Updated: January 2013
By the end of 2012 the status of control efforts was as follows:
Ground ivy: Less than 5% of the Park only slightly infested and untended, with an additional 35% of the Park initially controlled (pulled at least once). Ivy in almost all locations visible from the upper loop trails near the Nature Center, and on the east side of the Creek from Red Fox Bridge almost to 4th Avenue, has been pulled at least once, and much of that area more than once. A similar effort has occurred on the west side of the Creek between Obie’s and High bridges. Recent efforts have extended north from the upper loop trails and in 2008 began moving into the North Horse Loop (NHL). By the end of 2012 nearly 90 percent of the interior of the NHL had been initially controlled. One area remaining there is the very steep head of the south ravine in NHL, where very steep slopes limit both the work season and the types of volunteers who can safely work there. Similar steep slopes remain to be cleared in the upper reaches of the two main branches of High Creek, the ravine south of NHL
What became notable in the spring of 2003 was the recovery of the trillium. When first released from the smothering ivy, the trillium responded well, but mostly as single plants; by 2003 many had reproduced to form clumps.
At the end of 2012 there were only half a dozen truly active adopted plots plus as many more with occasional activity. The number of plots peaked at 32 in 2004, but many adopters quickly lost interest. Most long-term adopters are returning periodically to get re-sprouts and new seedlings, an essential maintenance step. Many areas west of the Creek which were pulled once aren’t being maintained, due to abandonment of adopted plots.
Ivy threatening trees: Cut once in over 95% of the Park, with most remaining uncut areas being steep slopes or difficult to access. In 2010 cutting began in the largest uncontrolled area, the often steep slope between Lake Oswego’s First Addition and the Creek. A second cutting has been done in most areas of the Park where substantial ground ivy remains, with additional cutting of re-growth continuing where trees are threatened again or ivy on them is flowering. Cutting the re-growth (stems usually no more than an inch in diameter) is less time consuming than initial cutting of stems that were often over two inches and as large as seven inches.
Himalayan blackberry: Dug and controlled in much of the riparian zone of Tryon Creek north of Iron Mountain Trail and below the 4th Avenue entrance, and many trail-side large patches. Some large patches remain, most being west of the bike path north of Iron Mountain Trail or east of the Creek south of that trail. Along the bike path digging has been done to reduce encroachment on the path. Locations where dense patches have been dug have been planted with conifers and shrubs and are receiving periodic maintenance to remove new blackberry plants until the planted trees create shade.
Clematis: North of Iron Mountain Trail all known patches (an estimated 600) have been dug at least once, and most, twice or more. Some are considered eradicated but ivy maintenance sweeps and early winter reconnaissance continue to find sprouts in many locations. In addition, previously unknown patches occasionally still are found and promptly controlled. South of Iron Mountain Trail many patches have been dug but some large ones near the Creek have not, particularly those in the canyon at the south end of the Park. Digging progresses in dry summers on a very large patch west of the Creek about halfway between Iron Mountain Bridge and Highway 43, but will continue slowly as soggy soils limit access to the driest time of year. A 2009 addition to the Park on the west side was heavily infested with clematis. Initial removal there was completed by the end of the year, with a second pass done in 2010.
Knotweed: Using herbicide injection many of the patches along the Creek were poisoned in 2004. Injection of stems large enough (a half inch or more) continued in subsequent summers. Three patches away from the Creek also have been treated. Stream surveys from 2007 through 2011 identified many small patches with stems too small for injection. In 2011 a City of Portland employee sprayed many of those patches plus a large patch on a steep slope far from the Creek. It is apparent that control efforts must continue for many years.
Garlic mustard, creeping buttercup and geranium Robertinium: Somewhat controlled along roads and trails near the Nature Center and on the upper loop trails, but regular maintenance is needed in those areas as, with a multi-year seed life, old seeds keep generating new plants. And they are continuing to spread along the edges of other Park trails, especially near the Park boundary, and to encroach into locations away from trails. Buttercup has become common in riparian zones and many lowland trail-sides Garlic mustard has particularly infested the edges of the horse trails. A recent priority has been pulling garlic mustard and geranium Robertinium near trails in areas of recent ivy removal, to prevent their taking over the ground vacated by ivy pulling. From 2009 through 2012 there has been a concerted effort to control all known infestations outside of the riparian zone. Surveys in late 2012 showed a notable reduction in garlic mustard rosettes along many trails as well as in some known off-trail sites. A particularly difficult garlic mustard patch has been on the west side of the Creek, by the oxbow below Old Main Trail, where it is mixed with reed canary grass. A City of Portland crew sprayed that patch in 2011, but it remained infested to a lesser degree in 2012.
Laurel, English holly, sweet cherry and non-native hawthorn: Some cutting, without stump-painting with herbicides, was done in the late 1990s.Herbicide painting of stumps, immediately after cutting, began in 2002 and is continuing. Smaller trees are dug. East of the Creek the focus of control has been the area of the upper loop trails and further north where the first pass of ivy removal has occurred Despite herbicide painting, holly and hawthorn often re-sprout after initial cutting, but a prompt second cutting and painting is usually effective. Near the west side trails much cutting and herbicide painting of all these species took place from 2003 through 2006, but holly re-sprouts are rampant and little maintenance is occurring, except in one active adopted plot.