Climate Change: New England Forest Soil Altered, Shifted

A study from Dartmouth College doctorate student Justin Richardson has found that evergreen conifers' numbers are being reduced in New England's forests, with climate change pushing deciduous trees, like maples, to replace them. This ultimately is leading these forests' soils toward holding fewer nutrients and metals, both beneficial and harmful.

Evergreen trees (conifers), which remain green-leaved throughout the year and shed their leaves gradually instead of all at once, stand a better chance at survival in the cold taiga forests found in New England. In these forests, organic matter in the soil decays slowly due to the cold, making nutrients less available to plants and giving evergreens a survival edge there. In contrast, deciduous trees shed their leaves all at once, and lose their nutrients when they do so, making them more suited to temperate climates, as they must use resources to survive the winter that evergreens do not.

The study found that due to increases in temperature and precipitation (as well as timber harvesting shifts) by 2085, coniferous evergreens in New England states like Vermont, New Hampshire and Maine are projected to lose 71 to 100 percent of their range, to be replaced by deciduous trees. This could greatly impact the cycle of nutrients and the soil's storing of toxic material, according to a news release.

"Based upon our findings, we conclude that a shift from coniferous to deciduous vegetation could decrease the accumulation and retention of major metals," says lead author Justin Richardson, part of Dartmouth's Department of Earth Sciences. "Our results can help forest managers and biogeochemists assess the future impact of changing vegetation type on plant-essential and pollutant metal cycling in forests across the region."

Richardson's team examined eight deciduous and coniferous forest stands adjacent to each other in the Green Mountains of Vermont and the White Mountains of New Hampshire. The team saw that the deciduous trees use their little layer to cycle nutrients more quickly than conifers do; however, the deciduous and coniferous trees have virtually no difference in the cycling of toxic metals in the soil.

Coniferous trees showed soil with 30 to 50 percent less calcium, potassium, manganese, zinc and magnesium compared to deciduous trees, and their needles held lower concentrations of metals than the leaves of the deciduous trees. Richardson's team also found that the coniferous tress held onto calcium, cadmium, potassium, copper, magnesium and manganese in their soil 40 to 200 percent longer than deciduous trees, emphasizing the coniferous metal cycle as slower than the deciduous. 

"As significant alterations to ecosystems resulting from global change become more likely, environmental scientists and the general public need to appreciate some of the potential outcomes," says senior author Andrew Friedland, a Dartmouth professor. "Our paper explores one of these outcomes: changes in beneficial and harmful elements in forest soils."

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