Nature, the world’s leading multidisciplinary science journal, has published findings from a new global study investigating which tree species fix the most carbon.

An international consortium of scientists which includes researchers from Forest Research, studied the growth of over 200 tree species planted in 160 experimental forests across the world (in Western Europe, United States, Brazil, Ethiopia, Cameroon and South-East Asia, for example).

The study, co-ordinated by INRAE (France’s National Research Institute for Agriculture, Food and Environment) and Bordeaux Sciences Agro, found that conservative species, which are the most efficient at conserving their resources (nutrients, water, energy), generally grow faster in forests.

Chris Reynolds, Forest Research said: “In regions where we know environmental stress is higher, or is likely to be in the future, the research shows that conservative trees such as firs, holm oaks, downy oaks and many types of pine trees, do in fact have more potential to fix carbon in their biomass. It also demonstrates the significance of local conditions in tree growth.”

Previous research had shown that under controlled conditions (often greenhouse experiments) species capable of efficiently acquiring resources (light, water, nutrients) generally grow quickly (e.g. maples, poplars, English oak, sessile oak).

These acquisitive species have traits that help maximise resource use (large specific leaf area, high specific root length) and improve their capacity to convert these resources into biomass. Meanwhile, species that are more efficient at conserving their internal resources (nutrients, water, energy) than extracting external resources are known as conservative species (e.g. fir, downy oak, holm oak) and are assumed to grow more slowly.

New understanding: conservative species grow faster in forests

However, under real-world conditions in boreal and temperate forests, the researchers showed that conservative species generally grow faster than acquisitive species.

This finding can be explained by the fact that these forests are generally located in areas with unfavourable growing conditions (low soil fertility, cold or dry climate), which gives conservative species an advantage since they are better able to resist stress and manage limited resources. In tropical rainforests, where the climate is potentially more favourable to plant growth, the two types of tree species show no differences on average.

The key role of local climate and soil for species choice

The study also sheds light on the importance of local conditions.

Growth conditions in some situations are sufficiently favourable for acquisitive species to grow faster than conservative ones. But the research showed that the key is to ensure that species are adapted to their local environment.

This means that in favourable climates and fertile soils, acquisitive species such as maples and poplars will grow faster and therefore fix more carbon than conservative species such as holm oaks, downy oaks and many types of pine trees. In unfavourable climates and poor soils, conservative species will have the greatest potential to accumulate carbon in the biomass.

Elena Vanguelova, Forest Research added: “This collaborative study is an important piece of research and a vital source of information for land managers when considering which species to plant to help mitigate climate change. Trees play a key role in capturing carbon and reducing global warming because of their ability to store carbon in soil and tree biomass. This adds to the evidence to reassure foresters, or anyone wanting to plant trees, that when you know your site and soils you can find the right tree to fit your end goal.”