On or after , all moneys received as contributions toward cooperative work in forest investigations, or the protection, management, and improvement of the National Forest System, shall be covered into the Treasury and shall constitute a special fund, which is appropriated and made available until expended, as the Secretary of Agriculture may direct, for the payment of the expenses of said investigations, protection, management, or improvements by the Forest Service, and for refunds to the contributors of amounts heretofore or hereafter paid in by them in excess of their share of the cost of said investigations, protection, management, or improvements. Payment for work undertaken pursuant to this section may be made from any appropriation of the Forest Service that is available for similar work if a written agreement so provides and reimbursement will be provided by a cooperator in the same fiscal year as the expenditure by the Forest Service. A reimbursement received from a cooperator that covers the proportionate share of the cooperator of the cost of the work shall be deposited to the credit of the appropriation of the Forest Service from which the payment was initially made or, if the appropriation is no longer available, to the credit of an appropriation of the Forest Service that is available for similar work. The Secretary of Agriculture shall establish written rules that establish criteria to be used to determine whether the acceptance of contributions of money under this section would adversely affect the ability of an officer or employee of the Department of Agriculture to carry out a duty or program of the officer or employee in a fair and objective manner or would compromise, or appear to compromise, the integrity of the program, officer, or employee. The Secretary of Agriculture shall establish written rules that protect the interests of the Forest Service in cooperative work agreements.June 30, 19141914-06-30