The Role of Fire Ecology in Plant Succession
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Succession is defined as a directional change in community composition and structure over time (Gurevitch et al, 2002). Succession is either primary or secondary. In primary succession plants grow and colonize earth for the first time. In secondary succession plants inhabit and colonize earth that was once inhabited by plants life.
A wildfire is one example of secondary succession. When a disturbance in the environment occurs, such as a wildfire, either part or all of the community is destroyed. The aftermath of the wildfire leaves a barren landscape open to new growth, vegetation, and re-colonization of plant species (Gurevitch et al, 2002). Various studies have been undertaken and completed regarding the restoration and recovery of plant communities following wildfires. These studies include aspects of species richness during colonization to niche development.
The Mediterranean plant Banksia and Hakea have the ability to build post-fire communities rather successfully due to seed storage. Almost all of the species studied stored their seeds in dense woody fruit. In order for seed dispersal to occur leading to germination and sprouting, the fruit must be dense woody structure of the fruit must be dried. The drying of the fruit causes cracking allowing for the seeds to disperse and germinate. The addition of occasional fires to these communities allow for the drying of the fruit quicker than in its natural state (Lamont et al, 1999). Since the seeds of the fruit can be stored for up to three years, fire is a necessary step in succession to continue the species evenness and richness.
Another study completed in the grasslands of California concentrated on Nassella pulchara also known as purple needle grass. The needle grass, a native species of California, was studied to investigate seed attributes of post fire communities. A ten-year seed from a post fire needle grass plant and another aged seed respectively from a non-fire treated plant were germinated. The resulting seeds from the burned plants were bigger in size and had a higher rate of germiability than those plants that had not been burned (Dyer, 2002). The results indicate that succession of the needle grass is somewhat dependent upon the fire due to the long-term viability of the seed size, the high germination rate of the seed, and the size of the seed itself.
A study done in Florida concentrated on the communities of the Pinus palustris also known as the long-leaf pine. This particular pine, in low density, supports the highest species richness in North America. In higher densities along with other species of soft-wooded plants and shrubs this richness decreases. By introducing fire to these communities the excess hardwood and shrubs are removed allowing for a lower density of hardwood. Lowering the density of hardwood also decreases the intraspecific and interspecific competition between the hardwoods. In turn a higher diversity of the pine species is achieved due to exposure to mineral soil once occupied by the burnt off trees and shrubs (Provencher et al, 2001). Succession is therefore occurring by in a sense lowering the species evenness and increasing species richness.