Answer. The hazard tree legislation is relatively new; it was passed by the Oregon Legislature in 2013. Here is a summary:
- "DBH" means the diameter at breast height, which is measured as the width of a standing tree at four and one-half feet above the ground on the uphill side.
- "Hazard tree" means a tree that:
- Is located on a rented space in a manufactured dwelling park;
- Measures at least eight inches DBH; and
- Is considered, by an arborist licensed as a landscape construction professional pursuant to ORS 671.560 and certified by the International Society of Arboriculture, to pose an unreasonable risk of causing serious physical harm or damage to individuals or property in the near future.
- Habitability. A rented space is considered uninhabitable if the landlord does not maintain a hazard tree required by the 2013 Act.
- Resident Duties re Trees Located on Space. A resident shall maintain and water trees, including cleanup and removal of fallen branches and leaves, on the rented space for a manufactured dwelling except for hazard trees.
- "Maintaining a tree" means removing or trimming a tree for the purpose of eliminating features of the tree that cause the tree to be hazardous, or that may cause the tree to become hazardous in the near future.
- "Removing a tree" includes:
- Felling and removing the tree; and
- Grinding or removing the stump of the tree.
4. Landlord Duties re Hazard Trees.
- Landlord shall maintain a hazard tree that was not planted by the current resident if the landlord knows or should know that the tree is a hazard tree;
- Landlord may maintain a tree on the rented space to prevent the tree from becoming a hazard tree;
- Landlord must provide residents with reasonable written notice and reasonable opportunity to maintain the tree themselves.
- Landlord has discretion to decide whether the appropriate maintenance of a hazard tree is removal or trimming.
- Landlord is not responsible for:
- Maintaining a tree that is not a hazard tree; or
- Maintaining any tree for aesthetic purposes.
- A landlord must comply with the access provisions of ORS 90.725 before entering a resident's space to inspect or maintain a tree. [Generally, 24-hour notice. - PCQ]
- Subject to the preceding, a resident is responsible for maintaining the non-hazard trees on the resident's space at the resident's expense.
- The resident may retain an arborist licensed as a landscape construction professional pursuant to ORS 671.560 and certified by the International Society of Arboriculture to inspect a tree on the resident's space at the resident's expense;
- If the arborist determines that the tree is a hazard, the resident may:
- Require the landlord to maintain the tree as a hazard tree; or
- Maintain the tree at the resident's expense, after providing the landlord with reasonable written notice of the proposed maintenance and a copy of the arborist's report.
- Tree Obstructing Removal of Home From Space. If a manufactured home cannot be removed from a space without first removing or trimming a tree on the space, the owner of the home may remove or trim the tree at the owner's expense, after giving reasonable written notice to the landlord, for the purpose of removing the home.
- Use of Landscape Professional. The landlord or resident that is responsible for maintaining a tree must engage a landscape construction professional with a valid landscape license issued pursuant to ORS 671.560 to maintain any tree with a DBH of eight inches or more.
- Access to Resident's Space [ORS 90.725].
- An "emergency" includes but is not limited to:
- A repair problem that, unless remedied immediately, is likely to cause serious physical harm or damage to individuals or property;
- The presence of a hazard tree on a rented space in a manufactured dwelling park.
- An "unreasonable time" refers to a time of day, day of the week or particular time that conflicts with the resident's reasonable and specific plans to use the space.
- "Yard maintenance, equipment servicing or grounds keeping" includes, but is not limited to, servicing individual septic tank systems or water pumps, weeding, mowing grass and pruning trees and shrubs.
- A landlord or a landlord's agent may enter onto a rented space to:
- Inspect or maintain trees;
- A landlord or the landlord's agent may enter a rented space solely to inspect a tree despite a denial of consent by the resident if the landlord or the landlord's agent has given at least 24 hours' actual notice of the intent to enter to inspect the tree and the entry occurs at a reasonable time.
- If a landlord has a report from an arborist licensed as a landscape construction professional pursuant to ORS 671.560 and certified by the International Society of Arboriculture that a tree on the rented space is a hazard tree that must be maintained by the landlord under this Act, the landlord is not liable for any damage or injury as a result of the hazard tree if the landlord is unable to gain entry after making a good faith effort to do so.
- If the resident refuses to allow lawful access, the landlord may obtain injunctive relief to compel access or may terminate the rental agreement pursuant to ORS 90.630 (1) and take possession in accordance with the Oregon eviction statutes. In addition, the landlord may recover actual damages.
8.Statement of Policy. It shall include the facility policy regarding the planting of trees on the resident's rented space. [See ORS 90.510]
Discussion. As you can see from the above, the definition of a hazard tree relates to whether it poses an unreasonable risk of serious physical harm or damage to individuals or property in the near future. The size of the tree alone, i.e. exceeding eight inches or more DBH, does not, in itself, make it a hazard tree; there must be potential for injury or damage in the near future.
Secondly, you will note that the hazard tree statutes make no distinction as to what part of the tree causes damage or injury. Although I had some involvement, along with John Van Landingham and others, in the creation of the legislation, speaking for myself, I was focused on the tree or branches falling on a home or resident. I was not thinking about damage from root systems.
Third, a landlord's removal obligation for hazard trees speaks to felling and removing them, and removing or grinding the stumps. Again, speaking only for myself, I was not thinking about tree roots that might remain after the stump is removed. (As a layperson, I think of the stump as the unremoved portion of the downed tree, and that portion below ground necessary to return the ground to its original level, sans the tree. But I certainly didn't focus on requiring that landlords remove root systems.
All of this is to say that my reading of the hazard tree statutes seems to make no distinction between damage above or below ground. Moreover, I suspect we would agree that damage to the foundation of a resident's home, could fall within the definition of what constitutes a hazard tree.
Remember that pursuant to ORS 90.730(4), the failure to maintain a hazard tree can constitute a habitability violation for which a tenant could bring a claim against their landlord.
Conclusion. Unfortunately, it appears to me that absent some language in the hazard tree statutes indicating an intent to exclude that portion of a tree below ground, i.e. its root system, a case could be made that remediating the damage caused by a hazard tree to a resident's home, or the cost to relevel it, is on your shoulders.
This does not mean, however, that the root systems of all felled hazard trees need to be removed. Once the tree is downed, and the trunk removed, the root system will not (as I understand it) continue to grow. That being the case, if the roots are not posing a danger to a resident's space or the common area, there should be little reason to remove it.
The take-away here, is that landlords should be proactive in assessing hazard tree issues. This may include inspection of resident spaces. And when evaluating risk, landlords should look down, as well as up.
One interesting question, which I will not opine on here, is what a landlord should do about an otherwise healthy tree that is least eight inches DBH, if its root system poses, or could pose, a risk of damage to a resident's home. Must the tree be removed now?
 I suspect the major exception is bamboo trees, whose root systems seem to have a zombie-like life of their own.