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.
Indiangrass:
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.
