Climate change often causes heat, drought and hurricane images. However, according to the latest US National Climate Assessment published on November 23, 2018, winter has warmed three times faster than the northeastern summer in recent years. These changes also have important effects.
Historically, more than 50% of the Northern Hemisphere has started snowing in the winter. Now the warmer temperatures have reduced the depth and depth of winter snow. Many people think winter is a dormant for organisms in cold climates, but decades of research show that winter climatic conditions, especially snowpacks, are important regulators of the forest ecosystem and the health of the organisms in which it lives .
In particular, our research in the past decade shows that hiding can reduce the ability of trees to shed water and air, which can harm the health of trees. According to our latest research, continued winter warming can cause a significant reduction in snow in the northeastern United States, greatly reducing tree growth and forest carbon stocks.
Eye as a blanket
We study 85,000 square miles of northern wooded forests dotted with sugar maple, birch, birch and American beech, from Minnesota and southern Canada to the Canadian seaboard and the northeastern United States. This forest is famous for its lively autumn colors. It attracts tourists, hikers, hunters and camper, and supports the wood and maple syrup industries to generate revenue. They also provide important ecological services such as storing carbon and maintaining water and air quality.
When winter is invaded in this area, often all temperatures need to be insulated. Tree roots and soil organisms, such as insects, rely on deep snow packs to protect themselves from the cold, snowy blanket. Even at sub-zero temperatures, if the snow is deep enough, the soil may not freeze.
After 60 years of research at the Hubbard Brook Experimental Forest in New Hampshire, it shows that snowpacks are shrinking in winter. Studies carried out by other scholars have shown that if this trend continues, it will have a detrimental effect on forest health and increase the likelihood of soil freeze-thaw.
Why do we need snow in the northern forests?
For over a decade, we have studied the effects of anticipated climate change on northern forests by manipulating Hubbard Brook's winter snowpacks. In early winter, we head outdoors after each snowfall to remove snow from our experimental plot. Then we analyze the effects of this insulating layer loss on wood and soil.
We found that frost penetrates more than one foot into the snow from the snow-removed plot, but does not extend more than 2 inches from nearby reference plots with unchanged snow packs. And as the freeze-thaw cycle makes a dent in the city's streets, and the abrasive that freezes the soil kills the surviving tree roots and damages.
This root damage causes a series of ecological reactions. Stimulates the loss of dead roots and the loss of carbon dioxide from the soil. Trees occupy less nutrients in the soil and accumulate aluminum, a toxic element in the leaves, to reduce branch growth. Nitrogen, an important nutrient, can be washed off the soil. Soil insect communities are less abundant and more diverse.
Reduced snowpacks affect tree growth.
In our most recent paper, our climate and hydrological models show that the area of forests that receive snow packs of adiabatic wet winters throughout the northeastern United States can be reduced by 95% by 2100. Today, 33,000 square miles of forests connecting northern New York and New Jersey typically use snow packs for several months in the winter. By 2100 the area can be reduced to a patch smaller than 2,000 square miles, about one fifth of Vermont.
This decline will undoubtedly hurt the ski and snowmobile industries and expose Northeast Road to more freeze-thaw cycling. It will also have a significant impact on tree growth.
To assess the relationship between snow packs and tree growth, we used a special hollow drill bit called an incremental bore to remove the straw-sized wood core from a number of sugar maple trunks. Each of these trees has a natural winter snow pack or five years in a row we have removed the early winter snow pack. When we wiped the nucleus and observed it under a microscope, they uncovered an annual growth loop that they could use to understand how each tree reacted to the environment.
In the first two years, our analysis showed a 40% decrease in sugar foliage growth in compartments without snow packs. The growth rate declined by 40 to 55 percent over the next three years. By contrast, in our reference map, where the snow covered the roots of trees in mid-winter, there was no decrease in sugar maple growth. This result is similar to the root mortality of other investigators observed in Hubbard Brook's initial snow removal experiments.
In Hubbard Brook, sugarcane can account for more than half of the annual forest biomass accumulation. As a result, climate change, which reduces winter snowpacks and increases soil freezing, can reduce forest growth rates in northern hardwood forests by 20% through their impact on wood. However, we estimate that our estimate of changes in overall forest growth is expected to be low because yellow birch trees also suffer root damage from soil freezing.
There is research that growing seasonal temperatures might stimulate the growth rate of trees to at least partly compensate for this damage. Little research has been done to understand how forests in seasonally snow-covered areas respond to the seasonal effects of climate change interactions. To address this gap, we conducted a seasonal change experiment at Hubbard Brook in 2013.
In this project, we warm up the forest soil to 5 degrees Celsius (5 degrees Celsius) using a forest heating cable during the off-peak season from April to November. In winter, we use a combination of heated cables and snow shovels to warm up and freeze-thaw the soil. Our results show that root damage and reduced tree growth due to the winter freeze-thaw cycle are not offset by growing soil warming.
Our study shows how often overlooked changes in winter climates can affect forest ecosystems. Lost snowpacks can reduce forest growth, carbon sequestration, and nutrient retention, which can have a significant year-on-year impact on climate change, air quality and water quality.