Foothill´s Changing Landscape: Oaks on the Edge
Where are the young saplings to replace our thinning oak woodlands? Splintered branches and fallen trees marked hillsides after last winter´s wet snow, but the real thinning is caused by oaks´ failure to regrow. For example, notice the lack of new oaks, especially the deciduous Blue Oaks, on hillsides as you drive down Highway 108 towards an optimistically named Oakdale.
There are many reasons for oaks´ failure to regrow ranging from weed encroachment, development, grazing, rodents, and climatic change. Public policy and conservation plans are beginning to require oak mitigation, but regeneration takes time. Heritage trees and oak woodlands require decades and more to regrow.
HERITAGE OAKS ARE CENTURIES OLD. A Blue Oak that is two feet in diameter may be 200 years old; one that is three feet may well have survived 300 years, requiring at best ten years to increase an inch in thickness. Every part of these oaks provides shelter and a cornucopia of food for wildlife—from the roots, branches, and bark, to the bushels of acorns produced in a good year.
Humans benefit not only from an oak´s wildlife contributions, beauty, and shade, but monetarily as well. Texas A & M University estimates that a single 18-inch Live Oak increases the value of a residential lot by $3,185. University of California research estimates that native oaks on rural subdivisions contribute as much as 27 percent to the value of the property and, according to the U.S. Forest Service, can reduce air conditioning by 30 percent.
OAK WOODLANDS ARE HOME TO MANY. Over 300 vertebrate species use oak woodlands, (defined as five or more trees per acre for most oaks) including 80 mammal species and 170 kinds of birds. Scores of these creatures are completely dependant on the woodlands.
As many as 30,000 acres of oak woodlands are converted for residential and commercial use each year. The resulting fragmented habitats restrict wild species´ movement and ability to locate mates and sites for raising families. Mate selection is then limited and the gene pool reduced. It is believed that more than 75% of woodland wildlife fails to adapt to urban pressures—noise, light pollution, road and foot traffic, off-road vehicles, and domestic animal intrusion.
THE REGENERATION CHALLENGE. Gravity and water conspire to move acorns downhill. Rodents and birds contribute to uphill movement by burying (and frequently forgetting) acorns for future meals. Jays are stars of this process, conducting an enthusiastic acorn airlift to new, widely spread sites, stashing acorns in soft soil where they are most likely to root.
Even so, it is a daunting challenge for acorns to survive to seedlings and saplings. Insects, fungi, drought, and trampling, hungry animals all take heavy toll over a seedling´s life.
NURTURE SEEDLINGS. If you have room for a new oak tree or perhaps an entire grove, here is how to give a hand. Much of the work is done if you already have young seedlings to nurture. (Remember those jays that plant far and wide?) Select seedlings where they have room to grow, beyond the drip line of existing large trees.
No seedlings? Start your own by collecting fresh acorns, preferably directly from the tree (knock to the ground with a long pole or pipe), or from the ground beneath an oak. Acorns are ripe if the cap can be twisted off cleanly without damaging the acorn.
Soak acorns in water a full day; throw out damaged floaters. Store in the refrigerator in a plastic bag until planting, best in November as the rains begin. Dig or auger a hole 24 inches deep and add a bit of nitrogen fertilizer to the bottom. (A 3-inch seedling will have a taproot 3 feet long!) Refill the hole, lay 3 acorns on their side and cover with one inch of soil. If the acorns are beginning to sprout, be careful to not break off the root. Thin to one seedling per hole once they are a few inches tall.
You can greatly increase survival by continuing care for at least three years. Occasionally water deeply during the hot summers, and keep annual grasses and weeds cleared for 3 feet around the seedlings. Grasses especially steal vital moisture during the early summer and provide cover for gnawing gophers and voles. (We´ve had oaks an inch in diameter chewed off by these critters!) A layer of mulch is welcome too, but keep it away from the trunk. Tubular trunk protectors, available from some nurseries, provide additional protection; sink a few inches into the ground. Fencing or sturdy wire cages protect from deer and livestock.
Oaks grow slowly and live long, but they are not enduring. Mature oaks need your help too. Many, even spreading heritage trees, are killed by well-intentioned kindness. Help existing oaks live onward by withholding summer water. Avoid changing the soil level and compacting the soil under the drip line. Future generations will thank you.
Sonora Master Gardener Vera Strader treasures the three heritage oaks in her front yard and the myriad of wildlife that depend on them.