CONSERVATION OF GENETIC DIVERSITY: THE ROAD TO LA TRINIDAD

by

F. Thomas Ledig

Introduction
In the time it takes to deliver the Leslie L. Schaffer Lecture, four species go extinct. And over the course of a day about 100 species are disappearing from the earth as a result of deforestation and other anthropogenic causes, never to be seen again (according to estimates by Myers 1984). Extinctions of this magnitude constitute a crisis worse than any in earth's geologic history because they will take place in a very brief span of time. They will also involve a wider range of taxa than any previous mass extinctions.

I want to share some thoughts on this impending crisis-this global threat to genetic diversity. By genetic diversity, I mean genetic diversity in the broad sense: the entire continuum that ranges between different forms of the same gene within a species, to the constellation of genetic differences that characterize different populations or races, and the whole libraries of genes that distinguish different species. The goal of conservation biology should be preservation of the entire triad: the species, populations, and genes.

My approach to the subject will be unusually personal for a scientist but, I hope, well-documented. The playing field is going to be the entire latitudinal gradient from British Columbia to Mexico and the tropics. First, I will review some facts about the distribution of diversity. The take-home lesson is that genetic diversity increases toward the tropics. With regard to species diversity, that is well known. But, it is also true with regard to diversity within species, at least within tree species. Second, I will give some examples of the loss of diversity. The point I want to make is that loss of species is only the tip of the iceberg. Loss of populations and genetic diversity within populations is even more extensive than loss of species. Third, I will outline the threats to diversity. These threats include overexploitation, habitat destruction, and environmental change. Overexploitation and habitat destruction, like diversity itself, increase toward the tropics. But environmental change, particularly global warming, is especially pertinent to British Columbia. Finally, I will remind the reader that diversity is important to society for economic, ecologic, esthetic, and ethical reasons. We all have a stake in maintaining diversity.

A Rescue Mission
To tie this all together, I'll tell a story about a recent trip to Mexico. The story gives the subtitle to this lecture, "The Road to La Trinidad". It's the story of a quest-the search for a rare Mexican spruce, called Chihuahua spruce (Picea chihuahuana Martinez). The species was discovered in 1942 in the western mountains, the Sierra Madre Occidental of Chihuahua and Durango (Martinez 1942). It occurred in populations of a few hundred trees each, isolated one from the other. Even adding up all the known populations, less than 20,000 trees exist (enumerated in part by Sanchez and Narvaez 1983). But it wasn't always that way. Pollen in Pleistocene lake sediments show that it grew all around the area now occupied by Mexico City (Clisby and Sears 1955). And further back, in the Miocene, it grew as far south as the Isthmus of Tehuantepec (Rzedowski 1978). Climatic change probably caused its decline; we may never know for sure. But the practical question is, will it survive another century? In addition to climatic change, it is now threatened by cutting, fire, and grazing.

To help ensure its survival, I was trying to organize seed collections-seeds for long-term storage and for test plantings that would help to preserve the species. All of August and September, my Mexican colleagues and I looked for Chihuahua spruce in the Sierra Madre Occidental and the Sierra Madre Oriental. We travelled to some of Mexico's most remote mountain country, flew into Indian cornfields, rode over terrain suitable for off-road vehicles, made repairs with barbed wire when the clutch cable broke, got isolated by torrential downpours and flooded rivers, and sampled the hospitality of the campesinos-much to my stomach's dismay. I've traveled in India, Africa, and many times in Mexico and never gotten sick before, but this time made up for that.

That brings me to La Trinidad. La Trinidad is in the eastern mountains, the Sierra Madre Oriental of Nuevo Leon. Chihuahua spruce was discovered in the Sierra Madre Oriental only five years ago (Muller Using and Alanis 1984), and the last stand on my itinerary was La Trinidad. As the head of the Forestry School in Nuevo Leon told me: "La Trinidad no es un viaje, es una aventura" - that is, La Trinidad is not a trip, it's an adventure. Four hours in a 4-wheel drive truck on a road hung on the edge of a thousand meter chasm showed me what he meant. Once or twice we encountered donkeys and their drivers, with barely enough room to squeeze by.

In addition to giving me an anxiety attack, the ride also gave me time to think about the significance of La Trinidad. Because the dominant religion of Mexico is Catholicism, La Trinidad is not an unusual name, but for me it was uniquely meaningful. La Trinidad refers to the Trinity, the Father, Son, and the Holy Spirit, which are, at one and the same moment, three entities and one entity in Christian belief. In my mind I drew an analogy between the Trinity and our conservation triad: Chihuahua spruce-the species, its populations or races, and its genes. Though a crude analogy, species give rise to races like the father begets the son. And to carry the analogy further, genes are the conceptual and self-replicating factors that give order to the physical manifestation of life; they could be considered the life force, the Spirit. Our objective then, and the objective of gene resource conservation in general, was to preserve this Trinity-the genes, and their manifestations, the populations and the species itself. All one and yet all different.

The trip to this point had been largely successful. The climbers got enough seed to ensure that the species will be preserved in seed banks, and they collected it from several populations in both Chihuahua and Durango. Adding La Trinidad to the collection would complete our work, ensuring survival of the entire gamut of genetic resources in Chihuahua spruce, from the western to the eastern mountain ranges and from the northernmost to the southernmost stands.

Did I ever reach La Trinidad? Did we capture the "spirit" of Chihuahua spruce? I'm going to hold that until the end of the paper. For now, I would like to review what we know about the distribution of genetic diversity.

The Distribution of genetic Diversity
Genetic diversity is not evenly distributed around the globe. Diversity tends to increase from the polar regions to the tropics. For example, British Columbia has 44 tree species, or perhaps less, depending on the definition of a tree (Hosie 1969). Their taxonomy is pretty well defined. True, the birches (Betula spp. L.) offer some problems, but most plant genera, trees and herbs, are represented by only a few species.

Going further south, California has twice as many trees, 86, also taxonomically well-defined (Griffin and Critchfield 1972). However, 5 to 10 new, non-tree species are described every year (Shevock and Taylor 1987).

In Mexico, conifers alone number 107 species (Martinez 1963), and hardwoods are in the hundreds. New species and new range extensions are discovered annually, and taxonomically the situation is a mess, even in woody genera. For example, does Mexico have four species of Douglas-fir (Pseudotsuga spp.) or just one?

But Mexico is largely a temperate country, and to really see a proliferation of species, head to the tropics. In some forests of South America, 300 different tree species per hectare are common (Gentry 1986); species diversity is at least an order of magnitude greater than in British Columbia.

I said I would switch back and forth along the continuum from species to genes within species. So let's look now at genetic diversity within species. Here too we find increasing diversity as we head south, at least in those species that were forced into southern refugia during glacial periods. Coulter pine (Pinus coulteri D. Don) is an exceptionally good example. Average heterozygosity, a statistic that population geneticists use to express the amount of genetic diversity, is twice as great in relict, southern populations as it is in more recently established, northern ones (Ledig 1987). Heterozygosity decreases in a step-wise fashion along the mountain ranges from Baja California to Mt. Diablo near San Francisco Bay. A similar situation is found in many other conifers (Fins and Libby 1982, Furnier and Adams 1986, Ryu and Eckert 1983, Steinhoff et al. 1983); e.g., giant sequoia (Sequioadendron giganteum (Lindl.) Buchholz) , Jeffrey pine (Pinus jeffreyi Grev. & Balf.), eastern white pine (Pinus strobus L.), and western white pine (Pinus monticold Dougl. ex D. Don). In western white pine, for example, genetic diversity north of California is low and no detectable differences are found among populations. In California, heterozygosity is much higher and populations are more distinct (Steinhoff et al. 1983).

Why do these trends exist? Perhaps, because these species were eliminated from the northern parts of their range during glacial periods and populations were reestablished by colonization after the glaciers melted. Southern stands remained in place for hundreds of thousands of years, maintaining fairly sizable populations, a situation which is conducive to high levels of genetic diversity. As the glaciers melted and new habitat opened-up in the north, it was colonized by long distance dispersal from the south. Each of these dispersions, or colonization events, may have involved only a few seed, carried by the wind or by birds. First from southern refugia, and in later generations from the small colonies founded by the early migrants. However, a few seed can carry only a sample of the parental genes. Therefore, each step northward was an opportunity for genetic erosion, genetic loss, because of successive subsampling from increasingly limited pools.

When we compare tree species (Ledig 1986a), we find that species whose ranges are totally, or almost totally, within areas glaciated during the Pleistocene have, on average, the least variation-like pitch pine (Pinus rigida Mill.) and jack pine (Pinus banksiana Lamb.). Those from areas south of the glacial front have more variation-like sugar pine (Pinus lambertiana Dougl.) from California and loblolly pine (Pinus taeda L.) from the southeastern United States. And species from latitudes that were relatively unaffected by the climatic changes associated with glaciation seem to have the highest levels of variation-like Caribbean pine (Pinus caribaea Morelet) and Ocote pine (Pinus oocarpa Schiede) from Central America. Exceptions are numerous, but the tendency appears real.

Extinction and the Loss of Genetic Diversity
Having reviewed the distribution of genetic diversity, let's consider its extinction and loss. I began by saying that we are losing genetic diversity within species and species themselves, which are whole genetic libraries, at an alarming rate. Most of you realize that these species are predominantly insects, because insects represent 90% of all species on earth. What about trees? After all, this is supposed to be a lecture in forest science. It's difficult to lose a tree isn't it?

No. In fact, trees are as vulnerable to extinction and genetic loss as other organisms. John and William Bartram, pere et fils, were two of the earliest botanists in colonial America. In 1765 the Bartrams made a collecting expedition to Georgia (Kastner 1977). One of their discoveries was a grove of small, flowering trees, the Franklin tree (Franklinia alatamaha Marsh.), William collected seed from the trees in 1776, and they were visited again in 1803. They have never been seen since-one of North America's first documented extinctions after colonization by Europeans.

In more recent times, a relative of the domestic avocado (Persea theobromifolia A. Gentry) was discovered by taxonomists in 1977. Unfortunately, locals in Ecuador knew it as an important timber tree much earlier. Today less than 12 trees remain (Gentry 1986). When I worked in Puerto Rico, I was lucky enough to see Luguillo lidflower (Calyptranthes luquillensis Alain) of which there were only 5 trees left. But I didn't see Puerto Rican crescentia (Crescentia portoricensis Britton) with only 4 trees left (Gentry 1986), and you or I may never get the chance to see it. Closer to home, only 7 trees of Catalina mahogany (Cercocarpus traskiae Eastwood) remain from a population of over 40 at the turn of the century (Martin 1986).

But the most common threat to genetic resources is not species extinction. It is loss of populations, loss of local genetic diversity. Unfortunately, we all concentrate on endangered species, which diverts attention from the more cryptic losses that are occurring every day, perhaps every minute. In virtually all tree species, low elevation populations were eliminated as land was converted to agriculture and urban uses. The genes that adapted those populations to long growing-seasons and to relatively deep and fertile soils are gone. And as agriculture moves up slope, particularly in the developing countries, more populations and more genes are lost (Jasso 1970), even though the "species" in the popular sense, is not in danger.

The loss can occur very quickly. In 1978 William J. Libby from the University of California-Berkeley visited Guadalupe Island off Baja California. Guadalupe Island had a population of 368 pines, an isolated population of Monterey pine (Pinus radiata D. Don). Today, 10 years later, only 45 remain and the feral goats of Guadalupe may soon destroy those 45. This is particularly unfortunate because the Guadalupe pines have proven quite resistant to western gall rust (Old et al. 1986) and to red band needle blight (Cobb and Libby 1968), diseases that cause concern in the Monterey pine-growing countries of the world. But there is no great public outcry about the loss of Guadalupe pine, is there? Why not? Because the "species" is not in danger.

In other cases, the genetic resource has been degraded even without the loss of populations. Mahogany (Swietenia mahogani (L.) Jacq.) has been seriously overexploited in the Caribbean. In many areas, tree-form mahogany are no longer found. The species has been reduced to a multi-stemmed shrub by selective harvesting of the larger, well-formed trees (Styles 1972). In this case, genes for tree form may have been lost even though the populations themselves are still extant.

In summary, the impending crisis is not simply one of species extinction, though that is a serious problem. The crisis includes the loss of the genetic resources that make populations and individuals within populations unique.

Threats to Diversity
Having looked at trends in genetic diversity and at the loss of diversity in forest trees, we should also systematically examine the threats to diversity. The threats to genetic diversity are many, and include exploitation, habitat destruction, fragmentation of habitat, and environmental change.

EXPLOITATION
As our countries developed westward, exploitation undoubtedly took its toll of genetic resources. In California, low elevation populations of ponderosa pine (Pinus ponderosa Dougl. ex Laws.), white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.), and sugar pine were eliminated a century ago because they were the most accessible sources of timber for construction, mining props, and railroad ties. Genes that enabled ponderosa pine to adapt to droughty, low-elevation sites may have been lost when those stands were cut. Where timber stands stood in 1849, brushfields of manzanita (Arctostaphylos spp.) and other chaparral species now grow (Bolsinger 1980; J.T. Rock, Klamath National Forest, California; personal communication 1988).

For example, la ceiba (Ceiba pentandra (L.) Gaertn.) supported five major plywood mills and ten small sawmills along the Amazon of Peru just 10 years ago. But by 1983 two of the plywood mills were already shut down, the other three were in the process of folding, and the 10 smaller mills were closed-because the ceiba were gone (Gentry and Vasquez 1988). In the Sahel of Africa, firewood scavengers, combined with drought, have eliminated all tree and shrub growth and resulted in desertification over a vast region. In Ethiopia, starving farmers were forced to eat the seed stocks of their wheat and barley land races, seed that should have been saved for planting the next season (Witt 1985), and which, by the way, may have contained genes valuable for breeding new and better cultivars for Canada.

What drives the machine? In many cases it is local need. Sahelians and other peoples from developing countries have no choice but to collect firewood-it is a necessity. And the example of Ethiopia needs no comment. The only real solution to these problems is population control. In examples like that of ceiba and mahogany, greed, a lack of concern for the resource, and, perhaps, ignorance are the problems.

Finally, consumerism threatens many species, especially animal species. I lost a pair of boots this summer and went shopping for replacements in Chihuahua. Chihuahua is the heart of cowboy country, home of the vaquero. We took words like lasso, rodeo, cayuse, and in fact the whole cowboy lifestyle from the vaqueros of Chihuahua. Chihuahua caters to cowboys. Probably half the stores in town sell boots, so it's a good place to buy. But, I found that many boots were made of caguama (the green sea turtle), elephant, ostrich, iguana, and armadillo. Certainly, caguama and the elephant are threatened species. They are made into boots not because their skins are surpassingly wonderful materials, but because of consumer vanity. Along the road, campesinos sell endangered parrots to passing motorists. In other parts of the world, travelers are offered leopard-skin coats or ivory bracelets. Canada and the United States nearly destroyed the sea otter to feed a demand for fur coats.

What can someone in British Columbia do to prevent overexploitation? With regard to overpopulation in the developing countries, very little. But we can contribute to organizations that provide advice and aid in family planning, and we can let our governments know that we support foreign aid for population control.

Universities can help by taking an active interest in training students from developing countries. If ceiba in Amazonian Peru could have been managed on a sustained basis, rather than "mined", it would have provided benefits to the local economy, the government, and the plywood industries in perpetuity.

With regard to the exploitation that feeds on vanity, the response is simple: avoid buying products made of threatened species. Curb your appetite for mahogany, even if you can afford it. Familiarize yourself with Canada's list of restricted imports and refuse to buy those products made from threatened species. I assume Canada has such a list, but if not, ask the International Union for the Conservation of Nature for theirs. Some people extend boycotts. For example, many are boycotting Icelandic and Japanese fish because those countries persist in whaling despite international bans. In short, be an intelligent and responsible consumer, a concerned, world citizen, and help educate others.

HABITAT DESTRUCTION
Habitat destruction is another threat to genetic diversity. Much forest land in Canada and the United States was lost to agriculture in the first three centuries of European colonization. At present, forest is being converted mainly to urban development, but the threat to forest species is the same. Take MacNab cypress (Cupressus macnabiana A. Murr.). MacNab cypress is a California endemic of limited occurrence. Recently, Constance Millar of the Institute of Forest Genetics went to collect seed from a population near the southern extreme of the species in the foothills of the Sierra Nevada. To her dismay, she found the site had been bulldozed for condominiums. Most of the cypress were piled for burning. Only a few trees remain as landscaping between the buildings.

Like diversity, the amount of forestland being lost increases southward. The British Columbia Ministry of Forests' Strategic Studies Branch (1984) estimated that the loss of productive forest will be less than 5% over the 25-year period that began in 1979. However, much of this "loss" is withdrawal of land for parks. Estimated loss of forest to roads, railways, and residences over recent years is negligible, less than 0.04%. In California loss of productive forestland to agriculture, residential development, roads, reservoirs, and powerlines in the 25-year period from 1952 to 1977 was 1.2% (Bolsinger 1980), but I believe that the statistics for the last 10 years will be higher. In Mexico widespread destruction of forests is obvious to anyone who visits there frequently. Deforestation from 1981 through 1984 was 5.2% (Office of Technology Assessment 1984), equaling or exceeding in only four years the projected losses in British Columbia and actual losses in California over recent or projected 25-year periods. Mexico's population increased from 51 million in 1970 to about 83 million today and is increasing at an annual rate of about 2.5% (Riding 1984). That equates to about 2 million more people annually. Most are born to subsistence farmers, meaning that more land must be put under cultivation. You can watch the fields climb the mountains!

And the worst destruction is in the tropical forest. Most habitat destruction in the tropics is a result of swingle, or slash and burn, agriculture. The life of new agricultural fields is brief, but the damage may be forever. In many cases, genetic resources are lost and some of the soils will not again support tall forest, at least not for hundreds of years. Norman Myers (1984) was accused of exaggeration when he estimated that tropical forests were disappearing at the rate of 7.3 million hectares per year. That was four years ago. Four months ago a study by the Brazilian Institute of Space Research reported that 20 million hectares of Amazonian forest were burned in 1987 (Roberts 1988). That is an area roughly one-quarter the area of British Columbia. And eight million hectares were virgin forest. Thus, destruction in Brazil alone exceeds what we thought was happening in the entire tropics (i.e., South America, Africa, and Asia). Myers exaggerate? The man is an arch conservative!

Large-scale disturbance in the tropics is much more likely to disrupt communities and lead to extinctions than it is in Canada. Such widespread disturbance might be tolerated by Canada's forests, and even by those in the United States, because our northern communities, made up of weedy, pioneering species, are more resilient. They are adapted to disturbance (Critchfield 1984). They have migrated back and forth as the glaciers waxed or waned. Environments have been somewhat more stable in the tropics, which is one reason for the high levels of endemism in the low latitudes. Tropical species may well be more specialized in their physical and biotic requirements than boreal and temperate species.

In addition, the distribution of endemic species itself contributes to the disparity between northern and southern latitudes. A few years ago the tropical botanist Alwyn Gentry (1986) found 90 new species of plants on Centinela Ridge in Ecuador, apparently native to an area only 5-10 kilometers square. Today they are gone. The last patch of forest on the ridge was cleared two years ago. A similar situation could not occur in British Columbia for the obvious reason that such endemic diversity does not occur there. But the loss of tropical species is a hidden threat - a time bomb that will explode in British Columbia as well as in the Andes and the Amazon Basin.

Fragmentation is the reduction of a species to small, isolated populations, a pervasive corollary of habitat destruction by agriculture and urban development. This has two effects. First, small populations are subject to inbreeding and genetic erosion, which reduce fitness and increase the risk of local extinction. Second, migration routes between patches are blocked by agricultural fields or urban areas, so populations can not escape environmental change by trans-generational movement through colonization. In the special case of forestry, remnant native forest may be fragmented when adjacent sites are planted with seedlings. These may be nursery-run or they may be the products of a tree improvement program. But pollen contamination from these planted forests constitutes a greater or lesser threat to the genetic integrity of adjoining natural populations. Rather than belabor this issue more, I will refer to the excellent book by Larry Harris (1984) called "The Fragmented Forest".

Perhaps the most pervasive threat to genetic resources today is environmental change. Widespread forest destruction in Europe is attributed to acid rain, resulting from the burning of fossil fuels. In addition to destroying entire populations of highly-sensitive species, pollutants may selectively eliminate genes in the others, reducing genetic diversity (Pitelka 1988).

Destruction of the atmospheric ozone layer is another threat. The earth's ozone layer is being reduced or destroyed by the release of chlorofluorocarbons and halons. The ozone layer shields the earth from ultraviolet radiation which causes sunburn and skin cancer in humans. But ultraviolet radiation may be detrimental to plants also (Caldwell 1979); it reduces photosynthesis, particularly in sensitive, low-elevation plants.

The most serious threat to forest communities, however, may be global warming, resulting from an increase in atmospheric carbon dioxide (CO₂). The evidence for increasing atmospheric CO₂ is now indisputable (see Harrington 1987). Increased levels of CO₂ are a result of burning fossil fuels, coal and oil, and - note the connection - the destruction of tropical forests. The destruction of tropical forests contributes to increased levels of CO₂ in two ways. First, conversion of tropical forests by burning releases carbon that has been stored in wood. Second, it destroys a potential sink for atmospheric CO₂, i.e., it reduces the amount of leaf cover, therefore, it reduces CO₂-uptake by photosynthesis. But increased levels of CO₂ by themselves might be a blessing; low CO₂ limits plant growth, so forest productivity should increase with increases in CO₂. The catch is that CO₂ is a so-called greenhouse gas. It allows solar radiation to pass into the atmosphere but absorbs long-wave radiation that the earth reflects back out toward space. Largely because of the increase in atmospheric CO₂, climate models predict an average global increase in temperature of 2.5 ºC by the year 2050 (Harrington 1987). But, the increase in temperature will be more pronounced in British Columbia than in the tropics. Decline will be common throughout the higher latitudes as forests are stressed by climatic change. Species with broad latitudinal ranges or wide ecological amplitude may survive, in part. Others may migrate by colonizing newly favorable habitat to the north or higher in elevation. However, many species will go extinct as the climate changes, because escape routes are already closed by agricultural or urban development.

What can we do about a problem as immense as global climatic change? To some degree we can change our lifestyles and help to educate others. Do you know what the number one source of chlorofluorocarbons is in the United States? Car air conditioners. As consumers we could demand cars without air conditioners, cars with light-color exteriors and upholstery to reduce the heat load. What is the second most important source? Styrofoam, including styrofoam cups. Why not demand a return to paper cups? That could be done by local ordinance. At work, we could bring our own ceramic cups. Substitutes are available, and Canada, among other countries, called for a cutback in global production of chlorofluorocarbons in the Montreal Protocol of 1987.

What about the increase in CO₂? We can use energy conservation measures to reduce fossil fuel consumption. And we can also work toward sustainable energy production systems (i.e., growing and using wood for power generation, which would demand a balance between CO₂-fixation and emissions). This will also have the effect of reducing acid deposition, since wood is low in sulfur.

The Rationale for Conserving Diversity
Most people are aware that the process of species extinction and genetic loss is greatest in the tropics, in the developing countries. Therefore, does genetic loss have anything to do with British Columbia?

It has everything to do with British Columbia. As John Muir (1916) said: "When we try to pick out anything by itself, we find it hitched to everything else in the universe". British Columbia can no more afford provincialism than can California or Mexico. Why should British Columbia: worry about conservation of genetic resources? For the same four reasons that should concern all of society-their economic, ecologic, esthetic, and ethical importance. Economic reasons sell better, so I will consider them first.

ECONOMIC REASONS
British Columbia has a stake in the genetic resources of the world. It depends on a variety of genetic resources that are non-native, and this dependency will increase in the future. Agricultural production in British Columbia is led by dairy products, fruit (mainly apples), and grains (wheat and barley), according to the Ministry of Agriculture and Fisheries (1988). None of these are native. Cattle were domesticated in the Middle East and Europe; apples originated in the Caucasus Mountains of western Asia; wheat in the mountains of Asia Minor and the Sudan of Africa; barley in Abyssinia or Tibet (Janick et al. 1969). British Columbia is not unique in relying on exotic crops. In the entire United States only five native crops are important agricultural commodities: sunflower, pecan, cranberry, blueberry, and Jerusalem artichoke (Witt 1985). Hardly what would be considered sufficient for a balanced diet. In brief, agriculture has been characterized by movement of crop plants and animals on a global scale.

By contrast, forestry is in a primitive state of development, still a primarily exploitive industry. But in the future, cultivars of forest trees may be shifted among countries like we now shift agricultural crops. The beginning of this can be seen with Monterey pine, a species that occupies less than 8,000 hectares in its native range in California but 3,000,000 hectares of plantations in Chile, Australia, New Zealand, and elsewhere (A.R. Griffin, CSIRO, Canberra, Australia; personal communication 1988). Similarly, species native to British Columbia, Sitka spruce (Picea sitchensis (Bong.) Carr.) and lodgepole pine (Pinus contorta Dougl. ex Loud.), are becoming the most important forest species of several European countries (Hermann 1987).

Can British Columbia hope to improve forest production by importing non-native tree species? Pacific Northwest conifers are often the best representatives of their genera anywhere in the world (Waring and Franklin 1979), and British Columbia has not needed to import exotic trees. In general, conifer genetic resources from the west coast of North America have proved highly exportable, as suggested above.

However, if predictions of climatic warming come true, British Columbia may be pushed to consider the import of new forest crops. If not new species, at least new provenances of the present species will be needed. With a doubling of atmospheric CO₂, southern boundaries of the cool temperate conifer forest that now lie south of the Klamath Mountains in California will be relocated northward (Warrick et al. 1986). In only 60 years, Vancouver will be near the southern extreme of the zone. The trees of local seed source that British Columbia is planting now, may never reach rotation. The correct provenances of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) for southern British Columbia may be similar to the ones now growing in northern California. Therefore, Canada has a real stake in how we protect genetic resources in the United States.

Even without climatic change, genetic resources in California, Mexico, and even the tropics are of potential value to British Columbia. Genes can now be transferred among virtually any organisms, not only from tree to tree, or between tree species, but even from organisms as phylogenetically distant as bacteria and insects (Ledig and Sederoff 1985); genes for disease and insect resistance, for new, valuable extractives, for drought and cold tolerance in fast-growing, domesticated tree species. To remain competitive in forest products, British Columbia may need genetic resources not native in its present forests. Many examples exist in agriculture; the gene to breed resistance to yellow dwarf virus was found in a single Ethiopian barley plant and a single wild Peruvian tomato was used to breed higher sugar content into processing tomatoes (Witt 1985). Could the rare Chihuahua spruce have genes that will prove of value to cultivated Sitka, white (Picea glauca (Moench) Voss), or Engelmann spruces (Picea engelmannii Parry ex Engelm.)? Unless we save Chihuahua spruce, we will never know.

What about protection of British Columbia's own genetic resources? Some aspects of forest management in the province may threaten local adaptation. Large clearcuts, on the order of thousands of acres, whether regenerated naturally or by planting, could possibly disrupt genetic structure, resulting in reduced growth and increased susceptibility to stresses. Obviously, this could have economic consequences. In addition, long-term evolutionary potential may be jeopardized if genes are lost, which could be very important if it becomes necessary for species to adapt to a warming climate. And finally, random reduction in genetic variation will place constraints on gains from breeding programs. This is not meant to condemn clearcutting; natural regeneration in small clearcuts probably causes no deleterious effects with respect to the genetic resource. In fact, they are to be preferred to selection cutting.

ECOLOGICAL REASONS
The life-support services provided free by ecosystems are important to us all, and genetic diversity is crucial to ecosystem function. Removing a few species here and there, or destroying a few populations with their more-limited genetic diversity, may have no great affect on ecosystem function. But then again, it may. Ecology has not yet matured to the level of predicting all such impacts, but intuition leads us to expect a cascade of extinctions when enough components of the ecosystem have been removed, particularly if keystone species are lost. Trees are particularly important because they provide habitat as well as food for a range of organisms, from bacteria and fungi to insects, birds, and mammals. For example, the loss of a few keystone species of palm and fig trees in the Amazon Basin of Peru would result in collapse of the frugivores, which in turn would cause a decline in the other plant species that depend on the frugivores for seed dispersal (Terborgh 1986).

Genetic diversity within species is also crucial to ecosystem function. Most populations are finely tuned (i.e., adapted) to their envir6~ment, including its climatic, edaphic, and biotic components (e.g., Douglas-fir as reported by Campbell 1979). Loss of genetic diversity eliminates the possibility of evolutionary modification, which is necessary if populations are to adapt to changing environments. Furthermore, populations, even though they are of the same species, are not interchangeable. Destroy a locally-adapted population and it may not be replaceable. Conditions under which in situ populations evolved probably no longer exist; a modified microclimate and competitive exclusion may preclude reinvasion and evolution by adjacent populations. Moreover, the way in which the elements of genetic diversity are combined in organisms and populations are as important as the elements themselves. If particular combinations of genes are destroyed, they may be lost forever. Theoretically, the genetic mechanism of sexual recombination could reconstitute the original population, but this may require periods measured in geologic time, which excludes it from practical consideration (Anderson 1949). The role of the original population in the ecosystem may never be refilled, or only partially filled, by other species or colonists from other conspecific populations.

Modification of the environment by humans is leading to changes on a global scale, changes that may endanger all life on the planet, even ours. We all have an interest in the vast changes that are occurring, even changes in the distant tropics, because they impact global climatic and nutrient cycles (for examples, see Ehrlich and Ehrlich 1981).

ESTHETIC REASONS
To be honest, esthetics is one of the major motivations for conserving genetic diversity, though we often mask that with some other rationalization. How much more interesting a diverse world is than a homogenized one, reduced to a few, widespread, weedy species. As proof of how human nature operates, think of the birdwatchers, thrilled by the sight of a species new to their checklists. Conversely, think of the most common form of punishment and torture, solitary confinement in a bare room; sensory deprivation is enough to drive many insane. Strangely, our esthetic sense is exercised even when we have little opportunity of enjoying this diversity first-hand. African lobelias and gorillas are a source of fascination and enjoyment to me, even though I will probably never see either in the wild. Freeman Dyson (1988), the physicist, captured this esthetic sentiment when he coined the principle of maximum diversity, which joyfully states that: "The laws of nature are such as to make the universe as interesting as possible".

ETHICAL REASONS
Finally, many people feel an ethical obligation to protect genetic diversity, particularly to protect endangered species. One way of expressing this may be to ask ourselves: How dare we have the arrogance to destroy other species by our own uncontrolled breeding, and by rampant consumerism? Those who plead for ethical behavior are not talking about choosing between our own species and others - that would be ridiculous. They merely ask that we allow other species to share this planet with us. We saw a regime 50 years ago that sought to eliminate human diversity, to use eugenics to breed a uniform Aryan race, and destroy another people - and the world condemned it. Is it such a major mental leap to think that someday we will condemn the wasteful destruction of another species?

This topic has attracted the attention of philosophers like Arne Naess (1986) and Bryan Norton (1988) and biologists like David Ehrenfeld (1988). However, I have a problem in separating their ethical arguments from purely esthetic ones. For example, is it true that we protect species of no value to us, as Naess suggests? Or do those species have, in fact, a value because they provide intellectual and esthetic enjoyment, even though they are used for no tangible product?

I close this section with a quote. Whether our concern for diversity is esthetic or ethical, economic or ecologic, Jose Ortega y Gasset (1914) wrote something that rings very true for me: "I am myself and what is around me, and if I do not save it, it will not save me". What we are, each of us, is as much a function of our experiences, our environment and our perception of it, as it is of our physical being. What are we if we do not save it?

Conservation Methods
Raving spent far too much paper on the threats to genetic resources and the reasons for conserving diversity, I can only briefly refer to conservation itself. However, strategies for conservation have been discussed elsewhere (e.g., Ledig 1986b), so I feel no guilt about slighting the topic here.

In short, conservation practices can be divided into those operating in situ, meaning in place, and those that are ex situ, out of place. A large literature has developed on in situ methods: the establishment of preserves, minimum viable population sizes, whether a few large or many small preserves is best, and their interconnection via migration corridors (e.g., Soule and Wilcox 1980). But the truth is, even in the rich, developed countries of the world, the area put aside in reserves can never be sufficient to assure the persistence of all species and populations. National Parks and Wilderness Areas in the United States occupy only 4% of its territory (Ledig 1988). In developing countries the figure is often smaller, and furthermore, population pressure makes reserve boundaries meaningless. Anthropogenic pollutants do not respect reserve boundaries either, and in parts of Europe and southern California, forest decline will make in situ conservation ineffective. When Leslie Schaffer and his family left Nazi Hungary in 1938, exactly 50 years ago last month, the world's population was just over 2 billion; today, 5 billion share the same resource base (Johnson 1986). That is the key problem in conservation.

Ex situ conservation in seed banks is a hedge against loss of in situ reserves. However, the majority of tree species, particularly tropical species, have seeds that don't store. These species can be maintained in arboreta or outplantings for several decades or even centuries, but the cost is high and saving a few specimen trees preserves only a fraction of the total diversity in a species. The process of regenerating them when they age will be plagued by the problems of inbreeding and by directional selection, which will further reduce genetic diversity.

To effectively conserve genetic diversity, conservation must be an integral part of land management. Neither reserves nor seed banks, alone or together, are sufficient. Conservation must be integrated with other land uses, such as timber harvest, grazing, recreation, agriculture, and even how we build our cities. Local communities, particularly in developing countries, must support conservation, not be displaced by reserves that constitute a further economic drain (Dasmann 1988). For excellent discussions of this topic, see Salwasser (1988), and Schonewald-Cox (1988). Elsewhere, I have argued that timber harvest and conservation of genetic resources are not necessarily incompatible (Ledig 1988). In fact, the real danger to diversity lies in the extreme position that reserves alone can maintain genetic resources and that all development can be halted or even reversed to freeze the system in some supposedly primeval state. That is too simplistic to work, and counterproductive as a strategy because it polarizes the problem. Conservation must be made an important consideration in every land use decision, on local and global scales.

British Columbians are responsible for the protection of their native genetic resources. But moreover, they must also shoulder a major part of the burden for saving tropical genetic resources. The developing countries do not have the financial resources to do it. Per capita income in British Columbia is about $14,000 in U.S. dollars. In California, about $15,155 (Fay et al. 1987). But in Mexico per capita income is only $2000 (Riding 1984), and Mexico is a rather affluent country relative to most of the developing world. You cannot expect people in developing countries to spend much on conservation when they do not have enough to even cover necessities.

Conclusion
In summary, genetic diversity is greater in the tropics than in temperate or boreal forests. Everywhere, this diversity is threatened by the loss of species, and even more frequently, by the loss of populations. Like diversity itself, the direct threats to diversity through overexploitation and habitat destruction are also greatest in the tropics. On the other hand, environmental change, through acid deposition, destruction of the ozone layer, and global warming will have a greater effect in northern latitudes. Global warming is just one reason British Columbia must be concerned about tropical deforestation, but all the world shares economic, ecologic, esthetic, and ethical reasons for stopping the loss of genetic diversity. The cost of conservation must be borne by affluent countries, like Canada and the United States. Establishment of reserves and seed banks should go on apace, but by themselves are insufficient to conserve genetic diversity. Conservation must be made a part of our life. It must be a consideration in every land-use decision.

By now you have probably forgotten that I began with a story about Chihuahua spruce and that this talk was subtitled "The Road to La Trinidad". Let me conclude by finishing that story. The road to La Trinidad eventually led me and my Mexican colleagues to a backwoods settlement, and we enlisted a local guide who said he knew where the trees were. We continued on, finally abandoning our truck to continue on foot in the quest for our personal Trinity. The rains began, and for hours we searched-but mists hid the spruce from us.

And that could be the end to the somewhat dismal picture I've painted for you in this lecture. But it doesn't have to be. I have played a role somewhat like that of the Spirit of Christmas Yet-to-Come in Dicken's famous tale, "A Christmas Carol". I have shown "shadows of things that May be". But if the course be departed from, certainly the ends will change. There is yet time. I'm not giving up on Chihuahua spruce. I'm going back to Mexico as soon as possible, and next time, I'll reach La Trinidad. And I call on you, to use science and humanity to combat exploitation, consumerism, and uncontrolled population growth in order to save this beautiful world.

Acknowledgments
I wish to express my thanks to the many colleagues who led me along the road to La Trinidad, especially Teobaldo Eguiluz Piedra, Jesus Sanchez Cordova, Knud Clausen, Jesus Ruiz Ramirez, Juan Manuel Cassian Santos, Jaime E. Flores Lara, Jose Guadalupe Sanchez, Rufino Benitez Trujillo, and Aurelio Olivas Meza. My thanks also to Constance I. Millar and Bohun B. Kinloch for their helpful comments on this manuscript. And finally my appreciation to Mrs. Kato Schaffer, who by establishing the Leslie L. Schaffer Lectureship, provided a forum for the story of La Trinidad.

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Last updated by W. Atkinson (atkinso@unixg.ubc.ca) on September 21, 1998.