Structure and Functioning of a Managed Grassland Ecosystem

CONTENTS

• Summary
• Key words
• Author
• Introduction
  • Aim
  • Division of the project into separate exercises
    Table 1. System analysis summary
  • Learning objectives
  • Ecological concepts
  • Skills required
  • Level of study
    
• Legislative and ethical considerations
  • Health and safety
  • Disability discrimination
  • Animal welfare
  • Environmental awareness
    
• Methods
  • Staffing and student group size
  • Study site
    Figure 1. Sketch of the site layout
  • Time of year
  • Data handling and statistical techniques
  • Preliminary field procedure
    
• Part I. Plant diversity
  
• Part II. Ecosystem analysis
  • Exercise A: Biomass and production of above ground vegetation
  • Exercise B: Biomass of below ground vegetation
  • Exercise C: Soil bulk density, moisture content and soil organic matter
  • Exercise D: Nutrient pools in roots and above-ground vegetation
  • Exercise E: Soil nutrient pools (plant-available Na, K, Ca and total soil N)
  • Exercise F: Fauna
  • Exercise G: Temperature
  • Exercise H: Precipitation (wet deposition)
  • Exercise I: Soil water (infiltration)
  • Exercise J: Carbon fluxes (CO₂-C)
  • Exercise K: Nitrogen mineralization
  • Exercise L: Denitrification
  • Exercise M: Soil solution sampling (mineral-N, SO₄^--, pH)
  • Summary of results for exercises A to M
    Table 2. Summary of results
• Discussion
  • Success in achieving learning objectives

SUMMARY

An area of seeded grass has been subject to two management regimes for more than 20 years. One area has been mown at intervals of two to three weeks throughout the growing season, while an immediately adjacent area has been left uncut and has undergone successional development and has now developed scrub cover (see photograph). The effects of mowing on the structure and functioning of the grassland are investigated by comparing mown and unmown plots.

The results demonstrate:

• how management selects for plants with particular adaptive traits
• interactive effects of management on the whole biological structure and functioning of the grassland system
• biophysical controls on carbon and nitrogen dynamics
• inputs and losses of nutrients by rainfall and leaching of soil solutions
• effects of vegetation cover on heat fluxes and nitrogen dynamics.

KEY WORDS

grassland, ecosystem analysis, carbon, nitrogen, succession, mowing, plant diversity, invertebrate diversity

AUTHOR

INTRODUCTION

Aim

To investigate the effects of mowing on grassland vegetation diversity and succession, and on nutrient pools and fluxes in plants and soil.

Division of the project into separate exercises

• Because of the large and comprehensive nature of this project it has been divided into two parts. Part I is an initial survey of plant diversity (herbs and shrubs) in mown and unmown plots, a study of adaptive traits of plants to intensive mowing and a comparison of enumeration methods. Part II is a system analysis comprising thirteen separate exercises (A to M), six related to pools and seven to fluxes. These exercises are described individually.
• The ecosystem project is best tackled in its entirety. The exercises are carried out singly or in combinations by separate small groups of students. Some exercises are more time-consuming than others, so shorter ones can be combined in single practical sessions.
• Alternatively, if resources are limited or a less comprehensive approach is required, the project may be reduced to a single exercise or a combination of a few of the exercises. Obviously, the value of the original holistic approach will then be greatly diminished.
• The results of the individual exercises are synthesised at the conclusion of the investigations. If all the exercises have been tackled an overall picture of the linked processes occurring within the grassland system and the differences caused by the two management treatments will be apparent.
• This project outline is not a comprehensive methods schedule, since background knowledge and technical backup is required for many of the exercises. The exercises can be used separately and/or be modified as required. The illustrative data for each exercise are from student practicals and may not necessarily show expected trends. The protocol can, however, be refined for research into ecosystem processes.

Table 1 is a summary of the complete system project components.

POOLS

FLUXES

Learning objectives

• Understand how to carry out an ecosystem study.
• Appreciate group objectives and team responsibilities.
• Understand experimental design, sampling methods and the importance of replication.
• Gain practical experience of a wide range of field and laboratory methods used in ecological studies.
• Understand processes of nutrient cycling between plants, invertebrates, litter and soil.
• Gain experience of the identification of herbs and diverse invertebrate groups to practical taxon (at least Class/Order).
• Understand the impacts of meadow management (mowing) on
  • plant diversity
  • plant succession
  • grass growth, biomass and nutrient quality
  • nutrient pools and fluxes
  • microclimate and habitat structure
  • surface-living and soil invertebrate communities.
• Understand the role of earthworms in soil structure and hydrology.

Ecological concepts

Vegetation management has fundamental and interactive effects on the structure and functioning of ecological systems. Different intensities of management (mowing) affect the composition of plant and animal communities and this has implications for different conservation objectives for flowers, butterflies, birds, mammals, etc.

Skills required

A level Biology and/or Geography
GCSE/AS Mathematics and Chemistry

Level of study

Undergraduate year 1 (for exercises on plant and invertebrate communities) or year 2/3 (for exercises on system analysis).

LEGISLATIVE AND ETHICAL CONSIDERATIONS

Health and safety

• The use of chemicals in the laboratory must be subject to COSHH regulations.
• Documentation available in the laboratory advises students of risks arising from their work and precautions to be taken where necessary.
• Precautions to be taken in the laboratory and with the use of reagents are mentioned in the Methods sections. Care should be taken with barium chloride (moderately poisonous). This could be omitted from CO₂ procedures, but with loss of analytical precision.

Disability discrimination

All the exercises could be carried out within the constraints of particular disabilities and accessibility of the field sites.

Animal welfare

• Extraction of earthworms from soil has traditionally been done using 0.25% formaldehyde solution, but its general use is now prohibited . Mustard and chilli solutions have been used to expel worms from soil, followed by washing to remove the irritants. However, digging up and hand sorting soil samples, although more laborious, is preferable, not only because it harms few earthworms but it is more effective for sampling juveniles and certain soil-living species. The process of hand-sorting also provides insight into the nature and structure of soil.
• Pitfalls containing a trapping solution inevitably result in the death of invertebrates (and very occasionally small mammals). It is impractical to use dry cups. Extraction of soil invertebrates into preservative kills thousands of small animals, but this is rarely regarded as a matter of concern by students, and raises interesting ethical issues about animal type and size.

Environmental awareness

The students should appreciate the value of long-established experimental plots and carry out their investigations with the minimum of disruption to the site. If the field area is small it is advisable to fill in holes using soil from the site and to avoid using the same plots the following year.

METHODS

Staffing and student group size

30-60 students in about a dozen small groups require at least 3-4 well-briefed demonstrators for the system analysis, because of the range of different exercises involved. The main recurrent problems are inadequate labelling of samples, and bulking materials rather than keeping separate replicates as a measure of sample variability.

Study site

An area of seeded grass on the University of Exeter Estate is used for this project. For more than 20 years half of this experimental area has been mown (without the mowings being removed) and half has been left unmown (Figure 1).

Figure 1. Sketch of the site layout

Time of year

April to October

Data handling and statistical techniques

Where appropriate the following are used for analysis of data gathered during the exercises:

• Spread sheets
• Regression (calibration of readings and standards, or interpolate graphically).
• ANOVA (comparison within and between treatments blocks if sufficient sampling intensity)
• t-tests (comparison of means).

Preliminary field procedure

A long-term experimental site is set up in grassland.

• One area is mowed at intervals of at least 2-3 weeks throughout the growing season, with the mowings not removed, while an immediately adjacent area is left uncut.
• The methods described here could be used on any paired treatments. These need not necessarily be contiguous, but the soils and other environmental conditions should be identical as far as possible, and have a record of past management.
• This is a long-term experiment, but sampling can commence one year after the experimental site has been set up. Selective effects of mowing on plant species can be observed within one season.
• One 10 m by 20 m plot is set up bridging the mown and unmown grassland areas (Figure 1). Alternating 1m rows are used for sampling and as paths. Students must avoid trampling the area until the plots are established.
• Replicate samples of plant material and soil are taken from mown and unmown plots, as detailed in the separate exercises.

Copyright 2003 British Ecological Society. All Rights Reserved