If you’ve traveled around the San Diego Zoo over the past five or so years, you may have noticed some areas that looked like they were right out of the pages of a conservation magazine discerning the woes of clear cutting in the Amazon rain forests. What’s going on?

Over the last 25 years or so, the Zoos’ grounds have lost around 75 percent of the tree cover that it had, due in part to construction of new facilities and old, unsafe trees that had to be removed. The final nail was put into the coffin on some of the eucalyptus (pictured) by the eucalyptus long-horned borer, the lerp psyllids, and drought during the years starting in 2000. Eucalyptus trees county wide were hit hard by the psyllids, and that was true here in the Zoo.

The Zoo’s Euc forests played a large part in what the San Diego Zoo was all about in its beginning and through the years when bioclimatic zones were put in place for the development of its exhibits in the 1970s. They are key to our being able to keep koalas in our collection, in that we are able to provide around 36 different species of eucalyptus to them through our browse program. We were losing our overhead canopy and that was 80 years’ worth of growth. If we started right away, a replacement canopy could not be grown in our lifetime, so it was important to develop a long-range plan for reestablishing the upper canopy for the Zoo and to make it something that was unique and complemented the direction for our horticulture collections.

With the establishment of a reforestation fund, we set out to complement the bioclimatic zones of the Zoo with trees that matched the areas we established them in. We looked at trees with economic value like shade-grown coffee, fruit and nut trees, and trees that were endangered in their home habitat. We were able to build on some of the established collections. We planted the trees in groves where possible and at least did companion planting’s of like planting material. An example of that is our geographic-based collections like the Madagascar, Mediterranean, and Hawaiian gardens.

We’ve recently worked on the area just below the camels. That area was an old browse area where the trees outgrew their usefulness and became an eye sore. It was re-established as a New World planting area with Chorisia, Tabebuia, Chiranthodendron, and Brighamia species. In a few years, as the trees take on more size, it will become a vibrant area with unusual, blooming trees of aesthetic and educational value. Further down the canyon is another area that has been cleared of iceplant and will be supplemented with additional plantings that tie it into the Mediterranean Garden.

A new, large-scale project which was the impetus to write this blog was just recently started on the hillside behind the Migratory Duck Pond. This is a major project and changes the face of that area quite drastically. There was a real fire danger on that hillside and the trees were in very poor condition, including the safety aspect of some of them. After evaluations were done, trees marked, and bids secured, work began in earnest and the area was started towards a new beginning. Large trunks were left crossways on the slope for erosion control, debris was chipped to provide mulch back on the slope, and a new irrigation system will be installed. The bottom of the slope will be used for browse trees (acacia, fig, and mulberry); the upper two thirds will be reforested with specimen trees that are indigenous to the New World. It will become a useful and aesthetic part of our horticulture collections and not just a tired old hillside.

Mike Bostwick is horticulturist for the San Diego Zoo.

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