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Measuring herbivory

September 4, 2010

Meg Lowman and leaf samples

Meg Lowman, in fact, pioneered single rope climbing as a canopy access technique in the 1980’s. She sewed her first harness out of seatbelt webbing and used her gear to sample leaves in the canopy. She was interested in looking at herbivory rates of leaves. She has been collecting data about herbivory in 300 species on 4 continents for 30 years. Here in Ethiopia, as in any other place she finds herself collecting data, she has sampled a handful of trees. She collects 30 leaves randomly from different species at different heights. Meg mostly used trees that were also being used by other members of our team just to simplify collection (meaning that trees that were already being climbed for other reasons – collecting epiphytes, soils, etc. – would also be collected from).

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Climbing Trees

September 2, 2010

The view from up here

As an undergraduate student back in 2002, I participated in a tropical biology field program in Costa Rica. We had the opportunity to conduct independent research. I wanted to know there were differences in nutrients between canopy soils (soils collected in the crotches of trees, a crotch being any place where a branch meets the trunk). In order to collect those canopy soils, I had to climb trees. You may suspect that I designed my project around the awesomeness of the collection technique and you would be right. Nothing seemed more exciting or romantic than climbing trees to collect data. Science and adventure in equal parts. I almost reveled the fact that collecting samples was such an involved effort. I loved the gear. You may recognize much of it as rock climbing gear, but both tree and rock climbing borrowed the techniques from spelunkers (cave explorers). Read more…

Malaise traps (flight intercept traps)

August 31, 2010

Malaise Trap - note the collecting bottle attached at the highest part of the tent

I’ve got to look into how these traps were named. It is the first sampling technique whose name tells you nothing about how it works. A malaise trap can also be thought of as a flight intercept trap. The ones that we used were the tent looking contraptions featured above. The “tent” is divided by a central wall. Upon running into that wall, some insects will fly upwards towards the top of the net. In that uppermost corner there is a passage which leads to a collecting bottle filled with alcohol (we are using 90% ethanol or dilutions thereof).

About 10 meters up in the forest canopy

The alcohol kills the insects and preserves them. The pitfall traps use soapy water because they are only meant to be set overnight. Malaise traps can be set up for longer periods of time. Short on time, we were only able to have them up for one or two days.

Diptera - Tabanid fly with striped eyes! Photo: Phil Wittman

Malaise traps target diptera (flies) and hymenoptera (ants, bees, wasps). Coleoptera (beetles) on the other hand, upon encountering a barrier will close its wings and drop to the floor. The malaise traps miss them entirely. This is also the first type of sampling technique that takes slightly more specialized gear. Though I bet a homemade one would be easy enough to construct.

Sweep Nets

August 29, 2010

Meg sweeps a teff field (teff is the cereal grain used to make the Ethiopian sour bread called injera)

The sweep net is the type of gear that I have always associated with entomologists (bug scientists). Sweep nets do not target one particular type of insect. Like beating sheets, they are used to sample for diversity and abundance. 20 half sweeps of the net samples 10 cubic meters. The nets are meant to be swept through foliage not above foliage, which is how my untrained mind would try to use it. Having one in hand gives me a strong urge to go chasing butterflies.

A happy helper of ours - I've often been asked where these children come from. Essentially, they see us drive up to the forest and curiosity does the rest.

Meg and I sampled by sweep net along the forest edge at both sites and in the barley and teff fields in Debresena. We also swept amongst Eucalyptus stands to see if we came up with a different set of insects. Without the data in front of me, I know that there were fewer insect orders and smaller numbers  of the ones that were present. As an introduced species, the eucalypts do not have many natural herbivores or inhabitants – in stark contrast to the native species. Though eucalyptus may be a good lumber and fuel crop, it doesn’t perform the same ecosystem services (home for pollinators, seed dispersers, seed germinators, herbivores, etc.) that native species do. If I haven’t mentioned it before, eucalypts are a huge drain on the water table and compete directly with local flora for water. The eucalupt fields are also difficult to recover once the trees have been harvested. The roots and stumps are difficult to remove and the soil is degraded.

Right outside the forest, amidst a Eucalypt grove, a man carries even more Eucalypt seedlings to be planted somewhere nearby

Pitfall traps

August 27, 2010

Pitfall trap

Different collecting techniques are employed to target different groups of insects. Pitfall traps are pretty self explanatory. They consist of a plastic container placed into a pit dug with a hand trowel that insects may stumble and fall into. They are filled with about an inch of water mixed with dishwashing liquid. The soap is supposed to lessen the surface tension of the water so that insects that would normally be able to rest upon the surface tension would instead pierce the surface of the water, sink, and be caught. In reality, these pitfall traps may also catch flying insects: diptera (flies) and hymenoptera (bees and wasps). Other common catches include isopods (pill bugs), acari (spiders and mites), coleoptera (beetles), and hymenoptera (ants) to name a few.

Edge between forest and field

We placed pitfall traps in groups of three at each of the following three sites: forest edge, interior, and field (outside the forest). We are looking for trends in diversity (total number of orders) and abundance (numbers of individuals in each order). We hypothesize that the diversity and abundance would be highest in the forest interior followed by the edge and the field. However, our forest interior site is in the clearing where the church itself is situated. These forests may very well have two edges: an outer edge and an interior edge. Edges exist whenever there is a boundary between two contrasting environments. In this case, forest interior vs. man-made clearing.

A handful of team members will be addressing this question of edge using different experimental designs/sampling techniques. Stay posted for more.

The church forests: what we’ve learned so far

August 24, 2010

Eucalyptus lumber for sale

Eucalyptus, a fast growing non-native species of tree, is grown widely as a lumber crop. You see huge piles like these lining the roads for sale. One would think that these Eucalyptus crops would be a sufficient alternative to cutting down trees in the church forests. But Alemayhu tells us that trees in the forest are still being cut down.

Eucalyptus (the stand of trees on the right) is a big cash crop and grown extensively

We have so many questions about the forest here. Many of us were surprised at the degree of degradation that this forest has been subject to. The understory of the forest has been cleared for food crops like coffee, foot paths criss cross the forest, only the trees remain of the original forest community.

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Day 12 – First day of sampling

August 23, 2010

Besides the usual call to prayer, we woke up to the sound of rain. Rain is not a good thing for most types of field sampling. Insects tend to go under cover. Our first of two church forest sites is about an hour’s drive north of Bahar Dar. We packed up the SUV’s and piled in. It was quickly established that all team members under 35 had to sit in the rear of the SUV’s. There is a 60 year age spread among our team from 19 – 79. I am the second youngest member at 28. My hats off to the folks over 75! A reminder that life is long and to never use age as an excuse for not doing something.

Churches are community centers, white robed church members fill the courtyard

We arrived at the church forest and took a walk around the 8 hectare site. 8 hectares not only sounds small, it looks small too (the forest may have shrunk some since the last time it was measured 2 years ago). Standing in the center of the forest, where the church is located, you can very nearly make out the edge of the forest. Yet it was refreshing to see a forest filled with indigenous (native) and endemic (found only there) species. A number of walking paths intersect the church, which contributes further to its fragmentation. The church clearing in the center of the forest acts an interior edge (120 divinity students live in this forest).

Hunched over a beating sheet, I am showing some local children what I've collected with my aspirator

We split up into teams to work on various projects. I started off sampling by beating sheet with Meg. We took our first set of data on the forest edge. We mostly sampled under an exotic (not native) bush with bright yellow flowers. We placed a 1m x 1m sheet of white ripstop nylon on a PVC frame (the beating sheet) underneath a bush before shaking it vigorously for 10 seconds. During the shaking, you look for insects dropping onto the sheet. Then you tally up the number of individuals for each order present. We sampled 6 times and saw primarily beetles, beetle larvae, thrips, leaf hoppers, weevils, flies, mites, spiders, bees, isopods, and ants.

Meg Lowman records data with future scientists lending a hand (that head covering on the left is a rolled up plastic bag which is slit open and used as an umbrella - the modern version of the woven ones)

We attracted a large following of passerbys. The children were excited to be sampling with us. A few young men spoke English well enough to ask us about our reasons for being in the forest. Though we have not been teaching in any formal capacity, we are here as ambassadors of conservation. These young men helped us to get our message across more clearly (in Amharic) to some of our younger helpers: we are studying the forests to find ways to keep it and the communities around it healthy for many generations to come.