{"id":51,"date":"2017-04-11T04:26:53","date_gmt":"2017-04-11T04:26:53","guid":{"rendered":"http:\/\/sites.warnercnr.colostate.edu\/larryr\/?page_id=51"},"modified":"2017-04-12T17:14:27","modified_gmt":"2017-04-12T17:14:27","slug":"structure","status":"publish","type":"page","link":"https:\/\/sites.warnercnr.colostate.edu\/larryr\/structure\/","title":{"rendered":"Structure"},"content":{"rendered":"

CENTRAL ORGANIZING IDEA: The structure of terrestrial vegetation is driven by the timing and amount of water available to plants as modified by seasonal temperature regimes. The most fundamental mapping unit of the rangeland manager is the range site, which represents areas of similar site potential.
\nOBJECTIVES:<\/p>\n

[2,4,6]Objective 1. Help students understand why plants with different life forms grow where they grow.
\n[2,4,6,7]Objective 2. Give students an overview of vegetation structure and productivity of world rangelands with emphasis on temperate grasslands and shrublands.<\/p>\n

Teaching points:
\n1. The life form of vegetation (Cover Type, e.g., shrubs vs grass) found in an area
\nis a function of the amount of precipitation and the coincidence of precipitation
\nand potential evaporation [examples are temperate areas that receive the bulk of
\nprecipitation in the winter (non-growing season) vs summer, growing season
\nprecipitation]. The composition of vegetation expressed on an area may be
\nmodified by, soil texture, associated plants (composition matrix), terrain (slope,
\naspect), salts, soil depth, water run-on, etc.
\n2. Vegetation is dynamic and may exist in several different mixes, depending on
\ninternal and external influences. [Although we will take up the issue later, we
\nneed to point out that the same area might support a continuum of early seral to
\nlate seral plants. We often see a large number of different kinds of plants that
\nmight occupy a site following disturbance, i.e., early seral stages; but in late
\nseral stages there is a remarkable convergence of plants that occupy similar
\nsites.]<\/p>\n

3. The ultimate integrator of environmental variables (habitat factors) is the
\nvegetation. The vegetation is an expression of site potential. Site potential is
\ncharacterized by species composition or productivity. In range management
\nthese ecological response units are called range sites.<\/p>\n

METHOD 1. [The book does not have a chapter that corresponds to this section]
\nShort lecture. Provide students with some general rules that relate climate to different biomes and other habitat factors and explain local variation.
\n1. Climate, represented by temperature and precipitation, determines
\nthe structure (life forms) of the vegetation.
\n2. Locally, soil water and nutrients determines the mix of plants in the
\nstand. These are often a reflection of soil texture. Soil texture
\nregulates that amount of water storage and the total water
\navailability.<\/p>\n

3. Rules:<\/p>\n

a. areas with >600 to 800 mm precipitation will probably
\nbe dominated by trees. Trees can grow in dryer areas,
\nbut are often absent because of fire or prolonged
\ndrought. In temperate zones, deciduous trees like
\nabout an equal amount of water in the non-growing
\nand growing season. If a mix of deciduous and
\nconiferous tree are found in the same area, the conifers
\noccupy the more xeric sites. Of course, trees exist in
\nareas of stored water can also support trees. The range of
\ntolerance of some tree species and potential
\nevaporation also broadly define where trees will grow.
\nSee Holdridge, page 5.
\nb. stored water is required to support shrubs. Therefore,
\nareas with mostly winter ppt often support shrubs,
\nwhile areas with growing season ppt often support a
\nherbaceous layer of grasses and forbs.<\/p>\n

c. dominance by shrubs or grasses depends on the
\ncoincidence of actual precipitation and potential
\nevapotranspiration, as that interacts with soil texture.
\nGenerally the greater the difference, the greater the
\nchance shrubs will dominate. Shrubs and grasses may
\nbe co-dominant under low coincidence and fine soils
\nor high coincidence and coarse soils.<\/p>\n

4. Rangelands are represented by many structural types representing very-arid to
\nsub-humid climates.
\nShort lecture. The figures on pages 3 to 10 are intended to illustrate (1) different patterns and amount of rainfall received in North America, (2) corresponding cover types and (3) world wide cover types.<\/p>\n

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\"\"\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\"\"<\/p>\n

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\"\"\u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0\"\"<\/p>\n

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TASK: Answer these questions:<\/p>\n

1. You are in the high desert of eastern Oregon; ppt is about 250 mm. What is the structure of
\n the vegetation?<\/p>\n

2. You are in the sandhills of Nebraska; ppt is about 400 mm. What is the structure of the
\n vegetation?<\/p>\n

3. You are in northeast Morocco; ppt is about 250 mm. What is the structure of the vegetation?<\/p>\n

4. You are driving up from Houston, TX on Highway 59 or 69 through a mixed hardwood
\n forest. Suddenly, like someone drew a line on the map, you are in a coniferous forest.
\n What probably happened?<\/p>\n

5. Think about the area you come from. What is the structure of the vegetation? Why do those
\n plants grow there? Are they native? Are they “good” plants?<\/p>\n

What distinguishes grasses from forbs from shrubs from trees? What do these plants look like?? What are the major grasses, forbs, shrubs or trees one might expect to see? You can’t be expected to know them all; nor am I able to show you a specimen of all the plants. I am trying to expand the resources available to you. Which plants are found where and what do they look like?<\/p>\n

I highly recommend you purchase from the Cooperative Extension Resource Center, 115 General Services Bldg, Bulletin 450-A, “Colorado Native Grasses.” (About $4.00) We use many plants as examples in this class.<\/p>\n","protected":false},"excerpt":{"rendered":"

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