Future Trees Trust: Oak takes centre stage at supporters' day

PRODUCING high-quality seed requires research and investment. The Future Trees Trust (FTT) is supported with grant awards from DEFRA, the Forestry Commission and from private donors, including various trusts, sawmillers and forestry companies. Others offer trees from which to genetically select material or land on which to host trials, most recently the National Trust with the gift of a 50-year lease of the FTT’s own research woodland (Craven Field) and its first permanent office at the 7,500-acre Buscot and Coleshill Estates in Oxfordshire.

This annual supporters’ day celebrates the oak. The event is hosted in the Granary, a multi-purpose events and exhibitions space within the renovated Home Farm Heritage and Rural Crafts complex, across the courtyard from the FTT’s new office.

CEO John McLaughlin opens the morning by thanking the FTT’s staff and supporters. He says this new partnership with the National Trust has, “for the first time, given us [FTT] somewhere to call home, land we have control over, and a base from where we can plan for the future.” 

Oak is an important species for forestry and conservation. Acorns are recalcitrant (they cannot be stored for long periods of time) and crops must be planted using the current year’s acorn supply. In a good mast year like 2020, this works. However, 2021 produced no acorns at all, with only moderate amounts in the following two years.

The Granary. (Image: Carolyne Locher)

The UK does not produce enough quality acorns to satisfy demand, but later the FTT’s Head of Research Dr Jo Clark shares news that this may improve.

In ‘Demystifying masting, understanding the mechanistic drivers of masting in Quercus robur and Quercus petraea’, Ryan McClory (PhD student, Reading University) shares the results of five separate studies undertaken in the last three years:

Study 1: ‘Individual-level drivers of masting at Wytham Woods’ (of 39 related trees) revealed one tree to be an acorn ‘super producer’.  Halo-thinning surrounding canopies could improve acorn production.

Study 2: ‘Weather as a large-scale synchroniser of masting’ offered no evidence that weather is an influential factor.

Study 3: ‘Does pollen influence acorn success?’ Yes. Out-of-stand pollen sources resulted in better acorn production.

Study 4: ‘[BIFOR] FACE: how does elevated CO2 influence acorn and flower production?’ revealed that when counting acorns and cups, first-year acorn production increased, before normalising. McClory wonders how elevated CO2 levels might affect seed predators.

Study 5: ‘Seeding vs. planting: direct seeding vs. direct planting for successful oak regeneration’ revealed that by excluding deer (fencing) from the trial site and after crunching the data, directly-planted acorns grew marginally taller than those germinated in a greenhouse. Both showed similar stem diameters. Root mass is yet to be measured.

Group shot in Coleshill Parkland. (Image: Carolyne Locher)

Following Ryan’s presentation, an audience member suggests a good mast year could just be a year when nothing has gone wrong. A masting expert agrees, saying there is no evidence of a masting cycle (e.g. every three to five years). “The super mast year (2020) may have blown out all their resources, which is why 2021 produced no acorns whatsoever.”

In ‘Genetics of Plus Tree Oaks’ Eamonn Cooper (Trinity College, Dublin) considers the genetic characterisation of oak for breeding and conservation. “A tree selected for ‘plus’ tree classification and breeding is the kind of tree you plant for afforestation and want to cut down for timber.” It is the dominant tree in a stand; tall, straight, stems without defects or branching, with good crown distribution. 

Both Quercus robur and Quercus petraea hybridise (seed pollen coming into a site and pollen from one species fertilising the other), over time Q. robur becoming more similar to Q. petraea, which could affect ‘plus’ tree genetic diversity (and genetic potential).

Investigating whether ‘plus’ tree cohorts already contain first-generation hybrids in the 480 trees genomically sequenced so far, Cooper found species identity was maintained, but hybrids are emerging.

In Ireland, the two cohorts are moving closer to each other, possibly the result of successive hybridisation over generations. Previous studies indicate this is probably happening across the rest of the UK, possibly as a result of climatic conditions, with hybrids better suited to wetter climates.

Using genetic sequencing, Cooper hopes to identify the regions hosting the qualitative traits (branching angle and forking or tree architecture) and quantitative traits (height, growth rate and vessel size) associated with ‘plus’ trees.

Using image processing to study leaf morphology, he hopes to distinguish species, even individual trees, and specific features associated with them.

In ‘Current Projects’, Dr Jo Clark updates the room on the Living Ash Project. On assessing the original archive of (approximately) 1,000 accessions selected for tolerance from across the UK and planted out in 2019, she says: “Last summer’s assessment showed a third dead, a third looking good and a third in between. With only 4–5 years of infection pressure and selection, that is pretty good.”

From Forest Research’s mass screening trials of 155,000 trees (10 years ago), 242 fairly healthy trees were selected and grafts made in January 2024.

Dr Jo Clark was presented with her medal by RFS president Ben Herbert (Image: Carolyne Locher)

When visiting the living archive, Dr Clark noted diamond-shaped lesions associated with chalara infection on two very sickly trees were beginning to heal, “almost like when you prune and a callus forms. The crown was very good.” A sample of a healed lesion was sent to Forest Research which found no signs of ash dieback (ADB). “The tree is somehow partitioning the infection.  Some trees are recovering and continue to grow and thrive.

In 2023, the FTT selected an additional 500-plus ash trees exposed to ADB for much longer (a decade of infection pressure, rather than only 4–5 years). Material taken from each was grafted last winter and will replace those that have died in the living archive. A second archive site is being established in Scotland. In all, the two sites contain 5,000 ash trees.

‘Supersizing Broadleaves’ is a three-year progeny trial, funded by the Forestry Commission’s Tree Production Innovation Fund (TPIF), to see what happens when genetically improved material (referred to as ‘qualified’ and comparable to ‘source identified’) from pendunculate oak, silver birch and sycamore is established (cell-grown vs. bare root, with root assessments made before planting) on ESC-identified land (marginal, suitable and highly suitable) and subjected to different treatments.

Three 2-ha trial sites together contain nearly 12,000 trees. Baseline data (plant height) has been collected and Year 1 growth will be measured in 2024/2025.  Birch is already growing well, but sycamore needs another year to get away. In Year 3, root architecture will be examined to see how each has established, should additional funding be received.

Dr Clark announces that the UK finally has its own ‘tested’ oak, the result of 25 years of work started by the British and Irish Hardwood Improvement Programme in the 1990s. In 2023, two orchards (1 x pedunculate/ 1 x sessile) were ‘rogued’ (thinned genetically based on family performance), allowing the remaining tree crowns to develop. “More space means more flowers. More flowers mean more acorns. [These two orchards are] the first to produce ‘tested’ seed of any broadleaf species within the UK and both will go on the FRM register.” For foresters, ‘tested’ seed offers superior growth and shorter rotations, and quality timber traits such as straighter stems and lighter branching.

Ben Herbert, president of the Royal Forestry Society, makes a surprise appearance in which he explains the RFS Gold Medal is given to individuals recognised as having made outstanding contributions to forestry.

Funded by a Seed Sourcing Grant, the FTT’s Ollie Stock is looking for ‘‘Plus’ Trees from Minor Species’, including beech, hornbeam and cherry (additionally small-leaf lime, wild service, field maple and Norway maple). He has ‘plus’ trees for beech and hornbeam in central and south-east England, and a ‘qualified’ beech orchard is to be planted at Craven Field, already a host to ‘source-identified’ blackthorn orchard. If any reader knows of beech and hornbeam ‘plus’ trees from further afield (and for cherry in Cornwall, Wales and the northwest), please contact Ollie Stock (oliver.stock@futuretrees.org).

Kevin Hobbs, previously wholesale nursery director of Hillier Nurseries and now lecturer, author and production director of Pinnacle Plants International, discusses ‘Oak around the World’.

Following 56 million years of evolution, there are 469 recognised species of oak across the temperate northern hemisphere, sub-tropical and tropical regions.

Myths and stories of oaks have passed down throughout the ages. In Europe, Druid means ‘knower of the oak tree’. The phrase ‘Green Man’ (coined by Lady Radlett in 1939 when writing about German folklore) symbolises a being which is “part human, part living oak”. The earliest European discovery of wooden architecture is a well, built from oak in Germany 7,000 years ago. More recently, cork oak was used in insulation for the space shuttle.

Currently 31 oak species are listed as endangered. “As an ornamental grower, I advocate for diverse non-native species in the built environment, using natives beyond that.”

For use in the urban environment Hobbs suggests Q. monimotricha (grows knee-high in shallow soil and can withstand wet or dry conditions, perhaps on a green roof), Q. semecarpifolia (east Afghanistan to northern Thailand) or Q. sadleriana (SW Oregon to NW California) and wild and cultivated hybrids. A chance crossing in his Hampshire garden, Q. macranthera (Turkey to N. Iran) x Q. petraea ‘Grace’ is now a compact, bushy 18-year-old.

Hobbs highlights that acorns can be grown for commerce, citing acorn flour ‘Oakmeal’ developed by Marcy Mayer in Greece, with the extruded tannin now used in a revitalised leather industry. He urges sharing information, as happens at the Future Forest Forum (September) in Germany. Now in its fourth year, the event began in response to the loss of conifer forests (spruce bark beetle) and beech forests (successive droughts) to look for ways to future-proof forestry production.

New areas of research are considered in a two-year TPIF-funded ‘Oak Vegetative Propagation’. John Vilasboa (Research Fellow, University of Nottingham) outlines the challenges and opportunities in propagating oaks by cuttings (clonal propagation) to streamline breeding.

Kevin Hobbs. (Image: Carolyne Locher)

The FTT’s oak breeding programme took 25 years. Provenance and progeny trials led to ‘plus’ tree selected populations, from which material was taken and grafted onto rootstock and planted out in seed orchards. Overcoming the roadblocks to vegetative oak propagation and introducing new techniques could offer genetic gains and gains in terms of time saved.

In clonal propagation, cuttings must first establish root systems. Oak produces a callus rather than a root at the (cutting) base. Vilasboa wonders why, when all commercial root enhancers contain the plant hormone auxin (which triggers formation of roots). Tests indicate that it matters not only how auxin is delivered, but when and for how long (slowly over a longer period of time), different accessions within the same species often needing different treatments. 

In Brazil, Vilasboa’s PhD studied eucalyptus and he found that applying root enhancers five weeks after taking the cuttings worked best. “Delaying hormone applications has benefits.”

Placing oak cuttings in a polychamber, giving them 16 hours of daylight and keeping the humidity high (misting every 30 minutes) had a positive outcome.

While cuttings taken last winter developed flowers rather than roots (“they were coming out of dormancy”), late-summer cuttings taken from 15-year-old trees developed roots. “Seasonality and the age of cuttings are major factors. Misting is crucial for leafy cuttings. Auxin as applied did not induce rooting.”

Further funding would facilitate research into cutting rejuvenation (tricking cuttings from older material into thinking they are younger) and investigations into why a callus forms rather than a root.

Vilasboa asks: “Why do horticulture, fruiticulture and silviculture not converse? There is evidence of how to propagate apple rootstock. Why has it never been tested in oak? The International Society for Plant Propagation is only about horticulture. Why is silviculture not part of that? We need to bring it all together to further propagation.”

Eamonn Cooper. (Image: Carolyne Locher)

In ‘Oak Silviculture’, Gary Kerr (Silviculturalist and Research Fellow, Forest Research) says: “If you are planting an oak tree, use the best material available. In silviculture, growing broadleaves for quality timber is the best objective, delivering the money to pay for multiple social and environmental objectives.”

He distils productive broadleaf silviculture into five principles, highlighting two.

1. Select the right species for the site.
2. Achieve an initial minimum stocking density (how many trees are needed on the ground).
3. Effective vegetation management.  
4. Protect trees from mammals.
5. Thin to silvicultural characteristics. 

“The minimum stocking density for new oak planting is 3,100, restocking 2,500 (less because of supplementary regeneration). As an example, Sotterley Estates (Suffolk) has planted 6,200 per ha to get to quality timber (extraction rate one in seven).” He mentions a second approach, cluster plantings: planting densely in small clusters, with wider spacing between clusters, emulating where final crop trees will be.

Thinning traditionally, establishing a high-density crop and crown-thinning little and often, results in 60 cm DBH at 150 years. 

In a free growth/active silviculture thinning scenario, 70 trees per hectare are selected and all competition removed (and continually removed) to get them to grow quickly. Using this system, a site in South Wales has achieved 60 cm DBH in 90 years. “Active silviculture treats the crop as an investment and results in a shorter rotation.” 

Downsides include issues with epicormics, grey squirrels and with climate-change resilience. “Selecting 70, what happens if some are storm damaged or suffer pest and disease?” He suggests a mixed thinning portfolio for the best results.

Congratulating Dr Clark on her RFS Gold Medal award and thanking the speakers and attendees, FTT chairman John Lee Pemberton closes the event, saying: “The day has shown us the range of activities the Future Trees Trust is involved in.”