Updated: January 2013
Invasive nonnative plant species have existed in the Park since before its establishment in 1971. Ring counts of English ivy stems cut on trees in the year 2000 were as high as 35 years. The earliest known attempts at control focussed on the ivy, the most visible and pervasive of the many nonnative species. In those days it was also the largest known threat to the ecosystem of the Park.
Elinor Levin started removing ivy occasionally in 1983, and more often starting in 1988. During her first few years of this effort, complaints about it at the front desk were common. At that time she collected the ivy in plastic bags for removal from the Park.
At a 1993 retreat, the Board of Directors of the Friends of the Park established a “Kill the Ivy” program under Elinor’s leadership. Thus began in 1994 the second Saturday (each month) community “ivy pulls” which were advertised for anyone to participate in. Help was also solicited from schools, some of which sent groups of students to perform community service under Friends’ leadership. The Multnomah County Community Corrections Dept. was also invited to send crews of people performing court-mandated community service, and did so at times.
Herbicide treatment of ivy was tested in a remote upland area of the Park with promising results. Due to concerns about effects on other species no broader application was tried.
In 1995 the Ivy Subcommittee was established after the Board retreat proposed developing an Adopt-A-Plot (AAP) program for control of ivy and other invasive nonnative plants. A draft proposal developed by Mel Taylor was reviewed by the Friends’ Board and Park staff, all supporting the program. Phil Hamilton agreed to coordinate the effort.
With these expanded efforts involving many people, the ivy pulled was no longer removed from the Park but was piled and left to die and compost. Second Saturday work parties cut mature ivy growing up trees in the vicinity of the Nature Center during the next few years and, with help from other groups, pulled ground ivy along trails in that area. In the early 1990s one busy volunteer cut ivy growing up trees on over a hundred acres. The AAP program quickly grew to about 10 adopters, where it plateaued, with most plots near Tryon Creek or the Nature Center. Six of the adopters aggressively attacked their plots and made noticeable differences.
In 1997 Dave Kruse got involved in the effort and took over management of the AAP program in 1998 while Phil, as Eco/Trails (formerly Building & Trails) Committee Chair, coordinated the various other nonnative species removal efforts. Within a couple of years the AAP program had 20 adopters, with many of the new plots concentrated on the west side of the Park near adopters’ homes. Simultaneously, the effort to cut mature ivy infesting trees expanded, with a few dedicated individuals plus volunteer groups from PGE (enlisted by Dave) working throughout the Park to save trees.
Attention started to broaden to other nonnative species in 1999, first focussing on Himalayan blackberries along Tryon Creek, where George Toepfer and Brent Foster began digging them. Dave Kruse and Phil Hamilton continued this work and later got help from several others. In 2000 observers first became aware of the invasiveness of clematis vitalba, a vine from Europe which was threatening to overtop trees in some locations just as ivy was. At first the clematis patches, which were more scattered than ivy (though numbering about 600 patches), were cut, a parallel with the treatment of ivy on trees. After observing 50 or more feet of annual re-growth of cut vines, emphasis shifted to digging its roots, often a major task as mature vines have very convoluted, overlapping roots
Garlic mustard, a biennial plant, was first noticed in the 1980s but was not recognized as invasive until 1999, when pulling efforts began. The other plant that was first noticed and dug about that time was knotweed, primarily a creek-side invader. Scots broom was showing up between the bike path and Terwilliger Boulevard, and was promptly dug or cut. In several parts of the Park, Dave Kruse cut English holly and laurel, starting in 1999.
In the early 2000s Dave Kruse and Phil Hamilton aggressively pursued all recognized clematis patches except a number south of Iron Mountain trail and northwest of Boones Ferry Road. The latter group were attacked by 2004, while control of many of the ones south of Iron Mountain Trail also began then.
Community service crews from Multnomah County had helped with ivy control in the 1990s, but in 2002 they increased their participation, so progress against ivy in the upper loops around the Nature Center, as well as some locations west of the Creek, accelerated. Those crews also helped to substantially reduce Himalayan blackberry infestations west of the Creek and along the bike path.
Starting in 2001 Clackamas County crews joined the ivy control effort and also dug many blackberries, mainly along Iron Mountain Trail. In 2004 they dug a series of major clematis patches along Terwilliger Boulevard south of Iron Mountain Trail. Those were the last major patches in the main unit of the Park that had been visible to the general public, other than ones in the steep canyon just upstream from the Highway 43 culvert on Tryon Creek. In the winter of 2005-2006 they killed ivy on many trees south of Iron Mountain Trail and east of the Creek, the second time that had been done. Later in 2006 Phil Hamilton led a few other people to cut ivy on trees previously not saved on the steep slopes and near the Creek in this area.
The first major restoration planting effort in the Park took place early in 2000 when the Friends of Trees and the Boy Scouts collaborated to plant hundreds of bare-root conifers and hardwoods in easily accessible areas along the Creek where blackberries had been dug earlier in the winter. This was under-planting of deteriorating alder stands.
Soon after that, with grants from PGE and donations from two PGE employees, the Friends bought conifers (mostly western red cedar) for planting in forest canopy holes where blackberry and/or clematis thickets had been removed. Later donations for plants came from private individuals. The objective was to develop shade over time to minimize reinvasion by these sun-loving non-natives. Experiencing difficulties doing regular maintenance of plantings of bare-root and small (one gallon) potted plants, which suffered from shading by nettle, in 2001 the Friends started buying two gallon (4 to 5 foot) trees to plant in accessible locations. By late 2010 well over a thousand trees larger than bare-root had been planted, some having grown by then more than 20 feet tall. Planting continued in 2011 and 2012, with plant purchase funded by grants from the Portland Bureau of Environmental Services.
Starting in 2004 willow and red osier dogwood cuttings were planted adjacent to Tryon Creek. From 2008 through 2012 other shrubs and some trees were planted inside the North Horse Loop in locations where little understory remained after removal of ivy and blackberries.
The attacks on invasive species continued throughout the early 2000s.