How Catalina Plants Have Adapted to Survive Drought Conditions

2014-10-29
Catalina Island Conservancy

California's prolonged drought conditions have presented a significant challenge to all of Catalina Island's residents. But its plant population has developed a number of coping mechanisms that ensure its survival during extended dry periods.

Southern California is classified as a Mediterranean-type climate, characterized by cool, wet winters and warm, dry summers. Other Mediterranean regions include Southwestern Australia, parts of South Africa, coastal Chile and the Mediterranean Basin itself; all located between 30 and 45 degrees north or south of the equator.

Plants in these regions have evolved during many long summer droughts. They have developed physical characteristics or seasonally driven life cycles that aid in their tolerance of excessive heat and light and minimal rainfall.

Some plants, like black sage (Salvia mellifera) and California sagebrush (Artemisia californica), go dormant to avoid desiccation. These types of plants are referred to as drought deciduous. While they may appear dead, they’ve only dropped their leaves to reduce their demand for water. They are still alive and will sprout new leaves when water becomes available again.

Other adaptations include specific leaf characteristics, stem adaptations and specialized root structure. For instance, certain plants, such as Catalina’s lemonade berry (Rhus integrifolia), have developed evergreen leathery (or sclerophyll) leaves that trap moisture to avoid dehydration and to help maintain leaf shape.

Other plants, such as the chamise (Adenostoma fasciculatum) have small leaves, which are efficient at shedding heat. These small leaves also have less surface area and fewer pores from which water can evaporate.

To avoid the absorption of sunlight, plants, such as the white sage (Salvia apiana), have light-colored or gray leaves.  Light colors reflect (rather than absorb) most wavelengths and, therefore, don’t absorb much heat. This is an especially necessary trait for vegetation living in California’s unforgiving sunshine.

Many plants in the chaparral and sage scrub communities have aromatic leaves that, according to the California Academy of Sciences, help to cool the plant through the evaporation of aromatic oils – similar to the way sweat cools humans. The pleasant aroma of black sage (Salvia mellifera) may actually help this plant to tolerate drought.

Fuzzy hairs on leaves, like on those of the Catalina Island mountain-mahogany (Cercocarpus traskiae), provide shade to limit transpiration and keep its surface cool.

Succulents resist drought by storing water in their swollen leaves and using it sparingly. The waxy outer layer keeps that moisture trapped inside. The endemic Catalina Liveforever (Dudleya hassei) is a great example of a drought tolerant species. It can be found on the Island’s sea-bluffs.

Cacti adapted spines, rather than broad leaves, to reduce surface area and, therefore, reduce transpiration. Spines also provide shade and dissipate heat. These adaptations have allowed coastal prickly pear (Opuntia littoralis var. littoralis) to thrive in Catalina’s semiarid climate.

Roots also play an integral role in plants’ abilities to absorb and store both water and nutrients. Some plants, like many evergreen shrubs, develop long tap roots that allow them to obtain water from deep sources. Even during drought, these plants are able to maintain relatively high water potential through roots that extend dozens of feet below the surface.

Buckwheats, like the endemic St. Catherine’s Lace, have vast lateral root systems that are near the surface. This adaptation allows plants to capitalize on every precipitation event. Even dense fog that saturates the soil can provide much needed relief when it’s quickly absorbed by these fibrous root systems. Oaks are champions in the drought race, developing both deep tap roots and abundant lateral roots, maximizing their absorption capabilities.

These many adaptions ensure the survival of Catalina’s plants – until the rains return.

By Alexa Johnson
Alexa Johnson is the Catalina Island Conservancy’s Outreach and Naturalist Training Specialist. For more information, please visit our website.