Buckthorn is a common invasive plant throughout Michigan forests. It quickly reproduces, pushing out other plants and outcompeting native plants for resources. It has invaded a local white pine forest. The Michigan DNR is looking for a solution to the problem. The solution has to last at least one year. The impact on native species is the most important factor in selecting a solution. After the impact on native species, both the cost and how long it works for are equally important. Use a decision making matrix and the rating information below to select a method for controlling this invader.

A constraint is "something that limits or controls." According to the information in the above, what is a constraint on the possible solution to the Buckthorn problem?

It must last for at least one year.

It cannot have negative impacts on native species

It cannot cost more than $3,000.

It must not require much effort.