This week was our 8th meet-up of the SCRAP online reading group–the last we are hosting before we take a summer break for the month of July. Thank you to all who have joined us over the past 8 meet-ups. A very special thank you to the 11 participants who joined us this week to discuss a review article chosen by Marieka Brouwer Burg, focused on the question of human-landscape interactions in the ancient Maya world. You can find below the summary and discussion questions provided by Marieka. We wish you all a wonderful and safe summer break, and we’ll see you back for reading group in August (date and reading TBA)!
Tim Beach, Sheryl Luzzadder-Beach, Duncan Cook, Nicholas Dunning, Douglas J. Kennett, Samantha Krause, Richard Terry, Debora Trein, Fred Valdez. 2015. Ancient Maya impacts on the Earth’s surface: An Early Anthropocene analog? Quaternary Science Reviews 124:1-30.
From a broad regional perspective (the entire Maya Lowlands), the authors of this article tackle the question of human-landscape interactions, with a specific focus on the impact of ancient Maya anthropogenic activities on the environment. They highlight the importance of establishing a firm understanding of shifting environmental conditions over the longue-durée in order to fruitfully investigate the rate and scale of human impact/s. The temporal scope of the article is on the Early Anthropocene; in Central America this period has been dubbed the “Mayacene” (3000–1000 BP) because it has been previously demonstrated that the ancient Maya impacted much of their environment in profound and irreversible ways. This article synthesizes the results of many studies that have employed a variety of methods to detect fluctuations in environmental variables through proxy data, including pollen and plants macroremains, transported sediment loads, altered soils, animal remains, human osteological material, artifacts, and computer models of climate and land surface change. Some new data is also reported on Maya-period soil strata.
Six stratigraphic markers (or ‘golden spikes’) distinguish the Mayacene, all of which are connected in some way to increased anthropogenic burning. They are:
- “Maya Clay” – clay rich facies dated to the Maya period in depositional environments (triggered by upstream disturbances that increase sediment transport and deposition downstream)
- ‘Mayasols’ – anthropogenic paleosol sequences that reflect changes from stable to unstable circumstances (may be depositional or erosion, indicative of human land-use change)
- Carbon isotope ratios (show increased 13C in depositional sediments dated to Maya period as a result of deforestation)
- Anthropogenic building materials and landscape modifications (mostly limestone and derivatives)
- Chemical enrichment of soils (mostly in Phosphorus and Mercury, other heavy metals)
- Maya-induced climate change (prompted, in part, by widespread deforestation)
After defining the range of environments and ecosystems in the Maya lowlands, the authors spend the bulk of the paper describing the variety of methods used, and results of, other studies that have investigated human-induced landscape change. I’ll briefly summarize the take-away of each section below:
|Mayacene climate (pg. 9)||Various dry events have been documented through different proxy data – what seems be apparent is that Maya deforestation (+urbanization and wetland farming) did, to some degree, drive regional and global climate changes (through changing albedo, increasing greenhouse gas emissions, atmospheric particulate matter and evapotranspiration)|
|Impacts on vegetation (pg. 9-10)||What can current forest composition tell us about the past? Legacy of impacts continues to today because of alteration of soil parent materials and slopes by terracing. Outside of cities, ecosystem impact still clear where there was severe erosion and sedimentation – ancient Maya colluvium chokes river valleys and has changes stream flows and ecosystem processes. Seems there was both intensive farmscapes that clear cut wide swaths of forests, but also were large areas where careful forest management was key to produce large beams. “Garden city concept”: patchwork of forests, fields, and successional plants surrounded Maya sites|
|Zooarchaeology (pg. 10-11)||Little information now to make any broad conclusions; research on human health status appears mixed. Copán study (Steckel and Rose 2002) suggest very poor health but a broader comparative study of remains from the Maya region (Wright and White 1996) does not show evidence of any apparent decline in nutrition or health based on urban/rural residence or over time|
-Limnological change (pg. 11)
|A number of studies focused on the Central Petén lake basins (and even as far north as Michoacán, MX)–using cores and seismic imaging–have shown that when ancient urban populations reached local and regional carrying capacity, the impact on vegetation, soils, and hydrology was significant; “even low numbers of people can have profound consequences with respect to soil erosion” (11). We might expect that the extreme climatic fluctuations of the Postclassic would also have driven some of this change, but the evidence pales in comparison to the environmental changes that were triggered by human modifications|
|-Wetter bajos and Maya-induced desiccation (pg. 12)||There’s quite a lot of variability in bajo hydrology, soil, and vegetation. They may have been preferred locations for the Maya, or not, given their specific circumstances. In fact, “the environmental histories of individual bajos have varied greatly” (12) meaning that we can make very few generalizations about their use in the past, or how they were impacted by human behavior. Many smaller bajos seem to have undergone desiccation with deforestation, while some large bajos were actually improved in terms of their arability through deforestation (see Figure 7)|
|-Wetland fields, canals, dams, and diversions (pg. 13-14)||Various different forms (irregular, cobweb, and rectangular); generally a Classic-period phenomenon. Generalized profile (bottom to top): “Archaic or Preclassic paleosol buried under 1-2m of gypsum and fine sediments with an intervening Classic-period paleosol at 50-100 cm below surface” (pg. 14, Figure 9)|
|-Fluvial valleys and floodplains (pg. 14-16)||Little research has been conducted on characteristics of the seven major fluvial systems of Central America. The authors have studied the Rio Bravo in NW Belize in detail and found that sedimentation increased 2x during the Classic period, likely as a result of deforestation and increased erosion due to land clearance, although the trigger for this increase may have begun before the period. Other research discussed for the Upper Belize, Xibun, Motagua, and Usumacinta River Valleys|
|Water management features (pg. 16-17)||These were important because of the bimodal precipitation patterns in Central America (rainy/dry seasons) – Maya had specific water management strategies for both seasons. Some research has been done on the many different types of features (reservoirs, dams, canals, wells, chultunob, terraces, aguada fills), indicates that local and regional needs dictated extent and type of water management features constructed. Functions included storage/preservation of water quality, defense, erosion/flood control, aquaculture, ritual. Also interesting to note that some naturally occurring features may have been passively utilized earlier on and later more actively managed. Hot off the press article on water quality and decline of Tikal! https://www.nature.com/articles/s41598-020-67044-z|
|Lithospheric impacts (pg. 17)||Includes soil impact, quarrying, and Maya building and other use of stone (plaster, etc.)|
|-Mayasols: soil impacts (pg. 18)||Anthrosols (human-induced soils) have been found throughout the Maya world, but the piecemeal nature of these soils is curious – in South America, for example, there are large tracts of terra preta humanly-enriched, nutrient dense ‘black earth’ soil. In Central America, this kind of rich soil is found on/near large urban sites (i.e., at Chunchucmil and Mayapan) as well as at coastal salt production sites (Marco Gonzales and Wits Cah Ak’al)|
|-Slope Sequences (pg. 18-20)||“Mayacene” produced Mayasols and Maya Clay in lowlands; in uplands, karstic processes (internal runoff) took place under forests until deforestation resulted in fluvial runoff, erosion, aggradation, and less groundwater infiltration|
|-Ancient Maya terraces (20)||-multiple types and functions of terraces. Studies are indicating they were used earlier than previously thought, and more extensively. Lidar has successfully revealed terraces in some places (around Caracol), but other methods (excavation) can also yield evidence. Would have provided some slope conservation (although still need to study whether their presence directly led to decreased erosion); other slope conservation techniques may also have been used (forest conservation, vegetative berms)|
|-Geochemical markers in Mayasols (pg. 20-22)||-while human occupation leads to changes in the amounts of many elements, phosphorous (P) has been most thoroughly studied. Typically, the soils of Central America have low P concentrations but this increases markedly with human occupation, providing a clear “chemostratigraphic” marker of the Mayacene. As yet, it’s unclear which anthropogenic activities lead directly to increases or decreases in P levels: agriculture, for example, can both concentrate and deplete soil P: “heavy maize production without fertilizer depletes P in soil, whereas growing legumes and fertilizing enhances P levels even though legumes do not fix P as they do N” (21). Overall, however, there is a correlation with elevated P levels and ancient Classic Maya sites. It is important to note that later (Classic) P levels have the potential to overwrite earlier signatures and thus analyzing lake sediment cores with an eye for changing P levels is critical. For now, it appears that “P levels began to increase above long-term ‘natural’ background levels as early as c. 3000 BP (Preclassic), but reached their late Holocene peak c. 1000 BP (Late Classic)”|
|-Carbon isotopes in dated profiles (pg. 22)||SOM: soils with organic matter? The rest is gibberish to me J Hopefully Sam can explain.|
|-Sites: slope sequences (pg. 22-23)
-Agricultural terraces (pg. 23)
–aguadas (pg. 23)
–bajos (pg. 23)
-Floodplains (pg. 23)
Wetlands and wetland fields (pg. 23-24)
|The concentration of 13C isotopes at different points in a slope as a way to determine what was going on there in the past, what was growing in those soils and what kind of erosion has taken place… distinguishing between 13C ratios of C3 and C4 plants. All comes down to how plants undergo photosynthesis and take in C plus photorespiration and stomata and other plant jargon. Most plants are C3 but some plants have figured out a way to avoid photorespiration by producing C4 instead and these include MAIZE, SUGARCANE, AND SORGHUM, all of which grow in Belize. When the authors looked at the ratio of C3 and C4 plants in wetlands, they found that “64% of the Late Classic vegetation was C4 species in areas that are today dominated by C3 tropical forests […indicating that] these fields were intensive farm systems” (24)|
The Mayacene stratigraphic markers are related to both positive and negative environmental changes, although it appears that the negative changes had profound degradational impacts that in some cases are still felt today in the region. Much more research is needed on environmental and climate change throughout the Maya period to fully understand the nuances of change over space and time.
- The authors note that the Mayacene had both “natural and human drivers” but that oftentimes, the static records we investigate today are equifinal, meaning that the end results appear the same. This scenario will obviously obfuscate understandings of which factor/s had a lesser or greater impact/s, so how can we begin to tease apart the differential impacts of human and natural drivers of environmental change?
- As a specific example: Space is given in section Ecosystems to the discussion of pine savannas and their derivation. Some researchers think they are natural while others argue they are a product of anthropogenic deforestation and burning. As I’m sure is the case for the Stann Creek area, and also in the BREA project area, we have lots of small interspersed pine savannas, which I had assumed were also around in Pre-Maya times. However, now I’m concerned (and also intrigued) that perhaps some of them may have been human induced by Maya activities. How can we determine savanna genesis at the local level?
- A comparison question for SCRAP: in the BREA area we have lots of evidence of raised fields and landscape modification in wetland environments, suggesting the importance of aquatic resources as well as sophisticated hydraulic systems for managing and diverting water (perhaps as a way to counteract fluctuations in precipitation during different climatic swings). Considering the extensive wetland fields in northern Belize (e.g., Chan Cahal, Birds of Paradise fields), our suspicion is that wetland modification was much more important and widely employed by the Maya than currently documented. Droughts in the past years have revealed more evidence in the form of satellite imagery to this end, which of course come with the need for ground-validation. What’s the evidence from the Stann Creek area?
- Modern-day vegetation patterns hold the potential to reflect ancient Maya forest and other agricultural/land modification practices. How could an archaeological research project attempt to understand some of these reflections? What are the tell-tale signs to look for in the modern-day environment? Stands of cacao seem to be the most obvious, but are there other forest mixes that could indicate past forest management?
- How can archaeological projects employ knowledge of paleosols and edaphic sequences to better understand the geomorphology of our areas? This is especially important for those of digging off-site or conducting non-site survey projects. I am thinking in particular about a trench excavation I conducted last January into a “dune”, expecting to find mostly sand, but was met with a much more complicated, sloped depositional environment. I needed a geoarchaeological eye but at that moment I had none. How can we better prepare ourselves as field researchers to understand our soil sequences in real time?
- Let’s say we are not working with a geoarchaeologist/palynology/paleoethnobotanist, but we plan (read: hope!) to work with one in future. What sorts of samples can we take while in the field that could be stored and potentially analyzed later for things like pollen, microbotanicals, trace elements, isotopic analysis, etc?
- The article doesn’t address how Mayacene activities may have actually improved preservation conditions in some locations. For example, we read a lot about how deforestation triggered slope erosion and increased alluvial deposits. Are sites located at the base of slopes thus better preserved? On the flipside, sites on hills or near slopes should be more exposed and prone to erosion. Could this help to direct salvage archaeology efforts and help us focus our efforts on sites at greater threat of erosional destruction?
- Is it appropriate to think of the ‘Mayacene’ as a construct equivalent in its broad-scale global impact as the Anthropocene? Scholars differ on timing of the Anthropocene, and there are a number who feel that it wasn’t until the Industrial Revolution that humans really began to tip global balances. Is calling the Maya-period the ‘Mayacene’ a form of exceptionalism?