How residential homeowners manage their trees – a Seattle case study

The importance of a diverse, plentiful, and healthy urban tree population of a town or city is well understood. For local authorities, who typically will own the largest amount of a town or city’s tree population, there is normally a ‘strategy’ employed that involves retaining and replacing trees for the (direct and indirect) benefits of the residents. However, many trees also exist within private property (such as front and rear gardens) and, unless a tree has statutory protection (a Tree Preservation Order, for UK trees), there is no means of safeguarding its presence. This study, which looks at homeowner attitudes to private tree maintenance, therefore offers a good insight into how residents seek to manage their own trees. Perhaps, the results of this study can be used as an indicator for homeowner attitudes in other urban areas, in the USA and beyond.

Before we go on, I think it is worth noting that the two questions the authors of the study sought to answer were: (1) What are urban homeowners’ past and future tree planting and care behavior patterns?, and (2) Are there variations in perceptions, attitudes, and behaviour patterns by geographic district?

In order to answer these two questions, the authors set up a web-based survey and encouraged a randomly-selected sample of homeowners (not those who rent) from across all of Seattle’s 53 districts to respond – personalised and hand-signed letters were sent out to inform the randomly-selected homeowners of the survey, and a week later personalised postcards were sent to those who had yet to respond. In addition to the personalised means of contacting the homeowners, each respondent was informed that if they completed the survey they would be able to claim a free meal at a local restaurant that was, at the time, being featured heavily in local newspapers due to their advertising regime.

In total, 2,485 homeowners were contacted, and 751 (31%) of the homeowners responded to the survey. Response rates varied between districts, with Central Seattle (including areas such as Madison Park and Capitol Hill) having the highest response rate at 41%, and South East Seattle having the lowest (15%).Demographically, the average respondent age was 51, and the average time the respondent had lived at their property was 14.6 years. Furthermore, 38% of respondents had a college degree, and 44% having a graduate or professional degree – this reflected in total earnings per year, with over 50% earning between $75,000-$150,000. In terms of ethnicity, 88% were white, 5% were Asian, 3% mixed race, and the remaining 4% of other ethnicity – this reflected the overall ethnic distribution of Seattle rather accurately. It is important to stress that the authors did not analyse how  demographics in the same – and across different neighbourhoods – impacted upon private tree management.

table1
A comparison of respondents from this survey and the 2006-2008 American Community Survey.

Moving onto the results of the study, the authors segmented the results for city-wide analysis into two sections – planting behaviour and pruning behaviour.

Planting behaviour

The respondents of the survey showed a distinct preference towards planting small ornamental trees, in addition to alack of desire to plant large coniferous and deciduous trees. However, there was a very marked intent by respondents to have their next planting be a fruit tree.

table2
The survey asked respondents to list their past and future planting choices – multiple options could be ticked, per survey completed.

Respondents were also asked as to what fuelled their most recent tree planting, of which nearly half stated it was either as part of a larger landscaping project within their property’s grounds, or to replace a tree that had previously existed within their property.

table3
This graph shows the principal reason behind the respondents’ most recent tree planting.

Of these recent plantings, 48% of respondents said they planted the saplings in spring, whilst 36% planted in autumn, 13% in summer, and 3% in winter.

Additionally, the survey asked whether the respondents would consider the possible future installation of solar panels as a determining factor in deciding what tree to plant, if at all, of which 7.5% said yes. Also, the survey results showed that the respondents have less of a desire to plant trees in the future, with an average of 3.4 trees planted per household in the past dropping to 2.1 per household in the future.

Pruning behaviour

88% of respondents stated that the tree(s) within their property had been pruned. Of this 88%, 60% did their own pruning work, 28% hired in certified arborists, and 10% hired uncertified persons. The motivation behind the pruning was, from the results, down to an attempt to improve the tree’s shape (64.2%), to remove dead or damaged wood (59%), to provide clearance for utility lines (23.4%), to increase sunlight levels (22.1%), to increase fruit production (19%), and to improve the view (13%). Multiple reasons could be ticked, per respondent.

Neighbourhood differences

On a neighbourhood level, past research has suggested that planting of 6.4 trees per acre is needed to reach Seattle’s goal of achieving 33% canopy cover (not including trees planted to replace old ones). However, no districts in Seattle, according to the results of this survey, will have enough trees planted to meet this target. Of course, the amount of future tree plantings varied between districts (from 2.4-5.4 trees per acre). Respondents were also asked whether they felt they had the knowledge needed to be able to select the right tree to plant, of which it was found between 8-32% of respondents were confident in their ability to select the correct tree.

table4
A choropleth map showing how different neighbourhoods surveyed vary in expected future tree planting rates (per household).

Analysing the results

In light of the aforementioned results, the authors were concerned over the falling desire by respondents to plant more trees. They were unable to assert whether this is a city-wide phenomenon, or is a trend across the USA. However, it was noted that the desire for tree planting by respondents may rise (or even fall) in the future. Regardless, the Seattle urban forest managers are concerned over the lack of intent to plant trees as the needed rate.

Turning attention towards the time of planting, concerns were raised following results showing 84% of trees were planted during periods of the year that were unfavourable. A reason for this, the authors allege, is that nurseries advertise during the spring, and as many homeowners reported they didn’t have the knowledge needed to be able to select the right tree, it is very likely their knowledge also was lacking on awareness of when to plant.

Furthermore, there is a discernible trend in “downsizing” mature tree height, with a very small desire for big trees to be planted. This may have marked implications for stormwater management, pollution reduction, and so on. As there are fewer spaces for large trees to be planted, mainly due to in-filling within cities, the future for large urban trees looks bleak in Seattle. The authors therefore suggest that there may be a need for the Seattle urban forest managers to work with homeowners to encourage, and even subsidise, large tree plantings.

Looking at the clear desire for homeowners to begin planting fruit trees (42% want to plant them in the future), the authors remark that this desire could be harnessed to get homeowners more interested in urban forestry on the whole. As there is a clear desire for homeowners to grow their own fruit (at least, in part), there may be scope to encourage homeowners to consider the needs of the urban forest on the whole, which may help the city achieve its 33% tree cover target. However, as fruit trees are generally small, there is a risk that an over-use of fruit trees may be detrimental to the goal.

Respondents’ desire to not use certified arborists for tree work was also a concern for the authors. As tree health can be greatly impacted by improper pruning works, the fact that only 28% of the 88% of respondents who had pruned their trees had used certified arborists, means many trees may not be receiving the appropriate level of care. Again, there may be scope here to encourage the use of trained arborists.

Survey limitations

The authors recognise that non-response bias (due to a lack of interest, or laanguage barrier) will have likely skewed the results obtained, particularly in districts where there is greater cultural diversity and / or the average income per household is lower. In fact, higher rates of response were received from the more affluent districts, which means data from poorer regions of Seattle may be both lacking and not as reflective of homeowner attitudes.

Source: Dilley, J. & Wolf, K. (2013) Homeowner Interactions with Residential Trees in Urban Areas. Arboriculture & Urban Forestry. 39 (6). p267-277.

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How residential homeowners manage their trees – a Seattle case study

2 thoughts on “How residential homeowners manage their trees – a Seattle case study

  1. Clare O'Beara says:

    Great study, thanks. In Dublin, only householders on the outskirts have large gardens and can plant large trees. Large trees shade neighbours as well as the garden they stand in, while leaf fall, root spread, crown spread blocking light from other plants and storm damage, plus the cost of pruning a large tree are good reasons for a householder to prefer smaller trees.

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    1. Morning Clare, and thanks for the comment. It’s much the same in many older towns, where the infrastructure was never ‘there’ for large trees along streets. ‘New towns’ built after the war are slightly different, though still gardens are very small and trees of any good mature size are simply not planted. I live on the edge of a town and the gardens are large enough to allow for many large trees per ‘plot’, and the biodiversity we get is much better, though head just 500m ‘into’ the town and it changes drastically.

      I get why houseowners want smaller trees, and they are perfectly justified reasons as well. It’s a shame, nonetheless. Large trees just aren’t feasible, unfortunately. The lack of knowledge people have on species selection is interesting, however. Scope for education, and it’d need to start in schools really.

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