Jack Pine, Mack Lake, and waxing poetic on CWD

This summer, I spent six weeks visiting the jack pine (Pinus banksitna Lamb.)  forests of the Highplains in northern Lower Michigan. My research goal is to quantify how the different jack pine-dominated ecosystems on the landscape continue to change following a 1980 wildfire.  Combined with last summer, this adventure has involved a lot of bushwacking, transect-rolling, tick-checking, second guessing, hunch confirming, tree measuring, note-taking, botanizing, and bonding with some awesome field assistants. It has been a ton of fun.

20170727_125540

Maybe you have heard of Kirtland’s warbler (Setophaga kirtlandii Baird) or the Mack Lake burn on the podcast Radiolab (https://www.wnycstudios.org/story/91723-weighing-good-intentions/)? This story of a prescribed-fire-gone-wild is a dynamic one – bringing sadness for the family of a brave firefighter who lost his life, and fear of wildfire for the nearby homeowners, while creating opportunities for jack pine trees whose cones open after fire, abundance for the endangered songbird who relies on young jack pine trees for habitat, and challenges for land managers who want to mimic natural habitat without fire.  Because I work out of lab that classifies land into ecosystems based on vegetation, soil and physiography, I am focusing here on the fire-prone jack pine, the groundcover that accompanies it, the sandy soil it all persists in, and the moraines, kames, channels, and outwash plains that house the soil. Our lab also seems to employ a “spaces over species” attitude about conservation (see Barnes, 1993).  My take on that is: protecting one endangered bird, or a game bird, is cool, but if we can protect the spaces and systems they occupy, we can do a lot more.

Working on this project so far has given me 1) the chance to return to the jack pine as a graduate student, looking at things more closely than I did as an undergraduate on my first field job, and 2) the opportunity to analyze three time periods’ worth of data for multiple permanent plots! My predecessors from the 1980s had the good thought to mark their sampling plots for future study with rebar. They were interested in how young naturally-regenerated forests differed in their speed and quality of providing habitat for the endangered Kirtland’s warbler (Zou et al., 1992). These study plots were revisited and expanded in 1996 to formalize their ecological classification (Walker et al., 2003), and again the next decade to marry the rebar with GPS coordinates for more reliable use in the future.

Even with a GPS unit and maps, re-locating these plots was harder than I thought. Rewarding at times, yes – to magically look in the right place and see a rebar standing amidst the brush after a long walk was cause for celebration. But frustrating or downright head-scratching at others – some plots revisited to no avail have had their paperwork cast to the back of my trapperkeeper, their hauntings cast to my bug-bitten stress dreams. But, last year, I managed to relocate thirty-nine of the plots before the bracken fern emerged, and discovered two more this spring.

Each rebar marks the northeast corner of a 200m^2 sampling plot. My field assistant helped me collect data at each plot on stand structure (density of live trees, other species besides jack pine present, how many are considered overstory or understory) and groundcover composition (how many species of groundcover, how do they vary in abundance, and are the ones we think have special site indicator powers present?).  This year, another field assistant*  has been helping me complete fuel surveys at each plot, using the rebar as the intersection of two perpendicular 50 m transects. For this, we quantified density of fine and coarse woody debris, as well as the amount of duff and litter atop the soil, and the abundance of live and dead vegetation.  Once analyzed (next adventure!), all this data should help managers better understand successional pathways and subtleties of the different jack pine ecosystems, as well as predict future fire behavior.

* Field assistants are awesome! I literally could not do it without them, and each fellow ecology researcher brought her own keen awareness to the project. *

 

 

The puzzle pieces of the bigger landscape picture are slowly coming together for me. I suppose it will continue to do so as I analyze, present, and write.  So this entry is one form of practicing my answer to the question: How is the forest changing? The most obvious answer to me is that there is probably more downed woody debris! I have spent a lot of time this summer counting twigs and measuring logs. It is interesting to shift perspective from the green vegetation around me to something most folks would consider dead. Franklin et al. (1987) point out that what is dead and what is living isn’t always so clear. They write, “In a live conifer, only about ten percent of the cells are actually alive: the leaves (three percent), inner bark (phloem and cambium, five percent), and ray cells in sapwood (two percent). Some processes associated with dead trees begin while the tree is still alive. For example, fungi are already at work rotting the woody material, and animals excavate the dead parts of living trees. In contrast, a dead tree or log in an advanced state of decay may include a considerable number of living cells, as much as 35% of the biomass may be live fungal cells alone (Swift 1973).”

 

 

Some of the woody debris I’ve measured was relatively fresh from wind throw, disease or rot.  Other downed wood is old, probably killed in the Mack Lake Burn but persisting as a dead snag until it was time to fall. And still other downed wood is even older, hidden in the soil, transformed, and decomposed. These coarse woody debris (CWD) and snags are important all throughout a tree stand’s life, from the time immediately after a fire to the development of a mature, closed canopy. Human tripping hazards? Sure. Aesthetic concerns? Depends on your definition of beauty. Ecosystem value? Definitely! Consider Yellowstone National Park (YNP) following the 1988 wildfire. CWD is very influential there, according to Tinker and Knight, who write:

“As the snags continue to fall in YNP and as new forests continue to develop, eventually removing from sight all of the CWD created in 1988, most park visitors will soon forget the forests of blackened trees. However, the dead wood on the forest floor persists for many decades, occupied by a plethora of living organisms and influencing numerous ecological processes. Some of the CWD will burn in the next fire, but much of it slowly contributes to the soil on which future generations of trees will depend – a process that has been underway for millennia, and one that depends on a rich array of forest organisms that most people never see.”

20180726_100249July26_2018

Downed wood and snags are important for succession because they create habitat, shade, and nourish the soil when they decompose. I expect the amount of  CWD to vary by ecosystem type. As Franklin et al. (1987) suggest, “The variety in patterns of death among tree species reflects such factors as differences in life-spans, vulnerability to various agents, and distribution in the landscape.” Perhaps there will be more CWD where ecosystem characteristics favor shallow rooting or wind throw. Franklin et al. (1987) add, “Tree mortality has important implications for succession because the individuals it removes may not be replaced.” So what species replace the fallen trees with time and no fire  – oaks, aspen, maples – is a factor my research will consider, too. In the meantime, perhaps you the reader will be moved to take a closer look at the ground on your next ramble through a forest. Hopefully, too, you will carry a deeper appreciation for all the seen and unseen contributions of a mossy log.

Papers Cited:

Barnes, B. V. (1993). The landscape ecosystem approach and conservation of endangered spaces. Endangered Species Update, 10(3&4), 13-19.
Franklin, J. F., Shugart, H. H., & Harmon, M. E. (1987). Tree death as an ecological process. BioScience, 37(8), 550-556.
Tinker, D. B., & Knight, D. H. (2004). Snags and coarse woody debris: an important legacy of forests in the Greater Yellowstone Ecosystem. After the fires: the ecology of change in Yellowstone National Park. Yale University Press, New Haven & London, 279-98.
Walker, W. S., Barnes, B. V., & Kashian, D. M. (2003). Landscape Ecosystems of the Mack Lake Burn, Northern Lower Michigan, and the Occurrence of the Kirtland’s Warbler. Forest Science, 49(1), 119-139.
Zou, X., Theiss, C., & Barnes, B. V. (1992). Pattern of Kirtland’s warbler occurrence in relation to the landscape structure of its summer habitat in northern Lower Michigan. Landscape Ecology, 6(4), 221-231.