It is often difficult to determine whether you have one individual or many. For example, how do you record the density of sod-forming grasses? It is very difficult to use density to describe fungi, mosses, or lichen. Density is a scale-dependent measure.
Importantly, it is dependent on both the size of the quadrat or other sampling frame you may use and the scale over which the species typically occupies. For example, if the species has a sparse population then you might need a very large sampling frame to capture any individuals. Alternatively, if the species occurs in patches, then depending on the size of your sampling frame you may record a high density where in other areas you may record none.
Determining density can be very time consuming in dense or complex environments. For example, imagine measuring the density of shrubs in the two figures below. Difficult on the left and easy on the right. Summary Questions. If we have a quadrat of size 12 inches by 12 inches what is the density in square feet if we record a 20 individuals, b individuals, c individuals and d 50, individuals? How would this answer change if we consider the measurement per square mile? This section explores the distinctions between indicators and methods, introduces the concepts of site descriptors and covariates that are used to help classify and interpret monitoring data.
This module focuses on plant density: what it is, how it is measured, and how density data are used by land managers to inform resource management decisions. Very simply, density is defined as the number of individuals per unit area, and reflects the closeness of individuals. This module focuses on plant frequency: what it is, how it is measured, and how frequency data are used by land managers to inform resource management decisions. Very simply, frequency measurements record the presence of species in quadrats or plots placed repeatedly across a stand of vegetation.
Frequency reflects the probability of finding a species at any location in the vegetated area. This module focuses on cover: what it is, how it is measured, and how cover data are used by land managers to inform resource management decisions. This module focuses on vegetation structure: what structure represents, how it is measured, and how information about vegetation structure is used to inform resource management decisions. Very simply, vegetation structure refers to the three-dimensional arrangement of plants and plant materials on a site or across a landscape.
Vegetation structure is primarily influenced by plant cover on horizontal and vertical planes. This module focuses on plant biomass: what it is, how it is measured, and how biomass data are used by land managers to inform resource management decisions.
This module focuses on plant utilization: what it is, how it is measured, and how utilization data are used by land managers to inform resource management decisions. This module focuses on plant community diversity: how it is described, how it is measured, and how diversity is interpreted by land managers to inform management decisions. Remote sensing techniques offer many opportunities to inform, supplement, and sometimes replace traditional field-based aproaches to vegetation assessment and monitoring.
This module explores ways in which remote sensing can be used in monitoring and provides example applications. This module explores some established rangeland assessment and monitoring programs, describes their protocols, and discusses how the collected data are used in management decision making. To add captions to this video click the CC icon on the bottom right side of the YouTube panel and select English: Corrected captions.
Density is a measure of the number of individuals within a unit area. Since density measurements may be done on plant parts or other counting units, a more inclusive definition is the number of counting units per unit area. We often use density to determine the effect of management practice or vegetation treatments targeting a specific plant. A measure of the target plant density is taken before and after treatment to determine the degree of control achieved by the treatment. Example 1: Researchers in Montana used density measurements to determine what effect spotted knapweed control had in the Bitterroot Valley.
Figure 1. Image of spotted knapweed Centaurea stoebe L. Density measurements are often applied when we want to monitor changes in a given plant species over long periods. Density can be especially useful to detect the response of plants to a given management action.
For example, density measures can reveal the success of reseeding efforts by quantifying the number of seedlings present within management areas. We may also use density to identify threshold densities in community dynamics, and to provide information needed to make timely decisions concerning vegetation management.
Researchers measured Douglas-fir Pseudotsuga menziesii densities in foothill grasslands with various levels of encroachment Figure 2. They identified a threshold density for management: herbaceous biomass i.
Figure 2. Images of foothills grassland with differing densities of Douglas-fir. Density was measured by counting individuals including seedlings in 30 m 2 belt transects, which were randomly distributed through multiple plots.
Figure 3. Measuring density may be difficult in a heterogeneous greasewood plant community a , compared to a homogeneous winterfat plant community b.
Several methods are available for measuring density. The study found that tree aboveground and belowground basic density varied between species and within species.
What do you mean by vegetation? Use the word vegetation to refer to all plants and trees collectively, typically those in a specific region. Vegetation, as well as meaning all plant growth, can refer to the growth process of a plant.
The lettuce you planted a couple weeks ago is at an early stage of vegetation. What are vegetation types? Vegetation regions can be divided into five major types: forest, grassland, tundra, desert, and ice sheet.
Climate, soil, the ability of soil to hold water, and the slope, or angle, of the land all determine what types of plants will grow in a particular region. What is specie density? What is tree density? Tree density gives foresters an idea of how closely trees are growing in a given area.
This value is always expressed as trees per hectare. The tree density is not an exact number of all of the trees in the region, but it serves as an estimate.
Tree density can determine the number of trees in an area. What is the difference between density and abundance? IRRI, Manila. Google Scholar. Int J Remote Sens 28 19 — Can J Remote Sens — Lewis, Boca Raton. Book Google Scholar.
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Balkema, Rotterdam, pp — Foody GM Status of land cover classification accuracy assessment. Irrig Sci — Kimball J, Mcdonald K, Running S, Frolking S Satellite radar remote sensing of seasonal growing seasons for boreal and subalpine evergreen forests.
Remote Sens Environ — Tellus 43B— Int J Remote Sens 30 12 — Lloyd D A phenological classification of terrestrial vegetation cover using shortwave vegetation index imagery.
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