Warming winters may reshape global plant communities

Many warming experiments may be painting an incomplete picture. Michigan State University researchers found that studies focusing only on summer heatwaves could be underestimate the effects of climate change.

Plants live through winter too. Ignoring cold-season warming misses key processes like root growth and nutrient cycling.

Their latest global meta-analysis, published in Global Change Biology, analyzed 126 open-top chamber experiments. These covered 13 plant traits across varied ecosystems, from Antarctica to Michigan.

The massive dataset helped identify how traits like biomass, nitrogen content, and flowering respond to warming.

Summer-only experiments fall short

“This important global synthesis of warming effects on plants across many ecosystems can be used to inform models of future impacts,” said Phoebe Zarnetske, professor in MSU’s Integrative Biology department.

Year-round warming triggered stronger changes. Aboveground biomass, fruit weight, and leaf growth all showed greater increases. In contrast, seasonal (summer-only) warming produced muted effects.

For instance, aboveground nitrogen content only dropped significantly under year-round warming.

Experiments that ignore winter might miss crucial ecological shifts. The study suggests that many past experiments may underpredict plant responses to climate warming.

Warming changes plant traits

The researchers categorized plant responses into growth, reproductive, chemical, and phenological traits. Some responses were predictable.

Warming increased leaf growth (Hedges’ g = 0.54) and belowground biomass (g = 0.60). It also led to earlier spring phenophases, though the effect was marginal (g = −0.12).

However, not all changes were positive. Aboveground nitrogen content fell (g = −0.41), likely due to nutrient dilution effects. Fruit weight increased with latitude, showing stronger responses at colder sites.

Colder areas show bigger plant changes

As latitude increased, reproductive traits became more sensitive. Number of fruits and fruit weight rose significantly in higher latitudes. Spring timing advanced more sharply near the poles.

Plants near their northern range edges also grew more under warming. These range-edge plants likely experience more variable climates.

That variability may help them adapt quickly. Species farther from the edge showed smaller or even negative changes.

Warming responses stabilize over time

Short-term experiments produced stronger trait shifts. Over time, communities may adjust, leading to smaller visible effects. For example, flower lifespan and fruit number showed weaker changes in longer experiments.

This pattern suggests plastic responses may fade or stabilize. Year-round warming more accurately mimics future conditions, especially with expected winter temperature increases.

Not all species react alike

Growth forms made a big difference. Graminoids, like grasses, responded to 9 of 13 traits. Shrubs followed, showing warming-related boosts in percent cover and fruit output.

Bryophytes and lichens, on the other hand, declined under warming. Their percent cover dropped, while vascular plants thrived. This contrast could offset community-level trends, masking specific plant changes in smaller species.

“Non-native species may benefit from future climate conditions,” the study noted. Yet, research on these species remains limited. Data on non-native responses were often too sparse for solid conclusions.

Warming studies need more plants

Phoebe Zarnetske’s SpaCE Lab contributed one of the 126 datasets. Their long-term warming plots at the Kellogg Biological Station captured seasonal changes often missed by others.

“This study is unique in terms of the size of the dataset we collected,” said Kara Dobson. “It brings together data from experiments across the globe and from all continents, including Antarctica.”

The team recommends a broader inclusion of species types. Non-native and non-vascular plants need more attention. Without them, predictions will remain skewed.

Climate change requires better models

Many past warming studies looked only at one context, such as summer, certain species, or specific regions. This analysis shows that no single trait tells the whole story.

Warming affects plants differently depending on latitude, plant type, and experiment duration. The good news is that coordinated global efforts, like the LTER and WaRM networks, are beginning to close these gaps.

Plants are not passive players. They adapt, decline, or thrive, sometimes all at once. But to understand these shifts, we need to look through all seasons and across all ecosystems. Not just when the sun shines brightest.

The study is published in the journal Global Change Biology.

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