Forests of slow-growing tree species often sequester more carbon
Which types of tree bind the most carbon? To answer this important question, an international research consortium has studied the growth of 223 tree species in 160 research forests in different parts of the world.
They found that tree species that were good at economizing with nutrition, water and energy often grew the fastest in nature, in comparison to tree species that have a high growth potential if conditions are good. The study that was recently published in Nature, sheds light to the great importance of the location for the growth for different species.
Forests provide many ecosystem services, such as regulation of microclimate, sustaining biodiversity, cleaning of air and water as well as protection from erosion. Together with the oceans they are one of the most important carbon sinks, due to the forests capability to store carbon in the soil and in the biomass of the trees.
Planting of fast-growing tree species can play a significant roll to mitigate climate changes. The raises the key question for forest managers: Which types of trees have the greatest potential within climate protection? A global study led by researchers at INRAE and Bordeaux Sciences Agro in France, with contributions from SLU researchers in Umeå, have now identified traits in trees that are beneficial for growth and therewith sequestering carbon into biomass. The researchers compiled growth data from 223 tree species that were planted in 160 research forests around the whole world (a.o. western Europe, USA, Brazil, Ethiopia, Cameroon, and south-east Asia). The species represent all major vegetation zones.
Current theory: Species with high growth potential grow the fastest.
Earlier research has shown that tree species that effectively harvest light, water and nutrition generally grow fast under controlled conditions, often tested in green houses. These "growth-oriented" trees often have traits that help them to optimize the use of their resources, like larger leaf area, longer roots etc. which improves their capability to turn resources to biomass with a higher maximum photosythesis rate and higher nitrogen levels in the leaves.
Species that instead are more efficient in saving their internal resources (water, nutrition, energy) than in exploiting external resources are know as "economizing" species and are expected to grow slower.
New understanding: "Economizing" species grow faster in the forests
When the researchers compared the growth between tree species of both types under natural conditions, in forests, they discovered that the theory does not reflect the reality in many cases. In boreal and tempered forests, (in the northen coniferous forest belt and forests in the area between boreal forests and the tropical region) growth in general was higher in economizing species in comparison to growth oriented species.
The most probable explanation is that these forests usually are located in areas with unfavorable growth conditions (low nutrition, cold or dry climate). This gives economizing species an advantage as they can better withstand stress and handle scarce resources. In tropical rainforests, where the climate can be more favorable for growth no difference between the avarage growth of the two groups could be determined.
The local climate and soil is most important for the choice of tree species
In the article, the researchers present common trends in boreal, tempered and tropical forests. In addition they show how essential it is to properly match the choice of tree species to the local conditions. Sometimes, growth conditions can be so favorable that in fact "growth-oriented" species would grow faster than "economizing" species, however the key is always to make sure the respective tree species are well-adapted to their direct surroundings. This includes that "growth-oriented" species will grow faster where the climate is favorable and the soil is rich. But if the climate is harder and the soil scarcer, economizing species have bigger potential to sequester carbon into biomass.
The study inlluminates how forest researchers and forest managers can make important contributions to mitigate climate change, by producing and using knowledge about how growth in different species is influenced by local conditions.
Two of the authors, Michael Gundale and Marcus Larsson, work at SLU in Umeå and have contributed with data from forest experiments in the north of Sweden.
This study shows mosty general patterns on a global level and it is not detailed enough to be directly applied in swedish forestry, Michael Gundale says. On the other hand, the problem can be illustrated with a comparison between poplar (growth-oriented) and spruce (economizing) in Sweden. If the global pattern that we discribe holds up in Sweden, we can expect that poplar and other broad leaf trees can underperform if planted in places where the soil is not rich enough to support their growth strategy. If one wants to maximize growth and carbon sequestration, good local knowledge about which tree species will thrive best.
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PersonMichael Gundale, Programledare T4FDepartment of Forest Ecology and Management, joint staff