Environmental ReviewA Monthly Newsletter of Environmental Science and Politics

Volume Six Number Six June 1999

CONTENTS:

THE VALUE OFANCIENT TREES:DAVID STAHLE

RAPID THINNINGOF GREENLAND'S

ICE SHEET:WILLIAM KRABILL

DECLINE &RECOVERY OF A

SMALL POPULATIONJEFFREY BRAWN

Using Ancient Trees toUsing Ancient Trees toUsing Ancient Trees toUsing Ancient Trees toUsing Ancient Trees toReconstruct ClimateReconstruct ClimateReconstruct ClimateReconstruct ClimateReconstruct ClimateHistoryHistoryHistoryHistoryHistory

Introduction:Tree rings can tell us how well a

tree has grown each year of its life. Across section of a tree reveals a bull'seye pattern of rings of wood, one ringfor each year of growth. If the tree hada good year — usually that meansplenty of water — that year’s ring willbe a thicker layer of wood; if theconditions were poor for the year'sgrowing season, the growth ring willbe thinner. Since trees can live formany hundreds of years, we can countback from the present time to see howclimate varied from year to year longbefore there was an instrumentalrecord of weather.

By sampling tree rings fromdifferent regions scientists can askmany questions about historicalclimate patterns: How long did ancientdroughts last? How large an area didthey cover? How frequent were ElNiños in the past? How severe werethey? How did they affect globalclimate? How did ancient droughtsaffect human history?

Despite a wave of deforestationthat accompanied human development,there are still ancient trees living inmany parts of the world. They needattention and protection not onlybecause they are part of our naturalheritage, but also because they are aunique source of historical informa-tion. We spoke with Professor DavidStahle about how tree rings have

extended our knowledge of climateand climate's effects on human history.

ER: Professor Stahle, what is yourtraining?

DS: I started as an archeologist at theUniversity of Arizona but I becameinterested in tree rings and moved outof archeology into climatology andgeography, and so I’ve got twodegrees, one in archeology and one ingeography and climatology. I was

trained at the Laboratory of Tree RingResearch in Tucson — dendrochronol-ogy in the United States was devel-oped there by A.E. Douglas at the turnof the century — and worked on theMexican Tree Ring Project..

So I am a dendrochronologistnow; that is, I use the annual growthrings in trees to study the history ofclimate and the environment. Myposition is professor of geography andgeosciences at the University ofArkansas, and I’m the director of theTree Ring Laboratory here, which Ideveloped. It consists of myself andDr. Malcolm Cleaveland, who is also afaculty member and a dendrochronolo-gist, and our assistant, MatthewTherrell. We’re part of the Departmentof Geosciences and we offerbachelor’s level degrees, master’slevel degrees, and a doctorate as well.Our principal funding comes from theNational Science Foundation ClimateDynamics Program.

ER: Why study tree rings?

DS: Trees are natural libraries ofenvironmental history, and if we candecipher that record, then it is invalu-able history of Earth’s environment.People are interested in this historybecause of the potential for humanalteration of both the environment andthe global climate. So in searching forthese natural archives we are hopingto place the twentieth century and eventhe twenty-first century into the morelong-term historical context.

We’ve been funded by NSF since1980 to develop a network of climati-cally sensitive tree ring chronologies,

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in the Southeastern United States atfirst, but now we’re also working inMexico and in Africa trying to developtree ring chronologies that mightrecord regional climate variability aswell as the world-wide influence of theEl Niño Southern Oscillation (ENSO).

So I and colleagues at otherinstitutions are going to those places ofthe world where El Niño has an effecton the regional climate and where alsothere might be trees useful for longpaleoclimatic studies.

ER: What do you do to a tree to getthat information?

DS: Oftentimes people think we’vegot to destroy the tree to get tree ringdata, but we don’t. We use a smallboring tool that removes a core fromthe tree approximately the diameter ofa pencil, that leaves a wound aboutone-half inch in diameter through theliving layer of the tree. Most species oftrees can compartmentalize the woundand show no ill effects, so it is consid-ered a nondestructive samplingtechnique.

ER: How do you get a history ofclimate from that?

DS: We would go into an old-growthforest and we would usually samplebetween twenty and forty trees, twocores per tree. Then we polish thecores and examine the rings under themicroscope and date them to theprecise calendar year in which thewood formed. We can compare treegrowth year by year, which is anaverage of all the trees at our site. Wecan then compare this average tree

growth for each year with the climatedata for the last hundred years andcalibrate the relationship between treegrowth and, for example, rainfall. Wecan then use tree growth to estimatehow much rain fell in the centuriesbefore instrumental observation began.That’s the nitty gritty ofdendroclimatic reconstruction.

ER: Don't you also look for dead treesto sample?

DS: Yes, we use living trees, but wealso often find old wood, fallen treesand old logs that oftentimes persist forcenturies on the forest floor, either invery wet environments or in aridenvironments. We can use thatmaterial to extend the tree-ring recordfarther into prehistory than would bepossible with any of the living trees.

We can plot the ring-widthchronology from the old log in a timeseries, and match that with the chro-nology of living trees. That point ofmatch might be hundreds of years ago.So suppose we have a 500 year-longchronology from a stand of livingtrees, and then we find a log that died300 years ago that also had 500 ringson it. The outer 200 rings of the oldlog will overlap the earliest portion ofour existing chronology. We canmatch up the growth rings and thenextend the chronology back anadditional 300 years with the deadwood, ending up with an 800 year-long chronology. So we look for theold living trees, but we also look forthese older sources of well preservedwood.

ER: Does data from a tree representits local environment or a larger area?

DS: There are many complicationsthat can obscure the climate signal intrees. A bear might come up andscrape the bark off of a tree; elephantsin Africa push trees halfway over andeat half the canopy; that is a tremen-dous insult to the tree, and it isreflected in the tree rings. The naiveinterpretation would be that elephantdamage was a period of prolonged

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drought, and of course it was not. Anyreflective person would realize thatthere’s the potential here for error intrying to estimate past climate fromtrees. But we armor ourselves againstthat error to a great degree by first ofall sampling a lot of trees at any onesite, and then sampling many sites.

The law of large numbers is onour side because by sampling manytrees at one site, even though the bearmay have disturbed tree number three,we still have thirty-nine other treesthat the bear did not disturb. So whenwe cross-synchronize and date the treering series and then average themtogether, those individual trees thatshow idiosyncratic response due totheir local micro environment or dueto their specific damage history tendnot to be expressed verywell in the final chro-nology. We refer to thecommon signal that ispresent in all the trees inthe stand and present inmany stands over theregion. That commonsignal almost invariably is the overrid-ing regional climate.

ER: Why try to reconstruct pastclimates?

DS: There are two main reasons forreconstructing climate. One is becauseit tells us about history, and that’swhere the story of the Lost Colonycomes in. The other reason is we’retrying to understand the dynamics ofclimate, what is predictable perhapsabout climatic variability. That’swhere El Niño Southern Oscillationcomes in, and global warming.

ER: That's why you need to use oldtrees.

DS: Yes. We often have this notion, Idid, and I know that many of myprofessional colleagues and certainlymany in the general public have thisnotion that there are no old trees left inthe eastern United States because welogged and cleared the primevalforests. So how in the world would webe able to reconstruct climate fromancient trees in southeastern Virginiaif all the trees were gone? To a degreeit is true to say that most of ourprimeval eastern deciduous forestshave been cleared since Europeansettlement, but it’s not entirely true.

In fact when you look back on thehistory of the eastern forests, it was aneconomically motivated disturbancewave that swept across the easternwoodlands. We logged the best timber

on the banks of the Ohio, the deepalluvial soils that were extraordinarilyfertile and supported the magnificenthardwood growth. Those hardwoodsare gone, and lamentably.

We have cleared the agriculturallyproductive soils of their originalforests, so there are very few originalforests that still survive undisturbed onthe valuable soils. But the easternUnited States was a mosaic of bothproductive and relatively unproductiveforests. There were the big magnifi-cent primeval trees, there were alsotrees growing on steep hillsides orrocky sites where tree growth was notfast and trees did not get very big.There were stunted forests, there weresteep forests, there were barrensinvolved. By some estimates as muchas 100 million acres of noncommercial

forests existed in the lower forty-eightstates.

Marian Clawson, a famouseconomist and forest historian esti-mated that the lower forty-eightoriginally had 950 million acres offorest cover, and 850 million acres ofthat was commercial and the other 100million acres was noncommercial.Much of that has been destroyed forone reason or another, but some of itsurvives in remote out of the wayplaces. So that becomes importantresearch material for dendrochronolo-gists. We’ve targeted these noncom-mercial forests that have trees that arecenturies old, in some cases over athousand years old.

It’s also an important conservationpoint. I argue that many people don’t

realize this, and we continueto destroy these ancientforests in the eastern UnitedStates, repeating the sins ofthe nineteenth century.

There are also a veryfew preserves of the originalprimeval forests, with the

tall magnificent trees, where theeccentric landowner wanted to havehis trees more than he wanted money.Thank goodness for those people. Wecan also study those few commerciallyvaluable sites too.

ER: Did you say over a thousandyears old?

DS: Yes. The oldest trees in theeastern United States are the famousswamp baldcyprus of the Southeast.That was a valuable timber, but it is aswamp-type species, some of theseswamps are nutrient poor and the treesare stunted and gnarly and twisted andwere not ideal for timber productionand in many cases they were leftuntouched.

The Jamestown colonists had the monumentalThe Jamestown colonists had the monumentalThe Jamestown colonists had the monumentalThe Jamestown colonists had the monumentalThe Jamestown colonists had the monumentalbad luck to arrive during the middle of abad luck to arrive during the middle of abad luck to arrive during the middle of abad luck to arrive during the middle of abad luck to arrive during the middle of a

seven-year drought.seven-year drought.seven-year drought.seven-year drought.seven-year drought.

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Tree ring data tell us there was a low point intemperature for the Northern Hemisphere atabout 1830, and since then the temperatureshave warmed up significantly...

Those are the trees we’ve used inour study of the English colonies atJamestown and Roanoke Island. Therewere old baldcyprus trees on theBlackwater River and Nottoway Riverin southeastern Virginia that we cored,and some of the trees were over athousand years old.

From them we were able todevelop a reconstruction of growingseason drought history that was 800years long. I wasn’t initially inclinedto do this, but my friend DennisBlanton, who is an archeologist atThe College of William and MaryCollege in Williamsburg, Virginia, andhas worked at Jamestown Island gotme involved in this. You may knowthat they recently found the originalJamestown Fort settled in 1606, thesite of the first successful Englishsettlement in the NewWorld.

ER: Is it not where thenational park is down onthe shore?

DS: Yes, but they’dalways assumed that theoriginal site was lost tobank erosion into theJames River. That’s now known to befalse and they have found the originalstockade archeologically.

Dennis was astute enough tospeculate that there might have beenmore to the environmental history ofthat early colony than was realized,because Jamestown is famous aboveall for the incredible hardship that thecolonists suffered there during the firsttwo decades. This is legendarysuffering where most of the peopledied. Of the original 104 settlers thatcame, only thirty-eight lived throughthat first year. There was some solidhistorical research to suggest that thesewere naive Englishmen, townsfolk and

tradesmen, not woodsmen, but neo-phytes in the wilderness, and it wastheir own ineptitude that led to theirappalling death rate. That is partlytrue, but we see now from the treerings that they also had the monumen-tal bad luck to arrive during the middleof a seven-year drought which was thedriest seven-year period in almost 800years.

The drought culminated in 1609-10 which was referred to as the dyingtime, the starving time. The tree ringsshow that this was the most severelydry year of the entire seven-yeardrought.

This is completely new andindependent evidence from ancienttrees suggesting that Jamestown wasbeset by extraordinarily unusualdrought during the initial settlementattempts. This I would argue puts a

new complexion on the historicalrecord and allows us a greater under-standing of the hardships that theysuffered.

And of course there’s also thefamous Lost Colony of RoanokeIsland in modern-day North Carolina.That was settled by agents of SirWalter Raleigh starting in 1585. Thecolonists, some one hundred people,were last seen in August of 1587.They disappeared from history, andthis of course includes Virginia Dare,who was the first English child born inthe New World. This is one of themost enduring mysteries in Americanhistory. What happened to the lost

colonists of Roanoke Island?Well, the tree rings indicate that

the year, 1587, was the driest singleyear in 800 years. It was an epicdrought that affected the entiresoutheastern United States. In fact, thethree-year period 1587, 1588, and1589 was the most intense three-yeardrought episode in 800 years. Thatdrought was part of an extendeddrought in the late sixteenth centurythat affected a great part of the NorthAmerican continent, all the way fromMexico to the Canadian border andfrom the Pacific coast of California tothe Tidewater.

The late 16th Century drought wasnot as persistent in the Tidewaterregion as it was out west. The droughtin the West lasted for up to thirty yearswith only minor interruptions. Nothinglike this incredible drought has been

witnessed in themodern era.

ER: How does itcompare to the 1930s?

DS: Much moreintense, much moreprolonged than the1930s Dust Bowl

drought or the 1950s drought of theSouthern Plains. So this was, I think,the drought event of the last thousandyears. In fact there is tree ring datafrom New Mexico that says the 16th

Century drought was unmatched inseverity and persistence for at least2,000 years. This was long before anyindustrialization of the atmosphere. Itwas a natural drought, no doubt, but itclearly had a huge environmentalimpact. And it must also have had ahuge impact on the societies that livedin North America at that time. Weresuch a drought to recur today, ofcourse, society would be hard pressedto cope.

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interinterinterinterinter esting and imporesting and imporesting and imporesting and imporesting and impor tant issues of our timetant issues of our timetant issues of our timetant issues of our timetant issues of our time .....

That story I think validates oursaying that trees are a natural libraryof environmental history. There’s noother way we could have learnedabout this Tidewater drought and theimplications that it has for both theSpanish and English settlement of theEast Coast of the United Stateswithout consulting the trees. There’sno other geological or botanicalarchive with enough precision torecord that drought accurately to makethese strict year-to-year comparisonswith the historical record. If we hadbeen so unfortunate as to lose all ofour ancient forests in the easternUnited States, this is an aspect of ourown history that might never havecome to light.

ER: What are the more modernapplications of your work?

DS: The other reason we value ancienttrees is because they can tell us aboutthe dynamic variability of climate. Weknow mankind has altered the chemis-try of the atmosphere, and I believethat the climate models are quite clearthat the accumulation of heat-trappinggasses is going to alter the energybalance of Earth on the global scaleand will lead to a warming of theplanet and a gradual change in re-gional climates.

I think the evidence is quite clearthat this is already happening. Irecognize some of the controversy thatsurrounds global warming science, butI think it’s inarguable in thepaleoclimate record and in the moderninstrumental record that our world ispresently warming up. The physics ofheat trapping by greenhouse gasses isalso quite well understood.

Tree rings have contributed to thisanalysis. In particular, trees growingon the frontiers of the Arctic and athigh elevation forests near the forest-tundra tree line are sensitive totemperature. The growing season isshort in northern Alaska and northernCanada and northern Siberia and thetrees grow better when it’s warm, andthey don’t grow as well when it’s cold.So the tree rings in those locations aretelling us about the history of tempera-ture in the circumarctic. Those treerings show century-scale trends ofcooler and warmer temperaturesstarting about 500 years ago.

These tree ring data which noware available from throughout thenorthern hemisphere are telling us thatthere was a low point in temperaturefor the Northern Hemisphere at about1830, and since then the temperatureshave warmed up significantly, and thatthe warming trend of the nineteenthand especially the twentieth century isunmatched in the last 500 years. Thatputs the modern instrumental andindustrial period in an important long-term perspective.

ER: What about El Niño?

DS: Some of the chronologies wehave developed in the southern United

States and Mexico are primarilysensitive to moisture and not too muchto temperature, and we have beeninterested in reconstructing otheraspects of climate variability, espe-cially the El Niño Southern Oscilla-tion. The El Niño Southern Oscillationis basically the great air-sea interactionover the equatorial Pacific Ocean.Depending upon the phase of thisoscillation, the general circulation ofglobal climate is perturbed and theclimate in certain regions of the worldis altered. One of those regions is thesouthern United States and OldMexico. Our tree rings provide arecord of the long-term teleconnectionout of the equatorial Pacific to thesubtropics in North America.

ER: I thought that the ENSO justaffected the west coast of North andSouth America.

DS: Oh no. ENSO affects southeasternAfrica, and east-central Africa; iteffects the West Coast of SouthAmerica, and then the northeast coastof South America in the Noresteprovince of Brazil; there is a big effectin the Gulf of Mexico sector, basicallythe whole Caribbean up to the Caroli-nas and across Arkansas, Oklahoma,Texas, down into old Mexico. That’s a

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The climate of Old Mexico, Texas, the SouthwestThe climate of Old Mexico, Texas, the SouthwestThe climate of Old Mexico, Texas, the SouthwestThe climate of Old Mexico, Texas, the SouthwestThe climate of Old Mexico, Texas, the Southwestand the Southeast is teleconnected to ENSO.and the Southeast is teleconnected to ENSO.and the Southeast is teleconnected to ENSO.and the Southeast is teleconnected to ENSO.and the Southeast is teleconnected to ENSO.

more stable influence, but theteleconnection to the west coast ofCalifornia is more unstable becausesometimes you get wetness there in anEl Niño year and sometimes youdon’t.

ER: How does El Niño compare toother climate cycles?

DS: It’s clearly been shown that the ElNiño Southern Oscillation is the mostimportant cause of interannual climaticvariability on this planet. What ispredictable about world climate today?There is the diurnal cycle of day andnight, which is perfectly predictable;there is the season cycle, which ispredictable, and before the discoveryof the El Niño Southern Oscillation,that was it for short-term variability.

Now we know about theMilankovich orbital cycles which areimplicated in the coming and the goingof ice ages, and those are predictable.In between we now havethe El Niño SouthernOscillation, for whichthere are computermodels that have done agood job of mimickingthis oscillation betweenthe ocean and the air in the equatorialPacific.

We also now have a monitoringarray in space and across the equato-rial Pacific where we can see the onsetand decay of warming and coolingevents in the ocean. So we’ve gottenbetter at predicting this oscillation. It’sbecome the basis for long-rangeclimate prediction that is showingsubstantial skill, and that has neverbeen possible before.

We’re pretty much hitting theskillful prediction wall after ten dayswith weather prediction; and skillfulclimate prediction has not beenpossible before the discovery of

ENSO. Now it is, and there is somesubstantial skill in predictions forthose areas of the world that areimpacted by ENSO. Not the wholeworld, just some regions, but stillthat’s a tremendous advance.

So because of this incrediblediscovery, there’s interest in the long-term variability of ENSO, whichmeans the paleoclimatology of ENSO.Our colleagues, for example, havebeen working with cores from coralsthat grow in the equatorial Pacific.Some coral colonies put on one layer ayear and it is possible to count thelayers much like tree rings and analyzethe chemistry of the layers andreconstruct sea surface temperaturesand even precipitation to the atolls, insome cases. So these are extraordinar-ily important paleo records right in thecenter of action in the generatingregion of ENSO.

We can also use tree ring data onthe land areas in those regions of theworld influenced by ENSO. The

climate of Old Mexico, Texas, theSouthwest, and the Southeast isteleconnected to ENSO. So trees fromthis region are important in that regard.We have used these subtropical NorthAmerican trees along with trees fromJava, Indonesia, to reconstruct ahistory of ENSO for 300 years. Itshows that this is not a fully stationaryphenomenon, based on our reconstruc-tions at least. There are changes in thevariability of the ENSO that the treerings show.

We made a time series reconstruc-tion of an index of ENSO variabilityover the last 300 years which showsthat it has been subject to substantial

variability. The variability has in-creased into the twentieth century, andit is conceivable that mankind’schanges to the global climate systemmight be implicated in changes in thevariability of ENSO.

ER: What do you mean by variability?

DS: The variability relates to theinfrequent occurrence of El Niñoevents. Every four to six years you getan El Niño event, like we had lastyear. With ENSO events you get warmwater near the Galapagos Islands inthe eastern equatorial Pacific; you getrainfall in dry coastal deserts of Peruand Ecuador that otherwise hardly seeany rain at all; you often times seestorms on the West Coast of theUnited States, including SouthernCalifornia. You get the wild weatherthat we saw in the eastern UnitedStates last year too, the incredible icestorm in the northeast and southeasternCanada and the wet winter in the

southeast, in Florida inparticular. These are someof the influences of ElNiño that we have come torecognize in the UnitedStates.

But the variability that I amreferring to is that in some El Niñoevents this happens in spades: you getstorms on the coast of California, youget incredible rain events over theSoutheast and flooding and loss of lifeand all the high drama of the 1997-98El Niño event. But not all of the ElNiños are that active, they are not allthat powerful. In fact 1982-83 and1997-98 were the two most powerfulEl Niño events ever recorded. There isactive analysis and research exploringthe possible link to a strengthening ofEl Niño events and global warming ofhuman origin.

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Another thing that has beenunusual about recent El Niños is thatwe got locked into a persistent El Niñopattern that lasted for four years in theearly 1990s and it was not interruptedby strong cold events. When scientiststalk about El Niño as a periodicwarming in the eastern Pacific thattends to happen every four to sixyears, well, that’s true over the longterm, say over the 120 years ofinstrumental observation. But latelythis pattern has been breaking downand we’ve been seeing more powerfulEl Niño events, less frequent La Niñaevents, and in fact persistent El Niñoevents.

The tree rings see this also. Thetree rings are telling us this augmenta-tion, this increase in the variability ofENSO extremes, both La Niña and El

Niño, has picked up since about 1870,1880, and continued into the present.We reconstructed every year back to1706 and there is a change that isstatistically significant in the envelopeof variability of ENSO after 1870.

This is another virtue, I wouldsay, of these insignificant ancientnoncommercial trees, trees that do notfulfill our stereotype image of an old-growth tree. When we think of ancientforests, we think of the redwoods orthe coastal Douglas fir in Washingtonand Oregon. Those are magnificenthuge ancient trees and they deserveour respect and attempts at preserva-tion, but all old trees are not big trees.

The ancient post oaks in the CrossTimbers of Oklahoma which are lowstatured, gnarly oaks and in some

cases are 400 years old, grow inforests that have been undisturbedsince European settlement. Theyprovide a record of regional climatevariability that is extremely accurate,and they also record the long-rangeteleconnection of the most importantcause of year to year climate variabil-ity on Earth, ENSO. Yet these treesare being bulldozed and burned tomake way for housing developmentsand shopping centers because we don’tappreciate the fact that they are old-growth forest. We don’t realize theirtrue antiquity. This is happening notjust in Oklahoma and Arkansas, it’shappening to ancient non commercialforests all over the United Statesbecause of our misconception aboutthe true history of our eastern andwestern forests.

Schematic diagram of areas of the world whose weather is influenced by El NiñosSchematic diagram of areas of the world whose weather is influenced by El NiñosSchematic diagram of areas of the world whose weather is influenced by El NiñosSchematic diagram of areas of the world whose weather is influenced by El NiñosSchematic diagram of areas of the world whose weather is influenced by El Niños

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... why would we be cutting our last remainingold-growth forests when we've got all these

other industrial forests?

This is something that our labora-tory is dedicated to try to change.We’re trying to educate our studentsand anyone else who will listen thatthe history of the eastern forest wasnot one of complete eradication of ourold-growth forests. In fact, old-growthforests still survive in remote out ofthe way noncommercial places in theeastern United States. There areancient chestnut oaks that line the BlueRidge Parkway, the most heavilyvisited park unit in our country andperhaps the world. These short buttruly ancient chestnut oaks are notinterpreted whatsoever by the BlueRidge Parkway. In fact, they say quitethe contrary, that European mancleared all the Blue Ridge forests, andthat’s incorrect.

There are ancient forests along oursouthern swamps and

bayous, the old-growthbaldcyprus. There are old-growth dry-site hard-woods on the OzarkPlateau and the OuachitaMountains of the centralUnited States. And, ofcourse, the Cross Tim-bers, which is the western frontier ofupland deciduous forests merging withthe grasslands of the Southern Plains.There are old-growth forests in thepiñon juniper woodlands that cover alarge fraction of the western UnitedStates; there are dry-site stuntedconifer forests all over the RockyMountains that are incredibly old. Allof this is in addition to the coastaltemperate rainforests of the PacificNorthwest that have received so muchconservation attention, as well theyshould. I’m just arguing that ourconservation attention ought to includeall old-growth forests.

Our laboratory is part of the

University of Arkansas museum, andthe collections that we gather arepermanently in our lab, which is asatellite of the museum. We have anaccessioning system and we have acuration system, and I regard this asthe most important work that we do inthis lab. These are ancient forests thatwe visit and sample and as yourreaders well know, these are endan-gered forests and they are beingdestroyed.

We are collecting a naturalarchive of environmental

history, and these archives are beingdestroyed. Our libraries are burningand being chainsawed. We havecollections here from old-growthbaldcyprus sites from Georgia thathave since been cut down and nolonger exist.

So even though I trust the conser-vation movement will protect a greatdeal of our ancient forests, inevitablywe’re going to lose some too. We’regoing to lose a lot, and so thesecollections become I think increas-ingly important to the future.

Plus, our techniques of extractingclimate information are pretty rudi-mentary. They are highly statistical,highly quantitative, but we’re basicallyjust measuring the width of the annualgrowth ring. There’s a lot of additionalinformation regarding the environmentthat is locked up in the wood itself, inthe chemistry of the wood and theisotopic composition of the wood, in

the density changes of the wood; wehaven’t explored that, but futurescience will. So these records, thesesamples that we’ve acquired areimportant to the future.

ER: What were you responding to inyour letter to Science1?

DS: I was responding to an article inScience magazine by Anne SimonMoffat, who is a writer in the newssection for Science magazine, and shewas reporting on an article by a groupof scientists, titled “Searching forLeverage to Conserve Forests.2” I wasnot in any way minimizing the impor-tance of that article. Jesse Ausubel haswritten me and told me that he agreeswith my viewpoint here. Their point inthe article is that there’s been atremendous amount of reforestation in

this country due to greaterproductivity of industrialforests and decliningdemand for wood. So whywould we be cutting ourlast remaining old-growthforests when we’ve got allthese other industrialforests? We should be

using them. The regrowth of forestsshould alleviate the pressure on ourlast remaining old-growth forests.

I was simply emphasizing thedistinction between these re-grownindustrial forests, the mongrel succes-sional forests, introduced eucalyptusforests, and the wall-to-wall Douglasfir plantation forests that are not at alla suitable substitute for the nativebiodiversity of our ancient forests.They are crops basically. That’s thesimple point of my letter. Our nativeold-growth forests that remain are stillundergoing enormous strain and stressbecause of economic greed, because ofregional air pollution, because oflandscape change, even because of

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conservationists buying houses in rurallands. We are all at times contributingto old growth destruction. It’s not justsome evil corporation, it’s the growthof our society, and I believe we shouldbe careful to identify and protect ourfinal few ancient forests throughoutthis country.

Literature Cited:

1 Replacing Ancient Forests 1999Science 283: 34

2 Wernick, I.K., P.E.Waggoner, andJ.H. Ausubel. 1998 Searching forleverage to conserve forests. Journal ofIndustrial Ecology 1:125-145

Rapid Thinning ofSouthern Greenland’sIce Sheet

Introduction:

The Greenland ice sheet is about600 miles long, 300 wide, and 2 milesthick in some places. NASA-fundedaerial surveys of the southern part ofGreenland's ice sheet were conductedin 1993 and again in 1998. Thesurveys found that the lower altitudereaches of east coast outlet glaciers arethinning at about one meter per year.While some parts of theice sheet had increasedin thickness, overall thesheet has gotten thinnerin the last five years,losing about forty cubickilometers of ice1. Thistranslates into about onemillimeter of sea levelrise. We spoke withWilliam Krabill, one of the authors ofthe report, about the Greenland survey.

ER: Professor Krabill, what is yourtraining?

WK: I graduated from college aboutthirty years ago with a degree in math.I went to work with a group of

engineers helping them look at radardata and then I switched over toworking on remote sensors fromaircraft. Fairly early on I got in on thedevelopment of lidar, where you put alaser system in an airplane and youpoint it down at the Earth and map thetopography of the ground.

For the first few years the problemwith this technology was knowingwhere the airplane was when you tookthis wonderful laser data. Then theGlobal Positioning System came alongand we extended that technology intothe airplane in the late 1980s and early1990s developing the GPS to go along

with the precise laser ranging.We had one of the first papers in

using this mode of GPS, which somepeople call kinematic GPS or carrierphase tracking in the Journal of theInstitute of Navigation in 1987 wherewe had a GPS receiver on the airplaneand one on the ground.

Then we convinced the people atNASA who were interested in doing

polar research that this combination ofairborne laser ranging and kinematicGPS, could make meaningful mea-surements of polar surfaces, in moni-toring the great ice sheets that may ormay not be reacting to global climatechange.

Starting in the late 1980s NASAsaw the utility of this application andprovided the funding that allowed usto do what ten years later turned out tobe a useful thing.

ER: Was it published in Sciencebecause this is a technical innovation?

WK: I think the reasonthat Science picked up onit is they have beenclosely watching thetechnologies that aregiving indication ofclimate change. Scienceas you know, is one ofthe most astute journals,and one of the areas that

they’ve chosen to target is monitoringand looking for whatever signals arearound, either the ice cores, or theocean bottom core samples, and all theother studies that might lead us to abetter understanding of climatechange.

ER: How big is the Greenland icesheet?

NOAA has an excellent Websitedevoted to ENSO atwww.ogp.noaa.gov/enso/

See also: Stahle, D.W., Cleavelenad,M.K., Blanton, D.B., Therrell, M.D.and D.A. Gay. 1998 The Lost Colonyand Jamestown Droughts. Science280:564-567

Greenland is the second largest ice sheet inthe world... about 600 miles long, about 300

wide and two miles thick in the middle.

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WK: Greenland is the second largestice sheet in the world, the first beingobviously Antarctica. Greenland isabout one-seventh the size of Antarc-tica, but still substantial. It’s about 600miles long and about half that width,and the ice sheet is two miles thick inthe center.

ER: That’s a big ice cube.

WK: Yes. It’s a big ice cube that sitsup there and nicely buffers globalclimate change, and it expands andretracts over millennia as globalclimate changes. One way to think ofit is that twenty-three centimeters ofice thinning in Greenlandwould raise sea level onemillimeter globally.

One millimeter ofglobal sea level change isdifficult to measure. Ifyou’re measuring sealevel relative to the landmass, you don’t know ifthe land mass is going up or down bythat much. On the other hand, twenty-three centimeters of ice sheet change isrelatively easy to measure.

That’s why look at Greenland: two-thirds of the population of the

world lives in coastal communities. Ithink the coastline of the U.S. alone isestimated to be worth 3 trillion dollars.So if sea level is rising substantially,it’s of interest to the world’s govern-ments.

ER: Why did you choose Greenland?

WK: Greenland turns out to be fairlyeasy to get to with an airplane, unlikeAntarctica. There are two airports thatwe can operate a large aircraft from togo and make these measurements,which makes it logistically a reason-able thing to do. NASA has one P3

Orion aircraft. For years and years itwas sub chaser aircraft, the UnitedStates would launch P3s continuouslyto try to detect and track Russian subs.They have long legs and enough spaceon board to be a good remote sensingplatform. NASA has one of theseplanes, and it just so happens it’sphysically located at the same facilitywhere I work, here at Wallops Island,Virginia. It was the obvious airplane touse up in Greenland because it can getto any point in Greenland and makemeasurements and then get backhome, unlike Antarctica. Antarcticahas only one place where an airplanelike that can go in, and being seven

times the size of Greenland, you justcan’t get your arms around it the wayyou can Greenland.

ER: How did you conduct the survey?

WK: After a proof of concept missionin 1991, we devised a series of flightlines that effectively sampled the icesheet in the southern half of Greenlandand the drainage basins associatedwith the major glaciers. We flew thatset of flight lines; then the next year,1994, we went back up and did thesame thing for the northern part, whichis somewhat larger than the southernpart. We sampled some other areas inthe intervening years, and then lastsummer went back up to Greenlandand resurveyed all the lines that weflew in 1993, about 22,000 kilometersof track line. That’s the set of flight

lines that were used to work up thedata. We color-coded the elevationchanges by differencing the 1998 datafrom the 1993 data and our data is ofan accuracy of the two-centimeter-per-year-level.

ER: That kind of accuracy is astound-ing.

WK: That’s right, considering we’rehopping over the ice sheet at 1,400feet above the terrain, and we’re as faras a 1,000 kilometers away from ourhome base, where the fixed GPSreceiver is, and we’re still getting thatprecision in our measurement.

ER: What did you find?

WK: We saw enormouschanges along the east coast.Very much a surprise toeveryone.

It’s quite a ruggedarea. Greenland is sort of aflip of the United States: the

west coast of Greenland has moreundulating lower relief, more weath-ered small mountains, whereas the eastcoast of Greenland is like the RockyMountains, very rugged, taller fea-tures. In parts of that area you fly overand see a Grand Canyon, then anotherGrand Canyon, then another GrandCanyon. It’s incredibly rough, and it’sa place where a lot of the great icesheet is penned from escaping bymountains.

And yet, for reasons that areunknown, this whole area is showingsignificant thinning, as much as twometers per year in a couple of theoutlet glacier areas. That’s a total often meters change in the last fiveyears; it’s a big signal, and it extendswell inland from the edge. It isn’t justthat the ice is falling off the edge,

... the southeastern area is showing significant... the southeastern area is showing significant... the southeastern area is showing significant... the southeastern area is showing significant... the southeastern area is showing significantthinning, as much as two meters per year... tenthinning, as much as two meters per year... tenthinning, as much as two meters per year... tenthinning, as much as two meters per year... tenthinning, as much as two meters per year... ten

meters change in the last five years... and itmeters change in the last five years... and itmeters change in the last five years... and itmeters change in the last five years... and itmeters change in the last five years... and itextends well inland from the edge.extends well inland from the edge.extends well inland from the edge.extends well inland from the edge.extends well inland from the edge.

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something’s causing these glaciers tocreep faster towards the ocean.

I’m not a glaciologist, I’m thetechnologist behind all this, but we’veshown this data to glaciologists. Dr.Robert Thomas who recently retiredfrom NASA and is working with uspart-time, his theory is that the glaciersare creeping faster because melt wateron the surface runs down the cracks tothe bottom of the glacier and itlubricates the bottom of the glacier,and therefore the glacier creeps alongat a faster rate. That’s his theory.There’s no way to go down there andprove such a thing but that’s theglaciological explanation for what’staking place.

ER: Has the overall massof the sheet declined?

WK: Yes. If we integratethat whole survey it turnsout to be a net loss ofabout eight cubic kilometers per year.I haven’t done the math to see whateight cubic kilometers spread outacross the world’s oceans is, but it’s asmall number. So we’re not takingabout an extreme situation. It’s notanything that’s going to worry any ofus in our lifetime, but I think that themain thing is that it warrants continuedmonitoring because if it accelerates, itwill be of concern. It’s not clear whatwe can do about it, but at least weought to know about it, and so that’swhy we’re advocating continuedmonitoring of the ice sheet.

ER: Did parts of the ice sheet getthicker?

WK: You can tell from our surveymap that we did observe some thicken-ing. It’s very small, maybe on theorder of ten to fifteen centimeters peryear. The speculation is that may be

associated with increased precipitationbecause as the warmer air travelsfarther north it can hold more moistureand then eventually dump that mois-ture in the form of snowfall up on thetop part of the ice sheet. And sothere’s slight thickening that we canobserve there.

ER: Why didn't the satellites see thisthinning?

WK: The problem with doing thiswork with a satellite instrument,particularly satellite radar, is that thefootprint is so large — it’s on the orderof a kilometer — that it only gives

reliable answers when the topographyis smooth and flat. As soon as you getany undulations or significant slopes,such as you would see on the edge ofthe ice sheet, then you get data backthat’s very difficult to work with. Sothe satellite information only showedthe slight thickening that’s taken placein the center part of the ice sheet and itdidn’t see any of this increasedthinning taking place that the aircraftdata was able to see.

ER: Would it be possible to use laserranging technology in Antarctica usingsatellites?

WK: Yes. That’s in the works rightnow. NASA will put a laser altimeteron a satellite and launch it in the year2001. It will have much better charac-teristics for the footprint problem thatthe radar altimeters had, it will have a

seventy-meter footprint. But still whenyou get down near the snout of aglacier, seventy meters is a fairly largefootprint. Whereas from the airplanewe can put down a one-half-meterspot. So I think there’s still a role forus to play. Plus, we will be asked to dothe calibration and validation for thesatellite sensor.

We should have the means formonitoring what’s going on in Antarc-tica by using the satellite data. Theproblem is, the satellite has only got athree-year design lifetime. Peoplehope it’ll last longer than that, but youcan’t guarantee it. And that’s a small

snapshot interms of thevariability ofone melt seasonto another.

ER: Then wehave to put up

another satellite to continue themeasurements.

WK: To the tune of 50 or 100 milliondollars. The nice thing about theaircraft experiment is I can go up toGreenland twice a year for the nextfifty years for the price of one satellite.But it is tough to do what we do inAntarctica. You can go into McMurdofor about one month, the month ofNovember, and we could maybe reachat most one third of Antarctica. It’slogistically a terrible place to work.

Literature Cited:

1 Rapid Thinning of Parts of theSouthern Greenland Ice Sheet. W.Krabill, E. Frederick, S. Manizade, C.Martin, J. Sonntag, R.Swift, R.Thomas, W. Wright, J. Yungel. 1999Science 283:1522-1524

One theory is that the glaciers are moving fasterOne theory is that the glaciers are moving fasterOne theory is that the glaciers are moving fasterOne theory is that the glaciers are moving fasterOne theory is that the glaciers are moving fasterbecause meltwater runs down to the bottom of the glacierbecause meltwater runs down to the bottom of the glacierbecause meltwater runs down to the bottom of the glacierbecause meltwater runs down to the bottom of the glacierbecause meltwater runs down to the bottom of the glacier

and lubricates it and therefore it creeps at a faster rate.and lubricates it and therefore it creeps at a faster rate.and lubricates it and therefore it creeps at a faster rate.and lubricates it and therefore it creeps at a faster rate.and lubricates it and therefore it creeps at a faster rate.

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Introduction:

The greater prairie chicken,Tympanuchus cupido pinnatus, is agrassland-dependent bird that formerlynumbered in the millions throughoutthe Midwest. Now, its population andhabitat are greatly reduced throughoutits former range. Illinois for example,was originally 60 percent suitablehabitat, but today less than 0.01percent of the state’s area is suitableprairie chicken habitat. In the 19th

century there were several millionbirds in the state; by 1962 there wereabout 2,000 birds scattered in patchesin the southern part of the state; by1994 about 46 birds remained in tworemnant populations in Jasper County,Illinois, 640 kilometers away from thenearest viable population.

The eastern subspeciesTympanuchuscupido cupido, alsoknown as the heathhen, has beenextinct since 1931,and Attwater’sprairie chicken,Tympanuchuscupido attwateri, which is restricted toTexas, is near extinction.

If one were to write an instructionmanual on how to drive a species toextinction, the first order of businesswould be to deprive it of places to liveand reduce the population size. Theoryand practice tell us that there is a

minimum number of individuals belowwhich a population is not likely toendure. One of the main reasons isinbreeding depression, whereby adultsare less likely to produce viableoffspring, and the offspring that areborn are less likely to survive andthrive.

In 1992 prairie chickens werebrought into Illinois from outsidepopulations, and both the fertility ofeggs and the success rate of hatchingincreased, indicating there was indeeda genetic component to the long termdecline of the population.

We spoke with Dr. Jeffrey Brawnabout this project and how it applies toconservation efforts in general1.

ER: Dr. Brawn, what is your training?

JB: I got my Ph.D. at NorthernArizona University in Flagstaff, and Igot a master’s at the University ofMissouri. I’m an associate professionalscientist with the Illinois NaturalHistory Survey, and I’m also affiliatedwith the University of Illinois inChampaign-Urbana. I’m a populationecologist but I also deal with conserva-tion genetics, habitat loss and the

effects of fragmentation.

ER: Was this prairie chicken work anongoing operation when you came tothe Survey?

JB: That’s right. When I started towork at the Survey eight years ago,Ron Westemeir wanted some statisti-

cal analysis on some of his data. Hehad years and years of data and it wasobvious the prairie chickens insouthern Illinois were decreasing; thehatch rates were decreasing on theprairie chicken sanctuary, which isnow on one relict population in JasperCounty.

He had been thinkingfor a while that they may besuffering inbreeding depres-sion because the eggsweren’t hatching at any-where near a normal rate.With the eggs not hatching

and the population numbers goingdown, the state was getting concerned.They had put a considerable invest-ment into maintaining the prairiechicken in Illinois. We used to be aprairie state, and ours is the onlynatural population of the greaterprairie chicken east of the Mississippi.

I had had some training in genetic

In 1810 there were an estimated 2 million prairieIn 1810 there were an estimated 2 million prairieIn 1810 there were an estimated 2 million prairieIn 1810 there were an estimated 2 million prairieIn 1810 there were an estimated 2 million prairiechickens in Illinois; by the early 1990s they werechickens in Illinois; by the early 1990s they werechickens in Illinois; by the early 1990s they werechickens in Illinois; by the early 1990s they werechickens in Illinois; by the early 1990s they were

down to almost single digits.down to almost single digits.down to almost single digits.down to almost single digits.down to almost single digits.

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Environmental Review

analysis of populations, but we alsohad another colleague here (KenPaige, who is on that paper), who ran agenetics lab. And as it turned out, Ronhad collected and saved quite a bit oftissue from roadkills and chicks andwhatnot over the years, and so thatgave us an idea that maybe we shouldstart analyzing the tissue to see if therewas a genetic problem in this popula-tion.

At the same time the state wassaying they wanted to bring in birds tobuild up the population. But we wereconcerned about bringing in birds untilwe knew what the genetic profile ofthe population was. We were afraidthat since the Illinois population hadbeen isolated so long thatthey may be a subspeciesor genetically unique, andwe didn’t want to breedthat out by bringing inother birds.

It turns out thatwasn’t the problem.When the data first startedcoming in it was obviousthat the big difference between theprairie chickens in Illinois and largerpopulations in Nebraska and Kansaswas that the genetic diversity of thebirds was much lower in Illinois. Itwas also clear that the eggs werehatching at a low rate compared tolarge populations, or even compared tothe Illinois populations in years past.

Other studies have shown thatwhen birds are suffering from inbreed-ing, one of the things that tends todecline is the hatching rates. In ourpopulation the eggs weren’t fertilizedor they didn’t develop correctly.That’s fairly common when you get aninbreeding situation.

So while we had quite a bit ofevidence that inbreeding was occur-ring, the state started to bring in birds.The thinking at the state DNR was,we’re going to lose these birds, we’vegot to do something, and it’s better tohave some prairie chickens with someIllinois stock in them than have noprairie chickens at all. So they broughtin the birds, and they were absolutelycorrect.

We took blood samples from allthe birds we brought in, so we knewthe genetic constitution of the popula-tion that we introduced. When the newbirds started to breed, some of themhybridized with the Illinois birds, andthe hatching rates went back up. Theyrebounded significantly. One previous

year the hatch rate was around 30percent, another it was around 70percent, which are both way too low.When the new birds were brought in,the hatching rates went up to above 90percent.

That was strong evidence that itwas the genetic constitution of the

population that was responsible for thelow hatching rates. The alternativeexplanations were that there might besomething in the environment, atoxicological problem or some disease.But if you bring in new blood into thepopulation and use the same environ-ment, you’re actually doing a test tosee whether it’s the environment orsomething intrinsic to the birds. Our

results pretty clearly showed that itwas something intrinsic to the birds.

ER: How does this relate to habitatloss?

JB: The big villain in this was habitatloss and habitat fragmentation. Prairiechickens are tightly associated withgrassland or prairie habitat. They likegrasslands, they like expansive largeareas without trees. They don’t evenlike to see trees.

They can go about some of theirbusiness in an agricultural setting;they’ll feed in a soybean field or in acorn field, but that’s not sustaininghabitat for them. They need nativegrassland, and that became smaller and

smaller in Illinois. We’velost over 99 percent of ournative grasslands here.

In 1810 there were anestimated 2 million prairiechickens in Illinois; by theearly 1990s they were downto almost single digits. In theJasper County population it

was certainly less than fifty and maybeas low as ten birds. And all the geneticdiversity that they could have waswithin that tiny population. Thereweren’t any other birds periodicallycoming in, there was no gene flow intothat population. In larger populationsyou’ll get some dispersal among areasand the birds don’t become demo-graphically isolated, but this JasperCounty population basically func-tioned as an island. Because it hadsuch small numbers it went through agenetic bottleneck, and what comesout of a bottleneck is less diversitythan what went into it.

ER: What’s the minimum populationsize to avoid that?

... the big difference between the prairiechickens in Illinois and larger populations inNebraska and Kansas was that the genetic

diversity of the birds was much lower in Illinois.

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Environmental Review

JB: Usually the minimum number thatyou see published for a bird populationis 500. That’s an estimate. But withprairie chickens that number isprobably even higher because prairiechickens are a lek breeding specieswhere two or three males in a smallpopulation will contribute to most ofthe fertilizations for that year. Thealpha and the beta male do all themating, so even if they have a lot ofmales there and quite a bit of geneticdiversity, many of thosemales aren’t contributingto the population.

ER: What is a lek?

JB: A lek is an arenawhere males congregate,and then the femalescome in and chooseamong those males. Thealpha male usually hasthe best place in the lek,and the females willprefer him. They are alsocalled booming grounds.The booming is themales' display: theyinflate their throat sacksand make a noise thatcan travel for a longdistance. That’s whatattracts the females to thelek. They don’t neces-sarily use high ground. Itmay be that they just pick a placewhere sound can travel well. This isIllinois, so we’re not talking abouthilltops, we’re topographicallychallenged here.

ER: So it depends on how many leksthere are rather than how many birds.

JB: Right. And this population wasdown to one or two leks in the early1990s, so one or two males were

basically doing all the fertilizing, andafter a while these birds start to get alittle bit more related to one anotherand start to develop some inbreedingproblems.

ER: Illinois used to be a prairie state,now it’s a corn field state.

JB: Yes, we call it the corn fielddesert. I’ve been in Illinois for eightyears, and for what little habitat we

have left I’ve never seen more interestin saving it or conserving it or restor-ing it. It’s a pretty neat place that way.The more you lose, the more you careabout it.

ER: And there are still some wonder-ful places there.

JB: Oh, yes. We have a national forestin the southern part of the state, andthe Forest Service has just started thenew Midewin National Grasslands upwhere the Joliet Arsenal used to be.You never know, down the road wemay be able to get prairie chickens inthere.

When we moved these birdsaround to genetically manage them,

there are a couple lessonsthere: one is that it canwork if we want toalleviate inbreeding. Butwe need to be cautious ifit’s an isolated populationif bring in animals fromelsewhere because that canactually be counterproduc-tive.

ER: In what way?

JB: We had the luxury ofhaving the demographicpopulation data that therewas an inbreeding prob-lem. Many places don’thave thirty years of data torely on. We had also donethe genetic analysis toknow that if we bring inoutside birds we’re notswamping out a subspe-cies. We had a lot of

information at our disposal thatallowed us to go ahead, and the statevery wisely made the decision to say,Let’s do it.

I’m afraid that people are going tocome away from this thinking everytime we’ve got a small populationwe’ve got to manage for inbreeding.We should only try to alleviateinbreeding where we know we have it.

... booming is a male's display: they inflate their... booming is a male's display: they inflate their... booming is a male's display: they inflate their... booming is a male's display: they inflate their... booming is a male's display: they inflate theirthroat sacks and make a noise that can travel for athroat sacks and make a noise that can travel for athroat sacks and make a noise that can travel for athroat sacks and make a noise that can travel for athroat sacks and make a noise that can travel for along distance. That's what attracts the females...long distance. That's what attracts the females...long distance. That's what attracts the females...long distance. That's what attracts the females...long distance. That's what attracts the females...

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Environmental Review

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What You Need to Know About Creation-What You Need to Know About Creation-What You Need to Know About Creation-What You Need to Know About Creation-What You Need to Know About Creation-ism:ism:ism:ism:ism: Robert PennockBrown Tree Snakes Cause an EcologicalBrown Tree Snakes Cause an EcologicalBrown Tree Snakes Cause an EcologicalBrown Tree Snakes Cause an EcologicalBrown Tree Snakes Cause an EcologicalDisaster in Guam:Disaster in Guam:Disaster in Guam:Disaster in Guam:Disaster in Guam: Thomas Fritts

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Coral Reefs: The Rainforests of theCoral Reefs: The Rainforests of theCoral Reefs: The Rainforests of theCoral Reefs: The Rainforests of theCoral Reefs: The Rainforests of theOceans:Oceans:Oceans:Oceans:Oceans: Don HinrichsenRed Cockaded Woodpeckers:Red Cockaded Woodpeckers:Red Cockaded Woodpeckers:Red Cockaded Woodpeckers:Red Cockaded Woodpeckers: ProtectedYet Declining: Jerome Jackson

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Tracking Radioactive Waste in theTracking Radioactive Waste in theTracking Radioactive Waste in theTracking Radioactive Waste in theTracking Radioactive Waste in theFormer Soviet Union:Former Soviet Union:Former Soviet Union:Former Soviet Union:Former Soviet Union: Don Bradley andMichael FoleyExotic Species and Restoration ofExotic Species and Restoration ofExotic Species and Restoration ofExotic Species and Restoration ofExotic Species and Restoration ofDegraded Ecosystems: Degraded Ecosystems: Degraded Ecosystems: Degraded Ecosystems: Degraded Ecosystems: Wayne Richter

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Health Effects of Mercury in theHealth Effects of Mercury in theHealth Effects of Mercury in theHealth Effects of Mercury in theHealth Effects of Mercury in theEnvironment:Environment:Environment:Environment:Environment: Rita SchoenyIs American Agriculture Sustainable?Is American Agriculture Sustainable?Is American Agriculture Sustainable?Is American Agriculture Sustainable?Is American Agriculture Sustainable?Paul FaethWhat We Know About Climate Change:What We Know About Climate Change:What We Know About Climate Change:What We Know About Climate Change:What We Know About Climate Change:Jerry Mahlman

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AugustAugustAugustAugustAugust

Mechanisms and Consequences ofMechanisms and Consequences ofMechanisms and Consequences ofMechanisms and Consequences ofMechanisms and Consequences ofNitrogen Deposition: Nitrogen Deposition: Nitrogen Deposition: Nitrogen Deposition: Nitrogen Deposition: Robert Howerth andPamela Matson

How to Think About Nature: The WisdomHow to Think About Nature: The WisdomHow to Think About Nature: The WisdomHow to Think About Nature: The WisdomHow to Think About Nature: The Wisdomof Aldo Leopold:of Aldo Leopold:of Aldo Leopold:of Aldo Leopold:of Aldo Leopold: Estella Leopold

SeptemberSeptemberSeptemberSeptemberSeptember

Is Sustainable Development a Myth?Is Sustainable Development a Myth?Is Sustainable Development a Myth?Is Sustainable Development a Myth?Is Sustainable Development a Myth?Michael SouléConservation Planning Based on EntireConservation Planning Based on EntireConservation Planning Based on EntireConservation Planning Based on EntireConservation Planning Based on EntireEcoregions:Ecoregions:Ecoregions:Ecoregions:Ecoregions: Gordon Orians

OctoberOctoberOctoberOctoberOctober

Rebuilding Wetlands:Rebuilding Wetlands:Rebuilding Wetlands:Rebuilding Wetlands:Rebuilding Wetlands: Joy ZedlerAre We Taxing the Right Things?Are We Taxing the Right Things?Are We Taxing the Right Things?Are We Taxing the Right Things?Are We Taxing the Right Things? AlanDurning

NovemberNovemberNovemberNovemberNovember

A Judge Orders Wolves Removed fromA Judge Orders Wolves Removed fromA Judge Orders Wolves Removed fromA Judge Orders Wolves Removed fromA Judge Orders Wolves Removed fromYellowstone: Yellowstone: Yellowstone: Yellowstone: Yellowstone: Robert Pletscher and RobertKeiterSustainable Development in the Tropics:Sustainable Development in the Tropics:Sustainable Development in the Tropics:Sustainable Development in the Tropics:Sustainable Development in the Tropics:Richard Rice

DecemberDecemberDecemberDecemberDecember

Sea Otters as Keystone Predators:Sea Otters as Keystone Predators:Sea Otters as Keystone Predators:Sea Otters as Keystone Predators:Sea Otters as Keystone Predators: JamesEstesTree Species Diversity in CommerciallyTree Species Diversity in CommerciallyTree Species Diversity in CommerciallyTree Species Diversity in CommerciallyTree Species Diversity in CommerciallyLogged Tropical Forests:Logged Tropical Forests:Logged Tropical Forests:Logged Tropical Forests:Logged Tropical Forests: Charles Cannon

Volume Six Number SixJune 1999

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ER: Inbreeding wasn’t what waskilling off the California condor.

JB: No. There can be all sorts ofreasons why an animal is going down.Sometimes if you mix stocks it can becounterproductive. If we had takenTexas prairie chickens that are adaptedto hot weather and maybe breed at acertain time of the year — this isarbitrary example — and brought themup and they interbred with the Illinoisbirds, the resulting hybrids may nothave been able to handle the Illinoiswinter. Or perhaps they would havegone into breeding condition andstarted booming in February whenthey were going to have an ice stormin March. So we need to be carefulabout this kind of thing. This turnedout to be a success story and we’rereally pleased, but there’s also a caveatassociated with this.

Literature Cited:

1 Tracking the Long-Term Declineand Recovery of an Isolated Popula-tion. RL Westemeir, JD Brawn, SA

NEXT MONTH

SETTING UP MARINERESERVES:

CRAIG DAHLGREN

LONG DISTANCEEFFECTS OFEL NI ÑOS:MICHAEL

McPHADEN

THE DEAD ZONEIN THE GULF OF

MEXICO:NANCY RABELAIS

Simpson, TL Esker, RW Jansen, JWWalk, EL Kershner, JL Bouzat, KNPaige 1998 Science 282:1695-1698

Volume Six Number SixJune 1999