Vegetation Flashcards
What is the main foci of vegetation sampling? (3)
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)
What questions need to be asked when conducting a vegetation survey? (9)
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
What are the different types of vegetation measures? (7)
Abundance Structural Growth Reproductive Condition Damage assessment Mapping
What typical vegetation abundance measures (how much or how many) can be obtained? (6)
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)
What typical vegetation structural measures (how big or what shape) can be obtained? (2)
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
What typical vegetation growth measures will be obtained? (2)
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
What typical vegetation reproductive measures can be obtained? (3)
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)
What typical vegetation conditions measures can be obtained?
Damage assessments - the proportion of plants killed by animals or the proportion of leaves/stems/plants damaged by animals
What mapping can be done for vegetation?
Vegetation community or habitat mapping - Assessment of landscape-scale distribution of habitat or communities (can be done using remote sensing)
What type of survey is appropriate for which vegetation measure? (4)
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
What time of year should vegetation surveys be conducted?
In the summer when species are easier to identify, reproductive traits are measurable, and abundance/structural measures attain their maximum values
What size and shape should be used for plot-based surveys? (4)
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
What is the size of the sampling effort? (4)
Sampling size usually increases with:
Variability of data
Level of precision needed
Survey area
Available resources
How will survey sites be established to ensure results are representative of the target population? (2)
Reasonable coverage of the survey area (systematic sampling) and,
Minimal bias (random sampling)
What measures will be taken to ensure surveys are both precise and accurate? (2)
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
What are the common types of vegetation surveys? (7)
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
Time and/or area-constraint searches (2)
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
Quadrat surveys (e.g. Daubenmire Method) (2)
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
Variable-radius circular plots (nested circular plots) (5)
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
Line intercept survey (3)
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
Ocular tube/densiometer survey (3)
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)
Point-centered quarter method (4)
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
Obstruction pole (Robel Pole) method (5)
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
