Future proofing Trinity College Botanic Garden by Professor Jennifer C. McElwain

Article from The Journal Autumn 2022

The oldest college botanic garden in the world, Orto Botanico di Padua, is in Northern Italy, a short trip from Venice. It was established in 1545 and has been in continuous use over its long history as a place of learning both scientific and cultural since its inception. It is recognized today as a UNESCO world heritage site. Trinity College Botanic Garden, like Padua, is a college botanic garden of considerable antiquity that was established in 1687 as a place of excellence for the study and use of plants for medicinal purposes (a physic garden) on Trinity’s main campus. The garden’s historical path has not been as continuous, smooth, nor perhaps as illustrious, as that of Padua as it has moved multiple times over the past 300 or so years, but today Trinity College Botanic Garden is an active research garden with quite a few horticultural gems occupying a multi-acre site at Darty on the Southside of Dublin.

The gardens contain an estimated 4000 plant species in its living collections, multiple arboreta, order beds, and glasshouses and a seed collection from over 60 native species within the National Threatened Plant Seedbank. Species of particular horticulture interest within the collections include Mackaya bella (Forest Bell Bush) named in honour of a former Curator of the gardens, James Townsend Mackay (from 1806 to 1862). This exceptionally rare and lovely shrub is a montane forest species native to South Africa. It grows best in dappled shade with glossy dark green evergreen leaves and stunning bell-like white to pale mauve flowers with dark pink veins that hint at the leafy evolutionary origin of petals. It will tolerate light frosts in Ireland. Another stunning specimen is Magnolia grandiflora, the Southern Magnolia. The family lineage of Magnolia trees dates back deep into the Cretaceous period over 95 million years ago when global climates were much warmer than today and the Earth was ice free. This tree will thrive in Irish gardens but needs some shelter. It is evergreen with enormous glossy leaves and unlike many other species of Magnolia produces huge sweetly scented saucer shaped flowers throughout the season. In an age of naturalistic planting schemes, we have Sanguisorba officinalis (great burnet) and Betonica officinalis (betony). Both are un-showy rare native perennials that are pollinator friendly and provide a long season of interest in borders and meadow planting. We are also growing the exceptionally rare and critically endangered Helianthemum nummularium (common rock rose). Although common in Britain it is restricted in to a single site in Ireland, the reasons why remain a biogeographic mystery.

TCBG is networked with 3758 Botanic Gardens through Botanic Gardens Conservation International (BGCI). Collectively this network are the custodians of over 105,000 plant species which represents 30% of the known global plant species inventory (Mounce et al., 2017). Approximately 1750 seed banks, many of which are housed within botanic gardens such as Trinity’s contain over 6 million seeds from an estimated 50,000 to 60,000 species (Walters and Pence, 2019). There is no question therefore that Botanic Gardens both small and famous cooperatively contribute to conservation endeavours to preserve and protect the world’s remarkable but threatened plant biodiversity. Every Botanic Garden has a role to play in the global effort because each garden holds a proportion of unique species and unique knowledge/research capacity found in few others. TCBG for instance currently contains 165 unique seed accessions collected from 60 species (29 families) in the Irish flora including species that are classified as critically endangered, threatened and vulnerable to extinction.
Our strategy over the next decade is to increase our seed bank holdings of rare native wild plants that are threatened by extinction and to highlight their plight and ecological and cultural importance through a series of short documentary films called ‘Five in 5’ https://trinitybotanicgarden.ie/5-in-five/. Another major aim is to set up a long-term ecological and environmental monitoring network at the gardens using trees as sensors of atmospheric pollution and as responders to climate change. This year is the inaugural year of this important long-term project. Twenty trees have been selected for their horticultural, scientific, and cultural value from our Arboreta; particulate matter pollution has been quantified on their leaf surfaces using scanning electron microscopy and each tree’s physiology has been measured to monitor its drought tolerance and adaptedness. Our ambition is that this long-term project will enable researchers at Trinity to both test the effectiveness of environmental policy and to provide invaluable insights on species resilience to rising temperatures and increased frequency of extreme weather events that are predicted as part of Ireland’s climate future.

Professor Jennifer C. McElwain
Director, Trinity College Botanic Garden

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Mounce R, Smith P, Brockington S. Ex situ conservation of plant diversity in the world’s botanic gardens. Nature Plants. 2017 Oct;3(10):795-802.

Walters, C. and Pence, V.C., 2021. The unique role of seed banking and cryobiotechnologies in plant conservation. Plants, People, Planet, 3(1), pp.83-91.