trees: health Ash trees are under attack from ash dieback. of the somewhat pejorative term ‘weed’, subjectively referring to a plant that is in the ‘wrong’ place. Horticulturally speaking, ‘disease’ and ‘pest’ can be also applied in the same way. Why yes? Most plant communities are broadly exposed to a diverse range of pathogens and pests, yet they co-exist in a healthy balance. A worrying weakness of modern agricultural and silvicultural planting is the reliance on monocultures, where genetically similar plants are cropped in large swathes. Be they spruce, poplar, barley or beet, all offer limited natural resistance to roaming ‘enemies’. Considering this vunerability in relation to wild plants of more northerly European latitudes, such as Britain and Scandinavia, trees often have a similar genetic paucity, a kind of natural monoculture. Given the experience in Denmark, where estimates suggest a 90% ash population reduction has already happened, we can expect massive ash mortality in the UK. The visual impact on the landscape is likely to be severe and worth considering ahead of time. In contrast, healthy, biologically and structurally diverse ecosystems tend to buffet the presence of pests and disease. This is why older, semi-natural habitats tend to be more species-rich and less susceptible to broad-brush tree demise. 90 the english garden February 2013 We are likely to see fewer ash trees in the British countryside in the future. Did you know? The Conservation Foundation is carrying out the Great British Elm Experiment. Cuttings taken from healthy native elms have been micropropagated and distributed to hundreds of people to grow on. Participants must log their tree’s progress for up to 15 years. To find out more, see www.conservation foundation.co.uk Phylogenetic diversity is the key to healthy woodland. One effect of disease is to increase habitat diversity and promote genetic diversity. Eventually, ash dieback will most probably acclimatise and be ecologically accommodated, contributing to an increase in the overall resilience of our native woods - in other words, no pain, no gain. Ash devastation should result in the survival of a diverse and also resistant population from which will emerge future waves of ash proliferation, birthing a stronger ash realm. While the outlook is somewhat disconcerting, it is only nature doing what nature does best: fluctuating, grabbing opportunities, making her power known to us. Focusing in at the garden level, though, what can we do? Firstly, it’s probably sensible to keep calm, not to jump to conclusions, and to keep observing. Steer your garden’s evolution towards healthy breadths both of tree species diversity and of age range. When selecting new trees, choose a mixture of sizes. Be thoughtful in specimen spacing, allowing for breezy air flow corridors, and consider sacrificing existing specimens in overcrowded areas. Physical wounds are the primary entry point for many infectious diseases. Protect trees from herbivores, minimise windblown rubbing or chafing by correctly fastening Check tree stakes and straps regularly. stakes and straps, and exercise constant vigilance to avoid physical damage through sloppy strimming, lackadaisical lawn mowing or poor pruning. Timing and technique for pruning must be considered carefully. Avoid pruning in wet weather, when pathogenic dispersal flourishes. Habitually clean and disinfect tools. Young trees will require nannying for a year or three, so instigate a disciplined nurturing regime of watering, mulching, feeding and weed control to optimise plant vigour and vitality. Water in the morning, rather than at night, to allow excess water to evaporate and minimise creation of damp pockets and humid microzones. Equally, establish appropriate watering regimes in periods of drought stress. Raise your levels of awareness by learning to identify the different pests and diseases. Inspect frequently for signs of stress or sickness. Record the presence and prevalence of all plant disease in your garden to ensure you understand the origin of illness and mortality, and be wellinformed on steps you can take for prevention, treatment and in some cases, cure. If you’re unsure, seek advice from organisations such as the Woodland Trust, the Forestry Commission or the RHS. This series is brought to you in association with Barcham Tree Specialists. For information about the nursery, visit www.buythetreeyousee.com or call +44 (0)1353 720950. IMAGES/LEFT - FORESTRY COMMISSION OTHERS - BARCHAM TREES
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