Climate & Ecology

The topography of Bhutan is truly amazing, ranging in elevation from 150 m to 7,000 m. The summer monsoon from the Bay of Bengal plays a critical role in the weather pattern in this mountainous land, bringing up to seven meters of rain per year. On top of this, temperatures range from minus 7 degrees Celsius to 30 degrees Celsius in areas that are less than 100 km apart. These climactic extremes influence vegetation profoundly, allowing for a incredible diversity of plants.

Tropical forests:


photo M. Noonan

In low elevations of 350 to 2,000 m, plants can grow actively all year.

A huge variety of trees are found there, including Bombax, oak, banyan, and pipal. Rufous-necked hornbills use Ficus trees for nesting. Leopards move during the day, to avoid the tigers prowling at night. Spotted deer are preyed on by dholes - a kind of wild dog. Wild boar eat roots, tubers, snakes, and insects. Gaur can weigh over 1,000kg, and are active at night in the hill forest of the Siwaliks. Rhinoceros eat short grasses and shrubs, and are able to cool off by wading in the water.

Temperate forests:

The plants and animals in Bhutan's temperate forests are adapted to the year-long moisture from rain, snow, and mist. Bamboo grows alongside conifer trees. Orchids grow on old trees, rocks, or even on the ground. They coexist with a fungus that absorbs nutrients. In the spring, the flowers of the orchids attract birds and insects. Coniferous trees also depend on fungi on their roots to absorb minerals. We humans rarely see these fungi until they reproduce via fruiting bodies that we call mushrooms.

Barking deer live by eating fruit and bamboo. Himalayan black bears primarily eat leaves and fruits, but also supplement their diet with meat when they can obtain it. Goral have long, narrow hooves that have soft soles for climbing steep, rocky terrain. They prefer grassy slopes near cliffs where they are mostly safe from predators.

 


                                                  photo M. Noonan

Subalpine forests:


                                                 photo M. Noonan

Fir forests grow on the protected, north-facing slopes of mountains, or on the highest ridges where low clouds bring moisture. The slant of the branches on these trees allows them to survive the winter without collecting heavy snow. Musk deer survive by living in the dense undergrowth and eating lichens off of the trees. These lichens, Usnea, grow on branches above the snowline.
                                                

Treeline:

At the treeline, the winds and cold light prevent trees from growing. Here, many animals change to adapt to the changing seasons. The Himalayan weasel, for example, turns gray-brown in the summer for camouflage, but becomes white in the winter when it preys on voles. Takin migrate from high elevations in the summer to low in the winter. The needles of larch trees stop producing chlorophyll and drop off every autumn in order to conserve moisture. As soon as the snow melts every spring, anemones bloom to maximize their sunlight exposure in the short summer months.

photo M. Noonan

The Alpine Tundra:


photo M. Noonan

At the highest elevations, winter lasts for eight months of the year. The bowl-shaped flowers of poppies and anemones focus the light from the sun for warmth, and red pigmentation in other plants serve as protection from the direct light of high elevations. Many alpine plants have thick or waxy leaves to avoid desiccation by the wind. Other plants, like the dwarf rhododendron and juniper shrubs, crowd into the few moist ridges and gullies. Here, animals have adapted to survive freezing temperatures and a severe shortage of food. Springtails, for example, feed on wind-blown pollen. Pika survive by gathering plants into their burrows during the summers in order to have a source of food for the long winters. Marmots, on the other hand, go into hibernation, surviving only off their body fat. Blue sheep manage to live out in the open all year, protected by their thick winter coats and eating frozen grasses. Snow leopards survive by eating these blue sheep.

Tree Rings and the Wheel of Time:

In ten years, a tree in the southern forest of Manas will grow twice the size of a tree near Thimphu at mid level elevations. And it will be four times greater than a tree growing in Laya in the subalpine forest. The short growing season and frigid temperatures at higher elevations stunts or prevents the growth of trees.

Much can be learned from looking at the rings of trees. Black rings tell us when fires swept through the forests. Wide rings mean long, warm summers, while thin rings are formed by slowed growth in the cold seasons. Trees are absolutely critical for future conservation. It is natural forests that support the biodiversity that allows nature to regenerate.
 

Content provided by Canisius College students under the direction of Michael Noonan, PhD.