Regional Gardening Reports :: National Gardening Association

In the Garden:
April, 2011
Regional Report

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Jason Lubar of the Morris Arboretum of the University of Pennsylvania's Urban Forestry Consulting Team shows the strategic limb propping that helps to keep this veteran magnolia alive at the arboretum.

Regenerating 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 their preservation at the Morris Arboretum of the University of Pennsylvania.

In recent decades, storms have wreaked havoc on older trees there. Each mature tree standing is precious and significant environmentally, genetically, historically, and sentimentally. The prominent gray-barked Bender oak with its 90 foot spread is thought to be 250 years old. The weeping European beech, planted before 1909, extends 90 feet wide through layering. Its branches have dipped and rooted to form rings of new trees surrounding the decaying mother tree.

These craggy, scarred, fissured giants 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. These veterans are history in themselves and for people who've climbed their branches, played tag under their canopies, leaned against their hefty trunks and shared secrets.

"Veteran trees have complex systems. They've seen the slings and arrows of 100 to 300 years," explains Lubar, an arborist, consultant and educator. As survivors they deserve TLC that is scientifically-based and naturally derived.

The aging cherry across from the Widener Education Center is considered a "phoenix tree." A new tree, called a cambium column, is growing 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 up 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 parent.

"We do cultural things to preserve the veteran trees, to keep them young,"says Lubar. The regenerative techniques he and his colleagues use for the arboretum's living collection are helpful for any mature tree in our yards, woodlots, or gardens. On Compton Hill, intricate copper cabling supports the historic Bender oak's massive limbs. Lightening protection saves it from electrical strikes.

Pruning veteran trees involves an approach different from young tree care. "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 encourage vibrant shoots, suckers, and water sprouts to produce more leaf mass. "Now we let water sprouts grow," he explains. "They will be the new trees, the new canopy. They will keep the mature tree growing." More leaves means more photosynthesis, hence more nutrients for the mother tree.

Above the meadow, staff have propped heavy limbs of a magnificent, splaying magnolia by attaching them via through-bolts to red cedar timber. Lubar nods toward a furrow of rotting wood in one of the old limbs. "This is rich in biodiversity. Having old trees like this supports a wide range of insects and grubs that birds eat." Looking down, he adds, "Mulch under the canopy to reduce compaction. The better you can make the soil around the old tree, the healthier it will be."

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