Trees that are 100, 200 or even 300 years old require special management techniques. Here are some examples of trees that are getting the proper care and some tips on how you can cultivate and coddle your own veteran trees.
Walking among centuries-old trees — magnolia, cherry, Bender oak, European beech, katsura — Jason Lubar puts it simply. “We are a tree museum.” Rather than remove aging trees, Lubar and members of Urban Forestry Consulting Team focus on veteran tree preservation at the Morris Arboretum of the University of Pennsylvania. They turn back the clock by regenerative pruning, propping and cultural practices.
Loss can make what remains more precious. In recent decades, storms have wreaked havoc on the arboretum’s older trees. Each mature tree standing is venerable and significant — environmentally, genetically, historically, sentimentally. The prominent gray-barked, upright Bender oak that welcomes arboretum visitors is thought to be 250 years old. All year round this flagship tree is most people’s first impressive, up-close-and-personal experience with the arboretum’s treasures. Strolling from the parking lot to the Widener Education Center, visitors walk under branches of its 90-foot-wide, deep green canopy.
Veteran trees are craggy, scarred, fissured giants who grab and hold our imagination. Their huge limbs give us places to hide and dream. Their split, pithy trunks are homes to insects and birds. They are history in themselves and for the people who’ve climbed their branches, played tag under their canopies and leaned against their hefty trunks and shared secrets.
Regenerating Veteran Trees
Steel cabling strung through the branches holds the Bender oak together.
Lightning rods of copper wire extend from a red oak top deep into the soil to capture and divert electricity from the tree into the ground.
Caring for them is different from young or even mature trees. “Veteran trees have complex systems. They’ve seen the slings and arrows of 100 to 300 years,” explains Lubar, ISA Board Certified Master Arborist and associate director of urban forestry at the Morris Arboretum. As survivors they deserve TLC — scientifically based, naturally derived TLC.
Europe with its history of old trees — some 800 to 1,000 years and aging — has developed the science and art of veteran tree care. The United States with its younger trees is just starting to become educated in preservation.
Centuries-old trees are consolidating their resources and energy; they’re getting smaller; they may die back, Lubar says. “We do cultural things to preserve the veteran trees, to maintain their vigor,” says Lubar. “The main thing is managing the leaves” — promoting as much growth as possible to photosynthesize, producing as much food as possible.
The regenerative techniques Lubar and his colleagues use for the arboretum’s living collection are helpful for any mature tree in our yards, woodlots or gardens.
One technique involves specialized pruning. “We turn back the clock by doing regenerative pruning,” Lubar says. To lessen stress and breakage, they reduce weight by removing large, long branches. They may make heading cuts to trigger interior canopy growth. A heading cut trims a branch back to a bud or a small branch.
Lubar and his team encourage and manage the growth of vibrant shoots, suckers and water sprouts to produce more leaf mass. “Now we let water sprouts grow,” he explains. “They will be the new canopy. They will keep the mature tree growing.” More leaves means more photosynthesis, hence more nutrients for the mother tree.
Above the sheep meadow, staff have propped heavy limbs of the magnificent splaying magnolia, using mostly through-bolts with red cedar timber. The red cedar, which resists rot, is taken from elsewhere in the arboretum. Lubar nods appreciatively toward a wide, deep furrow of rotting wood on a supported limb. “This is rich in biodiversity. Having old trees like this supports a
wide range of insects and grubs that birds
eat.” Lubar looks down. “Mulch under the canopy to reduce soil compaction,” he says. “The better you can make the soil around the old tree, the healthier it will be.”
New from Old: Phoenix Tree
Across from the arboretum’s Widener Education Center, the aging cherry tree is considered a “Phoenix Tree.” A new tree — called a cambium column — grows from the declining mother trunk. This new tree uses the same roots and has the same genetic material as the mother tree. Another Phoenix rebirth occurs in a nearby linden. One partially broken limb touches the ground. Staff propped the limb to keep it connected to the mother tree. So far it’s forming a cambium column, a new tree with genetics identical to its mother.
The 90-foot-wide weeping European beech, pre-1909, puts out its progeny through layering, Lubar says. Layering involves the limbs dipping and rooting to form rings of new trees surrounding the decaying mother tree. New rooted trees will have the same genetic material as the mother tree.
Holding the Parts in Place
Morris Arboretum’s Associate Director of Urban Forestry Jason Lubar shows how a red cedar timber from elsewhere on the property has been cut and bolted to prop up a large magnolia branch.
Look up into the massive Bender oak on Compton Hill. There, regenerative TLC involves steel cable strung through the branches, attached to bolts, weaving throughout the crown. “The cabling is a supplemental support system helping to hold up the big limbs,” explains Lubar. “We also cut off the ends of larger limbs to relieve weight and trigger growth.”
Copper conductor is used as lightning protection. The lightning rod carries the electric charge to the ground where the energy is dispersed. The main conducting cable runs from the highest accessible point in the tree down the trunk and into the ground. A large or forked trunk requires two or more cables on opposite sides of the trunk as well as small connecting cables along major branches. Cables are grounded — placed some 10 feet deep in surrounding soil.
Regenerative Tree Care Techniques
• Leave the autumn leaves under the tree. Use a mulching mower to shred leaves or just allow fallen leaves to stay. Trees evolved in a forest setting where leaves naturally dropped and decomposed into nutrients.
• Mulch with organic matter — no more than 2 inches of shredded leaves or shredded bark — under the tree canopy for a healthier root system.
• Do not have mulch touching the trunk or covering above-ground roots. Mulch against a trunk or on top of roots can hold moisture and more, causing tree parts to rot.
• Trees need as many healthy roots as possible. Growing grass under the branch spread of an old tree undermines that. Digging to plant shrubs, perennials and annuals can damage tree roots, too.
• Consult an arborist trained in regenerative tree pruning. Correct care of veteran trees differs from young and mature tree care.
(From State-by-State Gardening January/February 2012. Photography By Charlotte Kidd.)