Adaptability is not always positive for plants tackling climate change

Adaptability to a changing climate might not always predict a plants performance when climate changes. This peculiar discovery by Block and colleagues is explained in detail in their paper in Oikos. After experimenting by changing the climate for 18 species the team found that success for plants depended on both species and context.

The adaptability that Block and colleagues examined was phenology, the study of seasonal events, such as budding and flowering. As the climate warms, the growing season should be both longer and earlier. A simple expectation is that the species best able to shift their behaviour should be able to cope better – but the authors say this might not be the case. “[W]hile advancing phenology can help plants exploit longer growing seasons, it can also result in mismatches with the timing of activity of mutualists or impose a higher risk of suffering frost damage, particularly for early-flowering species…” they write in their article.

To find out how climate change might affect plants, the team transplanted some plants in 50cm × 50cm turfs from 2000m up in the Swiss Alps down to 1400m. The plants in the new site had only moved a couple of kilometres but were now around three degrees Celsius warmer. They then watched how the plants flowered at both the old and new sites to compare the results.

They found that some species adapted by flowering earlier, as anticipated. However, the team found no correlation between how the phenology of the plants changed, and how their coverage of their turfs changed.

Block and colleagues had a few ideas why advancing phenology was not always a benefit. For early flowering species, flowering earlier still could still leave them at the mercy of the last days of winter. Early flowering and a sharp frost would leave them more exposed to damage.

There are also problems in that the phenology of plants will differ to the phenology of insects. There are already examples of plants moving out of sync with their pollinators. Not all pollinators will react the same, so the plants with the better-adapted pollinators will benefit more from advanced phenology. Block and colleagues also note that herbivores tend to advance more than plants and carnivores. The result being that earlier developing tissues may be victims of more hungry mouths, without the aid of predators to reduce herbivore populations.

So while adaptability should be good, in reality it’s the context the plants are adapting into that matters. “[W[hile there might be a general benefit of phenological plasticity in changing environments, the net demographic consequences are likely to depend strongly on species’ physiology and ecology…, and the degree to which the cues regulating species’ phenology maintain their temporal association with optimal environmental conditions.” the authors conclude.