Not all ecology is done at ground level – in this Insight, Evan Gora, a postdoc at the University of Lousiville, talks about looking at decomposition when the dead wood stays in the canopy.

Gora, EM and JM Lucas. 2019. Dispersal and nutrient limitations of decomposition above the forest floor: evidence from experimental manipulations of epiphytes and macronutrients.

About the Paper

What’s your paper about and why is it important?

This paper investigates how nutrient availability and microbial dispersal limitation influence decomposition above the forest floor. This is important because approximately half of wood necromass is not in direct contact with the forest floor, yet nearly all information about the process of decomposition comes from ground-level studies. This disconnection is problematic because the process of decomposition changes above the forest floor due separation from soil resources and soil biota. To start addressing this knowledge gap, we experimentally manipulated epiphytes and macronutrients to test how the removal of soil resources influences decomposition.

How did you come up with the idea for it?

The ideas for this project developed over a little more than a year. I started thinking about dead wood in the canopy because of a conversation I had with my then-boss, now postdoc advisor, Steve Yanoviak while we were working in the canopies of adjacent trees (I was a technician assisting with canopy ant research). We were discussing the role of dead wood in the canopy and how this might be important to broader patterns within a tropical forest. Over the next year, I consumed all the literature that I could find on the topic and, when I returned to the tropics, I intended to conduct a water addition and nutrient fertilization experiment to test canopy level decomposition. Once I arrived back at the field station, I sought advice from Joe Wright and Mike Kaspari about the logistics of this project because they had relevant experience with nutrient manipulations. I was promptly informed that my plans were infeasible (they were!). However, Mike also suggested considering natural sources of nutrients and soil in the canopy, such as epiphytes. After a couple of months of reading about epiphytes, I devised a plan to use epiphytes to test the nutrient and dispersal limitation hypotheses, as outlined in the paper.  Working with Jane Lucas, we then developed the nutrient fertilization experiment to more directly test the nutrient limitation hypothesis.

What is the key message of this article?

The general takeaway is that the mechanisms underlying decomposition differ between the forest floor and higher locations within a forest.  This means that our ground-based understanding of decomposition is potentially flawed, and a more holistic approach is necessary to understand how actual substrates, such as entire trees, decompose in situ.

About the Research

What were the challenges you faced setting up this experiment?

The most difficult part of this project was climbing into and within the canopy to set up the canopy resource experiment. Climbing is hard work, especially with multiple bags of equipment and the complex vegetation that exists in a mature tropical forest. I used a single rope climbing technique to get into the crowns of these large Anacardium excelsum L. trees. First, I hiked out into the forest to find a suitable focal tree. Once I found a tree, I used a small wrist slingshot to shoot a fishing line with a 1oz fishing weight over the branches that I wanted to climb. I used the fishing line to pull a paracord up into the tree and that paracord enabled me to pull up a climbing rope. Once my rope was set, I then climbed 25-35 meters into the canopy with my primary pack on my back and trailing a second gear bag, which held another 20 pounds of equipment for manipulating epiphytes and sampling microbial communities. Once I was in the canopy, I anchored myself and started the multi-hour process of climbing around the canopy to set up the experiment. I typically repeated this process 2 or 3 times a day, starting at 7am and finishing at 6pm or whenever a storm made it too dangerous to climb. This was one of the most physically demanding projects I’ve ever conducted.

Where you surprised by anything you found?

The patterns associated with our hypotheses are largely what we expected. However, our results in this project and some of our related work indicate that there might be interesting dynamics between fungal and bacterial decomposers in the canopy. It is possible that saprotrophic bacteria are pioneers of decomposition in the canopy due to dispersal limitations experienced by their fungal competitors. This is interesting because bacteria were historically considered not important for wood decomposition, but our observations contribute to a growing body of work demonstrating that bacteria are more important than previously believed. The pattern I described here was incidentally captured by these projects and we only have circumstantial evidence, but it is ripe for further exploration. I hope that myself or someone else has the opportunity to follow up on this dynamic in the near future.

About the Author

How did you get involved in ecology?

I was always interested in nature and its function. However, I had no idea that you could have a career investigating natural processes until my sophomore year at the University of Pittsburgh. I made this discovery during Walter Carson’s ecology course, in which he used examples from his own research to reinforce certain lessons about ecological principles. After a few weeks of class, I approached Walt and asked him if he had any opportunities for research assistants at Pitt’s field station in Pymatuning. Walt connected me with his graduate student, Eric Griffin, who offered me my first research position, in which we investigated the effects of invasive Purple Loosetrife on wetland plant communities.

What is the best thing about being an ecologist?

For me, I love two things most about this job. First, there is nothing more rewarding than mentoring and counseling students on how to conduct research or pursue careers in science. Second, it is pure joy to spend time in a forest observing natural phenomena and developing hypotheses about how these phenomena really work.

What do you do in your spare time?

I enjoy many things typical of ecologists, such as hiking and traveling, but I am also a passionate Pittsburgh sports fan. I have only missed 5 Pittsburgh Steelers games over the past 20 years (an American football team) and I watch the vast majority of Pittsburgh Penguins games too (an ice hockey team).  With some creativity, I’ve been able to continue following these teams despite living at a field station in Panama half-time since 2014.

Read the article in full here or the plain language summary here.