At the end, I am at home in the woods
Very few Sitka alders established during the first two decades after the retreating Muir Glacier exposed my youngest study site (Site 1) at Glacier Bay. Older sites in Muir Inlet had abundant alder plants by the time the surface was 20 years old, and it seems likely that the difference was caused by a shortage of alder seeds arriving at the young site. Today there are a few alders at Site 1, and what they have done (or not done) in the last three decades suggests a more nuanced explanation.
The young vegetation on the north side of Upper Muir Inlet in Glacier Bay National Park is developing dramatically differently from older vegetation a few km away. Today, five decades after the retreating Muir Glacier exposed my youngest study site (Site 1) to plant invasion, it supports an open shrubland of willows with most of the ground still carpeted with low-growing Dryas drummondii. At the same age (in 1995), the next older site (Site 2) had no Dryas and was a dense thicket of 6 meter tall Sitka alder shrubs. The distinct successional pathways being followed at these sites have critical ecological differences (e.g., alder is an important nitrogen fixer) and suggest that inferring ecological change from a sequence of different aged sites in this part of Glacier Bay does not work.
My favorite hypothesis to explain this is that early seed rain of alder differed between the two areas. Ice margins in Glacier Bay have been retreating to the north for almost three centuries, and invading newly exposed terrain requires that plants can migrate as fast as the ice retreats. Alder was apparently doing a good job of chasing the ice along most of Muir Inlet where my reconstructions of invasion histories at four study sites confirm that alder was an important early invader.
Continue reading “When alder can’t keep up”
I was able to get some aerial photos of most of the plots after I had marked each seedling with pink flagging. I flew a dual camera KAP rig with normal and infrared-modified cameras lofted by a kite. I will be experimenting with false color IR (NRG) and NDVI images which can be created with information from both cameras. Continue reading “Sprucing up the hills”
