Here is the City of Eugene's web page on this project: https://eugene-or.gov/3578/Skinner-Butte-Habitat-Enhancement According to the information there, the goals of this project, along with removal of invasive species, included removal of smaller trees and shrubs, in order to reduce canopy crowding and open up the understory.
In general I support this type of work, because so many wooded sites in the Willamette Valley have developed much more dense canopies and understories than the historical norms. This negatively impacts many native plants, insects, herps, etc. along with native birds like Chipping Sparrows that used to be much more abundant as nesting species.
However I can understand the sense of shock for birders who were not aware of these plans.
This is another good reason for birders to get involved in planning for local parks and natural areas. Then if you know of particular features that have high value for birding (such as the round bush and cluster of small trees mentioned that tend to be good for viewing migrant passerines), you can advocate for modifications in the plans to preserve those features. Sometimes the land managers aren't aware of the specialized recreational value that some of these features hold for birders.
For example, at Luckiamute State Natural Area's north unit (sometimes referred to as "Luckiamute Landing"), I was able to convince managers to phase in a project to replace non-native blackberries and other brush with native shrubs, rather than clearing the whole area and replanting in one go. So even though the vegetation has changed dramatically over the past 6 years, there have always been some patches that were good for wintering Lincoln's Sparrows, Swamp Sparrows and other brush-loving birds that birders tend to be interested in, even while waiting for the new, native shrubs to grow in.
I hope this inspires more birders to get involved in the planning process (and as volunteers) for your local birding spots. It's much easier to influence the process in a collaborative, proactive way.