Logging effects on liana diversity and abundance in Central Guyana

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Methodology Individuals were not tagged, so it was not possible to monitor individuals over time. Changes in species composition had to be done by assessing changes at subplot (enumeration unit) and plot level. Table 2.2 Categorisation of lianas and subplot sizes used for sampling in the field and for analysis. See 2.4, p.18for explanation of Sample A and Sample B. Subplot dimensions (m) Area sampled per plot (m 2 ) Size class (field procedure) Sample A Sample B Large adults 20 x 20 10,000 ≥10 cm dbh Only in 10 x 10 Only in 5 x 5 Adults 10 x 10 2,500 ≥2 m height,
<strong>Logging</strong> <strong>effects</strong> on liana diversity and abundance in Central Guyana 2.4 ANALYSIS 2.4.1 Data preparation Data storage The data were initially stored in separate databases for plots (plot database, containing the information from Table 2.1), species (species database, containing information about names), individuals (individuals database, containing the information obtained from the field measurements, see “measurements”) and habitats (habitat database, containing identifiers and coordinates of the polygons describing skidtrails and gaps). Subplots were used as identifiers to relate censuses from different years in the Pibiri plots, while this was not possible in the remaining plots due to shifts in plot locations. Information on individuals measured in each census could not be related to each other, as they were not individually tagged. The individuals database and the habitat database were spatially linked using the PCraster GIS package. Before this was done, habitats were mapped and 5 m border zones were defined inside and outside gaps. This was done for two reasons: the methodological uncertainty associated with determining gap edges in the field, and to cater for possible ecological edge <strong>effects</strong> of gaps into forest surrounding gaps and of surrounding forest into gaps. Possible ecological edge <strong>effects</strong> include the micro-climatological <strong>effects</strong> of shading or insolation into the gap and forest, respectively (van Dam 2001), the different probability of propagule arrival close to edges as compared to gap centres and other differences such as litterfall (van Dam 2001). In the data analysis, when gap size is described this was based on the gap definition as used in the field. However, when subplots were assigned to habitat-categories (gap/non-gap), the 5 m zone into the forest was included in the gap definition, for the reasons described above. In the database, individuals can be linked to habitats in two ways. Either the coordinates of each individual and the coordinates of the various habitat categories can be linked to give individual habitat assignments, or subplots can be assigned a code on the basis of the most extensive habitat. There were two habitat variables coding for ground-level disturbance (on or off a skidtrail) and for canopy-level disturbance (location in forest, forest edge, gap edge and gap interior; both edge zones are 5 m wide). Habitat categories were merged for analysis if necessary (e.g. gaps were defined as forest edge + gap edge + gap interior for some analysis). For analysis, given the uncertainty associated with determining coordinates in the field, preference was given to the second method of assigning habitat codes to individuals, i.e. by means of uniform codes at the subplot level. All subplots were classified in one of four habitat categories: skidded gap (canopy and soil disturbance), skidtrail (soil disturbance), gap (canopy disturbance) or forest interior (no disturbance). Selection of data – Sample A and Sample B In the individuals database, individuals were selected for analysis based on a number of criteria: • Seedlings as enumerated in the 2 x 2 m subplots were retained for descriptive purposes of population size distribution only. They were not included in the analysis of compositional change and species responses to logging. • The size criterion for large adult lianas (dbh>10 cm) made that few individuals were measured at the level of the 20 x 20 m subplot (Table 2.2). Before the logging, only 1.9% of the total measured population in Pibiri consisted of individuals of this size (average 0.8 per subplot or 21 per ha, range 7-34). Therefore, this spatial level was only used for descriptive purposes but not most analysis. Instead, two samples were created at different spatial levels of analysis (Table 2.2). Sample A includes all lianas > 2m sampled within the 10 x 10 m subplots. Sample B includes all lianas ≥ 0.5 m height within the 5 x 5 m subplots. All lianas satisfying the criteria for inclusion in 18
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Logging effects on liana diversity and abundance in Central Guyana

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