The University of Adelaide’s Waite Arboretum is a place of tranquil beauty and botanical treasures. It comprises 27 hectares and 2,500 specimens from around the world, growing on annual rainfall of 618 mm without supplementary watering after establishment.
There are towering trees like the Sugar Gum (Eucalyptus cladocalyx, specimen #1201G) at 35m, the height of a 12-storey building. There are rare species endangered in the wild like the Torrey Pine (Pinus torreyana #499A). There are trees like Tree Fuschia (Schotia brachypetala #324) ablaze with scarlet flowers in November and a-chatter with Rainbow Lorikeets imbibing the abundant nectar.
There are dense shady trees like Small-leaved Rock Fig (Ficus brachypoda #199) with its wide-spreading canopy touching the ground creating a hidden cubby house for nature play. There are gnarled remnant trees like the Grey Box (Eucalyptus microcarpa #1621) with hollows for possums and kookaburras and crevices for geckos and microbats.
Less apparent, but quantifiable, are the multiple ecosystem benefits the Arboretum trees deliver. Our urban forest cools the air, improves air quality, sequesters and stores carbon, captures rainfall to avoid runoff and soil erosion and promotes well-being.
Dr Jennifer Gardner, Marian McDuie and Arboretum Officer Erica Boyle have completed a research project to quantify and assign monetary values for these ecosystem services on 1,255 Arboretum specimens representing 601 species in 146 genera.
This process used the open source i-Tree Eco software, developed by the US Forest Service, and standardised field data, collected by Erica and her team of volunteers.
Quantifying these benefits has added a new perspective to our appreciation of the Arboretum trees and the urban forest more generally.
Arboretum Tree #1201J, Sugar Gum (Eucalyptus cladocalyx). Age 140 years, Canopy area 718 m2, trunk diameter 202 cm, height 34 m, carbon sequestered 10 kg/yr, carbon stored 6.2 tonne, total pollution removal 5.3 kg/yr, Structural Value A$56,891. Photo: J. Gardner.
The structural value of the surveyed trees (50% of the Waite Arboretum collection) was calculated to be A$13 million.
Aerial image of Waite Arboretum Survey trees showing the location of trees of different size classes – from smallest (lightest shade) to largest trunk diameter (darkest shade).
Additional structural and functional values of the surveyed trees were:
- Carbon storage: 1,167 tonnes (A$26,600), equivalent to annual carbon emissions from 910 vehicles or 373 single-family houses
- Air pollution removal (O3, CO, NO2, SO2 and particulate matter <2.5 microns): 1.2 tonnes / year (A$4,840 / year) equivalent to annual emissions from 160 vehicles or 36 single family homes
- Carbon sequestration: 34.3 tonnes / year (A$783 / year)
- Oxygen production: 91.5 tonnes / year
- Avoided runoff: >1,072 cubic metres / year (A$2,420 / year).
The full report is available on i-Tree Eco Resources / Project Reports https://www.itreetools.org/resources/reports/WaiteArb_iTree_2017.pdf.
A map is also freely available in ArcGIS online maps, in which selected environmental benefits of each of the 1,255 specimens surveyed are now available at the tap of a finger.
This data will also be integrated with the Waite Arboretum App, which is free to download from the iTunes App Store and Google Play. Download the App and visit the Arboretum on a beautiful spring day while the grass is green and the blossoms at their peak. When you pause to admire a tree take a moment to appreciate its environmental benefits as well as its beauty.