US loses four million trees a year – conference report

Keith Sacre of Barcham Trees ( pictured)  attended the International Society of Arboriculture (ISA) Annual International Conference and Trade Show in Orlando, Florida, in August. Colin Hambidge took the opportunity to ask him his views on the event.

Are you a regular visitor to the ISA Conference, and what was your main reason for attending this summer?

I do attend regularly, but not annually. My main aims in attending this year were to renew acquaintance with experts such as Ed Gilman, Gary Watson and Nina Bassuk, who have all presented at Barcham’s Big Barn Conferences through the years, and to find and meet potential new speakers for the series of seminars we run every year for arboricultural and other professionals who have an interest in trees.

Conferences through the years, and to find and meet potential new speakers for the series of seminars we run every year for arboricultural and other professionals who have an interest in trees.Keith Sacre

Were there many delegates form the UK at this year’s Conference?

One or two old favourites were there, such as Russell Ball and Glynn Percival, but very few others. This is a shame in many ways as the amount of information available is potentially huge, and the opportunities to network with others who have different experiences and perspectives are obviously valuable. Florida is, however, a long way and travelling the distance to speak only to people from the UK would seem a bit counter-productive.

Did you attend all the presentations over the four days of the Conference?

That would have been impossible, I’m afraid, because there were usually several presentations being made simultaneously, so some careful planning was needed to ensure I could attend as many sessions as possible on the development of the urban forest and the rôle tree nurseries have to play in that development. This particularly interests me.

And do you feel you made the right choices?

Yes, I did! The Conference could not have got off to a better start than with the address given by David Nowak of USDA Forest Service, Syracuse, New York. He spoke about why we care for trees, saying that politics flows from people’s wants. He told us that by 2050 about 66 per cent of the world’s population will live in urban areas, with the urban forest consequently becoming more important and under increasing pressure from a number of sources. Delegates were told arboriculture has to move into a bigger world, where it must work with other disciplines, such as architects, planners and landscapers.

How do we put a value on trees?

Unfortunately, the benefits of trees are not measured in a tangible way, so can easily go unrecognised. It is tree populations which really deliver benefits. David Nowak told us the urban forest in the USA was worth around $730 per acre per annum. He also stressed the importance of canopy cover; where studies have been conducted into urban forests in the States, it stands at around 35 per cent, of which 75 per cent is residential or ’empty’ land. Of these trees only one in three is actually planted – natural regeneration does the rest. When humans move out of an area and it becomes neglected, trees will move in. Nowak then made the statement that grass in towns and cities keeps trees out. He believes the annual cost of managing grass in the USA is between $49 and $134 billion. But huge plantings of trees in a short period of time is not the answer, even though it is sometimes politically expedient. He spoke of tree population ‘bubbles’, with the results of such all plantings all maturing at the same time. The changes which are coming – whether in climate change, pests and disease, development or species shift – will put the emphasis on good tree management even more. He also told us the USA loses 20,000 acres or four million trees a year, although these are not all large trees by any means.

Which other speakers impressed you?

Justin Morgenroth, of the University of Canterbury in New Zealand, presented on exploring the structural diversity in urban forests. He believes that while species selection and diversity are frequently addressed, less attention is paid to structural diversity, and that large trees seem to be disappearing. He has looked at 23 i-Tree studies in the US, and found that at least 40 per cent of trees were under 20cm girth, and that 30 per cent were under 40cm girth. At present his work has not reached conclusions, but is ongoing, and I found his presentation particularly thought-provoking, although limited at this moment in time.

Arne Mattsson of the City of Malmö and Johan Östberg of the Swedish University of Agricultural Sciences also made an excellent presentation on how species diversity can reduce the impact of emerging diseases, based on 30 years of practical work in the city. Malmö is Sweden’s third largest city with a rapidly growing population of 300-400,000 people of more than 170 nationalities. It boasts 500 species of trees, with 1000 to 1200 new trees planted every year. But monoculture can still be a problem in some areas, such as a public park in the city centre where a large, significant monoculture of beech is threatened by Phytophthera.

The event was also in part a trade show. What caught your eye on that side of the Conference?

I spent some time at the trade show and was pleased to see Hansatech were there promoting their Arborcheck tree health testing system. Every time I passed their stand they were busy with both American and European delegates. It pleases me to think that this system is based on the Barcham benchmark system, which was developed on our nursery in the UK.