Life After the Fall: Teachers Explore Tropical Forest Canopy Gaps

Field Notes From the Amazon

Field Report: 2023 Impact of Tropical Forest Canopy Gaps on Biodiversity and Growth


Date: July 12 – 19, 2023
Location: Napo-Sucusari Biological Reserve, Loreto Peru
Study Site: The Napo-Sucusari Biological Reserve / The Amazon Conservatory for Tropical Studies (ACTS)
Lead Researchers: Dr. Rob Naczi and Dr. Lindsey Swierk
Team Members: Kathy Hockman*, Terry Wilson, Marissa Copan, Shannon King, Christa Dillabaugh (* author of this report)


Introduction
Primary producers (trees and other plants) are the basis for the food webs and nutrient cycles in the tropics. Tropical forests are constantly changing, from the timing of leafing, flowering, and fruiting of trees, to the changes in the community dynamics and energy available on the forest floor after a tree fall or after flooding. Forest structure in rainforests leads to consistent patterns of trees, both in size and species.
In this long-term study, we monitor succession (natural changes in the structure and diversity through time) in the forest surrounding a tree fall. These activities were designed to examine the theoretical frameworks of community ecology and forest succession while learning to measure the biodiversity of plants and animals, monitor phenology (the “timing of life”) while monitoring ecological community change.
We are documenting how forest structure and biodiversity change after a canopy-level tree falls, creating a light gap. Specific questions of interest are:
• What are the differences in abiotic factors between tree fall gaps and other forest areas?
• How do the changes to the primary producers change the animals?
• Do tree gaps follow the same phenological patterns as the surrounding forests?

Methods
We designated two 10 x 10m square plots for study: one around a recently fallen canopy tree, and the other in forest without a fallen tree. Each plot was divided into four even sections (quadrants), and the centers of each quadrant were marked with flagging tape. To estimate canopy cover, we took a canopy photo using a camera and level at the center of each quadrant for both plots. We will use digital image analysis to quantify the percentage of each photo covered by forest canopy and monitor canopy regrowth over time.

Identifying and marking trees for growth determination
We chose one representative tree in each quadrant of both study plots to mark and monitor for annual growth. On each tree, we identified one branch to measure primary growth using elongation of shoots. Primary growth occurs in the apical meristems of root and shoot tips resulting in increases in height and length. We marked one shoot tip per tree for a total of 5 different trees in the treefall plot, and then marked shoot tips on 5 different trees in the control plot. To mark shoot tips, we used permanent white paint, applied with a small brush. Using the brush, we were able to apply the paint only to the tips of the shoots. Assuming the paint will be permanent, next year, we will relocate the paint marks, measure the distance from the paint mark to the current shoot tips, and then apply new marks at the current shoot tips. Secondary growth was measured on 5 different trees per plot by measuring diameter at breast height (DBH).

Fig 1: Marking Branch Growth in the Plot

Insect survey
The trap design (Fig. 1 ) used to collect specimens on the plots is a version of the Vertical Flight Intercept Trap (V-FIT) described by W. B. Warner (Löbl, Leschen, & Warner 2021). Each trap used 4 corner posts placed in a rectangular shape with a length of 3 m (10 ft) and a width of 1.5 m (5 ft). An appropriately located tree trunk is acceptable. We placed 4 aluminum trays (single-use food service trays, about 32 cm × 25 cm × 6 cm deep) under the bottom of each of the traps to serve as catchments. Each tray was filled with a water/dish soap solution as a non-toxic preservative so that the water surface was 5 cm or less from bottom of trap.

Fig. 1: Vertical Flight Intercept Trap (V-FIT)

We checked traps daily. We poured each collecting pan’s contents through a sieve into another vessel to collect the organic material. The organic material was transferred to a collection container of 65% Ethanol and labeled with plot ID. Collection pans were then returned to the traps and the liquid was restored to proper levels.

Fig 2: V-FIT trap monitoring team

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; insects and identifiable insect parts were then sorted into categories based on tentative identification. Once division and identification were complete, we counted insects in each category and recorded results.

Fig. 3 Identifying insects from V-FIT collection bins

Results
During the first year of this planned long-term monitoring project, we successfully identified plots, quantified canopy cover, made initial measurements on tree secondary growth and marked trees for future primary growth measurements, and conducted insect surveys.
We were able to gather data for the first day of trapping with the V-flight intercept trap. The results for Year 1 are reported as Supplementary Table 1.

Discussion
We anticipate that community-level data in both the treefall and control plots will be collected in 2024, which will allow us to begin to address our primary and secondary questions with preliminary observations or measurements.
Several additional questions have been identified following our work during Year 1 of this long-term project:
• What are the differences in abiotic factors between tree fall gaps and other forest areas? The photos of canopy cover and better weather data collection will help to answer this question about each plot.
• How do the changes to the primary producers change the animals? We will need to decide on a way to collect animal data whether by camera trap, observations, tracking, or other methods.
• Do tree gaps follow the same phenological patterns as the surrounding forests? This question remains to be answered and is one of the key reasons for the study.
We also installed a platform from which members of the community can observe the treefall plot, take photos from a camera “cradle”, and share with us on an online database. We expect to use these “Community Science Steps” photos to document overall changes in vegetative growth over the years.

Next Steps
For the 2024 season, we plan to collect data on primary growth from branches that were painted to mark growth, and secondary growth data will continue to be collected from DBH measurements. The V-FIT traps will be reinstalled for comparative collections. Photo data from the Community Science Steps will be reviewed, analyzed, and organized.
New data will need to be collected from each quadrat of both plots to keep track of canopy coverage and weather data for correlations, if any, with the growth observations.

Literature Cited
Löbl, I., R. A. B. Leschen, and W. B. Warner. 2021. Scaphisomatini of Arizona (Coleoptera, Staphylinidae, Scaphidiinae) collected by V-flight intercept traps. Revue Suisse de Zoologie 128: 173-185.


For additional information or questions about this field report, please contact Dr. Lindsey Swierk (lindsey.swierk@actsperu.org), Director of Scientific Research for The Morpho Institute and Associate Director of Research for the Amazon Conservatory for Tropical Studies.

Learn more about the Amazon Research Initiative for Educators (ARIE)

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Supplementary Table 1: V-FIT Trap Insect Counts for Control and Treefall Plots

 ColeopteraDipteraHemipteraHymenopteraLepidopteraOrthopteraTotal Insects
Control    14 Jul356452759
Treefall    14 Jul4684311375

Materials
Vertical Flight Intercept Traps (V-FIT)
10 meters parachute or similar cord
2 sheets of clear plastic, 5 ft/1.5 m by 8 ft/2.4 m, 6 mil, sometimes 4 mil, “natural” (semi-transparent)
8-10 large binder clips
4 6 foot posts (handhewn) for corners, if needed
8 aluminium “half sized steamer trays” (single-use food service trays, about 32 cm × 25 cm × 6 cm deep)
4-5 L Water per steamer tray
7 oz Dish Soap
1-2 small diameter (3-4 inch) hand held kitchen sieves/colanders
2 Collection Containers (covered), for example Rubbermaid TakeAlongs, 3.2 cup Small Bowl Food Storage Containers Set of 4

Insect Collection Processing
1 L Ethanol (65%)
Tweezers / Forceps
White Plate or other sorting backgroud

Forest Plots
Metric measuring tape (at least 10 m long)
3-4 rolls Flagging tape, different colors
DBH tape
30 +- Aluminum Plant Tags/Labels 1 roll Floral Wire to attach tags
2 bottles Multi Surface Touch Up Paint
GPS and/or compass
Field book (Rite in Rain)
Pencil or Pen, Rite in Rain
Camera

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