Climate change doubles tundra plant life, boosting shrubs, grasses

Desert – tundra – forest
The major Arctic vegetation zones include the polar deserts,
tundra, and northern part of the boreal forest. The northernmost
zone that covers most of the high Arctic is the polar
desert, characterized by open patches of bare ground and an
absence of even the smallest woody shrubs. Tundra is
characterized by low shrub vegetation. Climate warming is
projected to cause vegetation shifts because rising temperatures
favor taller, denser vegetation, and will thus promote the
expansion of forests into the Arctic tundra, and tundra into the
polar deserts. This change, along with rising sea levels, is
projected to shrink tundra area to its lowest level in at least the
past 21,000 years, greatly reducing the breeding area for many
bird species and the grazing areas for land animals that depend
on the open landscape of tundra and polar desert habitats. Not
only are some threatened species very likely to become extinct,
some currently widespread species are projected to decline
sharply.
...
Countervailing Forces on Climate
The projected reduction in tundra and expansion of forest will
cause a decrease in surface reflectivity, amplifying global
warming because the newly forested areas are darker and more
textured and thus absorb more solar radiation than the lighter,
smoother tundra. For example, black spruce is the least
reflective of any vegetation type on Earth and it is likely to be a
large part of the mix of new trees in North America. In
addition, expanding forests will mask highly reflective snow.
The darkening of the surface that results from these changes
will create a feedback loop whereby more warming will lead to
more tree growth, which will cause more warming, and so on.
On the other hand, the expanding forest vegetation will be more
productive than the existing tundra vegetation, and the tundra
will be more productive than the polar deserts it displaces.
Model results suggest that this could increase storage of carbon,
slightly moderating the projected amount of warming. The net
effect of these countervailing forces involves multiple
competing influences that are not fully understood. However,
recent studies suggest that the increase in absorption of solar
radiation will dominate over the increase in carbon storage,
resulting in a net increase in warming.

http://acia.cicero.uio.no/factsheets/3_vegetation_zones.pdf