解：生态园的面积能为$40m^2。$$\because$四边形$ABCD$是矩形，$\therefore AB = CD，$$AD = BC。$设$AB$的长为$x m，$则$BC$的长为$\frac{18 - x}{2}m。$由题意，得$x\cdot\frac{18 - x}{2}=40。$整理，得$x^2 - 18x + 80 = 0，$因式分解得$(x - 10)(x - 8)=0，$则$x - 10 = 0$或$x - 8 = 0，$解得$x_1 = 10，$$x_2 = 8。$$\therefore$生态园的面积能为$40m^2，$$AB$的长为$10m$或$8m。$
