DISTRIBUTION OF THE GIANT SEQUOIA AND ITS RELATIVES
The origins of most living organisms are lost in antiquity, lost in strata of ancient rocks buried in deep and inaccessible places; obscure and small beginnings therefore have escaped discovery. The paleontological record of the sequoia line stretches back perhaps 150 million years to the Jurassic period. Conifers which were probably ancestral to these ancient sequoias are found as early as the Devonian, some 300 million years ago.
The two closest living generic relatives of Sequoiadendron are Sequoia (coast redwood) and Metasequoia (dawn redwood) (Stebbins 1948). These trees have a history in the rocks much like that of the giant sequoia. All three probably had a common ancestor. Fossil evidence shows that the genus Sequoia occurred in most regions of the Northern Hemisphere and, interestingly, also at the extreme south of the Southern Hemisphere. There are fossil records from Chile, southern Australia and Antarctica. According to Martin (1957), continental drift explains this unique distribution. Now increasingly accepted by geologists, this hypothesis would explain the present wide separation between known Sequoia fossils. The alternate hypothesis is that ancestral sequoias migrated southward to reach the continents' southern tips (Berry 1924). As the rocks in between have no fossil evidence supporting this idea, continental drift is a most plausible possibility. It too, however, raises some difficult questions, because the continents apparently started to drift apart in the early Mesozoic, long before the first sequoia-like fossils appear (Dietz and Holden 1970). Recent evidence (Emberger 1968) indicating that the South American fossils are Taxodium and not Sequoia would eliminate the controversy.
Metasequoia fossils found in rock formations throughout the Northern Hemisphere begin with the Cretaceous, about 125 million years ago (Emberger 1968). During the Eocene, some 40-60 million years ago, these trees, along with Sequoia, grew in the region that is now Yellowstone National Park. At Amethyst Cliff there are remains of 18 successive forests, each killed and buried in turn by volcanic materials (Dunbar 1960). These are spectacular remains, for many stumps still stand erect, and one diameter measures some 14 ft. By Pliocene time, Metasequoia was restricted to the Asian subcontinent and now lives only as a relict species in central China. For many years the fossil remains of this genus were mistakenly identified as either Taxodium or Sequoia, until discovery of the living Metasequoia resolved the confusion (Chaney 1951).
The earliest close relatives of the giant sequoia were probably Sequoia reichenbachii and Sequoia couttsiae, which appear as fossils through much of the Northern Hemisphere in Cretaceous and Tertiary age rocks. They are present in Greenland, Alaska, Canada, and England (Chaney 1951). Although no doubt they are related to the giant sequoia, their morphology differs sufficiently to show that they are not its immediate ancestors (Axelrod 1959). The oldest fossil sequoia considered directly ancestral to the living giant sequoia, in Idaho, is from the Miocene. This species not only closely resembles our giant sequoia but was associated, according to the fossil records, with plants not easily distinguishable from those of present sequoia communities (Axelrod 1962, 1964).
The most recently discovered North American fossil in presumed direct lineage with the giant sequoia is at Trapper Creek in southern Idaho. These remains show that it grew some 400 miles northeast of the present groves on the Sierra Nevada's western slope in California (Axelrod 1964). The species is called Sequoiadendron chaneyi. Other finds of this fossil in western Nevada bring the giant sequoia's ancient range closer to its present one. Some four known localities are within a radius of about 100 miles not far southeast of Reno.
Only a few million years ago the giant sequoia was on the east side of the Sierra and probably was growing at an altitude of about 3000 ft (Axelrod 1959). How did it cross the Sierra, and which natural forces enabled it to do so? What possible geologic and climatic forces split the groves into their widely spaced northern elements, yet left the southern belt more or less continuous? These are the major questions raised by the giant sequoia's relatively recent history.
This fossil form of sequoia, ascribed to the same genus as our present giant sequoia, is therefore regarded as its closest ancestral form. It occurred in western North America and reportedly also in Europe, where it existed as late as the Pleistocene Martin (1957). We will discuss primarily its migration from the more central continental United States to its present range in California.
Plant forms of ancient fossil communities compared with those in their modern counterparts indicate that they occupied similar environments. We can interpret the association of certain fossil plants with Sequoiadendron chaneyi remains as representing a low-elevation, relatively moist community. The Idaho community in part, consisted of maple, dogwood, oaks, and Douglas fir much like Present closely related species. Axelrod (1964) has suggested that the annual precipitation was 45-50 inches and was well distributed throughout the year. Temperatures were probably moderate in the summer and cool during the winter. Overall, the climate was temperate in contrast with today's.
The two important climatic changes concurrent with the Sierra's rise were the reduced summer precipitation and the increased range of annual temperature. These apparently preceded the rise of the Sierra sufficiently to force further evolution of the ancestral giant sequoia while it migrated in a southwesterly direction. Increasingly severe winter temperatures would favor the southward migration, while diminishing summer rains would also favor the westward migration toward the Sierra Nevada. If this general movement to the southwest occurred during the Pliocene, it would have allowed the giant sequoia ample time to reach the Sierra's eastern margin long before that mountain range began rising to its present heights of more than 14,000 ft.
The giant sequoia's passage across the Sierra Nevada was probably not over an isolated single route, but possibly via several low passes serving as access routes to the west. The present groves' proclivity to extend both up and down stream courses strengthens this belief. If true, the foregoing might help explain the disjunct or disrupted distribution of the present sequoia groves. It is still uncertain, although frequently assumed, that formerly a continuous belt of this species existed in the Sierra Nevada. Comparing the known localities of the fossil giant sequoia in Nevada, and considering the position of the groves on the Sierra Nevada's west slope, we can visualize the possibility that they may always have existed in a disjunct pattern (Fig. 27).
Almost since the giant sequoia's discovery, many different explanations were offered for its greatly restricted and interrupted range. The disadvantage of early observations was that only about a dozen groves had been discovered at the time. The larger and better-known groves were often the ones in the seemingly better sites, while some of the groves discovered at later dates were smaller and often removed from the normal courses of human travel. Undoubtedly, the marginal environmental requirements of these groves should supply the reason for the disjunct range of the species. The last of the groves was discovered in 1933.
There are now 75 named community units known as "groves" in which the giant sequoia is but one member. These groves, listed in Appendix VI, are taken from Rundel (1969). The land comprising these groves is an area of some 35,607 acres (State of California 1952). In none of them does this species grow in a pure stand, although in certain limited localities it is overwhelmingly predominent. Such areas as the Senate and House Groups in the Giant Forest and the Sugar Bowl in the Redwood Mountain Grove of Kings Canyon National Park are always popular with the park visitor because they are nearly pure stands (Fig. 28).
The term "grove" is still inadequately defined for geographic delineation. Guidelines should be adopted and the necessary changes in geographic place names should be made to eliminate confusion over multiple groves with a single name, and multiple names for what is really a single grove. For instance, we logically use one name, the Redwood Meadow Groves, to designate four separate units of sequoia trees in the Redwood Meadow area of Sequoia National Park. They are all in the same drainage and in close proximity. In Sequoia National Forest, three grove names are assigned to one unit of contiguous sequoia trees. This is also true in Kings Canyon National Park, where lobes of the large Redwood Mountain Grove are named Buena Vista Grove and Big Baldy Grove, although they are nowhere detached from it and are all in the Redwood Creek drainage system. We recommend that the Redwood Mountain Grove designation include the smaller segments. Where two groves spill over a drainage divide as a narrow belt that widens out with decreasing altitude, they often bear separate names despite their continuity. The Garfield and Dillonwood groves are good examples of this dichotomy, but apparently cause less confusion because two separate drainages are involved. In the Sierra Nevada, the individual groves are scattered over a 260-mile narrow belt nowhere more than about 15 miles wide, and generally less. The range is from 35&000;deg51' N to 39°03' N and is restricted to the western slope at elevations averaging about 5000-7500 ft, depending upon the latitude, direction of exposure, position on the slope, and proximity to subsurface moisture (Blick 1963). The map of grove distribution (Fig. 26) suggests clearly what many people postulated earlier, that the severe winter climate at the higher elevations and at its northern limits on the one hand, and the aridity at the lower elevations and at its southern limits on the other, acted to limit the distribution of this species (Wilson 1928). Its narrow, discontinuous form alone suggests, moreover, that the species possesses a narrow tolerance range during the period of regeneration. Before this aspect was clarified in relatively recent times, Blick (1963) felt that there must be climatic unity throughout its range, at least within the groves' restricted areas and the few isolated individual situations where sequoias are found. His assumption is undoubtedly rather close to the truth, although climatic data from the various groves are few indeed. Muir (1878), Wulff et al. (1911), and Shinn (1889), among others, have also based seemingly accurate analyses of the disjunct range on climatically regulated factors, but in very broad generalities without considering the stage of sequoian life cycle in which the limiting factors are strongest. Sequoias have been so well planted and cared for outside their natural range that, once beyond youth, their future is pretty well assured. Irrigation of many of these specimens, however, introduces an artificial factor that negates their comparison with trees occurring as natural populations. The reproductive stage of most organisms is usually the most vulnerable, and so it is with the giant sequoia. We will discuss this later in some detail under the Life History of the Giant Sequoia.
The cause or causes for the very wide gaps between the northern populations will probably never be completely explained. Despite their discontinuity the groves as a whole are distributed in the form of an elongate, narrow belt which suggests strongly that at some time in the past, possibly during both pre- and Post-glacial times, the groves may have been more continuous than they are now. But field evidence of their former occurrence in the present gaps is lacking. John Muir was the first to note that there were no sequoia-wood remnants to be found anywhere between the groves, an observation which is valid today. Groves probably became isolated long ago, because phenotypic (appearance) attributes peculiar to individual groves suggest that mutations have occurred following isolation. A good example is the bark's spiral growth pattern common to many specimens of the Mountain Home Grove (Fig. 13).
Three main hypotheses have been offered to explain the great isolation of the northern groves: (1) that seeds by fortuitous dispersal reached distant favorable terrain and there established new populations; (2) that slow climatic changes narrowed and ultimately disjoined a once more continuous range; or (3) that there were several migrational routes across the Sierra Nevada. The latter seems more logical for a species whose seed dispersal pattern, under normal circumstances, is usually not much more than twice the height of the tree. But even the rationale of these hypotheses poses difficult questions when we consider that the northernmost Placer County Grove is farther than 60 air miles from its nearest neighbors, the Calaveras Groves, and that it had only six living sequoias when discovered. There are also two downed sequoia logs in this grove, but they offer little clue to its survival pattern throughout Pleistocene and Recent times. The total lack of natural sequoia reproduction there suggested that the range was indeed being pinched out at the northern end, and most observers offered the frigid winter climate as the prevailing reason. Yet, temperature measurements there by a maximum-minimum thermometer indicate that winter lows are about the same as in the southernmost Deer Creek Grove. Perhaps environmental conditions, inadequate for a long period, provided limited reproduction and seedling survival. This grove is well advanced in plant succession, a result of prolonged absence of fire or other disturbances. Whereas the almost total lack of downed sequoia trees apparently contradicts this assertion, the relative lack of fire may best explain the existence of this small remnant population.
Wulff et al. (1911) suggest that the cooler climate of the Pleistocene Epoch may even have reduced grove populations to a single tree, which could have served as a nucleus for the present groves. The observations of several early workers may yet lead toward a plausible hypothesis, especially if the results of studies by Rundel (1969) support them.
Of paramount importance is the availability of sufficient soil moisture during the sequoia's growing season, a function of both precipitation patterns and soil texture, which Barry accurately identified in 1855 as mostly sandy loam. Donaghey (1969) recently indicated a new factor in soil-moisture relationships; the heat from wildfires destroys soil organic compounds and causes wetabiliity of the soil.
John Muir was perhaps the first writer to single out the role of soil moisture. He found that medium soil moisture is optimal for sequoia growth.
Even though he failed to indicate the necessity of sunlight for seedling development, his assumptions are essentially correct, and many writers have repeated them in modified ways. Invariably, these modifications involve the effect of climatic differences, soil type, depth of organic layer, leaf litter, shading, etc.
Recent investigations, curiously, do not bear out the belief that rich, deep soils are a necessity for sequoia growth. Observers have tended to compare forest soils to agricultural soils. While crop plants need nutritionally rich as well as moist soils, trees depend mainly upon available soil moisture. The grayish podzolic soils of the Sierra are less than impressive to the serious farmer. Furthermore, many people tend to grossly underestimate the complexity of soils. By and large, Sierran podzolic soils are relatively thin and not abundantly nutritious. With clay a minimal soil constituent, the total moisture-holding capacity of these soils is limited by the amount and distribution of precipitation, subsequent density of vegetation, temperature and relative humidity during the growing season, and the wetability factor of the soil. Sequoias show a strong tendency to favor drainageways where the requisite degree of moisture content is constant. Yet the drier slopes also support sequoia growth wherever the trees can become established (Wulff et al. 1911). Contrary to popular belief, then, soil depth and richness are clearly secondary to soil moisture availability. Sequoia distribution within groves strongly reflects its affinity for soil moisture; a crown that may weigh a ton or more seems to demand it.
Muir (1911, 191 2) was a proponent of the thought that sequoias created their own moist environment.
Perhaps Muir failed to understand the magnitude of transpiration, i.e., the vegetation "pumping" soil moisture back into the atmosphere. It is true that forest vegetation regulates the yearly flow of water, thus modifying the distribution of runoff and moderating the extremes. Forest trees play an important role in cycling water from the ground back into the atmosphere. Removal of the transpirational pumps, namely, the trees, has often converted a dry forest into a swamp.
The patterns of growth- and site-selectivity all bespeak the species' affinity for high soil moisture and reflect the effect of temperature and relative humidity perhaps more than does precipitation alone. The ratio of evaporation potential to precipitation as an environmental factor is important, and its recognition has produced the widespread belief that the sequoia grows best in protected locations where the average annual precipitation is from 45 to 60 inches (Schubert 1952).
Rundel (1969) amplified this interpretation somewhat. He found that sequoia stands on northerly slopes have greater density than on slopes of other aspects, although the total number is generally less. It is perhaps perplexing that these trees, admittedly with an affinity for abundant soil moisture, are much more numerous on westerly and southwesterly slopes, which are potentially the drier ones because of the sun's more nearly direct rays. Thus, for example, relatively moist drainage bottoms and meadow margins, although small in their total acreage, support dense stands of sequoias. Even rocky slopes support some 3% of the total sequoia population in the Giant Forest. Contrary to the records of John Muir, large specimens are fairly common on slopes exceeding 30° and we find some on slopes approaching 45°. We conclude that, regardless of a grove's geographical position, this species favors avenues of surface or subsurface drainage. Although surface drainage patterns are obvious, subsurface drainage may be too obscure for visual identification. The Grizzly Giant in Yosemite's Mariposa Grove, a good example, grows on a low ridge which appears well drained, but an apparently abundant subsurface flow of soil water is undoubtedly a major reason for the tree's great size.
Evaporation potential is partly a function of temperature. Since temperature decreases with increasing latitude, average temperatures in the north are the same as at higher elevations in the south. Thus, the mean altitude of sequoia groves in the Kaweah Basin to the south is 6600 ft, whereas it is 5400 ft in the northernmost grove. In the northern groves sequoias are found mostly on south-facing slopes; in the southernmost, on north-facing ones. Altitude and direction of slope, then, indirectly reduce water loss from the trees while maintaining an optimum temperature regime for growth.
The stream drainage channels are also channels of cold air drainage, especially if they descend from high mountain peaks, so that the value of available moisture must be pitted against the limitations of winter survival when temperatures may drop to sub-survival values. The same drainage channels, however, transport cones and seeds that are carried downslope where grove extensions form long, narrow fingers and occasional detached outliers.
In the Mariposa Grove, flooding, not too many years ago, carried seeds along a tributary of Rattlesnake Creek, and today there are numerous thriving young sequoias mostly at high flood level on either side of the creek. No parent trees grow above them, although some are so close to the drainage divide that chickarees might have carried the cones into the other drainage basin to eat them.
Perhaps the best-known and most classical grove extension is along the South Fork of the Kaweah River below the Garfield Grove. A dozen sequoias line the river bank at elevations as low as 2800 ftone specimen growing on a gravel bar in the river channel, a most unlikely site (Fig. 29). The altitude is the lowest known in the world for a naturally seeded giant sequoia. An increment boring indicates that this tree was seeded in the middle 1880s, when a torrential flood also floated huge sequoia logs through the town of Visalia some 40 miles to the west in the San Joaquin Valley.
Muir (1911, 1912) first explained the sequoia groves' disjunct distribution as the result of glacial ice flowing through the canyons and completely destroying the trees and their habitats there. Muir had overestimated the Pleistocene glaciers' extent in the Sierra, so that today his hypothesis is largely discounted. He had based it on the finding that, in the more southerly part of the range, the groves are in pairs separated by drainageways. Yet none of these pairs is separated by a drainage which contained glacial ice during the Pleistocene Epoch. If the ice age were an influence, it is more likely that cold air drainage down some of the longer canyons was a strong influence in separating the trees into groves. Although three of the groves are growing on glacial outwash, none is recorded on glacial till.
We know little of how winter cold affects sequoia distribution. While the tree is not nearly as frost-hardy as other tree species associated with it, this seems to pose little problem for it within its native range. Winter temperatures in the groves seldom reach 0°F and when such lows do occur, deep snow usually covers and protects the tender young seedlings. Temperatures in the intervening drainageways often fall to zero and below, especially when the stream's headwaters are on the slopes of high mountain peaks. The confusing part of the temperature relationship is that specimens planted in the eastern part of the United States are severely frost-bitten or killed by temperatures no lower than -15°F Yet, in Europe, specimens not only have survived this temperature, but are surviving in Poland, Austria, and Hungary where it has dipped to as low as -32°F Possibly the differences between the two continents lie in the soil's condition at time of death. In the Sierra, generally at least 3-6 ft of snow, and occasionally much more, protect the soil. Schubert (1957) records snow 29 ft deep in the Giant Forest during the winter of 1905-06, with isolated drifts still 12 ft deep in the early part of summer.
Soil type is probably less a controlling factor in the present distribution of sequoia groves than many earlier writers realized. Sequoia groves are mostly on granite-based residual and alluvial soils. Three groves are on glacial outwash, one is on metamorphosed basalt, and parts of others are on soils derived from schistose rock. Soil texture, however, does not vary much. Soils, generally very sandy, are low in their clay fraction, which nevertheless plays the most significant role in nutriment retention. Furthermore, we should point out that sequoias cultivated in various parts of the world are growing vigorously in clays, gravels, peaty soils, and even alkaline desert soils in Spain, all drastically different from soil types in their native Sierra Nevada. Soil type alone apparently has insignificant influence on the distribution of these trees.
Although soil moisture availability has long been thought to play a significant role in the natural distribution of giant sequoias, it remained for Rundel (1969, 1971) to refine and amplify this broad hypothesis into a more meaningful explanation. In study transects which crossed grove boundaries, he obtained substantial proof that soil moisture was more available within the perimeter of the grove than outside, and that often the difference was marked. He used an experimental device known as a pressure bomb to measure moisture stress in the xylem tissues of sequoias and other trees and found convincing evidence that the stress was much greater outside the groves than in trees within the groves. The sensitivity of the sequoia seedling to moisture availability will be further discussed in the section of the species' life history.
Having identified moisture stress as the major limiting factor in sequoia distribution, Rundel delved into the post-Pleistocene climatic changes that may have influenced the present fragmented distribution of groves. There is good evidence that approximately 8000 years ago the climate of the earth began to warm, making the Sierra Nevada drier than it had ever been. Rundel called this the "Altithermal Period." He postulates that with increasing soil moisture stress, reproductive success declined, the old trees died and fell, and new ones either were not forthcoming or else grew in insufficient numbers to maintain the former extent of the stands. With this trend, their range of distribution shrank and the drier ridges and slopes became untenable for sequoia existence. Thus the process of fragmentation into the mesic sites which are the present groves was intensified, especially in the southern part of the range.
The implications of his altithermal hypothesis led Rundel to still another study, which strengthens his contentions. He notes a great diversity in sequoia age-class distribution among groves, some groves comprising all age classes and a few being almost devoid of the younger trees. These various age-class distributions reflect a continuum of progressive development for sequoia which Rundel divides into four sequential stages and designates as follows:
1. The adolescent stage, or one in which trees of younger age classes are abundant.
2. The mature, steady-state stage, or one in which a wide range of age groups is well represented and in which the population size and age distribution are likely to remain static.
3. The senescent state, or one in which the population size is expected to dwindle for lack of replacement stock.
4. The decadent stage, or one in which only older individuals remain.
Without the benefit of Rundel's groupings and terminology, Aley (1963) predicted that, barring environmental changes over time, some groves will disappear.
As warming trends create increasingly xeric conditions, the isolated "islands" of sequoias that were trapped in the slightly less mesic sites were seriously threatened. Moisture stress, which seems to become critical within a rather narrow tolerance range, will probably tip the scales against both germination and seedling success if warming trends recur.
Certainly the term "senescent" does not apply to existing trees which are producing cones and viable seeds at the normal rates.
The above might well lead to the assumption, which Rundel verifies, that the adolescent stages are rare at present. Mature, steady-state groves, however, do occurfor example, in the large Giant Forest and the Redwood Mountain Grove. On the other hand, the groves in general may be regarded as senescent. They are apparently unable to maintain their present proportionate number of larger specimens. Muir Grove (Sequoia National Park) and South Calaveras Grove are good examples of the senescent stage.
Groves in the decadent stage are few, small, and rather isolated. Rundel cites the Powderhorn Grove as the prime example in which reproduction is virtually nonexistent and where only 10% of the population falls within the 1 to 5-foot-diameter class. In these circumstances, without factors favorable for regeneration, the giant sequoias constituting this grove will probably disappear, however slowly.
Rundel's altithermal hypothesis seems to support the long-held and widespread belief that the giant sequoia not only has stagnated, but is headed for extinction. However, not all grove boundaries are static or shrinking; some are measurably expanding, though slowly. This is evident in the Lost Grove, in parts of the Muir Grove, the Giant Forest, and in South Calaveras Grove. In the Lost Grove, the uppermost trees on the slopes are considerably smaller and younger than the next adjacent trees below them. Increment borings in several of the trees yield growth patterns clearly showing that the smaller, younger trees began their growth at a time corresponding to a growth-release pattern shown in the larger and older adjacent trees downslope. This correspondence very likely represents the occurrence of a fire, probably in 1872 or 1873, according to release patterns from the older trees. The younger trees are more than 100 ft up-slope from the larger specimens which perhaps supplied the seeds. Because the Lost Grove is a small one, its percent of expansion is fairly large. Although this expansion has not been well studied, we find similar evidence in the other groves mentioned above. The percentage of additions to these much larger groves would, of course, be less.
The future of sequoia's total range will depend, then, upon climate and modifications by fire and other disturbances. If warming and drying should resume, however, most certainly grove perimeters will shrink and the total population of giant sequoias will be reduced.
With the giant sequoia's discovery, it was to be expected that people would want to grow specimens in their yards, gardens, and public parks for ornamentation and as scientific curiosities. This horticulture began just a year after Dowd discovered the Calaveras Grove when a John D. Matthew sent a packet of seeds to his father at Gourdie Hill, near Perth, in Scotland. The seeds arrived there on 28 August 1853, the first to be shipped from the New World, and they were quickly planted. Other seeds and seedlings arrived in Europe the same year. Many of the seeds had been collected from the "Mother of the Forest" in the Calaveras Grove following that tree's unfortunate divestment of bark.
The British, with their characteristic fervor for gardening, raised many of the seedlings in their nurseries. At the outset, one-year seedlings sold in England brought the handsome price of £10 each (about $50 at the 1850 exchange rate), so that for a time their use was rather restricted to the wealthy for planting on the larger estates. Saunders (1926) stated that no other species of tree ever introduced into England had caused such excitement or had been so costly. Today, Alan Mitchell of the Royal Forestry Commission makes the statement (pers. comm.) that there is scarcely a hilltop or mountain peak in Great Britain from which a sequoia cannot be seen. They grow rapidly in that country, especially in the more humid regions of Scotland. A handsome specimen of some 8.5 ft dbh and 150 ft tall, the largest tree in all Great Britain, grows at Leod Castle north of Inverness.
It is estimated that in Europe there are perhaps as many as 10,000 sequoia trees. They are abundant in France, Germany, Switzerland, and the Low Countries, and easily identified as the tallest trees projecting themselves above the general tree-crown canopy. The most northerly are in coastal Norway, where the Gulf Stream lowers winter temperatures and cold climate is not a limiting factor. On the north shore of the spectacular Sogne Fjörd, in the yard of an ancient church in the town of Leikanger, at 61° 11' N latitude is the northernmost specimen. Planted in the 1880s, it is now nearly 4.5 ft in diameter.
Progressing south and east across Europe, sequoias are increasingly fewer. Yet they grow well in Czechoslovakia, Hungary, Romania, Bulgaria, and along the Black Sea Coast of the USSR. They appear to be limited by continental cold air masses in Poland, northern USSR, Finland, and Sweden. Of the several that were introduced into Poland, only one has survived the frigid winter weather, a specimen growing near the city of Szezecin in the western part of the country.
In southern Europe, the seasonally arid Mediterranean climate inhibits growth unless summer watering is provided. Although there are several specimens in Yugoslavia, Italy, and Spain, the trees have not survived climatic conditions in Greece and Albania. In southern France, specimens are found more commonly at higher elevations where more mesic conditions prevail. By far the largest specimens in all of Europe are those in the palace grounds at La Granja, Spain, northwest of Madrid. In a warm climate and with regular lawn watering, the larger specimen is 13 ft dbh and 130 ft tall, while the smaller of the two is more than 10 ft dbh and 133 ft tall (Fig. 30). These two specimens were planted in the late 1800s. Because they grow in the open, they have retained their branches down to the ground and display a form that is rarely seen in its native habitat.
Specimens are also known to be growing in Turkey, Egypt, Lebanon, Israel, Cyprus, Japan, South America, Australia, New Zealand, and in British Columbia, Canada. In the Southern Hemisphere, they seem to be indifferent to the reversal of the seasons and grow vigorously, particularly in New Zealand.
The sequoia's successful existence in such diverse and widely scattered environments abroad has provoked many to ask why its natural range is so restricted. This logical question fails to take into account its nurture by man and the fact that nowhere outside of its native Sierra Nevada has the giant sequoia ever been known to re-seed itself by natural means. Yet even in the Sierra, wherever the necessary conditions for natural re-seeding are fulfilled, the early seedling stage is always the most vulnerable to environmental vicissitudes.
However unique the ecological relationships within the perimeters of extant sequoia groves, probably the only plant exclusively found in these groves is the giant sequoia itself, and even the combinations of plants and animals associated with it vary from grove to grove, resulting in different biotic interrelations. We will treat this complex subject in more detail later.
But first, what is ecology? What major ecological principles apply to the life of this fascinating tree?
Last Updated: 06-Mar-2007