As organisms became more complex, evolving into plants and animals, they began to colonize shorelines creating microbial mats that soon spread inland diversifying into a great variety of fungi, lichens, and mosses. The early moss created wetland bogs, creating a buildup of dead organic material known as peat. We can speculate that on occasion in times of drought, these bogs dried out on the early earth and burned, ignited by lighting just as they do today. In such a manner the bog, rejuvenated by fire, fills up with open water when the rains come, and the process of succession begins anew.
Over hundreds of millions of years the continental tectonic plates have drifted all over the globe. This drift has created vast super continents like Pangaea where species mingled together. Some species perished, and others flourished as they competed and cooperated among themselves for life's necessities. When the continents drifted apart, this sent different species on different evolutionary trajectories caused by changing environmental and genetic conditions in different locations and climate conditions.
Over thousands, millions, and hundreds of millions of years the climate was fluctuated extensively from very warm to very cold. The cause could be external impacts like asteroid impacts, massive volcanic eruptions, continental drift, and even massive global change caused by the evolution of life itself. For instance some scientists speculate that one global ice age was caused by the colonization of the land by mosses. This in turn caused atmospheric changes plunging the whole earth into a deep freeze, causing the extinction of 90% of the animals and plants at the time.
Through it all there was always fire, just as much a force of nature affecting natural ecosystems as is climate, water, atmosphere, and continental drift. It is obvious that when vegetation dies it either must decompose or burn. In warm, moist environments as in the tropics it can quickly decompose. In drier climates decomposition is much slower. Fire allows nutrients to quickly get back into the soil, reduces plant and animal diseases and pests, and eliminates the mulching out of new growth.
Sometimes the vegetative fires during geologic times were diminished, as during ice ages and when oxygen levels were low, and sometimes fires were very prominent and frequent, when oxygen levels were high and the earth warm as in the carboniferous and cretaceous. During these periods of warm climate just about every kind of plant and animal developed adaptations to fire, becoming fire dependent.
Most people today are unaware of the critical importance of fire in nature's ecosystems and this has led to severe environmental consequences for all life on earth including man. It is imperative that environmentalists, politicians, and land managers both public and private understand this critical role of fire in the environment in order to adequately preserve and protect the fragmented ecosystems still remaining on earth.
Most ecosystems around the globe are so fragmented by modern man that light natural fires can no longer be allowed to burn freely and frequently as they have for hundreds of millions of years. This has resulted in huge unnatural catastrophic accumulations of fuel in forests, savannas, and grasslands. Sooner or later these fuel loads will be ignited by lightning, or by man, forcing huge unstoppable catastrophic fires damaging to both nature and man.
So the remedy for fire in the environment is not more fire suppression, but controlled or prescribed fire to simulate natural fire. Plant and animal life adapted and used fire for competitive advantage for at least 420 million years as evidenced in the fossil record. This has created a wide spectrum of planetary diversity from very many plants with at least some fire resistance, to a very few, very fire-tender plant species and their animals dependent on these ecosystems.
During the fiery carboniferous period of geologic history oxygen levels were much higher than they are today. These higher oxygen levels allowed dead vegetation accumulating in early forests and savannas to burn much better than even today. Many species of plants like the palms evolved very fire-resistant trunks to protect against frequent ground fires. But these early forest plants went even further to use fire to their competitive advantage.
The palms evolved flammable fronds that when the individual fronds died and fell to the ground they burned out the competition. By becoming so fire adapted they thrived at the expense of their competitors and so became a fire-dominant species, spreading all across the supercontinent of Pangaea. Other palm species like the palmetto and the ferns closer to the ground formed the understory and adapted by developing flammable fronds and strong underground root systems. When frequent fires burned, killing everything close above ground, they quickly sprouted back using the energy reserves stored in their roots.
Later, pine trees evolving in the fiery cretaceous when oxygen levels were again very high evolved thick insulating bark and flammable needles, following the example of the palms using fire to burn out the competition. Later the grasses evolved in these high-fire environments and used the same fire-adapted natural strategies as had the ferns, palms, pines, and palmetto, to burn out the competitions and to sprout back quickly after a fire and grazing.
In a short span of only a few days after a rain, a blackened burn will once again become green. The grasses sprout from their fire-protected roots underground, in the same manner following the example of the palmetto and the ferns. Additionally, the fresh ash with the first rain soaks into the soil giving this new growth even more vitality.
All this time while the plants were evolving in fire ecosystems in Pangaea and Gondwanaland the land animals were not standing still. They were also adapting to low-intensity and occasional catastrophic fires. The best I can tell the ocean arthropods began moving onto land as they do today to colonize and feed on the detritus being washed up on beaches and in lagoons where early ocean plants were also taking root. These early arthropods evolved into the insects we have today and went from jumping, to gliding, to flying, to get around and to feed on fresh vegetation and other insects on land. In the carboniferous the fishes followed the insects onto land and evolving into amphibians and reptiles.
I would speculate that one of the reasons that insects developed wings was to get out of the way of frequent ground fires as well as predators. They also could dig into the damp ground or crawl down in openings at the base of plants. The amphibians and reptiles had to use other strategies like fast flight, or diving into water to avoid getting burned. It was not until the dinosaurs developed wings that land animals were able to fly to avoid fire, or to fly back into the blackened burn to forage for roasted insects and small reptiles and small mammals now openly exposed to view.
Most people all over the world know about the almost indestructible palmetto bug or cockroach. Well, it's an example of a very well-adapted fire species that evolved in the carboniferous among the palm trees and the palmetto. Cockroaches are able to scurry down into the ground, or fly away to avoid fire, only to quickly return to feed on the greening vegetation and any other insects that might have not been so well adapted.
I cannot but be impressed, when we simulate natural low-intensity fires in fragmented ecosystems, that we are burning through a mosaic of ancient and modern plant and animal species. In a layering process over hundreds of millions of years, newly evolving species of plants and animals enter the ecosystem, forcing out less adaptable species. However, when new species evolve in the ecosystem, they often do not always destroy earlier plants and animals that continue to successfully adapt. The older species may simply be pressured into moving into new niches being created by the newer invading species.