While most of the forest observation plots have improved, a few have declined. Plots in the Espanola, Minden, Parry Sound and Owen Sound areas have either continued to decline, or have not improved. Insects, disease and climate may have affected some plots. Other plots have soil with low pH and high water-soluble aluminum, which is related to poorer tree health. Only by surveying forest health over the long term will we detect important changes in the forest.
Trees have long lives, and changes in forests often happen slowly.
By monitoring the forest over many years we will learn if declines or improvements in forest health are permanent, or simply part of the natural forest cycle, or caused by air pollution. We know that on sites with acid-sensitive soils, acid removes from the soil the nutrients trees need to grow. On some sites the nutrients are lost faster than they can be restored by natural processes. In fact, scientists in Quebec and the northeastern United States believe that hardwood forests growing on acid-sensitive soils are losing nutrients from the soil at the rate of 2 to 3 per cent per year. We do not know if Ontario forests are losing nutrients from the soil, or how the forests will be affected if nutrients are lost.