Warmer temperatures are associated with mismatches between forest plants


Boston University press release

A new study published in the Journal of Ecology found that in response to warming temperatures, deciduous trees and shrubs advance their leaf bud timing faster than native wildflowers in eastern North America—leading to a potential decline in native wildflowers as they receive less sunlight for photosynthesis in spring.

Native wildflowers, like Dutch pants, don’t keep up with the trees as they sprout with warming temperatures. Credit: Andrew Cannizzaro.

Many plants react to a warming climate by sprouting and flowering earlier in spring. However, mismatches can occur when species react at different rates, leading to disruptions in ecological relationships. A new study found that deciduous trees and shrubs are leafing out faster with warming temperatures than native wildflowers in eastern North America. This discrepancy can lead to a decline in native wildflowers as they receive less sunlight for photosynthesis in spring. The results were published in the British Ecological Society Journal of Ecology.

Blooming in spring, many native wildflowers perform most of their photosynthesis before the tree canopy leaves overhead and shades them. The lead author Dr. Tara Miller explains, “During warm temperatures, trees and shrubs can block sunlight from reaching the forest floor earlier in the year, resulting in native wildflowers taking less time to photosynthesize in full sunlight.”

The study builds on an earlier publication that used flowering and leaf budding observations by Henry David Thoreau from the 1850s in Concord, Massachusetts, combined with modern observations to show that wildflowers are less responsive to climate change than trees. The current study significantly expands the geographic scope of this previous paper.

Just a few days without access to sunlight can mean a significant reduction in a wildflower’s carbon energy supply.

The study assessed when 21 plant species sprouted and flowered using over 3,000 herbarium (pressed plant) specimens from across eastern North America. The timing of leaf bud break or flowering was then compared to historical temperature data to determine the plants’ responsiveness to warming temperatures.

In cooler springs (average March/April temperature of 32°F), native trees sprouted 15 days after native wildflowers. However, in warmer springs (average 20°C), native trees sprouted just 8 days after native wildflowers, giving wildflowers about half as much time to photosynthesize in full sunlight. dr Mason Heberling notes that “just a few days without access to sunlight can mean a significant reduction in a wildflower’s carbon energy supply.”

In addition, native trees and wildflowers in the warmer southern part of their ranges have advanced their leaf budding and flowering times faster than those in colder northern locations. “The disparity was greater in the southeastern United States, where native wildflowers are more likely to be shaded by trees earlier,” explains Dr. Sara Kuebbing.

Native and non-native shrubs have also advanced their leaf bud break and flowering time faster than native wildflowers, potentially posing a shading threat to native wildflowers.

This research demonstrates the value of newly available digitized herbarium specimens in studying the impacts of climate change over larger spatial areas and greater biodiversity than would otherwise be possible. dr As Richard Primack points out, “Before images of these specimens were available online, researchers would have had to travel to many museums scattered across the country.”

The study highlights the impact that climate change can have by causing discrepancies between different groups of plants. The authors provide suggestions for land managers and wildflower enthusiasts who may be considering steps such as thinning tree and shrub canopies, removing non-native species, and planting rare wildflowers farther north to preserve native wildflower populations.

You can read the full research article here:


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