From Glacial Scars to Endemic Blooms, The Forging of Island Ecologies

“ There are large quantities of mud on and through the ice, so that all the streams discharging from it are very dirty. At some former time this glacier filled the entire valley extending to its mouth five miles away, and depositing against the rocky walls banks of boulder drift to a height of four hundred feet above the present level of the sea. There is no doubt that in the glacial period the size and extent of the glaciers of Baffin island were much greater than at present ”

“ On the northern, southern, and especially the eastern face, the rock was steep; on the western aspect, there was a more gentle slope down to the floe, the rock being almost concealed by big snow-drifts. There were signs of previous glaciation in the form of erratics and many examples of polishing and grooving. The rock was very rotten, and in many places, especially about the penguin rookeries, there were collections of soil. Two deep gorges cut through the island from north-west to south-east, in both of which there were small ponds of fresh water. ”

“ The sides of Blossom island are rough and precipitous. The glaciers flowing past it cut away the rocks and, as the surface of the ice-fields was lowered, left them in many places in rugged cliffs bare of vegetation. The top of the island was also formerly glaciated and in part covered with débris; but the ice retreated so long ago that the once desolate surface has become clothed in verdure. Everywhere there are dense growths of flowers, ferns and berry bushes. On the rocky spurs, thrifty spruce trees, festooned with drooping streamers, shelter luxuriant banks of mosses, lichens and ferns. ”

“ The Thousand Islands is no misnomer, for they seem to be beyond number, scattered like a myriad of emeralds, with deep water between, and yet so close together that they may almost reach hands across the breach. Every islet is a dome of rock, ground into symmetrical shape by glacial action long ago, then covered by a sediment from the river sufficient to support a profuse vegetation. The Canada pine is conspicuous, lifting its scraggy head to a great height, and pointing its stout branches in every direction, a stately figure among the brushwood that surrounds it. ”

“ Furthermore, because it is distributed along the lower portion of the range, which was the first to be left bare on the breaking up of the ice-sheet at the close of the glacial winter, the soil it is growing upon has been longer exposed to post-glacial weathering, and consequently is in a more crumbling, decayed condition than the fresher soils farther up the range, and therefore offers a less secure anchorage for the roots. ”

“ The inferences derived from these and similar observations made on the phenomena of peat bogs and their buried forests in many other parts of Scotland, are somewhat conflicting. There can be no doubt that the climatal conditions that permitted oaks to grow on the higher slopes of the hills in the north of Scotland, as well as trees of considerable size in the Orkney and Shetland Islands, where scarcely a stunted shrub is now to be seen growing in a wild state, were more favourable to the growth of forest trees than those which now prevail. ”

“ On the whole, the evidence of general glaciation of our islands as interpreted by geologists almost postulates the extinction within our area of the whole existing flora and fauna, and consequently its reconstruction by immigration when a temperate climate returned. But there is a body of evidence to be drawn from the present and past distribution of the existing plants and animals which is of great importance in this connection. ”

“ It has been stated by an eminent geologist that during part of the Glacial period the climate was such that neither plants nor animals could have existed in the British Islands. If that had been so, it is evident that very few organisms could have even survived in France, though a number of Arctic species might have dragged on an existence in Southern Europe. At any rate, on the return of more genial conditions, the Arctic species would undoubtedly have been the first to gain admission to the British Islands, to re-people the arid wastes. ”

“ While therefore we may believe that the larger part of the existing flora reached the islands since the glacial epoch, a portion of it may be more ancient, as there is no doubt that a majority of the species could withstand some lowering of temperature; while in such a warm latitude and surrounded with sea, there would always be many sunny and sheltered spots in which even tender plants might flourish. ”

“ Many parts of the land must, indeed, have been stocked with plants from various sources, and by agencies—as that of the sea—which might at first sight seem adverse to their distribution. The British Islands, for example, have no indigenous plants. Their flora consists mainly of Germanic plants, which must have migrated to Britain in that very late period of the Post-glacial when the space now occupied by the North Sea was mostly dry land. ”

“ Plants of subarctic character then would flourish to the water's edge, but when a new state of things commenced, when the bed of the glacial sea was upheaved, its islands converted into mountains, its climate changed, and a suitable population of animals and vegetables diffused over its area, the plants of the colder epoch survived only on the mountain regions which had been so elevated as to retain climatal conditions similar to those which existed when those regions were low ridges or islands in the glacial sea. ”

“ But we know that in all parts of the world islands are the refuge of species or groups which have become extinct elsewhere; and it is therefore in the highest degree probable that some species which have ceased to exist on the continent should be preserved in some part or other of our islands, especially as these present favourable climatic conditions such as do not exist elsewhere. ”

“ A subsidence of land separating a large island from a continent would affect the animals and plants in a variety of ways. It would at once modify the climate, and so produce a series of changes from this cause alone; but more important would be its effect by isolating small groups of individuals of many species and thus altering their relations to the rest of the organic world. Many of these would at once be exterminated, while others, being relieved from competition, might flourish and become modified into new species. ”

“ Thus islands far away from land almost always have very peculiar animals found nowhere else; as is strikingly the case in Madagascar and New Zealand, and to a less degree in the West India islands. But shallow straits, like the English Channel or the Straits of Malacca, are not found to have the same effect, the animals being nearly or quite identical on their opposite shores. A change of climate or a change of vegetation may form an equally effective barrier to migration. ”

“ Darwin has shown us how we may determine in almost every case, whether an island has ever been connected with a continent or larger land, by the presence or absence of terrestrial Mammalia and reptiles. What he terms "oceanic islands" possess neither of these groups of animals, though they may have a luxuriant vegetation, and a fair number of birds, insects, and landshells; and we therefore conclude that they have originated in mid-ocean, and have never been connected with the nearest masses of land. St. Helena, Madeira, and New Zealand are examples of oceanic islands. ”

“ On a small and isolated island, however, with few species, and these not adapted to much diversified conditions, such changes instead of merely increasing the number of certain species already adapted to such conditions, and decreasing the number of other species, would be apt to affect the constitutions of some of the insular species: thus if the island became damper it might well happen that there were no species living in any part of it adapted to the consequences resulting from more moisture. ”

“ On the island it met with very changed but highly favourable conditions,—an abundant shrubby vegetation and a tolerably rich flora; less extremes of climate than on the mainland; and, most important of all, absolute freedom from the competition of rival species. The flowers and their insect inhabitants were all its own; there were no snakes or mammalia to plunder its nests; nothing to prevent the full enjoyment of existence. The consequence would be, rapid increase and a large permanent population, which still maintains itself ”

“ It is interesting to note that while the non-peculiar genera of flowering plants have little more than two species to a genus, the endemic genera average six and three-quarter species to a genus. These may be considered to represent the earliest immigrants which became firmly established in the comparatively unoccupied islands, and have gradually become modified into such complete harmony with their new conditions that they have developed into many diverging forms adapting them to different habitats. ”

“ Although in oceanic islands the species are few in number, the proportion of endemic kinds (i.e. those found nowhere else in the world) is often extremely large. If we compare, for instance, the number of endemic land-shells in Madeira, or of endemic birds in the Galapagos Archipelago, with the number found on any continent, and then compare the area of the island with that of the continent, we shall see that this is true. ”

“ I was struck, in these walks, by the amazing abundance of the wild flowers which covered the natural meadows and lower hill-slopes—an abundance, as I have since remarked, equally characteristic of both the northern and western islands of Scotland. The lower slopes of Gairloch, of western Sutherland, of Orkney, and of the northern Hebrides generally—though, for the purposes of the agriculturist, vegetation languishes, and wheat is never reared—are by many degrees richer in wild flowers than the fat loamy meadows of England. ”

“ But on windy Hebrides there is hardly a tree to shiver, where docken, broom, or thistle may be the best substitute for a switch, and every drifting log or plank of shipwreck washed up from the Atlantic is treasured to make the rafters of a human nest. A woman brought to the mainland had no conception for trees but giant cabbages; and when a basket of tomatoes came on shore an old Highlander was excited to see “apples” for once in his life. The wild carrot is the finest fruit that grows here naturally among the scent of the heather. ”

“ From the intermediate position that Macquarie Island occupies relative to Australasia and the Antarctic continent, it was highly important that its biology should be fully determined. Investigation of the marine and terrestrial fauna and flora shows several facts indicating the part this island has played in the supposed connexion of the great land masses of the southern hemispheres. It is an established fact that the flora of New Zealand has strong sub-antarctic and South American affinities and the problem is to account for this distribution. ”

“ From base to summit the hills are a velvet sward, willow shrubs the size of one's finger, grass waist high, and such a wealth of flowers—poppy fields, anemones, snowdrops, rhododendrons—that one might be in a southern climate instead of close proximity to frozen zones. Fogs wreathe the island three-quarters of the time; and though snow lies five feet deep in winter, and such blizzards riot in from the north as would tear trees up by the roots, and drive all human beings to their underground dwellings, it is never cold, never below zero, and the harbors are always open. ”

“ Other peculiar species are common to two or three islands only.
The soil is very rich. With irrigation three harvests a year are regularly gathered on Canary and Teneriffe. The water supply is largely kept up by the cloud belts, which even in the driest seasons form almost daily over the higher mountains, feeding the springs there which are the life of the land. But, as has already been said, the rocky, volcanic nature of the coast forbids the entrance of many plants, and this fact has had great influence on the character of the flora. ”

“ The warm moist Atlantic climate has had almost the effect of a hothouse on the flora of these sheltered valleys, whilst above, on the summits of the mountains the first snow and storms of the winter and early spring produce a rugged wildness that is only to be found in the British Islands on mountains over 3000 feet high. ”

“ He further says that the Composite flora is almost as strictly endemic as that of the Sandwich Islands, and that it is much diversified, with evidences of great antiquity, while it shows insular characteristics in the tendency to tall shrubby or arborescent forms in several of the endemic or prevailing genera. ”

“ Confining ourselves always to flowering plants, we find that the flora of New Zealand is a very poor one, considering the extent of surface, and the favourable conditions of {489}soil and climate. It consists of 1,085 species (our own islands possessing about 1,500) , but a very large proportion of these are peculiar, there being no less than 800 endemic species, and thirty-two endemic genera. ”

“ When we consider that the number of plants now found on the island is 746, and that out of these fifty-two alone are indigenous species, the rest having been imported, and most of them from England, we see the reason of the British character of the vegetation. Many of these English plants appear to flourish better than in their native country; some also from the opposite quarter of Australia succeed remarkably well. The many imported species must have destroyed some of the native kinds; and it is only on the highest and steepest ridges that the indigenous Flora is now predominant. ”

“ But when in such an island we regard the intermediate region between the uplands and the coast, usually the forest-zone, we find an area of change not only for the plants but also for the birds. It is here that the new genera of plants have been developed that distinguish the floras of the Pacific groups each from the others; and here also the migrant bird, having from some cause changed its ways, has given rise to new varieties and to new species. ”