The Great Plains

Main characteristics of grassland areas:

Tallgrass Prairie

The most mesic of all central plains grassland types: receives the most rainfall, greatest longitudinal diversity, and greatest abundance of dominant species (Sims 271). From Tallgrass lecture, 500-1000 mm precipitation annually, mostly in Spring and Summer.
Large ecological amplitudes and geographical range (271)
Vegetation is long-lived perennials, and varies with climate and soils; primarily bunchgrasses and sod-forming grasses (271).
Three grassland Associations: Bluestem/True Prairie, Nebraska Sandhills, and land from Canada to Kansas/Nebraska/The Dakotas (271).
Most now in cultivation- used for livestock grazing (272)
Fire suppression has led to an increase in woody vegetation (273)

Mixed-grass Prairie:

Serves as an ecotone – Blend of Tallgrass and Shortgrass Prairies (274)
Lies west of the Tallgrass Prairie (274)
Richest floristic complexity of the grasslands; vegetation includes intermediate/short stature grasses, tall grass, forbs, suffrutescens, and low growing shrubs (274).
Vegetation fluctuates due to climate (Shortgrass will occur in more arid environments and is more drought tolerant), fire suppression, and livestock/wildlife grazing (275).
Associated with rolling topography (275).

Shortgrass Prairie:

Large expanse of vegetation east of the Rocky Mountains (278)
Cool season grasses in the north, shortgrasses dominate the west, while tall grass and mixed grass is more prominent in the East (278)
Evolved to adapt to grazing- first buffalo and then domestic livestock
Location of the 1930s Dust Bowl in which the shortgrass prairie was plowed for farming (278)
Fire is detrimental to most vegetation (279)

California Grasslands:

Known as the Pacific Prairie (279).
Original vegetation included cool-season perennial bunchgrasses, annual and perennial grasses, and forbs. Now it is mostly dominated by weedy annuals, and annual forbs (279).
Land has been cultivated for ranching/farming, urbanized/industrialized, and introduced to Invasive Plant Communities (279).

Desert Grasslands:

This arid environment extends from Shortgrass Prairie in Texas and New Mexico, South to Northern Mexico (280).
Three types of Mesquite have increased on all soil types (280).
Have been modified for such a long time, that no standard for comparison exists (280).
Grazing has influenced fluctuations between grassland and shrubland ecosystems (280).

The Great Plains

Physical characteristics:

Precipitation and temperature are the most important variables (Lauenroth 229).
Annual precipitation from 300 mm in the West to 1000 mm in the East; seasonality and amount as snowfall varies, winter is the dry season (229).
Mean annual temperatures range from 2 (in the North) to 18 (in the South) degrees Celsius (231).
Mostly dry sub-humid or semi-arid environment, less than 1% arid (233)
60% of the region has been converted to agricultural ecosystems (233).

Ecological characteristics

Physical characteristics of the region influence large-scale changes and variability in vegetation
Soil texture influences vegetation type, net primary production, SOM, nutrient availability, and land use (233).
West to East Precipitation gradient influences shortgrass growth in the West and Tallgrass growth in the East (235).
Precipitation and Temperature gradient result in changes in composition of C3 and C4 grasses; where C3 dominates colder drier regions, and C4 is more abundant in warm, humid areas (235)
“The multidimensional gradients in climate, soil and plant-type gradients across the central grassland region result in a complex spatial distribution of potential plant communities” (237)
Arrival of European settlers resulted in the introduction of exotic plants; leading to a reduction of native vegetation and an increase in Invasive plant communities (247).
Most of the area has been converted to cropland, in areas where precipitation, temperature, and soil make land the most suitable for farming; leading to loss of native vegetation, net primary production, and changes in balances of nitrogen and carbon (247).
Disturbance could be fire, drought, human activity, invasive plants, grazing, etc.
Habitat and food source for livestock and wildlife

Important Grass Species
Big Bluestem:
family- Poaceae
Scientific Name- Andropogan gerardii
Origin- Native
Lifespan- Perennial
warm season grass
deep roots, rhizomes in top 10 cm
climax species
forage for sheep, horse, cattle, elk, deer, pronghorn. Preferred by livestock over most other grass species. Birds may eat seeds.
Essential cover for birds and small mammals, highly nutritious and palatable.
Shade tolerant, tolerates moderate grazing.
Family- Poaceae
Scientific Name- Sorghastrum nutans
Native Perennial
1-2 meters tall, warm season grass, scaly rhizomes, germinates from seed
climax species but can also invade disturbed sites
Eaten by livestock and wildlife in the summer. Seeds eaten by small mammals. Excellent cover for certain birds.
Moderately tolerant of salinity and acidity.

I think these two species of Tallgrass are some of the most important in the Great Plains because they both serve as a food source for livestock and wildlife, habitat for wildlife, and possess important adaptations. They are also both considered a climax species, and will dominate an undisturbed ecosystem.

One of the things that makes The Great Plains so important is the vast land area it covers in the United States. It has a broad and variable range of precipitation, temperature, and soil that produces a unique ecosystem. The vegetation provides valuable forage for livestock and forage/cover for wildlife.This landscape also provides great topography for agriculture, farming, and ranching; contributing to the economic productivity of the United States. The grassland ecosystem influences nutrient cycling, water quality and quantity, and other ecosystem goods and services. The Great Plains are greatly threatened by anthropological activity (agriculture, urbanization, energy development), overgrazing, fire (suppression), drought, and invasive plants. Unsustainable use of the Great Plains leads to degradation and a threatened status.

Luaenroth, W. K.; Burke, I .C.; and Gutmann, M. P., “The Structure and Function of Ecosystems in the Central North American Grassland Region” (1999). Great Plains Research: A Journal of Natural and Social Sciences. Paper 454.

Sims, Phillip L., “Ch 9: Grasslands” North American Terrestrial Vegetation. Cambridge University Press. 1999.

C3 Plant Metabolism vs. C4 Metabolism

Photochemical reactions of photosynthesis are the light reactions of plants. The chemical equation is 2 H2O + 2 NADP+ +2 ADP + 2 PI – 2 NADPH2 + 2 ATP + O2. Special adaptations plants have evolved include extended and broad, lateral leaves that absorb more radiation for photosynthesis. The organelle responsible for photosynthesis is the Chloroplast. The chloroplasts contain many different pigments that allow for light absorption. Chlorophyll is a main pigment and stable molecule that has the ability to gain and lose electrons; therefore able to pass on excited electrons to other molecules. Photochemical reactions occur in the Thylakoids and Thylakoid Membrane. 3 things occur in excited pigments: energy is transferred to a reaction center, heat is produced and energy is lost, fluorescence releases photons and energy is lost.

The Enzymatic reactions of photosynthesis are processes that involve the dark reactions and do not require light. These processes take place in the stroma, aqueous medium. Photorespiration in the Glycolate pathway is an inefficient process that increases in hot temperature and low humidity climates and: fixes O2 instead of CO2, a major disadvantage of C3 photosynthesis.
NADPH and ATP are important in both types of photosynthesis because they are the energy that combine with carbon dioxide and water to produce glucose and oxygen. Photosynthesis= 6 CO2 + 6 H2O + energy -> C6H12O6 + 6 O2. Photosynthesis is a biological process in which solar energy is used to form chemical bonds. Photosynthesis is important for many reasons including oxygen evolving photosynthesis producing and regulating atmospheric oxygen for respiration and forming the ozone layer, protecting Earth from UV radiation.

The main differences between C3 and C4 grasses:
C3 Metabolism:
used by all plants,
the most prevalent and primitive pathway,
evolved with climates of high CO2 and low O2
C4 Metabolism:
PEPcase Phosphoenolopyruvate carboxylase (higher affinity for CO2 and none for O2) is the initial receptor of CO2 instead of Rubisco,
occurs in Mesophyll cells and Bundle Sheath cells (contain chloroplasts) surrounding the Xylem and Phloem (veins),
is an adaptation that solves the problem of photorespiration,
evolved 7-9 million years ago in a period with high O2 concentration

C3 and C4 grasses are highly linked to different environments because of different advantages/disadvantages the C3 and C4 photosynthesis/pathways evolved. The advantages of C4 Photosynthesis include no photorespiration, CO2 fixation is resistant to heat and drought, higher water use efficiency. Disadvantages include cold sensitivity (therefore evolving to be warm season plants); and contain more bundle sheath cells (high in fiber)/less mesophyll so are more fibrous than C3 grasses. Photosynthesis relies on Rubisco to fix CO2; factors affecting Carboxylation (acquisition of CO2 by Rubisco) include Rubisco quantity/activity, CO2 concentration, acceptor concentration (RuBP), protoplasm hydration, temperature, and minerals (P). Since C4 is reliant on PEPcase as an initial receptor and not Rubisco, it evolved to reduce photorespiration before carboxylation occurs. C3 pathway evolved during a time in history where the atmosphere was high in CO2, low in O2; while C4 pathway evolved during a period that the atmosphere was high in O2. So climatic conditions influence what environments C3 and C4 grasses grow in. Areas with higher O2 concentration will have more C4 grasses because of their adaptation to photorespiration (a disadvantage of C3 photosynthesis), in hot and humid environments. The C3 pathway is more evolutionarily ancient because it speciated before the C4 pathway. The C4 evolved this adaptation due to natural selection making them more fit for environments the C3 grasses can not survive in.

Rangeland- Grasslands

Rangelands are arid and semiarid wildlands that make up to 60% of the world’s land mass; composed of native vegetation of grasslands, shrublands, and open woodlands. For various reasons (low precipitation, rough topography, cold temperatures, etc) Rangelands are unsuitable to grow timber and crops. Rangelands provide multiple ecosystem goods and services such as grazing for livestock and habitat for wildlife, serving as a watershed, improving soil and water quality, providing clean air, open spaces, and recreation.
Grasslands can be defined as land composed mostly of grass species, members of the family Poaceae, with little or no woody vegetation. Sufficient precipitation is needed to be able to support grasses, but not trees and shrubs, in this biome. Grasslands occur on every continent and are around 23% of total land cover.
Grasslands are important economically because of grains from cereal grasses that provide food for animals and humans: wheat, rice, corn, oats, barley, rye. Grasses also provide hay and pasture for livestock. Grasses are important ecologically because they have an extensive root system that improves soil quality and prevents erosion. They also influence sequestration of CO2. They are worth studying because of the ecosystem goods and services grasses provide.

Grasslands are threatened by a variety of human activities including agriculture, fragmentation, invasive species, lack of fire, desertification, urbanization, and livestock. Grasses are being converted to cropland and infrastructure, suppressed of fire, and overgrazed by different animals. All of these things contribute to the loss and degradation of grasslands. It is important to conserve grasslands because of the regulating, provisioning, and cultural services that they provide. Grasslands provide food and habitat, improve soil and water quality, play a role in nutrient cycling, and have cultural value. It is important that we manage grasslands sustainably so that these goods and services continue.

E.O Wilson identified two laws in biological/ecological systems: properties of life are obedient to laws of chemistry and physics, and all biological processes and differences that distinguish species are evolved from natural selection. Species originate from the evolution of some difference that adapts them to the environment. Natural selection is the process by which organisms that have physical/molecular traits that better adapt them to their environment will tend to survive and reproduce. Speciation is the formation of new and distinct species, from the splitting of one evolutionary lineage into two. Natural selection is the primary influence driving evolution, and therefore speciation.
Grasses are in the division Magnoliophyta, class Liliopsida, in the order Cyperales, part of the family Poaceae (Gramineae), have 600 genera, and have around 9000 species. They occur in arid or semi-arid environments. They are annual (reestablish by seed each year) or perennial (persist from year to year) herbs that have noded stems. The have leaves with two parts: sheath surrounding stem and a linear, flat blade. Flowers are formed by inflorescence subdividing into spikelets, which other flowering plants do not have. The dry fruit is called caryopsis (grain). Grasses have rhizomes, stolons, basal leaf meristems, high shoot/root density, underground nutrient reserves, deciduous roots, and rapid transformation/growth.
The main adaptations of grasses involve responses to the disturbance of drought and open space. They have evolved to be wind pollinated and drought resistant. Grasses are able to spread during periods of increasing drought because of traits such as Basal meristems, small stature, high root and shoot density, deciduous roots, underground nutrient reserves, and rapid transformation and growth. Rhizomes and Stolons are used as growth strategies to extend the root system laterally. Other adaptations include how rhizomes evolved because of trampling by large herbivores, basal leaf meristems evolved as an adaptation to grazing, and wind pollination evolved due to open conditions of savannas.

Grasslands are abundant because of the genetic traits that have evolved that help them better fit their environment, to survive and reproduce. Therefore, natural selection has influenced Poaceae to survive throughout history due to specific beneficial differences evolving in response to disturbance and environmental change, and thrive in today’s biosphere. The specific traits that grasses have evolved through natural selection is basal leaf meristems, high root/shoot density, underground nutrient reserves, deciduous roots, and rapid transformation/growth, rhizomes and stolons. All of these characteristics contribute to drought resistance. As an adaptation of moving from woodland to open landscapes, grasses evolved to be wind pollinated and can reproduce more efficiently. Rhizomes and stolons produce lateral growth without the use of seeds, increasing distribution and abundance. The morphology of grasses is important to grassland abundance because without the evolutionary process forming this vegetation type, Poaceae would have never developed traits that help them better adapt to their changing environment; and they would eventually go extinct. Basically, the current state of grass species morphology is produced by species adaptation to environmental change. Overall, grasslands are abundant because of their resistance and resilience to environmental change; because of their ability to easily adapt to disturbance because of traits they evolved due to natural selection and speciation.