Answer to Question No. 1. Generally, an "Act of God" is considered to be a natural disaster that is outside of human control. That would include earthquakes, windstorms, floods, tsunamis, etc. If you are asking about insurance exclusions for Acts of God, you'll have to read you policy. Generally, however, as a landlord, you should make sure you have broad general casualty insurance coverage (as opposed to liability insurance coverage), since the former would cover casualty losses (fire, wind, flood, etc.), regardless of causation or negligence, whereas the latter would provide coverage for you only if you caused the damage. Broad insurance coverage against casualty losses, e.g. from Acts of God, is what community owners should have. Whether residents have such coverage is less certain, since the rental/lease agreements I've seen either do not require any form of insurance, or occasionally only liability insurance. And unless their lender requires it, it is unlikely that many owners of older homes have any insurance against loss or damage.
Answer to Question No. 2. As to uprooted trees, let's go to the legal definitions. A "hazard tree" under ORS 90.100(20) must include the following elements:
- It is located on a rented space in a manufactured dwelling park;
- It measures at least eight inches DBH; and
- It 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. (Emphasis mine.)
I draw certain corollaries from this definition - some may disagree:
- A tree is a large living plant that grows out of the ground; if it is blown down, it is no longer a "tree" in the conventional sense. I have no recollection of discussing downed trees as "trees" that would somehow be subject to the hazard tree legislation. I would defer to John VanLandingham's recollection on this, however. This answer would seem to dispose of the above question, but I will continue, just to address the other unasked questions that will inevitably arise.
- If a tree does not measure at least eight inches, DBH, it is not a "hazard tree". This is not to say that the tree is necessarily "safe" or that it may be ignored by landlord or resident. In the final analysis, landlord and managers should monitor the condition of all trees, both in the common areas, and on the tenants' spaces. Just because a tree is not a hazard tree does not mean they can be ignored. Similarly, just because the tree is a resident's responsibility does not mean it should be ignored by management. If it is the resident's responsibility, management should encourage compliance - since a falling tree limb or the entire tree, may cause damage or injury to other spaces and other residents.
- If a licensed arborist has either said the subject tree does not pose a risk of harm, or the arborist has never opined at all, it is not a "hazard tree". Again, this does not mean the tree may, or should be, ignored.
- Lastly, remember that all of the above three elements (on the resident's space; eight inches DBH, and considered dangerous by a licensed arborist) must occur together before a tree can be considered a "hazard tree".
Answer to Questions Nos. 3 & 4. I believe the answer to who responsibility for maintenance, removal and disposal are addressed in ORS 90.727 (Maintenance of trees in rented spaces). Although the statutes do not referral to "disposal" they do refer to removal. I read these words as interchangeable in this context. For example, removal of garbage and debris from one's yard, reasonably includes disposal. The statute provides:
(1) As used in this section:
(a) "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.
(b) "Removing a tree" includes:
(A) Felling and removing the tree; and
(B) Grinding or removing the stump of the tree.
I suppose the next question is whether "removing a tree" can refer to downed trees. I think not, since the follow text quoted above, refers to "felling" it.
Conclusion. As noted above, landlords, more likely than residents, have insurance that deals with Acts of God. These types of natural events do not distinguish between whose property is affected, e.g. common areas vs. resident spaces. In some instances, strict enforcement of the hazard tree statute could impose a catastrophic expense to a resident that might be covered under the landlord's insurance. In such cases, consideration should be given to providing assistance/coverage rather than forcing a tenant into bankruptcy or financial distress.
 I regard a tree never "planted by the tenant or landlord" as owned by the landlord, since they own the ground. When the landlord bought the property, they assumed the obligation to maintain the trees that came with it (assuming the resident didn'tplant them, and assuming the statutes don't provide otherwise).
 "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.
 The balance of the statute is relevant to who has the responsibility, and is addressed here. It provides: (2) The landlord or tenant that is responsible for maintaining a tree must engage a landscape construction professional with a valid license issued pursuant to ORS 671.560 to maintain any tree with a DBH of eight inches or more. (3) A landlord: (a) Shall maintain a tree that is a hazard tree, that was not planted by the current tenant, on a rented space in a manufactured dwelling park if the landlord knows or should know that the tree is a hazard tree. (b) May maintain a tree on the rented space to prevent the tree from becoming a hazard tree, after providing the tenant with reasonable written notice and a reasonable opportunity to maintain the tree. (c) Has discretion to decide whether the appropriate maintenance is removal or trimming of the hazard tree. (d) Is not responsible for maintaining a tree that is not a hazard tree or for maintaining any tree for aesthetic purposes. (4) A landlord shall comply with ORS 90.725 before entering a tenant's space to inspect or maintain a tree. (5) Except as provided in subsection (3) of this section, a tenant is responsible for maintaining the trees on the tenant's space in a manufactured dwelling park at the tenant's expense. The tenant 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 tenant's rented space at the tenant's expense and if the arborist determines that the tree is a hazard, the tenant may: (a) Require the landlord to maintain a tree that is the landlord's responsibility under subsection (3) of this section; or (b) Maintain the tree at the tenant's expense, after providing the landlord with reasonable written notice of the proposed maintenance and a copy of the arborist's report. (6) If a manufactured dwelling cannot be removed from a space without first removing or trimming a tree on the space, the owner of the manufactured dwelling may remove or trim the tree at the dwelling owner's expense, after giving reasonable written notice to the landlord, for the purpose of removing the manufactured dwelling.