29 Aug 2011: Report

Climate Relicts: Seeking Clues
On How Some Species Survive

In pockets ranging from mountain peaks to bogs, scientists are discovering plants and animals that survived previous eras of climate change. Now, conservation biologists say, these climate “relicts” could shed light on how some species may hang on in the coming centuries.

by carl zimmer

A two-hour’s drive north of Madrid is an extraordinary sight: forests of beech trees. It’s not the European beech itself that’s extraordinary. After all, Fagus sylvatica grows across a wide swath of the continent. It’s beech trees in central Spain that are strange. To grow, beeches require a moist, relatively cool climate — a climate that’s almost impossible to find in central Spain. “They’re limited to cool moist valleys in a hot, dry mountain range,” explains Alistair Jump, an ecologist at the University of Stirling who studies the trees.

The trees, which lie about 200 miles south of the edge of the main range of European beeches, did not get to central Spain recently, their seeds carried on the shoe of some German tourist. Evidence from both fossils and genes shows that beeches have lived in some parts of Spain since the last Ice Age. At the time, most of Europe was either buried under ice or too harsh a climate for the beeches to survive. But after the Ice Age, suitable habitats opened up, and the beeches expanded from their southern refuges into the north.

At the same time, Spain became so hot and dry that most of its beeches began to disappear. As the northern edge of the tree’s range expanded, the southern edge retracted. But in a few moist, cool mountain valleys in central Spain, pockets of beeches have survived, from the age of wooly rhinos and Neanderthals to today.

The beeches of central Spain are known as climate relicts. For decades climate relicts have suffered from a benign scientific neglect, considered little more than biological oddities. But Jump argues that it’s urgent that we understand how they have managed to hold on. In a paper to be
For decades, climate relicts have suffered from benign scientific neglect, viewed as biological oddities.
published in the Annual Review of Ecology, Evolution, and Systematics, Jump and Arndt Hampe of the Doñana Biological Station in Spain point out that most species mainly found in temperate regions have left behind climate relicts. They also observe that global warming is starting to push species into new ranges. As some of those species retreat, they may leave behind climate relicts of their own. And today’s climate relicts may hold clues about how to protect species from global warming-driven extinction.

“Understanding how they exist is of fundamental importance,” says Jump.

Climate relicts are often found in places that are several degrees cooler than their surroundings. Mountains offer lots of chilly real estate, but they don’t have a monopoly on climate relicts. Bogs have them, for example, as does the rocky debris that surrounds ice-filled caves. “You have a flow of cold air coming out of ice caves,” Jump explains. “It’s like if you leave the fridge door open.” In northeast Iowa, the ground around ice-filled caves turns out to be home to plants, snails, and mites ordinarily found in the boreal forests of Canada.

It’s not enough for climate relicts to be sheltered from warmer climates. They also need to be sheltered from the species that move in when temperatures rise. Small plants can be shaded out by trees that move in with a climate shift. The grey jay, a bird that lives in Canada, is suffering from an invasion of microbes. Normally, the grey jay survives through the winter on berries, bugs, and other foods it stores away in caches. At the southern edge of its range, the climate has warmed so much that microbes can infest the caches in the fall. The food rots, and the birds have nothing to eat.

To find refuge from these competitors, climate relicts often end up where their rivals can’t get to them. It’s no accident that many climate relict plants grow on cliffs and other rugged places that trees can’t colonize
To find refuge, climate relicts often end up where their rivals can’t get to them.
easily. These refuges can also protect climate relicts from diseases that might otherwise endanger them. Butterflies are typically attacked by parasitic wasps, which lay eggs in their caterpillars. Camille Turlure of the University of Louvain in Belgium and her colleagues recently examined relict populations of cranberry fritillary butterflies that survive in bogs. They couldn’t find a single wasp egg in the insects.

Even in a hospitable microclimate, supported by friends and protected from enemies, climate relicts still face a tenuous existence. They face droughts and heat waves. Trees may lose the services of insects that pollinate their flowers. Jump suspects that climate relicts survive on this razor’s edge with some life-saving strategies. Rather than relying only on pollination, for example, many climate relict plants can clone themselves. To weather droughts, they store extra carbon in their roots. Climate relict animals can also survive by adjusting their behavior. Insects can lay their eggs on cool north-facing leaves, for example, instead of the hot south-facing ones.

The mere existence of climate relicts can give ecologists headaches. A number of researchers have been developing computer models that can predict where species can be found today based on the kind of climate they can survive in. Part of the motivation for these models comes from the desire to understand why species shifted their ranges in particular patterns in the past. But many scientists also hope these models will help predict what happens to the world’s biodiversity as the planet warms over the next century. They’re already documenting hundreds of species either moving toward the poles or heading up the slopes of mountains, tracking the climate they prefer.

These models can potentially allow researchers to look into the future. They may be able to predict which forests will become most prone to fires,
Some researchers are worried that time is running out to study many climate relicts.
for example. Many researchers are also concerned that many species won’t be able to shift to ranges of equal size. Instead, their ranges will shrink, putting them at greater risk of extinction. Climate models could potentially allow scientists to identify the species that are most vulnerable.

Climate models are far from perfect, though. For one thing, they can’t predict the existence of today’s climate relicts. They are too coarse to include details about the small habitats where species can find refuges. “We’re cutting climate relicts out of the picture,” says Jump.

That omission won’t matter in large-scale projects of how climate change will affect biodiversity, Jump says. But it will be a problem when ecologists try to determine whether a species is going to entirely disappear from a region. Climate relicts may hang on when computer models say they can’t. “It goes from being common to being rare, but it doesn’t go extinct entirely,” says Jump.

Today’s climate relicts are also important for managing species, Jump argues. Because these populations managed to survive in unforgiving places for thousands of years, it’s possible that during that time, they’ve evolved, picking up valuable adaptations. It might be possible to identify the genes that make climate relict trees drought resistant, for example, and


First Comes Global Warming,
Then an Evolutionary Explosion

First Comes Global Warming, Then an Evolutionary Explosion
In a matter of years or decades, researchers believe, animals and plants already are adapting to life in a warmer world. Some species will be unable to change quickly enough and will go extinct, but others will evolve, as natural selection enables them to carry on in an altered environment, Carl Zimmer writes.
use them to breed trees that farmers could plant in arid regions. Climate relict genes “could increase the resilience of a species across its range,” says Jump.

But Jump is worried that time is running out to study many climate relicts. Some may not be able to withstand the coming climate change, which is expected to go rapidly beyond anything these relicts have withstood over the past 11,000 years. Jump is even more concerned about the pressure that farming, tourism, and other human activities are already putting on climate relicts. Relict stands of beech trees in the Montseny Mountains in eastern Spain, for example, stop abruptly at a high-elevation plain where sheep and goats are grazed. “That plain would be perfect to support more trees,” Jump says wistfully.

POSTED ON 29 Aug 2011 IN Biodiversity Business & Innovation Science & Technology Science & Technology Asia Europe 


Are the "species islands" from the north of plant ranges also climate relicts? I'm thinking of the prickly pear cactus in NW Ohio and the big leaf magnolia in the Red River Gorge aria of Kentucky specifically.

Posted by donK on 29 Aug 2011

Wonderful article, as always Carl. I live in Madrid and have visited many times the Beech Forest of Montejo (Hayedo de Montejo), but wanted to tell you that the beechs as a climatic relic is only true in that part of central Spain, since they grow naturally in many areas of the rainy northern Spain forming huge forests (in fact, the Irati forest in the region of Navarra is considered one of the biggest and best preserved beech forests in Europe). In fact the beech is one of the most usual trees in the north of the country.

Posted by MrO on 29 Aug 2011

The simpliest of solution; humans should feed these birds, The grey jay. We have a greater responsibility to our environment then many are willing to accept.

Just like so much flooding in one area, while total devastation and drought ridden areas like we are experiencing in central texas. So where are the aquaducts, the transportation of water to areas drought ridden. We put man on the moon.

Posted by Flora Rager on 29 Aug 2011

Reforest The Tropics manages a UNFCCC-AIJ program of applied research to improve carbon-offset forests on farms in the tropics. Among our research goals is the reduction of risk of species loss in our forests due to climate change by developing various models of sustainable mixed-species forests.

Presently we manage 41 research farm forests in Costa Rica sponsored by 71 US emitters.

This article and common sense justifies this approach. Our web site is reforestthetropics.org. Tel: USA 860-572-8199.

Posted by Herster Barres on 01 Sep 2011

@Herster Barres - yes, I agree. I have not yet looked into your specific program regarding re-forestation practices, but if it is as you say it is, then the work done is needed, indeed.

However, I think that the CO2 and the reforestation issue are slightly divergent from the main point of the article. If we are to understand an ecosystem, then we need to understand all players. And these players are, as outlined by this research, poorly understood. A comment on Carls blog linked to Ouimet Canyon in Canada, near Thunder Bay. It is a widely known place to visit for its geology, but its biology is largely unknown. But, after simple research the relict populations were found. Now we have a more profound understanding of this ecosystem. This informs our conservation techniques and dollars, helps us fill in gaps of ecological communities and interactions.

A good read, interesting thoughts and im off to the races to learn more. Thanks, again, Carl.

Posted by Monkey on 04 Sep 2011

In SW Ohio, there are several relict plant populations surviving in Clifton Gorge. Examples include white cedar (Thuja occidentalis L.), red baneberry (Actaea rubra (Ait.) Willd.), and eastern hemlock (Tsuga canadensis (L.) Carrière), all are well south of their normal ranges. There are several papers concerning those relics, with the earliest published in 1928 (Braun, E. L. 1928. Glacial and post-glacial plant migrations indicated by relic colonies of Southern Ohio. Ecology 9:284-302).

@donK: No. Eastern Prickly Pear (Opuntia humifusa (Raf.) Raf.) ranges from Montana east to Massachusetts, south to Florida and west to New Mexico. The Ohio populations are well within its normal range. You'll be interested in a recent publication on O. humifusa in the Toledo, OH area (Abella, S. R. and J. F. Jaeger. 2004. Ecology of the eastern prickly pear cactus (Opuntia humifusa) in Oak Openings Preserve, northwestern Ohio. The Michigan Botanist 43:1-11).

Posted by Jim Milks on 06 Sep 2011

These isolated pools of species reminds me of land-locked Galapagos Islands. They are isolated from the larger gene pool and forced to live in extreme environments and have, as a result developed unique characteristics. Perhaps extremophiles, such as the microbes found in thermal pools in yellowstone national park, are relict species that eventually evolved into a new niche. Or maybe that is taking it a bit too far.

It would be interesting to test how big of a genetic difference there is between the relict beech tree and its unisolated counterpart. It is thought that species that are isolated may evolve at a different rate than those that are not. Could these species give a preview of the evolution of their counterparts, or a glance into their genetic past?
Thanks for the thought provoking article!

Posted by Kelly Conde on 11 Sep 2011

Never thought that i would find a beech tree in Europe. I thought that only New Zealand that has five species of beech, each prefer different soil and climate conditions, has beech trees. But Spain is practically my neighbourhood. Will definitely visit it.

Posted by Linda on 06 Mar 2012

Comments have been closed on this feature.
Carl Zimmer writes about science for The New York Times and a number of magazines. A 2007 winner of the National Academies of Science Communication Award, he is the author of six books, including Microcosm: E. coli and the New Science of Life. In previous articles for Yale Environment 360, he has written about how ecologists are using network theory and about how global warming will cause an evolutionary explosion for animals and plants.



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