Last year was the warmest on record, just ahead of 2022 and 2023. As the climate continues to heat up, many trees will face challenges such as slowed growth and higher death rates, especially among younger trees and those sensitive to moisture shortages.

Are droughts more common in the UK?

A drought is a complex combination of conditions, as figure 9 demonstrates. Low rainfall by itself does not constitute a drought, nor does a prolonged period of higher temperatures. Several periods over the past 25 years have nonetheless clearly met drought conditions in the UK. Between 2004 and 2006, persistent below-average rainfall resulted in a multi-year drought, leading to low river flows and low groundwater levels, as well as depleted reservoir stocks.

More recently, the UK has witnessed severe summer droughts, rather than multi-annual occurrences. 2022 saw one of the UK's most severe and widespread droughts in the last 50 years, and temperatures exceeding 40°C for the first time.

By the end of the 21st century, all areas of the UK are projected to be warmer. In the high emissions scenario used by the Met Office, summers could be anywhere from 1.3°C to 5.1°C warmer, and winters could be 0.6°C to 3.8°C warmer.

At the same time, in the worst-case scenario, there could also be as much as 45% less precipitation in summer by 2070, and 39% more precipitation in winter. This means it is not simply rainfall shortages, but rainfall patterns, that are likely to cause stress.

Figure 9 appears to indicate the anticipated trajectory of future drought occurrences. Multi-year droughts, such as those between 2004 to 2006 and 2010 to 2012, are projected to become less common, whereas severe summer droughts appear more likely.

Case study: Royal Botanic Gardens, Kew

The majority of the huge variety of trees in the Royal Botanic Gardens are at risk from climate change

Climate warming will be felt most acutely in urban areas, where considerations such as the urban heat island effect intensify rising temperatures. Urban trees already endure constrained and often poor growing environments, leaving them even more susceptible to this additional stress.

Many of the tree species within the Royal Botanic Gardens at Kew and the wider London area will be vulnerable to changes in the UK climate. Research by Kevin Martin, Head of Tree Collections at the Royal Botanic Gardens, highlights the scale of the challenge; by 2090, Mr Martin reports that the climate at Kew is projected to resemble that of Altamira in northern Spain, nearly 600 miles south of Kew.

According to this research, in these much drier and warmer conditions, only one of the 100 assessed focus tree species (holm oak) is deemed to have “high suitability” with high confidence in these Iberian conditions. The species included within the study represent 95% of London’s tree population. Almost two-thirds of the trees assessed were rated as having low suitability. Furthermore, one-in-ten of the trees were found to be “vulnerable” to the projected conditions by the end of this century, meaning the capital’s urban forest could look markedly different as a result.

Defining climate resilience in forestry

A tree’s origin often reflects its climate adaptability. For example, European beech struggles in hot summers, whereas Oriental beech is more heat-tolerant. Mr Martin's research explains why some of these species cope better in dry conditions. Important factors include the turgor loss point of leaves and leaf dry matter content.

Turgor loss point (TLP) measures how low the water pressure inside a leaf can drop before it wilts. A lower TLP means a plant can handle greater drought stress since its cells keep functioning even when water is scarce.

Leaf dry matter content (LDMC) is the ratio of fully dry leaf mass to water-saturated, fresh mass. Species with high LDMC and dense wood typically grow at a slower rate but are better equipped to withstand heat and drought.

Improving forestry resilience

Using the findings of Mr Martin's research, it is possible to draw conclusions that could inform future planting strategies in the UK to improve the resilience of the nation’s trees and forests.

1. Plan using climatic moisture
   
   Mr Martin's studies use the Climatic Moisture Index (CMI) as a better guide to how well a tree will grow than temperature or precipitation considered in isolation. CMI defines how much water is available to a tree, after taking into account both rainfall and how quickly water evaporates in hotter conditions. Combined with soil maps and site assessment, this makes the CMI a useful tool to spot sites that are likely to become drought-prone.
   
   
2. Match tree sources to future climate conditions
   
   Knowing the projected future climate allows climate‑analogous regions to be identified. Researching and anticipating the climate of a region where planting will occur can allow foresters to select provenances from regions with those conditions (figure 10). This helps ensure that the genetic material planted today is pre-adapted to the climate it will face in maturity.
   
   
3. Select trees with beneficial traits
   
   Some tree species cope far better with drought than others. Traits such as TLP, LDMC and wood density give a good indication of how well a tree can tolerate extended dry periods. That means planting stock can be chosen from species and provenances that already show strong, measurable drought‑tolerance traits. This improves resilience across both timber‑producing and broadleaf planting schemes.
   
   
4. Design for water resilience
   
   As much as the tree can be selected to be resilient to drought, designing for water resilience is essential. This might include practices such as:

• Improving infiltration and soil water storage by breaking compaction layers through targeted ripping or subsoiling
  
  
• Using mulch or brash retention to moderate soil temperatures and reduce evaporation
  
  
• Direct planting into pasture as opposed to traditional ground preparation
  
  
• Adjusting initial spacing and early thinning to encourage timely canopy closure
  
  
• Consider using cell-grown trees instead of bare root stock, which typically provide better drought resistance
  
  
• Adapt weeding regimes to the weather, recognising that leaving more vegetation can offer shelter, shade and improve moisture retention

Figure 11 illustrates a species distribution model for silver birch (Betula pendula), a “vulnerable” species, and holm oak (Quercus ilex), a “high suitability” species. Each point represents an observation of the species in relation to its climate. It also suggests that by 2050, Betula pendula will be approaching the limits of its climatic tolerances. The larger orange points represent the current and future climates of London.

_{Read the articles within The Forestry Market – 2026 below.}