# A woodland ecosystem is described as being in a climax community. Explain why the net primary productivity (NPP) of a climax woodland community is lower than that of a young, rapidly growing woodland of the same gross primary productivity (GPP).

> OCR A-Level Biology A (H420) — 6.5 Ecosystems · Explain · 4 marks

> Ecologists studying woodland succession measured the gross primary productivity (GPP) of two woodland sites. Site A was a young, rapidly growing woodland established 10 years ago. Site B was a mature climax community of oak woodland. Both sites had identical GPP values, yet Site B had a significantly lower net primary productivity (NPP).

## Mark scheme (4 marks)

1. NPP is defined correctly as GPP minus respiratory losses by producers
2. The climax community has a greater total biomass / larger number of large woody plants requiring more energy for maintenance respiration
3. Greater biomass in the climax community means more energy is used in (maintenance) respiration
4. Therefore, with the same GPP but greater respiratory losses, NPP is lower in the climax community

## Key terms

- [net primary productivity](https://www.gradenine.co.uk/glossary/net-primary-productivity)
- [gross primary productivity](https://www.gradenine.co.uk/glossary/gross-primary-productivity)
- [climax community](https://www.gradenine.co.uk/glossary/climax-community)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-woodland-ecosystem-is-described-as-5ba1d048) · Published by Druglandscape Ltd.