Soil disturbance, extreme chemical change or erosion, elimination of the sunlight, or increased moisture can create a niche for a weed to thrive and spread. The hill's worst weed threat comes from non-native trees, mainly eucalyptus. Planted after the Pearl Harbor attack to conceal the water tank from Japanese planes, the trees now shade the natives, collect and drip moisture, drop tons of debris, and alter the soil composition. Cape ivy, sheep sorrel, oxalis, and erharta grass. Erosion allows weeds to attack native habitats rather like the way a wound on the body can become infected.
Erosion is caused by people wandering off trails or dogs digging up the ground.
The hill is not a dog run, and dog feces and urine are problems that support weeds. Designated as one of the Recreation and Park Department's thirty Significant Natural Resource Areas, Tank Hill is part of the department's Natural Areas Program. The program focuses on native plant propagation and planting, weed and erosion control, and public education. Volunteers are needed and appreciated.