Sycamore and Shumard Oak


Two common trees in this area are sycamore (Platanus occidentalis) and Shumard oak (Quercus shumardii). There are several specimens of both of these species on campus. Both grow to be large and impressive trees, but there are some serious drawbacks to having sycamores as specimen trees. The biggest one is that the wood is relatively soft, so branches break easily during storms with high winds. I have seen instances of large sycamore branches that have fallen on cars and houses, causing considerable damage. Also, sycamores have root systems that are shallow, so they will break up sidewalks and foundations of houses. I would never plant a sycamore near my house or driveway. There are also drawbacks to having oaks as specimen trees, the biggest of which is that they grow slowly, so it takes a long time for them to provide significant shade or cover.

One of the reasons that sycamore wood is soft is that it is a fast-growing tree. Fast growth is part of this species' "life-history strategy". Life-history strategy refers to the timing and rate of somatic growth and reproduction during the lifespan of an individual organism. Life-history strategy includes growth rate, age (or size) at reproductive maturity, overall lifespan, number and size of "propagules" produced, and whether propagules are produced once or repeatedly. Sycamores grow fast, don't live very long (for trees), mature early in life (relative to oaks), and produce large numbers of small propagules. Oaks, in contrast, have hard wood, they grow slowly, live a long time (200-300 years is not uncommon), don't begin to produce offspring until they reach a respectable size/age, and produce relatively small numbers of large propagules (acorns). These species (sycamores and oaks) represent two ends of a spectrum of life history strategy, commonly referred to as "r selected" and "K selected". What "r" and "K" mean in this context will be explored more fully in the days to come, but for now, "r" is the "intrinsic rate of increase", which measures how fast a population is capable of growing. So "r selected" refers to species that emphasize high reproductive rates and rapid population growth rather than stable, long-lasting individuals and thus populations. The alternative, "K", symbolizes the ecological quantity "carrying capacity", which refers to how many individuals the environment is capable of supporting. So "K selected"  refers to species whose populations exist at or near their carrying capacity, and are thus stable in size, with long-lived individuals, where high rates of reproduction and rapid population growth is not possible. We often think of "r selected" species  as inhabitants of unstable or unpredictable habitats (sycamore is most common in stream-bottoms that flood periodically), and "K selected" species as inhabitants of stable environments (oaks are common on hillsides and uplands that are rarely disturbed). "K selected" species are subject to intra- and inter-specific competition for resources (light, nutrients), so are better off producing fewer, larger offspring that start life with enough metabolic resources to effectively compete for limited resources. In contrast, "r selected" species are often in habitats where disturbance "wipes the slate clean", so these species emphasize ability to reproduce quickly and re-populate a habitat where there is little on no intra- or inter-specific competition.

Of course these life-history strategies make sense only when used in comparison to ecologically similar or phylogenetically closely related sets of species. Comparing oaks with sycamores makes some sense (they are both trees, so share similar ecology); comparing oaks with people, or people with ants, or ants with turtles, makes little sense. Also, any particular species is a conglomerate of adaptive characteristics, and may fall somewhere between the extremes of "r" and "K" selection.