Let’s Go Plant an Oak

A handful of acorns makes the pesticides go down

Last month we discussed photosynthesis and took a close-up look at leaves. This month we’re going to zoom way out and take a look at how the Earth’s vegetation cycles affect pest pressure.

If we look at the Earth from space, paying attention to the vegetation and using a little imagination, we observe a fascinating phenomenon. The earth’s surface in the tropics is green throughout the year, for the most part, with a few seasonal changes in color between dry season and rainy season. As the seasonal growing conditions change in temperate zones, however, there is a dramatic color change. As spring unfolds in the north, the green color of the tropics flows northward like a green army advancing northward. The flush of green flows northward to the edge of the Arctic Ocean, then retreats to the tropics in the fall. The pulse of green then goes to the south as the southern hemisphere enters spring while the north experiences fall and winter. 

As long as there have been green plants, this heartbeat of green has been happening. The pulse of green is a massive accumulation of energy and nutrients that maintains the ecological economy. Each spring across the temperate zones there is an explosion of fresh, tender foliage that is closely followed by an explosion of the insects that eat that foliage. This population eruption of insects is a resource bonanza for insectivorous creatures: amphibians, reptiles and especially birds; this is part of why so many birds migrate seasonally. Our crops, whether annual or perennial, are part of the pulse of green that feeds insects, and that population boom can reduce crop yields, spread disease in our crops, introduce premature decay, and cause cosmetic flaws on crops. As the season progresses, plant growth slows down, pest populations decline, predator populations follow suit, decomposer populations increase, and soon we are back into a season of dormancy.