Social-ecological memory revisited: Human (re)learning and the persistence of oaks
In a previous Watershed post, I explored the concept of social-ecological memory through an examination of the presence of tallgrass prairie plants in a local cemetery. As a reminder (and if you’ll again pardon my ecologically based terminology), social-ecological memory can be defined as the collective memory of management practices that sustain ecosystem services within social-ecological systems, which are inextricably linked and interdependent systems of people and nature (Barthel et al. 2010). Crucial to the maintenance of social-ecological memory are social and ecological memory carriers—the repositories and structures by which social-ecological memory is transported through space and time (Anderson & Barthel 2016). This post considers the generation, loss, and rediscovery of social-ecological memory in oak–hickory forests of eastern North America, paying special attention to human land management practices as social memory carriers and oak populations as ecological memory carriers as well as the effects of interactions between these carriers on social-ecological memory. However, before I get to memory, some history is needed.
Although oaks were once dominant canopy-level trees throughout eastern North America, they have been in widespread and steady decline since the early twentieth century. These declines are attributable to a number of factors, perhaps the most important of which is decreased fire frequency. In short, oak woodlands and forests are fire-dependent ecosystems, and without frequent fire, open-canopied oak woodlands transition to closed-canopied forests composed of more shade-tolerant tree species. This replacement of oaks with non-oaks first occurs in forest understories at the developmental stages of seedling and sapling. Then, as mature oaks in the forest canopy grow old and die, there are no younger oaks to replace them, and the forest as a whole drifts away from its oak-dominated state.
Although described above in purely ecological terms, the waxing and waning of oak dominance in eastern North America has been largely driven by human activity. Through centuries of active fire setting, Indigenous Americans gave oaks a long-term competitive edge over their shade-tolerant—but fire-intolerant—competitors. By promoting the survival and reproduction of mast (i.e., acorn) producing oaks and the numerous species that rely on them for food, Indigenous cultures structured ecosystems at a sub-continental scale. Early Euro-American settlers also actively set fire to eastern North American landscapes, but this burning was paired with land-clearing for the provisioning of fuel, building materials, and space for agricultural production. Oaks were quick to resprout and grow into dense forests following initial clearings; however, as settlement progressed, strict policies of fire suppression were adopted, which pushed forests into shade-dominated states that were inhospitable for oak regeneration. In sum, differences in the predominant land management practices of Indigenous and Euro-American cultures pushed eastern deciduous forests in opposite directions—between extremes of open-canopied oak savannas and woodlands on one end, and dense, close-canopied forests dominated by non-oak species on the other.
By the early twentieth century, widespread oak declines were beginning to be evidenced throughout eastern North America. However, it took scientists at least another 50 years to discover—or perhaps rediscover—exactly what was behind the ‘problem’ of oak regeneration. Euro-American settlers encountered dense forests with oak-dominated canopies in eastern North American landscapes. In light of these consistent, widespread observations, early American ecologists hypothesized that oak–hickory forests constituted a climax stage, toward which all regional ecosystems would trend in the absence of disturbance. The problem with this perspective was that it ignored the potential for alternative stable states in these ecosystems (e.g., savanna vs. woodland vs. forest), and in doing so overlooked the ecological effects of frequent and widespread Indigenous burning. With this ‘new’ knowledge, contemporary foresters and ecologists have begun reintroducing fire to eastern deciduous forests in order to promote oak regeneration and thereby retain oak dominance. However, the effectiveness of these management actions in restoring oak forests and woodlands may largely depend on the degree to which the memory of oaks has been retained in these systems.
Oaks are frequently used as examples of ecological memory carriers, but which of their characteristics confer them with this potential? First, oaks are long-lived and therefore have far-reaching memories. For instance, the oldest documented tree in Fontenelle Forest, just southeast of Omaha, is an approximately 300 year old bur oak (Ratzlaff & Barth 2007). In this particular location, the human actors forming the social components of the social-ecological systems that this tree ‘remembers’ could range from contemporary elementary school students on field trips, to the Lewis and Clark expedition that camped nearby in 1804 (when the tree was already 80 years old), to the Omahas and Otoes who possessed and interacted with the land as the tree grew from an acorn into a seedling. In addition to longevity, oaks are capable of withstanding frequent disturbance. Instead of allotting a large proportion of their energy to aboveground growth during early developmental stages, oaks build extensive root systems, thick bark, and xeromorphic leaves. Although the aboveground memory of an oak seedling may be temporarily erased in a disturbance, its underground assets increase its potential to survive and resprout the following year. Finally, as mast (i.e., acorn) producing trees, oaks maintain mutualistic relationships with other organisms. For instance, acorns provide birds and mammals with an energetically dense food source, thousands of which they cache in the surrounding landscape. Some of these stashed nuts inevitably escape consumption and grow into oak seedlings. Therefore, although the effects of fire suppression have stressed oak populations for more than a century, the persistence of oaks as memory carriers preserves a window for recovery. However, oak persistence can only extend the potential for recovery; achieving recovery necessitates interactions with the social memory carriers of human land management practices, which from the perspective of a 300 year old oak tree, likely appear erratic and uncertain.
In another recent Watershed post, Jonathan Carter thoughtfully engaged the phenomena of social memory retention and expulsion in the current U.S. political scene, drawing on Bernard Stiegler’s (2014) conception of primary, secondary, and tertiary retentions in storing and synchronizing memory within and across individuals. I was previously unaware of Stiegler’s work, but found Jonathan’s overview and application of it thought-provoking in the context of social-ecological memory. If I can make some comparisons, my treatment of social-ecological memory seems to be based in Stiegler’s secondary and tertiary retentions, as might be expected. But what exactly are these social and ecological retentions, and what are the implications of their rigidities and interactions with one another for social-ecological memory? In a broader sense, what might the persistence of oaks teach us about disturbance, memory retention, and restoration in other contexts? Perhaps this is an opportunity for some interdisciplinary (re)learning.
Andersson, E. and S. Barthel. 2016. Memory carriers and stewardship of metropolitan landscapes. Ecological Indicators 70:606-614.
Barthel, S., C. Folke, and J. Colding. 2010. Social-ecological memory in urban gardens—Retaining the capacity for management of ecosystem services. Global Environmental Change 20:255-265.
Ratzlaff, N.S. and R.E. Barth. 2007. Field guide to trees, shrubs, woody vines, grasses, sedges and rushes of Fontenelle Forest & Neale Woods Nature Centers. Fontenelle Nature Association, Bellevue, NE, U.S.A. 218 pp.
Stiegler, B. 2014. Symbolic Misery Volume 1: The Hyper-Industrial Era. Polity, Cambridge, U.K. 128 pp.