The Austrian pines (Pinus nigra) in my backyard have been declining for several years.
These were the first trees I planted at my new home in 1988. At 3 feet tall, they were as much tree as I could wrangle into the back of a Ford Escort station wagon. Sited in the southwest corner, this small grove of pines promised to eventually grow tall enough to provide shade and nesting for birds, to block winds from the south and west, and to screen out large houses in a neighboring development. A decade later, they had.
The proved disastrous to pines across our region. What we hadn’t understood until then was how perilously close to the edge our pine forests had been living. Looking back, it should have been obvious. Seemingly minuscule changes in habitat have a huge impact on plants in our semiarid region. Native pines don’t show up in metro Denver until precipitation reaches about 16 inches per year, creating a lower tree line at about 6,000 feet in elevation.
Denver, at 5,280 feet and with 15 inches of precipitation, has no native pines. Just 5 miles south of where I live in eastern Centennial is the northern edge of a forest of another black pine, the native-to-Colorado Pinus ponderosa. The forest reaches over Monument Hill into Colorado Springs. I figured that with only a bit of supplemental irrigation, a different black pine should thrive at my house at 5,800 feet. The Austrians did, for a time.
When the drought struck, my pines, like so many of their brethren, fell victim to borers. Pines, adequately watered, fight back against these natural foes. Stressed trees can’t defend themselves.
The first mistake I made was choosing Austrian pines. Although these are close relatives of our native ponderosa pine, they are from Europe, not Colorado. As a general rule, pines prefer well-drained soil, and my alluvial silt certainly meets that condition.
But I sited my trees on a southwest-facing slope — the hottest, driest area on my property — where I discovered they required much more water than I had anticipated. The larger they got, the more water they demanded. Irrigating for only 15 minutes, once a week made my pines vulnerable to borer damage.
Pines aren’t the only trees in my backyard struggling with drought. Two large aspens produced few leaves this spring; an apple is fireblight-ridden; and a formerly magnificent sumac is down to one stem. A few mature trees have A Russian hawthorn, a mugo pine, a Thunderchild crab apple, a juniper, a sea buckthorn and a black locust remain healthy.
Still, it’s difficult to watch trees fail when you had once hoped they would be a legacy to the next generation of homeowners.
I need to remember what I once told a horrified neighbor after hail knocked down a prized green ash: Most trees aren’t well-suited for life on the high plains of Colorado — especially not below 6,000 feet in elevation.
E-mail Marcia Tatroe at mtatroe@q.com
