The world's oldest tree, a 9,550 year old spruce, was recently discovered in Sweden.1 This new-found spindly record holder is old even for a tree... right? Perhaps you are asking: How long does a tree live? While there are a few ancient giants (and dwarfs) who have seen humans move from tribal life to the modern industrial world, most trees don't have much more than human lifespans. Like animals, the lifespan of a tree depends on its species.
The previous world record holders were the dwarf-size 4,845-year-old and 5,062-year-old Great Basin bristlecone pines (Pinus longaeva) in the White Mountains of California.2 In contrast, the Western White Pine (Pinus monticola), the Idaho state tree, has been known to have a lifespan of up to 350 years. This tree reaches its full height of around 150 ft at 150 years.3 Even with the western white pine there are exceptional ancients. A western white pine (on the White Pine Scenic Route at the Giant White Pine Campground) died in 1998 at the ripe age of 600 years.4 Like other living things, after reaching maturity, a tree's health starts to decline and it can be subject to disease or other problems. Blister rust, for example, is a common problem for the white pine and when added to the other forest diseases, has become a serious threat to the health of our forests.5
But talking about one species and a single tree's life-span, you only see the tree and not the forest. Unless planted in cities where they are maintained by people, trees typically live in forests which are complex renewable systems - a system in which many things depend on each other in order for life to continue in a healthy balance. Trees can't just live on their own; they would die. Like people, trees need a diverse community of other living things that provide them food, shelter, and water.
Forests constantly change over time in a dynamic natural process called "succession." As with people, trees start with conception (seed), moving into birth (sprout), then infancy (seedling), growing rapidly as a youth (sapling), maturing into adulthood (mature), aging to elderly (decline), and then finally arriving at death (snag/rotting).6 Like baby humans, young trees need the protection and nurturing of older trees, nutrients from soil provided by beneficial fungus and insects, water pulled up via bigger trees and plants' root systems as well as mulch from forest debris. The healthier the forest, the healthier the tree and longer the lifespan. However, as trees move into decline and death, they can harbor disease or even be a danger for those who work or play in the forest. The term "widowmaker" refers to a hazard limb or tree that is at risk of falling on a forest worker - sometimes causing fatalities. While rotting "nurse logs" can be the nutrients for saplings, they can also be hosts for disease and fuel for forest fires.
For millennia, natural disturbances like fire, wind, ice storms, and insect outbreaks have created diversity in ecosystems by interrupting the reproductive cycle of trees. Why is this good? Disturbances, including logging, wipe out disease and increase genetic diversity, which in-turn increases forest resiliency - allowing trees to live healthier lives for longer. Historically, in western forests before modern times, the most common disturbance was fire.
We now know that fire was an essential ingredient for a healthy forest. Before European settlers, ponderosa pine forests, for example, were open with a few dozen trees per acre. Today, we might have hundreds or even thousands of small trees crowded into the same area. All those trees have to compete for a limited amount of water and nutrients, making them more susceptible to drought, disease, and insects. Prior to European settlers, many Native American communities used fire to manage the forests to optimize forest health, so that the plants and animals would thrive. 7 8
Fires have severe social, economic, and ecological impacts and it has been a practice in the United States to extinguish forest fires for nearly a century. The result of a hundred years of fire suppression is that our forests are unhealthy and their survival is at risk.9 Climate change related drought and high temperatures have increased the frequency and intensity of wildfires, threatening both property and forests in Idaho. Moreover, these hotter and drier summer conditions could reduce the range and health of certain tree species, increase their susceptibility to fire and possibly permanently destroy these forests.10
What can people do about this threat to our forests? We can help the forests through smart management. 'Forestry' is growing trees using art, science and application of management at certain points of succession. This means human involvement in the life-cycle of the forests. Logging may be the end of a tree but the beginning of a forest. When forests are harvested, Idaho law requires they be reforested within 5 years. The forest succession cycle continues.
Like most of North America, much of Idaho's forests are not in a "natural" condition and haven't been for over 100 years. Federal forests that have not been harvested and have been protected from fire are in severe decline. Modern policies have caused the current condition, causing as many problems as past overharvesting did. The cycle of forest succession continues regardless of human intervention. However, we should not expect to have healthy forests without disturbances.The question is what kind of disturbance is acceptable?
While Nature always takes care of itself in the long-run, Idaho forests are in trouble. It is obvious that humans need trees: For more than just the ecosystem benefits such as clean water, clean air, wildlife, fish and others, we use trees for building our homes, printing our books, and a host of other very useful things. Yes, people need trees! But with climate change, disease, drought, and ecosystem changes perhaps it's time to ask the glaringly human-centric question, if we want to see healthy forests... do trees also need people?
1 Umeå University. "World's Oldest Living Tree -- 9550 years old -- Discovered In Sweden." ScienceDaily. ScienceDaily, 16 April 2008. www.sciencedaily.com/releases/2008/04/080416104320.htm.
2 Goldbaum, Kate. "What is the Oldest Tree in the World?" Live Science. Life Science, 23 August, 2016. http://www.livescience.com/29152-oldest-tree-in-world.html.
3 Sibley, David Allen. "Sibley Guide to Trees." Random House Inc., New York, 2009.
4 600 year old White Pine. https://www.fs.usda.gov/recarea/nezperceclearwater/recreation/camping-cabins/recarea/?recid=80085&actid=29
5 US Forest Service. "White Pine Blister Rust." USDA, https://www.fs.fed.us/rm/highelevationwhitepines/Threats/blister-rust-threat.htm
6 http://texastreeid.tamu.edu/content/howTreesGrow/ Texas Project Learning Tree: sponsored by Texas Forestry Association and Texas A&M Forest Service. Media Line: 979-458-6606
7 US Forest Service. Four Threats. https://www.fs.fed.us/projects/four-threats/
8 National Park Service. "Human Use of Fire." US Department of the Interior. https://www.nps.gov/fire/wildland-fire/learning-center/fire-in-depth/human-use.cfm
9 Danahy, Anne. "Suppression of naturally occurring blazes may increase wildfire risk: Penn State's Alan Taylor uses model to help predict the unintended consequences of suppressing wildfires." Penn State's Earth and Environmental Systems Institute. March 26, 2013. http://news.psu.edu/story/270206/2013/03/26/research/suppression-naturally-occurring-blazes-may-increase-wildfire-risk.
10 National Service Center for Environmental Publications (NSCEP). https://nepis.epa.gov United States Environmental Protection Agency, Office of Policy (2111), Title: Climate Change and Idaho, EPA 236-F-98-007f September 1998