Atlantic Forest

Exercise 8: Forest Fragmentation Impacts on Decomposition Rates
Module 8: Decomposers: The End and The Beginning

Your Questions

1. Does rate of decomposition differ between the forest and the forest edge?
2. Does the forest edge change the community of decomposer species present relative to plots deeper in the forest? This is a subsidiary question because we will be pointedly addressing this in a different manner in Exercise 13, but still one to think about here.

Background

Decomposition is the process by which organic matter is physically broken down and converted to simpler chemical substances, resulting in the production of carbon dioxide, water and the liberation of energy. This important ecological process represents a loss of energy and material from the ecosystem as well as the transformation and movement of organic matter within the system. By the decomposition of soil organic matter and litter plant nutrients are released in the ecosystem, making them available for uptake and further plant growth.

Litter production by the above-ground vegetation represents a major component of the net primary production in forests. Soil fauna play an important part in the mineralization and release of plant nutrients within the litter layer in forests ecosystems. The organisms that comprise the litter detritivores are mostly arthropods, mostly very small, and therefore very difficult to see with your naked eye. These animals include mites, pseudoscorpions, millipedes, woodlice or pillbugs, springtails, beetles, snails, roundworms, earthworms, and bacteria. In the tropics, ants play as significant of a role in the decomposition of litter as do any of these other organisms, which is not as true in the temperate regions. In fact, in the Amazon rainforest, ants do the majority of the litter decomposition.

Litter production can be defined as the weight of dead material, of both plant and animal origin, that reaches the ground surface during a period of time. The rate of accumulation of litter upon the surface of the soil is the result of the interaction between litter production and the rate of litter disappearance. Litter recycling is important not only because it liberates the resources that are bound up in the litter for other plants. If litter were not recycled, it would build up to cover the planet and eventually putrify through bacterial activity, thereby creating a horrible stench as well.

Habitat fragmentation, which we will address at length in Module 13, has been suggested to alter the functioning of many ecosystem functions - including decomposition, photosynthesis, water and air purification, carbon sequestration, among others. We are interested to see whether this is the case for the Atlantic Forest and to what extent the edge effects may percolate into the forest.

Your Assignment

In this exercise, we will measure rates of litter disappearance. Although bags will be placed in the appropriate places at the start of class so that we can harvest them during the third week of course, students will make litter bags of their own and also place them in the field. You should think of variables that could keep you from finding out what you want to find out. How would you try to minimize their effects?

Litter bags have to remain in the field for at least 3 weeks. Litter should be contained in some way that makes it possible to retrieve them at a later date and allow us to determine the rate of disapperance of the litter. Thus, our final results obtained today will be gathered three weeks after the bags have been placed in the field by the TAs.

Objectives

• Introduce the concept of decomposition.
• Begin to understand the many ways in which habitat is negatively affected by habitat fragmentation.

Key Skills

• Constructing, processing, and evaluating litter bags.
• Further develop ability to apply the scientific method to a diverse array of questions.

Timetable