Plants can't get up and move, so expansion of their range as conditions change can only happen by seed spread, and is a gradual process.
Trees can live tens or sometimes hundreds of years so will need to survive plenty of storms and droughts if they are to mature and reproduce.
It is well known now that plants are making long-term adaptations to a warming climate: research shows that hawthorn is typically flowering around 13 days earlier than it did in the 1980s, and horse chestnut around 10 days earlier, but did you know that individual plants can also take action?
I recently learned about the phenomenon of stress flowering: plants native to deserts evolved to flower and set seed in a matter of hours as soon as a little rain falls, but even Cumbrian plants will flower early in response to drought conditions, in an effort to set seed and ensure the survival of the species.
This is stress flowering. I've seen it for the past two years on my wildflower lawn in the face of the extreme dry conditions through April and May: my yellow rattle has had ripe seed by late May; the birds-foot trefoil has set seed about the same time, and then has a second flush of flowers – and subsequent seeds – later in the summer.
Drought conditions also lead to stunted growth in plants – a small plant needs less water, smaller amounts of nutrients, so that they have a better chance of survival.
One with smaller leaves loses less moisture, but may also produce smaller or fewer fruits or seeds so whilst it’s more likely to survive, it may be less successful in reproducing.
Trees can also close pores on their leaves to reduce moisture loss, and will do so even if they don’t get enough water one single night; that’s like a human not sweating because they didn’t drink enough the previous day!
At the opposite end of the scale, too much water is also a challenge: flooded plants suffer from lack of oxygen (which they mostly absorb through their roots, but there is less in waterlogged soil).
Wetland plants such as rushes have stems filled with a kind of spongy pith, which is full of air pockets to store enough oxygen to survive being submerged.
However, research on thale cress – often seen as a weed, and common on road edges and waste ground, but not a wetland plant – has shown that low oxygen triggers a stress response in their cells. This makes them produce other chemicals that help them cope without it. This means that even species not adapted to living in wet conditions are quite resilient in the face of short-term flooding.
Nature is nothing if not resourceful. I’ll be looking with a newfound respect at the plants that surround us.
