School is out


How does it feel to be done with school, forever? My PhD dissertation is defended, submitted, and approved, and a diploma will arrive in the mail in a few weeks. It has been a long road to get here, and it feels worthwhile to reflect on the experience.

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Graduate school was a five-year experience for me, one that I almost never entered. I was teaching science in central Idaho beforehand, and the Arizona state legislature decided cut the funding for my PhD a few months before I was due to move. I nearly decided against changing life-paths because of this, but some alternative state and then federal funding came through at the last minute. At this moment, going to graduate school feels like it was a good decision. I feel that I now have the tools, the experience, and the connections to begin making my own mark in ecology. I see the world through very different eyes now, and will forever be grateful for the chance to broaden my viewpoints in these ways.

Looking back, I am struck by how much of a difference having research money has made in terms of being able to finish projects. I never had to spend much time working on other peoples’ projects, or teaching in areas that did not interest me. I owe much of that to two factors: first, the encouragement of my supervisor, Brian Enquist, and second, the availability of consistent funding support for my research and travel. Most graduate students receive far less funding and independence than I was able to find, and I don’t think that this difference has anything to do with merit. I think instead that small successes have a snowball effect, with the chance of getting fellowships and grants strongly reinforced by having had a fellowship or grant. The experience is a lot harder for students who aren’t lucky enough to escape a poorly-paid teaching assistant position, or those without US citizenship who can’t apply for many federal funding sources. I don’t know what the solution should be, but the current situation is demonstrably unfair.

The actual experience of doing a dissertation was not very helpful for me. The final document comprises a set of papers, all of which are either published or in review at scientific journals. These papers will be widely read and discussed by the scientific community, because they are searchable and available on the public internet. The actual dissertation, on the other hand, will probably languish unread in a university library for the next several decades. I was required to spend a large amount of time formatting and collecting chapters for this document. I think that process was a waste of time that will not benefit myself, the university, or the wider scientific community, but which costs a large amount of administrative time as well as fees paid to private publishing and printing companies.

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Someone asked me if it feels different to have a degree rather than to be a student. It does and it doesn’t. I think about science questions and work on manuscripts just as before. I get more respect from some people for no very good reason, other than that a few letters are now attached to my name. I feel like an unwanted barrier has been placed between me and some friends who are earlier along in their graduate school experiences. But there is much joy in having accomplished something difficult, and I look forward to being able to operate with more independence and chase after my own sources of research funding.

My degree will be conferred this Saturday, but I won’t be attending the ceremony. I’ll be teaching a program at the Sky School, and will then be disappearing into the outdoors. Exploring these natural worlds is what keeps me excited about science, and I wouldn’t have it any other way.


Drying up

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Even a little water is worth fighting over. The summer is coming early this year, and what little surface water remains in many of the canyons is beginning to dry up. While walking in Finger Rock Canyon the other weekend, deep within a mesquite bosque, I found just a single small seep coming from a fissure in a boulder.

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The water was being put to good use. Honeybees (Apis sp.) crowded the seep, drinking what little was available. Occasionally a yellowjacket (Vespula sp.) would fly in, and easily be accommodated. But the scene cleared out immediately when a large wasp or two (Polistes sp.) appeared.

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I didn’t see any direct conflict, but it was very clear that wasps could dominate the resource despite their more limited numbers. I wonder how this conflict will play out as the heat increases, the water slowly disappears, and all creatures wait in hopes of the summer monsoon rains…

Fighting over science

Most academic publications go ignored and poorly cited; fewer make an impact or controversy. I recently had the dubious honor of two papers being ‘debunked’ in the scientific literature.

My papers were focused on explaining the leaf economics spectrum – a global pattern that describes leaves use resources like carbon and nitrogen (Wright et al., Nature 2004).

My central hypothesis was that the leaf’s venation network is important in determining multiple aspects of the leaf’s functioning. One paper was published in Ecology Letters in 2011, and the other in Journal of Ecology in 2013

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A few months ago, Lawren Sack and colleagues published a paper in the Journal of Experimental Botany, in which they argued based on both empirical and theoretical grounds that venation networks were not a useful explanation for the leaf economics spectrum.

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They state in their abstract:

Leaf vein traits are implicated in the determination of gas exchange rates and plant performance. These traits are increasingly considered as causal factors affecting the ‘leaf economic spectrum’ (LES), which includes the light- saturated rate of photosynthesis, dark respiration, foliar nitrogen concentration, leaf dry mass per area (LMA) and leaf longevity. This article reviews the support for two contrasting hypotheses regarding a key vein trait, vein length per unit leaf area (VLA). Recently, Blonder et al. (2011, 2013) proposed that vein traits, including VLA, can be described as the ‘origin’ of the LES by structurally determining LMA and leaf thickness, and thereby vein traits would predict LES traits according to specific equations. Careful re-examination of leaf anatomy, published datasets, and a newly compiled global database for diverse species did not support the ‘vein origin’ hypothesis, and moreover showed that the apparent power of those equations to predict LES traits arose from circularity.

I’m not much for controversy, and this paper caught me by surprise – our research groups hadn’t had any behind-the-scenes discussions beforehand. But scientific criticism is healthy – it helps a field determine which ideas are worthwhile and supported by evidence. We read the criticism carefully, worried that it raised some points that would undermine our work. Our worry was not about our egos – more concern that we had done something unhelpful for the field of ecology.

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After a lot of thinking and re-analysis, we decided that Sack et al. raised some important points, but that their major criticisms were unfounded. We disagree about how to interpret empirical data, and also how to build a useful model – and we disagree about how to carry out certain calculations.

We just published a response in the same journal, saying:

Our model for the worldwide leaf economics spectrum (LES) based on venation networks (Blonder et al., 2011, 2013) was strongly criticized by Sack et al. (2013) in this journal. Here, we show that the majority of criticisms by Sack et al. are based on mathematical and conceptual misunderstandings. Using empirical data from both our original study as well as others in the literature, we show support for our original hypothesis, that venation networks provide predictive power and conceptual unification for the LES. In an effort to reconcile differing viewpoints related to the role of leaf venation traits for the LES, we highlight several lines of further investigation.

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Check out our response in the Journal of Experimental Botany and decide for yourself. We’re glad to share the debate with the whole field.

New paper: predicting climate from leaf venation networks

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If you travel from the alpine zone to the lowland tropics, more than just the climate will change. Species composition follows changing environments: there is a reason why a Cyathea tree fern doesn’t live in Colorado but does live in Costa Rica. (Note of course that many millions of years ago, when the earth was warmer, rain forest could be found even in what is now Antarctica!).

What is it about a tree fern that prevents it from living in a cold environment? A central idea in modern ecology is that measuring properties that reflect an individual’s function, performance (and ultimately fitness) can explain this pattern. My main hypothesis has been that leaf venation networks are the key ‘trait’ to measure. Here’s why. Plant growth requires water loss through transpiration in the leaves, and transpiration requires water supply, which is provided by the leaf veins. If there is a preferred growth rate and water loss rate set by the environment, then only certain leaf venation networks should be viable in each environment.


I just published a paper that tests this idea. I had noticed early on that different vein networks were associated with colder and warmer, or wetter and drier environments, as you see above. To see how general these patterns were, I went in search of leaves from a broad range of climates.

First, Dr. Brad Boyle led a botanical expedition on the western slope of Costa Rica. We started in lowland moist forest, as you see below. Access to one field site required hiking past a beautiful beach, and it was very tempting to ditch our equipment and sweaty clothes in favor of a late-afternoon swim.

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We collected plants all the way up to cloud forest and páramo vegetation, across an elevation gradient of more than 3000 meters.

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Second, I made collections in the Colorado Rocky Mountains. Here, sites ranged from high desert to subalpine meadow.


My favorite sites were in aspen forest, where Neill Prohaska helped me with tree climbing (aspen bark is very slippery).

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We found an intriguing pattern – vein density (length of veins per unit area) decreases with elevation, meaning that lowland sites have higher resource fluxes than montane sites. But the slope of the line wasn’t constant: the relationship depended on whether we were in the tropics or not.


I decided to try to explain this pattern based on plant physiology: perhaps the slope difference reflects differences in climate, i.e. growing season temperature, carbon dioxide availability, or intensity of solar radiation. We developed a mathematical model that uses vein density to quantitatively predict these climate variables, based on the idea I wrote about at the beginning of this piece: there is an optimal physiology for a given environment, so that the water supply in a leaf matches the water supply in the environment.

I was surprised by how well it all worked. Below is an observed-predicted plot: we compare observed values of climate to values predicted from measurements of vein density, such that a perfect fit falls on the diagonal.


You can see that we sometimes over-predict or under-predict – but in all cases, the model explains nearly all the variation in the empirical data, with trends in the correct direction. I think this means that the model is capturing some important aspects of reality. The paper’s main contribution is showing that leaf veins provide an important explanation for why species are only found in certain climates around the world.

You can read the paper in New Phytologist (link, or free PDF reprint). It’s been more than three years between conceiving the project, doing the fieldwork, doing the math, and seeing this published. Science isn’t always fast. We certainly had setbacks, and I’ll close by showing you one of them. Visualization of leaf veins requires some chemical work in the lab, and we had a very exciting hotplate malfunction one day. Fortunately everyone’s eyes and fingers survived the accident, and our dataset is just a little bit smaller as a result!


An early summer for the snakes

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The sound of a rattlesnake is unmistakable once you’ve heard it once. But this sound wasn’t on my mind when I almost stepped on one a few weekends ago. I was in the Santa Rita mountains of southern Arizona. The highest peak, Mt. Wrightson, looms 7000 feet above the Tucson basin.

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In late March, mountaintops like these are in the final clutches of winter. Snow patches and ice survive on north-facing slopes, trees have yet to leaf out, and perennial forbs are just beginning to push through the topsoil. It is a quiet and cold landscape – not the place one would expect to see a snake.

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Yet that snake did appear, at 8800′ elevation on a day that couldn’t have been much warmer than 60°F. Despite its kind and persistent rattling I put a footstep just a few inches away from its body before recognizing that sinuous movement and particular shaking sound.

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Here it is – the twin-spotted rattlesnake, Crotalus pricei (identification by Dennis Caldwell). This species is protected in Arizona, and was a first sighting for me.

I was curious about why a snake like this would be out on such a cold day so early in the season, and asked a few herpetologists who know more than me about the subject. Two ideas came up.

First, drought might have pushed this snake out of its hibernation. Limited moisture in the environment can mean slow dehydration – so better to chance a cold and prey-poor environment than face a sure death from lack of water. Second, microclimate variation means that a chilly air temperature might translate to a reasonably warm temperature immediately above rocks exposed to the sun in just the right way. This snake might have been taking advantage of warmer conditions immediately near its home. I like imagining all the fine-scale variation in an environment that we humans have difficulty perceiving.

Ultimately I don’t know what caused this snake and me to cross paths. I paused for a quick photograph, then left the snake to its business, whatever it may have been.

Connecting Children to Science and Place in the Sonoran Desert

(Re-blogged from a piece I wrote for the White House)


My great-grandfather immigrated to the United States from China in 1915, at the age of 11. He soon became the owner of a corner grocery store in Tucson, Arizona, and stayed in the community for decades. Now, almost a century later, I find myself living in this same desert city, honored to share my experience bringing science education to communities in southern Arizona.

I came to the Sonoran Desert for a graduate program in ecology at the University of Arizona, and became captivated by the border region. Tucson itself brings together Native Americans, more recent immigrants, refugees, military families, students, retirees, and everyone else in between. We share an arid landscape situated between the Coronado National Forest, Saguaro National Park, and the Tohono O’Odham Nation. Living here, I saw that our natural areas are not equally accessed or appreciated, especially by the children who are our next generation of conservation leaders.

When I wasn’t studying ecology, I was teaching science at a middle school in the Tucson Unified School District and leading hiking trips for The Sierra Club Foundation’s Inner City Outings program. These experiences showed me many children who could benefit from a deeper sense of place and scientific focus on our environment. Science education can build broader minds, better jobs, and more thoughtful stewards of the land.

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In late 2011 I proposed creating the Sky School  a science education program that would connect youth to our environment through inquiry-based outdoor science education. With support from the University of Arizona’s College of Science and the Forest Service, we have made that vision a reality. Our home is the summit of Mt. Lemmon, rising 6000’ above the Tucson basin. We’ve transformed a 25-acre observatory into a residential school, with hiking trails providing access to thousands of acres of public land.

We take school groups to our site for a week at a time, where students work in small groups to conduct original research with graduate students and other scientists. For many, a Sky School trip is their first experience outside their neighborhood, their first visit to public land, and their first contact with a real scientist. I know that these experiences can have a transformative effect on a life.

In our first two years we will have served more than six hundred students from seventeen primarily low-income schools. The community response has been overwhelmingly positive. Students have said, “I enjoyed what I was doing so much that I said I want to become a scientist”; “This has opened my eyes to all of the possibilities for myself in the scientific field”; “This is the best field trip I have ever been on.” Teachers agree, saying “To get them outside seeing what they’re studying is so important” and “this immersive, stimulating and engaging program will become a fixture in our school district’s science curriculum.” We are excited to keep growing and bring this experience to more schools in the Southwest.

My passion for science education was sparked by an AmeriCorps service year with the McCall Outdoor Science School. I lived in central Idaho, where I taught environmental science and saw firsthand the positive impact of environmental education. Much of what we are now doing at the Sky School is inspired by my time there. I hope that this chain of inspiration will continue, so that some of the Arizona youth we now serve will find ways to become the scientific and conservation leaders of tomorrow.

Talking about science education at the White House

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I was honored yesterday to speak at the White House about my work with the University of Arizona’s Sky School. We are a residential outdoor science school located in the heart of the Coronado National Forest. Our mission is to connect K-12 students to science and environment, and so inspire the next generation of conservation leaders.

The trip east was part of an Obama administration initiative, Champions of Change, intended to highlight people and projects that are making a difference in communities across the country. My work was highlighted along with thirteen other conservationists from around the country, who I feel inspired to have met.

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We were able to share our work with a diverse audience, including Sally Jewell (Secretary of the Interior, seen above, also with Sky School team member Pacifica Sommers) and Rhea Suh (the assistant Secretary of the Interior, seen below). Both photos are by the Department of the Interior. The Sky School model – connecting underserved students with authentic inquiry-based science education in the outdoors – is a replicable one, and I hope that our trip to DC will inspire others. My own inspiration for the Sky School comes from my AmeriCorps service at the McCall Outdoor Science School in central Idaho, where I was a part of a very similar vision.

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You can read more about our work at the Arizona Daily Star as well as at the Corporation for National and Community Service.


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