Trees

When wildfire smoke is in the air, doctors urge people to stay indoors to avoid breathing in harmful particles and gases. But what happens to trees and other plants that can’t escape from the smoke? They respond a bit like us, it turns out: Some trees essentially shut their windows and doors and hold their breath. As atmospheric and chemical scientists, we study the air quality and ecological effects of wildfire smoke and other pollutants. In a study that started quite by accident when smoke overwhelmed our research site in Colorado, we were able to watch in real time how the leaves of living pine trees responded. How plants breathe Plants have pores on the surface of their leaves called stomata. These pores are much like our mouths, except that while we inhale oxygen and exhale carbon dioxide, plants inhale carbon dioxide and exhale oxygen. A highly magnified view of stomata in a maize leaf. Umberto Salvagnin/Fli...

As intense heat breaks records around the world, a little-reported fact offers some hope for cooling down cities: Under even the most intense periods of extreme heat, some city blocks never experience heat wave temperatures. How is this possible? Civilizations have recognized the power of cities to heat themselves up and cool themselves for centuries. City architects in ancient Rome called for narrowing streets to lessen late afternoon temperatures. Narrow streets were found to cool the air by limiting the area exposed to direct sunlight. The whitewashed architecture of the Greek Isles demonstrates another long-practiced strategy. Light-colored walls and roofs can help cool cities by reflecting incoming sunlight. Whitewashed buildings on the Greek island of Folegandros help deflect the heat rather than absorbing it. Etienne O. Dallaire via Wikimedia, CC BY In hot and humid regions of the southern...

When you walk through a forest, it may feel like a static setting where very little is happening. But trees are constantly interacting and reacting to each other as they grow. There’s intense competition for light and space. Every shift affects the overall makeup of the forest in some way. Forest scientists like me spend a lot of time thinking about forest succession – a predictable process in which plant species colonize and dominate a piece of land. The basic sequence is for land to evolve from an open field to brush and shrubs, then to young trees and ultimately to large, mature trees. Disturbances, such as a major storm or wildfire, can interrupt or set back forest succession. I study ecological changes in species composition, tree arrangement and forest development that occur during succession and after disturbances. My research team analyzes conditions in mixed-species deciduous, or leafy, forests. Using tree rings, we reconstruct what previous forests looked l...

In the wake of North America’s recent solar eclipse, another historic natural event is on the horizon. From late April through June 2024, the largest brood of 13-year cicadas, known as Brood XIX, will co-emerge with a midwestern brood of 17-year cicadas, Brood XIII. This event will affect 17 states, from Maryland west to Iowa and south into Arkansas, Alabama and northern Georgia, the Carolinas, Virginia and Maryland. A co-emergence like this of two specific broods with different life cycles happens only once every 221 years. The last time these two groups emerged together was in 1803, when Thomas Jefferson was president. For about four weeks, scattered wooded and suburban areas will ring with cicadas’ distinctive whistling, buzzing and chirping mating calls. After mating, each female will lay hundreds of eggs in pencil-size tree branches. Then the adult cicadas will die. Once the eggs hatch, new cicada nymphs will fall from the trees and burrow back underground, st...

In Argentina, where beef is a symbol of national pride, a government-led partnership has started certifying certain livestock as carbon neutral. It’s a big step that shouldn’t be underestimated, but getting the certification process right is crucial. The world’s livestock sector is a key driver of climate change, contributing around 12% of global greenhouse gas emissions. Two-thirds of agriculture’s annual greenhouse gas emissions come from livestock, with raising cattle for meat typically being the most emissions-intensive activity. While shifting diets to plant-based foods and alternative proteins can help reduce emissions, global meat consumption is growing with an expanding population and rising prosperity. There are ways that livestock producers can reduce those emissions. However, beyond social pressure, ranchers have few incentives to do so. Unless those steps to reduce emissions also increase productivity, they typically become costs with little...