Edge Effects

If an 10 mile by 10 mile (16 x 16 km) reserve of rainforest is set aside, and the surrounding forest is cleared and settled, the actual area preserved is actually much smaller once edge affects are accounted for. Increased drying wind penetration and the invasion of alien species means that much of the reserve is altered. Foreign animals, like dogs, pigs, and cats will roam up to 3 miles into the reserve. The light green area represents the reserve, 100 miles square (259 sq. km), while the darker green area, 16 miles square (41 sq. km), represents the part of the forest that will not be affected by alien animal species. So in other words, as much as 84% of the reserve could be affected by alien species.

50% of the world's parks and reserves are under 38.6 sq. miles (100 sq. km) in area.