L17 Flashcards
The Stand
-Observable patch of similar vegetation
- Some stands are obvious
- Vegetation can flow into each other making it tricky to identify
- Boundaries may be sharp (ecotones) or diffuse (ecoclines)
- Can have more than one species in a stand
- Ecocline is a gradual wide transition between stand types
- May be important to define ecotones vs ecoclines
Ecotone
- Sharp boundary
- Little overlap between species
Ecocline
- Diffuse boundary
- Some species occur across boundaries
- Less clear cut than ecotone
Stand sampling
- Ecotones are often limited in their quadrats
- Ecoclines are often featured highly in ecoclines
- Depends on area of interest in the study
- Total randomisation is not the best approach
Releve stand sampling
- No fixed shape or size
- Can vary based on plant community, soil, slope etc
- Choose own Releve area
- Depended on own judgement to best capture area of interest
Releve sampling, 3 conditions
- Uses just a single sample to represent a stand.
Conditions include:- Being representative of the stand as a whole
- Being uniform away from the stand boundaries
-Be sufficiently large to include most species (concept of the minimum area)
Area required for releves?
- Estimate ‘Minimum Area’
- Species area curve
- Each time you half effort
- Can make sensible decisions on the size of the Releve
-Based on the curve we can look at getting the majority of the types of species
The number and area of samples depends upon:
- Purpose of study
- Measurements being made
- Eg frequency estimates require more samples than generation of a species list
- Size of individual plant species
- Evenness of distribution of species
- Sample area and number of species may be interrelated
Quadrat
-Quick
- Can use 100% cover or >100% cover
- Lower accuracy (what is your aim?)
Subdivided quadrat
- % cover in each square, the average across quadrat
-Slower (time consuming)
-Greater accuracy (what is your aim?)
Point survey (drop lots of large pins in a regular grid)
- Can use first hit or all hits on the way down to the bottom
- Need lots (100 is not enough)
- Need to do many pin points
- Does Not rely on estimation, no subjectivity
Characterising vegetation
- Species compositionSpecies richness
- Simply the number of different species - Species diversity
Includes other factors such as “evenness” of species abundance
Plant strategy theory:
CSR: another concept from Phil Grime
- Competitive stress tolerator ruderal
Two pressures dictate species area:
Stress
Disturbance
- Combinations of these factors, include graphic
Low stress and low disturbance = competitors win
Low stress and high disturbance = ruderals (opportunists) win
High stress and low disturbance = Stress tolerator
High stress and high disturbance = proposed many plants cannot have both and survive,
CSR Triangle
- Competition increases to the top of the triangle
- Stress gets stronger to the bottom of the triangle
- Disturbance goes from right to left (left = strongest disturbed)
Can
