Gettysburg battlefield; now under attack by emerald ash borer (from Faith Campbell’s blog post)We don’t often talk about the Eastern forests, but Faith Campbell has an interesting post about regen in eastern National Parks. Faith examines and puts in context a paper by Kathryn Miller and colleagues.
Kathryn Miller and colleagues (full citation at end of blog) have published a study that examined the status and trends of forest regeneration in 39 National parks from Virginia to Maine. Four-fifths of the forest plots in the study are classified as mature or late successional – so at first glance the forests look healthy. However, the researchers made an alarming finding: in 27 of 39 parks, forest regeneration is failing – either imminently or probably. Acadia National Park is an exception; it is the only park in the study experiencing healthy regeneration. They warn that without intense, sustained – and expensive! – intervention, these forests are likely to be converted to other types of ecosystems. [I blogged recently about findings regarding regeneration in eastern forests: here and here and here and here.
The forests’ understories have too few seedlings and – especially – saplings to maintain themselves. Worse, in many cases the seedlings and saplings are not the same species as the mature trees that form the canopy. The saplings are shorter species that never reach the canopy. That is, species like pawpaw (Asimina triloba), American holly (Ilex opaca), American hornbeam (Carpinus caroliniana), and eastern redbud (Cercis canadensis) are regenerating, rather than the oaks (Quercus spp.), hickories (Carya spp.), maples (Acer spp.), and pines (Pinus spp.) that constitute the canopies of mature forests in these parks.
It sounds like species that do well growing in understories are doing well, and species that need light and bare mineral soil to become established are not doing so well. In many places in New England, stands regenerated post-agricultural clearing. If you want certain species, it seems like you may have to manage to get them back. But this paper seems to imply the interesting idea that “what used to be there” is what should go back… even though “what used to be there” might just be an artifact of the stand history.. and influenced by non-Indigenous as well as Indigenous residents of these landscapes.
Miller and colleagues call these “regeneration mismatches.” In about half of the parks, these native canopy tree species make up less than half of current saplings and seedlings. This situation suggests the forests’ species composition will shift substantially, thereby undermining resilience in the face of other challenges, such as invasive plants and pests and climate change.
I think the idea that any shifts will ipso facto undermine resilience is questionable. A few concepts to consider: invasive species have been a separate problem from climate change (that is, climate change in the current anthropogenic global warming sense). One can imagine that invasive species could do better (or worse) as the climate changes (whether due to human or other factors). We can also imagine that invasive species could make ecosystems more or less resilient to climate change.. depending on how you define resilience (some green stuff covering the soil? specific species in specific places they used to be?).
Let’s think about a western situation, say, there’s a great deal more true fir than ponderosa pine regen without intervention. If a forest went to true fir, would it be by definition less resilient to invasive plants, pests and climate change? Now with true fir, we have a good history of their tendencies to succumb to native diseases and insects, and we think conditions will get drier due to climate change, and they won’t like that. In fact, there wouldn’t be so many of them around except for fire suppression and in some places the removal of overstory pine.
Of course, in the East, deer and invasive plants are also a problem.
Many of the parks experiencing the most severe impacts of chronic deer browse also have the highest invasions by non-native plants. A natural process of regeneration occurs when the death or collapse of mature trees create gaps in the forest canopy. Where deer and invasive shrubs overlap, this process is often hijacked. Instead of nearby native tree species accelerating their growth toward the canopy, thickets of invasive shrubs crowd the space.
For this reason, Miller and colleagues recommend that park management prioritize treating invasive plants in canopy gaps of disturbed stands to avoid forest loss. They recommend deliberate creation of canopy gaps to promote resilience only for parks, or stands within parks, that have low deer and invasive plant abundance or the capacity to intensively manage invasive plants in gaps.
The authors also recommend actions to open the canopy or subcanopy to facilitate growth of saplings belonging to desired species. They caution that deer predation must be controlled. Furthermore, either invasive plant cover must be low, or management must ensure that that the park has sufficient resources to sustain an invasive plant control program – especially if invasive plants are combined with abundant deer.
Parks experiencing compositional mismatches and that are dominated by oak–hickory forest types might also benefit from prescribed burning. Again, deer browse pressure must be minimized. In addition, regeneration of oaks and hickories must already be present.
It seems like they are saying “if you want early successional species, you need openings (plus protection from deer)”- seems like “leaving mature and old growth alone” as a strategy may have unintended (albeit predicted, based on forest ecological knowledge from the 1970’s) negative consequences.