Fire and Plants

I’m Glad You asked
Garden Director Lew Feldman

Plants have evolved many strategies to avoid damage due to fires.

An example of one such strategy is the production in many plants, such as in oaks, of an external layer of cork that functions to insulate interior living tissues from periodic, fast-moving grass fires.

Cork oak (Quercus suber), located in the Crops of the World Garden.

Another strategy to avoid fire damage is the production of a specialized structure known as a lignotuber, which is a swelling at the base of the stem enclosing dormant buds. Fire damage to the shoot systems stimulates buds to sprout from the lignotuber enabling the rapid re-establishment of the plants aerial shoot system following fire. This ecological function, and the widespread occurrence of lignotuber-bearing plants in Mediterranean climate plant communities, is well documented.

Above: A lignotuber (swollen base) of a Banksia aemula shrub located in the Australasian Area, bed 510.

Here in the UC Botanical Garden many of the plants from Mediterranean climates, especially those from Australia, such as Eucalyptus and Banksia, produce lignotubers. On your next visit, look at the Banksia stem just above the soil surface. About half of the Garden’s Banksia species produce lignotubers!

Burls

Many of the California native plants also produce lignotubers, sometimes called burls. Burls (lignotubers) occur in many of our native California chaparral shrubs, including, in some species of Manzanita (Arctostaphylos), California-lilac (Ceanothus) and Silk-tassel bush (Garrya). The term burl is also applied to woody outgrowths on the base or trunks of coast redwoods (Sequoia sempervirens). In redwoods, burls may function to help re-establish a tree if it should be seriously damaged—eventually many buds (shoots) will sprout from the burl, thereby ensuring the survival of the plant.

In California, as in Australia, the evolution and development of lignotubers occurred in environments in which annual, short duration fires occurred, thereby preventing the buildup of flammable matter.Lignotuber structure and function evolved to survive these short, not too intense annual fires. However, by suppressing wildfires (a frequent, past management practice during the last 150 years), this allowed for the accumulation of considerable flammable materials, resulting in longer, hotter fires and often, therefore, in the destruction of the lignotuber and in the concomitant loss of ecosystem restoration following fires.

For further reading on lignotubers and burls; S. James (1984) Lignotubers and Burls—their structure, function and ecological significance in Mediterranean ecosystems. The Botanical Review 50, 225-266.