Vegetation

Question 1

What is the main foci of vegetation sampling? (3)

Answer 1

Surveys focused on the biology of plants that are subdivided into surveys that focus on one or a few target species (used to study abundance/distribution, response to changes in abiotic factors, biotic factors, treatments etc.) or surveys that focus on entire plant communities (used to study all the above plus competition, succession etc.)

Surveys focused on the importance of vegetation as habitat for other species (May focus on specific plant species that have high value)

Question 2

What questions need to be asked when conducting a vegetation survey? (9)

Answer 2

Which species will be surveyed
What vegetation measures will be obtained
What type of survey is most appropriate
What time of year should research be conducted
What is the sampling area
For plot-based surveys, what size and shape of plot should be used
What is the size of the sampling effort
How will surveys be established to ensure representation
What measures will be taken to ensure surveys are precise and accurate

Question 3

What are the different types of vegetation measures? (7)

Answer 3

Abundance 
Structural
Growth 
Reproductive
Condition 
Damage assessment 
Mapping

Question 4

What typical vegetation abundance measures (how much or how many) can be obtained? (6)

Answer 4

Presence/not-detected - whether or not a species is present in a given area

Percent cover - measure of relative abundance - the proportion of an area covered by a species of interest

Volume - relative abundance or structural measure - 3 dimensional

Density - number of individuals per unit volume (e.g. 32 red alders/ha)

Total abundance - the total number of individuals in an area (e.g. 32 red alders in Stanley Park)

Biomass - amount of ‘plant material’ in a specified area (71g wet mass/m2)

Question 5

What typical vegetation structural measures (how big or what shape) can be obtained? (2)

Answer 5

Physical dimensions - height and width may be measured for woody vegetation

Diameter at breast height (DBH) - measured for trees at least 4.5 ft off of the ground and usually used in estimations id tree or stand volume or age

Question 6

What typical vegetation growth measures will be obtained? (2)

Answer 6

Annual growth of stems - often used as a measure of forage available for browsing wildlife

Annual growth of tree rings - width of rings usually used to infer growing conditions

Question 7

What typical vegetation reproductive measures can be obtained? (3)

Answer 7

Abundance of reproductive structures - May focus on the frequency of individual plants that have flowers/fruits/seeds, or abundance of flowers/fruits/seeds on individual plants

Reproductive success - abundance of new individuals

Recruitment - number or proportion of individuals that grow into the adult population (success measured when seedlings reach 2-2.5m height)

Question 8

What typical vegetation conditions measures can be obtained?

Answer 8

Damage assessments - the proportion of plants killed by animals or the proportion of leaves/stems/plants damaged by animals

Question 9

What mapping can be done for vegetation?

Answer 9

Vegetation community or habitat mapping - Assessment of landscape-scale distribution of habitat or communities (can be done using remote sensing)

Question 10

What type of survey is appropriate for which vegetation measure? (4)

Answer 10

Presence/not-detected - time- and/or area- constrained searches

Percent cover - variable radius (nested) circular plots, Daubenmire method,, line-intercept method, densiometer surveys, ocular tube surveys

Volume - obstruction pole (Robel Pole) surveys, density board surveys

Density - quadrat or circular plot surveys, point-centrered quarter method

Question 11

What time of year should vegetation surveys be conducted?

Answer 11

In the summer when species are easier to identify, reproductive traits are measurable, and abundance/structural measures attain their maximum values

Question 12

What size and shape should be used for plot-based surveys? (4)

Answer 12

Differences between many sampling units Id only a matter of degree (e.g. transects are just really long quadrats) but the type used depends on specific conditions

Size of unit should increase as abundance of target species decreases

Rectangles are better at sampling items with clumped distributions

Transects are more efficient and convenient when sampling along linear features

Question 13

What is the size of the sampling effort? (4)

Answer 13

Sampling size usually increases with:

Variability of data
Level of precision needed
Survey area
Available resources

Question 14

How will survey sites be established to ensure results are representative of the target population? (2)

Answer 14

Reasonable coverage of the survey area (systematic sampling) and,

Minimal bias (random sampling)

Question 15

What measures will be taken to ensure surveys are both precise and accurate? (2)

Answer 15

High precision - suitable observer training and regular maintenance of sampling devices

High accuracy - ensuring observers have suitable and equal training and surveying at the right time of year

Question 16

What are the common types of vegetation surveys? (7)

Answer 16

Time- and or area- constraint searches

Quadrat surveys (e.g. Daubenmire Method)

Variable radius circular plots (nested plots)

Line intercept method

Ocular tube/densiometer

Point-centered quarter method

Obstruction pole (Robel Pole) method

Question 17

Time and/or area-constraint searches (2)

Answer 17

This technique is generally used in broad-scale floristic inventories

Vigour is added to a simple presence/not-detected survey by documenting the specific area surveyed, as well as the number of person-hours entailed in the inventory

Question 18

Quadrat surveys (e.g. Daubenmire Method) (2)

Answer 18

Can be used for all species, especially in the herbaceous layer

Daubenmire has 6 cover categories used to estimate percent cover of each species within plots that are usually 20 x 50 cm

Question 19

Variable-radius circular plots (nested circular plots) (5)

Answer 19

Intended to provide an efficient way of estimating cover separately for multiple height strata

Each plot is defined by a radius and a height category, but plot arrangement and size vary greatly among studies

All species within a given height category are recorded

Cover categories are used to reduce observer bias in estimating cover

Studies focused on woody vegetation often use multiple height strata for trees and shrubs

Question 20

Line intercept survey (3)

Answer 20

Used for any species, especially shrubs

Along an established transect, lengths at which target species intercept the vertical plane of the transect are recorded

Total amount of intercept divided by the transect length is used as an estimate of percent cover

Question 21

Ocular tube/densiometer survey (3)

Answer 21

Measures percent canopy cover

Ocular tube - observers record whether or not crosshairs hit vegetation for each of the many vertical sightings (and this is reported as percent canopy cover)

Densiometer - provide estimates of canopy cover using either convex or concave mirrors. It is held 1m off of the ground, and the observer records the extent of canopy vegetation reflected in the mirror (which is converted to percent cover)

Question 22

Point-centered quarter method (4)

Answer 22

Used for any species, often shrubs

Measures density

At each sampling point, the distance to the nearest target species is recorded in each of the four quadrants

Density (per m2) is then estimated as 1/(mean point-to-plant distance in m)2

Question 23

Obstruction pole (Robel Pole) method (5)

Answer 23

Used for any species, generally understory vegetation

Measured volume

Vertical pole with marked increments is sighted from a set distance and height from 4 quadrants

For each sighting, the number of increments obstructed by vegetation by st least some threshold amount (e.g. >25%) is recorded

Volume is estimated by the mean fraction of obstructed increments