Why Big Trees are More Valuable - Size Matters

When it comes to trees and the benefits and services they provide to us size makes a huge difference....put at its simplest...the bigger the better.

There are a great many studies from different parts of the world that all come to the same conclusions bigger trees, bigger canopies give us greater benefits.

It's not all that difficult to understand why since it is the canopy, the surface area of the foliage which has the greatest impact on many of the services that our urban trees deliver. Let's just recap what some of those key services and benefits are....

• Provide shade - regulating temperature and reducing levels of UV radiation
• Capture airborne pollutants - removing both microscopic particles and noxious gases
• Intercept rainfall - reducing peak storm water flows
• Capture Carbon - both in their wood and in the soil
• Enhance residential and commercial values
• Improve physical and psychological human health

Larger Canopy = Greater Benefits

When it comes to establishing just how much more benefit we receive from larger trees compared to smaller trees I think the best summation comes from one of the co-authors of i-Tree David Nowak USDA  Forestry Service

A mature tree that is 30” DBH (Diameter at Breast Height) provides 70 times the ecological services (clean air; clean water; wildlife habitat, etc.) of a young sapling that is only 3” DBH 

Now there are some obvious immediate implications for the management of our urban forest that result from this well founded well researched argument.

When it comes to urban planning decisions;

The retention of existing established large trees should be a key objective 

Now I am sure that most of those reading this will have heard claims about replacement/mitigation plantings more than making up for the loss of existing trees....

Well it is a sad fact that in the last 50yrs we have been spectacularly unsuccessful in growing large trees in our urban areas. Partly this is due to a failure in the past to understand the soil volume requirements for healthy stable tree growth, it is also due to a failure to recognise the importance of our urban trees, cutting costs in planting preparation, establishment maintenance and a total failure to protect that growing space against pressures from in ground services.

Diagram showing the minimum volume of soil required to support healthy tree growth

It seems to be a fairly simple equation, big trees in our urban areas are immensely valuable, growing replacement big trees in our urban areas is very hard...we should therefore place far greater value on the big trees we already have, retaining and protecting them within new developments should be the default urban planning position.

Our council should be providing the best outcomes for everyone in our city, not just the developer who wants to maximise their profits by cramming in the biggest floor space permitted in the planning scheme, or getting the absolute maximum number of dwellings in a subdivision.

Changes to the Resource Management Act not withstanding it is the responsibility of our council to ensure that urban planning decisions are balanced and that we the residents and ratepayers actually get the liveable city our civic leaders love to bang on about in press releases and sound bites. 

 

An Urban Forest Strategy for Auckland

Since moving to NZ, living and working in and around Auckland I have witnessed the rapid erosion of environmental protection across our city. I have seen the consequences of the last seven years of changes to the Resource Management Act (RMA) and in the last three years as part of The Tree Council here in Auckland I have been personally involved in arguing for a more robust and sustainable approach to tree protection in the Auckland Unitary Plan hearings.

Tree scapes like this in Albert Park central Auckland do NOT happen by accident this requires planning and adequate resourcing

I have read and heard many views on what needs to be done, and I am in agreement with many of those oft repeated arguments. Urgent review of tree-protection measures are needed

There are those both inside and outside council chambers that will argue that under the current regulatory framework of the eviscerated RMA that protection of urban trees is a lost and futile cause….I most definitely do NOT share this view.

I certainly do think that the past years of changes that have weakened the RMA should be reversed as soon as possible, without such reversals it is not possible for local councils to enact stronger tree protection through by-laws or enforcement. However whilst we are waiting for the rest of the country to wake up (or for this conservative government to reject the demands of the developers lobby) there are real concrete actions that local government can take to significantly improve the situation in their regions.

It is almost inconceivable to me that in 2016 Auckland, New Zealand’s biggest and fastest growing city has no documented plan for the future of its remarkable urban forest. Our trees define Auckland just as much as our twin harbours, in fact the two are inexorably linked since it is the trees which play a critical role in reducing not only the flow of stormwater into the sea but also in filtering out many of the most harmful pollutants which would otherwise have negative impacts on our valuable sea life.

Auckland's street trees deliver critical services every day of the year cleaning the air and the water in the urban environment

Why do we need a long term strategy for the management of trees in our urban areas?

At its most basic there is intense competition for space in every town and city and when it comes to planning the future growth of our urban areas there are competing values and objectives. 

Without recognition of their importance and their requirements for healthy growth trees consistently lose out in the competition for space

An Urban Forest Strategy can provide a clear and balanced approach to the management of the trees we already have, and the rational framework for the management of the trees we (and future generations) will need in the future.

Auckland needs a strategy that provides the vision and strategic direction for planning, planting, protecting and maintaining our trees within the municipal boundary regardless of land type or ownership. Auckland’s urban forest includes trees in private yards, street trees, park and reserve trees, woodlands, green space and wetlands.

Our remarkable urban forest is comprised of trees in all kinds of locations under public and private ownership

Auckland needs a strategy that extends beyond the tenure of any one council term, at least 20yrs (preferably 50yrs) with reviews carried out every five years.

Now more than ever we need to elevate the importance of the urban forest across our community, our elected representatives need to put real substance behind the soft statements repeated in the Auckland Unitary Plan which pay lip service to the values contained in this cities urban forest.

If Auckland is really going to be the liveable city as proclaimed by our civic leaders for the growing population that has been predicted then we have to retain and protect those living assets which make it a place where people want to live, work and play and in the process create an environment that is resilient to change.

Properly accommodating trees into new developments demands a commitment of resources over the life span of the trees not just within the short term profit margin of a development company

Our urban planning policies should incentivize developers to incorporate greater numbers of existing trees as well as new trees into proposed new developments. The core of any Urban Forest Strategy is to raise the importance of our urban trees among council officers, businesses, institutions and the general public so that trees are recognised as valuable infrastructure assets.

Our Auckland Council has the raw data required to deliver a comprehensive and up to date inventory of the urban forest, but as yet has no means to apply that information to maximise the performance of those assets.

An Urban Forest Strategy would clearly define the objectives of maintenance programs for existing trees and any new planting programs; incorporating the careful consideration of species, shape, stature and quality of planting stock. The strategy would deliver not just the right tree for the right place but ensure that sufficient soil volume and adequate soil quality is provided to each tree enable the growth of a healthy mature tree.

Without a strategy beautiful street scapes like this one which make Auckland a liveable city will become a thing of the past

Tried and tested blueprints for such a strategy can be found in many large metropolitan areas in Australia, Europe and America…there is no need to reinvent the wheel…we just need local politicians with the vision and foresight to start the process here and now in our city, in Auckland in 2016.