Southwest Agave Project

Discussion Question #1:
provides a look at the distribution of Zone 2 rockpile fields (cluster of blue polygons lower and to the left) and Zone 4 rockpile fields (blue polygons upper and to the right) within ecologically viable areas. As you can see in , rockpile fields are not dispersed evenly throughout the generally defined ecologically viable regions, but remember, as explained earlier, both cultural and ecological factors influence site location. Take a look at , which includes the habitation sites of both Zone 2 and Zone 4. Do you think there is a general relationship between distributions of rockpile fields and habitation sites in the two zones? If so, what is this relationship? Use to identify and discuss cultural factors that might help to explain the distribution of rockpile field sites.

Discussion Question #2:
Use , which includes the rockpile fields and habitation sites from Zones 2 and 4 as well as buffer lines demarcating the areas within 1 kilometer and 2 kilometers radii from habitation sites, to compare and contrast the spatial relationships between habitation sites and rockpile fields within Zone 2 and Zone 4 separately. Do you think that the distributions of rockpile fields and habitation sites in each zone support the previously mentioned hypothesis, which states that Early Classic Period inhabitants of Zones 2 and 4 followed different subsistence strategies? That is, are there significant differences between the patterns of the two zones, such as field size, field location, and distances from fields to habitation sites? Consider and discuss the general differences between relative sizes of fields and habitation sites in the two zones and distances between fields and habitation sites within each zone. Use buffer lines (purple = 1km radius around habitation sites and black = 2km radius around habitation sites) to gauge field distance from habitation sites. Which zone contains larger fields (on average)? Which zone contains fields farther from habitation sites (on average)? What do these settlement patterns say about the subsistence systems of the Marana Community Hohokam farmers in each zone; were they different? Finally, discuss possible (ecological and/or cultural) explanations why the settlement systems of the two zones might have been different and use spatial patterns from the view to support your reasoning.

Discussion Question #3:
depicts the major geologic landforms- along mountain fronts,
(Example: ) formed by streams transporting sediment from uplands, and left by the Santa Cruz River--of the southern half of the Marana Community. Mary Ann McKittrick (1988) determined landform boundaries by considering the elevation, topographic
, and soil condition of geologic deposits on aerial photographs and from field-testing. The same variables also aid in assigning relative geologic age ranges to the deposits. For example, due to sediment transport, erosion, and soil condition, alluvial fans with less relief and more developed soils are older than deposits with more relief and less developed soils.

Different types of soils have characteristics that influence the locations in which particular plants can successfully grow. Brief descriptions of the different deposits in are as follows:

M1 (red): oldest alluvial fans in the area, is well developed, occur close to
mountain fronts, medium-sized cobbles present
M2 (yellow): recently abandoned (by depositional processes) alluvial fans, caliche is only
slightly developed and discontinuous, occur away from mountain fronts
Y (green): active and recently active alluvial fans, lack caliche, flooding occurs
seasonally in broad channels, usually restricted to mountain fronts
Y/M1 (orange): mixture of Y and M1 deposits
Br (grayish-tan): bedrock and bedrock pediments
Ch (turquoise): historically active channel deposits, flooding and sediment transport are
frequent but not necessarily annual
Cha (dark blue): active stream channel, flooding and sediment transport occur seasonally
T1 (grayish-purple): lowest and youngest distinct stream terrace, poorly developed soils
T2 (khaki green): historically abandoned stream terraces, gravelly sand sediments
T3 (purple): narrow discontinuous stream terrace, weakly developed caliche

Like most plants, agaves have certain physiological features that adapt them to a specific type of ecological setting. One of the most notable features of this sort is their shallow, dense, and spreading root system. In arid environments, moisture is the most elusive and, therefore, most valuable resource. In the desert Southwest rainwater appears and disappears quickly, evaporation rates are high given the intense heat and near constant exposure to sunlight, and water quickly runs off hard surfaces and seeps deep into dry soils. Agaves' shallow root systems allow them to capture water most efficiently in this type of environment when they are located above certain soil types. Hard calcic layers, sometimes called , present just below the ground's surface provide a competitive advantage to agaves. Subterranean caliche horizons are relatively impermeable and disallow seeping water easy access to the sediments below, thereby, trapping large amounts of water above them but below the surface of the ground--at the exact depth of the short but dense agave root systems. In this way, caliche layers slow the downward seep of rainwater just enough to provide an expertly placed agave plant an adequate supply of water. Interestingly, caliche layers hinder the growth of plants with vertical root systems designed to obtain water at depth.

provides a close-up view of the distribution of Zone 2 rockpile field sites (dark blue polygons) in relation to the geologic landforms of the area. Why is the correspondence of rockpile fields to M1 deposits so striking? Use and the landform description list to formulate and support an answer. Remember to consider the availability of moisture and rockpile construction material (medium to large-sized cobbles) in your assessment. In addition, give two ecological reasons why agave rockpile fields were not located on M2 deposits.