Applicability of Modified Whittaker plots for habitat assessment in urban forests: Examples from Hannover, Germany

- We studied the applicability of Modified Whittaker plots (MWP) for habitat assessment.
- Total and endangered plant species richness were surveyed in urban forests.
- Time efficiency and effectiveness of MWPs were compared to complete field surveys.
- MWPs were time efficient in large habitats but showed limitations in detecting endangered species.
- Habitat evaluation based on MWP data mostly resulted in lower habitat values as compared to the complete field surveys.

In ecological planning, cost-effective but accurate methods for the assessment of habitats and species are needed. In this study we investigated whether the multi-scale Modified Whittaker plot (MWP) method is suited for vascular plant surveys as a basis for habitat assessment. We measured total and endangered species richness in ten urban forests in Hannover, Germany. The MWPś time efficiency and effectiveness in capturing species richness were quantified and compared to complete field surveys. The MWP method estimated both greater and lower species numbers per habitat, the absolute deviation ranged from +60 to −15 species. It generally captured fewer endangered plant species than the complete field survey. In particular, the method did not detect species with a high category of endangerment. Regarding time efficiency, the MWP method took an average of 186 minutes per habitat, while the complete field surveys were more time consuming (mean = 265 minutes). In small habitats (<1.0 ha) the full survey took less time than the MWP method. To determine the applicability for nature conservation and ecological planning, we evaluated the species data derived from the two methods by using common habitat evaluation criteria. In most cases, the species data received from the MWP method resulted in lower habitat values compared to the use of data from the full surveys. We conclude that comprehensive habitat evaluation exceeds the applicability of the MWP method which may miss locally rare species. However, the MWP method provides an opportunity to efficiently estimate plant species richness patterns in urban forests and, thus, holds the potential to convey basic information for an overall monitoring of species diversity and may lead to specific habitat assessment efforts.