THE GREEN CITY POST

Green City Post

CULTIVATING PLANTS FOR LANDSCAPE RESILIENCE: ARE WE WELL ENOUGH PREPARED FOR THE FUTURE?

AUTHOR: ALISTAIR YEOMANS. CHARTERED FORESTER AND CHARTERED HORTICULTURIST Urban forest in northern Manhattan in Riverside Park along the Hudson River.

To answer this key question, the horticultural industry is recommended to undertake a mapping exercise to collate and assess the knowledge, databases, and tools that are available to contribute to our ability to identify and produce plant species and cultivars that will thrive in a changing environment. Landscape resilience is a key factor in responding to future environment impacted by a changing climate, increasing numbers of plant pests and diseases, and, in certain situations, land management that falls short of best practice. Enhancing landscape resilience requires an understanding of ecological processes in modified or natural ecosystems. Either in the urban or rural setting, ecological resilience is highly dependant on biodiversity.

From a biodiversity perspective, the UK is one of the most nature-depleted countries in the world, leading the government to develop A Green Future: Our 25 Year Plan to Improve the Environment. 1 This strategy aims to protect and grow natural capital in the UK with a 25-year vision. Natural capital consists of ecosystems, which deliver a wide range of valuable services that are essential for human well-being2. Plant life is a critical component of natural capital providing humans with food, fibre, and fuel, and deliver a wealth of other wellbeing benefits from gardens, urban landscapes, and the countryside.

We rely on a diverse range of plants to provide these ecosystem services; some species are considered native; others are introduced and include cultivars arising from plant breeding initiatives. Through agricultural, forestry, horticultural and permaculture practices, plants are grown in a range of systems from monocultures to complex assemblages. In all of these cases, we modify the landscape through selecting plant species to grow and perform certain functions. Climate modelling is a specialised area of research. Recently complex data has been packaged to be readily

REFERENCES

1. A Green Future: Our 25 Year Plan to Improve the Environment. HM Government. 2018 2. Natural capital and ecosystem services. EEA. 2015 3. Understanding climate change from a global analysis of city analogues. Bastin et al. 2019 4. Climate change: What food could be grown in London in 2050? October 2020

understood by the lay person, and one of these predictions is that London’s climate will resemble that of Barcelona in 20503. This prospect has led garden designers to imagine what exotic plants could be grown in cities in the future4 . In some managed landscapes, annuals, biennials and herbaceous perennials could be substituted relatively quickly with better suited species and cultivars. The implications of warmer climates (reduced days without frost) could have profound physiological implications for woody shrubs and trees, such as reduced ecological competitiveness due to insufficiently cold winters to break dormancy mechanisms. Also needed is consideration of how this impacts on management of plant pests, some which have a broad range of host plants e.g. Asian Longhorn Beetle, Phytophthora spp. and Xylella. An example of a practical question that a landscape architect may ask is: what species of oak will thrive in a UK city park in 2050, and will it be safe for people to sit under (given the likely spread of Oak Processionary Moth and its capacity to cause irritations and allergic responses)? An oak tree with 25-30cm girth for planting can take 30 years to produce, so the answer to such questions should be a current focus, not a future consideration.

Whether we use natural succession methods to ‘grow our natural capital’ or rely on breeding and cultivation, we will increasingly look to the diversity of plant genetics to deliver nature-based solutions. This leads to ask how well prepared we are locally, nationally, and globally, to answer the simple question - which plant species / cultivars should we rely upon and plant now to build landscape resilience for the future? In the short term, the goal of the proposed mapping exercise is to focus the minds of horticultural producers, designers, trade, and land managers on how they can access practical information to specify and grow plants that improve landscape resilience. In practical terms, the objective is simply to identify work that has been conducted, and to identify gaps which may be useful in steering the research agendas of others. The mapping exercise may present multiple and complex corollaries for both commerce and conservation, highlighting synergies and parallels in these multi-disciplinary sectors.

Schloßpark Ludwigslust

VISUALLY INTERESTING CAREX

Author. Giacomo Guzzon is a senior landscape architect - head of planting design at Gillespies, academic tutor and lecturer in several universities and colleges in the UK.

Carex divulsa at Elephant Park, London, in October. Credit: Giacomo Guzzon.

As a landscape architect working mostly in the public realm, I am always looking for tough plants that are visually interesting and will survive with little care. More than huge and fancy double flowers or variegated vegetation, I am mainly interested in plants that are resilient, robust, and will withstand challenging environmental conditions. The public realm is indeed a very different environment than a private garden where we can easily control the care and limit human-animal disturbance. Continuously faced with these challenges, I became more and more interested in growing different species of the grasslike genus Carex. These plants have proven to be well behaved with different degrees of self-seeding, creating neat clumps, requiring little care, and being very versatile also in difficult locations around trees or in dry shade. Carex can be very long lived in the public landscape when planted in the right spot, and maintenance is really minimal since they are mostly evergreen species. Sometimes in a particularly cold winter with harsh frost, they can be cut back in the spring but not at soil level. They need to be left with enough vegetation to cope with the ‘haircut’, and must be cut at least 15 cm high to avoid killing them.

Carex is a large genus with over 2,000 species in the Cyperaceae family. Surprisingly, only a handful of species are commonly grown in large numbers in the UK and mainland Europe. The majority of the species available are from Asian origin and often with variegated foliage, with Carex oshimensis and Carex morrowii being undoubtedly the two main protagonists in the trade. In the USA on the contrary, there are specialised nurseries growing native Carex species in deep plugs specifically for landscape projects. Moreover, the Mt. Cuba Center botanical garden in Delaware is currently conducting a trial of many common and rare native species, with the aim to assess their potentiality for landscaping and inform the industry and professionals about new worthy plants. In Germany, the ‘Staudensichtung’, the Perennials Examination Group, is currently trialling 48 native and non-native Carex species across Germany and Austria. Through my travels in the US and Europe I have collected several species and I have been growing them and studying their behaviour in the UK and in northern Italy. In my experience some of the most promising candidates with fine leaves are: Carex divulsa (UK native), Carex remota (UK native), Carex cherokensis (US native), Carex pennsylvanica (US native), Carex lenta ‘Kyoto’ and Carex ‘Osaka’ (Japan origin). In the landscape industry we need more of these robust plants that are not particularly showy for garden centres but indispensable for designing resilient and low-maintenance landscapes that nowadays we are all aiming to create.