Category Archives: Plein Air

A Conversation with Trevor Hocking

In this conversation (7 October 2008) Collins, Goto and Hocking are discussing graphs from work done at the Headlands Center for the Arts in Aug and Sept 2008.  Hocking is looking for scientific accuracy as the baseline condition of our sound interface. Each data set was marked with a green highlighter if Hocking considered the data to be exemplary.  Sheets marked in pink were considered problematical. Data that was usable but no exemplary have no mark.

Thinleaf Alder (Alnus incana tenuifolia)

24 September 2008




Tim Collins:  These are only 15 [minute graphs], 30 [minute graphs].

Trevor Hocking:  Would the leaf have gone in at that point with CO2?  Do we know what is causing the spike – was that you?

Reiko Goto:  I am breathing into this. (Alder 14:30)

Trevor Hocking:  That’s your breathing into it—ok.  So that is really just testing the system—and that is 30 minutes.  This—the leaf in the system again, here?

Tim Collins:  Yes.

Trevor Hocking:  At this point?

Tim Collins:  Hm hm.

Trevor Hocking:  That’s amazing.  That is a really fluctuating …

Reiko Goto:  It is gradually showing more details.

Trevor Hocking:  Yes, more detail, but I’m really looking at the magnitude of the fluctuation.  The magnitude of the fluctuation is really quite high.  There must be a lot of activity somewhere that is causing that fluctuation.  You are going up to 380, 390, 400 …

Tim Collins:  This is the day you were running the tests.  I’m driving back and forth in the car.

Trevor Hocking:  See, again—I don’t think what we’re seeing here …  The overall effect of the leaf—of the photosynthesis—is essentially the same.  The net …  You know, it is just running on here and what you’ve got here is an awful lot of fluctuation because of something that is going on outside.

Tim Collins:  So, basically, we’re shooting video, trying to get that linked up to that video tape.

Trevor Hocking:  So this is human activity?

Tim Collins:  This is Reiko and I going back and forth in a truck and in a car.

Trevor Hocking:  So I think that’s right.  I think these are not plant-related phenomena—these are human-related phenomena and the plant is just about ticking over, I would have said.

The strange thing about this one is, it has got negative transpiration pretty much the whole time.  I need to sit down and think through this.  I don’t think that is possible physiologically.  I think that must be a phenomenon that this is …And the other thing is that the light does some weird things (the graph 14:30) on this day as well.  I’m a bit worried about this sensor.

Tim Collins:  Well, we actually sent it back and got a new one because we were having trouble with it.

Trevor Hocking:  Yes, it doesn’t look right to me.  It is not producing.  I mean, the only sensible curve I’ve seen so far is that one.

Tim Collins:  Yes, we’re not seeing this in terms of the monthly progression, because you’ll see there is a point where we started having real problems with the light sensor, so we stopped taking data.

Trevor Hocking:  I don’t think, physiologically, there is anything right there.



Coast live oak (Quercus agrifolia)

26 August 2008, 9:35-11:50



26th:  Oak.  A lot of fluctuation to begin with.  It doesn’t like it to begin with, but it does settle down and it does give you a little bit of photosynthesis here; reasonable transpiration; and then it goes into this cross-over.

I’m happy with that up to there, but when it goes into this cross-over, I really don’t know what it is doing there.  Why this humidity should drop off …  Well, I think it is corresponding to that increase in temperature.

I think this is basically a weak response, but dominated by a temperature change.

Tim Collins:  Yes, the temperature goes down.

Trevor Hocking:  I think this is very much a temperature-dominated set of data.

Tim Collins:  So this is good data?

Trevor Hocking:  It is interesting data as far as the temperature response is concerned, but I think the effect is mainly physical.  I don’t think it is a biological response.  I think it is a mainly physical response to increasing temperature.


Coast live oak Quercus agrifolia, 26 August 2008, 12:00-15:30



This one …  So this is oak on the 26th of August, in the afternoon at 12.  This is a very impressive response.  This is one of the biggest photosynthetic responses we’ve seen here. A massive depletion.  The depletion is up to around 20 parts per million, so a really big depletion giving you a really nice photosynthetic curve here that then settles down to a steady state.  That is a really good response.

And the transpiration similarly looks very encouraging.  During the steady stage it dips and then rises again.

Tim Collins:  That’s interesting.  I assume the stomata is stable here?

Trevor Hocking:  Yes, probably.

Tim Collins:  So how is it cutting off transpiration with the stomata opening, because I was thinking of it as a physical response?

Trevor Hocking:  Well, I would tend to look at the temperature then.  If you look at the leaf temperature, the leaf temperature has changed a fair bit after 60, and the transpiration starts to [deep dip] [6:51] after 60.  So I would say this is probably a temperature phenomenon – not the leaf responding per se.  It is the temperature effect on the transpiration.

Tim Collins:  On the humidity scale?

Trevor Hocking:  On the humidity measurements, yes.  I think this represents a physiological response with the leaf really photosynthesizing well, but then it is overridden by this temperature response.


Coast live oak Quercus agrifolia, 26 August 2008, 15:30-17:00


Trevor Hocking:  And is this the same leaf?  Is this the oak later on in the same day?

Reiko Goto:  Yes.

Trevor Hocking:  And then obviously the temperature has settled down a bit now.  It is still slowly declining, but you haven’t got the same decrease that you’ve got there – so that is reasonably stable.  Then you’ve got a nice steady state of photosynthetic rate there.

The only thing we need to worry about is whether that is also a calibration phenomenon because that difference is actually (because you’ve recalibrated this) – is only about …  This is 340, 350 – so that is 2, 4, 6 …  So that is a differential of only about 4.  So my worry there is whether that is a real rate, or whether that is just a calibration difference, because it is very similar to this calibration difference that we’ve got here.  So that might not be a real photosynthetic rate.  That is a calibration issue, I would say, there.

Tim Collins:  So we call that calibration …

Trevor Hocking:  Yes, I think that is a calibration …

Tim Collins:  But anything with a yellow mark we’ll consider good data?  Reiko, good data on this one.  (Oak, 12:00)


Coast live oak Quercus agrifolia, 2 September 2008, 9:20-17:00


Trevor Hocking:  This is ok up to here.  Ok – oak.  September 2nd in the morning.  Again your light sensor is screwed.  Air temperature is slowly increasing so you would expect that going through the morning …

Tim Collins:  No, remember—part of it was, you said, “Get the light as close to the leaf chamber.  And, because we have these tall trees, part of the thing was, I think we were getting leaf shading.  So, at that point, I put the light sensor two feet away from the tree so that I get clear light.

Trevor Hocking:  Yes, that’s it—but the key thing to know is what light is the leaf in the chamber actually receiving.  That is why I’m saying …

Tim Collins:  Does that actually go into the photosynthesis calculation?

Trevor Hocking:  Oh, yes.  Yes.  Absolutely.  Well—calculation.  It goes into the photosynthesis mechanism.  What the leaf in the chamber is responding to is the light it is intercepting.

Tim Collins:  Yes, I understand that, but the question is—in terms of a public exposition of this stuff …  If the light doesn’t go into the photosynthesis and humidity calculation, then a general light reading is probably something that most people will respond to.

Trevor Hocking:  Yes, it is ok, so long as the leaf is not being artificially shaded or stimulated, yes.  No, that’s ok.


Coast live oak Quercus agrifolia, 6 September 2008, 8:30-16:00


Trevor Hocking:  You’ve got a strange response there because you’ve got your leaf …  No, that’s humidity.  Yes, that is really strange.

Tim Collins:  That’s a huge spike.

Trevor Hocking:  Huge spike, yes.  Going from 60 to 70.  But it is not photosynthesizing very much and it is just oscillating in the bottom.  Again, not as good as those data there.

Trevor Hocking:  6 September – oak.

So, this is another whole day one.

Yes, you haven’t really got much depletion there.  I think the leaf is …

Tim Collins:  Yes, I think this is when we got the light meter back again.

Trevor Hocking:  It certainly is not as convincing as some of those traces.  It looks like you’ve got a little bit of depletion here.  That’s not as good.

Ah!  I think that is good-looking (Oak, 26 August 2008, 12:00). That is a good-looking sheet.

It’s ok, but it is not in the same magnitude as these yellow ones.

Tim Collins:  So the pink sheets are definitely not good.  Something that is really wrong.  Otherwise we’ll leave it as ok, then we’ll focus on the yellow ones.



Coast live oak (Quercus agrifolia)

18 September, 12:40-20:40


Trevor Hocking:  18th.  This is oak again, starting in the afternoon.  This is positive, so this must be blue; this must be red.  That first bit looks fine.  You’ve got a nice photosynthetic rate there.  Good depletion.  You’ve got quite a mixed transpiration pattern.

You see, that’s quite odd, isn’t it?  If you look at that period there, you’ve got almost static – well, stable – CO2 differences, and yet the humidity has gone really quite crazy there, hasn’t it?

What has happened to the air temperature?  That is around 150.  So it has not done much there, has it?  Why it should do that, I don’t know.  I mean, it has picked up …  That has produced that big difference in transpiration, but photosynthesis has carried on – it has almost disregarded it.

Tim Collins:  There were some really negative numbers all the way up the transpiration chamber.

Trevor Hocking:  Yes, that’s worrying.  The photosynthesis data looks fine.  This—I’m worried about that.

And these are presumably human peaks, are they?

Tim Collins:  Yes, yes.  Car activity.

Trevor Hocking:  Car or humans—yes.




Arroyo Willow (Salix lasiolepis)

28 August, 9:15-14:15


Willow—not much photosynthesis to begin with.  You got a bit of depletion long term, so that is quite a nice photosynthesis response.  But again, you’ve got negative transpiration going through there.  So, by the time you are getting the photosynthesis response, you’ve got something very odd because that doesn’t make sense.

If the stomata are opening, and if the leaf is taking up CO2, it would normally have to be giving out water vapour.  So this should really be the other way round.  It is very difficult to explain having a positive photosynthetic rate and a negative transpiration rate.  So that is a conflict.

The dilemma for plants is typically that they can’t photosynthesise without losing water at the same time.  So the fact that you have photosynthesis activity here, and negative transpiration there—it’s impossible for the plant to do that—to take up CO2 and at the same time stop water getting out—not possible.  So that is certainly a pink.

Arroyo Willow (Salix lasiolepis)

28 August, 15:00-17:00


Trevor Hocking:  The 28th – well, that’s the same leaf.  Would that be the same leaf?

Tim Collins:  28th – that is three o’clock.  Yes, the same leaf.  It is likely the same leaf.  Once in a while I did change it, depending on …

Trevor Hocking:  Again, you’ve got a relatively small difference here.  I’m not sure that that is not a calibration difference.  A slow steady state photosynthetic rate, but again, negative transpiration.

I would put that down to zero, effectively.  I would say that that difference is a calibration difference, and this negative transpiration is just something that the leaf is doing.

Interesting, the temperature patterns is very different here.  It is quite stable, but just a slow decrease.

Tim Collins:  Yes, it was from three o’clock in the afternoon as the sun is going down.

Trevor Hocking:  And if you look at that curve—that decrease looks sensible.  So the issue is just what is going on in the intervening period.

Tim Collins:  What a leaf.

Trevor Hocking:  Yes, but that decline could reflect that.  I would say the leaf isn’t doing very much there. Still good in the morning.



Red-osier Dogwood (Cornus sericea)

25 August, 9:00-11:15

Trevor Hocking:  That is a nice depletion.  It is on the 25th of August.   Nice depletion.  Nice photosynthetic rate.  Nice transpiration rate.  Yes, you’ve got good light data there.

You see, that is sensible light data.  That is the morning trend.  So that increase there is what you would expect to see over a morning period going up to midday.  So that is a nice dataset, I would say.  That is a yellow one.

The plant is doing everything that you would expect it to do under those circumstances.



Red-osier Dogwood (Cornus sericea)

25 August, 14:00-16:15


So this is the same leaf, same day, but in the afternoon now, and the temperature is declining but your light …  Yes, your light sensor has gone funny again.  You’ve got negative transpiration with this below [?______] reference.  So, poor data.  I wouldn’t …  There is something going on.

But you’ve gone from that situation which is what you would expect—positive transpiration, nice photosynthetic rate, to a complete reversal.  You’ve now got this humidity being lower, so you’ve got a complete switch-over there.  I wouldn’t trust that data, personally.  Something has gone on there.

California all spice (Calycanthus occidentalis)

27 August 2008, 9:15-11:30


Trevor Hocking:  Sunday, the 27th.  What is that?  Oh, August.  Is this dogwood again?

Tim Collins:  Oh, no.  All spice.

Trevor Hocking:  Oh, All spice.  You’ve got an awful lot of noise in the CO2, but no clear differential and you can see that.  You’ve got a pretty static photosynthetic rate.  The leaf is transpiring.  Here it is transpiring as you would expect.  It has gone into negative there.  What is the leaf temperature doing?  The leaf temperature is going up …  Yes, this transpiration rate looks like it is responding to the increase in temperatures.  The photosynthesis is staying the same, and the transpiration is responding to the increase in temperature, I would have said.




California all spice (Calycanthus occidentalis)

27 August 2008, 13:00-16:20


The same one, same day, afternoon.  Again, I think that is just the calibration.  I don’t think the plant is actually photosynthesising.  I think that is probably [?______].  You are just getting wild fluctuation.  You’ve got negative transpiration here with this humidity below.



Western burning bush (Euonymus occidentalis)

29 August 2008, 9:30-16:00


Tim Collins:  This is the one that made the leaf chamber wet .

Trevor Hocking:  This one …

Tim Collins:  Oh, this is a different one.  This is burning bush.

Trevor Hocking:  Burning bush.  9:30 in the morning.  Oh, just look at that – oh, that’s humidity.  That is going with the …  You see, that is really odd.  That is really, really, odd.

Reiko Goto:  What do you mean?

Trevor Hocking:  You see, you’ve got a really nice photosynthetic response here with the depletion, and you can see that increase in photosynthesis.  But at the same time, you’ve got that transpiration …  That is basically impossible.  That is really interesting.  I mean, it is really interesting data.  Explaining that would be fascinating.  You’ve got this nice depletion, but you’ve got this reversal of the humidity showing a negative transpiration right there.  That is almost impossible.  You would nearly always expect that, as you got an increase in photosynthesis, you get an increase in transpiration – instead of which you’ve got this increase in transpiration here which then goes into a decrease again.


Something is going on with the temperature there.

Tim Collins:  That started at 9:30, so two hours—10 to 11:30—that’s just the peak of the day.

Trevor Hocking:  So, interesting, but I don’t know what is going on as far as the plant is concerned.  It is the fact that that has gone up, and that has gone down.  That is very odd.


Blue gum eucalyptus (Eucalyptus globules)

21 August 2008, 8:25-10:00


Eucalyptus.  A lot of fluctuation in the CO2.  You must have had a lot of other activity going on here.  Again, relative humidity ok with the leaf higher than the sample, so that looks sensible.  Positive transpiration rate, and you’ve got pretty much negative photosynthesis.  I don’t think it is doing anything photosynthetically.  I think it is inactive, photosynthetically.  But the plant is transpiring alright—but no photosynthesis.  I think all you’ve got here is whatever is causing this is just responding.

Tim Collins:  Did you print out last week’s data too?

Reiko Goto:  Yes.

Tim Collins:  Is everything up on the wall, or just part of it?

Reiko Goto:  Everything except the Wolverhampton ones.




Quaking aspen (Populus tremuloides) 21 August 2008, 14:00-16:10


Trevor Hocking:  This looks nice.  Nice depletion here, giving you nice photosynthetic rate here.  Relative humidity is sensible, the leaf chamber is much higher than the reference.  So you have a nice transpiration curve there.

Reiko Goto:  21 August.

Trevor Hocking:  You’ve got fluctuation, but actually this is very small scale.  It is only a four degree fluctuation there.  A shame your light sensor is missing there.  But that is good.  I would say that is yellow data.

That development of photosynthesis and its stabilisation is absolutely classic.  That is really good.  And you’ve got positive transpiration throughout that period.  So that is nice data.



Quaking aspen Populus tremuloides, 30 August 2008, 9:30-10:30


Quaking Aspen Populus tremuloides, 30 August 2008, 13:00-15:40



Trevor Hocking:  Oh that’s a different day – much later on.  Still aspen.  Hmm—this is interesting.  Much less variation, but a really nice differential.  Almost from the word go you’ve got a differential there.  You’ve got quite a substantial photosynthetic rate.  Relative humidity is the right way round.

Tim Collins:  [?______].

Trevor Hocking:  Almost, yes, that could actually be a light response because your temperature, in this case, is relatively constant so that is not a temperature-related phenomenon.  That could well be a light phenomenon.  And you’ve got a nice positive transpiration so that is good data, yes, definitely.

Trevor Hocking:  This aspen gives you big differentials!  This is all aspen?  That’s a hell of a differential!

Tim Collins:  Yes, this is …

Trevor Hocking:  Flipping heck.  Look at that!  That’s 60ppm.

Tim Collins:  Yes, and this is the morning. (Aspen, 30 August 2008, 9:30)

Trevor Hocking:  Oh, that’s the afternoon. (13:00-) That’s a massive …  So would the leaf have been in all this …  Same day?

Tim Collins:  Probably, yes.

Trevor Hocking:  Yes, so it struggles to begin with.  It is really struggling.  But in the afternoon it is really …  I mean, it is built up here.  Yes, it is really going!  It is really [?______].  That’s a phenomenal depletion.  And it has maintained it for two hours! It is really …

But the only problem with this one is the humidity is bizarre.  So that is a really good photosynthetic depletion, but you’ve got low humidity in your leaf, so you’ve got a negative transpiration rate which does correct itself.

You see, what is going on there – you’ve got pretty much no change here …

Tim Collins:  There’s a drop in air temperature.

Trevor Hocking:  There is a drop in air temperature – yes, that could correspond to that.  But you can see that that has not responded, but the transpiration has responded massively.  So, this is pink because of this negative transpiration.

Tim Collins:  We’ll call them good data, but with a problem.

Trevor Hocking:  Yes.  Interesting data, certainly.  But the fact that aspen …  I mean, that is about the biggest differential we’ve seen, isn’t it?

Tim Collins:  Yes.

Trevor Hocking:  I don’t think we have seen as big as that.  No, it’s pink.  It’s definitely pink.  All I’m saying is this is big depletion.  If that is real, that leaf is really – phooh – that is really taking up some CO2!  Massive.

Tim Collins:  Which is doing the same thing here.

Trevor Hocking:  Yes!  Yes, it obviously struggles to begin with, but then it gets into a bit of a groove and then really motors for two hours.

Tim Collins:  Now our humidity is balanced here.

Trevor Hocking: Yes.  The humidity is right there.

Tim Collins:  This is the morning.

Trevor Hocking:  Yes, the humidity is right there.  But when it really takes off …  Well, no—it takes off here and this is really odd.  I don’t understand that.

Tim Collins:  Is this good then?

Trevor Hocking:  That’s fine.  It’s just not as dramatic as that.  I would say that is ok, yes, because the humidity is in the right orientation there.  But you can see that something has gone on here.  There has something really odd gone on here because when this differential really sets up—this is when you get this massive change, and then when you set up it up again (when you switched it on again)—it is back down here.  So it was up here—it was up at 75—this is the leaf chamber?

Tim Collins:  So this is 720 to 150 [?______] 820, 920, 1020, 1120—and we don’t set it up until …

Trevor Hocking:  Gone three o’clock.  But by that time—between there, you’ve got a complete reversal.  So, what’s happening here is very odd.  The only thing you can say is that the leaf is continuing to photosynthesise.  But what has gone on with the relative humidity, I don’t know—to go from that position to a complete reversal—dodgy.  I just don’t understand that.


Quaking aspen Populus tremuloides, 1 September 2008, 7:20-10:20


Quaking aspen Populus tremuloides, 1 September 2008, 10:15-15:15


Trevor Hocking:  This one …  An initial depletion.  That is interesting data.  What has caused that?

Tim Collins:  That’s the aspen again.

Trevor Hocking:  Yes.  One, two, three …  Thirty minutes.  Oh no—that’s twenty.  So, 20, 40, 60, 80.  So that is forty.

Tim Collins:  Yes, the temperature hits that mean point.

Trevor Hocking:  Yes, the temperature has gone up.  But that is really a marked response going from high photosynthesis down to here and then up again.  And the transpiration has gone on a similar pattern, so you’ve got this decline in photosynthesis, decline in transpiration.  So that is the kind of relationship that you would expect to see.

But then this recovers again.  And the transpiration stays negative.  That’s odd.  That’s a nice depletion.

Tim Collins:  So it will just be ok?

Trevor Hocking:  Yes, ok data.

Quaking aspen Populus tremuloides, 19 September 2008, 13:15-18:15


With this one you’ve got a nice depletion to begin with.  In the first hour or so you’ve got a nice photosynthetic rate and you’ve got positive transpiration.  So this must be the blue.  That must be the red.  All of that looks absolutely fine.  And then the photosynthesis just shuts down, basically.  So this is ok data.  This initial data is fine and then it just tails away.  Actually, it tails away because the time of day.

Tim Collins:  In that case, it is good data?

Trevor Hocking:  Yes, actually, it’s good data, yes, because it has actually shown that it is just fading away at the end of the day.

Maple Acer macrophyllum, 23 August 2008, 9:14

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So this is maple in the morning—23rd—foggy to begin with.  Now that’s odd.  I don’t think we’ve ever seen that before.  You’ve got not much variation in your leaf chamber, but you’ve got a lot of fluctuation in your reference.  That’s unusual.

But by and large, when they’re both fluctuating, they’re both fluctuating so that’s quite strange—but not much photosynthesis there.  So photosynthesis is pretty much flat.  I don’t think the leaf is photosynthesising.  You must have a fair amount of disturbance there with that reference going up and down.

Relative humidity is the right way so you’ve got positive transpiration.  I would say the leaf is transpiring, but not photosynthesising.  So that is just ok data.


Bigleaf maple Acer macrophyllum, 23 August 2008, 11:20-13:30


Now that’s maple—same day, a bit later, still foggy.  [Computer] photosynthesis.  So that carried on from there?

Tim Collins:  Hm, hm.  More or less, yes.

Trevor Hocking:  So it is starting to photosynthesise, you’re starting to get rid of depletioncy, and you’ve got a slightly increasing light.  The light is going up there, isn’t it?  The net …

Tim Collins:  Because the highest [?______] was ten.

Trevor Hocking:  Yes.  And this is up to about 25.  So you’ve got a small increase in light, small increase in photosynthesis, and transpiration is positive.  That is good data.

Tim Collins:  Good.  You want to call it good?

Trevor Hocking:  Yes, consistent.  Because you’ve actually got a nice trend in the light too.  The light sensor looks like it [isn’t] working there.

Bigleaf maple Acer macrophyllum, 23 August 2008, 14:00-16:20


Maple.  Afternoon, same day.  Is this a different leaf, or could this still be the same leaf?

Tim Collins:  It could be same leaf, yes.

Reiko Goto:  Yes, it’s the same leaf.

Trevor Hocking:  So it is still photosynthesising.  Depletion here.  Depletion there.  Humidity is the right way so you’ve got positive transpiration.  Yes, that’s ok data.

Tim Collins:  Ok or good?

Trevor Hocking:  The only thing that makes me worry about it is the leaf has now been in since nine in the morning, so it is now up to seven hours in here.



Quaking aspen Populus tremuloides, 16 September 2008, 14:00-20:30


So this is aspen?

Reiko Goto:  Yes.

Trevor Hocking:  A different day.

Reiko Goto:  I’m sorry—I’m mixed up.

Trevor Hocking:  Aspen, the 16th of September.  Two o’clock in the afternoon.  This looks like nice data, initially.  So you’ve got in the first hundred hours reasonably constant temperature, reasonably constant air temperature.  Light obviously quite high—again, what is going on with this fluctuation—but quite high because you’re in the afternoon so it is still quite bright.  Nice photosynthesis.  Nice depletion.  Nice photosynthetic rate, and then you’ve got a decline up to 3:00 hours …

Tim Collins:  That is two o’clock.

Trevor Hocking:  Yes, that’s right.  The light is really coming down and you’ve got the photosynthesis coming down.  That is good data, yes.

Reiko Goto:  Actually, aspen did it better.

Trevor Hocking:  Aspen is phenomenal at depletion!  If I was choosing, from all these data, if I was choosing a plant …

Tim Collins:  … to mitigate CO2, the aspen would be the way to go.

Trevor Hocking:  Well, I wasn’t going that far.  You jumped about three years’ work.  What I was going to say, I would choose aspen as an experimental plant because it shows such good depletion.

Tim Collins:  But in terms of [?______] sequestration, they claimed that a mature oak, over the life of the oak, has sequestered more.

Trevor Hocking:  Absolutely.  You look at the length of the plant, the size of the canopy …  Don’t forget—all we’re looking at is one leaf.  In terms of sequestration, how big is the plant, how long does it grow for, how many leaves has it got?

Tim Collins:  So this is a matter …  Actually, I’ll have to go back and look at that Lancaster Report and see what he says.  Of course, he didn’t refer to California.

Trevor Hocking:  No.  But experimentally, any plant that gives me that kind of depletion, is a plant I like working with.  The thing about a plant that gives you big depletion—you can do more with it.  You’ve got a photosynthetic rate to manipulate experimentally.

Tim Collins:  So, the thing to do next summer (if we can get some funding) would be to actually run experiments that are chosen off his (what does he say?) [?______]?  He doesn’t include aspen.  Willow, larch …

Trevor Hocking:  Aspen isn’t a UK species, you see.

Reiko Goto:  [I thought it was.]



In the following discussion Collins, Goto and Hocking are talking about continuing the work through the winter by moving into the University of Wolverhampton’s Crop Technology Unit Laboratories, and plans for the spring, including a potential exhibition of the work at the new David Brower Center in Berkeley CA.

Winter experiment

Trevor Hocking:  What is going through my mind is the need to start growing some seedlings under artificial conditions so that we’ve got stuff to work on during the winter.  See, I’m worried that we’re only going to be left with annual species and they are so different to …

What we could really have done with—and we should have done it already, really—is get some trees growing in the greenhouse so that we’ve got material that we could work on over the winter.

Tim Collins:  Somebody might have greenhouse trees somewhere.

Trevor Hocking:  They might have, but they had to have kept them growing.  They really needed to have germinated them in the summer.

Tim Collins:  I’d prefer that they be native species.

Trevor Hocking:  We could get hold of the seed and we can germinate it, but we just haven’t got time to grow the plant—that’s the trouble.

<A break>

Trevor Hocking:  What have you got in pots now?

Reiko Goto:  We’ve got ash, beech, field maple and oak (that has already turned yellow), and then Scots pine—we didn’t do that.  But we could do holly.

Trevor Hocking:  Yes …  The trouble with holly—because it has got such a thick cuticle, it is quite difficult to measure its photosynthetic rate, and it won’t flatten very easily in the leaf chamber.

What I was thinking of is, if you’ve got something that is still in leaf …

Reiko Goto:  Still green is hawthorn, and of course [?______] – but those are totally exotic plants.  But this oak was very much like holly.  I mean …

Trevor Hocking:  Yes.  When it was put in the leaf chamber, did it flatten out nicely?

Reiko Goto:  It was so difficult.  Tim had to open it up and put it in the chamber …

Tim Collins:  Yes, it was a trick.  You had to take the whole thing out and then slowly squeeze it.

Trevor Hocking:  Yes, I can imagine.  And you were confident it did flatten down and sealed?

Tim Collins:  Oh, yes.  I got it flattened down and sealed.  Some of the leaves were very, very tiny.  I get two little tiny leaves right off the end of a tip.

Trevor Hocking:  All I was working to is, if we can find a potted tree plant that was still going, I was going to suggest that we put it in the greenhouse now …

Tim Collins:  What about the two that we have?

Trevor Hocking:  … and get it under lights and see if we can keep it going for a bit longer.  Because they are going to get frosts now, so they are going to go off very quickly.

Tim Collins:  We can bring them right over.

Reiko Goto:  Ok.

Tim Collins:  So what do you have?

Reiko Goto:  We have ash—the ash is a good size.

Trevor Hocking:  Is it still green?

Tim Collins:  It is still green.  This is changing the colours.

Trevor Hocking:  Which one is …

Reiko Goto:  That’s a birch.

Trevor Hocking:  That’s a birch, isn’t it?  Because that is starting to go.

Reiko Goto:  The ash is still very green.

Trevor Hocking:  Yes.  I’m thinking we’ll get those in the greenhouse, actually.



A Proposal for the David Brower Center

Reiko Goto:  We were invited by a new art gallery in Berkeley in the David Brower Center—they are going to focus on environmental and political issues—so they are very interested in what we’re doing.

Tim Collins:  David Brower was an environmental policy guy.

Trevor Hocking:  Where is he based?

Tim Collins:  He was in California, but he worked on a national level as well, so they put this whole centre together which is intended to promote environmental thinking in Northern California.  They had actually hired a curator who we got to know pretty well.  There is also a museum there that is interesting, The Oakland Museum, as well as near woods.  If we can get something together.

What we talked to people about was …  The David Brower Center is a two-storey [building] opening in the lobby with a seminar centre so there will be huge gatherings of crowds, so we could set up an indoor version of the plein-air easel and just human breath would indicate changes.  With the guy in Oakland, we talked really briefly about the two or three different variations we could do.  We could do a full-blown project with you where we are actually working with on-site trees, or we can do some kind of a gallery-based version of it.  He said, “Well, let’s just talk when you get your ideas a little bit clearer.”

Reiko has a relationship up in Aberdeen that wants a [temporary project].  So the other thing is, with the [temporary] project, there is also the opportunity that, if we get this system sorted, we can get Matthew to figure out how to sonify your portable system at which point the ideal would be to actually set it up so that Reiko could do some performances with it.  At that point we can call her project closed—temporary projects, temporary performances—call her project closed and then we can move into this whole process where we’ve got multiple disciplinary voices working together and actually probably lecturing together would be the ideal so that we talk about one aspect, you talk about another aspect, and if we can get a committed sound person, that would …

Trevor Hocking:  So, once Reiko’s finished her PhD, there is no problem about her staying on the project—she doesn’t have to go off and do something else?

Tim Collins:  No, especially with a little bit of planning—it makes it easy.

Trevor Hocking:  I’m just concerned because I know how demanding it is to write up …  If she’s got to write up over the next twelve months, she really has to focus on that.

Tim Collins:  That’s why I think that if we can keep this going through December, get some good data, get the system working properly and then let it wind down for a couple of months at which point we’ll know about the [RAE].  Potentially we’ll get another PhD student in on it at which point Matthew will stay with it three to six hours a week which isn’t much.

Trevor Hocking:  How long is he employed for?

Tim Collins: He’ll finish his PhD in January 2010.  The other thing is—and this is the thing that I find rather funny—because when I came back, two of the PhD students grabbed me and three members of staff have basically told me that they want to see a presentation on this and they’ll come to work with us on this with no question of money.  They just said that they would like to support it if they could.

Trevor Hocking:  Right—colleagues from your school?

Tim Collins:  Yes.  So they’re interested in the sound aspect—mostly.

Trevor Hocking:  They don’t get a lot of opportunity to experiment with sound, do they?

Tim Collins:  There is one PhD student who is actually trained as an attorney before he decided to come in for his PhD in art and design—he got all excited about this as a way of talking about environmental conditions and going into long-term questions of policy.  And he asked me if I would sit down and talk him through that.  His PhD is in something else, so I’ve got to be careful not to …

Trevor Hocking:  Well, it is so easy to get diverted.

Tim Collins:  Yes.  Lots of people [were nervous] about Matthew getting interested in this.  But now, he’ll get the real-time thing up and running, but then he’s going to build us a variation on the system he is using on his PhD.

So I said, “If you buy the parts and let me test them, then I’ll only have to pay once for the parts that work for me.”

Reiko Goto:  Just a question—it may be naïve.  I haven’t enquired what kind of plants you like to use, but I’m coming from making a proposal for the new gallery.  It has huge glass windows.  The system will stay for about one month, so we cannot really use outdoor plants for the inside.  What would happen if we used indoor houseplants?

Trevor Hocking:  Well nothing happens.  It is just indoor houseplants respond very differently.

Reiko Goto:  Irregular or unpredictable?

Trevor Hocking:  Yes.  Well, they’re typically much less responsive.  The reason why plants end up being good indoor plants is that they tend to be much less responsive than outdoor plants.

Reiko Goto:  To the light?

Trevor Hocking:  Yes, because they have to cope with low light levels, they have to cope with a lot of pollution, they have to cope with high CO2 levels.  Very often, if they’re in centrally heated premises, they have to cope with fluctuating temperatures over a day, so they have high temperatures during the day and low temperatures at night.  So, by and large, good house plants are plants which cope.  They adapt well to those sort of environments, so they’re typically tend to be not very responsive.

Reiko Goto:  I see.  The data would be random—how to read what is going on, that is more difficult.

Trevor Hocking:  Yes.  The only way we could test it, would be just to do it.  It is very difficult to predict.

Reiko Goto:  But how to emulate the data from the aspen which is pretty good.

Trevor Hocking:  Yes.  But you see, that is outside, high levels of light.  You see, as soon as you move inside, your light levels—compared to a sunny day—they’re down by fifty per cent and more.  That is why we have to have big chambers just trying to simulate the sunlight again.

I mean, what indoor plants did you have in mind?

Reiko Goto:  Like a [?______]?

Trevor Hocking:  Yes, that would be a classic, wouldn’t it?  Because that is quite tough.  That is quite a good plant.

Reiko Goto:  Also, in Asia, it grows so big.

Trevor Hocking:  Yes, and it is an attractive plant, so it is aesthetically pleasing as well, and it is a tree.

Tim Collins:  And ultimately the project is intended to show the relationships so it is something you would see everywhere.

Trevor Hocking:  Yes.  I think that would be worthwhile.  Why don’t we buy one and do some work on it?

[Is there a fourth person in the room? K]  I think that would be a good idea.  I think that would be a good plant to do tests on.

Reiko Goto:  Ok.  There is a window along here, so I can test that.  Another random question—when we were in Berkeley, we also looked at the street trees.  They were all varied—different types—but we also found that the native oak is used as a street tree.

Trevor Hocking:  Is it really?

Reiko Goto:  There were a few of them.  How could they breathe, and how could the stomata be opened?

Trevor Hocking:  Not easily—no is the answer.

Reiko Goto:  So the trees are very unhappy?

Trevor Hocking:  A big problem, yes, absolutely.  That is absolutely classic.  I mean, oak—that is why you wouldn’t normally use oak.  We tend to use plane trees because they are remarkably resistant to the pollution.  You get articulate pollution.  A lot of diesel particles end up on the leaf services.  You get dreadful lead pollution around the streets—no, that’s bad.

Reiko Goto:  It was really bad.

Tim Collins:  It actually needs to be washed.

Trevor Hocking:  Ideally, yes.  Where you have high rainfall, then very often that is really critical of washing the leaf surfaces off again.

Tim Collins:  So that could be something we could propose as part of that exhibition …

Reiko Goto:  Washing the leaves!

Tim Collins:  Washing the leaves of trees.

Trevor Hocking:  Well, you know—if you’ve got a houseplant, you do look after it and you can buy leaf washes.  You can buy stuff that you can actually wash the leaves.

[Tim Collins:  Do I hear an ‘only in California’?

Trevor Hocking:  No.  [Chuckles]]

Tim Collins:  The last four years there’s been a group of protesters up a grove of redwoods at California campus—huge battles.  And just as we got there they finally got them down out of the trees.  So we’re standing on University Avenue looking at this oak tree and Reiko is touching the leaves, and this State [Cal] policeman actually pulls over and rolls down his window and he says, “You’re not going up it today, are you, folks?”


Trevor Hocking:  So arrested for potentially damaging a tree.  What were they protesting about?

Tim Collins:  Basically it is an old grove of trees …

Trevor Hocking:  Oh, and they didn’t want it to be cut down.

[Talking about the tree protest that has continued for 21 months.]

Trevor Hocking:  We’ve had it in this country typically when they tried to build motorways or bypasses—so the protesters go and camp in the wood that has to be cleared, and they tied themselves to trees before now.  But only for days …

Reiko Goto:  We could measure the tree, and then after washing the tree, measure it again!

Trevor Hocking:  Yes, absolutely.  But they have to be washed carefully, obviously, because you can do more harm than good.

Tim Collins:  You know, there is one person that I have met in my life that has the care and the patience of Job, and that is Reiko!

Trevor Hocking:  We could do a really interesting study on the street trees in Wolverhampton, using my portable kit, before and after washing the trees.

Tim Collins:  Well that would be something you could do.  So that could become part of the performance that you’re proposing for Aberdeen as well (which she actually won’t be able to do until spring next year)—but still, it will be able to fit in.

Trevor Hocking:  Well, the best time to do this would actually be in the summer after the leaves have had some time to …  Because, obviously, the leaves start again in spring, so it builds up, so by August time, you’ve got quite a layer of contaminating material on the leaf’s surface, and that would be the best time.  Earlier in the year, obviously, they’re fresh young leaves—they’re not so bad.

Reiko Goto:  I think you have to be the artist.