2ND EXAM CH 6

Question 1

What is plant succession in the classical sense (Clementsian)? What is the term used for the final, stable community?

Answer 1

Plant sucession involves the replacement of one plant community by another until the replacement of one plant community by another until the final community is reached.

Climax: final stable community.(controled by the macro climate)

Question 2

Distinguish between the types of causes associated with primary versus secondary succession.

Answer 2

Primary Succesion: starting from bare ground and open water.

Secondary Sucession: follow disturbances such as fire, destructive grazing.

Question 3

What is the term used when the climax community is degraded?

Answer 3

Disclimax

Question 4

What are some common criticisms of the various successional theories (see p. 103)?

Answer 4

• it doesnt proceed in a regular, smooth pattern.
• the rate of sucession generally slows down durring a series of years.
• Much variation and flcutuation occur.

Question 5

What tends to happen between palatable and unpalatable plants under heavy grazing?

Question 6

What are the main driving forces in succession? How does this vary between range types (think of the types we have covered)?

Answer 6

The driving forces in sucession are moisture and temperature.

In wet humid range type: recovery after retrogression is both rapid and predictable. Climax plants ussually dominate after 5 years.

In drier range type: the recover is much slower, retrogression can occur in a few years, but it can take about 20 years for the cliamx plants to return.

Question 7

Fill in the table with the numerical values for remaining climax community associated with range condition terms (Dyksterhuis’ adoption of Clements’ theory for Range). Note that if a range site goes from Excellent to Good (or lower) its “trend” would be downward. If the trend goes from, say, fair to good, that would be termed an “upward trend.”

Answer 7

[CLIMAX] [Late Seral] [Mid Seral] [Early Seral]

[EXCELLENT] [Good] [Fair] [Poor]

FORAGE PRODUCTION 764 501 210 55 (lbs/ac/yr)^a

FINANCIAL RETURN +3.49 +2.14 +0.67 -0.16 ($/ac/yr)^b

Question 8

What are Increasers, Decreasers and Invaders?

Answer 8

Increasers: Unpalatable shrubs and annual plants (poisonous)

Decreasers: Palatable productive perennial grasses.

Invaders: Lower palatability and productivity.

Question 9

Why (and how) is it easier to document vegetation changes than to give causal mechanisms for these changes?

Answer 9

Causal mechanisms are complex and in most cases, only the changes has been documented, not causal mechanism. It is likely that a combination of factors is responsible for these dramatic shifts

Question 10

Name three ways in which fire benefits grassland vegetation.

Answer 10

1. Reduces competition from shrubs,
2. Speeds the cycing of nutrients ties up in the dead vegetation.
3. Reduces allelopathic and pathogenic substances associated with old decaying vegetation.

Question 11

Why is the impact of livestock grazing on forage productivity and plant species composition so variable?

Answer 11

It is extremely difficult generalize becuase of different in climate, resistance of different species to grazing, stocking levels, composition of vegetation, grazing season, and others.

Question 12

“Production” refers to the amount of herbage grown every year by plants. Based on Table 6.5, how variable is production when moderate grazing is compared to no grazing? Would it be reasonable to average these values and apply it to any rangeland site?

Answer 12

Looking at the big picture, moderate grazing had the best result.

No, every site has different variables.

Question 13

How does the Society for Range Management define drought? (see text glossary or p. 114)

Answer 13

DROUGHT: is a period of low precipitation in relation to a long-term average.

Question 14

Examine Figure 6.14 carefully. Basal area is a measure of plant dominance or cover on the ground. Black grama is a highly valued forage grass (decreaser). Each of the four graphs shows a different grazing regime, yet trends are coarsely similar from year to year. What appears to be the primary cause of fluctuations in black grama cover?

Answer 14

The graph that was conservatively grazed seemed to be the most productive.

Question 15

Give a definition of “competition” from the standpoint of plant ecology.

Answer 15

A process whcih occurs when two or more organisms are making a common endeavor to gain one or more requisites in excess of the immediate supply.

FREE ANSWER - It requires that 1) animals utilize the same resource, 2) that the resource is limiting and 3) that it is in demand at the same time and place.

Question 16

List five mechanisms that can produce complex ecosystem dynamics that deviate from linear succession. (Hint: Demographic Inertia is the first)

Answer 16

1. Demographic Inertia: some plant pop may require a rare event for establishinment to occur, but once this has occured, the resulting cohort can persist for a long time.
2. Grazing Catastrophe: grazer intake and plant net growth and reproduction respond to plant abundance according to ninlinear functions. These functions are shaped in such a way as to suggest that plant abundance may vary discontinuously and irreversibly responce to change in stocking rate.
3. Priority in Competition: Alternative stable states may result when the outcome of competition depends on the initial abundances of the competitors.
4. Fire Positive Feedback: Some vegetation components, many grases, promote fire and are also themselves promoted by fire.
5. A Vegetation Chnage that Trigger a Persisting Change in Soil: conditiond may not be reversible on a time-scale relevant to management.

Question 17

Give brief definitions of “states” and “transitions.”

Answer 17

States, there may be several states for an ecosystem. But once the vegetation has passed from one state to the next it cant come back with out extreme measures.

Transition, is the period of time between the states.

Question 18

What kinds of rangeland ecosystems often conform to traditional linear succession models? What kinds of rangeland ecosystems may be better described by State-and-Transition Models. Explain. (Refer to assigned readings: Westoby; Stringham et al.)?

Answer 18

.The temporal scale is defined by the performance of the current climate regime.

Question 19

Bestelmeyer paper - Give an example of a biotic versus abiotic threshold.

Answer 19

Biotic Threshold:a transition from savanna to a shrub-encroached woodland state is precipitated by gradual or episodic loss of grass due to continuous grazing and drought, resulting in a loss of fuel connectivity and lack of fire disturbance.

Abiotic Threshold:

Question 20

Bestelmeyer states that: “The abandonment of active management in rangelands and their condemnation as ‘‘irreversibly degraded’’ via the threshold concept may have an insidious consequence for land use and human welfare in the American West.”

What is the “insidious consequence”?

Answer 20

We often fail to appreciate that the assertion of degradation based on comparisons with “reference” or assumed pre-European vegetation types and associated agricultural uses does not account for other functions of the land.

Harmful yet un-notisable in the begining.

Question 21

Write a brief essay that agrees with or disagrees with the following statements (be prepared to cut and paste your essay):

Question 22

Joan Chevalier (speech writer) is baffled at the inattention to rural states that essentially gave the election to George Bush in 2004. What did President Obama do differently?

ESSAY

Answer 22

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Question 23

What is the “Radical Center”? Check out the following website for the California Rangeland Conservation Coalition. (http://www.carangeland.org) Be familiar with one political issue that is discussed under the “News” heading on this web site of interest to ranchers (and environmentalists).

ESSAY

Answer 23

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Question 24

Drum Hadley – Find an advertisement in a magazine or other media that is selling what you believe to be former ranch property in the Intermountain West (excluding California). Using maps find out if it is adjacent to any public lands. What is the approximate price per acre? Quiz questions may ask you to comment on development pressures that some ranchers feel, especially near metropolitan areas or where ‘trophy homes’ are popular.

ESSAY

Answer 24

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