Narrator: Listen to part of a lecture in an environmental science class.
Professor: So we’ve been talking about the way climate change can impact plant and animal species. In particular, in the Sonoran Desert, in the Southwestern United States, over the last… oh, hundred years or so, temperatures have increased by about 2 degrees Fahrenheit. And scientists have been studying the effect of this change on Piñon pines.
Piñon pines are a pine tree native to the Sonoran Desert. They have adapted to a hot, dry environment. Piñons are… really interesting. Like other pines, they reproduce by shedding their pine cones, which can then grow into new pine trees. But instead of reproducing on a set schedule, Piñons wait until the climactic conditions are just right for reproduction. They tend to shed their pine cones every three to seven years. In years when the climate is hotter and dryer, and the pine cones might have trouble growing, the Piñon pines will delay shedding their pine cones.
Female student: So, because of the climate and the fact that Piñon pines can change their reproduction, they should be really adaptable to climate change, right?
Professor: Yes, that’s right. Piñon pines are perfect for an environment that varies from year to year. In fact, in the 1950s, there was a large drought, but most of the Piñon pines were unaffected. The oldest and weakest pines did not survive, but the vast majority of the Piñon pines made it made it through with basically no trouble. The process of shedding their pine cones, which is called a masting event… well, the Piñons reduced their masting events.
Male student: Um, I‘m sorry, when you say reduced their “masting events,” do you mean that they didn’t have as many or that when they had masting events, they shed fewer pine cones?
Professor: Good question. Actually both. The Piñons didn’t have as many masting events as they would have had in normal years. And the masting events that they did have produced fewer pine cones than usual. So the Piñon pines were able to survive and wait until the timing was right to reproduce in large amounts.
Okay, so why are we talking about these sturdy plants in regard to climate change? It seems like a small temperature increase is something these pines can deal with. Well, the problem is there are many other factors that come into play. Climate change is a long-term shift, so Piñons can’t just wait for it to stop before their next masting event. But the hotter environment reduces the masting events anyway, so we have fewer new pines growing. And some insects that feed on the Piñon pines are thriving in this hot environment.
One type of insect, the bark beetle, flourishes in hot environments. And because the pine trees are not reproducing frequently, they are more susceptible to the bark beetle’s invasion. Fewer pine trees are being created, and those that are created tend to be more sickly as a result.
Not to mention, Piñon pines use unseasonably low temperatures in late summer as the sign to start their masting event. And when the temperature doesn‘t get unseasonably low, the masting events don’t occur. What’s worse is that in the midst of this climate change, there are still droughts. In the 2000s, a drought that was even worse than the one in the 1950s hit the Sonoran Desert. It affected all ages of Piñon pines. The sickly Piñons were already infested with bark beetles, and now, they did not have enough water. So many Piñons did not survive. It’s estimated that the population fell by about 40 percent.
Female student: What about human intervention? Can’t we use, I don’t know… insect repellent or something? There has to be a way to get the bark beetles away from the Piñon pines.
Professor: Well, human intervention is controversial. Probably the best thing we could do for them is start controlled wildfires. Piñon pines group so closely together that it’s easy for the beetles to migrate from one tree to another. A wildfire would thin the groups of pines, making it harder for bark beetles to expand their range. At the same time, the wildfire would reduce the grasses and shrubs growing around the Piñon pines, so there’d be less competition for nutrients. But starting a forest fire isn’t something most people would support.
Female student: But if we know it would help the pines, shouldn’t we be able to convince people who are against wildfires?
Professor: Maybe. But we’re not completely sure what the effect would be. Maybe thinning the groups of pines would allow more sunlight to reach the bases of the trees, which could be harmful to them, for example. We have to proceed very carefully when we consider intervention.
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What is the lecture mainly about? |
Gist-content. The professor discusses the reproduction process of Piñon pines, and the factors currently threatening them. |
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| ✓ | A Factors involved in the decline of Piñon pine populations |
Correct. Temperature variations, droughts, and infestation are are discussed to explain why the Piñon pines are experiencing difficulty. |
| ✗ | B How unseasonably cold winters might be affecting Piñon pines |
This idea is not mentioned in the lecture. |
| ✗ | C Why the population of bark beetles has been declining |
The lecture contradicts this idea. |
| ✗ | D Reasons that Piñon pines are expanding their range |
The population of Piñon pines is diminishing. The professor does not discuss Piñon pines expanding their range. |
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According to the professor, what are two features of masting events for Piñon pines? Choose 2 answers. |
Detail. A masting event is the process by which Piñon pines shed their pine cones for reproduction. |
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| ✗ | a They occur only in cold climates. |
This is contradicted by the lecture. Piñon pines grow in the hot, dry environment of the Sonoran Desert. |
| ✗ | b The rate at which they occur depends on the age of the pine trees. |
Age of the pine trees is not discussed in relation to masting events. |
| ✓ | c They are influenced by changes in temperature. |
Correct. Masting events are triggered when the temperature is appropriate for reproduction, and delayed when the weather is too hot and dry. |
| ✓ | d They involve the release of pine cones. |
Correct. A masting event is defined as a period when the Piñon pines shed their pine cones. |
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What is one reason for the decrease in Piñon pine populations in the Sonoran Desert? |
Detail. The professor mentions several factors that threaten Piñon pines, but specifically states that one combination led to a decrease in population: bark beetles and a drought. |
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| ✗ | A Decreases in the amount of nutrients in the soil have increased competition among Piñon pines. |
This idea is not discussed in the lecture. |
| ✓ | B Increases in the number of bark beetles have left them more susceptible to drought. |
Correct. The drought in the 2000s is cited as so deadly for Piñon pines largely because they were weakened by bark beetles. |
| ✗ | C Increases in the average temperature have caused masting events to occur more frequently. |
There have been increases in temperature, but this has resulted in a decrease in masting events. |
| ✗ | D Increases in rainfall have altered the natural environment of the Piñon pine |
This idea is not mentioned in the lecture. |
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Why are humans NOT intervening to protect Piñon pines? |
Detail. The professor mentions that some people may disagree with intervention, and that any intervention would need to be carefully thought through. |
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| ✗ | A Most Piñon pines are in locations that humans cannot easily reach. |
This idea is not mentioned in the lecture. |
| ✓ | B The actions humans would need to take could be controversial. |
Correct. The professor directly says this. |
| ✗ | C The bark beetle also needs to be protected by human intervention. |
This idea is not mentioned in the lecture. |
| ✗ | D Masting events have decreased in recent years. |
If anything, this fact argues in favor of human intervention, not against it. |
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Why does the professor mention the 1950s drought, which did not severely affect most of the Piñon pines? |
Organization. The professor mentions this event in response to a student’s question about how adaptable the pines are to hot, dry environments. |
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| ✓ | A To suggest that healthy Piñon pines can survive in dry environments |
Correct. This drought is also used to contrast with the 2000s drought, in which many pines did not survive. |
| ✗ | B To explain how Piñon pines can expand to wetter environments |
Piñon pines survived, but did not expand, and there is no discussion of moving to wetter environments. |
| ✗ | C To cite a similarity between Piñon pines and other types of pine trees |
Other types of trees are not mentioned in this example. |
| ✗ | D To explain how increasing temperatures can encourage the growth of bark beetle populations. |
This fact is unrelated to the 1950s drought. |
Narrator: What does the professor imply when she says this:
Professor: Okay, so why are we talking about these sturdy plants in regard to climate change? It seems like a small temperature increase is something these pines can deal with.
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Function of What Is Said. The professor is indicating that there is a reason to discuss the topic beyond what has already been mentioned. Note that “these sturdy plants” refers to Piñon pines. |
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| ✗ | A The adaptability of Piñon pines is an important enough theme to be repeated. |
Piñon pines can adapt to temperature changes up to a point. But this question sets up a discussion about limits to their adaptability. |
| ✗ | B Climate scientists should not bother studying the impact of a temperature increase on Piñon pines. |
The professor implies that such a study would be useful. |
| ✓ | C The climate change she is describing involves more factors that have not yet been discussed. |
Correct. The professor goes on to talk about the various ways that an increase in temperature, over the long term, can weaken the pines and potentially threaten their population. |
| ✗ | D Students should be able to answer this question quickly. |
There is still much that needs to be discussed before this question can be answered. |