When was the last time you were so disoriented – if just for a moment – that it made you question the fundamental nature of space-time? The first time I experienced that was my first week of junior high, before I understood that the building (which was considerably larger than the elementary school I had attended) had two different sets of stairs. For the first day and a half, I struggled to understand why sometimes I arrived immediately at my new locker and between other classes I wandered through three hallways before finding it.
Arguably I have come a long way from that navigationally challenged twelve-year-old. I know how to use a topo map and a compass, and have even on occasion been entrusted with groups of small children out in the mountains. I think the fact that I keep bringing them back speaks well of my ability to get my bearings (eventually). And last August, I was ready to test those skills in one of the most challenging navigational situations on Earth: the Amazon rainforest.
For more on what I was doing in the Brazilian Amazon, you can skip to the section below, but to briefly set the scene, I had been there for about two weeks, and I was on my way to one specific individual tree about 600 meters (0.6 km) into the forest. I was not carrying a compass. Two intersecting trails could get me within 30 meters (90 feet) of the tree before I had to set off into the undergrowth on my own. The first trail, T2, is a straight line from the research base extending out for a full kilometer. Halfway down T2, it is intersected at a right angle by T4, another kilometer-long straight line. The route to the tree in question involved turning left onto T4, then after nearly 100 meters, striking off to the right into the forest:
I would find the point of departure from the trail using the PVC pipes marked with distance every 25 meters. I also had hiked to this tree several times in the last two days, so I had a vague memory of the lianas and fallen branches that marked the point.
Walking 30 meters from the trail would be straightforward in the desert or mountains, unless there were a cliff or an enormous cactus garden in the way. But in a dense forest like the Amazon, you can neither see your target nor where you came from. There are understory plants, lianas, fallen logs, and other hazards to throw you off course. Since I knew we had thrashed a bit of a break in the undergrowth over the past two days, and I also knew where to start from off the trail, I would just walk in a straight line from there to the tree, following those gaps.
However, another grad student who would be joining me shortly to climb the tree had only been to that particular tree once. He probably did not remember the exact place to leave the trail for easiest travel. So I scuffed a little mark on the ground with my toe. We would be within shouting distance, and I could tell him to look for that mark.
This time out, I was wearing a heavy backpack, full of climbing rope and rigging slings. I moved more awkwardly between the leaves, seeking larger gaps and snagging on thorns. I wasn’t sure I was following the same route I had before, but kept finding my way through gaps out toward the tree. I thought I recognized a downed log and went around it. I started to wonder if I had passed the right tree by then. Then suddenly, I stepped out onto a straight and well-beaten path where none should have been. I was stunned. Had I walked far enough and at enough of an angle to have arrived farther down T2? I looked left and right to see where the nearest meter marker might be. Then I looked down.
I was standing exactly on the scuff I had made before leaving T4. Somehow, without ever realizing it, I had walked a neat little circle, no more than 30 meters in diameter, and arrived exactly where I had started while thinking I was walking in an approximately straight line. I had heard of people walking in circles in forests, but pictured it happening to completely inexperienced hikers, maybe over the course of a few miles. Not to me, and not in so small a space.
Not long before I set out, another grad student there, Ty Taylor, had been talking about his strategy for navigating in the dense forest: get a sense for where the sun is, and walk straight relative to that. In other words, keep your head up, your focus on a higher objective, and avoid the trail-blindness trap of blundering into each next easiest vegetation gap.
The sun had been dodging to and fro behind clouds that afternoon, but, once my head stopped swimming, I turned around and got a good look at the angle of the shadows. I started walking toward my target tree, following the shadows, and not minding so much the snagging on vegetation. This time I walked straight to it.
I have kept thinking back to moment in the two months since, as I finish writing my dissertation. I like it for a number of reasons. Foremost was the profound wonder at understanding I had walked in a circle, laughing at the magic trick the forest had played on me, but also fairly awed at how completely I had been taken in. And of course there is also the physicality of the obvious metaphor: marching on with the heavy pack and trying again, where I had failed the first time – but this time maintaining perspective, context, and direction. Heading where I wanted to go, rather than focusing on finding the easy path that had been walked before.
For the curious: Why was I stalking a tree in the Amazon rainforest?
Last August, I spent several weeks helping with the Saleska lab’s research as part of an international collaboration in the Brazilian Amazon. The overall effort is broadly focused on predicting whether the largest carbon sink in the world will be able to absorb excess CO2 from the atmosphere, mitigating climate change, or whether it will die off and spew the carbon from decomposing wood into the air, which would accelerate climate change. One important piece of predicting whether a forest will die back or thrive under the potentially hotter and drier conditions is to know whether leaves can continue photosynthesizing. By measuring the water released by a leaf or the carbon dioxide taken up by a leaf, researchers can calculate their activity. But here’s the challenge (well, one of many challenges of doing research in the Amazon, really): conditions on the forest floor are pretty different than in the canopy. Sounds obvious, but it becomes important when you try to measure sensitive leaf behavior. So you have to get into the canopy.
Getting to the canopy means climbing up a tree anywhere from 20-50 meters. That’s about 60-150 feet! Rope systems are a must – if only because smooth, bare tree trunks are difficult to climb themselves, to say nothing of the risk of falling.
But if you are securing yourself to strong forks in the trunk, how do you safely work your way to the edge leaves that get the sun? Branches get thinner, and you are farther from your anchor point, meaning a longer fall and a nasty swing toward the trunk.
Professional arborists and experienced researchers can set up rope systems between multiple trees in a Tyrolean traverse to work their way out to a canopy in the middle, suspended by the ropes from other trees. But that is physically difficult, and can take several days to set up to sample a single canopy. Besides, where do you set your sensitive leaf-measuring equipment then while dangling there?
Solution: invest the time and expense to build platform walkways between some trees. And that is what they are doing, and what I helped with.
But once you spend the time and expense to build a small number of platforms, you want to make sure each one is really worth it – that it is safely built on large and healthy trees, with no big dead trees looming over it and ready to fall, and with multiple canopies of interesting species along the walkway.
It turns out these criteria are remarkably difficult to satisfy. After spending a day and a half searching about 25 meters to each side of an entire kilometer-long transect, I, along with an English arborist and a local forester had located only two potential sites. Part of the survey process involved sending the arborist up at least one tree in question to have a better look, which is why I had walked back and forth from the well-traveled T4 path to my target tree several times in two days.
This was the worst kind of exam: where your life might depend on remembering the material. Since I was lucky, I checked my answers against credible sources afterwards.
Here’s what happened:
About ten days ago, I was out at the site of one of my field studies for my dissertation research. This particular site was in Saguaro National Park West, the Tucson Mountains. It was a grass-covered hillside about two miles from the road. I have logged literally hundreds of hours at that site during monsoon season in 2012 and 2013. I have weathered storms there and on other mountains. I knew thunderstorms were possible that Thursday, as they often are during monsoon season, and I thought, “Great! If it’s overcast, it won’t be so hot.”
Something I did right: The Park rangers knew the location of my fieldwork for the day, and my housemate knew to expect me home by 5pm. ALWAYS tell someone where you are going and when you should return. I could have been more organized about leaving a map and the phone number of the rangers for my housemate.
I was out there removing nails and string that had marked my old study plots, now that the data was collected and the paper written. I had only a few more to go when I straightened up to look out at the view (it is a pretty beautiful site), and noticed the thunderstorm was, in fact, headed my way. Wind patterns can be unpredictable, and I have seen storms pass by miles away many times, so I waited until I saw lightning on the next set of hills, about 6-10 miles away, before realizing I might really get wet. Fortunately, I had only three more plots to go, so I hurried to jam the last of the materials in my backpack, then turned towards my car.
Something I did wrong: I should have just left much sooner. It turns out you are so much safer in a car or modern building (not a bicycle or tent) that that option trumps anything you can do to minimize your chances of being hurt if caught out in the open.
The first raindrops fell as I reached the bottom of the hill. My phone was already in a waterproof case, but I had forgotten a larger waterproof bag for my camera, so I wrapped it inside my hat, stuffed that inside my backpack, and hiked faster. The thunder was rumbling closer, and I was glad I had only flat desert and washes in the 1.75 miles left between me and my car.
Then the first ground strike hit between me and my car. I can only describe the shocked feeling I had as having been cheated or betrayed by the desert. I was supposed to be safe once I was off that hill! What was the lightning doing, hitting the low desert? Counting the seconds (“one-one-thousand, two-one-thousand…”), I guessed it was about a mile and a half away. The storm was sweeping toward me from my shelter, and I had nowhere to run.
I stopped and crouched down, then checked my watch, thinking that if no more lightning hit for fifteen minutes, I would keep moving in that direction.
Something I did right: It might be that crouching down doesn’t do much to minimize your chances of being hit. I was in the middle of a forest of 20 foot tall saguaro cactus – me going from five feet tall to three feet tall was unlikely to do much good. But it doesn’t hurt, especially as even shrubs in the desert can be hit, as long as you minimize your contact with the ground, and keep your feet together. Read on for why those are important.
Another ground strike burned a bright connection between clouds and the green haze of the rainy saguaro forest in front of me. I counted until I heard the thunder. This one was a little closer. I checked my watch. Barely a minute had passed since the first ground strike.
I thought about all the nails in my backpack. I couldn’t remember if having metal on me would make me a more likely ground leader. I took the backpack off and moved about twenty feet away, still crouching.
Something I did kind of wrong, but kind of okay: The sources I looked at said having metal hiking poles or electronics will not make a big enough difference in conductivity to make you an attractive ground leader. If you have a backpack that is full of something other than metal nails, it even makes a good insulator between you and the ground in the event of ground current. Up to half of lightning fatalities are caused by ground current – electricity spreading through the ground up to 50 or 60 feet away from the strike. The more insulation between you and the ground, the better. Sit on top of a backpack or crouch sleeping pad if you have one. I say I did it kind of okay because I took it off for the wrong reason, and didn’t think to empty out the nails and get on top of it, but I was more comfortable without the weight on my shoulders, and there wasn’t much in there to really insulate me.
I started going through a checklist of everything I could remember from outdoors leadership trainings on lightning safety. I still felt terribly exposed on the open, flat ground between the low shrubs and saguaros. Shallow washes ran parallel to me, the nearest one about 100 feet away. I ran to it, and down the bank. I crouched on the side of the wash, not down in the bottom where water could pool and run, but still lower than the flat ground surrounding the wash. I made sure I was at least 30 feet from all the saguaros and other tall plants.
Something I did right: Getting into depressions or washes is better than being on flat ground. NOAA says that probably does more to decrease your chances of being hit or taking ground current than just crouching down. However, water conducts electricity very well. Current could spread much further through water than solid ground, so make sure to stay out of any water in the wash. Also avoid holding on to wet ropes, metal railings and fences, and other long conductors.
Something else I did right: You probably know not to stand next to a tall tree (or cactus) in a lightning storm, because the current could arc out sideways (called side flash) and through you. There is less good data on how far away that arc could travel even than on how far ground current travels, but 30 feet away is probably safe. Stay crouched in a small ball away from tall trees to decrease your chances of side flash.
Ground strikes continued to hit the flat ground within two miles of me every one to three minutes for the next twenty minutes. I kept good track of that time, even though I stopped counting the strikes. Some were simultaneous sound and light, so I guess less than a quarter mile away. Some were long; the bolt burned white for what seemed like nearly a full second. I remember being surprised my ears were not ringing from those, but probably I wouldn’t have noticed them ringing over the constant grumbles overhead and the racket of the pouring rain on desert stone.
Have you ever tried to hold a crouch on your toes for twenty minutes straight? It’s really hard on your leg muscles. Mine were burning. I tried to shift positions, but I thought I remembered something about it being safer to have your feet or ankles touching, which limited the number of positions I could really get into.
Something I did right: Here is where I really suggest checking out the NOAA guide for their silly farmer and cow diagrams. Remember how I said up to half of lightning fatalities are caused by ground current? If your feet are together, the difference in voltage between your feet – leading current up through your body – is negligible. If your feet are apart, that difference in voltage can be fatal. This may have been one of the actions I took that improved my chances the most.
And after twenty minutes, the ground strikes retreated to the ridges. And ten minutes later (thirty minutes after the first ground strike between my car and me), I checked my watch, as I continued to do with every strike, and another one never hit. During the fifteen minutes I decided to wait until moving from my wash, from an abundance of caution, the rain stopped, then the rumbling overhead, then the sun came out. By the time fifteen minutes was up and I was walking, blue sky was visible overhead. I was shivering, but not cold enough that I had ever really worried about the hypothermia being more dangerous than the lightning.
I looked around for saguaros that looked like they had been hit during the storm, but you have to remember that I was in Saguaro National Park. There were at least hundreds of saguaros within two miles of me. This is the only one I found that might have been a hit, but I have no way of knowing whether it was during that storm or a previous one:
In the end, I probably just survived through luck, because no bolts hit close enough for ground current to affect me. But I minimized my chances of getting hurt should one strike close by getting down in a wash, away from tall saguaro, and squatting in a tight ball with my feet touching. If I had continued to run for my car, my path would have taken me near tall saguaros and eventually fences, with my feet apart as I ran. I guess, given that I had made the mistake of staying out too long in the first place, I made the right choice in getting down rather than continuing to move.
Summary: If you are outside and see or hear lightning coming….
If you can reach a car or modern building, go. If you are leading a hike, fieldwork, or some other trip, be vigilant and ready to turn back early if you hear thunder. Don’t get into a situation where you are playing your chances with lightning.
In the event that you are inevitably trapped an hour or more from your shelter, find a wash or depression. If you have a group, spread people out 20 feet apart so that not everyone gets hurt from the same event, and someone is still available to help evacuate, perform CPR, and call for help if a group member is injured. Stay 30 feet away from tall objects, and stay out of water. Get into “lightning position”: Squat down in a ball, keeping your feet together, on a backpack or sleeping pad. Do NOT lie down or otherwise increase your contact with the ground.
Wait ten minutes after the last strike with a ten second count between strike and thunder (about two miles) before moving out of your position.
Does it ever seem like the universe is has something against your field experiment? That’s not your imagination. Nature is definitely trying to undermine you.
Whether you’re in middle school searching for a science fair project, 84 years young and trying to determine what sort of animal is eating your garden, or a struggling PhD student hoping to make a career out of field research, I hate to tell you this, but your experiment isn’t going to work the way you thought it would. Instead, you’re going to learn so much more. Or you won’t, either way. So try to enjoy it.
My friend Ben Blonder learned a little about precipitation instead of plants when he arrived high in the Rocky Mountains of Colorado to set up a long term field experiment earlier this summer, and found the entire site was still under several feet of snow. You can read about his subsequent adventures that he detailed on his blog.
These are the steps that are usually left out of how the scientific method is taught in school. You thought there was only: 1. Make observations, 2. Form a question, 3. Define a hypothesis, 4. Design methods, 5. Collect and analyze data, 6. Draw conclusions, and 7. Communicate your results.
What they don’t tell you is that in between the steps of collecting and analyzing data, you have to insert: 4a. Realize your methods don’t work the way you expected, 4b. Redesign methods, 4c. Collect more data the new way, 4d. Repeat an unknown number of times.
I like to think that with more experience, those steps might drop out of the method. But I have a sneaking suspicion that instead, you simply become resigned to their presence and learn to expect them.
I have been learning a little about expecting the unexpected from some nocturnal research this summer. I have been trying all summer to get data from a field experiment on where pocket mice cache seeds (see my previous posts about this effort for details). I had designed an elaborate procedure to glean information about their movements from every spec of fluorescent powder they tracked away from my fluorescent dust covered experimental seed depots, combining that with video data to identify the animals. But then I realized two things:
- I could identify the trails and general movement if I just zoomed out, got my nose off the ground, and walked around (their little feet and tails and tummies track it around widely).
- This species does not tend to cache seeds outside their burrow as often as I thought they did.
Actually, I realized a third thing, too:
- Animals are jerks (they really are) and will do whatever you least expect them to do.
I realized I needed to examine a much larger set of instances of animals taking seeds from experimental depots I provided. I also realized this was possible to survey much faster with less detail, but greater understanding, if I walked around and generally looked at their movements – and that way, I might actually find some of the caches I was really interested in.
But of course my experimental depots were washed away by a large rainstorm in the driest part of the driest mountain range near Tucson. So, with a sinking feeling that I was wasting my time, I spent a few hours re-baited them all, even though it was predicted to rain again. This is monsoon season in the Sonoran Desert, after all. But it was a lovely few hours hiking in the desert, and hey, I probably needed the exercise.
Then, last week, armed with my UV flashlights, I headed out to survey for footsteps and caches.
I still had never found one of their caches. I knew what to look for by reading about them: signs of recent digging, with fluorescent dust in the apron of disturbed soil. I had seen the disturbed soil after recent digging was recorded by my game cameras. And on this rocky, hard-packed desert pavement hillside, recent digging is pretty rare and noticeable.
Fortunately, I brought a friend along who thought a night time hike in the desert with black lights sounded like a great way to see some scorpions, tarantulas, and other wildlife. (Lightning, too, as it turned out.) As we surveyed the second-to-last depot, he pointed at something glowing bright.
Uphill of the depot was a little pile of nine seeds, carefully piled between some pebbles. This was not a random arrangement of some seeds that had been dropped.
As we walked back along the rest of the depots, we found several more definite caches, and a few that were definitely non-randomly placed, but didn’t look very well hidden from pilfering neighbors, so I’m not sure what to make of those. But it turns out I wasn’t finding dug caches because these pocket mice don’t try to dig most of them – would you? If all you had was your hands and nails against the caliche and the rocks? Instead, it might be easier to cover them in a little pile with rocks in a crevice, or under a nice dense bunchgrass.
Just when I was ready to finally give up on this doomed field project, it reeled me back in by spitting out some data. This may be the most emotionally abusive research ever, or, well, just the usual doomed research process.
So with that thought, I provide you, fellow young scientist, with a field guide to handling the fact that your research is totally doomed:
- Have fun. If nothing is going to come of this anyway, make sure you got a lovely hike in, or listened to some rad music while collecting your useless data, or otherwise enjoyed the wasted time.
- Try to adopt a framework that includes variability in the environment as part of your understanding, rather than pretending it doesn’t exist.
- Be flexible, and ready to improvise.
- Get your friends involved, whether or not they’re experts in this arena. They have good ideas. Don’t be embarrassed to talk about the project with anyone you can bring it up to – you never know where that key suggestion or offer of equipment will come from.
- Don’t give up. Every research project is doomed, until it isn’t anymore. Maybe you can’t collect enough data to be useful in one season, but after 20 seasons, it might be pretty interesting.
What is the ecological footprint of your lunch today? Seriously, think about what you brought with you, or where you went out to today. How much land was required to grow the crops or raise the animals involved? How much water did they require? What additional processes go into that food beyond just growing it, like the oil burned to ship ingredients to you?
If you live in Tucson or in Hermosillo (or really in any city with increasing food cart culture now), your routine might include a visit to the nearest taco cart for some carne asada. And a team of researchers have now calculated the ecological footprint of all the carne asada from taco carts in Hermosillo. Their results will appear in a special issue of the Journal of the Southwest this fall.
Carne asada, as I recently learned from two of the authors, Nemer Narchi of ColMich and Alberto Burquez of UNAM in a presentation about their research, has a more specific cultural history and context than just beef that is grilled. This particularly North Mexican dish is a specific process of grilling beef on mesquite charcoal and is a relatively recent culinary invention dating from Jesuit arrival. Carne asada is typically served on wheat tortillas instead of corn tortillas. The article traces the way cattle and wheat together were major agricultural introductions that settled a traditionally nomadic indigenous dominated north, allowing it to be incorporated into the centralized Mexican state. As mining and cattle culture spread, carne asada served alongside tortillas and salsas was born from family celebrations after butchering cattle to serve miners in mining camps. As the population of Northern Mexico became more urban, unemployed butchers during recession cycles opened mobile restaurants serving snack-sized combinations of these ingredients: the taco carts.
The researchers then calculate the environmental and socioeconomic costs of the industry that has formed to produce the now ingrained culinary traditions. When you eat carne asada from a taco cart in Hermosillo, the cattle were likely raised on the extensive ranches surrounding the city. Throughout the state of Sonora, ranch lands are being converted from native Sonoran Desert thornscrub plants, including native grasses, to bulldozed and planted pastures of a grass introduced from Africa, known as buffel grass (Pennisetum ciliare). Yes, this is the grass that I have been studying for a good part of my dissertation research. It has a large effect on the native plant species. Between the bulldozing, the buffel grass planting, the water required, and the potential erosion and other effects of overgrazing, cattle ranching in Sonora to produce the legendary carne asada can have a heavy footprint, as well as a large one.
And then you must consider the wheat grown to produce the tortillas. And the native mesquite trees cut, frequently from ecologically fragile riparian areas, to produce the mesquite charcoal used to grill the beef. So what is the final footprint? You’ll have to check out their article this fall or some recent press coverage for more details.
But almost more importantly, this research focuses on the footprint of everyday objects, and provides a model for how to start researching that. You can plug your life statistics into online calculators to find out your overall ecological footprint, but it feels a little more abstract than knowing what this one taco required some specific amount of acreage and, increasingly importantly, some specific amount of water. They also examine why that footprint is what it is, what social and economic choices and policies and trends shaped that footprint.
What are the footprints of the small pleasures and cultural anchors of your daily life? What would be your taco cart if you were to follow the lead of Nemer, Alberto, and their coauthors, to find out what something you consume regularly costs ecologically and why it is made that way?
I can hear the cicadas buzzing outside, so I know it must be hot. The predicted high on NPR at dawn this morning was 99 degrees Fahrenheit. Not so warm for June in the Sonoran Desert, but uncomfortable. My fieldwork for several summers involved starting at dawn, but staying out all day in this, marking little seedlings on exposed hillsides. (You can see very preliminary – not peer reviewed yet – results of what I found at the Southern Arizona Buffelgrass Coordination Center website.) All summer. It was, well, tough. I have a rather unique data set as a result.
I was listening to the NPR weather report at dawn today because I was on my way to a field site to retrieve some plastic trays of seeds coated in fluorescent powder I had left out all night before. I am interested in the places nocturnal seed-eaters go. The wind picks up during the day, so I wanted to minimize the powdery spray between the time the seed eaters tracked it around, and when darkness falls and I can return to trace their pathways with blacklights (and friends!). I explained a little about the goals of the project in my previous post.
This dawn and dusk schedule is much more comfortable, convenient for me getting other writing done during the day, and also for attracting volunteers. Many animals adopt this schedule in hot deserts. The schedule even has a name: crepuscular, although I call it the siesta schedule. This will be key because I am detecting fewer pocket mice per night than I had hoped. So I may be in for many more crepuscular days of leaving little offerings to the desert, trying to increase my sample size.
Here is a teaser of the pocket mouse (genus Chaetodipus) jamming the fur-lined pockets next to its mouth full of seeds, then burying them nearby like a pirate with treasure, or a squirrel with nuts. Most animals that “scatterhoard” their seeds in many small caches near the source later return to move them to secondary caches, or even eventually to their “larder” in their burrow. I suspect these pocket mice behave in a similar way.
And as a bonus, when the little guy (or gal) first showed up, before eating anything, it did my favorite “dancing” behavior:
Was it marking this resource for itself? Attracting a mate? Doing an instinctive behavior in response to positive stimulus? We need an animal behavior specialist to get on testing this.
And a few last gratuitous shots of the experimental set-up during a beautiful Tucson sunset:
Ever wondered what a javelina (Pecari tajacu, syn. Tayassu tajacu) looks like from underneath? Yeah, me neither.
I did wonder, however, whether pocket mice (genus Chaetodipus, yes, the dancing ones), known for foraging under cover to avoid predation by owls, would tend to bury palo verde or other seeds under buffel grass (Pennisetum ciliare). Buffel grass is an invasive bunch grass spreading through the Tucson Mountains that inhibits native seedlings from establishing – and provides some nice cover to these mice, potentially attracting them to bury native seeds in the worst possible place: right under buffel grass.
To test this hypothesis, I left fluorescent-dusted seeds on fluorescent-dusted trays in the desert to see where mice would take the seeds, planning to return tonight with UV flashlights to follow their luminous footsteps. It felt like leaving sunset offerings to the tiny, dancing desert gods.
Much like the fantasy world of Game of Thrones, however, the Sonoran Desert has many gods who are more than happy to accept offerings. Most seed trays, it turned out, were visited by a roving band of javelina. Check it out:
You get a great view of their four-toed front feet, of their flexible snout at work, at their lumbering gait, and their curious investigation of the seed trays, marking flags, and cameras, and their powerful molars grinding the seeds of the foothills palo verde (Parkinsonia microphylla). One of the major reasons scatterhoarding rodents like pocket mice may be beneficial for the trees is that they protect some seeds from destructive consumers, like javelinas.
Often thought to be pigs, javelina are in a different family, although still related. This is an animal that is hunted for sport and meat, and is seen as a menace and a pest as it roves through town, knocking over trash cans. It lives in a wide variety of habitats, including even cloud forests and swamps as far south as Ecuador. Check out more information on them from the Arizona-Sonora Desert Museum, or visit in person to see some javelina yourself.
Driving down the Catalina Sky Highway from the summit of Mount Lemmon, Tucson looks at first like a dusty blond blur. As you approach the base of the mountain, patches of brilliant lemon resolve themselves.
As anyone with allergies knows, the palo verde trees (genus Parkinsonia) are blooming in force right now. But which neighborhoods are so infused with the native trees? Where do they start and end? From thousands of feet up, drawing patch lines seems trivial, but walk through the streets under the branches themselves, and you feel less certain. Is this block in, or does the patch start one more over?
You may begin to notice patches even within neighborhoods. At what scale should the palo verde patches be drawn?
The patch size of interest probably depends on your question. If you are seeking palo verde trees in Tucson to photograph (or seeking to avoid their pollen), a map with the raw number of trees per block might be helpful without trying to draw lines around patches. So why bother delineating these categorical zones at all? Why not measure some continuous variable, such as the number of palo verde trees on the block?
In other cases, a patch size itself is an important variable, so you have to stand back, squint your eyes, and draw the lines. The local invasive bunch grass buffel grass (Pennisetum ciliare), for example, grows outward in roughly circular patches. To track the rates of its spread in the foothills of the Santa Catalina Mountains, researchers have used repeated aerial photographs and traced polygons around the visible buffel grass patches.
I just returned from four days at UA Science Sky School, where we had snowball fights between the pines and aspens! There are no palo verdes to be seen on top of Mount Lemmon, which is a Sky Island, a little patch of pine forest in a desert sea. But where does that patch boundary lie? In fact, the vegetation changes in several dramatic and distinct zones as you travel up the mountain, but trying to pinpoint the transition point is an exercise in frustration.
The groups of students from Flowing Wells High School that I mentored this week at Sky School also had to confront these questions as they conducted field-based scientific research. To answer their question about how resources for plants (and animals) changed as a result of forest fire, we needed plots on either side of a burn boundary. The boundary of a fire seems abundantly clear until you are forced to locate a 10m x 10m plot right along that boundary.
Fortunately, the students in my group were focused on what characteristics mattered for their question. The question of where a boundary lies, at what scale, can be a very scaly problem indeed, and they resolved it by drawing a thicker boundary line between the burned and unburned areas, on either side of which the light, vegetation, and water availability was less affected by proximity to the other type of area.