Saturday, May 20, 2017

Trees on the Move

Till Birnam wood remove to Dunsinane, I cannot taint with fear. -  Macbeth- William Shakespeare

Not since Shakespeare has there been talk about forests moving until now.  I received this Science Alert news article from Mike Chiles MN, highlighting research showing the "migration" of tree species over 30 years.  The trend is for northern migration of conifer species and westward movement of deciduous (broad-leaf) species.  It gives a good explanation of the factors of temperature trends and changing precipitation patterns as well as humans' land use.

One statement in the article puzzled me, that the "young trees were more likely to have made this migration than the older ones."What was meant by "young trees?"  The actual scientific article refers to "saplings" and gives a good explanation.
"It is not surprising that saplings have experienced a higher proportion and faster rate in poleward and westward shifts than adult trees, because new recruitments (that is, young trees) are expected to respond to climate change more quickly (23, 24). The observed differential shift rates could also be due to the fact that saplings are more sensitive to droughts in terms of survival than adult trees (25), as substantial drought was observed in the southeastern region of the study area during the study period. The differential shift rates among subpopulations in the four cardinal quadrants further confirmed that the observed range shift is primarily due to the changes in the leading edges of species distribution ranges, which agreed with early findings by Woodall et al. (23) of significant poleward shifts of seedlings for most of the northern species in the eastern United States."
"You can't teach old dogs new tricks."
It probably isn't so much a matter of teaching an old tree as it is young trees having more time to adapt.  The younger trees have a longer time to let natural selection occur.

After the last ice age, Missouri went through a long period of boreal reforestation before our oak-hickory forest developed.  We don't know the time frame of that shift but it is likely that humans had some influence with their use of fire.  Now we are at it again.