Cultural-ecosystem resilience is vital yet under-considered in coastal restoration

The persistence of economically significant and culturally unique coastal communities threatened by environmental change hinges not only on physical landscape management but also on human endurance and adaptation, conceptualized as resilience. In resilience theory, complex systems lack stasis and are characterized by change, dynamism, adaptation, and flexibility across multiple timescales, which is relevant from human generational to millennial landscape-archaeological records. Coastal environments are among the most densely inhabited and at-risk globally; archaeological sites provide the only millennial-scale records of human adaptation in North America and thus inform sustainable coastal engineering. Along the Gulf Coast, Indigenous shell and earthen mounds are persistent places contributing to cultural resilience and function as keystone landscape features that add elevation, visibility, and biodiversity within the low-lying MRD. The authors define "cultural-ecosystem resilience" (CER) as the intertwined dynamic whereby cultural practices depend on and shape natural forces to promote community stability. The study tests how CER manifests in a culturally significant coastal landscape—the MRD—by integrating archaeological records and Indigenous worldviews. Focusing on the Lafourche Bayhead delta, the MRD’s most recently abandoned subdelta, the study conducts three analyses: (i) interpret oral traditions of Gulf Coast and Southeastern Indigenous peoples regarding land selection and ceremony; (ii) quantify the relative relief of Indigenous mounds using LiDAR; and (iii) assess mound persistence and reuse via optimized chronologies and archival disturbance records, situating findings within the changing coast to inform management priorities.

Background synthesis emphasizes the MRD’s Holocene evolution through avulsing subdeltas (Teche, St. Bernard, Lafourche, Modern), natural levee formation, and the recent anthropogenic imbalance causing rapid land loss due to subsidence, canalization, and river-floodplain decoupling. Archaeologically, the Southeast US hosts some of the earliest North American monuments (e.g., Watson Brake, Poverty Point). Across 7000 years, earthen and shell mound construction remained central to lifeways in the Lower Mississippi Valley and coastal Louisiana. Coles Creek and Plaquemine cultures (ca. 700–post-1200 CE) along the Gulf Coast maintained hunter-fisher-gatherer lifeways with increasing sedentism, ceramic production, trade networks, and construction of mound-plaza complexes; notable sites include Bayou Grand Cheniere, Magnolia Mounds, Grand Caillou, Adams Bay, and Buras. Prior work links mound construction to natural land-building processes and settlement on natural levees. Recent geoarchaeological advances (OSL chronologies of Lafourche subdelta formation and site-level dating) allow refined coupling of deltaic geomorphology with archaeological site emergence, positioning. Despite extensive research on social hierarchy, ceramics, and site systems, explicit integration of sustainability, vulnerability, and resilience into Indigenous lifeways has been limited; this study addresses that gap by linking geology and cultural prehistory to evaluate CER.

The study employed three complementary analyses: (i) Oral traditions: Compiled published primary-source oral histories from Indigenous Gulf Coast and Southeastern communities focusing on ethnogenesis, world formation, and mounds, recorded by anthropologists or Indigenous community members/descendants. Excerpts were reviewed (see Supplementary Information) and synthesized to interpret cosmological meanings and landscape engineering implications of mounds (e.g., Earth-Diver narratives). (ii) Relative relief: Mapped coordinates of 36 pre-contact mound sites (from Chamberlain et al., 2020) in ArcGIS over State of Louisiana pre-processed LiDAR (2000). Recognizing LiDAR processing clipping of vegetated mounds, sites were categorized as: visible in satellite and LiDAR; visible in satellite but not LiDAR (clipped); not visible in either (likely destroyed). For visible sites, recorded elevations at mound summits and adjacent land; for clipped/destroyed-appearing sites, measured landform elevations at recorded site coordinates. Cross-checked LiDAR mound elevations with Site Record Forms when available. Excluded 7 sites outside LiDAR coverage; two sites had two mounds, yielding 31 elevation data points. Elevations are present-day NAVD88 and represent minimum site elevations due to subsidence; average bayhead-delta elevation likely a maximum due to water conversion bias. A site was considered to exhibit CER-related elevation if its landform elevation exceeded the average elevation within a 25 km² daily foot-travel range. (iii) Persistence age: Used optimized terminus post quem and likely construction ages for 36 sites (Chamberlain et al., 2020) and analyzed Louisiana Site Record Forms to determine first disturbance, destruction (if any), and disturbance agents. Excluded 3 sites for insufficient data. Verified present-day condition via site visits and Google Earth where possible. Calculated maximum persistence (destruction or present-day minus terminus post quem) and minimum persistence (last recorded minus likely construction age). Classified disturbance agents: erosion, industrial infrastructure, agriculture, intrusive historic cemeteries, domestic residences, other (e.g., shell mining, road construction), and unknown/not recorded.

• Oral traditions: Indigenous Gulf Coast and Southeastern narratives (e.g., Earth-Diver myths involving crawfish and birds) encode world-building and land-creation processes, paralleling deltaic sediment deposition. Mounds function as axis mundi linking cosmological realms and as engineered earthworks that materialize mythology while creating durable, meaningful, elevated places.
• Relative relief and elevation (LiDAR-based):
  • Average present-day elevation of natural land surface adjacent to mound sites: 0.74 ± 0.09 m NAVD88.
  • Average elevation within 1 km² viewsheds: 0.46 ± 0.06 m; within 25 km² daily travel ranges: 0.36 ± 0.05 m.
  • Average present-day Lafourche bayhead-delta elevation (LiDAR-covered area): 0.45 m.
  • On average, mound sites are on land 0.3 ± 0.1 m above their 1 km² viewsheds and 0.4 ± 0.1 m above their 25 km² travel ranges—differences comparable to the local mean tidal range (~0.4 m), conferring meaningful habitability advantages in a microtidal landscape.
  • 81% of sites are located on land naturally elevated above the broader surrounding landscape, indicating widespread selection of high-elevation landforms consistent with CER.
  • Average mound-summit LiDAR elevation: 1.95 ± 0.14 m (likely underestimated due to LiDAR clipping; archival records report mounds up to ~7 m above natural surface).
  • Estimated inland siting relative to coeval shoreline: with shoreline progradation 100–150 m/yr and site construction 200–400 years after land emergence, sites were likely 20–60 km inland when built.
  • No clear relationship between preservation status and site elevation/relief or distance to coast, implying additional drivers of site loss beyond coastal erosion/submergence.
• Persistence and disturbance:
  • All sites persisted at least ~5 centuries, typically to the late 19th or mid-20th century, after which disturbance accelerated, coincident with industrial expansion (notably oil and gas).
  • Recorded outcomes: 9 sites (27%) destroyed; 8 (24%) unverified with modern imagery/records; 16 (48%) verified extant in some condition.
  • Disturbance/destruction agents include erosion, industrial infrastructure (e.g., canals, oil and gas fields), agriculture (notable inland), domestic residences, intrusive historic cemeteries, other (shell mining, roads), and unknown/not recorded. Erosion and subsidence are concomitant and not differentiated.
  • Reuse as historic cemeteries is among the earliest disturbances; all such sites persist, suggesting high cross-cultural valuation and legal protections contributing to persistence.
• Overall: Earthen and shell mounds are persistent keystone features enhancing physical resilience (elevation, visibility, biodiversity) and cultural continuity; however, rapid 20th-century losses jeopardize CER for modern MRD communities.

The study set out to define and evaluate cultural-ecosystem resilience (CER) in the MRD by linking Indigenous cosmologies, archaeological monumentality, and geomorphic context. Findings demonstrate that Indigenous mound construction enacted cosmological narratives and created persistent, elevated hubs embedded within natural levee settings. Quantitatively, the preferential siting of mounds on land a few decimeters higher than surrounding landscapes provided significant daily habitability advantages in a microtidal delta, concentrating access to diverse ecotones within a day’s travel. Multi-century persistence and cross-cultural reuse (e.g., cemeteries) show enduring societal valuation, reinforcing mounds as keystone landforms where cultural and ecological functions coalesce. The lack of correlation between preservation and simple geomorphic metrics indicates that modern anthropogenic drivers—industrial infrastructure, canalization, and agriculture—are primary threats, aligning with broader mechanisms of MRD land loss. These insights directly address the research question by evidencing how cultural practices co-evolved with deltaic processes to foster resilience and by highlighting that omitting cultural archives from restoration planning overlooks critical, millennial-scale parameters of human–environment adaptation. Integrating archaeological records and Indigenous knowledge into coastal management can improve identification of restoration priorities, anticipate the socioecological consequences of engineering, and strengthen community resilience.

Cultural-ecosystem resilience encapsulates stabilizing feedbacks between cultural practices and physical environments in coupled human–natural systems. In the MRD, earthen and shell mounds materialized Indigenous cosmologies while providing functional elevation, inland siting, and access to diverse resources, thereby enhancing resilience. Quantitative analyses show that mound sites occupy naturally higher land with additional anthropogenic elevation, conferring meaningful advantages in a microtidal delta. The long persistence and frequent reuse of these features underscore their high societal value across time and cultures and support interpreting mounds as keystone landforms integral to landscape stability, biodiversity, and cultural continuity. Given accelerated 20th-century losses driven by erosion, subsidence, and especially industrial/agricultural activities, urgent protection of pre-contact sites is warranted. Coastal restoration efforts should explicitly incorporate archaeological sites and Indigenous perspectives as core components of sustainable landscape management and modeling. Future research should expand high-resolution geomorphic and chronological datasets, improve present-day condition inventories, and evaluate how integrating cultural archives into restoration planning affects ecological and social outcomes.

• Elevation uncertainties: LiDAR processing likely clipped vegetated mound summits, underestimating mound heights; site elevations are present-day minimums due to subsidence. Conversely, average bayhead-delta elevations may be overestimated because lowest-lying areas have converted to open water lacking LiDAR data.
• Spatial coverage: Seven of 36 sites fell outside LiDAR coverage and were excluded from elevation analysis; three sites excluded from persistence analysis due to insufficient archival data.
• Process resolution: Erosion and subsidence are concomitant and not differentiated in disturbance attribution.
• Temporal records: Louisiana Site Record Forms have sparse 21st-century updates, creating uncertainty in current site conditions and disturbance timelines; some sites may have been destroyed before systematic recording began.
• Verification constraints: Several sites could not be verified in modern imagery or via visits, limiting confidence in present status and persistence age estimates.