Surveying the Heat Island Effect across Large Divisions Act or the SHIELD Act This bill provides for the Department of Defense (DOD) to direct the commander of each large military installation to analyze and report on (1) how the heat island effect (i.e., the heating effect in an area with a high concentration of structures that absorb and re-emit the sun's heat) exacerbates summer heat conditions and necessitates the increased use of air conditioning on the installation, and (2) the percentage of tree cover and plant shade trees on the property of the installation. DOD must review the reports, identify any installation that is a significant heat island, and direct the commander of any identified installation to increase the tree coverage by 10% to 30% by September 30, 2025.