Why is tree line

But the farther away, the lower the tree line gets. Within latitudes, however, the tree line can differ significantly. The tree line in the U. Because of the arctic fronts that move down from Canada, those temperatures occur more in the Northeast than the west. It takes one rising to 10, feet in Wyoming to routinely achieve those temperatures. By the way, treeline is only 5, feet in mild Washington, where temperatures rarely drop below 0F even in the mountains.

Huge deep snowpacks that bury trees till July. Or at least 3 of 4. Snowpack certainly would have an effect more snow means longer snow means colder soil. Cooler ambient air temperature certainly contributes. Why does it take longer at treeline for the soil to warm up? Is it a difference in the soil? Soil moisture? Air temperature? To ensure a respectful dialogue, please refrain from posting content that is unlawful, harassing, discriminatory, libelous, obscene, or inflammatory.

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Thanks for joining the discussion. September 17th, by Michael Snyder Autumn Treeline in the East is lower than out West. Photo by Thomas Jones. Enter characters shown:. Citation: Berdanier, A. Nature Education Knowledge 3 10 High-elevation treelines are a global phenomenon, but the large-scale ecological and physiological mechanisms that define their existence still elude ecologists.

Aa Aa Aa. This stems mainly from: the many environmental conditions that change when moving from low-elevation tree-covered areas to high-elevation treeless ecosystems, and the multiple biological mechanisms that could explain the boundary based on these different environmental conditions.

Trees, Treelines, and Global Patterns. Figure 1: Satellite view of a treeline in Colorado, USA, demonstrating the complexity of the treeline boundary. Figure 2: Conceptual representation of the timberline the limit of closed tall forest , the treeline the limit of groups of trees over 3 m high , and the tree species line the limit of all individual trees. Explaining Treeline Patterns.

Problems with Multiple Conditions. Treeline was identified with satellite imagery as a point where tree density decreased sharply. Possible Explanations. Stress — physiological tissue damage due to low temperature or dessication. During the coldest part of the year, frost can damage cells by freezing or photoinhibition.

This is pronounced for trees due to their height, which results in a tighter coupling to the atmosphere than other short, alpine plants. Additionally, frozen soil can limit water availability, causing dessication of plant tissue, contributing to reduced tree growth at high elevations. Disturbance — mechanical damage due to wind abrasion, herbivory, snow loading, or fungi infection.

In high-elevation ecosystems, snow and ice loading can break or remove biomass on trees. Additional damage to needles occurs with high wind that often exists at and above the treeline. Wind damage may be more pronounced for trees than for the short, alpine vegetation that often exists far beyond the treeline. Additionally, when snow covers much of the surrounding alpine vegetation, the vegetative growth and meristems of developing trees are particularly susceptible to herbivory.

Snow mold and other fungal pathogens can also damage tissue. Reproduction — reduced seedling and sapling establishment due to decreased pollination, seed development, seed dispersal, germination, or seedling establishment. While the treeline is a clear boundary for the existence of trees, small shrubs and other low-lying forbs and grasses often exist above the treeline in the "alpine" vegetation zone. Carbon balance — photosynthetic carbon gain minus respiratory demands is not enough to maintain minimum growth.

The primary component of growth is net carbon gain, through photosynthesis minus respiration. The main restriction of carbon gain in these ecosystems is from the length of the growing period. If temperatures are too low and the growth period is too short for photosynthesis in the growing season to exceed the annual respiratory demand, a tree will not be able to survive.

Growth limitation — reduced development of new plant tissues due to low temperatures. The second component of growth is the use of photosynthetic sugars and amino acids to produce new cells and grow new plant tissues. Even if carbon supply from photosynthesis is sufficient, low temperature could limit growth and development. For example, both above-ground and below-ground tree plant tissues may experience colder conditions than low-lying alpine vegetation see below.

Four hypotheses have been proposed to explain this pattern: the immaturity of volcanic soils found on most of the islands, the absence of well-adapted high-altitude tree species that are found on continents, aridity and drought above the treeline on trade wind exposed islands, and altered vertical temperature gradients on mountains of different sizes called Massenerhebungseffekt , or the mountain mass effect, Leuschner Current Main Theories for Treeline Position.

The main explanations for global treeline position focus on a distinction between establishment Smith et al. Other explanations e. Both establishment and growth hypotheses are based on a strong relationship between vegetation and microclimate, emphasizing a connection to temperature, while one focuses on range expansion at the upper tree limit and the other on survival.

Limited Seedling Establishment. Reduced seedling establishment is a critical limiting factor on the colonization of trees at high altitudes. The inability of trees to become established defines the upper boundary of tree existence the tree form limit. Both tree germination capacity Viereck , Holtmeier and establishment Germino et al. While seedlings within a patch of trees near the treeline are protected by their neighbors, at the tree form limit seedling establishment may depend on physical objects e.

For example, in the winter, seedlings may be protected from ice crystal abrasion, dessication, and diurnal temperature fluctuations whereas in the summer seedlings benefit from decreased sky and wind exposure increasing daytime temperature. Growth Limitation. The tree line near Mt. Rainier, US. Benjamin Elisha Sawe April 25 in Environment. Puma, Cougar, Or Mountain Lion? Bhopal Gas Tragedy. Greenland Shark.

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