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Seasonal Science: What Lurks in the Leaf Litter?

An autumnal activity from CityScience



George Retseck

Key Concepts
Biodiversity
Biology
Soil
Invertebrates

Introduction
Do you enjoy walking through piles of autumn leaves and hearing the crunch underneath your feet? Those leaves you're stepping on might actually be home to a wide variety of plants and animals! Leaves, twigs and pieces of bark that have fallen to the ground make up leaf litter. Leaf litter is an important component of healthy soil. Decomposing leaf litter releases nutrients into the soil and also keeps it moist. It also serves as great nesting material, hiding places and protected spots for animals. This dead organic material provides the perfect habitat for a plethora of organisms, including worms, snails, spiders, and microscopic decomposers like fungi and bacteria. For this reason, leaf litter is considered very biodiverse.

"Biodiversity" is a concept that refers to the variety of different life forms, from the genetic level to the species level. Species diversity in particular is a subcategory of biodiversity that refers to the number of different species represented in a set. Where can biodiversity be seen in your everyday life? Just look outside your window! The different types of trees, flowers and insects are all examples of a biodiverse community.

Scientists use various mathematical formulas and indices to calculate biodiversity. The level of biodiversity in an ecosystem is believed to indicate how healthy and stable the ecosystem is. Generally, a higher biodiversity level indicates a healthy ecosystem that is capable of supporting life well. To learn more about biodiversity, you can examine leaf litter in your neighborhood!

Background
Most of the tiny animals that are found in leaf litter are invertebrates, meaning that they lack a backbone. Some of these little critters feed on the litter and break it up into smaller pieces. Microscopic organisms like bacteria and fungi then decompose the litter, converting it into beneficial chemicals and minerals that can be absorbed by plants.

Animals you may find living in leaf litter include slugs and snails, worms, animals with jointed legs (like millipedes and centipedes), spiders and beetles. The type and amount of organisms found varies with time of year. Some animals spend their entire lives in soil and leaf litter, while others are found there only at certain points in their lives. Some use the litter specifically for nesting or hibernating.

In this activity, you will be able to see the biodiversity levels of leaf litter in your neighborhood and how human activity has impacted these levels.

Materials
•    A partner
•    A trowel or short shovel
•    Gloves (gardening gloves or winter gloves will do)
•    One large tray (aluminum trays work well)
•    One small tray
•    Two magnifying glasses
•    Tweezers
•    Meter stick
•    Rope
•    Pencil and paper
•    Field guide or identification key (optional)

Preparation
•    Locate a nearby public park or forest to conduct the activity. Acquire a map of the area.
•    The best time to conduct this activity is in the autumn months.

Procedure
•    Travel to a nearby park or public forest. Locate an area that has been relatively undisturbed by human activity. There should be many fallen leaves, twigs and pieces of bark. Remember to have a partner with you at all times.
•    Once you've found a suitable patch of leaf litter, measure out an area of one meter squared using the meter stick. Use the rope to build a rough frame. This will serve as a one-meter vegetation sampling frame. Have you seen any animals in your sampling area so far? How many types of animals do you think you will find?
•    With the vegetation sampling frame on the ground, put on your gloves and use the trowel to collect all the leaf layer and soil within the frame (down to a depth of approximately two centimeters (cm) from the surface). 
•    Place all the leaf litter in the large tray. Using your fingers but keeping your gloves on, spread out the leaf litter so an even layer is created. Keep your eye out for little critters!
•    With your magnifying glasses, you and your partner should examine the leaf litter for any worms, snails, spiders or other insects. Use your gloved fingers to gently sift through the litter.
•    Using tweezers, gently place any animals found in the litter into the smaller tray. You should find specimens like snails, worms and spiders. Don't worry if you can't get all the insects.
•    Using the magnifying glasses, examine the small animals. How many legs are there, if any? Do they have an external skeleton or a hard shell? Do their legs appear to be jointed? Scientists use questions like these to categorize animals into different groups.
•    Look out for obvious differences like color, size, and shape to distinguish species. Record the number of different species you can see. If you see many different species, there is a high biodiversity. If there are only a few species present, there is a low biodiversity.
•    Return all specimens and leaf litter material to where you originally found them. Disassemble your rope frame. Make sure you do not leave anything that you brought behind!
•    Travel to another location with leaf litter. However, this time find an area that has more human interference. These are areas that people frequently use – places like walking and hiking trails.
•    Reassemble the vegetation sampling frame and place on the ground.
•    As with the previous location, gather the leaf litter and soil within the sampling frame (down to approximately two cm deep). With your gloved fingers, sort the leaf litter in the large tray. Transfer any specimens found into the smaller tray and examine them under the magnifying glass.
•    Count and record the number of species you see in this set. If you see many different species, there is a high biodiversity. If there are only a few species present, there is a low biodiversity.
•    Return all specimens and leaf litter material to where you originally found them. Again, make sure you do not leave anything you brought with you behind!
•    Which area had the higher biodiversity level – the one with little human interference or the one with much more? What types of animals did you find? Remember that organisms like fungi and bacteria also live in leaf litter, and these organisms cannot be seen without a microscope.
•    Extra: Instead of just counting the number of species, you can identify them like a real research scientist would! Using a dichotomous key like the ones listed in the "More to explore" section, you can narrow down your specimen to the family, genus or species level!


Observations and results
Did the leaf litter found in an area with lots of human interference have a lower biodiversity?

In recent years, there has been a significant loss in biodiversity, caused primarily by human activity. Such biodiversity loss usually occurs on a large scale, and is due to habitat destruction, invasive species, overexploitation and climate change. In the areas with lots of human interference, human activity has contributed to a lower biodiversity. People might litter on the ground or simply step on animals. Other times, people may add chemical fertilizers and pesticides to the soil. These activities all contribute to a loss of biodiversity. A low biodiversity is unfavorable because these ecosystems take longer to recover from environmental changes.

On the other hand, the first sampling site with little human activity should have had a higher biodiversity level. A higher biodiversity level means that site has a more stable ecosystem. High biodiversity is also important because it supports many ecological processes. For instance, a high biodiversity of decomposers and small insects is important in regulating soil chemistry, recycling nutrients and providing fertile soils.

More to explore
Hope College Leaf Litter Arthropod Key from Hope College
Life in the Leaf Litter (pdf- English, pdf- Spanish) from the American Museum of Natural History
Scientists Spend 10 Years Watching Leaf Litter Decay for Clues to Climate Change from Scientific American
Spiders in Borneo: Spiders in leaf litter from Scientific American


This activity brought to you in partnership with CityScience
CityScience

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