Survey Site Selection and Establishment

URI: http://linked.data.gov.au/def/corveg-cv/d3465997-9408-4816-af98-646af318e6b1

Date created: 2019-07-31
Date modified: 2020-07-18

Purpose

Survey Site Seletion Method is applied to identify study locations suitable for repeatable vegetation assessments.

Survey Site Establishment Method is carried out during the initial site visit in order to establish a study location for repeatable assessments of vegetation and physical features.

Abstract

Synopsis (Survey Site Selection Method)

Study locations are selected to ensure that all vegetation and Regional Ecosystems are adequately sampled across their geographic range. Allocation of study locations should be generally proportional to the area of each vegetation type, except for rare vegetation types. The study locations are distributed in such a way as to sample as much as possible the environmental variability across the landscape, given the time and accessibility constraints. The total number of study locations depends on the variability in the vegetation, the amount of remnant vegetation present and the number of existing study locations in adjoining regions. While study locations are located to describe typical examples of each vegetation and aerial photo-pattern type, care is taken to sample the full range of variation within a vegetation association or regional ecosystem. The general location of each site is predetermined in the office through preliminary stratification using geology, forestry, topographic and rainfall maps as well as Landsat satellite images and aerial photographs. However, it can sometimes be necessary to relocate a study location when it is first visited because of accessibility problems, disturbance to the site or if the stand area is found to be less than 1 hectare. Furthermore, additional sites can be established if variations to the preliminary stratification are encountered during initial visit to the study location.

Synopsis (Survey Site Establishment Method)

The study location is established during the first visit to the study location prior to conducting the assessment of the study location features. In order to physically establish the study location and prepare it for the subsequent assessments, the field observers record its geographic location and select a 50m x 10m quadrat within the study location. This sampling quadrat will be used to carry out the physical and vegetation assessments.

Key Features (Survey Site Selection Method)

• Method: GIS analysis, field confirmation
• Target: vegetation communities
• Classification: geology, forestry, topographic and rainfall maps, Regional Ecosystems

Key Features (Survey Site Establishment Method)

• Method: location recording, sampling unit set up
• Target: study location, sampling unit

Procedure

Technique (Survey Site Selection Method)

Location of study locations

In general survey data should cover the full range of environmental space and be sampled proportionally (Margules & Stein, 1989) or biased to less common types (Austin & Heyligers, 1989), with replicates covering the geographic range of the biota studied (Nicholls, 1989). For surveys conducted by the Queensland Herbarium, study locations are selected to ensure that all vegetation and regional ecosystems are adequately sampled across their geographic range. Allocation of study locations should be generally proportional to the area of each vegetation type, except for rare vegetation types, which are often oversampled relative to area (Neldner et al. 1995). The study locations and traverses are distributed in such a way as to sample as much as possible of the environmental variability across the landscape, given the time and accessibility constraints. While study locations are located to describe typical examples of each vegetation/photo-pattern type, care is taken to sample the full range of variation within a vegetation association or regional ecosystem.

The preferred method for study location selection is a relaxed grid survey (Reid, 1988) with stratification similar to that discussed in Vegetation Survey and Mapping of Upper North East New South Wales (NPWS, 1995), and field study locations located subjectively. This approach evolved from the stratification method documented by Neldner (1993).

The following steps are used to develop a preliminary stratification for mapping at 1:100 000:

• preparation of a geology overlay at 1:100 000 scale from the best available geology mapping;
• delineation of preliminary strata on an overlay using the geology overlay, and patterns on the LANDSAT image and black-and-white 1:83 000 aerial photographs. A main aim at this stage of the methodology is to identify land zones. Land zone recognition is essential for defining regional ecosystems (REs). The preliminary strata include cleared land and major photo-patterns which correspond to the geology; and
• flagging of the major vegetation and regional ecosystems with the aid of the photo-patterns delineated in conjunction with forestry, geology, topographic and rainfall maps, and existing data from reports, maps or other sources.

A sampling density of 100 secondary study locations for a full 1:100 000 sheet is recommended however sampling density does vary with map scale (refer to Table 1). In practice the number of study locations could be greater or lower, depending on the complexity of the vegetation, the amount of remnant vegetation present and the amount of existing data about adjoining areas. A minimum of three secondary study locations per vegetation regional ecosystem type is desirable. An informal indication of adequate sampling can be determined when additional study locations do not add substantial numbers of additional species or structural variation.

Scale of published map Hectares on the ground per cm² of map cm² of map per km² on ground Observation density per km²
1:5000 0.25 400 100
1:10 000 1.00 100 25
1:20 000 4 25 6.25
1:25 000 6.25 16 4
1:50 000 25 4 1.0
1:100 000 100 1 0.25
1:150 000 225 0.44 0.11
1:250 000 625 0.16 0.04
1:500 000 2500 0.04 0.01
1:1 000 000 10 000 0.01 0.003

Table 1: Recommended minimum ground observation density for land surveys at various scales. Observation density km² figures from Gunn (1988, Table 6.2) and based on 0.25 observations cm² of published map.

Number and density of study locations

The total number of study locations required to adequately sample an area depends on the variability in the vegetation and the condition of the ground layer as well as mapping scale, the amount of remnant vegetation present and the number of existing study locations in adjoining regions. The minimum recommended ground observation density for soil surveys is a useful framework for planning and appraising vegetation surveys. Under these soil guidelines the minimum number for sampling a standard (e.g. 1:50 000, 1:100 000 etc) map sheet at the specified scale is about 625 study locations. However, sampling densities do not need to be as high for vegetation surveys. This is because vast amounts of mapping data can be rapidly gathered as informal observation while traversing (on foot, by vehicle or aircraft), as opposed to soil surveys, which require subsurface sampling (Neldner 1993). For example, Neldner et al. (1995) used a minimum sampling index of half those listed in FAO (1979). Offsetting the need for fewer study locations for vegetation compared to soils is the fact that the minimum size of areas delineated by the Herbarium is smaller than the minimum size on which the soil sampling densities are based. Therefore, the minimum density of study locations listed in Table 1 is adopted by the Queensland Herbarium as the minimum standard that the Herbarium aims to collect to ground truth each map sheet.

Types of study locations

The total number of study locations is a mixture of detailed (secondary) and less detailed (tertiary) study locations. Generally, of the 625 study locations required for a full 1:100 000 sheet, 50-100 will be secondary or tertiary study locations and the remainder quaternary sites, as well as additional unrecorded observations made between study locations. In practice the number and mix of types could be greater or lower, depending on the complexity of the vegetation, the amount of remnant vegetation present and the amount of existing data in similar vegetation in adjoining areas. A minimum of three secondary study locations per vegetation community/ regional ecosystem type is desirable. An informal indication of adequate sampling of a vegetation community/regional ecosystem can be determined when additional study locations do not add substantial numbers of additional species or structural variation from that already sampled.

Technique (Survey Site Establishment Method)

• Although approximate study location locations are generally predetermined in the office previous to the fist site visit, it is sometimes necessary to relocate study locations during the initial visit to the study location because of accessibility problems or disturbance to the site. Study locations are relocated when the remnant vegetation area is less than 1 ha or there is excessive disturbance associated with edges of roads, tracks, quarries, fence lines or other cleared areas. This is especially desirable to minimise possible bias in the basal area sweep.
• Additional study locations may be established if the preliminary stratification and selection process did not account for the variation of vegetation types observed in the field.
• The coordinates of the study location are recorded at the centre of the sampling unit, ideally using a hand-held GPS.
• The study location encompasses a sampling unit which should represent the features of the study location. It is delineated by laying out a 50 m measurement tape on the ground. The sampling extends 5 meters on both side of the tape (see Figure 1).
• If the landscape or the vegetation structure does not allow this setup to properly represent the study location, the size and shape of the sampling unit can be adapted.
• The sampling unit is generally located near the centre of a pattern on the aerial photo used during the site selection process and along any observed contour, so as to typify the pattern of the study location.
• The sampling unit and the study location are only set up for the time during which the assessment methods are carried out, and are not permanently marked.

Figure 1: Setup of the study location and the sampling unit

Variations

For study locations located in rainforests, the sampling unit is generally 1000 m², but may vary according to species richness.

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