Foresters to the rescue!
In this case, though, it appears the ailing 60 to 100-year-old birches will need to be cut down and replaced so that the chancellor's lawn looks its best for the university's centennial celebration in 2017.
Glen Holt, UAF Cooperative Extension Service's eastern Alaska forester, visited the property recently with forestry professors Glenn Juday and John Yarie. Since Extension and the School of Natural Resources officially merged July 1, it was a golden opportunity for the faculty to work together.
"There's something pervasive here," Juday mused while examining the trees, which are dying back from the top. The explanation for a homeowner’s unhealthy trees can often be found in lawn care or nutrient deficiencies, and sometimes in insect outbreaks, Holt noted. But as they looked, the SNRE crew saw some symptoms of a factor most interior Alaska trees have had to cope with recently: water, or the lack of it.
"We had unprecedented heat last year," Juday said. Birch trees get water to their upper crowns through evapotranspiration, a process in which molecules stick together in a column flowing through tube-like xylem cells. The force tugging the water column up from the soil through the tree and out into the air can be enormous, especially on a hot day.
"I'm speculating, but last summer's record number of 80-degree and warmer days and below normal precipitation could have caused a caving in of the xylem in the trees," Juday said. "That's my hypothesis."
The birch dieback isn't limited to the chancellor's yard. Foresters have noticed the same symptoms generally in the Fairbanks area and Nenana Ridge, including Bonanza Creek Experimental Forest, in the Tanana Valley State Forest particularly in older tree stands.
Stressed trees can get substantial relief if extensive watering is done during times of excessive heat. "But it's important to start watering healthy trees right away during the hot weather," Holt said. "Don't wait until after."
Most boreal trees, such as black spruce, simply lack the ability to function at high temperatures, Juday explained. "Physiologically they have a switch that turns off when it gets hot. Even if their roots are in the water caused by melting permafrost, they won’t try to grow. Birch and white spruce are also cold-climate adapted trees and become stressed in their own ways when the temperature sizzles."
Holt is often called to consult with homeowners about their trees. "We can assess what is affecting trees and pass on recommendations," he said. This was the first time he's been asked to do so on campus.
Holt and Yarie recommended that Facilities Services replace the birch with Siberian fir, Siberian larch or Siberian pine, species that grow well in full sunlight at this latitude. "We have to locate suitable growing stock that is tree size, six-feet tall and more as more as replacements for the most prominent yard trees,” Holt said.
Juday agreed and pointed out that planting more diverse trees at UAF could move the campus toward a "tree identification role" that would offer students the chance to identify northern species that they would otherwise seldom see.
In the notes he provided the Extension Forester Glenn Holt, Juday said:
"It's awesome to work together and have all this knowledge and previous experience," Holt said.Lodgepole pine has shown the most promise among all potential introductions for good growth and survival in our emerging climate. It is also a native North American species. We even have a good idea of the best locations for seed sources. Many provenance selections have had a problem of twinning or forked stem from failure of the leader, but a very few are just fine.Most firs, such as Siberian fir, are sensitive to vehicle traffic on their roots. Nearly all Abies species have poor stomatal control, and leak water to the atmosphere freely, so they may be unsuitable for most campus locations except irrigated lawns.
Siberian pine (Pinus sibirica) is a beautiful five-needle pine with soft needles. Fairbanks' precipitation is at the lower range of suitable, so planting it on deep soils seems to help. A certain amount of foot traffic may be tolerable, but soil compaction can be a moderate problem for this species group. A grove or mass planting can help insure an appropriate number of desirable specimens will ultimately occupy a desired location.
Siberian larch seem to have a much better resistance to larch sawfly defoliation than the native tamarack. Appropriate selections have superior height growth, but the three or four species are very shade/competition intolerant, and have required thinning to really prosper where I have seen them used around town.
White spruce is still a good choice, and the younger populations seem to be performing better in our hotter and drier climate trend than older populations, so I would not rule this species out. I supervised an SNRE M.S. thesis study by Brian Glaspell in which we compared growth of white spruce on the most highly impacted campground sites in interior Alaska to natural forest. We found no significant difference in growth. The species is really tough in areas with foot traffic and other soil impacts.
Aspen and birch started from cuttings or seedlings will probably grow adequately for decades around the campus. Where seasonal sunlight is needed they still have a role. Of course, it appears they may be a risky choice for big specimen trees as long as recent weather/insect trends continue.
To contact Holt for a consultation, call 474-5271.