138 May et al.: Managing and Monitoring Tree Health and Soil During Extreme Drought Regardless, the predicted future climate change scenarios for southern Australia suggest increased rainfall variability and increased frequency and intensity of drought events. The condi- tions experienced during the 13 years of the drought between 1997 and 2010 may provide a foretaste of what Melbourne’s climate could be like under future climate change conditions. METHODS AND RESULTS Soil Moisture Monitoring In 2009, Melbourne started to monitor soil moisture content change at a number of locations around the city. At potential monitoring sites, ground-penetrating radar was used to ensure that there were no buried services in a zone of approximate- ly 1 m2 of 127 sampling points. At each sampling date a soil gouge auger (Spurr Dig Stick™ at each site. Ten precincts were monitored at a total , Adelaide, South Australia, Australia) provided an intact 0 to 600 mm deep soil core sample at each point. Soil moisture content was assessed using visual and tac- tile indicators (Handreck and Black 2010). This approach does not generate quantified soil moisture content but rather esti- mates the proportion of the soil’s available moisture remaining in the sample. As an example of the data collected, Figure 2 shows soil moisture (expressed as % available water remain- ing) between October 2009 and March 2011, averaged across 14 sampling points in The Domain Park, an area of parkland just outside the Melbourne central business district. Soil drying in late spring 2009 (November) and early summer 2010 (Janu- ary) is evident, as is the improvement in soil moisture condi- tions from autumn 2010 (April) onwards. These soil monitor- ing data were used to negotiate continuation of the irrigation exemptions allowed by the local water supply authority and were also used as triggers for the start of each summer’s irriga- tion program. The data was not used to schedule irrigations. Table 2. Tree health data from The Domain Park, February 2010. Scientific name Acmena smithiiz Agathis robustaz Angophora floribundaz Araucaria spp.z Cedrus deodara Cinnamomum camphora Corymbia citriodoraz Corymbia ficifoliaz Corymbia maculataz Eucalyptus botryoidesz Eucalyptus camaldulensisz Ficus macrophyllaz Lophostemon confertusz Phoenix canariensis Pinus radiata Pittosporum undulatumz Platanus × acerifolia Populus spp. Quercus canariensis Quercus palustris Quercus robur Tilia cordata Ulmus spp. Total z Trees native to Australia. ©2013 International Society of Arboriculture Common name lilly pilly Queensland kauri flowering apple southern pines deodar cedar Camphor laurel lemon-scented gum red-flowering gum spotted gum southern mahogany gum river red gum Moreton Bay fig Queensland brush box Canary Island palm Monterrey pine sweet pittosporum London plane poplars Canary Island oak pin oak English oak linden European elms (n) 35 28 15 52 55 33 38 70 52 17 38 64 47 83 21 26 158 86 35 37 88 46 209 2252 Tree Health Surveys Tree responses to the drought included the following symp- toms: reduced shoot extension, reduced leaf size, pale foli- age, premature autumn leaf drop, death of fine branches in the canopy, canopy thinning, growth of epicormic shoots, death of large branches, and whole tree death. To collect data on the extent of these responses, a series of surveys of tree health were undertaken, beginning in 2009. The canopy condition of each tree was rated as either 1-Healthy, 2-At Risk, 3-Declin- ing, or 4-Dying, based on assessment indicators of i) foliage color, ii) canopy density, iii) presence of epicormic growth, and iv) canopy death. The categories were based on the mor- tality spiral published by Clark and Matheny (1991). Figure 3 shows photographs of trees that exemplify each canopy condi- tion. A total 25,000 trees were surveyed. From these surveys, Figure 2. Available soil moisture (%) in The Domain Park from Sep- tember 2009 to March 2011 in relation to monthly rainfall (mm). Dying (%) In decline (%) 6 0 0 0 2 3 3 1 0 0 0 3 0 0 5 0 17 28 3 5 10 4 14 7 0 4 0 0 2 6 0 3 0 0 0 2 0 0 0 12 18 6 3 8 19 11 25 8 At risk (%) Healthy (%) 6 4 0 4 4 6 0 16 2 6 0 47 9 1 10 8 46 16 40 11 30 24 42 22 89 93 100 96 93 85 97 80 98 94 100 48 91 99 86 81 18 50 54 76 41 61 20 64
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