From Westword (Alan Prendergast):
Park officials say there are several factors behind the rash of tree removals. Some of the elderly conifers were simply at the end of their lives, they suggest; some had been stressed by drought or attacked by bugs; some apparently never recovered from a couple of vicious cold snaps in recent years, including a 77-degree temperature drop over three days last year. John says she doesn’t doubt that a few individual trees might have fallen victim to such predations, but that doesn’t begin to explain what happened on Evergreen Hill.
“The official line is that there are many things that cause trees to decline and die,” [Sonia John] notes. “Virus. Bacteria. Fungal diseases. Weather. Anthropogenic causes, like compacting the soil with construction equipment. But nobody has come up with a credible potential cause of this die-off that will explain why that cause isn’t operative on trees in neighbors’ yards across the street from the park.”
The primary reason for the die-off, John contends, is much simpler: The healthy trees on private property across the street from the park receive potable water — not the recycled water that’s been used in Washington Park since 2004.
Last June, Denver Water officials agreed to meet with members of Denver INC, short for Inter-Neighborhood Cooperation, a coalition of registered neighborhood associations and other groups. High on the agenda was a discussion of Denver Water’s recycled-water program, which provides wastewater that’s been sufficiently treated for irrigation purposes at a fraction of the cost of drinking water. The meeting was the first opportunity that John and others had to question the program’s boosters about several studies that had been done, mostly at the utility’s request, on the program’s impact on soils, vegetation — and especially trees. Collectively, the studies make a persuasive case that foliage and soils in city parks treated with Denver Water’s recycled product contain high amounts of sodium — which, over time, can be particularly lethal to conifers, since they draw water from their roots most of the year.
Washington Park was one of the first city parks to convert to recycled water; John says it’s no surprise that the ill effects should surface there more rapidly than at other parks. But 20 percent of the department’s irrigated properties are now using recycled water, which involves an entirely separate delivery system from that used for potable water. Park advocates say the high-sodium regimen is beginning to claim evergreens in other parks, too, and John fears it may be only a matter of time before deciduous trees get affected as well; she’s already seen “a lot more leaf scorch” on lindens in Wash Park, a possible indication that the trees are overdosing on salt. The City of Denver now saves a million dollars a year on park watering costs because of recycled water, but the park department’s critics claim that the city hasn’t embarked on any “meaningful remediation” to address a problem it’s known about for years.
Denver Parks deputy manager Scott Gilmore says the situation isn’t as black-and-white as the neighbors want it to be. “When people say it’s reused water, that’s trying to simplify a very complicated situation,” he sighs. “This isn’t Seattle. This isn’t California or back east, where you have lots of natural forest. This is an urban forest that humans created. We’re losing trees because of weather conditions and drought — and reused water. All those things coming together.”