from a thin surface-layer to peat-deposits, 12 m. deep, as in the page 52Chatham and Lord Auckland Islands. The rain-forest climate is eminently favourable for the production of humus. The subantarctic and wet high mountain climates favour the formation of raw humus and peat.

Volcanic soils, pumice excepted, though of wide occurrence in many parts of the New Zealand region, are generally local and limited in extent. They are specially fertile and the distinction between the vegetation of volcanic and "gumland" soils in Auckland is striking. The other soils mentioned above need no special comment here, but some come into consideration — as do soils of all kinds — when dealing with the plant-communities.

The terms "fertile" and "fertility" have been used in this chapter, and are to be found here and there in other parts of this book. All the same, it is not a really valid ecological expression, for the idea of fertility is derived entirely from the soil in relation to crops, and to the plant in wild nature no soil is fertile or unfertile. In fact, the whole idea of epharmony is opposed to such a term.