Helping Forests Walk 04 B - Is this an Old Growth Pawpaw Patch? (Michigan, 2021)

Описание: The previous episode in this series is titled, "Helping Subcanopy Trees Migrate." There Connie Barlow suggests that a wild pawpaw patch she explored two months earlier has characteristics of "old growth." This video is therefore offered as a supplement, showing raw footage of that fruited patch along the Saline River near Milan, Michigan. It is a way for viewers to "explore" this same patch and then make their own interpretations. Do you think this patch may, indeed, be old growth? (Post your views in the comments.)

What are the signs of old growth? Connie didn't recognize these signs while she was exploring the patch — only later while editing the video. The key old growth characteristic she suggests in her subcanopy Episode 04 video is that, while pawpaw grows no taller than 30 feet, in the core of this particular patch there are no overstory trees shading them. Indeed, the amount of sun reaching the patch is strong enough to yield a total of 60 fruit visible from ground-level.

The way that subcanopy pawpaw can ultimately out-compete the overstory tree species and thereby assume the "canopy" position itself is a two-fold process. First, pawpaw spreads clonally by sending near-surface stems (rhizomes) laterally, which then pop up new vertical stems distant from the original. Pawpaw can grow vegetatively very well while shaded by a deciduous overstory; it just can't produce much fruit. But this species is very patient about reproducing. Overstory trees such as walnut and maple and hackberry eventually succumb to death by old age or windfall. But any of their own seeds that germinate and attempt to establish from their former sites will now be challenged by pawpaw putting the ground level into deep shade — too much shade for the overstory species to establish. Henceforth, the patch remains as the canopy itself. Patch stems last only half a century, max. But the cloning ability keeps popping up young ones within the patch's own shade.

Connie might not have arrived at this hypothesis had she not created a video a few months earlier that aggregated raw footage of native yew (Taxus) species in North America that she had filmed in previous years: HFW 03 - "Thinking Like a Yew"    • Helping Forests Walk - 03 "Thinking Like a...  

Go to timecode 40:36 of the yew video to see Connie talking about USDA information on Pacific Yew's "vegetative regeneration" whereby the yew "expresses climax sociological dominance over tall conifers." The method is similar to that of pawpaw, except yews do not produce lateral stems (rhizomes). Instead, they are masters of bending without breaking. So when a canopy tree or windfall branch smashes onto, say, a 25-foot-tall yew and pushes it over, the formerly vertical stem now stretches some 20 feet horizontally. Moreover, in the consequent sunlight, new "branches" emerge and grow upward, ultimately becoming new leaders themselves, while the original fallen trunk may itself sprout roots wherever it is in full contact with the soil.

Pawpaw's ability to send rhizomes laterally without requiring overstory treefall offers an even more assured opportunity for working toward "climax sociological dominance." And as Connie mentions in the previous (04) episode, it appears that the only place that the overstory tree species can keep re-establishing from seed is in the forest sections too often flooded with ephemeral pools for tap-rooted pawpaw to survive. But Black Willow, Cottonwood, Silver Maple, and perhaps Black Walnut can tolerate periodic flooding. So do look for that phenomenon when watching this video.

UPDATE Oct 2022: I've been editing the wikipedia page on Pawpaw (Asimina triloba) and learned that the same USDA site as for yew (above) confirms that pawpaw can dominate the "canopy": "Pawpaw creates heavy shade that reduces seedling recruitment of white oak (Quercus alba) and shagbark hickory (Carya ovata). In southwestern Illinois, an increase in pawpaw cover was attributed to defoliation of overstory trees by the linden looper. The pawpaw canopy suppressed seedling establishment of less tolerant species." The USDA webpage: https://web.archive.org/web/201106280...

Connie's interest in posting and linking to key documents and scholarly papers about THE ECOLOGY OF PAWPAW and its reproductive habits (and especially the mysteries of pollination and pollinators) has led to a very long and illustrated webpage, which she will continue to update: http://www.torreyaguardians.org/pawpa...

Previous episode in this "Helping Forests Walk" playlist is HFW 04 - "Helping Subcanopy Trees Migrate":    • Helping Forests Walk 04 - Helping Subcanop...  

An annotated, topic-organized version of this playlist (and playlists focused on single tree species (including Joshua Tree, Alligator Juniper, Coast Redwood) is here:
   • Helping Forests Walk (climate adaptation)