Lignotubers and burls— their structure, function and ecological significance in Mediterranean ecosystems

Vegetative regeneration provides for immediate tissue replacement and reestablishment of the “parent” genotype, after the aerial canopy of a perennial plant is partially or wholly destroyed. If the frequency of destruction of above-ground biomass (e.g., by fire) is such that tissue replacement (production) is the predominant mode of growth, this regenerative capacity may preadapt the plant for reproduction via vegetative growth. In the perennial shrubs of the California chaparral, and in other similar Mediterranean-type ecosystems, one of the most significant modes of reproduction is characterized by sprouting after injury of new stem or root tissue from an ontogenetically produced swollen stem base/root crown known as a lignotuber (or “burl”). Lignotubers have been well described inEucalyptus (Myrtaceae) and observed in other families in the Mediterranean-type climate regions. “Burls” of shrubs in the family Ericaceae are morphologically similar to lignotubers. The term “burl” is vague in meaning, since it has been used to describe any anomalous or unusual woody structure with a swirled grain. The term lignotuber, which has a more restricted usage referring only to ontogenetically produced structures, should henceforth be used to describe these swollen “root crowns.” Investigations of lignotuber (burl) anatomy have revealed that the wood contains dormant buds, carbohydrates, and nutrients necessary for bud development. Reproductive strategies and tactics have evolved partially in response to the frequency and severity of disturbance (e.g., fire in shrublands of Mediterranean-type ecosystems). Reproductive strategies are defined by the timing and mode of production and reproduction. Reproductive tactics are the options of “reproductive effort” and energy allocation within each strategy. In the chaparral, fynbos, macchia, etc., one prevalent tactic in the sprouting strategy is the allocation of energy to the woody structure which has sprouting as its prime function—the lignotuber.