2024 FIELD REPORT: TREE FALL PLOT BIODIVERSITY STUDY (pdf)
5E Lesson Plan: Coming Soon
Date: July 12 – 19, 2024
Location: Explorama’s Napo-Sucusari Biological Reserve, Loreto Peru
Study Site: The Amazon Conservatory for Tropical Studies (ACTS)
Lead Researcher: Dr. Rob Naczi and Dr. Lindsey Swierk
Team Members: Debby Prestridge*, Jordan Wolf*, Piero, Andrea, Dr. Jeannine Richards, Josias, Kirsten Franklin, Christa Dillabaugh, Matt Naczi (* = authors of this report)
Abstract
Data collection at field stations is critical to long-term environmental studies of natural systems. Since tropical forests sink half of the carbon, having a better understanding of the amounts will help us build better models to predict the pace of climate change. A tree fall, opening up the canopy provides an opportunity to examine emergence of species and rate of growth. Two ten- meter areas were marked off, one with a newly fallen tree and a connected control plot. We used four methods to collect data from each tree plot including: 1) digital image analysis and canopy densiometer measurements to quantify the percentage of light available through the canopy, measure the 2) primary and 3) secondary annual growth for selected trees, and 4) collect flying insects in the Vertical Flight Intercept to sample organisms present. The canopy was more closed in the tree fall plot than the control. There were increases in both plots in both primary and secondary growth since 2023, with larger increases in the tree fall plot. However, difficulty relocating marked branches and errors in measurement make it difficult to conclude there are significant differences between the plots.
Lay/Marketing Summary
Sunlight is critical to plant survival, accounting for the aggressive growth after a tree fall, fighting for the light available through the canopy gap. Seeds lie dormant underground, ready for rapid growth to take over the opening. Since rainforests store about half of the world’s carbon, understanding the new growth in a tree plot extends our knowledge of rain forest dynamics and carbon absorption that help us address climate changes in other ecosystems. Measuring changes in plant life, organisms and light density over time provides insight into how tropical rainforests evolve as carbon sinks for the world.
Introduction
Primary producers, such as trees and other plants, are the basis of food webs and nutrient cycles in tropical ecosystems. Tropical forests are constantly changing, from the cycles of leafing, flowering, and fruiting, as well as shifts in community dynamics and energy availability following events like tree falls or flooding. In this long-term study, we are monitoring ecological succession – natural changes in structure and diversity over time – in the forest surrounding a tree fall. Our objectives are to examine the theoretical frameworks of community ecology and forest succession, measure biodiversity among plants and animals, and monitor phenological changes (the “timing of life”) in the area surrounding a tree fall gap.
Specific questions of interest are:
- What are the differences in abiotic factors between tree fall gaps and no-gap forest areas?
- How do changes to primary producers affect animal communities?
- Do tree fall gaps follow the same phenological patterns as the adjacent no-gap forest areas?
By investigating growth rates in light gaps, we aim to contribute to knowledge of the relationships between rainforest trees and carbon sequestration, in addition to the broader ecological changes occurring in plants and animals following a tree fall. To achieve this, our efforts are currently centered on documenting how forest structure and biodiversity change following canopy-level disturbances creating light gaps.
Materials and Methods
In 2023, we established two 10 x 10 m square plots for study: one surrounding a recently fallen canopy tree, and another nearby plot with intact canopy trees. Each plot was divided into four quadrants, with the center of each marked with flagging tape. Bioacoustics recorders were placed in each plot along the edge farthest from the trail to measure bird and amphibian plot visitations; bioacoustic analysis is ongoing and results are not reported here.
Canopy cover estimation
Each year, to estimate canopy cover and change over time, we took a photograph of the canopy at the center of each quadrant using a camera (Olympus Tough TG6) and level, held at ca. 1.4 m above the ground. These photos analyzed using the automated Canopeo program (Patrignani & Ochsner 2015). A densiometer was used in 2024 as a second measure of canopy cover at each quadrant center, and various smartphone apps were also pilot tested (Figure 1). We used Wilcoxon rank sum exact tests to compare differences in canopy cover from year to year, and between treefall and control plots each year, using both Canopeo data (for all) and densiometer data (for 2024 treefall and control plot comparisons).
Identifying and marking trees for growth determination
Within each plot, one representative tree per quadrant was selected in 2023 for annual growth monitoring. For each tree, we identified a branch to measure primary growth by tracking shoot elongation. Primary growth occurs at the apical meristems of root and shoot tips, resulting in increased height and length. We marked one shoot tip per tree for a total of 5 trees in the treefall plot and 5 trees in the control plot. The shoot tips were marked with permanent white paint, applied with a small brush. Secondary growth was assessed by measuring the diameter at breast height (DBH) taken 140 cm above the ground, of 5 different trees per plot. In 2024, we relocated the marked shoot tips, and we measured growth from the painted tip to the new shoot tip. We then marked the current shoot tips with yellow and white paint markers in a white-yellow-white pattern around the stem (Figure 2).
Flight-intercept insect trapping
An insect survey was conducted at both the treefall plot and the control plot using a modified version of the Vertical Flight Intercept Trap (V-FIT) as described by Löbl, Leschen, & Warner (2021). Each trap was constructed with four corner posts arranged in rectangle (ca 1.5 x 1 m), on which a clear plastic sheet was hung on ropes stretched from post to post. The plastic sheet was draped between the two longer sides of the rectangle, with a long pole placed at the bottom, so that the plastic formed a V-shape when viewed from the side. Beneath the lower point of the “V” on the forest floor, we placed four aluminum trays (single-use food service trays, approximately 32 × 25 × 6 cm, length x width x depth) to collect specimens. Each tray was filled with a non-toxic solution of water and dish soap, maintaining a liquid level no higher than 5 cm from the trap’s bottom. Insect flight is intercepted by the plastic sheet and insects fall into the tray traps below.
We collected insects from traps daily by pouring each collecting pan’s contents through a sieve into another vessel to collect the organic material (Figure 3). The organic material was transferred to a collection container of ethanol and labeled with plot ID. After each collection, the trays were returned to their respective traps, and the liquid levels were adjusted to the proper height. Following preservation, contents of each collection container were placed into a white sorting dish. Using tweezers, a magnifying lens, and light, we carefully separated non-insect matter from insects. The insects and identifiable parts were then sorted into categories based on tentative identification. Once sorting and identification were complete, we quantified the insects in each category.
Results
In 2023, canopy cover in the treefall plot was significantly lower than that of the control (W = 16, P = 0.029), but this difference disappeared by 2024 (W = 14, P = 0.114; Figure 4). Although the control plot canopy cover did not differ between years (W = 3, P = 0.200), the canopy cover of the treefall plot greatly increased from an average cover of 14.6% to 44.8% (W = 1, P = 0.057). The densiometer data collected in 2024 demonstrated a different pattern from the data from our canopy cover photos, with greater average treefall plot canopy cover than control plot (95.1% vs. 92.9%, respectively; W = 0, P = 0.029).
Recovery of primary growth tree markings from 2023 proved challenging, with only 5 out of 10 (50%) markings successfully identified. In the treatment plot, 3 of the 5 trees exhibited broken branches and missing paint marks, limiting primary growth measurements to just 2 of the 5 trees. Three trees in the control plot were measurable for primary growth. The control group exhibited a mean increase of 5.0 cm, while the treatment group showed a much higher mean increase of 29.8 cm. For secondary growth, the treatment plot showed a mean increase of 0.82 cm, compared to a mean increase of 0.16 cm in the control plot. However, this difference was not statistically significant (W = 20, P = 0.140).
Discussion
Our initial hypotheses suggested that the treefall plot would exhibit increased growth compared to the control plot. The data collected by the 2024 ARIE treefall team (Figure 6) generally support this idea, and the increase in branch elongation observed in the treefall plot deserves further investigation; however, the issues with data collection—such as broken branches and fading markings— limits the strength of these conclusions. The findings highlight the need for improved data collection methods, specifically the use of paint markings used to track growth. This year, we implemented a three-band color pattern using alternating yellow and white paint to enhance visibility, which should enable more effective tracking in future years.
In the long term, we hope that our data collection will enable us to make comparisons between the distinct phenological patterns in tropical rainforests compared to other forest types. Unlike deciduous forests, where growth is strongly influenced by seasonal temperature and daylight variations, tropical rainforests experience relatively stable abiotic conditions. Here, rainfall patterns and the wet-dry season transitions are likely to play a crucial role in influencing growth.
Several key questions remain that will guide the next phase of this long-term project:
1. Abiotic Factors: What are the differences in abiotic factors between tree fall gaps and surrounding forest areas? Future studies should collect weather data, particularly rainfall and temperature, to address this question.
2. Impact on Fauna: How do changes in primary producers affect animal populations? We will need to develop a systematic approach for collecting animal data, which could include methods such as camera traps, direct observations, and tracking. Our bioacoustic recorders placed at each of these plots offers a good option for animals that can be detected from their vocalizations.
3. Phenological Patterns: Do tree gaps follow the same phenological patterns as the surrounding forests? Ongoing annual data collection will help us address this question.
Overall, addressing these questions and improving data collection methods will enhance our understanding of the dynamics within tropical rainforest ecosystems to inform future conservation efforts.
References:
Farrior, C. E., Bohlman, S. A., Hubbell, S., & Pacala, S. W. (2016). Dominance of the suppressed: Power-law size structure in tropical forests. Science, 351(6269), 155–157. https://doi.org/10.1126/science.aad0592
Hoffner, E. (2019). Long-term ecological research threatened by short-term thinking. Mongabay Environmental News. https://news.mongabay.com/2019/06/long-term-ecological-research-threatened-by-short-term-thinking/
Lõhmus, A., Lõhmus, P., & Runnel, K. (2018). A simple survey protocol for assessing terrestrial biodiversity in a broad range of ecosystems. PLOS ONE, 13(12), e0208535. https://doi.org/10.1371/journal.pone.0208535
Löbl, I., Leschen, R. A. B., & Warner, W. B. (2021). Scaphisomatini of Arizona (Coleoptera, Staphylinidae, Scaphidiinae) collected by V-Flight Intercept Traps. Revue suisse de Zoologie, 128(1), 173-185.
Patrignani, A., & Ochsner, T. E. (2015). Canopeo: A powerful new tool for measuring fractional green canopy cover. Agronomy Journal, 107(6), 2312-2320. https://doi.org/10.2134/agronj15.0034
Sakai, S. (2001). Phenological diversity in tropical forests. Population Ecology, 43(1), 77–86. https://doi.org/10.1007/pl00012018
Previous Field Reports
For additional information or questions about this field report, please contact Dr. Lindsey Swierk (lindseyns@gmail.com), Director of Scientific Research for The Morpho Institute and Associate Director of Research for the Amazon Conservatory for Tropical Studies.
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