November 21, 2022
You may have noticed that it’s been quite warm recently! It now seems inevitable that the climate is changing, and we, and the natural world, are going to have to adapt.
Temperatures are increasing, both in terms of the extreme heat events that we have seen in July, and prolonged, sustained periods of warmer weather. The frequency of hot days has tripled since records began in 1880, and across Western Europe the length of summer heatwaves has doubled. Alongside rising temperatures, water is also becoming more scarce, resulting in droughts.
In this article, we will look at how to support your newly-planted trees. We will also look to the future, what climate change means for new planting, managing pests and diseases,and looking at our wider needs for shade and protection.
Establishing a robust and sustainable maintenance regime for young tree establishment is an essential part of any estate management plan, especially watering. The watering system should be designed to accommodate typical conditions, but also have contingency plans for very dry or hot spells.
This is particularly important for large planting stock, which need lots of water as it establishes. This stock will have been grown in pampered conditions in nurseries, and it can be a shock for such trees to suddenly have to fend for themselves. Just like children, taking care of them during their early years, whilst teaching them independence and resilience for the future, is vital for their future prospects.
The goal is to wean the tree off extra watering over a period of 3-5 years, lowering the overall amount of irrigation each year. Large tree establishment in very difficult sites may require more prolonged intervention. Often it is not considered economic to water small 50cm tall planting stock, rather let it take its chances as it is cheap to replace. However, increasingly sporadic watering of higher priority plantings of small stock is seen by landowners as a worthwhile option.
The approach also has to take account of the increasing pressure on national water resources.
Where situations allow, a piped irrigation system is a good solution. A central pipe will run underground from the water supply, with smaller pipes running off it to take water to individual trees. Often this takes the form of a perforated pipe (or dribble pipe) which will coil around the root system delivering a steady supply of water. These can be on automated timer systems.
If an irrigation system like this isn’t possible, then an alternative watering plan that will carry you through the summer is essential. Watering directly from the mains water supply with a long hose, or using a vehicle-towed water bowser are the other obvious options.
Whatever watering regime you are using, the summer period can be a challenge. Using more water less frequently is better than vice versa; for example, if a tree requires 40 litres per week, its best in 1 or 2 doses rather than being spread over 7 days. Lots of light waterings don’t give enough water to deeper roots and encourage shallow rooting. Different sizes of tree or shrub need different amounts of water and its best to get advice on this. Increasing the water dosing, even doubling it, may be required during very hot dry periods.
July and August usually coincide with staff holidays resulting in a lack of irrigation during these critical months. September often arrives with trees showing signs of significant drought stress and possibly irreversible damage.
We can find ways to maintain young, establishing trees, but how can we prepare for the future? The growing environment is changing, and our native and naturalised trees may no longer thrive in 100-200 years time in areas where currently they are abundant.
Our best option is to assess what thrives now, understand the likely direction of climatic change, and make the best -informed judgements we can on what to plant.
Here are some important considerations in this respect.
It is essential that we plant a variety of species wherever appropriate, so that we are not overly reliant on one or two species which may then succumb to pests, diseases, drought or temperature stress, and we are left with a decimated tree cover. In a woodland context, this may mean planting a mix of native broadleaf trees ( e.g. Oak, Lime, Hornbeam, Beech, Field maple,Wild cherry, Rowan, Birch) along with naturalised species (e.g. Sycamore, Sweet Chestnut), and native / naturalised conifers ( e.g. Scots pine, Yew, Corsican pine, Douglas fir).
If one or two species struggle, there are still others which can sustain the overall tree cover.
The woodland ecosystem as a whole is based on complex inter-relationships between flora, fauna and fungi, and the diversity of this ecosystem is reliant on trees that have been here the longest – our native trees. Flora, fauna and fungi have evolved together over millions of years, and therefore native trees which have been a long term part of this process provide much greater habitat diversity than more recent introductions.
We must design a careful balance between a significant percentage of native trees and shrubs, and a greater species diversity.
It is important to plant tree species which have the potential to thrive in the likely future climatic conditions – increased temperatures and less predictable rainfall patterns. Trees have a different physiological response to heat and drought stress. It is not necessarily the case that a species which copes with one will cope with the other; however there is clearly overlap in these two climatic factors.
At present, there is little scientific research on this issue. Anecdotal evidence suggests that the natives Field maple, English oak and Small-leaved lime cope better. Non-natives, Norway and Red maple, Red oak, Silver lime and Sweetgum are also good choices.
It is helpful to understand where non-natives originate from in the world. Trees which originate in hotter, drier regions are potentially good choices for planting. For example, Sweet chestnut originates in hotter, drier parts of Southern Europe and is long established in many parts of the UK.
We will probably discover that the ideal conditions for our native trees will move further north as the climate changes. Prior to humans moving plants around, the native range of Beech was the south-east of England only. However, increased heat and less predictable rainfall in the future will probably push the optimum growing conditions for this species into the northern parts of the England and Scotland.
Changing conditions provide an added complication in the form of pests and diseases. Trees which are stressed by heat and lack of water will be more vulnerable to attacks, and not have the resilience to withstand them. Native and naturalised trees such as Ash,Horse chestnut, Wych and English Elm are currently unavailable to plant owing to disease issues.
So there are clearly significant challenges facing our tree stock over the coming decades; however, with careful planning, research and consideration, we can make trees part of the solution to the climate change problems facing life on earth.