ECOR 9200 Field Applications Flashcards
What are the critical assumptions of a Relative Abundance Survey?
- Identical or statistically comparable methods are used.
- Environmental, biological, and sampling factors are kept as constant as possible.
- Surveys are independent; one survey does not influence another.
- Capture probabilities are the same between areas.
What is the Measure of Abundance for time and/or area- constrained searches with vegetation surveys?
Species surveyed: Any
Measure of abundance: presence/not-detected, relative abundance
Methods overview: This technique is generally used in broad-scale floristic inventories. Rigor 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.
What is the Measure of Abundance for quadrat surveys with vegetation surveys?
Species surveyed: Any, usually plants in the herbaceous layer
Measure of abundance: percent cover (relative abundance), density
Methods overview: This technique is generally used to estimate abundance of grasses or forbs, as well as other categories such as mosses, litter, and bare ground. For percent cover estimates, cover classes are usually used to reduce bias of visual estimates. The size and shape of quadrats can vary greatly, including especially squares, rectangles, and belt transects (see considerations above). One of the most commonly used specific type of quadrat survey is the Daubenmire Method, for which six cover classes are used to estimate percent cover of each species within plots that are usually 20 × 50 cm.
What is the Measure of Abundance for nested circular plot surveys with vegetation surveys?
Species surveyed: Any
Measure of abundance: Percent cover (relative abundance)
Methods overview: This technique (which is really an extension of quadrat surveys) is intended to provide an efficient way of estimating cover separately for multiple height strata (see figure at below left). Each plot is defined by both a radius and a height category, but plot arrangement and size vary greatly among studies. For a given height category, usually all species that occur in a given height category are recorded (e.g., the shrub strata may include many tall herbs). Usually the observer records cover (most often separately for each plant species) as it would appear from an overhead perspective (see figure at below middle). Most surveys permit cover of species in a single plot to add to more than 100% (called overlapping cover), which is more realistic given the 3-dimensional nature of vegetation. Cover categories are used to reduce observer bias in visually estimating cover. Studies focused on woody vegetation often use multiple height strata for trees and shrubs (see figure at below right, and definitions of the tree [A1–A3] and shrub [B1–B2] layers below).
What is the Measure of Abundance for Line Transect surveys with vegetation surveys?
Species surveyed: Any, but often shrubs
Measure of abundance: Percent cover (relative abundance)
Methods overview: Along an established transect, lengths at which target species intercept the vertical plane of the transect are recorded. The total amount of intercept divided by the transect length is used as an estimate of percent cover.
What is the Measure of Abundance for Ocular tube/densiometer surveys with vegetation surveys?
Species surveyed: Any canopy species
Measure of abundance: Percent canopy cover
Methods overview: With ocular tubes, observers simply record whether or not crosshairs hit vegetation for each of many vertical sightings (and this proportion is reported as percent canopy cover). Spherical densiometers provide estimates of canopy cover using either convex or concave mirrors. Specifically, the densiometer is held level at 1 m off the ground, and the observer records the extent of canopy vegetation reflected in the mirror (which is converted to percent cover).
What is the Measure of Abundance for Point Centered Quarter surveys with vegetation surveys?
Species surveyed: Any, but often shrubs
Measure of abundance: Density
Methods overview: At each sampling point, the distance to the nearest target species is recorded in each of four quadrants (see figure to right). Density (per m2) is then estimated as 1 ÷ (mean point-to-plant distance in m)2.
What is the Measure of Abundance for Obstruction Pole surveys with vegetation surveys?
Species surveyed: Any, but usually focused on understory vegetation
Measure of abundance: Volume
Methods overview: A vertical pole with marked increments is sighted from a set distance and height from each of four quadrants. For each sighting, the number of increments obstructed by vegetation by at least some threshold amount (e.g., >25%) is recorded. Volume is estimated by the mean fraction of obstructed increments.
Define density (in survey context)
The number of individuals per unit area or volume (e.g., 3.6 Marbled Murrelets/km2).
Define presence/non-detected
Whether or not a species is present in a given area. (Note: many people will not consider this a measure of abundance given how little information it conveys.)
Presence/not-detected surveys are suitable for broad inventories or pilot studies
Define relative abundance (in survey context)
The number or proportion of individuals without specifying the size of the sampling area (e.g., 5.6 American Robins/point count survey).
Define total abundance
The total number of individuals in a specified area (e.g., 52 Golden-crowned Kinglets in Central Park).
What affects your sampling size?
Sample size usually increases with:
- The variability of your data (more variable = larger sample size)
- The size of your survey area (larger area = larger sample required)
- Level of precision required (high precision = larger sample size)
- Available resources (Available resources should not influence sample size from a scientific standpoint, but resources often constrain logistics.)
Define Site Series.
The smallest unit of classification in BEC is the site series.
Site series are defined as ecosystems that have similar soil moisture and soil nutrients and have plants species that are indicative of the potential vegetation community that can occupy a site at maturity.
Therefore, the description of site series in the field manuals always represents the mature site conditions (climax communities).
- Site series are plant associations that occur within a particular biogeoclimatic subzone or variant.
- Site series are described in the Regional Field Guides to Site Identification
- Site and soil conditions as well as the vegetation community are used to identify site series
What are Zonal Sites?
Site series that best reflects the regional macroclimate of the BGC subzone or variant.
These sites do not drain or collect soil moisture excessively nor do they have an overabundance or lack of nutrients.
Typically, they occupy:
gentle slopes < 25%
Deep (> 1 m ) deposits of medium-textured (loamy) soils
Middle slope position
No root restricting layers
Not subject to frost pockets or cold air drainage or other abiotic site features.
