Phenology and the Mojave Desert

Last spring I found myself transfixed by the brilliant crimson petals of a Mojave mound cactus and the seemingly endless procession of bee pollinators that crept into its petals.  Flowers and fruit are pleasing to the eye, so it’s no wonder that in the Mojave Desert they attract bees and also many wildflower enthusiasts.  But it’s important to remember those flowers, insect pollinators and the fruits and seeds they ultimately produce are far more than just aesthetic; they’re an essential part of plant reproduction.

The life cycle of plants and its relationship to the birds, bees, and other animals has fascinated United States Geological Survey Scientist Kathryn Thomas for many years.  Thomas, an ecologist with the USGS, is interested in phenology, the timing of life history events in plants and animals.  In plants it’s when flowers germinate, pollinators arrive, fruit appears and even the time of year herbivores eat the plant.

“People have been paying attention to phenology since the caveman," says Thomas, who points out that scientists, naturalists and even farmers have observed this type of data for centuries.  But like with so many natural phenomena, a seemingly simple question like “What time of year do plants flower and produce fruit?”  has a complex answer.  For example, many plants in the Mojave Desert flower in response to temperature and precipitation, and some plants depend on insect pollinators for successful reproduction. 

 Thomas and other scientists are wondering, “How will climate change affect the phenology of plants in the Mojave Desert?”  Many scientists believe that climate change will disrupt ancient natural relationships like the one between flowering plants and their pollinators.  The changes in temperature and precipitation associated with climate change could cause plants to bloom earlier and miss the adult phase of a crucial bee or fly pollinator.  Such an ecological mismatch would result in failed reproduction - no fruit or seeds - for the plant.  Changes in temperature and precipitation could also cause shrubs to germinate earlier, fruit later and grow later in the season.

A change in the phenology of plants due to climate change will affect many animal species.  Along the Colorado River corridor, changes to the timing of mesquite flowering might impact migrating birds who fatten up on juicy insects feeding off the flowering mesquite.  “If the birds arrive and the insects aren’t there you have a mismatch in the food web,” says Thomas.  Here in the Mojave, a change in the life cycle of plants could affect the desert tortoise, an endangered herbivore that dines each spring on annual wildflowers.

No single scientist has enough time to understand the big picture of how climate change will affect the phenology of plants and animals, but the National Park Service is beginning to develop programs that will use citizen science to answer this question.  One such program is collaboration between the USA-National Phenology Network and the National Park Service.  The USA-NPN has a website (http://www.usanpn.org) that gives directions on how to monitor plant phenology and allows citizen scientists to submit data about the phenology of certain plants.  The National Park Service believes that this information can be used to understand how climate change is altering the life cycle of certain plants on the landscape level.

“When selecting species to monitor we are looking for plants that are widespread, can be easily identified and if they have some sort of ecological, economic or social importance.  We want to include species that more than one person will monitor,” says Thomas.  One of the target species for the California Desert is Larrea tridentata, the creosote bush.  Creosote bush is a widespread shrub at lower elevations in the Mojave; is important shelter to a variety of animals; has distinctive leaves and smell and is an allergen.

The National Park Service plans to increase the number of desert plant species that it will collect data on through the USA-NPN website, train volunteers to identify the different phenophases (leaves, flowers, fruit) of these plants, collect data and pilot the program in the spring of 2010 in Joshua Tree National Park, provided funding is available.

The National Park Service and National Phenological Network program will help scientists better understand the effects of climate change on the Mojave Desert.  For scientist Kathryn Thomas using citizen science to gather data in the national parks will help answer key questions related to the timing of natural life cycles.  “We need to have lots of people looking at phenology- not just scientists, farmers and professional naturalists- in order to understand how our world is changing.”

Seth Shteir is senior program coordinator for air and climate at the National Parks Conservation Association in Joshua Tree, California.