The Sixth Extinction by Elizabeth Kolbert

Several years ago, National Geographic published a story repeating the conclusion that half of the world’s species could die out by 2050. However, many species won’t be able to find comparable temperatures.

A more optimistic scenario would be that the world’s species could prove to be resilient by migrating north to find temperatures at which they could survive. Taking this principle into account, scientists have estimated that between 30 and 50 percent of the world’s species will disappear by the year 2050. Humans decrease the amount of land available for species to inhabit, and therefore decrease the total number of species, too. This law is helpful to understanding the impact of humanity on biodiversity. There appears to be a strong positive correlation between the two variables, such that the number of species in a region is directly proportional to the square root of the region’s total area. In ecology, there’s a familiar rule that the greater the size of an area, the more species are likely to live there. Other trees, such as those in the genus Ilex, are so resilient that they’ve remained largely “inert” in the last decade. Every year, Schefflera trees die off, and every year, their replacements show up at a higher altitude, reflecting the overall changing temperatures of the forests.

For example, there is a Peruvian tree of the genus Schefflera, which has an especially short lifespan. Silman, working with one of his students, Kenneth Feeley, has found that, on average, the increasing temperatures of the Peruvian forests have driven plants and animals to higher altitudes at a rate of eight feet per year. For more than a decade, Silman has been recording the diversity of life at seventeen different “tree plots.” At each one, Silman and his assistants record the average diameter of a tree, the different life forms they find, and other pieces of information. He takes Kolbert to some of the different “levels” of the forest, each with its own unique temperature, humidity, and, therefore, life forms. In the thick forests of Peru, Silman shows Kolbert some of the different species of trees that he has discovered in the last few years.

The Sixth Extinction by Elizabeth Kolbert