Caracterização e Avaliação da Flora e Vegetação no

1 Objectives
VIII Assessment of Ground Vegetation 5
Within the framework of intensive monitoring activities at Level II, vegetation assessment is
important for two different reasons. Firstly, vegetation is a major component of forest ecosystems.
Vegetation layers contain a large part of total forest biological diversity. They play a
direct role in water or nutrient cycling, and strongly interact with other biotic components (insects,
game, etc.). Vegetation has been also identified as a specific target for the calculation of
critical loads/levels. Secondly, vegetation is a good bioindicator of environmental changes. Our
current knowledge of the ecological niche of numerous plant species allows changes in underlying
environmental factors to be deduced from vegetation changes. Thus, the long-term study
of vegetation dynamics at selected locations will provide information on changes in other forest
ecosystem variables (soil, microclimate, etc.).
The two main objectives of the vegetation assessment are:
• characterization of the current state of the forest ecosystems on the basis of their
composition;
• monitoring of the vegetation changes due to natural and anthropogenic environmental
factors.
The characterization will allow plots to be positioned within identifiable vegetation types. The
aims of studies of vegetation dynamics are to describe, explain and model succession, by an
analysis of pathways, causes and mechanisms of vegetation changes.
2 Sampling design
Since there is a trade-off between the accuracy of species cover estimation and the area which
can be surveyed, two different sampling designs may be used, which either lead to a more
qualitative or to a more quantitative characterization:
• in the first case, the dynamics are assessed by monitoring changes in the species composition
of a large number of species over a large area, utilizing sampling units greater than
100 m 2 , with a low to medium accuracy in estimates of changes in cover for each of these
species;
• in the second case, the study concentrates on population dynamics (expansion or regression)
on a smaller area. Small sampling units (in general under 10 m 2 ) are used for a more
accurate estimation of species cover.
The area selected for vegetation assessment must be representative for the plot, in order to
allow the comparison with other parameters recorded on the same plot. Several sampling units
can be used in order to obtain statistical replication.
2.1 Total area surveyed, number and shape of sampling units
According to phytosociological usage, the minimal requirement is to sample almost all of the
species at the plot level. In order to achieve comparability of results between countries, a
common sampling area (CSA) of 400 m 2 , representative for the ground vegetation of the Level
II plot, is mandatory. This area can be reached as the sum of smaller sub-plots within the Level
updated 06/2002