Monoculture forests less susceptible to spring droughts

Research into the vulnerability of UK woodland to dry weather has identified marked differences depending on species. 

Monoculture forests may be less susceptible to spring droughts than those with more than one species of tree, according to a new study by the University of Stirling. 

The work looked at a long-term experimental forest near Inverness, with experts measuring the impact of extremely dry weather in the spring of 2012 on monocultures of two species – the Sitka spruce and Scots pine. These were then compared with the effects of the climate conditions on areas with a mixture of both species growing together in different proportions. The two types of tree make up 68% of the UK’s coniferous forest area, with the Sitka variety alone accounting for 51%. 

‘As expected, we found evidence that Scots pine was more resistant to drought than Sitka spruce. However, to our surprise, monocultures of both species appeared to be more resilient to spring drought than any of the mixtures of the two species that we considered,’ said PhD researcher Tom Ovenden, of the Department of Biological and Environmental Sciences at the University of Stirling, who led the study.

‘As we rapidly try to adapt our forests to deal with the challenges of a changing climate, it’s important that decisions on how best to achieve this are based on robust scientific evidence,’ he continued. ‘This work is important because it demonstrates that simply adding more tree species to a forest does not automatically increase its resilience. Instead, the existence of any beneficial effects of species mixture likely depends on which species are mixed, their characteristics and how they interact.’ 

Ovenden pointed to the study’s significance in terms of understanding how to effectively increase forest resilience to drought, which is essential to ensure these ecosystems continue to provide vital carbon sequestration and habitat for a wide range of species. The work also revealed that, contrary to assumption, competition from surrounding trees may not have a role in regulating their resitance to and ability to recover from drought, although this may be due to the young age of the experimental forest at the time of data was collected. Overall,the team say their efforts reveal a need for more investigations into the tree resilience to soil and climate conditions. 

The results of a separate study published in April this year helped scientists create a clearer picture on how much drought is too much for forests.