cc  >> Nadia Dominguez: Thank you  for joining me for Wednesday  Nite at the Lab at UW-Madison  Biotechnology Center.  Tonight, we welcome Professor  Joe Mason at the Department  of Geography at UW-Madison.  Dr. Mason earned a BS degree  in natural resources  at UW-Stevens Point,  an MS in soil science from  the University of Minnesota,  and his PhD from UW-Madison.  In 2003, he became a faculty  member here at UW-Madison, and  over the past 20 years he has  studied wind-blown sand dunes  and dust deposits of the  Midwest, the Great Plains and  northern China.  So please join me in welcoming  Dr. Joe Mason to Wednesday Nite  at the Lab.  [APPLAUSE]  >> Joe Mason: I want to thank  the organizers for inviting me  to Wednesday Nite at the Lab  and also thank all of you  for coming out.  It occurred to me on the way  over here that most of what I'm  going to talk about tonight  really isn't in the lab unless  the lab is the whole world out  there.  I'm going to talk mostly about  research I've done over the last  four or five years in northern  China at kind of the margin of  the deserts that occur right at  the boundary between China and  Mongolia.  And I want to make sure to  remember to acknowledge the  source of funding for this  research and also to point out  this is really a collaborative  project between two universities  in the US, UW-Madison and  University of Nebraska, and the  University in China, and the  research is funded by the  National Science Foundation of  the US and also the National  Science Foundation of China.  The other thing I wanted to say  while this slide is up is this  is really a kind of ground up  collaboration. 

 This is a group of researchers  from different countries and  different universities who found  they had interests in common in  things like sand dunes and put  together a project to study  these in China.  So my involvement in this  project really stems from very  similar work I did for many  years in the Great Plains in  Kansas and Nebraska looking at  changes in the activity of  wind-blown sand dunes, how  mobile are they or how stable  they are under vegetation.  Also looking at prehistoric  dust storms and trying to put  together a geologic record, a  record from geologic evidence of  how these processes of sediment  moving in the wind have changed  over long periods of time, over  10,000 years or more, and how  that's related to change in  weather and climate, especially  drought.  So during the course of this  research in the Great Plains,  I, first of all, got to know  Jim Swinehart who was involved  in this project in China and a  bunch of other friends in  Nebraska, but also the lead  author of this paper that was  our main product of this project  was from China, as you can  probably guess from his name.  My PhD student here who then was  a big help in putting together  links with a researcher in  China, his former adviser at  Nanjing University.  So that then led to, eventually,  a major project looking at the  same kind of issues in northern  China.  So over the course of the last  four or five years, we've done a  lot of work at the desert margin  in northern China and also eaten  a lot of good meals in the field  like you see here.  What we've got in this photo,  first of all, Jim Swinehart from  Nebraska is over here on one  side and our main collaborator  in China from Nanjing University  is on the other side of me and  then in the background we have  all the staff of this restaurant  at a small town in inner  Mongolia who was just really  delighted to have the sand dune  experts come and eat in their  restaurant.  So these are the senior  personnel of the project, and  then I also want to acknowledge  a bunch of grad students who  really worked very hard on this  entire project including my  student here at Madison,  in the middle and several other  grad students who put a great  deal of effort into this project  and also shared in the good  meals during field work.  This is at a little truck stop  out in the middle of a dune  field at the edge of the desert  in northern China. 

 Just a more personal  acknowledgement, I wanted to  mention that one of my big  motivations for trying to get to  China and work on something  there has to do with my family.  My mother is on the right.  She taught in China in the 1980s  at a university there.  And she's actually sitting in a  lab where her father, my  grandfather taught science in  south China in the 1930s and  '40s.  So I'm the third generation to  work in China in my family.  So where I've done most of my  research is in the northern part  of China.  Everything I'll talk about today  is in this area in the northern  part of China.  This is Mongolia up to the  north, and what we're looking at  here is a map produced from  satellite images that have been  processed to reveal the  greenness of vegetation.  So where it gets greener on this  image, there's more green  vegetation.  And most of China is relatively  green in the south, but when you  get up here toward the north  you're getting toward the edge  of the Gobi Desert and so it  becomes much less green. 

 And that's really the area that  we're working in, and we're  interested in that particular  area for a number of reasons but  one has to do with the fact that  it's right at the edge of what  we call the monsoon circulation  or just the summer monsoon.  And this is a textbook map of  the monsoon.  To make a long story short, what  happens in Asia with the monsoon  is that during the summer the  winds blow from the south or  southwest and carry moisture  into India and southern China,  and in the winter the winds blow  the other way so it's dry, but  the areas that we're working in  this project are right at the  northern limit of these monsoon  rains.  And so just to look at one more  map of Asia as a whole, this is  colored to represent  precipitation in July and where  it's blue there's a lot of  precipitation, where it's green  or yellow not much at all.  And so this is that limit of the  monsoon rains going right across  northern China here.  And that's where our study areas  are located.  Because you're at the limit of  the monsoon rains there, what  you have in many places along  that boundary, that boundary  between blue and green in the  map, is areas of wind blown  sand.  And they're often much like this  in that some of the sand is  covered with vegetation like you  see on the left.  Some of it's completely bare of  vegetation.  So what I'm going to refer to as  mobile dunes is what you see on  the right here. 

 On the left is stabilized dunes,  and, because this is an area  right at the fringe of where the  monsoon rains get to in the  summer, it doesn't take much to  push these sand dunes from being  covered with vegetation if it's  a little wetter or to being bare  and mobile if it gets a little  dryer.  There's other factors besides  the rainfall but that's one of  the big influences on these  dunes.  So I don't want to spend a long  time talking about our detailed  research questions.  We actually had quite a few  topics we were working on as  part of this larger project.  One of the things we wanted to  find out most basically is just  how has that mobility of the  dunes changed over time and is  it increasing or decreasing  today.  I often get asked about the idea  are the deserts on the march  here in northern China, are they  advancing towards Beijing, for  example.  I don't think they are at all,  actually, but that's one of the  questions we wanted to look at  in this project.  We're also interested in a very  long-term view going back from  decades to even millennia into  the past on how the mobility of  these dunes has changed.  We're also interested in what's  influencing the dunes besides  climate, things like human land  use, grazing animals and so on.  And eventually we want to try to  use the results of this project  to look at what may happen in  the future with projected  climate change over the next  century. 

 I won't say much about that in  this talk because I have plenty  to talk about looking back into  the past before we actually  start talking about predicting  the future.  So I have really two parts to  this talk.  One is looking back just over  the last four decades at changes  in the amount of mobile or  active dune sand.  So what I hope you can see here  is the dunes are partly covered  by vegetation in this case.  It's most of what you see here  is something called artemisia --  which is something like our sage  brush in the western US, it's a  related plant.  But in the background you have  dunes that are just completely  mobile.  So we want to look at how the  pattern of vegetation cover and  dune mobility has changed over  the last four decades.  And we actually have many study  sites all across the northern  part of China for this project.  When I first made this map, I  realized that our study sites  reached more than halfway to  Korea, which is here, to India,  which is here.  A long ways across Asia if  you've ever traveled in China or  in Asia in general. 

 Where these sites sit relative  to that map of greenness from  satellite images is shown here,  and I've also labeled our major  study areas.  So most of what I'll talk about  tonight has to do with the Mu Us  desert, these are Mongolian  names, Otindag dune field or  desert up here, something called  the Horchin dune field or desert  here.  I won't say much about the  Alashan dunes, that's really the  driest part of our study area.  And there the dunes are mobile  all the time.  So there isn't much change to  look at in that particular  region.  So before I talk about some of  our results, I need to fill you  in at least on a few of the  basic kind of principles of  studying dune processes that  have been put together over the  last 50 or a hundred years of  research on sand dunes.  One of the things that we know  pretty clearly is that there's  what we call a threshold of wind  speed.  So the wind speed has to  increase above a certain level  before much sand movement  occurs.  And when you have vegetation  cover on the dunes, that  threshold gets far higher.  So even a little bit of  vegetation can drastically  reduce the amount of sand  movement in the wind on a sand  dune. 

 There's a study in the Mu Us  region, one of our study areas  in China, actually right about  in the region of this photo and  this one, where they measured  the rate of sand movement and  estimated how much moves in a  year and it was 200 times  greater when you don't have  vegetation cover.  So the vegetation is really the  key and any influence that  climate or human activity has on  these dunes happens through the  vegetation, really.  I tried to come up with a  simpler version of this, but  this is really one of the basic  concepts that dune researchers  have used in recent decades.  This is an idea put together  been someone named Nick  Lancaster who has worked on sand  dunes all over the world.  And he argued that the mobility  of sand dunes is really  controlled by, what he called,  effective moisture which is the  ratio of the precipitation to  how much evaporation can  potentially take place.  That's really telling you how  much water is available to meet  the demand of plants for water.  So it's the effective moisture  available to plants.  So he said the mobility of dunes  is related to that ratio which  is the horizontal axis of this  graph, and the percent of time  the wind is above the threshold  to move the sand, that's the  vertical axis here.  And you can plot different dune  fields, based on their modern  day weather or modern day  climate, on this diagram.  And the ones that fall over here  with a lot of moisture and not  much wind should be inactive or  stabilized by vegetation. 

 The ones over here with a lot of  wind and not much water should  be fully active, not covered  with vegetation at all.  This doesn't turn out to work  very well in many parts of the  world, but it's a good start at  figuring out what controls the  activity of sand dunes.  Some other researchers, Dan  Moose and Vance Holliday, both  of whom had my position in the  Geography Department before I  got it, so there's a lot of  Madison connections here, they  argued that really the wind  doesn't matter much.  When they looked at dunes in the  US from the Great Plains to the  Colorado desert in California,  they think that everything is  controlled by effective  moisture.  So the wetter dunes are stable  or largely inactive, the dryer  dunes over here are largely  inactive and the wind doesn't  really matter.  To a good approximation, that  seems to be a more realistic  view of what's happening in  China because lots of what we  see in terms of how much  vegetation is stabilizing the  dunes or not stabilizing the  dunes seems to be related to  effective moisture, the ratio of  precipitation to potential of  apparition.  So where that ratio is really  low, when you're in a really dry  climate, the dunes have almost  no vegetation out in the Alashan  Desert, for example.  As we go toward wetter  conditions, we see much more  vegetation in general on the  dunes.  So in this region, the Mu Us  Dunes, the ratio is a bit higher  and there's a fair amount of  vegetation.  There's still some sand that  moves in among these shrubs when  the wind blows strong and hard  enough but these dunes are much  more stable. 

 And then when we get to the  wettest climate, our wettest  study area in this, the Horchin  Dunes, everything is covered  with vegetation in most of the  landscape.  So moisture, how much moisture  the vegetation growing on the  dunes is getting in a year seems  to be really one of the key  issues in how mobile the dunes  are.  But we know that that's not the  whole story.  We're not satisfied with saying  it's all moisture that  influences the vegetation.  We think possibly wind or maybe  other factors have something to  do with it.  Because we do have places where  it's relatively wet.  This is a relatively wet climate  but there's lots of mobile dunes  in this particular small area.  So it turns out that when we  looked at weather records from  near our study sites, there's a  sort of what I would call a  natural experiment that took  place over the last three or  four decades, since the 1970s,  that allows us to look at how  important wind is relative to  other factors in the climate.  And so this, I'm not going go  into the details of how this is  calculated, it's really kind of  a strange number, but there's  this number we call drift  potential or DP that's an index  of how much potential there is  for movement of sand by the  wind.  And we can actually get this  from weather station wind  measurements. 

 What it's really telling us is  how much wind would move in a  given period of time if there's  no vegetation cover on it.  So it tells us how much power  the wind has to move sand.  And there's a really strange  phenomenon that seems to be real  that's created what I'm calling  a natural experiment.  We looked at this number drift  potential for many weather  stations across northern China.  These are just a few examples  from a couple of our study  areas.  This drift potential has  decreased drastically, that's  the vertical scale on both of  these graphs, and the lines  wiggle up and down but they  generally drop off from 1973,  more or less when they start, to  a little bit after 2000.  This is a very large decrease in  the potential of the wind to  move sand in this region.  This actually is known to  meteorologists in China, and  there's a lot of concern about  this because they're putting up  all these wind power generating  stations across northern China,  and if the wind is actually  decreasing like this, the wind  power is decreasing, that means  much less energy can be  generated by some of these  stations.  So it's a major concern and it's  really recognized as a real  phenomenon, and it gives us this  idea of a natural experiment  because we can look at what  happened to the dunes when the  wind power decreased, when the  drift potential decreased over  this time period.  And what's even better, natural  experiments, in general, are not  very good compared to real  controlled experiments because  there's always variables that  you don't want to vary that are  a varying, but in this case the  moisture side is not changing  much. 

 So I know there's just a lot of  noise here but really  precipitation has gone up and  down in our study areas but  there's no real trend over time  since the 1970s unlike the wind.  So moisture is not really  changing in most of our study  areas.  This is just a few examples from  weather stations.  So what has happened to the  dunes over that time period?  And the answer is not much in  terms of a consistent trend in  one direction or another.  I talked about the deserts not  really being on the march to the  south.  And what's actually happened is  an increase in the mobility of  dunes in some places and a  decrease in others.  What we've done is used  satellite images, these are  readily available data from US  satellites now.  In the two images on the left  here, on the top and on the left  on the bottom, red means green  vegetation.  So where you see red, it's  really intensely green  vegetation.  Where you see kind of a dark  gray color is vegetation but  maybe not as green, so it might  be dormant grass or it might be  shrubs without a lot of leaves  on them, but it's vegetation  holding the dunes in place. 

 And then where you see this kind  of a light tan color here,  that's mobile sand dunes, that's  bare sand.  So we looked at satellite images  from sometime in the 1970s and  sometime around 2000 and  compared the change and we've  got that mapped on the right  here.  So where you see green, that's  where the dunes became more  stable, that's where more  vegetation covered the dunes.  Where you see yellow, that's  where the dunes became more  active.  And in some areas, the dunes  became more stable.  The desert is actually  retreating if you want to think  of it that way.  In other areas, the dunes became  more active.  And there's no consistent  pattern to this.  In many places there was really  very little change at all.  I think you can see, if you look  at this image in particular,  there's a big area that's  covered with vegetation here,  kind of this grayish-red color  in the middle of this image, and  on the right here by 2000 it's  become mostly mobile dunes. 

 Same thing up here.  Yeah?  >> What are those vein-like  structures?  >> Those are river valleys.  >> So are there actually flowing  rivers?  >> Yeah, there are.  This is one of the strange  things about sand dune fields,  even in deserts lots of the rain  that falls infiltrates down into  the groundwater and you have  flowing water where you don't  have it in the surrounding  areas.  You have lakes in many of these  dune fields.  So that's one of the kind of  unexpected things you find when  you go into desert dune fields  is lots of water, actually, down  in the groundwater or in the  streams.  So these are river valleys, and  this is an area that's active  sand in the past but now has  become stable.  So the change is going in both  directions.  And we looked at bigger areas.  These are maps of parts of three  major study areas. 

 There's lots of change in the  one on the left, the Mu Us dune  field, but it's in both  directions.  It's yellow in one part and  green in another.  So more active one place and  green another place.  The Otindag dune fields in the  middle kind of more trend toward  mobility but really patchy.  And then the Horchin dunes on  the far right there really  showed very little change at  all.  I'm not sure you can see any  color there at all.  So no real consistent pattern of  stabilization.  So the first conclusion is that  wind is not an overriding factor  here.  Wind power is really not one of  the major controls on the  activity of these dunes.  Because the trend is in both  directions. 

 If the wind were the main factor  we'd expect all stabilization  because the wind power has  decreased.  But it's going in both  directions and we can't explain  that with change in the wind.  We also can't explain this with  change in other climate factors  like moisture because remember  they didn't change.  So we need some other  explanation for why parts of the  dunes are becoming more active  or less active.  And this is where we get into  the whole problem with natural  experiments.  You can't control all the  variables.  So this is a photo I took from  an airplane flying home from  China in 2008.  And toward the lower right of  this image is mostly mobile  dunes.  That light colored area is  mostly mobile sand.  Toward the upper left is mostly  vegetation covered, and there's  a straight line between them. 

 That's a fence.  That's a fence line.  So there's more grazing on one  side and less grazing on the  other.  That's the only really  reasonable explanation of that  boundary that I know of.  So this is really, right on the  face of it, evidence of human  impacts on these dunes.  There are places where there's  probably been overgrazing,  grazing that's too intensive,  mostly sheep in this case, not  cattle, that decimated the  vegetation and made the dunes  mobile.  So that's one factor that's  causing this patchy change in  dune mobility.  But there's also big programs of  dune stabilization.  This is yet another complication  in trying to understand how  climate influences the dunes.  The Chinese government and the  provincial governments and so on  are sending out thousands of  people to put sticks in the  ground, for example. 

 These are rows of sticks.  They're not plants, they're rows  of stick stuck in the ground.  They reduce the wind speed near  the ground and make the sand  less mobile.  They don't allow the wind to  attack the sand surface.  So once you get these sticks in  the ground then vegetation often  comes in.  So some of the patches that  became stable since the 1970s  might be where this activity  worked, where this stabilization  project worked.  There's been lots of commentary  about the dune stabilization  programs that it's all a show or  it's kind of a waste of money or  a waste of labor anyway, I think  that there is some evidence that  it works in some areas, that the  dunes actually are being  stabilized significantly in some  areas, and that's also causing  some of the patterns of change  that we see since the 1970s.  One of the directions we're  going in next with this, that's  kind of where we're at this  point in terms of looking at  change over the last few  decades.  One of the things we're trying  to do now is extend that time  period a little bit farther into  the past and look at things at a  much more local scale.  So now we've got lots of  digitized declassified US spy  satellite photos. 

 These are beautiful photos.  Very high detail.  You can see individual trees or  shrubs sometimes.  And we've got those from the  early 1960s, and then we compare  them for satellite images from  2000 or even later, and we so in  this case there's a big patch of  mobile dunes here in 1962,  another one up here, most of  this view is stabilized by  vegetation with little patches  of sand.  Sorry.  In this 2000 image, most of the  area has now become mobile sand.  So there's actually been a big  change in dune activity.  The little red dots, if you can  see them, are places where we  actually made observations in  the field in 2008.  So we're also looking at ground  truth in these areas in 2008.  And these are really striking  because point A was stable  vegetation covered dunes in  1962, it's now become almost  completely bare sand. 

 Point B was stable vegetation  covered dunes in 1962 and it  still is.  It has very dense vegetation  cover.  Again, it's that artemisia,  the Ordos wormwood that grows  everywhere on these dunes.  So some areas have remained  stable throughout this time  period.  And we're hoping that if we look  at local cases like this in many  places across the study areas,  we can start to see patterns  that will point to particular  changes in land use or other  factors that caused some dunes  to become stable or some dunes  to become mobile over the last  few decades.  Or at least we'll have an idea  of where to look if we have to  go back out to the field to  actually do the research there.  All right, so the second part of  this talk really changes gears  in terms of the time period  we're talking about.  And I'll explain what those  white things are in a minute.  But this was really what we  spent most of the time in the  project on was trying to  understand changes in dune  mobility over the last 13,000  years or more, although we've  really got good data for just  the last 13,000 years.  And so what we do in this  project, this is where this  really isn't in the lab at all. 

 We go out across beautiful  striking landscapes in inner  Mongolia and other parts of  northern China, many thousands  of kilometers on the road in  this project, we get to sand  dune fields, and we often locate  our study sites using satellite  images, park the cars, you can  barely see them in the back  there, walk out across the sand  dunes, often several miles, and  look for study sites that will  contain where we can find  geologic evidence of past  changes in dune mobility.  And I'll try to give you a few  simple examples of the kinds of  things we're looking at to  determine when the dunes were  mobile, like you see here, and  when they were stabilized by  vegetation.  So we go out and dig a lot holes  in the ground and look at what  is exposed in the sand and  interpret it.  So this is really not very high  tech at all.  This is just very careful  observation of structures in the  dune sand that we've exposed in  a hole to try to determine what  processes were active there in  the past.  And I look the a this and I hope  this isn't my colleague Jim  Swinehart's passport that he's  leaving here in the field.  I don't think it was.  So this is one example of  something we can find looking at  structures of the sand in a hole  in the ground, very carefully  shaved off.  These are beds of sand that dip  down at an angle.  And they're certain other  characteristics we can see here. 

 But in the end, what we're  fairly certain we're looking at  in this case is a place where in  the past there was the what we  call the front end of the dune,  the down wind end of the dune,  the side of the dune away from  where the wind is blowing from.  And it will be this very steep  face that you see here, this  very steep slope that comes  along here.  If you've walked on dunes on the  beach, you've probably seen sand  avalanching down the face like  that.  That's the side that faces away  from the wind because the wind  blows the sand over the top and  it drops down the front.  And we're seeing that some time  in the past when we see beds  like this.  In fact, if we can date when  this sand was deposited, we can  actually tell which direction  the wind was blowing because  that face is always away from  the direction the wind is coming  from.  So that's some important  information.  Certainly this tells us that  there were mobile dunes when  this sand was deposited.  Another example, these thin  layers of sand, this is about a  foot high here, and these thin  layers or laminae of sand are  produced by ripples blowing  across a mobile sand surface  like this.  This has been established by  experiments and observations in  lots of parts of the world. 

 So we know that there was mobile  sand here.  And then these kind of worm-like  things that come down through  the wood grain appearance, those  are insect borrows.  So there was mobile sand but  there was enough vegetation  around to support a pretty large  community of insects living on  these dunes.  So maybe not completely barren  of vegetation.  So that's another kind of  evidence.  But the most important evidence  that we have of dune activity or  not or stability has to do with  something like this.  You can barely see it here  because we haven't dug it out  yet, but it's that dark ledge  across the upper part of the  image here.  This band right here.  When we dig that out, it becomes  clear that that is a buried  soil.  That's the top soil, the dark  organic matter rich top soil  that formed on a dune when it  was stabilized by vegetation. 

 So this was the land surface up  here, vegetation was growing on  this surface adding organic  matter, making a soil,  essentially, here.  So the dunes were probably quite  stable to have enough vegetation  to produce a soil like this.  And what we really have here  then is a sequence of events.  We have mobile dunes that  deposited the sand at the bottom  up to the top of that soil.  Then you had a period of  stability when the vegetation  covered the dunes and formed  that soil.  Then that soil was buried by  another period of dune mobility.  So we have a sequence of events  from mobile to stable to mobile  again.  And we can actually determine  when that happened by using a,  it's not quite cutting-edge  anymore because it's 15 or 20  years old now, but it's really a  key technique for this whole  area of research, and it's  something called optically  stimulated luminescence dating  of sand movement by wind.  It's actually the same principle  as radiation badges that people  who work with radiation have to  wear, and it records their dose  of radiation.  So what happens, the way we use  this is if with you can imagine  a sand grain sitting in a pile  of sand in the dune and it is  getting dosed with natural  radiation, there's always  natural radiation produced at  low levels by other sand grains  around this one. 

 So that sand grain is, one way  you can think of it, it's almost  getting damaged by the radiation  slowly over time.  So the longer it sits there, the  more it is affected by the  radiation and it acquires what  we call a luminescence signal  which means when you shine a  light on this grain in the lab  it will give off a little burst  of light itself.  That's luminescence, optically  stimulated luminescence.  And the longer it sits here and  gets dosed with radiation, the  bigger the pulse of light it's  going to give off when you shine  a light on it in the lab.  So that is very useful for us  because if the wind picks up  that sand grain at some point in  time and carries it through  sunlight it's going to give up  its luminescence signal.  It's going to be rejuvenated.  It's going to turn into a sand  grain that has no luminescence  signal to begin with when it  gets buried again.  So then it starts picking up  that luminescence signal again  over time, and we can tell how  long it's been since sand grains  were carried in the wind by  using this technique, by  measuring the amount of light  they give off in the lab.  So what we have to do is collect  samples, that's what those two  white dots are.  We're collecting a sample from  the dune sand without letting  any light get on it until it  gets in the lab, so it's in a  pipe. 

 That pipe has to get wrapped up  and shipped with a USDA permit  to the University of Nebraska  and it has to get analyzed  there.  And then we find out when the  sand was deposited, when the  sand was moving in the wind.  And I'm sorry these slides are  from another talk so there's  some code here.  KA, the way we talk about this  KA means a thousand years ago.  So, the sand below that soil is  4.97 KA or about 5,000 years  old.  The sand above it is about 2,300  years old.  We also did carbon dating,  radiocarbon dating on the soil  itself and that age falls right  in the middle.  So we can tell that there were  active dunes at this site 5,000  years ago and 2,300 years ago  and in between was stability.  And we've done that kind of  study at many sites across these  dune fields.  This is just a small selection  of many of the sites that we've  sampled. 

 And what we're seeing here, each  of these columns is the stack of  sediments that we saw at each  site when we dug out pits or dug  out road cuts or whatever.  So where you have a dark layer,  that's a soil, that means  stability.  Where you have light colored,  kind of light yellow or light  tan, is mobile dune sand.  And it's impossible, you really  have to summarize this  information somehow to make it  clear.  What I've done here is look at a  whole series of time slices,  four different periods in time  and whether there was active  dune sand, mobile dune sand or  stability with vegetation cover.  This image, we're looking at the  same area here in northern China  near Mongolia.  13,000 to 11,500 years ago  everything was active, there was  mobile sand everywhere.  Same thing 11,500 to 10,000  years ago, mobile dunes  everywhere.  Things started to get more  stable 8,000 to 10,000 years  ago.  A little bit of dark brown color  starts showing up here. 

 That's where we started to see  some soils.  And then by 6,000 to 8,000 years  ago there was really widespread  stability in vegetation cover on  the dunes.  So there are major changes over  the last 13,000 to 6,000 years  only, not evenly looking at the  period since 6,000 years ago, in  how much activity of dunes was  going on at this area in the  desert margin.  So if you want to talk about the  desert being on the march when  it really was advancing  southward was 13,000 years ago  or 11,000 years ago.  More recently, it's really been  stable, like 6,000 to 8,000  years ago, or just kind of  moving a little bit one way or  the other.  So this is long before there  were people grazing cattle here  or sheep, especially 13,000  years ago.  We believe these changes are  mostly related to climate.  And mostly related to moisture,  although we're not really sure  of that.  I talked about how wind probably  isn't a big fact, we think  moisture is a big factor, but we  haven't really had an natural  experiment on moisture yet to  test that.  So we think this is mostly  changes in moisture. 

 So it's dryer in these earlier  periods when there was lots of  mobility, wetter when there was  stability and soil formation.  So our conclusion at this point  is there were lots of mobile  dunes, dunes were mobile at many  sites between 11,000 and 8,000  years ago.  There were soils indicating  vegetation cover 8,000 to 3,000  years ago, more or less.  And this is actually really  surprising based on other  research on the past climate of  China and the monsoon.  And I apologize for not having a  simpler graph to show this.  I'll just try to give you my  crude explanation of this  research done by other people.  But the time that we find lots  of active dunes is right in this  period.  This is from the present day  back to 16,000 years ago across  this graph.  We find a lot of active dunes  around 8,000 to 11,000 years  ago.  This wiggly line is supposed to  represent how much monsoon  rainfall was received at this  place called Dunhuang Cave in  south China. 

 So where it's high, there's a  lot of monsoon rainfall; where  the wiggles get lower here, it's  dryer.  So in south China this was a  period of very high monsoon  rainfall.  So it was wet in the south, dry  at the desert margin in the  north.  So if you want me to say one  thing about climate change in  the future, there's lots of  projections that it will  actually get wetter in south  China because of a stronger  monsoon over the next century or  so, but that doesn't necessarily  mean it's going to get wetter in  these desert areas to the north  because looking at the past we  find it actually got dryer in  the north at the desert when it  was wetter in south China.  All right, so I just wanted to  end up with kind of a completely  different direction here and try  to leave you with the idea that  certainly we're nowhere near a  conclusion to this project in  the sense that we can really  explain everything about these  dunes or even most things about  these dunes.  This is an image of dunes in  northern China showing areas of  highly mobile dunes and  completely vegetation covered  dunes off to the right.  And when you look at a picture  like this or when you stand here  in the field and look at this  scene, you realize it's actually  all about the individual plants.  Whether the dunes are mobile or  active depends on how successful  these individual plants are in  moving out across the dunes and  getting themselves established.  So when we talk about response  of the dunes to climate or to  grazing or whatever, it's really  all about the individual plant  species here and how they're  responding to grazing or dry  conditions or strong winds and  whether they're successful in  colonizing the bare dune sand.  So we really need to look at the  individual plants and how they  respond to changing  environmental conditions. 

 That's really hard to do  logistically in remote areas in  China.  So what I'd like to do next is  do that project but in Wyoming  where I can get to very easily.  These are sand dunes in Wyoming  that look a lot like the dunes  in northern China.  They're partly active, partly  stable.  I know what the plants are here.  This is all a grass called  Indian rice grass that grows out  across these dunes and  stabilizes them.  And I'd like to do experiments  here on how individual plants or  plant species respond to  changing conditions so we can  understand better what really  controls the mobility or  stability of the dunes.  One of the things that's really  important in these dunes in  Wyoming, and I bet it's  important in China, is that the  first plants that come out on to  the bare dune sand are able to  fix nitrogen, they're able to  capture from the air and fix  nitrogen and then make that  nitrogen available to other  plants that move in following  them.  So I'm betting that the nitrogen  fixing plants are really the key  in understanding how they  respond to moisture or wind or  whatever.  So that's what I'd like to do  next if you want to know where  this research is headed. 

 But really where it's at right  now is kind of like where we're  at walking up this dune.  We're part way up and we're kind  of slipping back all the time.  Every step forward we're  slipping back a little bit as a  new problem arises.  But eventually we're going to  get higher up on the dune and  understand this really  interesting and beautiful  environment in northern China  and other parts of the world.  So that's it.  [APPLAUSE]