Our field site is located in the eastern part of the Amazon basin in the Brazilian state of Pará:

Credit: Google Earth Maps

Zooming in, you can see we are just to the east of the Tapajós River, and to the west of the road that heads south from Santarém (the nearest city). The road is called the BR-163.

Our field site (known as “km-67”, because it is 67km along the BR-163 road from Santarem) is located at the red star in the Tapajós National Forest. Credit: Google Earth Maps

This four-month campaign is being conducted by four PhD students working with Scott Saleska at the University of Arizona: Ty Taylor, Loren Albert, Jin Wu and myself (Marielle Smith), professional arborist Mick Eltringham, research technician and tree climber Neill Prohaska, as well as many collaborators in Brazil and the U.S. We arrived mid-August and will be here until mid-December to observe the whole dry season.

This is the core crew, but we’re working in collaboration with a large group of Brazilian researchers and students, as well as other researchers in the US. Top, left to right: Marielle Smith (me), Jin Wu, Mick Eltringham. Bottom: Ty Taylor, Neill Prohaska, Loren Albert, and Sabrina Garcia (visiting PhD student from INPA, Manaus). 

Why are we here?

Graph showing how total forest photosynthesis (or GPP, gross primary productivity) changes throughout the year at our field site (km-67). Graph credit: Saleska and Huete 2010.

The graph above is the reason we’re here. It shows how GPP (gross primary productivity)–total forest photosynthesis—changes throughout the year at our field site (km-67). The shaded part of the graph shows the wet season months (January to about June), while the white part shows the dry season (July or August to December). The green shaded area shows data collected from the “eddy flux tower” (so called because the tower has an instrument positioned above the canopy which measures changes in concentration of carbon dioxide, CO₂, by using wind currents, or eddies; see the photo of the tower below). The brown and blue lines show model (computer simulation) predictions of how forest photosynthesis changes throughout the year. What you can see is that measurements from the forest show an increase in photosynthesis during the dry season, peaking mid-dry season (October - November). This does seem counter-intuitive when you think about it – because this is the time in the year when the trees have the least amount of water, and yet they are somehow able to photosynthesise more. Models predict exactly the opposite pattern: a decrease in forest photosynthesis (GPP) during the dry season. This discrepancy is partly because we don’t yet understand the physiological mechanisms driving tropical trees to change their behaviour through the seasons – the phenology of tropical forests. So basically, our campaign seeks to understand why tropical trees are photosynthesising more during the dry season. If we can gain a better understanding of this, we can use this information to improve computer models, so that they can more accurately predict the future of Amazon forests. In addition, the dry season may give us an indication of how tropical forests will respond to climate change–the Amazon is expected to get hotter and drier with climate change, changes which are experienced on a shorter time scale every year during the dry season.

The eddy flux tower at km-67 (our field site), which measures forest photosynthesis, rises out of the canopy to a height of 65m.

So why does forest photosynthesis increase during the dry season? One simple answer could be that the trees are responding to an increase in sunlight (fewer rain clouds). There could also be more leaves at this time (i.e. higher leaf production). There may also be a greater number of new leaves, which have been shown to have higher photosynthetic rates. We hope to answer these questions using a variety of different instruments that can measure aspects of the forest at different scales—from a view of the whole forest down to an individual leaf.

Measuring the forest from the ecosystem level down to an individual leaf. From left to right: I am using a terrestrial LiDAR instrument to measure how leaf area of the forest changes throughout the dry season; Jin Wu is using a hyperspectral camera to see if remote sensing techniques can detect seasonal changes in leaf properties (photo by Neill Prohaska); Loren Albert using a LICOR-6400 to measure leaf-level photosynthesis; Ty Taylor measuring VOC (volatile organic compound) emissions from leaves.

Given that the leaves of most big tropical trees are way above our heads – over 30m in some cases – we are having to tree climb using ropes. We have professional arborist Mick Eltringham with us to help us to rig trees and get into them with our instruments safely.

Our work is taking us up into the trees! Left: Loren, Mick, and photographer Jake Bryant climbing one of the core study trees (photo by Neill Prohaska). Right: me climbing a tree to install a PAR sensor to measure light in the canopy.

By combining all of these measurements we hope to understand why forest photosynthesis increases during the dry season. Our goal is for the data from this campaign to go towards improving computer models that can then make better predictions about the future of Amazonian forests, which are so critical for global climate and biodiversity.

I met Mrs. Green through a science communication fellowship program, the Rachael Carson Scholars put together by the University of Arizona’s Institute of the Environment.  Mrs. Green contributed to the fellowship awards.  Her radio show, Mrs. Green’s World, focuses on sustainability and environmental science, especially emphasizing the US desert southwest.  On this show, though, she gave me the opportunity to branch out and talk about tropical forest research.  She recognized the relevance of this research to the desert southwest.  The responses of tropical forests to climate change (in the case of the Amazon, a warming and drying climate) will strongly feed back to in turn drive climate change.  Our studies are therefore relevant to other parts of the planet that may face particularly strong effects from climate change, such as the US desert southwest.

In this interview, we do a broad sweep across the tropical forest research projects I’ve been involved in.  There is too much to cover in one interview, so maybe when I get back from the Amazon we will have to do another!  I’m currently writing this post from the Tropical Hotel in Santarém, Pará, Brazil, situated along Amazon river in the eastern third of the Amazon basin.  I’m working on some posts from our research and fun here so far, so stay tuned and hopefully they will come soon.

Once more, here’s the link to the interview, enjoy!  Ty’s Mrs. Green’s World interview

You can also click these logos below to see the University of Arizona’s Institute of the Environment home page and the Mrs. Green’s World site.

]]> http://www.tyeenandmaz.com/?feed=rss2&p=2022 0 http://www.tyeenandmaz.com/?p=2031 http://www.tyeenandmaz.com/?p=2031#comments Sun, 23 Sep 2012 18:36:36 +0000 Marielle Smith http://www.tyeenandmaz.com/?p=2031 Here is a video documenting Ty’s and my first week in the Brazilian Amazon as part of a 4-month research campaign. We started off by picking up instruments and visiting friends at the University in Manaus – INPA.

Then we journeyed by boat from Manaus to Santarém along the Amazon River. It was a fantastic start to our trip.

More posts about the goals of this research campaign are coming soon!

Moss clad branches line the road that leads up to the cloud forest at Cuerici.

Hiking through cloud forest has a dream-like quality: clouds drift in and out, hiding and exposing different layers of the canopy. I really felt like I was walking through Tolkien’s Middle Earth.

Cloud forests are found at the same elevations that clouds form (which varies depending on where you are). In fact, “horizontal precipitation”–the direct deposition of droplets from clouds and mist–is an essential form of precipitation in these forests (although of course it rains as well).

Due to the so-called “rain shadow” effect, the Pacific slope of the Talamancan mountains (where we were staying) gets 3.5 m of rain per year, whereas the Atlantic slope receives 6 m. This is because the prevailing winds – the trade winds – from the east pick up water from the ocean and deliver rain to the Atlantic slope (on the eastern side of Costa Rica) first, and by the time the air masses pass over the Pacific slope, they contain much less water.

Clouds roll in over the Pacific slope – this side receives much less rain than Costa Rica’s Atlantic slope due to the “rain shadow” effect (see above). As such, the Pacific slope has been much more extensively deforested, probably because it is easier to clear the land and keep cattle on it (see the foreground). There is only one area of contiguous forest from the lowlands to cloud forest left on the Pacific side.

 Species richness (the number of species in an area) tends to decrease with increasing elevation. Accordingly, we found 18 tree species in the 0.1 hectare plot we surveyed at the Cuerici cloud forest, whereas you might expect to find some 200 species in the same sized plot in the Amazon basin. This decline in the number of species at higher elevations is due to decreasing temperature, decreasing area (you physically can’t pack in as many species at the top of a mountain as at the bottom), and isolation. The Talamancan mountain range resembles an island in many ways – it has been isolated from the rest of Central America for a long time, and so species have gradually been lost over time.

The Talamancan mountains form a “backbone” down the centre of Costa Rica. Endemism (the existence of species found nowhere else in the world) is very high here due to the lengthy isolation of this region, which has provided the opportunity for many speciation events. 

Cloud forest flora overlaps very little with tropical dry forest and lowland  rainforest floras (the two forest types we will visit next), but interestingly it does share many plant families with the temperate zone. In fact, the forest at Cuerici is 85% white oak (family: Fagaceae). Other families you might recognise from the temperate zone are Betulus (alder), Urticaceae (e.g. nettles), and the genus Rubus (blackberry).

Cloud forest flora consists of many temperate plant families – albeit different species (NB: families contain many species). That is, the cloud forest contains many plant species from plant families that are most diverse and originated in temperate regions. Left: oaks (family: Fagaceae, genus: Quercus) are the dominant tree in the old growth cloud forest we visited in Costa Rica; right: another representative from the temperate zone: the genus Cornus from the family Cornaceae (dogwood).

 Carlos and his family own and run the cloud forest field station at Cuerici. He has an impressive knowledge of the forest – knowing local and scientific plant names as well as medicinal uses. In his own words, the forest is both his “super market and pharmacy”.

Carlos is also an experienced backcountry hiker. He and his friend Alberto once hiked all the way from Cuerici to Panama over the Talamancan mountains, some 150 miles off-trail through dense forest! Both Carlos and Alberto helped me and our group tremendously, and I hope to go back and visit their beautiful forest again one day.

We conducted a couple of Gentry plots whilst we were at Cuerici – my first! These forest inventory plots are known as Gentry plots because they were used extensively by the famous tropical botanist Alwyn Gentry. It involves recording and measuring the diameter of all shrubs, trees and lianas over 2.5 cm in diameter in a 0.1 hectare area. The class did one Gentry plot in a primary forest, and I conducted another Gentry plot in an area of secondary forest with a smaller group. It will be interesting to analyse the differences, but already it was surprising to see that we recorded a similar number of tree species in both plots.

We started off by taking a trip to the Costa Rican National Biodiversity Institute (INBio), a non-profit organisation based in San Jose that has been collecting, identifying, and classifying the country’s biological diversity since 1989. In that time, INBio has documented an impressive 300,000 specimens, including over 10,000 plant species (Costa Rica has an estimated 12,000 plant species, so they’re nearly there!). This incredible feat has been made possible by the organisation training up local people to collect specimens, so called “parataxonomists”, many of whom have continued in science and have made huge contributions to our knowledge and understanding of tropical biodiversity. Sadly, INBio is experiencing hard times financially and has had to significantly scale down its operations. I really hope they can obtain funding to continue this work.

Brad Boyle, one of the OTS coordinators and instructors, stands in front of piles of plant specimens waiting to be pressed and dried at INBio’s herbarium

Just some of the thousands of plant specimens waiting to be correctly identified. Each specimen will be entered into the INBio database, one of the largest on-line herbaria resources in the world.

The final product: this is a photo of a plant specimen like those in the herbarium at INBio (photo courtesy of Las Cruces Biological Station). Herbaria records like this one are an important resource for many biologists, providing a long-term record for each species. Herbarium records enable us to keep track of the total number of species known to science, and help us to confirm that new species are really new. I will most likely use herbaria in the future to compare their named specimens with my own collections to check that I have identified plants correctly. 

Following the trip to INBio, we headed southwards to our first field station location: Las Cruces Biological Station, making regular stops to identify plants. The photos are from our visit to a very interesting páramo bog. Páramo is a high-elevation ecosystem (the bog we visited was at approximately 2,800m) found above the tree-line, and it tends to have very high levels of biodiversity and endemism (i.e. species that are found nowhere else on the planet). It can be thought of as “tropical alpine”. (NB: not all páramos are bogs.)

Who would have guessed that this tree hung with epiphytes (plants that grow on other plants) was an oak?! Check out its leaves and even an acorn we found on the ground underneath it in the photos below.

Robbin Moran, our second course instructor, holding the stem of a fern we found  growing in the bog. The pattern on the stem cross section is due to the vascular bundles (xylem and phloem) and is characteristic of this type of fern (family Cyatheales).

A young fern frond or “fiddlehead” unfurling (of a different species).

The top leaves and unopened bud of the bromeliad Puya dasylirioides (family Bromeliaceae), which is endemic to this particular area of Costa Rica – the Talamanca Mountains (meaning it occurs nowhere else in the world). To me it looked rather like an alien coming up from the bog, but it’s possible I have an over-active imagination… It can grow to be up to 2.5m tall.

More stories and photos from Costa Rica coming soon! Please let me know if you have any questions about anything I write on here – it would be great to get more of a dialogue going.

Thanks!

Marielle.

The forest at SERC was not what I was expecting – it was much bigger (35-40m high) and more lush than I had imagined. For some reason I had thought it would be more like an English forest…

In many ways, the SERC forest reminded me of a tropical forest–with abundant epiphytes (plants that grow on other plants, like the vine growing on the tree on the left), and huge trees with thick vines trailing between them (see photo on the right). The climate is also reminiscent of the tropics–hot and humid.
It is actually a ‘moist temperate forest’.

Some of the dominant trees in the SERC forest are tulip poplar, sweet gum, oaks, red maple and beech.

Left: tulip poplar; left middle: sweet gum; right middle: huge leaves of the black oak; right: Sassafras (Genus), which is a tree that has three different types of leaves: one with three lobes, one with two lobes (like a mitten), and one unlobed–see if you can spot all of them in this photo.

I went to SERC to learn how to use an instrument called a ground-based LiDAR, which stands for Light Detection And Ranging. We call it ‘ground-based’ because we use this instrument by walking along the ground (there are also versions that can be mounted to aircraft). The LiDAR shoots thousands of laser beams up into the forest canopy each second and measures the height of leaves by recording the amount of time it takes for each laser beam to leave the instrument, intercept a leaf, and then return to the sensor. This gives us a vertical “slice” through the forest that we can use to analyse aspects of forest structure, such as canopy height, forest gaps (e.g. where large trees have fallen), and the total leaf area of the forest along a transect. Forest structure describes the position and density of leaves and branches in a forest, and is an important factor in understanding how forests store and process carbon. Until the development of this instrument, there weren’t many quantitative ways to assess forest structure, so the LiDAR is really a breakthrough in this area.

Left: me using the ground-based LiDAR; right: close-up of the ground-based LiDAR showing the metal frame which holds a laptop computer and the laser unit at the front (photo courtesy of Scott Stark).

http://youtu.be/JC2uv5ITuV8 

This video shows me taking my first ever transect with the LiDAR! It’s important to walk slowly and as smoothly as possible because the data analyses we do afterwards assume a constant speed through the forest. If I speed up during the transect at some point, fewer laser beams will contact with that part of the forest and so it will be under-represented (it will look as if that area has been “squashed” together).

Because the LiDAR really takes a random sample of the forest, it’s important to stick to the transect line (which is marked with white poles every 10m in the SERC forest). But this isn’t easy when there are large fallen trunks to cross! It was good practice though, as doing this in the Amazon is likely to be much more challenging! To keep a constant speed through these areas, you need to turn the laser off when you reach the obstacle and turn it on again on the other side (e.g. of a fallen log).

Encountering fallen logs means that you have to turn the LiDAR off, scramble over or go around the debris and then turn the laser back on. This ensures that we keep a constant walking pace through the forest.

So, what did we find? Here is a graphical representations of one of the transects we walked in the SERC forest:

Graph produced from the LiDAR data taken during one 110m long transect. The X-axis shows the distance along the transect, and the Y-axis shows the canopy height. The coloured areas are where the laser came into contact with leaves or branches (so areas that are more coloured in have a higher leaf or branch density). Basically, these areas give us an estimate of the total leaf area of the canopy along this transect. So you can see that the leaf cover is pretty consistent between 0m and 10m, but that there are only a few areas where leaf cover extends to 35m.

The graph above showed the forest to be much “gappier” than we had expected. This seemed strange because when we’d been in the forest, it always felt pretty dense overhead; but perhaps this was a weird trick of our own perception – the canopy cover is quite dense and continuous up to about 10m, but opens up above that. We probably often couldn’t see right up to the top of the canopy and so assumed it was denser that it really was. To confirm this, we hiked up to the top of one of SERC’s towers to get a better view of the forest. Sure enough, we could see lots of gaps in the canopy (with many holes between individual trees). Sean suggested this may allow the trees in this moist temperate forest better access to light, since light comes down at an angle in temperate regions such as Maryland. In contrast, tropical forests receive sunlight from directly overhead and so may be flatter on top, with fewer gaps, in order to capture as much sunlight as possible.

A view over the SERC forest from one of the towers showed how the forest is characterised by many gaps between trees, giving the top of the canopy a “holey” texture.

http://www.youtube.com/watch?v=iR-h_dORDOc

In this video,  Dr Sean McMahon compares the structure of the SERC forest to tropical forests like the Amazon.

Sean and me on top of the SERC tower.

Thanks so much to Sean and all his colleagues at SERC for giving me a great introduction to the LiDAR and to the beautiful forest at SERC!

]]> http://www.tyeenandmaz.com/?feed=rss2&p=1654 1 http://www.tyeenandmaz.com/?p=1590 http://www.tyeenandmaz.com/?p=1590#comments Sun, 06 May 2012 02:23:49 +0000 Ty Taylor http://www.tyeenandmaz.com/?p=1590 [Ty]  This climb has been a long time coming! I feel like Babo is a sort of right of passage to novice climbers in Arizona. My main motivation for learning to climb in AZ has been to learn the technical skills necessary to step up our outdoor pursuits to include mountains and more technical terrain. Baboquivari has been synonymous in my mind with my introduction to mountain climbing. I climbed with Marielle Smith, and Martin and Martine von Arx in two teams. We successfully summited safely via the southeast arête. We did it in four climbing pitches, but roped up on a couple scrambles as well.  The elevation gain is 800 feet or so (including scrambling) with a lightly technical descent. It was pretty straightforward, but I consider having reached the skill level required to make this climb straightforward to be a great accomplishment and a landmark in our outdoor careers!

Some ‘beta’ for climbers:  Make sure you take the FIRST right turn once you’re on the ranch road on your way in (it’s at about 2.4mi, not 2.8 like Mountain Project says).  The descent is notoriously the most difficult part (in terms of getting lost), but if you print the instructions on Mountain Project for descending down the Forbes route, just follow them carefully and you won’t go wrong; we had no troubles.  You’ll need at least 60m ropes for the descent, and doubles is nice for the second rappel so you don’t have to downclimb at all.  We used half-ropes, twin-rope style (instead of clipping each independently) because we placed pretty sparse protection due to the constant interspersion of easy climbing or scrambling in each pitch with short sections of a couple harder climbing moves.  We ran pitches long at the cost of a lot of rope drag, and totaled four real climbing pitches (but actually stayed roped for some exposed scrambling).  Placing protection was straightforward and there were usually plenty of options.  We had a standard set of nuts, and cams from micro sizes (which I used a lot) to 3.5.  We didn’t use our 3.5, but we missed the lieback pitch, in which Martin said he could have used a 3.5.  Belay anchors are made from trees or rock horns or tunnels, and are abundant.  If you can find the base of the second pitch in the notch, from there you can just go up and it’s hard to go wrong (but follow directions carefully for the traverse left to the lieback pitch if you want to do it, I skipped it and just went straight up with a couple 5.8+ moves using pockets and then onto easier climbing and scrambling).

Baboquivari peak viewed from the East on the trail up to the NE saddle.  The southeast arête route climbs the buttress on the left side of the peak.

This is NOT what your approach should look like!  If you drive to this mountain from the East side, make sure to take the FIRST right  after turning onto the ranch road.  We ended up at the wrong ranch and hiked up the wrong drainage, making for a lot of unnecessary off-trail!

The biggest Fouquieria (ocotillo) we’ve ever seen!

Off trail in spine country!

View of the southeast arête (middle of mountain) that you shouldn’t have unless you go up the wrong canyon and reach this saddle!  It’s actually a great view of the climbing route though.  The climbing starts at the vegetated ledge you see on the shadowed face half way up.  You can see the shadowed notch at the base of the second pitch, at which point you step out left and get a sweet, exposed couple of moves!

Morning light on Baboquivari. We started out at 6am. We should have been starting from the saddle at the right base of the mountain, but because of our false start the previous day, we hadn’t made it that far.

Scrambling up the canyon on our way to the saddle.  The trail is mostly pretty clear, actually.

The gaping maw of I’itoi’s wife!  It is said that the wife of the mischievous god, I’itoi, lives on Baboquivari, while I’itoi himself travels between here and Pinacate in Mexico.  I believe I have caught the face of I’itoi’s wife here on camera.  See if you can see her!  Her face is in supine profile and resembles that of a desert tortoise.

Lion’s ledge now clearly visible across the face. The approach to the southeast arête traverses the ledge from right to left. The southeast arête climbing route roughly follows the horizon line of the buttress at the left. Then you drop down into the notch separating the buttress from the summit, and do one more short, very exposed pitch before a scramble to the top. The descent route (mostly the Forbes ascent route) comes down behind the right horizon line of the mountain.

View from a bit below the saddle.

Traversing the ledge.

This is what a lot of the ledge looked like, though in a couple places we had to crawl on our bellies between trees and undercut rock when the ledge got narrow.

Peregrine falcon visible left of cliff face.

Looking southish along the lion’s ledge. This ledge was so badass! It just traverses narrowly through the middle of cliff faces, but never leaves you abandoned or unsafe. There are several little caves that would be great for sleeping in and waking up to look out over this view. It would be worth coming to Babo just to traverse the ledge! The climb starts at the crack separating that big boulder from the face at the end of the ledge in the distance.

A beautiful little spring, which apparently never runs dry, dripping into a bucket.

Martin and Ty freeclimbing up the crack to chimney to the base of the first real pitch (though you might want to rope up right here on the ledge and place a piece in that crack on your way up).  There’s a tree at the top of this from which you can belay up your followers.

Marielle reclines at the beginning of the second pitch.  The start of that pitch was really fun.  There is some serious exposure (lots of drop!) to Marielle’s and climber’s left, and you have to start out on that face, sort of stepping off the ledge to start up a crack!  BTW, we backed up that horn by running a sling through a rock tunnel in the notch to protect from a  fall out to the left.

Ty placing a cam on the second pitch.

Top of second pitch (our second pitch, we ran long pitches, skipping some that are described in different resources).

Third pitch (some people’s fourth).

Belaying Marielle up to the top of the third pitch.  (most people’s fifth). We missed the fun lieback pitch following the airy traverse left. I couldn’t find the bolts and didn’t want to use up my cams for an anchor so I backtracked and made some .8+ moves straight up toward easy climbing and a scramble to tree belay. That works just fine and had some fun moves, but I think we missed a fun lieback crack!

That is one healthy Echinocereus.

Safe on the summit with plenty of daylight to go!  Sat next to the ‘shrine to I’itoi’ (equals ‘people’s trash on the summit’ in Ty’s opinion).  But we did leave a ‘gift’ as is tradition; ours was a couple of boxes of waterproof matches for stranded climbers (which happens a lot).

Steep gully full of loose rubble ending in cliffs, exactly as advertised.

Martine rappelling down the “ladder pitch” of the Forbes route. Piece of metal bottom left is a remnant of the ladder that the Civilian Conservation Corps built for this pitch.

Martin stepping down to set up the second rappel on the descent amongst spectacular rock fins.

Marielle on the second descent rap.

Final rap down the chimney to the home stretch! (at least the home stretch to the saddle, still a very long way from the car since we parked in the wrong drainage!).

Lots and lots of bushwacking on the descent to the saddle after the third rappel down the chimney.

Echinocereus cactus flower.

Explaining leaf level measurements and reasons for conducting the up-coming B2 tropical forest drought to B2 visitors

 The LICOR measures photosynthesis in plant leaves. The leaf is clamped by the chamber head, and the instrument measures how the concentration of carbon dioxide (CO₂) declines as CO₂ is draw into the leaf during photosynthesises. Plants take in CO₂ and water during photosynthesis, and use energy from light to produce glucose, releasing oxygen as a by-product. The LiCOR is an amazing piece of equipment because it enables us to effectively look inside leaves and see what they are doing under different conditions. We can change the temperature, amount of light, and the concentrations of CO₂ and H₂O that the leaf receives in the chamber. This can either mimic ambient conditions, or put the leaf under stress so we can measure how it responds to extreme conditions (e.g. dry or hot conditions).

Measuring photosynthesis in leaves taken from the B2 tropical forest using the LiCOR 6400

 
Left: A leaf inside the chamber of the LiCOR head; right: the main “box of tricks” that controls the LiCOR head

The porometer measures stomatal conductance. This is a measure of how many stomata, or pores on the leaf surface, are open, and the degree to which they are open. Stomata allow CO₂ to enter the leaf and H₂O to be released. This movement of water up through the plant roots and stem and out through the leaves is called transpiration. When a plant has enough light and water, it transpires and photosynthesises, and the stomata are open. When a plant gets too hot, or runs out of water, it closes its stomates to prevent water loss and in doing so, can no longer photosynthesise. So stomatal conductance really tells us how much the plant is transpiring.

The Decagon porometer measures stomatal conductance, or the degree to which water is moving through the plant (transpiration).
Photo credit: www.decagon.com

 For the outreach event, we measured branches taken from the top, middle, and bottom of the mountain in the B2 tropical forest. The leaves from the top of the mountain had the highest stomatal conductance values (470 mmoles m^-2s^-1), the leaves from the middle had the next highest values (235-350 mmoles m^-2s^-1), and the leaves from the bottom had the lowest (190 mmoles m^-2s^-1). This makes sense if you think that the leaves at the top were experiencing higher temperatures and light, and therefore were transpiring, and probably photosynthesising at faster rates.

One of the most rewarding parts of the day was witnessing an important realisation by one of the children I talked to. I had explained the concept of transpiration to a boy as he had taken a measurement using the porometer. His attention then turned to the water cycle ball wall (that I designed as part of a hands-on exhibit for the Landscape Evolution Observatory, a big science project going on at B2). He fed a ping-pong ball (symbolising a water droplet) into the plant part of the ball wall and the air stream running through the plant shot it up into a cloud. I pointed out to him that this was exactly like the measurement he had just been taking and he exclaimed “ah, so the water is leaving the plant!”, to which his mother said something like “I love it when they have those moments of realisation!” That was really special.

The water cycle ball wall at Biosphere 2 allows you to make your own water cycle; air jets running on the outside of the magnetic wall and through the plant in the centre shoot ping-pong balls (“water droplets”) up into the clouds

I will be using both the LiCOR 6400 and the porometer to measure the effects of a drought, which will be starting in the B2 tropical forest in the next couple of weeks. This work is motivated by predictions that there will be more droughts in the Amazon rainforest in the coming century. Drought years (2005 and 2010) in the Amazon have already been shown to cause widespread tree mortality, and reduced forest uptake of carbon. We can use the B2 forest as a model system to understand the mechanisms underlying natural forest responses to climate changes. A series of droughts were conducted in the B2 forest during 2000-2002. They found that forest uptake of carbon decreased by 30%, mainly due to the trees dropping their leaves (10% of the leaves were lost; see Rascher et al. 2004, Plant, Cell and Environment 27, 1239 for more information). We may see a similar leaf drop event in response to the up-coming drought. If so, I want to find out where most of the leaves will be lost from – the top, middle or bottom of the trees, and will old or new leaves be lost? I will also be measuring photosynthetic rates and stomatal conductance on the leaves that remain. It makes sense that most leaves will be lost from the tops of the trees, since these will come under the greatest heat stress (it’s very hot at the top of the forest – imagine being at the top of a greenhouse in the desert!) The leaves that remain at the top, may slow down, or “shut down” their rates of photosynthesis so that they don’t lose precious water.

Understanding which leaves are lost, and which leaves “slow down” will help us to understand why forest carbon uptake tends to decline during periods of prolonged drought. In turn, this knowledge can feed into computer models of forest responses to climate change and help us to improve our predictions of the future.