complete 9 questions on worksheet
Unit 13 Local Vegetation Analysis In our lecture on vegetation systems, we mostly described vegetation patterns on fairly coarse scales that do little to account for subtle variations in topography, microclimate, or soil. The maps on the following pages, however, depict topography and vegetation over a much smaller area (between 2 and 3 square miles) in the Ochoco Mountains, located in the drier eastern end of Oregon. Notice the difference at this scale: broad generalizations about topography and Rainshadow do not account for the vegetation changes. Instead, at this scale we find complex vegetation patterns that respond to localized variations in topography (such as aspect and slope steepness), microclimate, and soil conditions. 1. Familiarize yourself with the local topography using the contour lines on page 2. Recall what we did with the topographic map reading lab at the beginning of the semester. To help yourself get oriented, pay attention to the places on the topographic maps in Figures 2-4 that are over 5000 feet, as exemplified in Figure 1. The shaded area in Figure 1 shows you where the ridges are located in this area. To help you answer the following questions, use this shaded pattern to determine which slopes on the map’s face in a generally southerly direction and which slopes face in the northerly direction. 2. At a regional scale in the state of Oregon, dry climate conditions can be found on the east side of the Cascade mountain range as a result of the Rainshadow effect. At the local scale expressed in Figures 1-4 here for this exercise, however, large-scale topographic influences such as mountains and Rain shadows are less important for our understanding of vegetation differences than smaller-scale topographic influences such as slope and aspect. On what slopes, for example, would you expect to find the driest and wettest conditions on these local maps? How does the compass direction of these changes differ from the patterns of moisture differences at the regional scale? Figure 1. Vegetation and environmental setting at a local scale Figure 2. West Juniper Figure 3. Meadow Figure 4. Ponderosa Pine 3. Western Junipers are usually found in drier regions in the Cascade’s Rainshadow that are usually at low elevations east of the mountain range. In Figure 2, however, we find many Western Junipers located on the highest ridge tops. Considering this, why do we find DRIER conditions (and hence Western Junipers) on ridge tops here at the local scale as opposed to the WETTER conditions we found at high elevations in the Cascades at the regional scale? 4. In Figure 3, notice the area on the upper left-hand corner where the land slopes downward from three different directions. Would you expect the base of this area to be wet or dry? Does the vegetation located at this site confirm your expectations? 5. Ponderosa Pines are found abundant in even drier conditions than the eastern side of the Cascades (Rain shadow). The Ochoco Mountains are located in a section of Oregon that is an example of such even drier condition. It isn’t surprising that we find so much Ponderosa Pine in Figure 4. But, are Ponderosa Pines located only in what we would expect to be the driest of areas in Figure 4? That is, are they located precisely only on south-facing slopes and not at all on north-facing slopes? What does your answer suggest about our ability to generalize about relationships between vegetation types and environmental setting at the local scale? Map of the Location of Individual Trees Figure 5 is a schematic map of a small hypothetical area located within the local map you just looked at. This very localized map depicts a meadow and three different types of trees: (1) Ponderosa Pines, (2) firs (consider the two types of firs together), and (3) Western Junipers. The relative size of each tree is indicated by the diameters of the circles. At this very local scale, notice the increasing complexity of vegetation distribution and the increasing difficulty of assigning fixed boundaries between vegetation types. For your convenience, the vegetation types involved in this exercise may be listed in order from the most moisture demanding to least moisture demanding: Meadow --> Firs --> Ponderosa Pine --> Junipers 6. Find the stream and the meadow indicated on this map. Draw a line as best as you can that demarcates the meadow’s boundaries. What are the soil conditions like in the meadow and what effect does this have on the vegetation here? What would you expect the topography of this site to be like (is it sloped, flat, poorly drained, etc.)? 7. Next, draw a line from east to west through Figure 5, signifying where you would expect to find the northern extent of the driest soils in this area. What trees allow you to find this boundary? At this scale, what topographic settings could produce these soil conditions? 8. Recall that Ponderosa Pines prefer relatively dry soils. While we may not be surprised to see them mixed in with Western Junipers at the south end of this map. It is, perhaps, surprising to see them in such close proximity to the meadow. What does the proximity of these two very different vegetation types suggest about the nature of the topographic boundary between the meadow and the Ponderosa Pines? For example, would you expect there to be an abrupt or gradual boundary between the moist meadow and the dry Ponderosa Pine zone? 9. Imagine walking from the south end to the north end of Figure 5. Draw a cross section representing the likely topographic profile along your route, taking into account aspect and slope steepness. It may help to draw the sun over your diagram so as to orient your cross section to its position in the southern sky at this location. (Note: if you do not have a software/app to draw digitally, feel free to print out the last page or sketch the picture on the piece of paper, draw rough boundaries between vegetation types, the cross section and the sun on the paper with hand, take a photo and submit on Blackboard.) 6