nature & planetanalysisThe Conversation
Don’t just plant trees, plant forests to restore biodiversity for the future
Mixed-species forests grow faster and support far more wildlife than single-species plantations. In a long experiment near Chesapeake Bay, planted since 2013 with 16 native species, trees in mixed plots were up to 80% larger than the same species grown alone. Mixed plots had fewer leaf pathogens and more caterpillars, and their diverse leaf chemistry seems to deter deer, which reduces browsing damage. Their fuller canopies create cooler, shadier understories, supporting up to 50% more insects, spiders and birds. Monocultures, by contrast, can fail all at once from drought, pests or fire, as happened when nearly 90% of 11 million saplings planted in Turkey died.
Tree species differ in their defenses, growth habits and the niches they fill. When several species grow together, pests that specialize on one species are less able to spread, and plant chemicals diversify, which can discourage browsing. Mixed canopies also create layered shade and microclimates that support more understory life, so the forest as a whole becomes more productive and more resilient.
Global tree-planting pledges count many monoculture plantations toward their totals, so the choice of species affects whether trees store carbon and support biodiversity. Across TreeDivNet, a network of more than 1.2 million trees, forests with mixed species consistently grew larger and withstood stress better.
Illustrative photo · ian shiell, CC BY-SA 2.0, via Wikimedia Commons
