ORS § 408.250
During the period any public officer is absent on leave pursuant to ORS 408.240, a substitute shall serve in the place and stead of the public officer. Such substitute shall be appointed by the authority having power to have appointed the substitute as successor had such office become vacant. The substitute shall qualify by taking an oath of office, and by giving bond in an amount and conditioned as required by law for the officer for whom the substitute has been appointed, or, in the event no bond is required by law, then as the appointing authority directs. The substitute shall be designated by the title of the office, followed by the words "pro tem." The substitute shall be invested with the authority, duties and responsibilities, and shall receive the emoluments of the office, in lieu of the officer for whom the person is the substitute.
ORS 408.250