Matt Ritter is a botany professor at Cal Poly, San Luis Obispo, director of university's plant conservatory, and author of a new field guide, A California's Guide to the Trees Among Us (Heydey Books, 2011). I recently visited Dr. Ritter at his Southern California home, and he gave me a tour of his favorite local plants, his eucalyptus-decorated office, and Cal Poly's wonderful herbarium. He showed me a preview copy of his new book, which is filled with wonderful stories and gorgeous imagery. We talked about what makes his field guide so valuable.
Garden Design: For a botanic enthusiast in search of a guide to California's plants, there seem to be a dizzying array of books. What prompted you to write yours, and what distinguishes it from other guides available?
Matt Ritter: There is no other guide like it. It treats all the commonly cultivated trees in California. There are many guides to native trees, [but there are] no guides to cultivated trees. It is written for everyone, from beginners all the way to experts who want to know the esoteric differences between different species of Acacia, or ashes, or maples. I spent a number of years traveling around California by car, bike, and foot, looking at trees and taking photographs. I spoke to many different people about their attitudes towards the trees among us, and collected information and natural stories that I could relay in the book.
GD: The language with which you classify trees is unlike other arborists, especially in California, who distinguish between native and invasive species. Instead, you refer to native and cultivated trees. How does this terminology differ, and did it affect your approach to talking about the trees in your book?
MR: I use the term "cultivated" on purpose, because there are many cultivated trees that never become invasive. As an example, the beautiful flowering tree, the Jacaranda, never reproduces on its own in Southern California. So it doesn't have the possibility of becoming invasive, it's just a nice cultivated tree, a very appropriate street tree in Southern California. The opposite also happens: the rare California native tree, the Torrey Pine (Pinus torreyana) that only occurs in San Diego and on the Santa Barbara Channel Islands near Santa Cruz, has become a weed near Santa Cruz and Santa Barbara. So you have a native, invasive species and a non-native cultivated tree that isn't invasive at all. This isn't to say that there are plenty of trees that are non-native that are brought into the western U.S. that can and have become very weedy and invasive. I talk about these in the book as well, and explain how they shouldn't be planted any longer in certain areas in California.
GD: California has historically introduced lots of new species, some with unanticipated consequences. Are there any plants you would cite as straight-up unfortunate additions to the native landscape?
MR: There are certain areas in California where some trees are extremely invasive and should no longer be grown. The blue gum in central-western California, the Tamarix tree in south-eastern California, and the Chinese tallow tree in the Sacramento area are all too weedy and shouldn't be grown in those areas any longer. This is the danger of bringing the biotic wonder of the tree world into California, some trees are going to grow too well where they are planted, and out-compete our native flora. It is important that we are conscientious about what trees we plant, that they are appropriate, and don't have the potential to become weedy.
GD: Outside of your book, much of your research focuses on California's eucalyptus, what drew you to those trees?
MR: They are conspicuous icons in California, the most commonly grown non-native trees, and the most controversial trees. I got a Ph.D. at UC San Diego, [whose campus] is cut out of a eucalyptus grove, and they always interested and fascinated me there. It didn't take long to figure out that there was very little research and science about eucalyptus in California—mostly stories and misinformation, often with the most emotive language, about how these trees are evil. I wanted to get the actual story. Are all eucalyptus invasive in California? Do they really kill birds? Do they kill other plants (allelopathy)? Some of the answers have been surprising.
GD: Another of your research interests is "Hypotheses about canopy cover in urban forests in relation to the socioeconomic status of different neighborhoods and cities." That sounds fascinating, something Jane Jacobs would applaud! Can you share some of your hypotheses?
MR: A good deal of data has surfaced recently that show a correlation between the economic status of neighborhoods and cities and the amount of tree diversity and canopy cover in those neighborhoods or cities. Why is this the case? What is it about having more money that allows for larger and better trees? These are complex questions without simple answers, but very interesting to look into.
GD: What's the Cal Poly Campus Flora Project?
MR: Cal Poly has a 100-year-old botany and horticulture program. Many rare and interesting trees have been planted on campus. The Cal Poly Tree Project is a project in which we have identified and labeled all the trees on campus. It has turned the inner campus area into a beautiful arboretum.
It is certainly worth a visit! And if you can't make it to San Luis Obispo, do say hello to Matt on his book tour.
Anna Laurent is a writer and producer of educational botanical media. Photographs from her forthcoming field guide to Los Angeles are available for exhibition and purchase at the author's shop.