From the Melting of the Snow to the Greening of the Fields

Changes in timing of spring snow melt, permafrost degradation, killing with greater declines in evergreen-dominated areas (Miles and Esau, ). to Arctic greening, discussing its drivers, subsequent consequences and.
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Their analyses show that the number of chilling days during warmer winters has decreased at low elevation but increased at high elevation, suggesting that lowland trees are not keeping up with the pace of phenological advance of their upland conspecifics, and that this is happening because they are receiving insufficient chilling during the winter. An interesting question, therefore, is to what extent the observed contraction in the elevation-induced shifts in the time of leaf-out is a local pattern in the European Alps or whether this is also happening regionally or even globally along elevation and latitudinal gradients?

To explore this, we compared the patterns in chilling days in the s and s from sites with contrasting climates across Europe from ca. These data illustrate, firstly, how and why climatic warming drives opposing trends in winter chilling at low and high elevations in the Alps.

In the temperate climates found at low elevations, chilling occurs throughout winter, and since the winter temperatures were already at the high end of the chilling spectrum in the s, the number of effective chilling days has decreased with climatic warming increasing number of observation points falling outside the blue box in Fig.

At high elevation, in contrast, the winter months are too cold for effective chilling, which therefore primarily occurs in autumn and spring; here, the number of effective chilling days has increased with climate warming more observation points falling into the blue box in Fig. The mean leaf-out dates were extracted from the study by Vitasse et al. There may be regional differences driven by the underlying patterns in chilling and temperature relative to the requirements for bud break; for example, the contraction of phenological shifts along elevational gradients is likely to be pronounced in oceanic climates at mid- but not high latitudes compare Fig.

The changing colors of the Arctic: from greening to browning - Luonnonvarakeskus

There may also be other sources of regional variation; for example, the contraction of the latitudinal phenological shift may be further exacerbated by faster warming in the high north 10 , illustrating how the alternative explanations put forward by Vitasse et al. For example, as illustrated by the prevalence of transhumance farming systems in seasonal climates worldwide 2 , 4 , 5 , tracking phenological shifts, and thus feeding on the high-quality early-season growth for an extended period during summer, can offer substantial energetic advantages to grazers 14 , with potential knock-on effects on their predators.

Earlier leaf-out in upland and high-latitude trees over a broad scale can also impact ecosystem processes, such as carbon dynamics, by extending the growing season, and hence increasing the carbon accumulation and accelerating the uphill and northward expansion of the tree line at high elevations and latitudes.

A climate change-driven contraction of the seasonal availability of this resource could thus negatively affect both higher and lower trophic levels. It is therefore crucial to understand phenological responses of different taxa to climate change, especially at a broad scale. The alterations of phenological gradients could also vary within trophic levels, such as across plant growth forms. There are a number of reasons why this might not be the case.

First, a number of ground-layer plants are herbaceous, and thus protect their meristems from frost by keeping them underground during the cold season Adding to this, snow, which is common in winter across the boreal zone, effectively decouples the apical meristems of field-layer plants from the cold winter temperatures. Hence, chilling requirements are unlikely to be controlling leaf-out in field-layer growth forms; indeed, spring ephemerals are regulated primarily by spring temperature If leaf-out in trees and field-layer plants are regulated by different climatic drivers, then climate change could result in phenological mismatches between growth forms.

For example, if upland and northern trees experience increasing numbers of chilling days, leading to earlier and faster spring leaf-out, the time window between snow melt and tree canopy closure may narrow, presenting a challenge to the characteristic spring ephemerals of the forest understory, which may not be able to reproduce before the canopy closes As illustrated by Vitasse et al. Published under the PNAS license. We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail.

We do not capture any email address. Skip to main content. Greening up the mountain V. Halbritter , and R.


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The authors declare no conflict of interest. See companion article on page Astrup NJ Soleienatt, Nasjonalmuseet, billedkunstsamlingene. Accessed December 19, Paine R Herds of the Tundra: Moktan MR , et al. Much of the time that we hear about the importance of winter snowpack in the mountains is in reference to when ski season starts.

Greening up the mountain

Seasonal mountain snow represents an important source of freshwater in many places. When the snow melts, it becomes water that can go towards supporting vegetation, adding to groundwater, and flowing downslope in rivers and streams. Check out this before and after image showing fields greening up after mountain snow melts. In some places like California, a substantial portion of the water across the entire state originates as snow in the Sierra Nevada. As a result, there is a lot of interest in understanding how much snow falls in the mountains and what happens to it.

In mountains with seasonal snowpack, after the snow falls, it will slowly ablate.

New Research In

Ablation is the term used to describe the disappearance of the snow and can happen by a number of different processes. Most simply, and most commonly, the snow melts. However, another important process is sublimation in which snow goes straight to water vapor and escapes to the atmosphere as gas. There are a few different types of sublimation. It can occur directly from the surface of the snow surface sublimation , when show gets caught in the trees canopy sublimation , or when snow is blown by the wind blowing snow sublimation.

Despite the fact that sublimation can be an important process in determining how much of the snowpack will eventually be available as water for us to use, there is still a lot that we do not know about the role that sublimation plays in the disappearance of snowpack. In order to better understand the role of sublimation now and in the future, a team of scientists, led by Graham Sexstone, conducted a study where they measured and modelled snow sublimation.

Specifically, they sought to answer the following questions:. In order to answer these questions, Sexstone and colleagues used both computer models and measurements taken at a field site. Their field site was an area of the Rocky Mountains in north, central Colorado. Within the field site, there were a number of different environments.


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There were alpine areas above the treeline, forested areas, and nonforested areas that were below the treeline. They measured snowpack levels, sublimation rates, and weather data at observation points across the field site for five years. They then took this data that was measured in the field and compared it to predictions for the same area made by a computer model. Finally, to assess the potential impact of disturbances and climate change, they ran the computer model again with these different scenarios to see how it impacted sublimation. In their data from the field site, the researchers found that there was a lot of variability in sublimation rates and type of sublimation process across the different environments and landscapes within the field site.

In years with lower amounts of winter snow, the total amount of snow sublimated was lower, but represented an overall larger portion of winter precipitation. Even with this range of different outcomes they observed in the field, the research team still found that the results from their computer model were pretty good at predicting these observations from the field. In the different future scenarios that were tested in the computer model, there were various impacts on sublimation.

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For both the climate change scenario and the bark beetle infestation which causes tree death , there was only a slight decrease in the amounts of snow that was sublimated in each case. However, this decrease was not a result of lower rates of sublimation.

In the case of the bark beetle infestation, they saw a shift in the type of sublimation processes that were occurring, as a result of there being fewer trees.