Trees and the Public Realm - Westminster City Council

Trees and the Public Realm (Draft) Page 27
51. The lifespan of trees varies considerably and many species have shorter than average
lifespans in the urban environment. Some like birch and cherry are relatively short-lived,
with a typical lifespan of 50 to 80 years. Others, most notably oak and plane, have
potential life spans of two centuries or more. Whilst it is possible to remove any tree, it is
worth noting that the removal of older and large trees, even for reasons of safety, can
be contentious.
52. The age of trees is increasingly of relevance in the preservation of boulevard or avenue
planting. Such planting has the best impact when trees are approximately the same
size. Conversely, if many trees die in a small space of time then the boulevard effect
will be potentially lost for decades. Fortunately, Westminster’s stock of mature planes
have 50 years or more of life remaining although it is likely that tough decisions on
whether to pursue a balanced age structure will need to be made in the future.
53. It is also worth noting that the shape of trees changes over time, depending on species.
Young trees often exhibit strong characteristics of “apical dominance”, in that they have
a central leading shoot and a crown shape that is compact and narrow. As the tree
matures the crowns of many species become broader, branches less upright, and
wider-spreading with the passage of time. It is therefore important that these changes
to shape and size over time, sometimes a very long time, are anticipated and factored
into the design requirements and choice of species. Larger species that tolerate
pruning are particularly valuable.