What brings May flowers?
NPS Photo by Tom Gray
As a child, you probably heard the hopeful singsong "April showers bring May flowers." You may have cursed it as you sat staring out the window, ball in hand, waiting for the rain to stop. And it may not be true: in Canyonlands, it looks like flowers are more dependent on what happens in October and the following winter months.
Every spring, National Park Service biologists monitor plants in 27 vegetation transects in Canyonlands. The transects are located all over the park in a variety of plant communities. Many have been visited on nearly the same day every year since 1987.
The data from this monitoring is being analyzed for long-term changes in the makeup and diversity of plant communities. Changes since the 1980s include an increase in non-native plants (the number of species as well as the percentage of ground covered), which is a concern for park managers.
Such long-term trends can only be seen after many years of data collection because yearly changes can obscure them. Natural factors like seasonal weather and precipitation can have a dramatic effect on short-term plant survival. For example, the chart below shows the number of vascular plant species found on several transects from 2001 to 2003. Notice that on every transect, a lot fewer species were found in 2002. What isn't shown is that it wasn't perennial plants (plants that usually live for several years) that died between 2001 and 2002. The dramatic difference lies in the abundance–or lack thereof–of annual plants like wildflowers that sprout from seed each year.
Ideal conditions for a good wildflower year are difficult to define. Every plant has its preferred winter conditions and water needs. Many plant species do not sprout without good fall rain. Others may die off during cold winters, or may be intolerant of long dry spells between October and April. Still others may only need good, soaking rains in the early spring.
You may have heard 2001, 2002 and 2003 called drought years in the Canyonlands region. All experienced less than average rainfall. However, 2002 was significantly drier than both 2001 and 2003. More importantly, the months prior to spring of 2002 experienced almost no rainfall. Any plants that sprouted in the fall probably dried out long before they could flower, and those that usually sprout in late winter or early spring may never have received the moisture trigger to make them sprout.
As a result, 2002 was a poor wildflower year. Even though there were April showers, by then it was too late. When annuals were seen in the transects, it was often one small sprout where in years previous there had been tens to hundreds of individuals.
Most of the transects rebounded in 2003, and some even had more species than in 2001. Given that very few annuals produced seed in 2002, where did these new plants come from?
Luckily, the annual plants here produce different types of seeds. Many are long-lived and sprout only when conditions are most favorable (see sidebar). These seeds survived the drought of 2002. Rather than April showers, desert annuals need seed adaptations for long-term survival, and regular fall and winter rain for a showcase wildflower spring.