The maintenance and improvement of natural resources on, or to benefit natural and historic research on, military installations and State-owned National Guard installations.

The maintenance and improvement of natural resources located off of a military installation or State-owned National Guard installation if the purpose of the cooperative agreement or interagency agreement is to relieve or eliminate current or anticipated challenges that could restrict, impede, or otherwise interfere with, whether directly or indirectly, current or anticipated military activities.

Funds appropriated to the Department of Defense for a fiscal year may be obligated to cover the cost of goods and services provided under a cooperative agreement or interagency agreement entered into under subsection (a) or through an agency agreement under section 1535 of title 31 during any 18-month period beginning in that fiscal year, without regard to whether the agreement crosses fiscal years.

If any funds are placed by a recipient in an interest-bearing or other investment account under paragraph (2)(B), the Secretary of Defense shall report biennially to the congressional defense committees on the disposition of such funds.

Cooperative agreements and interagency agreements entered into under this section shall be subject to the availability of funds.

Notwithstanding chapter 63 of title 31, a cooperative agreement under this section may be used to acquire property or services for the direct benefit or use of the United States Government.