Pam Peirce on Gardening and Climate Change
The past few years have brought surprising variations in the rainfall and temperature patterns of our winters. Gardeners have been puzzled as their plants bloomed out of season, and pests' seasonal visits shifted over time and space.
Pam Peirce discusses our historic weather patterns and current global climate change, addressing how plants and insects are responding to these changes. Pam invites those interested to participate in citizen scientist observations of plants and insects as valuable input for tracking current patterns and preventing future disruptions.
Resources on Climate and Weather of the US and the Bay Area
http://planthardiness.ars.usda.gov/PHZMWeb/ Takes you to the USDA Plant Hardiness map. You can search for the hardiness zone of a particular location by zip code or can call up enlargements of particular states.
http://www.ahs.org/ Click on "Gardening Resources", "Gardening Maps", & “AHS Heat Zone Map,” to see the heat zone map and an article about it and how plants respond to heat stress. The map is no longer downloadable. It can be purchased online for $10. This site also links to USDA Hardiness Map and Sunset Zone descriptions.
http://www.wunderground.com Search for locations by name or zip code.
Under "More" you will find Historical Weather, where you can search for the weather of any particular day and location in the US back to 1945.
http://weatherwest.com A Blog about California weather as it develops. Really helpful illustrated articles by a climate scientist on underlying causes of weather episodes such as droughts or storms.
http://www.sfgate.com For fog forecasts, click on the weather icon (cloud, sun, etc) on the left side of the header bar, (if needed, click first on the drop down menu and change the location to San Francisco). Once you are on the San Francisco weather page, scroll down and click on the gray and green square "Fog Map" icon. Here you will see several views of a changing map that takes you through a forecast for the next 24 hours. Is it accurate? Relatively often, and it's fun to watch. There is also a satellite map showing current fog conditions.
http://ggweather.com/ Web site of Jan Null, a California weather consultant, with great info to explore. Also, under “Weather Links”, click on “Research and Articles” and then on some of the articles. Also check out "Weather Corner" Archive--articles that once appeared in the San Jose Mercury News.
http://www.ucsusa.org/ Web site of the Union of Concerned Scientists. Click on "Our Work", then "Global Warming" for a section on global warming science. The many different articles are all interesting, so click around.
Note: Websites change formats from time to time. I have updated this handout on 9/23/2016.
http://www.baynature.org This regional magazine often publishes articles on local climate and the local effects of climate change in the magazine and sometimes online. They are presently offering a printout of an article called Taking the Heat: Bay Area Ecosystem in the Age of Climate Change for $3.00.
Golden Gate Gardening: The complete guide to year-round food gardening in the San Francisco Bay Area and Coastal California, Third Edition, Pam Peirce, Sasquatch Books, Seattle, CA, 2010. Explanation of the climate and the microclimates of the Bay Area and Information on how it affects gardening, particularly food gardening.
Plant Life in the World’s Mediterranean Climates: California, Chile, South Africa, Australia, and the Mediterranean Basin, Peter R. Dallman, California Native Plant Society, University of California Press, Berkeley, CA, 1998.Explanation of mediterranean climate and the plant adaptation it requires. Descriptions of mediterranean habitats and representative plants from all 5 of the world’s mediterranean areas.
Sunset Western Garden Book, Kathleen Brenzel, ed. Sunset Publishing Corp., Menlo Park, CA, 2007 (newest edition). Includes maps that divide the West into 24 climatic regions, with brief explanations of each. An encyclopedia of plants includes codes telling which climatic regions are appropriate for growing each plant, sometimes with different cultural advice for different regions.
Weather of the San Francisco Bay Region, Harold Gilliam, University of California Press, Berkeley, CA, 1962. A small book that explains the reasons for historic Bay Area weather patterns.
Wildly Successful Plants: Northern California, Pam Peirce, Sasquatch Books, Seattle, WA, 2004.Basic ornamental gardening taught with a focus on fifty heirloom Northern California plants, including explanations of how the climates of the places they grow wild prepared them to thrive here. Includes explanations of mediterranean climate in general and northern California climate in particular.
Bibliography © Pam Peirce 2017
Some Terms Related to Climate and Climate Change for Gardeners
The San Francisco Bay Area has a maritime climate. This term means that the climate is strongly influenced by the ocean. Most of the winds that blow over the region blow from the direction of the ocean. The main effect of this is that the summers are cooler and the winters warmer than would be expected at our distance from the equator. Wherever there are openings between hills, the ocean winds can blow farther inland. The San Francisco Bay is a large enough body of water that it also has the effect of making summers cooler and winters milder around its shores.
The climate of our area can also be described as mediterranean. This is a climate similar to that around the Mediterranean Sea, for which it is named. It is a climate that is subtropical (meaning it has mild winters, but freezes are possible), is often maritime, and has moderate rainfall in the winter months, but dry summers. Some Mediterranean areas have warm summers, others are cool in summer. We have a cool summer caused mostly by wind blowing from over a very cold band of water off of our shores, and partly by the fact that the wind often bears fog. Mediterranean climate is found on the west coast of continents from about 30-40˚ north or south of the equator. You will find it in California west of the Sierra, in Central Chile, west of their mountain range, on the west coast of South Africa, on part of the west and southwest coasts of Australia, and all around the Mediterranean Sea. Mediterranean areas of the world are important sources of ornamental plants and food crops that thrive in our area.
Chill factor refers to the fact that some plants require a certain amount of winter chill to be able to bud out properly in spring and bloom. The amount of cold needed is cumulative. The temperature required to count toward a chill requirement varies among plants, but a typical one is 45 degrees F. Time above that would subtract from the total hours of chill, and time below 32 degrees F doesn’t count. Most kinds of peonies and lilacs, and some kinds of roses, apples and pears require more winter chill than we get in San Francisco. So do oriental poppies, which, after the first year, may bloom, but on short stems, low in the plant. Note that this is different from hardiness, which indicates the lowest temperature a plant can survive. Hardiness is known for most domesticated plants, but the amount of chill a plant needs to bloom well can be difficult to find, other than for deciduous fruits.
Continental influence reaches us carried by winds from inland. Near the coast, wind is almost always from the ocean, but it usually does shift a few times a year. When winds blow from inland, the affected areas get periods of unusually hot summer weather with hot winds that increase fire risk and damage, or, in winter, unusual cold, bringing frosts in areas nearly to the coast. With climate change, we could see hotter summer spells, and mild weather blowing from inland in winter instead of cold (this last occurred in the winter of 2015-16).
Phenology is the study of when, in the course of a year, plants and animals carry out life stages, known as phenophases, such as opening leaf and flower buds and ripening seed, and how long these stages last.
Citizen Scientist: A person who records scientific data as a volunteer. This is being done for phenology as well as to record astronomical and other data from the natural world.
Become a Citizen Scientist to Record Plant and Animal Responses to Climate Change
For the past few years, citizen scientists have been helping phenologists study climate nationwide by recording when plants or animals are doing what. For example, they record when plants leaf out, flower, fruit, form seed, or lose leaves in winter. One organization that depends on citizen observers, the United States National Phenology Network (www.usanpn.org/natures_notebook), sponsor of the National Phenology Project, studies both plant and animal species. Another, Project Budburst (budburst.org), studies only plant responses. Both can be accessed from either a computer or a mobile device.
Reporting observations to these projects is fun and will prove exceptionally useful as we track climate change. Scientists use data to compare recent years and compare these years to data from historic sources. Whether you are one observer or a teacher (at any level) with a classroom full of science learners, your participation is urgently needed. Both sites mentioned above offer curriculum guides for various ages, and a partner site Budburst Buddies (budburstbuddies.org) includes journal pages and games for child participants.
You will find that many of the plants being monitored on these sites are natives, which are certainly important to study, with only a few non-native garden plants. Apple and common lilac are on both lists, certain magnolias on both, flowering plum and evergreen azalea hybrids, both of which are good indicators in our gardens, are on neither. If you select plants that are important to you that are not on current lists, both systems allow you to enter your data anyway, starting a new observation base for that plant. © Pam Peirce 2017
Golden Gate Gardening
Pam Peirce is a San Francisco-based author, photographer, and lecturer. She has taught horticulture at City College of SF for nearly 30 years and has written for the SF Chronicle. Her books Golden Gate Gardening and Wildly Successful Plants: Northern California are available for purchase.