Climate change in the Botanical Gardens

Global Warming has been identified as the single most pressing environmental planning issue facing the world. Its impact on our lives will be significant and Botanic Gardens will not escape this impact. To be responsive to changing climate, Castlemaine Botanical Gardens needs to start planning now!

Climatic conditions in Castlemaine have changed markedly since 1910 and most rapidly since 1950 due to increased population, increased productivity and increased emissions. The average annual temperature in the Castlemaine region has increased by 1.2 to 1.4°C since 1950.

Change in rainfall is more difficult to assess, it has varied considerably but was greatest at the time the Gardens were established, being as much as 664mm in 1889 and falling to a low between 1925 and 1940, of 458mm. The ten year average to 2017 was 546mm.

But things are likely to change!

The extent of climate change that Castlemaine may experience depends upon the scientific model that is adopted. Maximum temperatures have been forecast to increase by as much as 1.4°C by the 2030’s and 2.4°C by the 2050’s compared to 1986-2005 conditions. Days of extreme heat above 38°C could increase from 4.2 days in 1981-2010 to 8-16 days by 2050.

By contrast, winter median temperatures are likely to increase by perhaps 0.8°C by the 2030’s and 1.5°C by the 2050’s with the number of cold days below 0°C likely to decrease from 11 days per year to as few as 4 over a similar time.

Change in rainfall is more difficult to predict. Suggestions have been made that Castlemaine’s rainfall may decrease by 24% by the end of the century with a 33% decrease possible for spring rainfall and an increase in intense downpours with potential for more flooding. This has significant implications for the Gardens’ facilities but also suggests that water capture and use is likely to increase in importance.

Increases in temperature and reduced rainfall are both likely to impact upon the growth and viability of existing plants in Castlemaine Botanical Gardens.

Increases in temperature will most likely impact those plants, especially the trees, from cool temperate climatic regions. It is not all bad news because trees requiring warmer conditions may perform better and a new suite of plants may be able to be grown at Castlemaine.

By computer modelling the existing distribution range of trees within the Gardens against existing climate conditions and projected climate conditions, it is possible to predict those tree taxa that may be adversely affected by climate change.
These will need to be managed carefully with any new introductions of these plants to the Gardens located in specific micro-climates that suit their specific cultural requirements.

Similarly, by reviewing those parts of the world that currently experience Castlemaine’s predicted future climate, horticulturists can identify trees that are likely to grow well in the Gardens in the future. By introducing these the health, verdure and interest of Castlemaine Gardens can be secured for future generations.

In the immediate future, horticulturists may need to change the existing balance of tree populations within the Gardens by reducing the numbers of those tree taxa that will be outside their temperature ‘envelope’ in Castlemaine’s changing climate and replacing them with more suitable species.

The evolving Gardens will not be any worse for this, visitors may experience a range of trees with which they are currently unfamiliar together with old favourites nurtured to perform their best in specific locations. This will make the Gardens more exciting.

Changing climate will lead to home owners reacting positively to make their home climate more comfortable. Plants have a valuable role to play in climate modification that is not always understood.

Castlemaine Botanical Gardens will develop as the focus in the Mount Alexander Shire for home owners wishing to develop their own gardens in response to changing climate. Not only will diverse plants suited to the emerging climate be grown in the Gardens but demonstration and display gardens will be developed that show how to garden in more extreme conditions.

Specific display gardens to show the benefits of shading trees and climbing plants, gardens that harness irrigation and mulches appropriately and provide insights into warm climate gardening will be a developing feature of Castlemaine Botanical Gardens.
The provision of lectures and demonstrations that reinforce these displays will ensure broad dissemination of the Gardens’ stored experience and knowledge.

Castlemaine Botanical Gardens is the place to be to understand the changing climate!

Plant provenance describes the specific origin of a plant. For a species with a broad distribution, genetic variation makes the species more suited to specific conditions at its different sites of growth. By collecting seed from healthy plants in similar environmental conditions to the proposed planting site then the plant is given the best opportunity for survival and growth.

This is unlikely to make a difference for plants with limited natural distribution but for plants that enjoy widespread distribution it can be an important consideration.

English Oak (Quercus robur), the most frequently planted tree in the Castlemaine Botanical Gardens, is an example.

Distributed throughout the British Isles, across Europe to the Mediterranean, to Russia, the Caucasus and middle east, even allowing for Italian trees to be considered a separate species, Q. brutia, those of south-eastern Europe, Q. pedunculiflora, and those of Asia Minor and the Caucasus, Q. haas; there is considerable opportunity for genetic variation within its remaining distribution, especially given its altitude range of distribution from sea level to 1,200 metres!

Trees in Castlemaine Botanical Gardens have been sourced from Britain but future introductions of English Oak could be sourced from southern France, seed from this provenance being likely to fit Castlemaine’s environmental envelope.

Plant collectors from Britain collected plants with a provenance that suited English conditions. Many trees, shrubs and perennials grown in our gardens might perform better if collected appropriately for Victorian garden conditions!