Tree planting is a process that has evolved. It should perhaps be a simple process that involves a small amount of horticultural knowledge and enough strength to dig a moderate size hole. However, what we are seeing is that there are far more constraints that make planting trees in the urban environment a real challenge. If you look at the diagram below, you can see just how little room trees are left with in our urban environments. Because of this, trees planted in these environments are subject to more stress than trees planted in rural locations. A tree in an urban environment can have its roots squashed by cars, leaves covered in pollution, roots covered by hard standing, less available water, heat scorching and being pushed around by passers-by to name a few things. Therefore trees in the urban environment sometimes need a little more help to establish.
(reference http://streetmix.net/ , 2017)
Jayne and I attended an event at Barcham’s on the 22nd of February with presentations given by Francesco Ferrini (supported by Alessio Fini), an urban forestry expert. It was a very interesting day that presented a selection of the scientific experiments that Professor Ferrini and his team have conducted in roughly the past 10 years. To set the scene, the majority of experiments have been conducted in Florence, Italy. Many may think that because of this, the results are not applicable to areas of England, however the low rainfall, clay soils with little topsoil, short sharp downpours of rain and long periods of relatively high temperature are comparable to many areas in east Anglia and the south east of England. It must also be remembered that our climate is changing and we need to look at areas of the world that are warmer in order to inform our plant selections for the future.
(Barchams, http://www.barchampro.co.uk/seminar-research-projects-improve-growth-and-stress-tolerance-nursery-and-after-transplanting-urban, 2017)
In summary, here is a snapshot of some of the things we learned on the day which are the results of Professor Ferrini’s trials. (Please forgive me if I have noted any of the information down incorrectly):
· Root circling – a tree cannot recover from root circling if it develops spiralling roots early on in its life. Nursery stock that develop circling roots will continue to develop spiralling roots even if they are no longer bound i.e. planted in the ground (unless they are root pruned). Therefore it is important that initial nursery establishment of the plant avoids root spiralling of any kind as this will stay with the plant indefinitely (Ferrini, 2017).
· Mycorrhiza – Help to improve access to and storage of nutrients given the correct conditions in which to survive (this varies depending on mycorrhiza). Increase the ability of tree root branching which may help plants to perform better in drought conditions. It would appear that mycorrhiza specific to different tree species and different tree environments produced the best root growth. However, increasing presence of mycorrhiza may not enhance root establishment on all trees (Ferrini, 2017).
· Mulching with compost – Mulching trees with course compost gave better growing results compared to pine bark mulch. Weed growth was significantly reduced in years 1 and 2. Recommended not to use over 10cm depth of course compost mulch extended out to the extent of the tree canopy (Ferrini, 2017).
· Sealing soil on newly planted trees – Different growth rates are seen when identical trees have differing types of hard standing around their root zone. The experiment sampled the effect of no hard standing, porous pavement, permeable pavement and impermeable hard surfacing. Growth rates were lower when a tree is surrounded by impermeable hard surfacing and least impaired with no hard standing around them. Porous and permeable paving surrounding trees showed tree growth rates only slightly lower than no hard standing but growth is expected to reduce in successive years. Permeable paving has an 83% reduction in ability to pass water as it gets filled with detritus (Ferrini, 2017).
From this contemporary research, Jayne and I have increased our knowledge of tree planting and what trees need in order to grow well. Our tree planting proposals at Liz Lake Associates have always been important to the company and are regularly updated to incorporate the most recent scientific knowledge we find and are adjusted to suit the environment in which the tree will be planted. This can sometimes be challenging but we understand that trees are crucial to the urban environment and we will do what we possibly can to ensure that trees don’t just survive, but thrive.