Interactions of Deciduous Trees and Soil

Sep 11, 2024

UBC Farm Lecture Notes

Introduction

  • Location: UBC Farm
  • Purpose: Study the influence of deciduous trees on the forest floor.

Importance of Deciduous Trees

  • Types of trees present: Bigleaf maple and alder.
  • Disturbance History:
    • Area cleared around 50-60 years ago.
    • Deciduous trees were the first to grow back in.

Organic Horizons vs. Agricultural Soil

  • Organic Horizons:
    • Forest soil contains organic horizons, unlike agricultural soil which consists only of mineral soil.
    • Organic horizons influence:
      • Nutrient Availability: Nutrients are held within organic matter and released as it decomposes.
      • Physical Properties: Improves moisture retention, keeping the site moist even during dry periods.
      • Temperature Regulation: Buffers temperature extremes in the mineral soil.

Carbon and Climate Change

  • Forest floor contains significant carbon:
    • Acts as a potential carbon sink or source.
    • Important for understanding global climate change.

Influence of Tree Litter

  • Litter from deciduous trees enriches the forest floor:
    • Contains nutrients, especially nitrogen from alder.
    • Supports organisms that mix organic material into the soil, creating AH horizon.
  • Seasonal Variation:
    • Less litter in summer due to decomposition; more litter expected in fall.

Measuring Soil Horizons

  • Mineral Horizons Measurement:

    • Measured from mineral-organic interface downwards.
    • Example: AH horizon depth approximately 15 cm.

  • Organic Horizons Measurement:

    • Measured from mineral-organic interface upwards.
    • Total forest floor depth: approximately 5-6 cm.

Characteristics of Trees in UBC Farm

  • Common trees: Douglas fir and hemlock typical of coniferous forests.

Forest Floor Observations

  • Thicker litter layer from coniferous needles:
    • Needles decompose slower due to high carbon and lignin content.
  • AH and F Horizons:
    • A thick AH is present but little to no F horizon noted.
    • Presence of earthworms mixing litter into the soil explains the AH development.

Conclusion

  • The study reveals the complex interactions between tree types, soil horizons, and environmental factors at UBC Farm.