South East Queensland dry sclerophyll forest header image

Succession Lab – SEQ Dry Sclerophyll Forest (Post‑Agriculture)

A South East Queensland grazing paddock has been abandoned. Over time, plants recolonise the site and the ecosystem’s structure changes (understory vs canopy). Your job is to use quadrat data to describe how community composition changes through secondary succession and to explain why those changes happen.
Ecosystem Dynamics • Year 12 Biology

Scenario

The site was previously used for cattle grazing. The disturbance removed much of the understory and limited tree recruitment. After abandonment, soil remains intact, and recolonisation occurs via seed bank, resprouting, and dispersal.

  • Location: Western Brisbane region (SEQ)
  • Ecosystem type: Dry sclerophyll eucalypt woodland
  • Sampling: 10 m × 10 m quadrats (each grid square = 1 m²)
  • Layers: Understory (0–2 m) and canopy (>5 m)
  • Time points: 5, 20, 50, and 100 years since abandonment

Species Key

○

Eucalyptus tereticornis

Forest red gum

▲

Acacia spp.

Wattles

■

Lophostemon confertus

Brush box

●

Native grasses

Themeda triandra

□

Banksia spp.

◇

Casuarina spp.

She-oaks

Quadrat Survey Data

Each grid below shows where individuals were recorded within a single 10 m × 10 m quadrat at each time point. Use the symbols to count each species and calculate percentage composition.

Understory (0–2 m)

Understory – 5 years
▲ ● □ ● ▲ ● ▲ ● □ ● ◇ □ ● ● ● ▲ □ ▲ ▲ ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ◇ ● ● ● Each square = 1 m² (10 m × 10 m quadrat)
Understory – 20 years
○ □ □ □ ▲ ● ● ◇ ◇ ▲ ● ◇ ▲ ▲ ● □ ○ ● ● ● ▲ ● ▲ ▲ ▲ □ ● ● ◇ ● □ ● ◇ ● ▲ ■ ○ ■ ● ● ● ▲ ○ ● ● Each square = 1 m² (10 m × 10 m quadrat)
Understory – 50 years
◇ ◇ ● ▲ ● □ □ ▲ ● ■ ○ ◇ ○ ▲ ○ ▲ □ □ □ ○ ● ◇ ■ ▲ ● ▲ ■ ● ■ ◇ ○ ○ ● ▲ ▲ □ ● ■ ◇ Each square = 1 m² (10 m × 10 m quadrat)
Understory – 100 years
□ ◇ □ ■ ○ ○ □ ○ ○ ■ □ ■ ● ● ◇ ● ■ ○ ▲ ○ ▲ ▲ ▲ □ ■ ■ ● ◇ ▲ ○ ◇ ■ ▲ ○ ◇ ◇ Each square = 1 m² (10 m × 10 m quadrat)

Canopy (>5 m)

Canopy – 5 years
◇ ▲ ▲ ▲ ◇ ▲ ◇ □ Each square = 1 m² (10 m × 10 m quadrat)
Canopy – 20 years
○ ○ ▲ ▲ ○ ▲ ○ ◇ ◇ ◇ ▲ ■ ■ ◇ ▲ □ □ ○ ▲ Each square = 1 m² (10 m × 10 m quadrat)
Canopy – 50 years
○ ◇ ○ ○ ○ ○ ▲ ■ ○ ◇ □ ▲ ○ ◇ ■ ▲ ■ ▲ ◇ ○ ■ ○ ○ ■ ■ Each square = 1 m² (10 m × 10 m quadrat)
Canopy – 100 years
○ ○ ○ ○ ◇ ■ ■ ■ ○ ○ ◇ ○ ○ ▲ ○ ■ ■ ■ ◇ ○ ■ ▲ ■ ■ □ ○ ○ ○ ■ ○ Each square = 1 m² (10 m × 10 m quadrat)

Environmental Data

Time since abandonment Air temp (°C) Soil temp (°C)
5 years3134
20 years2928
50 years2624
100 years2422

Hint: As canopy cover increases, soil surface temperatures usually decrease due to shade and increased moisture retention.

Percentage formula

Percentage composition = (Number of individuals of a species ÷ Total individuals) × 100

You will create two data tables:
• one for the understory (5 → 50 years)
• one for the canopy (5 → 100 years)

Part A — Construct data tables

  • For each grid, count the number of each symbol.
  • Calculate percentage composition for each species at each time point.
  • Record totals clearly (show your working).

Part B — Construct graphs

  • Graph 1: Understory species (% composition) from 5 → 50 years.
  • Graph 2: Canopy species (% composition) from 5 → 100 years.
  • Axes, scale, title, and legend must be included.

Part C — Data interpretation

  1. Which species dominate early succession in the understory? Explain why.
  2. Which canopy species increase the most over time? What does this suggest about community structure?
  3. Describe the relationship between soil temperature and time since abandonment.
  4. Does species richness appear to increase, decrease, or stabilise? Support with evidence from your tables.
  5. Is there evidence of competitive replacement? Use at least one example.

Part D — Mechanistic explanation

Use correct ecological terms to explain why the community changes over time. Include:

  • Facilitation: early species modify the habitat (e.g., shade, litter, soil moisture) making it easier for later species.
  • Competition: changing light, space, water, and nutrient availability affects survival and recruitment.
  • Tolerance: later species can persist under lower light and altered soil conditions.
  • Structural complexity: biomass and canopy cover increase over time.

Remember…