Gardeners get to see first-hand the impacts and changes a shifting climate brings. More extreme weather events, milder winters, and earlier springs are just some of the discernible changes we’ve seen within a single generation. If these changes are noticeable to gardeners, it follows they will also be having wider effects on British wildlife and the species we share our gardens with.
There are winners and losers. Let’s look at some of the trends and effects in Britain;
Shifting seasons
When we look at phenology records, which gather data on the seasonality of plant and animal activity, climate effects are starting to clearly show. Some British wildlife is emerging earlier in spring or staying active longer at the end of summer. Queen and worker garden bumblebees (Bombus hortorum), for instance, are staying much more active in winter.
Plants and wildflowers are also responding to the weather, some flowering earlier or later. There have been worries that this might lead to flora and fauna getting out of sync – for instance, a flower being over or not yet open by the time its pollinating insect is active – but as yet this does not appear to be a significant problem.
However, the way ecosystems work means there are lots of interconnected effects which climate can disrupt. In a garden pond, for example, frogs are usually the earliest amphibian to arrive which gives their tadpoles a head start over predators such as newts. With a warming climate, frog spawning dates have moved earlier in spring but not by as many days as the arrival of newts in a pond. This gives newts a competitive advantage over frogs.
Shifts in ranges
Some animals are on the move. This includes new arrivals to Britain as they expand their range northwards, such as several dragonfly and damselfly species, the bryony ladybird (Henosepilachna argus) and the tree bumblebee (Bombus hypnorum). But species already resident have also been seen to be shifting. This might mean spreading north, infilling where they were patchy or moving to higher elevations. The garden tiger moth (Arctia caja), for example, is becoming increasingly rare in the south as it moves north due to poor winter survival of caterpillars in warmer weather.
There is also some evidence that some species are changing their ranges by broadening their food-plant niches. A good example is the brown argus butterfly (Aricia agestis). Its expansion northwards in England, most likely as a result of climate change, is averaging at 3km a year – making it one of the fastest of any British butterfly species. The speed of its expansion is thought to be linked to the widening of its larval food diet to include various garden varieties of hardy geranium.
Mobility and availability of suitable habitat
Plants and animals which are not very mobile are likely to be ‘losers’, as are those for whom suitable habitat at the edge of their range expansion is missing. Most at risk are the species associated with mountain habitat because they will simply run out of places to go as temperatures increase. Others may find refuge in gardens and connected green spaces.
Weather extremes
Extreme weather events such as heatwaves or flash floods have always resulted in casualties in the natural world. But population recovery appears to be hampered by the increased frequency of those events. In one example, a study into bumblebee species in Europe and North America connects bumblebee declines with the increase in hot days associated with climate change.
General declines
Despite some winners, the overall backdrop is a long-term decline across all taxonomic groups. Some of the clearest examples are where we have good long term datasets, such as for the UK’s moths. The most recent State of Nature report covers species beyond gardens but is a good overview of trends, showing that more species have declined than increased in abundance since the 1970s. Factors other than climate, such as habitat loss and fragmentation, are also to blame but a rapidly changing climate will be an added pressure.