The question may seem esoteric, but if we’re looking at plants to provide landscape functionality and to do that in a low maintenance way, understanding basic principles through the eyes of ecologists could be insightful. So why would a plant choose to take on the form of shrub from an evolutionary/ecosystems standpoint?
In an open source article in Frontiers in Plant Science ecologists make four hypotheses:
1—The multiple stems of a small shrub give faster growth than a small tree. They believe shrubs have higher growth than small trees with the same amount of above ground woody volume. Shrubs have more cross-stem area, which should mean more sapwood and therefore more leaf mass than a small single-stemmed tree. Shrub stems also enable greater bark photosynthesis, especially in leafless periods, after drought or defoliation by insects. Greater bark area also translates into greater area for buds to sprout and theoretically a greater canopy. Shrubs also have the ability to sprout horizontal branches, thus producing leaves that don’t shade other portions of the plant and can result in faster growth. These ideas were for the most part supported in a literature review of 14 studies.
2—The fast maturity of shrubs enables earlier seed production compared to trees. Theoretically this would enable seed from shrubs to germinate and occupy open patches on disturbed land, giving them an advantage.
3—The multiple stems in shrubs insure future survival and growth if one or more stems die. Shrubs can lose some branches and still survive.
4—The short stems of shrubs improve survival compared to tall tree stems. Low growing shrubs are less affected by storms or snow than trees.
“Shrubs seem to survive by combinations of fast growth and persistence, including early seed production and long-distance dispersal.”
Shrubs haven’t been studied as often as other plant types. Why are then neglected? The authors speculate that it might be because they’re hard to define. Terms used to describe them are oftentimes negative: thicket, scrubby, etc. Shrubs dominate some types of habitat. The authors ask if trees have become more important in some climates because of human intervention/exploitation.
Horticulturally shrubs are extremely important, to the detriment of larger plants in today’s more confined residential landscapes. Shrubs seem to have evolved to compete and win. Seeing a space through the eyes of a plant can be insightful.
NewTerrain October 17, 2016.