The Importance of Trees

As described in our History, the land that Mill Hill Park sits on was originally (along with the rest of England) heavily forested.  This changed radically with the 10-16th century clearance of trees to provide grassland for grazing stock.  Early in the 14th Century the area forming the majority of what is now Mill Hill Park was the farm of John Daws, who primarily used it to provide hay for the horse-driven traffic of London. The solitary ancient oaks occurring every few hundred metres along the grassed playing fields of the Park mark the boundaries of the fields of Daws farm (see photograph). One oak is quaintly within what is now the upper cricket pitch, fielding at Square Leg.  Since the Park’s opening in 1924, there have been successive substantial plantings of trees particularly around the A1/A41, and alongside the paths running through the Park – culminating in the 2021 Memorial Woodland in the Flower Lane section.  

This combination of grassland edged with woodland fosters tranquillity, making the Park a natural destination for joggers and strollers, parents with prams, dog-walkers, discussion groups and the like, who have very much come into their own during Covid 19 lockdowns.  But we now face the different order of magnitude of challenge posed by global warming, in which Britain’s parks must play a critical role.  

Global warming can be combatted in either of two ways.  One is to replace the use of fossil fuels with non-heat generating alternatives, such as insulating and re-designing our houses, while connecting them to fossil-fuel-free electricity; and replace transport with clean electric or hydrogen motors. In addition, a major step will be agricultural reform, since animals (particularly bovine) emit a large proportion of current “green-house” gases.

These steps can be implemented right now, but cost a level of finance that will be beyond the reach of many households in our current economic recession. Their effect is to stop Carbon Dioxide (CO2) emissions rising precipitously as they have been for recent decades.  But by themselves they will only reduce the rate of accumulation of new CO2 in the atmosphere. They do not remove any of the existing already excessive CO2.  Current levels of global catastrophes will remain, destroying with flood and fire yet more of our fragile ecosystems, forcing yet more refugees to seek habitable homelands. 

The second, independent, way to lower global warming is to actively remove CO2 from the atmosphere. This is exactly what plants do, converting atmospheric CO2 into structure.  The bigger the plant, the more CO2 they remove. Trees, which grow many metres below and above ground, spreading their roots and canopies widely in 3 dimensions, are unsurpassed removers of CO2 from the air (as are ‘trees’ of sea weed in the oceans).  Grasses, limited to a few centimetres’ growth above and below the ground, play a negligible role in removing CO2.

Our Park, emerging from John Daws hay fields, started with a very low number of large trees.  Fortunately, astute planning to commemorate national/royal anniversaries, and to shield us from the heavy A1/A41 traffic, provides a good basis to build upon.  Last year’s planting of a 500-tree Memorial Woodland in the Flower Lane section was a timely, professionally implemented step to increase CO2 capture by the Park.

Now, Britain must massively increase its density of large trees. The UK Committee on Climate Change calculates that we must plant 1.5 billion trees by 2050 (or 50 million per year) to meet our climate mitigation targets.  At the international level, studies led by ETH Zurich indicate that the most effective method to lower CO2 levels globally is to plant, professionally, a trillion new trees. I say “professionally” because rapid growth of small saplings into large trees requires them to be nurtured in the early stages by mulch, and grassland suppressed (e.g. by weeding).  Simply sticking a sapling into grassland will lead to many trees dying or having stulted growth, slowly capturing very little CO2.  Planting of trees in Mill Hill Park demonstrates good and bad practice. We have room for improvement.

I am very aware, in this first blog, that I am skipping over many issues that should be the subject of several blogs.  One over-riding issue is how woodlands differ from grasslands, and why it is woodlands that have such beneficial effects on human mental health and diversity of wildlife. Grasslands, in the form of sporting pitches, also play essential roles in the life of Mill Hill Park.

Roger Morris,

Chair of Friends of Mill Hill Park 

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