Tree Pests and Diseases

Earl of Caithness Excerpts

Thursday 13th February 2020 Lords Chamber

[The Earl of Caithness (Con)]

My Lords, in the last two decades alone, there have been 14 new diseases and five new major pest outbreaks that threaten our woodlands. All these pests and diseases have been aided and abetted by the single most dangerous pest to woodlands in the UK: we humans. Not only have we imported many of the pests and dispersed them around the country, but despite having an excellent climate for growing trees in this country we are, in general, bad at forestry and silviculture. The statistics make dismal reading. Despite the fact that the amount of land under woodland has tripled in the last century, the UK is the world’s second largest net importer of timber. Some 77% of our broadleaf woodlands are still represented by only five species, and disease is currently wiping one of them, ash, out.

Some 15% of our broadleaf woodland, including our best beech trees, are damaged by grey squirrels. It almost impossible to grow commercial broadleaf timber in the UK. Importantly, and I stress this, 58% of our woodlands and 80% of our broadleaf woodlands are unmanaged or badly managed. We are woefully ill equipped for the further challenges of rapid man-made climate change. Unmanaged woodlands are a result of years of Governments virtually ignoring the needs of private sector forestry and receiving poor advice. The Forestry Commission is no longer fit for purpose. Its structure is flawed and it remains, in good communist fashion, the regulator, prosecutor, judge and jury of forestry in this country. The noble Lord, Lord Carrington, reminded us that as a large landowner it has got away unchallenged with its own mistakes while costing the taxpayer a great deal of money.

Poor or no management occurs primarily because it is uneconomic to manage woodland as a timber crop. It is a well-established fact that trees get stressed and when they do, they, just like us humans, are much more susceptible to diseases and pests. The condition of individual trees and the structure of stands are important determinants of the extent of such damage, but the degree to which this is true, and the mechanisms, vary. Where most trees have vigorous, healthy crowns and a suitably large growing space for their position in the structure, they are much more resilient than where excessive lateral competition produces stands with poor crowns. Unfortunately, our planting system of even-aged, single species grown in straight rows, as preferred by the Forestry Commission, leads to dense stands with quiet, humid conditions. Trees in this situation are under severe stress and species such as ash and oak, which are particularly intolerant of lateral competition, become highly susceptible. Conditions in dense stands of ash lead to increased spore production and greater damage from ash dieback, while in oak stands, the beetle causing acute oak decline is attracted to the stressed individuals. Unmanaged woodland—more than half our woodlands is in this condition—becomes a haven for pests and diseases.

Owners are also implementing non-intervention management because of a misguided intention to help wildlife. However, there is strong evidence from studies of plants, insects and birds that some of our best-loved woodland wildlife is in crisis. The richness of woodland plant species has declined by 19%, woodland butterfly populations by 74% and birds by 32%. Poor or no management is putting at risk not only our biosecurity but our biodiversity. To mitigate these threats, it is long overdue that we move to a more sustainable tree management system that avoids large concentrations of young, dense, pole-staged stands with low air movement and potential for high build-up of fungal spores and pests.

We should aim for woodlands of mixed and uneven aged species. These more open stands have better airflow and can develop under-storeys which are beneficial in deflecting spore movement. I have advocated this for more than 50 years and I am delighted that there is growing support for it from companies such as SelectFor Ltd. Sadly, there are still far too many flat-earthers in positions of control and influence in the forestry world who are protecting their established ways. Ideally, such a system as I recommend should include self-sown trees, but that is unlikely now, given our inability to control the deer population explosion. Lovely as they are, excessive numbers mean they become a pest and are a threat not only to young trees but to biodiversity, the environment and humans.

My noble friend Lady Byford was right to say that good management is expensive. I shall give one example. Richmond and Bushy Parks have an annual budget of £200,000 to manage the problem of oak processionary moth, and last year 9,000 nests were removed. How many landowners and farmers, whom the Government are encouraging to plant trees, does the Minister know who have budgets to control the moth in the same way as the Royal Parks?

The new enthusiasm to plant trees is welcome, but that is the easy bit. On its own, the Forestry Commission’s mantra of “the right tree in the right place for the right reason” is just fatuous claptrap. As the Royal Forestry Society accurately states in its latest report, Forestry and Climate Change, planting more trees is fine but managing them and our existing woods is a long-term commitment requiring considerable skill and perseverance. There are exceptions but generally, as the noble and right reverend Lord, Lord Chartres, has just told us, we are woefully lacking in those skills in the UK and there is no structure or funding to redress that. If forestry is not profitable, the taxpayer needs to help those who plant and manage trees, just as we do with those who plant crops. If we do not do this, our grandchildren will end up with empty plastic tubes and distorted, valueless timber.

I will finish with a quote from Tony Kirkham, the head of the arboretum at the Royal Botanic Gardens, Kew. Although it is contrary to our current forestry practice, I commend it to the Government and all who plant trees. When referring to the great storm of 1987, he said:

“The golden rule that I got from the storm was that you’ve got to copy nature and run with her and you’ll succeed.”