Topic Introduction

Many people entering a tropical forest and seeing the very large canopy xxs immediately associate the forest with temperate old growth forest. However, to do so is a mistake. While some trees are certainly very old, the size of a tree in a tropical forest is not a good surrogate for its age. Some of the smaller sub-canopy trees may actually be much older than the canopy dominants. The very rapid growth that occurs, particularly in gap-colonizing species, can also be a source of confusion.

As we learn more about tropical forests, it is becoming increasingly apparent that many, and perhaps all, are in a constant state of change. A range of different disturbances ensures that there are always gaps in the forest, and these take time to fill. If the gaps are large, early colonizing species will gradually be replaced by shade-tolerant species. This process may take 100 years or more, as is discussed in the case studies for, for example Danum Valley in Borneo (5.2) and Luquillo Experimental Forest in Puerto Rico (5.3).

In this topic, we will examine the nature of forest disturbances in the Tropics, and we will also examine some of the impacts.

Outcomes

By the end of this topic, you should be able to:

• Describe the main forms of disturbance that tropical forests are exposed to.
• Compare the disturbance regimes of tropical moist and tropical seasonally dry forests.
• Compare the impacts of different types of disturbances of the structure and composition of tropical forests.

Topic Readings

Required Readings

• Ghazoul, J. and Sheil, D. 2010. Tropical Rain Forest Ecology, Diversity, and Conservation. Oxford, Oxford University Press, 516 pp. Chapter 11.

Optional Readings

• Brokaw, N., Crowl, T.A., Lugo, A.E., McDowell, W.H., Scatena, F.N., Waide, R.B. and Willig, M.R. (eds.) 2012. A Caribbean forest tapestry. The multidimensional nature of disturbance and response. Oxford: Oxford University Press.
• Crawley, M.J. (ed.) 1997. Plant Ecology. 2^nd Oxford, UK: Blackwell Scientific. 717 pp. Chapter 4.
• Kricher, J. 2011. Tropical Ecology. Princeton, New Jersey, USA: Princeton University Press, 632 pp. Chapter 13.

Fundamental Concepts

PPT Presentations

This topic contains a single presentation.

2.3.1 Disturbances in tropical forests.pptx Download 2.3.1 Disturbances in tropical forests.pptx

Self-check Quiz (For certificate learning only)

After viewing topic presentations, take this self-check quiz to check your own progress. This quiz is designed to see how well you remember some of the more important issues presented in the topic. There are five questions, and each has a potential of 4 answers, only one of which is correct. When you are ready, click the link Self-check Quiz 2.3 to start taking the quiz.

Pre-readings and Discussion (For certificate learning only)

Once you have read Chapter 11 of Ghazoul, J. and Sheil, D. 2010. Tropical Rain Forest Ecology, Diversity, and Conservation, choose to post post one thought provoking question related to the material that you have read, and answer/respond to at least one other student’s question on Module 2 discussion board Module 2 Discussion.

Graded Assignments (For certificate learning only)

Six Sentence Answer #4

Please refer to the course pages on graded assessments to see details of the Six-sentence Answers (6SA) exercise. You should not attempt to do this assessment until you have read and fully understood the requirements. 

The Case

You are a member of a major international forest consultancy firm that specializes in doing surveys of forests around the world. Your company is now working on a contract looking at the effects of past and present management practices on the forests and savannahs of East Africa. This area is very diverse, including many different forest types. They range from grass and tree savannahs through seasonally dry woodlands and forests to Afromontane rain forest.

You have managed to obtain some detailed records from a series of large plots established 25 years ago and remeasured every five years. The data show a gradual increase in biomass in the plots over this period. When you present these results to your colleagues, one immediately says that this is clear evidence of carbon dioxide fertilization. Using the 6SA format, argue why this might not be the correct interpretation of the data.

Remember to follow the structure of the 6SA outlined in the section on graded assessments.

Formatting:

• Double-space the text.
• 12-point font in New Times Roman or Calibri. 
• Put your name (Family or last name, followed by your first name), student number, the title “Topic 1.1 assignment”, and the date at the top of the first page.
• Name the e-file: your Family or last name_your first name_ Topic 1.1_Assignment.doc (or .docx). Example: Innes_John_Topic 1.1_Assignment (or .docx).
• Standard English usage, clear writing style.
• All assignments should be submitted through Canvas before the deadline.

Topic Summary

In this topic, we examined the various different types of disturbance that are found in tropical forests. Some only affect a part of a tree (such as a branch-fall). Others can affect large areas of forest (such as a cyclone). The effects of disturbances can be long-lived, with disturbances that affect larger areas tending to have longer-lasting effects.

Disturbances are important as they enable turnover in the forest. Many canopy trees require a gap to form in the canopy before they can put on the growth spurt that will enable them to reach the canopy. These gaps occur frequently, and the result is a mosaic of different aged patches within the forest. This needs to be taken into account when looking at the population dynamics of trees, as well as when looking at carbon dynamics and growth patterns.

Topic Self-review (For self learning)

To review what you have learned in the topic, you are encouraged to use the following reflection questions as a study guide to do a self-review for the topic:

• What are the main forms of disturbance that tropical forests are exposed to?
• How do the disturbance regimes of tropical moist and tropical seasonally dry forests compare?
• How do different types of disturbances differ in their impacts on the structure and composition of tropical forests?
• Why is it so important to recognize the disturbance-induced dynamic nature of tropical forests?