Topic Introduction

One of the most contentious topics in tropical forest ecology is the extent to which humans have affected the structure and composition of tropical forests. Some scientists believe that the forests are so vast that while there may have been some very localized impacts it would be impossible for humans to have had widespread effects. Others point to the greater than expected occurrence of trees useful to humans, the presence of massive earthworks under the forest, and the presence of anthropogenic soils. Some of the most contentious debate has been around tropical moist forests, but there is an equally vociferous debate about the role of humans in seasonally dry forests, particularly their use of fire. Humans seem to have evolved in savannah landscapes, and the savannahs of the Paleotropics have experienced much longer human impacts than those of the Neotropics.

In this topic, we will examine some of the evidence for widespread human impacts. The emphasis here is on the impacts of humans in the distant past, rather than in the much more recent deforestation and forest degradation that unfortunately characterizes the tropics today.

Outcomes

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

• Describe how humans have affected tropical forests.
• Compare the roles of humans in forests in the five tropical forest regions.
• Evaluate how humans have affected the composition of forests in the Amazon Basin.

Topic Readings

Required Readings

• Ghazoul, J. and Sheil, D. 2010. Tropical Rain Forest Ecology, Diversity, and Conservation. Oxford, Oxford University Press, 516 pp. Section 14.1.

Optional Readings

• Kricher, J. 2011. Tropical Ecology. Princeton, New Jersey, USA: Princeton University Press, 632 pp. Chapter 13.

Fundamental Concepts

PPT Presentations

There is one presentation associated with this topic:

2.4.1 Humans in tropical forests.pptx Download 2.4.1 Humans 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 2.4 to start taking the quiz.

Pre-readings and Discussion (For certificate learning only)

Once you have read Section 14.1 of Ghazoul, J. and Sheil, D. 2010. Tropical Rain Forest Ecology, Diversity, and Conservation, choose to 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. 

Activities & Assignments (For certificate learning only)

Graded Assignments

There is no assessment associated with this topic.

Topic Summary

In this topic, you have been presented with evidence that humans have been affecting the structure and composition of tropical forests for a long time. Impacts started at different times around the world, reflecting the differences in the length of human occupation. Although humans first emerged in East Africa, surviving evidence of impacts there is quite limited. Humans gradually spread out through Asia, and there is evidence of impacts in Southeast Asia and Australia dating back 40,000 – 50,000 years. This doesn’t mean that that earlier impacts were non-existent, only that no evidence has so far been found of earlier impacts.

Humans reached the Neotropics more recently. Earliest evidence of impacts dates to 12,000 – 13,000 years ago, presenting intriguing questions as to how they got there so soon after the last Ice Age. Conventional wisdom states that humans colonized the Americas from the north, having crossed the Bering land bridge at the end of the last glacial period. However, there is evidence, hotly disputed, that humans may have been present earlier, working their way around the coast. In South America, it seems remarkable that humans could have worked their way through North and Central America in such a short period, and an alternative theory is that they crossed the Pacific. This remains to be established.

However and whenever people got to the Neotropical rain forests, it is evident that they have had significant impacts, and that these have been underestimated in the past. The emergence of large areas of geoglyphs, supported by a wide range of other evidence, suggests that human populations in Pre-Columbian times in the Amazon were much higher than now, and that these populations affected the forests. Quite how much they did so remains uncertain.

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 evidence is used to determine when humans first arrived in particular forest areas?
• How did humans affect tropical forests prior to the modern era?
• How are these effects determined?
• How have the roles of humans in forests in the five tropical forest regions differed?
• How have humans have the composition of forests in the Amazon Basin?