Forest management yields higher productivity through biodiversity, say researchers
Scientists conducting the first worldwide study of biodiversity and its impact on the productivity of forests have concluded that a decline in the number of species leads to massive cuts in the productivity of forests. Conversely, monocultures converted into mixed stands can yield significantly higher levels of timber growth.
The study was conducted by the Global Forest Biodiversity Initiative (GFBI), an international collaboration of researchers which began in 2016 (www.GFBinitiative.org/).
The study collected data from more than 770,000 observation points from 44 countries. Samples were brought together from 8,700 species of trees – this included trees in tropical rainforests, Central Europe, tundras, dry savannas and Mediterranean forests.
Biodiversity reaches its peak in forests, but deforestation, forest degradation, and climate change are having a serious impact on half of all tree species. Although the preservation of tree stock and sustainable forest management have been the subject of much discussion and have been promoted through environmental measures across the globe, the general decline in species, along with its serious consequences, continues. The study published in the current issue of Science illustrates how the global decline in biodiversity is accompanied by a decline in timber growth.
“On the one hand, the study sets new standards because of its geostatistical methodology and global scope. It included an immense volume of data on biodiversity and productivity from nearly 50 countries throughout the world, which has never been done before in this field of science,” said co-author Professor Hans Pretzsch, the Director of the Chair of Forest Growth and Yield Science at the Technical University of Munich (TUM).
On the other hand, the research results also lend further weight to the Brundtland Report and the Helsinki and Montreal resolutions. “The conclusion of our study is that, for example, when the number of species declines by 10 percent the wood production decreases on average by six to seven percent. And the rate of decline increases exponentially with further reduction of species richness” said Pretzsch. His team contributed a comprehensive data set of inventories and long-term experimental plots of pure and mixed stands in Central Europe.
150 years of experimental data
“The inventories and experimental plot data from more than 150 years demonstrate how timber growth decreases in parallel with the number of species,” Professor Pretzsch explained, “and how it can increase toward mixed stands again with the conversion of forest monocultures.” Particularly in the 1950s and 60s, Germany heavily relied on forest monocultures with only one species, such as spruce or pine, “a policy that we have consciously backed away from in the recent years. Meanwhile, the silviculture guidelines of many countries stipulate that, whenever possible, stocks should be comprised of two or three species.”
The study published in Science, which took into account the major global forest ecosystems, clearly shows that in addition to the many ecological and social benefits, mixed stands can also provide a material benefit in terms of increased productivity.
Annual loss estimated at around $490 billion
The authors have hypothetically calculated what would happen if the species continued to decline throughout the world as they have in recent years: If mixed forests continue to be cleared and converted into monocultures such as eucalyptus or pine, then productivity will steadily decrease.
With a species impoverishment of 99 percent, the approximate loss in value would be of 166 to 490 billion US dollars per year. The authors of the study note that these high losses amount to the double times the annual global expenditure for the conservation of biodiversity. Other losses caused by the reduction in biodiversity include decreases in genetic diversity, protective functions, and recovery functions, which go far beyond the reduction in timber production.
The results of the study provide the Intergovernmental Platform on Biodiversity and Ecosystem Services (UN IPBES) and the United Nations Convention on Biological Diversity (UNCBD) with an important quantitative basis for the intelligent protection and sustainable management of forests.