The many species of American oak trees often live for centuries if circumstances are favourable. Pin oaks are among the least vigorous with an average lifespan of only 100 years. In general the red oak varieties with open heartwood pores do not live as long as white oaks. White oak heartwood is more dense and less susceptible to insect and fungal attack. Red oak commonly lives to about 200 years. White oak's average lifespan is about a century longer.
The longest lived species of oaks--with a usual maximum lifespan thought to be about 600 years--seldom die of old age. Drought, lightning damage and insect attack all take their toll. Dead branches and lightning scars expose the trees to fungal infections that can completely rot away the heartwood. Hollow or partly rotted trees are easily downed by wind storms or burdens of winter ice.
Few truly aged oaks remain in today's American forests. Oaks in Indiana forests, for example, are nearly all younger than 100 years with most of the older trees between 60 and 80 years of age. Many regions have been logged off several times since the original forests were first harvested. The introduction of new diseases and insect pests also places new stress on the species. The wood of mature trees often shows considerable damage and has reduced value.
Non-profit organisations such as the National Register of Big Trees work toward the preservation of individual trees of great age and size. States recognise such trees as cultural treasures. Donations help treat injuries and diseases of American Champion trees. America's oldest oak, the Angel Oak, is the centrepiece of a park established around it on John's Island, South Carolina. Perhaps the oldest living thing east of the Mississippi River, the Angel Oak may be 1,500 years old. The trunk of this live oak measures 25 feet across, and its spreading limbs are so heavy that a few dip below ground level. Though most of the truly ancient oaks are American, the world's oldest is the Granit Oak in Bulgaria--1,674 years old.
New insect pests such as the gypsy moth threaten the health and longevity of American oak forests. One of the newest problems, a fungal disease called Sudden Oak Death, first showed itself on the West Coast in California oak trees. Travelling along with nursery stock shipped from that area eastward, the disease has been slowed by new restrictions and better sanitation procedures in tree nurseries.
Live oaks in the southern United States suffered major damage from several bad hurricane seasons in recent years. In Mississippi, Hurricane Katrina destroyed 3.5 million trees. Live oaks in urban areas were especially hard hit, with some trees in New Orleans continuously flooded for as long as three weeks and then poisoned by salt. Manmade disasters also threaten champion oaks. Old Dickory, a champion live oak in Harahan, Louisiana, was saved from a bulldozer in 2003 when the state highway department yielded to public pressure and routed a new highway around it.