Community Recovery from Wildfires

Rate of shrub recovery varies with elevation, slope aspect, inclination, degree of coastal influence, and patterns of

Figure 3 Postfire resprouts from basal burl of chamise with meter stick. Photo by J. E. Keeley.

precipitation. Recovery of shrub biomass is from basal resprouts (Figure 3) and seedling recruitment from a dormant soil-stored seed bank. After a spring or early summer burn, sprouts may arise within a few weeks, whereas after a fall burn, sprout production may be delayed until winter. Regardless of the timing of fire, seed germination is delayed until late winter or early spring and is less common after the first year. Resilience of chaparral to fire disturbance is exemplified by the marked tendency for communities to return rapidly to prefire composition.

Shrub species differ in the extent of postfire regeneration from resprouting versus reproduction from dormant seed banks. Most species of manzanita and ceanothus have no ability to resprout from the base of the dead stem and thus are entirely dependent on seed germination. Such shrubs are termed 'obligate-seeders'. A few species of manzanita and ceanothus as well as chamise resprout and reproduce from seeds, and these are referred to as 'facultative-seeders'. The majority of shrubs listed above, however, regenerate after fire entirely from resprouts and are 'obligate-resprouters'.

In the immediate postfire environment the bulk of plant cover is usually made up of herbaceous species present prior to the fire only as a dormant seed bank or as underground bulbs or corms. This postfire community comprises a rich diversity of herbaceous and weakly woody species, the bulk of which form an ephemeral postfire-successional flora. This 'temporary' vegetation is relatively short-lived, and by the fifth year shrubs will have regained dominance of the site and most of the herbaceous species will return to their dormant state. These postfire endemics arise from dormant seed banks that were generated after the previous fire and typically spend most of their life as dormant seeds. These are termed 'postfire endemics' and they retain viable seed banks for more than a century without fire until germination is triggered by heat or smoke of a fire. Postfire endemics are highly restricted to the immediate postfire conditions and if the second year has sufficient precipitation may persist a second year but usually disappear in subsequent years.

Not all of the postfire annuals are so restricted, rather some are quite opportunistic, taking advantage of the open conditions after fire but persisting in other openings in mature chaparral. Such species often produce polymorphic seed pools with both deeply dormant seeds that remain dormant until fire and nondormant seeds capable of establishing in or around mature chaparral. These species fluctuate in relation to annual precipitation patterns, often not appearing at all in dry years.

Herbaceous perennials that live most of their lives as dormant bulbs in the soil commonly comprise a quarter of the postfire species diversity. Nearly all are obligate resprouters, arising from dormant bulbs, corms, or rhizomes and flowering in unison in the first postfire year. Almost none of them produce fire-dependent seeds; however, reproduction is fire dependent because postfire flowering leads to produce nondormant seeds that readily germinate in the second year.

Diversity in chaparral reaches its highest level in the first year or two after fire. It is made up of a large number of relatively minor species and a few very dominant species and is illustrated by dominance-diversity curves (Figure 4). Dominance in chaparral is driven by the fact that a substantial portion of resources are taken by vigorous resprouting shrubs and much less is available for the many annual species regenerating from seed.

Plants are not the only part of the biota that has specialized its life cycle to fire. Smoke beetles (Melanophila spp.) are widely distributed in the western US and are attracted by the infrared heat given off by fires. Often while stems are still smoldering they will bore into the scorched wood and lay their eggs.

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Figure 4 Dominance-diversity curve based on cover of species in sequence from highest to lowest from postfire chaparral.

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