FUN!ctional Traits: Stomata Density

Cananga odorata abaxial leaf surface @ 100x with stomata circled in red.

Cananga odorata abaxial leaf surface @ 100x with guard cells and stomata circled in red.

Stomata are the microscopic pores that facilitate the movement of gasses into and out of leaves. Carbon dioxide goes into the leaf, while oxygen and water vapor go out. The opening and closing of stomata (stoma=singular) are mediated by the guard cells, which can expand and contract depending on their turgor pressure. Turgid guard cells open the pores, flaccid cells close them. Stomata are key to evapotranspiration and water and solute transport from roots, to shoots, to leaves. Coupled with other plant functional traits, stomata can indicate how a plant is interacting and coping with its environment. In an upcoming project I will being quantifying stomatal density with other traits, among different species along an environmental gradient.

From reading the literature, it is apparent that changing one variable in a leaf, such as stomatal density, can have a cascade of effects on other traits and photosynthetic rates. However, I cannot think about stomata density without first considering Woodward’s 1987 paper, ‘Stomatal numbers are sensitive to increases in CO2 from pre-industrial levels.’ I really like this study because it used herbarium records dating back 200 years to show stomata densities have decreased over time. After growing plants in varying concentrations of carbon dioxide, Woodward was able to show that the decreases in stomata density of herbarium specimens likely resulted from increases in global CO2 concentration.

It is interesting to note that atmospheric CO2 concentrations were 340 µmol/mol at the time of Woodward’s study. We have just recently passed the grim 400 µmol/mol milestone, which is disconcerting in light of another observation Woodward made: Some plants did not change their stomatal density above ambient CO2 (340 µmol/mol) conditions. What does that mean for plant physiology?  Rico et al. 2013 suggest plants may shift towards lower water requirements and greater xylem fortification – in other words – plants become more drought tolerant…if they can.

While I’m reading up on that, I will leave you with a 400x close up of the more stomata (below). In both top and bottom pictures, I have circled some of the stomata. The guard cells look like two touching crescents. The guard cells are mostly closed, because the leaves are dead (ultra-flaccid), plus the cells have probably contracted some. The black cone shapes are hairs. These images are nail polish molds of the the abaxial (bottom side) of Cananga odorata. The green color is an after-effect.

Cananga odorata abaxial leaf surface @ 400x with two stomata circled in red.

Cananga odorata abaxial leaf surface @ 400x with two stomata circled in red.

Works Cited:

Rico, C., Pittermann, J., Polley, H. W., Aspinwall, M. J. and Fay, P. A. 2013. The effect of subambient to elevated atmospheric CO2 concentration on vascular function in Helianthus annuus: implications for plant response to climate change. New Phytologist 199: 956–965.

Woodward, F. I. 1987. Stomatal numbers are sensitive to increases in CO2 from pre-industrial levels. Nature 327:617–618.

A successful seminar , congratulations Ken!


Ken Feeley, the head of our Lab, gave a well received and incredibly successful departmental seminar today as he begins the process of tenure application (picture above). Ken discussed his past, present and future research on how plants will respond to modern climate change. He primarily discussed our Lab’s research on long-term vegetation plots in the Peruvian Andes, summarized past findings and presented the exciting directions our future research will be going in! Congrats Ken!

Researchers predict environmental factors will imperil banana production by 2060

This is repost of an article in FIU News written by Evelyn Perez about work done by upwithclimate contributors Brian Machovina and Ken Feeley.  The original article can be found HERE.


In the next 50 years, approximately 50 percent of conventional plantations in Central and South America are predicted to become unsuitable for the production and export of bananas.

This is a claim made by FIU biological sciences researchers Brian Machovina ’91, MS ’94 and Kenneth Feeley in their study titled, “Climate change driven shifts in the extent and location of areas suitable for export banana production.”

The researchers used global climate projections for the year 2060 and species distribution modeling (SDM) to predict the geographical shifts and map areas predicted to be suitable for commercial banana production. They found climate change, deforestation and lack of water availability will cause banana plantations currently found in areas suitable for production to shift to other countries. Countries such as Mexico, Ecuador and Peru will gain suitable cultivation areas while other countries will lose suitable areas, including Honduras and Colombia. In fact, it is estimated that Colombia will lose an estimated 62 percent of its cultivation areas.

Machovina holds a banana sprout soon headed for a plantation in Costa Rica.

Machovina holds a banana sprout soon headed for a plantation in Costa Rica.

“Climate change is real and it is impacting our food systems and what people eat around the world,” Machovina said. “Recently, drought in the U.S.  affected corn crops to the point where we had to import corn from other countries to make up for the loss in yields. With climate change, we expect extreme weather events to occur more often around the world and, as years pass, we will have more and bigger problems as they relate to food.”

According to the study, a decrease in areas suitable for conventional banana production is expected. However, areas suitable for organic banana cultivation will increase due to the generally drier climate predicted for this region in the future thus creating opportunities for organic farming in the area. Conventional farming focuses on monoculture, or the mass production of one crop in one location, and uses synthetic pesticides and fertilizers to yield crops. Conversely, organic farming employs polyculture, or the production of multiple crops in one space, and natural fertilizers and pesticides, to produce crops.

To maintain the long-term global system of commercial banana production, the researchers recommend that agricultural management and policy decisions maximize water conservation and availability to offset changes in climate; shift location of commercial banana cultivation zones; and invest in research and development of climate-resilient bananas.

“I believe human beings are resilient and adaptive,” Machovina said. “We are undergoing a learning phase and will hit road bumps along the way that may be very stressful for society, but in the face of climate change we will have to learn to adapt our global food production systems to feed people.”

Bananas are the developing world’s fourth most valuable food crop and the world’s 12th most important plant crop in value and quantity. Production is concentrated in Africa, Asia, India, Latin America and the Caribbean, with Ecuador, Costa Rica, Colombia and the Philippines currently the world’s largest exporters. Bananas have long been the leading fresh fruit imported into the U.S.

Machovina is set to present his research at a meeting hosted by the Food and Agriculture Organization of the United Nations to discuss the future of Ecuador’s banana production in the face of climate change.

The study, titled “Climate Change driven shifts in the extent and location of areas suitable for export banana production,” was published in the scientific journal Ecological Economics.

trees move up but the treeline doesn’t

Picture1Work from our team has showed provided evidence that cloudforest tree species from the Andes and from Costa Rica are shifting their distribution upslope, possibly in response to increasing temperatures.  For the Andes, we conducted a follow-up study where we predicted the future population sizes, and thus extinction vulnerabilities, of the migrating species under different warming scenarios and sets of competing assumptions.  What this exercise clearly showed is that the future of these cloudforest species depends very much on what happens at the upper limit of their distributions – the treeline*. If species are able to migrate upslope and extend their ranges past the current treeline to occupy the parts of the puna (high elevation grassland habitat above treeline sometime referred to as paramo in other parts of the Andes) that become climatically suitable, then we predict that their population sizes may actually increase.  The reason for the increase, and apparent benefit of climate change, is simply that the cross section of the Andes is more trapezoidal than triangular; consequently, as species migrate up off the steep slopes, past treeline and onto the high plateau (altiplano), the amount of land area that they can occupy increases.  In contrast to this relatively rosy scenario, if the treeline remains where it currently is and doesn’t shift upslope with warming (e.g., due to cattle grazing and human activities above the treeline), we predict that all cloudforest species will suffer massive decreases in available habitat area and their population sizes (and hence increases in their risks of extinction) as the lower elevations become ‘too hot’ but they are unable to occupy the ‘just right’ temperatures at higher elevations.

Picture2So we need to know, “will treeline move with warming?”  Well, we now have several decades of climate change behind us so we can look back and ask if treeline has moved or not in response to the 0.5-1oC of warming that the Andes have already experienced over the last several decades.  As part of his dissertation research, our colleague, Przemek Zelazowski, looked at Landsat images collected over the Andes from 1970 to 2000. Due to warming, treeline should have shifted upslope between 90 and 140 vertical meters over this time period.  He found zero change.  Yes, treeline moved up in some places, but in other places it moved down and the modal change, by far, was zero zero zero.  Now, a new study by David Lutz et al. conducts a similar analysis but using much higher-resolution imagery of the areas around Manu National Park where my team works. Over the 4 decades for which they had imagery, they found that 80% of the treelines that they looked at showed zero net change, and the average change across all treelines they looked at was an upslope shift of 0.14 vertical meters per year. This is in the right direction, but it is just 1% the rate that was required to keep pace with concurrent warming.

Treeline has not moved in response to past warming.  It is doubtful that it will move in response to future warming. Cloudforest species will continue to shift their disruptions upslope.  They will be unable to invade the puna. They will suffer decreases in their population sizes. They will be at danger of extinction.

All bad news, right?  Well there is one result from the Lutz et al. study that may be the silver lining on an otherwise very dark cloud.  When Lutz et al. compared the rates of movement of the treelines in the protected areas of Manu National Park to the rates of movement of the treelines in unprotected areas outside the park, they found that protected treelines migrated upslope 5 times faster than their unprotected counterparts (0.24 vs. 0.05 vertical meters per year).  The rate of migration in the park is still way too slow, but this difference does indicate that parks and protection work.  If we could make the parks better park (e.g, remove cattle and stop fires) and make the parks bigger, then at least some Andean treelines might move faster and some extinctions may be avoided.

-Ken Feeley

*My grad student, Evan Rehm, is probably cringing at my use of the word ‘treeline’. I will leave it up to him to define the correct use of ‘treeline’ vs. ‘timberline’ vs. ‘tree species line’ and to better explain why the treeline or timberline is not shifting upslope faster in Manu.

NPR on the effects of climate change on tropical forests

NPR is playing a new story about the effects of climate change on tropical forests featuring the work of KJ Feeley and his colleagues in the Andes Biodiversity and Ecosystem Research Group.

Listen or read here:

tropical forests move upwithclimate due to lowland dieback

One of the primaImagery ways that climate change is predicted to affect the natural world is through changes in the geographic distributions of species.  For example, increasing temperatures are expected to force species to ‘migrate’ to higher elevations and/or higher latitudes into areas that were previously too cold for them.  Evidence has been rapidly accumulating showing the expected migrations of species in North America and Europe.   In contrast, very few studies have documented species migrations of tropical species. This is despite the fact that tropics house the majority of earth’s species, that these tropical species are expected to be especially sensitive to climate change (due to greater specialization on stable climates), and that tropical species are known to have migrated in response to past climate change.

In 2011, Feeley et al. published the first-ever study showing evidence of contemporary species migrations in tropical trees.  Using data from repeated censuses of tree plots situated along a steep elevational gradient in the southern Peruvian Andes, they documented patterns of compositional change through time that were consistent with expectations of upward species migrations.  Despite the strength of their findings, the question remained as to whether these results were driven by idiosyncratic factors such as land use change, succession or regional climate patterns, and thus specific to the study region, or if they reflect the effects of global warming and thus are more generalizable to the greater tropics.


In a new paper, “Compositional shifts in Costa Rican forests due to climate-driven species migrations” Feeley show that forests in Volcan Barva, Costa Rica, are likewise showing strong evidence of upslope migrations.  More specifically, Feeley et al. used herbarium collections data to characterize the ‘preferred’ temperatures or elevations of thousands of Costa Rican tree species.  They then used the relative abundance of the different tree species in 10 1 ha tree plots established along the Volcan Barva to calculate each plot’s ‘Community Temperature Score’ or CTS. A plot has a high CTS has a high relative abundance of species with lowland affinities (i.e., species that prefer hot climates); in contrast a plot with a low CTS  has a high relative abundance of species with highland affinities (i.e., species that prefer cold climates).  Feeley et al. then tracked how the CTS of the Volcan Barva plots changed during the course of 10 years of annual plot censuses. Mirroring their results from the Andes, Feeley et al. found that nearly all of the Costa Rican plots had increasing CTS.  This means that the relative abundance of lowland species in the plots increased through time – exactly as predicted under climate-drive upward species migrations.


The fact that the two studies by Feeley et al. (2011 and 2013) show such similar results despite a separation of thousands of kilometers, zero overlap in species, and different methods and personnel being used to collect and analyze the data, strongly suggests that species migrations are a general phenomenon in tropical forests and thus that the most likely explanation is a large-scale driver such as global warming.

A very important, and often overlooked, consideration is that apparent species migrations can be driven by several different processes including “range skew” (i.e., no movement along the species’ trailing or leading edges but a shift in the relative abundance of individuals at different elevations within the range), “range shifts” (i.e., the leading and trailing edges of the species’ distribution migrate at the same pace), “range expansion” (i.e., the leading edge moves faster than trailing edge), or “range contraction” (i.e., the leading edge moves slower than the trailing edge).  Depending on which of these processes is occurring, predictions for the future of ‘migrating species’ will vary from positive (under range expansions), to neutral (under range shifts) to dire (under range contractions).  Most studies, including Feeley et al. 2011, only look at changes in the mean elevation/temperature of species and/or changes in the overall relative abundance of species at a site, making it impossible to distinguish between the four possible underlying processes.  In their new analysis of Costa Rican forests, Feeley et al. go the extra step and determine the individual contributions of tree mortality, recruitment and growth to the observed changes in the species composition of the study plots.  They find that most of the observed changes are driven by mortality.  In other words, the plots are increasing in their relative abundance of lowland species but this is actually due to the dieback of highland species rather than the encroachment of lowland species.  This suggests that the compositional shifts are driven by range contractions.  If range contractions continue in the future it will spell trouble for these species, and if generalizable it will spell trouble for tropical, and hence global, biodiversity.

Feeley K.J., Hurtado J., Saatchi S., Silman M.R., and Clark D.B. 2013. Compositional shifts in Costa Rican forests due to climate-driven species migrations. Global Change Biology, Available Online. DOI: 10.1111/gcb.12300

Climate change must not blow conservation off course

One of the paths that our lab meetings seem to inevitably, and unintentionally, follow is to end up discussing whether science research consistently focuses on topics that we think are the most important. Conservation is a tough science to be in. The discipline exists because something is wrong and needs fixing, however recent emphasis on global climate change suggests problems like these have already reached a point that is irreversible, so it has developed more into a task of planning and mitigation.

A recent paper in Nature argues this point. Although climate change will continue to be the most important theme in the foreseeable future of conservation science, it must be noted that topics that have received more interest historically, such as deforestation and habitat fragmentation, have not lessened their threat to species extinctions.

Tingley et. al. warn although climate change is receiving an awful lot of research attention at present, in most  cases of biodiversity conservation it is not the most urgent threat. We know so little about how species will respond to climate change that modelling its effects on species based on arbitrary metrics (e.g. kilometres/year climate change velocity) may prove ineffectual.

In fact, the authors point out, the closer we look at species’ responses to our warming planet, the more surprises we uncover. Despite a 1-2C mean temperature increase in nearly one hundred years, only half of the birds in California’s Sierra Nevada responded by moving to higher elevations as one may have predicted. Closer to home in Florida, rapid evolution of thermal physiology (1, 2) have allowed species to persist in areas that previous ecological data suggest they wouldn’t have been able to.

Finding a way of combining the multiple axes of biodiversity threats remains one of conservation science’s biggest challenges. No one aspect will dictate the success of species in the future. Various methods exist to help conservationists to factor climate change uncertainties into their priority-setting, but as yet there is no consensus on how the future threat of climate change should be compared to ongoing and more certain threats, such as land-use change.

However, this itself presents a moral dilemma; why save species from immediate threats when their long-term survival is in question? I view this as short-sighted. Although our success with some species may be limited, what we do know from millennia of science is that theory builds on theory. It is likely that the state of the world’s ecosystem is ever going to plateau but instead continue on its negative trajectory. Although the success of individual species conservation efforts may be hard few and far between, the applications for these methods, and interpretations from their results, will continue to help conservation efforts in the future.


– James Stroud