If e-the initial hight of the tree, and the function imply some brackets like
f(x)=30/(1+29e-0.5x) then
for every

the rate of growth is negative, the maximum growth per unit of time would be 30ft
If

then

so the tree couldn't be 2ft tall initially
if the brackets are something like
f(x)=30:(1+29e)-0.5x then the results may differ