Principles of Vegetation Measurement & Assessment
and Ecological Monitoring & Analysis


Veg Sampling
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Variables to Describe Plant Communities

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Readings & Instructions

  1. This lesson provides an overview of how individual attributes are combined into more comprehensive vegetation assessments.
  2. Read through the Text and work through the Summary Questions at the end of this page.
Summarizing values to Describe Plant communities

Summarized Descriptive Variables

The first set of numbers obtained in an assessment of vegetation are called Raw DATA or Field Values. Getting good raw data depends on:

  • Site selected for study
  • Method or protocol used
  • Skill of field technician
  • Quality or type of field equipment
  • Field conditions at the time of study
  • Etc., etc., etc.

The next step to getting an answer is to summarize the data and create a data summary. Data summaries often include descriptive statistics such as:

  • Mean or average
  • Median value
  • Standard error or Standard deviation
  • Minimum and maximum values
  • Etc., etc., etc.

The goal of vegetation assessment is to interpret field data and make decisions about the status or condition of the plant community relative to management plans or conservation goals.  But, to get a clearer picture of what is going on, we often create new variables that combine the raw or summarized data in ways that will facilitate interpretation. These descriptive variables include a whole range of indexes, ratios, quotients, rates, and combined terms including:

  • Relative abundance
  • Species composition
  • Diversity
  • Dominance
  • Similarity

Many summarized descriptive variables are well described with set parameters such as the Shannon-Weiner Index of Biodiversity. However, you are free to summarize and combine field values in any way that will help to "tease out" or make apparent the trends in the plant community that you are trying to ascertain.

Summary Questions

  1. What determines the quality of field data?

  2. Can you think of and describe a common combined variable (e.g., ratio or index) that is used to describe plant communities?

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