People sometimes tell me “trees aren’t everything,” and that’s obviously true, but in this part of the world, one would be hard pressed to find a group of plants more significant in defining the landscape. You don’t have to look back very far and the landscapes here would be exclusively forest. We can’t realistically return to that, but because trees are important for the ecosystem services they provide, they have always figured prominently in the Botanical Garden’s collections. And while established trees in the Garden are generally well adapted to the conditions we provide them, the climate is, by all accounts, changing. Thus, we need to adapt both our plant choices and the practices that accommodate them. We have to contend with a future that predicts less available water, more summer heat and greater rain intensity in winter. Our curatorial choices have always been critically assessed; i.e., potential acquisitions are rated on scientific significance, conservation impacts, horticultural adaptability, garden potential, cultural values, etc., but future climate resilience has become an increasingly important criterion in our calculus. Have a look at the climate resilient trees indicated here, but note that this is only a small sample of the species we are studying in the Garden.
Botanical Garden visitors that use our parking lot will notice a recently planted Acer ‘Molly Fordham’ next to the ticket dispenser. This handsome trifoliate-leafed maple is marketed under the name Cinnamon Girl™ maple. It is a cross between two adaptable species, the Chinese paperbark maple, Acer griseum, and the Japanese Nikko maple, Acer maximowiczianum. Somewhat intermediate in appearance between the two parents, ‘Molly Fordham’ is noted for its peeling bark and excellent autumn colour, as well as (for a maple) heat and drought tolerance. A somewhat more surprising addition to the drought-resilient stable of trees is Nyssa sylvatica (black tupelo), which is native to the southeastern US. Despite its provenance, black tupelo famously tolerates both flooding and drought and grows well locally. There are established wild-provenance specimens in the Carolinian Forest Garden and a large fifty-year-old tree next to the Food Garden. Nyssa sylvatica ‘David Odom’ (Entrance Plaza Bed west) is our first foray into cultivated selections, of which there are now several available that exhibit uniform branching and reliable autumn colour. ‘David Odom’ (marketed as Afterburner®) is outstanding in this regard.
As you might expect, the Asian Garden, home to plants that are more likely to suffer summer monsoons than summer droughts in their native haunts, holds several trees that are drought adapted, including a variety of Asian oaks and oak relatives, and members of the pine family. Of the more significant acquisitions, the rare Chinese Cathaya argyrophylla (a pine relative) stands out, both for its attractive leaves (long, silver-backed needles) and tough constitution. There are two plants, both grown from commercially derived seed. One is in the Campbell Glade (viewable from the boardwalk) and the other, a larger, more robust specimen, on Decaisne Trail east of Lower Asian Way.
The Roseline Sturdy Amphitheatre plantings include a wide range of drought-adapted shrubs, trees and herbaceous perennials. Acer opalus (Italian maple) stands out as a superb performer. The dense developing crown and distinctive blunt-lobed leaves make it easy to recognize (there is another individual in the west Entrance Plaza bed). A Chinese lacebark elm, Ulmus parvifolia, also a tougher-than-expected tree, is located across the path, near the top of the rise above Hypanthium (the William Pye water-sculpture). A somewhat scraggly collection of the same elms is scattered around the Amphitheatre’s risers. These were planted last winter and are finally settling in. Planted to provide shade to seated visitors, the trees were chosen for their (eventual) elegant stature, flaking bark, pest and disease resistance and general resilience. Diospyros lotus (date plum) also appears to have promise in the predicted future climate conditions. The small grouping of youngish trees on the west side of the Amphitheatre plantings seem unbothered by heat and dry weather. A couple of female trees in the pack even appear to be maturing their notoriously slow to ripen fruits. Note that the impressive date plum planted next to the Asian Garden pond has never in its fifty years produced fruit (it is a stranded female).
In the E. H. Lohbrunner Alpine Garden, where heat and drought tolerance have always been normal requirements, the tree list includes few surprises. Eucalypts (Eucalyptus species) figure highly in the Australasian section, as do pines across the Northern Hemisphere sections (Asia, Europe, North America). In the North American section, Acer grandidentatum (bigtooth maple) has long been recognized as an excellent performer. The drainage it enjoys is undoubtedly a factor, considering it grows out of canyon walls of the American Mountain West. Similarly, Cercis siliquastrum ‘Album’ (northwestern corner of the European section), the white-flowered form of the Judas tree is, like the more common pink version, famously heat and drought tolerant. Spanish fir, Abies pinsapo, like other Mediterranean mountain dwellers, is tougher still. Two specimens—an older, declining (root compromised) tree and a rapidly growing seedling—are located west of the main path through the European section.
I would be remiss if I failed to mention some recently planted trees in the Pacific Slope Garden, the majority of which are adapted to the climate conditions expected in the future. A number are only theoretically good choices, as they haven’t yet proven themselves over time or in the wider landscape. We are optimistic, however, when we see the performances of a wide range of trees from the mountains and foothills of southern Oregon and northern California, especially pines, cypresses, oaks and oak relatives. A small sampling of standouts so far include Quercus kelloggii (California black oak), the evergreen tanoak, Notholithocarpus densiflorus, Pinus muricata (bishop pine) and Hesperocyparis bakeri Siskiyou cypress (also in the Alpine Garden). All of these are visible along the main path through the Pacific Slope Garden.
Written by:
Douglas Justice
Associate Director, Horticulture and Collections
UBC Botanical Garden
