On Saturday, July 16, longtime Friends of Trees volunteer Jim Gersbach shared his knowledge of the beech family, Fagaceae, with Friends of Trees staff and key volunteers during a morning tour of the NE Ainsworth Linear Arboretum.

A crew leader, neighborhood coordinator, and former board member, Jim also gives PowerPoint presentations to homeowners several times a year to help them choose which tree to buy for their planting strip or yard. He led the effort to designate two miles of NE Ainsworth Avenue as an arboretum where people can see more than 60 tree species in an urban neighborhood habitat.

The NE Ainsworth Linear Arboretum not only provides shade and beauty along a boulevard the Olmsted brothers originally hoped would be included in Portland’s park system along with Forest Park, but it provides a living laboratory for testing tree species from regions in the world with climates similar to the climate Portland might experience in the future as a result of climate change.

In addition, the arboretum encourages people to consider planting a diversity of species. During the July 16 tour, Jim reminded the tour participants that decades ago Dutch Elm Disease spread from one elm to the next along boulevards where only elms had been planted. The elm beetles carrying the pathogen spread through the elms’ interconnected roots and touching limbs.

“In a natural forest,” Jim said, “the greater the diversity, the healthier the forest. By planting a wide variety of tree species, we have the best insurance against catastrophe.”

Meet the beeches

The July 16 tour focused on the beech family, Fagaceae, which includes beeches, oaks, and chestnuts. The first was the European beech, whose “squirrel-mediated reproduction” benefits the species by ensuring wide dispersal of the acorns.

The second of the beeches was the Purple European beech, whose purple-tinted leaves are the result of anthocyanin dominating chlorophyll in the leaves. Trees in which chlorophyll dominates “survive better in nature,” Jim explained, so you’re more likely to see trees with purplish leaves in cities, where individual trees can be nurtured.

Jim also showed the group a Southern beech from Chile and western Argentina. When explorers rounded the horn of South America and found this species, Jim said, they thought they’d discovered a beech. But since that time, the tree has been reclassified as a “false beech,” or Nothofagus. Like a true beech, it’s also “wind pollinated.”

Jim noted that the climate in Chile, where he’s seen the tree growing in the wild, is very similar to the climate in Oregon. When it’s mature, the Southern beech looks like an oak.

One of the oaks on the tour included the Sawtooth oak.  Jim pointed out the contrast between the tree’s new leaves, which were light green, and its mature leaves, which were dark green and had a protective coating that helped the tree survive. Jim also noted that after the tree’s leaves turn their fall colors, the leaves wither, and the tree holds onto its leaves. They don’t drop the leaves until spring, when new growth begins.

Oaks are generally well suited to Portland, though watering a lawn where a young oak is planted might create a biological pathology in the soil that can kill the oak. “Grass will come back [in the fall] but the oak tree won’t come back because of the pathogen.”

Some of Portland’s oaks predate the founding of Portland, Jim said, and some Willamette Valley oaks are more than 250 years old.

Adding some history to the tour, Jim explained that Willamette Valley tribes used to set periodic fires, which made the land easier to traverse and led to an increase in the game animals that the tribes hunted. After the tribes were forced onto reservations, they no longer set seasonal fires, and Douglas-firs became dominant instead of oaks.

The question is whether oaks or Douglas-firs should be considered the naturally dominant native tree. There is value to both species. About 20 kinds of birds, for instance, depend on Oregon white oaks for their food or homes.

Other trees besides beeches

Some of the trees in the tour weren’t in the beech family but provided examples of species that are no longer candidates for future plantings in Portland. These included the beautiful but short-lived Raywood ash, whose trunk grows faster than its roots, making it unstable in Portland’s water-soaked soil during windy fall storms, and the Japanese pagoda tree, which is resistant to drought but is proving susceptible to a fatal canker disease in the Linear Arboretum.

“Friends of Trees provides follow up to each tree planting,” Jim explained. “They keep a database to follow how a tree is doing five to ten years later. “That’s how we know now that this tree [the Japanese pagoda tree] has disease issues.”

The goal, Jim said, is to “plant trees that will live a long time and are generally free of diseases and pests.” We’re looking for trees that are adaptable to our climate, that have more of a Mediterranean background. “We’re not sure how long we’ll have enough water.”

The tour included two Persian ironwoods, which have many of the same characteristics as oaks, such as strong wood, which is why the tree is named “ironwood.” The first Persian ironwood had weed whacker damage at the base of the trunk, which  contributed to its diminished size in comparison to the next Persian ironwood, which was planted more recently and was taller and healthier.

“There’s a genetic cap on trees,” Jim said, “but a lot of how a tree flourishes is in its cultivation.”

Mr. Howell, who planted the thriving Persian ironwood, sauntered out his front door to chat with Jim, who’d helped him select the tree for his planting strip. “It’s a handsome tree,” he said, clearly pleased with its progress.

Two of the final trees on the tour included a Chinese fringe tree, which Jim hopes can be offered as an alternative to homeowners who want to plant dogwoods, a species that has been overplanted in the city, and a Japanese umbrella tree (pictured at right), which has its own family, genus and species. The Japanese umbrella tree grows well in Portland. It also retains its leaves in winter, which is good for capturing stormwater during the wet fall and winter months.

At the end of the tour, the group paused by a towering oak next to a baseball diamond.

“We need to think long-term,” Jim said, gazing up at the arching limbs above him. “We need to think of the trees as they’ll be in 40 years, like
this one.”

–TR

Filed under: Neighborhood Trees

Tags: education, street trees, yard trees