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Mammal biomass

  • Biodiversity

  • Compostion
  • Function
  • Structure


Mammals have important influences on ecosystem processes: nutrient cycling, energy flow, top-down influences (e.g. predation), bottom-up influences (e.g. herbivory), seed dispersal (Lacher et al. 2019). Biomass provides an indication of abundance and whether species are declining or increasing (Damuth 2023). Biomass can give a more meaningful assessment of the impact of a species on an ecosystem, allowing comparison between species with different body sizes (Greenspoon et al. 2023).

Species-specific monitoring may be relevant to certain project objectives. Small mammals are an important prey resource and are seed predators and dispersers in woodlands (Sunyer et al. 2016). Large herbivores, particularly deer, can have a negative impact on woodland regeneration and can degrade peatland, and therefore numbers are often monitored (Putman et al. 2011).

Methodology summary

Biomass can be estimated from the number of individuals and their average body mass (Damuth 2023). Standardised methods of estimating numbers of small mammals and deer are outlined below. Camera trapping can be deployed to support and complement these direct methods (Smart et al. 2004).

The Mammal Society National Woodland Small Rodent Survey (Flowerdew et al. 2003):

  •  7×7 grid, 2 traps per point to survey 0.81 ha area May-June and November-December

For monitoring deer populations (Smart et al. 2004):

  • Direct counts are only possible in open habitats (see Deer Initiative Vantage Point Counting Guide below)
  • Indirect methods e.g. Faecal Standing Crop (FSC) and Faecal Accumulation Rate (FAR) can be used in woodland, FSC is more accurate but requires the decay rate to be determined (see Smart et al. 2003 for method)
  • FSC – randomly placed plots stratified by habitat type – converted into estimates of deer population size and density (based on defecation rates and dung persistence rates)

UK Environmental Change Network Rabbits and Deer protocol.

The Deer Initiative Dung Counting Best Practice Guide, method for Faecal Accumulation Rate.

Method for Faecal Standing Crop in Smart et al. 2003 Monitoring woodland deer populations in the UK: an imprecise science.

The Deer Initiative Vantage Point Counting Best Practice Guide

Metric threshold or direction of change

For deer densities thresholds for impacts on habitats are given in Putman et al. 2011, but should be interpreted alongside direct monitoring of habitat impacts:

  • For woodland regeneration – 4-5 large deer or <25 roe deer per 100 ha.
  • Open habitats suffer light/moderate impacts at 7-8 red deer per 100 ha.

Technological innovations

  • Earth Observation sensors generate high resolution imagery, which can be used to identify larger species. (Lausch et al. 2016).
  • Advances in machine learning are increasing the efficiency of classifying and processing camera trap imagery (Tabak et al. 2018).

  • Agricultural
  • Forest
  • Grassland
  • Heathland
  • Other
  • Peatland
  • Saltmarsh
  • Wetland


  • Population


  • Medium


  • Future

Technical expertise

  • Medium

Standardised methodology

  • Partial