Enriching Natural Regeneration
Trees do not need man’s help to establish themselves. They will seed themselves on any land that is not continuously cultivated. The woodlands that develop from this natural regeneration may not be ideal in terms of the wildlife that they support or the timber that they produce, but they can be enriched by planting with a light hand.
The obvious tree species to enrich natural regeneration is oak (Quercus sp.). It has always been the most valuable UK timber tree and is widely desired for construction, flooring and furniture. The majority of oak timber used in Britain is imported. Oak trees are also excellent for wildlife, having more insect species than any other native British tree.
The site chosen for enrichment is a 1.5 hectare field on limestone brash soil. Not ideal for growing oaks but an oak planted on the site 4 years ago has grown well. The field has been kept as permanent grass for many years with no added fertiliser. It had been topped every year in the Autumn. The field has regenerating hawthorn, elder, Rosa sp. and goat willow, and a smattering of ash and hazel.
About 1 hectare of the field was enriched with pedunculate oak, Quercus robur, of good timber provenance at 10 metre spacing (total 100 trees). Half a hectare was left to regenerate without any enrichment.
The 15-20cm tall oaks were grown in a compost that produced a ball of fibrous roots that encouraged quick establishment. Each oak tree was protected with a 20cm tall vole guard and marked with a 90cm bamboo cane. No herbicide sprays will be used. The total cost of enriching one hectare was £200 per hectare.
The intention was to see if the oak trees could establish themselves in the grassy sward with minimal maintenance. Conventional planting methods would insist that each oak was protected with a 1.2m tall shelter supported by a stake to stop grazing by deer, rabbits and hares. A circle of 1 metre diameter around each tree would have two applications of herbicide per year for two years to stop competition from the existing vegetation.
Oak is a pioneer species that can grow in dense grassy swards. Competition from the surrounding vegetation will mean that shoot growth is restricted in the early years, but it will quickly establish a tap root that will allow it to survive Summer droughts.
As the oak trees mature they will become the mother trees, producing crops of acorns which will further enrich the site with oak saplings. There is little evidence of rabbits in the thick grass, although they are grazing the mown grass on the edge of the site. Roe deer and muntjac are present and may browse the young trees, but oaks have evolved to cope with this. The trees will initially be very branchy, but as they grow the deer will only be able to browse the outer branches allowing a leading shoot to grow unmolested through the centre of the tree. I expect them to grow into strong, straight oaks, sheltered by the surrounding developing scrub.
The importance of the vole guard was demonstrated when we returned the following day to attach them. Many of the small trees had already had their stems nibbled overnight. One had been totally demolished with a well used hole beside the remains of the tree. My previous experience has shown that vole guards are effective whereas a standard tree shelter with an 80mm diameter makes the ideal nest site, with breakfast included.
I returned to this site in mid June 2020 to check on survival of the oaks. We have just had the wettest February since records began, the sunniest spring on record and the driest May for 124 years so I was a bit concerned. I checked 93 trees. 62 were alive and 31 apparently dead. Most of the dead trees were in one corner of the site. The leaves on the live oaks were generally small with very little shoot extension, but they must have grown a good root to have survived their first spring in such adverse conditions.
I returned to the site 3 years later on 2nd June 2023. Most of the marker canes had gone and the natural regeneration had grown considerably, however we did find 12 canes and 8 live oak trees. From this it appears that most oaks that had survived the first Spring in 2020 were still alive. Many of the oaks were still very small (less than 60cm) after 3 growing seasons, but I hoped that they had developed strong roots.