Vegetation Analysis
Calculate IVI, basal area, and stand structure metrics.
Overview
Vegetation analysis tools help characterize plant communities through standardized metrics. FieldEco calculates these automatically from quadrat and transect data.
Importance Value Index (IVI)
Comprehensive measure of species importance combining three metrics.
Formula
IVI = Relative Density + Relative Frequency + Relative Dominance
Components
Relative Density
RD = (Density of species / Total density) × 100
Relative Frequency
RF = (Frequency of species / Total frequency) × 100
Relative Dominance
RDom = (Basal area of species / Total basal area) × 100
IVI Range
- Maximum: 300 (dominates all three metrics)
- Typical dominant species: 30-80
- Rare species: <10
Interpretation
| IVI Range | Role |
|---|---|
| >50 | Dominant species |
| 20-50 | Co-dominant |
| 10-20 | Associate species |
| <10 | Rare/occasional |
Basal Area
Cross-sectional area of tree stems.
Per Tree
BA = π × (DBH/2)²
Or using circumference:
BA = C² / (4π)
Per Plot/Hectare
BA/ha = (Σ individual BA / plot area) × 10,000
Reference Values
| Forest Type | Typical BA (m²/ha) |
|---|---|
| Young secondary | 10-20 |
| Mature secondary | 20-30 |
| Old-growth tropical | 30-50 |
| Temperate rainforest | 40-80 |
Stand Density
Number of trees per unit area.
Calculation
Density/ha = (Count in plot / plot area) × 10,000
Example
- 25 trees in 0.1 ha plot
- Density = 250 trees/ha
Frequency
How often a species occurs across samples.
Formula
Frequency = (Plots with species / Total plots) × 100
Frequency Classes
| Frequency | Class | Interpretation |
|---|---|---|
| 1-20% | A | Rare |
| 21-40% | B | Occasional |
| 41-60% | C | Frequent |
| 61-80% | D | Common |
| 81-100% | E | Constant |
Coverage Analysis
Percent cover by species or growth form.
Visual Estimation
- View from above
- Estimate horizontal projection
- Allow overlap (can exceed 100%)
Classes
| Cover | Description |
|---|---|
| <1% | Trace |
| 1-5% | Rare |
| 5-25% | Sparse |
| 25-50% | Moderate |
| 50-75% | Abundant |
| >75% | Dominant |
Stand Structure Metrics
Size Class Distribution
- Diameter classes (5 or 10 cm intervals)
- Height classes
- Shows regeneration and population structure
Canopy Stratification
- Emergent (above main canopy)
- Canopy (upper layer)
- Subcanopy (intermediate)
- Understory (lower layers)
- Ground layer
Using Analysis in FieldEco
Running Vegetation Analysis
- Complete quadrat survey with tree data
- Include DBH for all trees
- Open Analysis → Vegetation
- View IVI table and graphs
Data Requirements
- Species identification
- DBH for trees (>10cm typically)
- Count per plot
- Presence across plots
Results Include
- IVI ranking table
- Basal area summary
- Density calculations
- Frequency distribution
- Graphical displays
Best Practices
Field Methods
- Use consistent DBH height (1.3m)
- Measure all stems above threshold
- Record to appropriate precision
- Note multi-stemmed individuals
Analysis
- Choose appropriate DBH cutoff
- Consider plot size for comparison
- Report number of plots/replicates
- Include confidence measures
Related Documentation
- Quadrat Survey - Data collection
- DBH Calculator - Measurement tool
- Diversity Indices - Community metrics