The Boreal (Taiga) Forest is the largest terrestrial ecosystem on Earth.
The tallest tree on Earth is over 100 meters tall. It is a Coast Redwood in California named Hyperion
Pando is an 80,000 year old colony of Trembling Aspen. Testing has shown Pando to be a single organism presumably connected by a single massive roots system.
The largest tree on Earth has a circumference over 10 meters. General Sherman is a Giant Sequoia and has a volume of 1486 cubic meters of wood.
Old trees sequester an increasing amount of carbon as they age. For some species, one old growth tree could sequester the same amount of new carbon in a single year as could be contained in an entire mid size/age tree.