24

Frogs in the Clear-Cut

I was crouched under some vines with my knees pressing into the soil. I carefully turned over clumps of dead leaves one after the other, feeling them crunch between my fingers. I could smell the leaf dust. My long brown hair fell in strands in front of my face and sweat rolled down my back. It was a warm September day, and I was searching for frogs. I peered through the vegetation looking for movement. Not seeing any, I rolled a small log and there it was! Something small and brown suddenly leaped away from the log. It was in one location and then suddenly somewhere else. The 3-cm-long juvenile Wood Frog (Lithobates sylvaticus) had such long legs that it could cover long distances (for its size) with a single spring. The Wood Frog’s skin was metallic brown, almost bronze, and it had a pointed nose and a dark brown mask around the eyes. Its very long legs had subtle, splotchy stripes. The frog escaped my grasp rather quickly. Then it disappeared, blending in with the leaves covering the ground. I had to chase it down.

My doctoral advisor, Ray Semlitsch, had talked me into studying Wood Frogs. I had resisted because it seemed like everyone studied Wood Frogs and there were already loads of data on them, partly because they are the most widely distributed species of amphibian in North America. I had wanted to study something unusual or a species that no one had bothered to study because I’ve always been intrigued by things that are different and unknown. This might be because I’ve always felt a bit different. I am generally quiet and drawn to the trees. This made me stick out as a child but are rather good attributes for an ecologist.

Despite their widespread distribution and abundance in some areas, Wood Frogs are a species of conservation concern in Missouri, where I was working, because this population was at the very southern edge of the species’ geographic range. By this time, I had also come to adore Wood Frogs. There was something mysterious about them. Adults appeared early in the year to mate and lay eggs when it was cold enough that I would wear a striped wool hat and bring a thermos of hot ginger tea to keep myself from shivering. It was strange to think the peak time for an ectotherm was when it was just warm enough for the pond’s ice to thaw. Some other graduate students and I would go count the egg masses in each pond and sometimes find over 100 in a tiny pond where the surface of the pond looked lumpy with all that frog jelly. After mating, adult Wood Frogs vanished into the forest for the rest of the year. I saw only one adult outside the breeding season in the four years working there, and it was the weirdest thing to see it hopping through the forest in the middle of a hot day.

While searching for juvenile Wood Frogs, I was in a 3 × 3 m terrestrial enclosure made from a fine steel mesh, extending a few centimeters down into the soil and coming up to my waist. I had 24 of these enclosures stocked with newly metamorphosed Wood Frogs in June and July. The enclosures allowed me to keep track of these juveniles while studying their survival and growth. If you release a juvenile frog into the forest, even with traps, you will likely never see it again no matter how much effort you expend. By confining the frogs, I was able to find them again to collect data. I was using these enclosures to study the effects of different forestry practices on juvenile frogs; the enclosures were placed within a larger experiment on forestry practices. Circular areas were defined around amphibian breeding ponds, and each circle was divided into four pieces like a pie, with a different forestry practice in each piece of the pie. The four forestry practices included uncut, mature forest; clear-cut with logs left on the ground; clear-cut with no logs; and forest that had about half of the trees cut to allow more light, like a savannah. The two clear-cuts were always opposite each other, so if you looked down from an airplane, it looked like there were bow ties cut out of the forest. With enclosures in areas with these different forestry practices, I would be able to estimate whether the juvenile frogs survived better or grew faster in areas with certain forestry practices. I also counted the number of logs and measured temperature, soil moisture, and vegetation cover in each of the enclosures to better understand what was most important to juvenile frog survival and growth. If these variables were more important than the forestry practice, I might be able to make recommendations to foresters about how to harvest trees for a profit but still conserve amphibians on the landscape.

So, that September day I had to catch that frog to find out which one had survived and measure its length and weight. Given that I was in an enclosure and the frog couldn’t escape, you would think that would be easy. However, I was also trying to avoid poison ivy to the face, the unrelenting thorns of blackberries and raspberries, and the never-ending radiating clusters of lone star ticks, each with a white circle on its back. I was a key victim of these ticks, frequently getting more than anyone else and earning the nicknames Tick Bait and Queen of the Ticks, neither of which I particularly liked. I had sent my volunteers to enclosures without poison ivy, since I didn’t react to it (though I have since lost this fieldwork superpower, unfortunately). After scrambling around for a bit, I managed to grab my little frog.

Holding small frogs is tricky because you have to be firm enough that they can’t wriggle their slippery skin out of your hand and escape but not so firm that you crush them. Wood Frogs are rather small and delicate as juveniles. I usually held them with my index finger and thumb at the waist so their long legs dangled down. I was sure this one was frightened to have a giant track it down, which made me feel a bit guilty, but I loved looking into their beautiful golden-flecked eyes and their hands held out like they wanted to shake mine in greeting. I inspected the frog’s fingers and toes to find marks that individually identified the frog. I called out to my undergraduate research student, Paula, to write down the frog’s ID number and the enclosure number on our data sheet, and then I placed the frog in a small plastic box with air holes in the lid and labeled it with the enclosure and the date. I would later take it back to the lab to measure.

In the other terrestrial enclosure in this clear-cut, we found a very large brown adult American Toad that was speckled with grey and rusty patches but not part of the study. When she saw him, Paula yelled Sapito! (meaning little toad) in her delightfully warm Peruvian accent and had the largest grin on her face. Paula loved toads because of their adorably grumpy demeanor. We gently let him go outside the enclosure and noted his presence on the data sheet. Then, we gathered up the gear, the box with the juvenile Wood Frog, and the other volunteers and moved on to the next set of enclosures.

As we walked toward the uncut forest, I looked back at Paula. She was carrying the clip board level and balancing the big toad on it, which was bouncing along in a seemingly contented way. I sighed and said, Paula, put the toad back.

She looked at me disappointedly, But he’s so cute.

Put him back. His home is back in the clear-cut.

She turned around begrudgingly. I went on to the next set of enclosures and got everything set up, so we could start the next set of searches. When Paula returned, we crouched down in the next enclosure, turning over every log, disturbing every pile of leaves, and investigating every hole in the soil.

We didn’t find any Wood Frogs in that one. We wrote that down and went on to the next one all day long until we had searched all 24 enclosures and found 26 frogs out of the initial 400. We returned the next day to make sure we didn’t miss any frogs. Of course, we did. It’s very difficult to track down every individual in an area. In fact, ecologists expect that and actually estimate what’s called the detection probability to account for it in statistical models. We found four more juvenile Wood Frogs the second day, along with a beautiful Earth Snake and a Leopard Frog. It turned out that we must have missed another three, because we returned the following May to look at survival and growth over the winter and found a few frogs that weren’t caught back in September. Paula worked hard with me every step of the way, spreading joy and generally making the work more enjoyable. I baked chocolate chip cookies, which she loved, to help keep her happy during the long work days. She often placed the cookies on the dash of my car to make them all warm and gooey. I brought watermelon for everyone as well, which helped cool us down after working in the heat.

In the end, we found that juvenile Wood Frogs had low survival, which is fairly common for young frogs. Only 12% survived from metamorphosis in June until September. For the frogs that made it to September, they had a 39% chance of surviving from September until May. The one thing that really helped the little frogs survive was logs. Having logs on the ground helped protect the soil from drying and gave the frogs a protected area to shelter from heat and predators. Many insects also like logs, so the logs may have provided a buffet of frog food. The presence of logs was actually more important than whether the area had been clear cut or not. My study was done three years after the initial forest harvest, so the clear-cuts didn’t look quite like you might imagine. By three years after the trees were cut, small trees, bushes, and brambles had grown up to my shoulders or higher. The presence of this vegetation shaded the ground enough that there was no difference in the temperature or soil moisture between clear-cuts and forest. It still got really hot and dry in summer in Missouri. My study showed that retaining some logs on the ground after harvesting timber could increase the survival of Wood Frogs. This may not be appealing to foresters because that might represent some loss of revenue, but they could choose damaged or crooked trees that are worth less as a way to help conserve Wood Frogs. To me, it’s a small price to pay to see those charming frogs with the bandit mask, bronze skin, and golden-flecked eyes.

I haven’t been to that site in Missouri in 10 years, and it was cut 18 years ago. I sometimes pull up the satellite images on my computer so I can see what it looks like. If I look carefully, I can still see the faintest of bow ties in the forest, where the trees are different heights from that clear-cutting. I wonder how the Wood Frogs are doing, and I miss my time in the forest with Paula and all my other friends who helped me catch frogs. I still catch frogs and more often listen to them sing, but there aren’t Wood Frogs where I live, and it’s not quite the same.