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In a recent study published in Forest Ecosystems, a team of researchers in China collected data from 1,076 sample plots of Pinus sylvestris plantations across the boreal zone of China.

Their findings suggest that contrary to common practices in tropical and subtropical zones, high-density monocultures (2,000–2,500 trees per hectare) are optimal for maximizing stand biomass in Pinus sylvestris plantations. This strategy, however, presents a trade-off, as it results in reduced species richness and smaller individual trees.

"We found that the positive impact of tree species richness on stand biomass shifts to negative as stands mature, while the effect of stand density remains consistently positive," said corresponding author Dr. Wei Chen from Institute of Applied Ecology, Chinese Academy of Sciences of the study. "Overall, the effect of tree species richness on stand biomass was negative, while the effect of stand density was positive."

"Contrary to our expectations, we did not find a consistent positive effect of tree species richness on stand biomass as observed in tropical and subtropical forest experiments previously," added first author Dr. Bingming Chen. "This was due to the negative selection effect offsetting the positive complementary effect."

"Although such negative selection effect was rare, they did exist, such as in cases from Europe and the US," said co-author Dr. Guangze Jin from Northeast Forestry University. "The selection effect could be positive or negative depending on location and species composition."

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