This is an important article, with lots of food for thought. The following is a brief summary, but read the original article, which is well illustrated with colored maps and photos. It can be downloaded as a PDF from several web sites.
Nowacki, Gregory J. and Abrams, Marc D. 2008. The demise of fire and “mesophication” of forests in Eastern United States
There has been a dramatic reduction in fire in Eastern U.S. forests since the 1950s, and this has had major ecological consequences, leading to the elimination of fire-dependent species and the replacement by species favoring more mesic conditions. There is a feedback system whereby preclusion from fire encourages the growth of shade-tolerant mesophytic hardwoods such as red maple, sugar maple, beech, birch, cherry, tulip poplar, and blackgum instead of oak, pine, and hickory. This results in a more closed canopy which discourages the growth of fire-tolerant species, including not only the oaks but also the high diversity of fire-tolerant herbaceous understory plants. By altering environmental conditions, maple and other shade-tolerant species deter fire through dense shading, promoting moist, cool, microclimates, and by producing fuels that are not conducive to burning. The authors call this process "mesophication".
Mesophication is a stable state that is difficult to reverse, so that once it occurs, a return to the previous state is difficult. Therefore, once ecosystems become mesophytic, restoration becomes prohibitively expensive. The prospects of returning fire to the landscape is limited because of the unfavorable climate of the forest floor and the loss of fire-adapted species from the ecosystem.
The authors conclude: “Restoration opportunities are rapidly waning as (a) fire-adapted floras are progressively lost to shading, competition, and preferential herbivory; (b) older seed-bearing individuals succumb to old age and existing seed banks lose viability over time; and (c) understory and forest floor conditions become increasingly mesophytic.”
This article makes a good case that we are in a crisis situation which can only be overcome by huge increases in prescribed fire on the landscape.