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Microclimate moderates plant responses to macroclimate warming

David Coomes' group have contributed to a paper published in PNAS (PNAS October 28, 2013) showing that the microclimate in dense forests can buffer the effects of climate warming on understorey plants.

Buffering effects

The cool microclimate in dense forests has buffered the effects of climate warming on understorey plants. Forests are cooler in the summer than more open areas such as grasslands. Also plants experience this cooling effect. The researchers showed that the increase of warm-adapted species due to climate warming is moderated in cooler, denser forests than in warmer, more open forests. Because forest management has changed considerably after the second World War, many temperate forests have become denser. The cool microclimate in denser forests thus buffers the effects of climate warming. These findings were published in the journal Proceedings of the National Academy of Sciences of the USA (PNAS).

Forest management

To meet increasing demands for woody biomass, among other reasons, some forests are again more harvested and tree canopies opened up. Increases in harvesting woody biomass may open forest canopies, decrease the buffering capacity of forests and increase temperatures at the forest floor. Warm-adapted plant species can then increase and cold-adapted species decline. The researchers suggest preserving enough dense forests as cool ‘refugia’ for cold-adapted plants in a warmer climate.

Effects of climate warming

The publication of the recent climate report of the United Nations again confirmed that the global climate is warming due to human influence. The warming of the climate has large effects on both plants and animals. In the Alps, for instance, many plant and animal species now occur hundreds of meters higher than several decades ago. This signal is now also detected in lowland forests. The researchers compiled more than 1400 vegetation surveys from European and North-American ancient deciduous forests. They found that cold-adapted species such as Herb Paris (Paris quadrifolia) decreased in abundance during the past 35 years. On the other hand, warm-adapted species such as common ivy (Hedera helix) are now more frequent than 35 years ago.