The Importance of Succession
When we include succession in our city landscapes, there is minimal need to replant trees as we continually do now.
By succession, we mean planting very young trees, including seeds, at the same time as we plant larger ‘now effect’ specimens in our streetscapes and homescapes.
These very young trees are planted right beside the ‘now’ trees and so benefit from the shade provided by the older trees. This enables a full and ‘normal’ root system to grow into the surrounding soils. Those of us who are familiar with planting very young trees in cities know that these young trees will quickly (often in less than 10 years) catch up and outgrow the traditional nursery-grown tree, usually planted at a larger size. This is because the root system of a larger tree has been heavily pruned so that it is less likely to go through transplant shock; however a consequence is that it only slowly adapts to its final home – if at all!
In contrast, young trees (especially when planted as seeds) will have minimal shock and so quickly grow an extensive root system, including the taproot which is so fundamental to a tree’s long life, and will have minimal maintenance needs. The tap root and its essential importance are another discussion we will have soon!
In these pictures of a naturally occurring woodland – where selective logging has removed large trees (but not all) – so many seedlings have sprung up that we recognize that it is a healthy forest landscape which has needed no effort by mankind.
Also, there are many species of tree here because it has not been replanted to be a monoculture for future ‘harvesting’. This diversity means it is not vulnerable to disease – only individual trees may be affected. But the most important benefit is in the soil – the symbiotic relationship between mycorrhiza and the young root systems is intact and ALL the trees are healthy and focused on competing for sunlight. Thus, a solid canopy is re-established within 10 years after the removal of the mature trees. If we compare this to a city scenario where development leaves few mature trees and the soils have poor or no mycorrhiza present, then it is even more imperative to anticipate and include the benefits of succession when creating planting designs. In this way, we can bring trees back into an often sterile city hardscape. And the long term cost savings are highly significant! Additionally, there is very little ‘upfront’ investment cost at the time of planting. This is because seeds or saplings are minimal in cost and simple to install. It does, however, require a different, but simple knowledge base rather than that which is presently taught or considered ‘normal’. When we look again at these pictures, we see a healthy group of young trees who will provide a city with the pleasure of once again being focused on nature and the wonder of how nature can grow such amazingly long-living life forms that are trees. And that as a group, they form small woodlands that we see are clearly happily living together. This contrasts with the traditional specimen tree planted in isolation – which rarely becomes a long-lived and happy tree! Trees like to be planted close together and they do especially well when planted as seeds.