Tamsin Douglas

1. Detecting changes in the aquatic flora of the tarns of Cumbria’s Lake District Tamsin Douglas

2. Rationale – methods used to assess the project data • Focus of the analysis, and why I had to limit the scope of the study • Results and interpretation

3. Rationale • Compare Stokoe’s data with project data collected up to 2006, focussing on species diversity and relating this to any changes in tarn ecology • To get meaningful results needed to use statistics – had to apply numerical values to species lists

4. Ellenberg values • Hill et al 1999 • Devised numerical scores based on ecological tendencies of plants • 5 categories, but only 3 relevant; • Nitrogen (N) • Reaction or pH (R) • Moisture (F) • Excluded stoneworts

5. PLEX (Plant Lake Ecotype Index) • Duigan et al (2006) • Numerical score reflecting several aspects of plant ecology • Specific to freshwater aquatic plants (excluded some emergent species such as Carex spp) • Scores from 1-10

6. Data overload! • Botanical presence/absence for almost 200 tarns in 1970s & 2000s • Restricted this to LDNP only • Restricted analysis to aquatic plants only • Some tarn’s datasets not valid ….left 93 tarns with good data

7. Problem of Cumbria’s varied landscape • 93 tarns split in 2 sub-groups based on altitude and land-use • 34 Lowland and 59 Upland type tarns

8. Species richness • Overall decline • Highly significant decline in ‘true aquatic’ species • Significant decline in upland tarns

9. Winners and Losers Ranunculus aquatilis Veronica beccabunga Lythrum portula

10. Isoetes lacustris • 29 tarn records by Stokoe • 17 records by tarns project volunteers (41% drop) • Characteristic ecology with high sensitivity to change • Also declines in other isoetids • Littorella uniflora stable, though it is a robust plant by isoetid standards

11. Lake ecology

12. Enrichment of lowland tarns • The 34 lowland tarns studied have higher pH and nutrient level now than 30yrs ago. • Most probably impact of agricultural runoff from fertilised pasture, and high over-winter stocking levels in in-bye areas. • Shift in species ecology, with an increase in more competitive emergent macrophytes and resulting decline in the most sensitive isoetids. • Shift in tarn ecotype – more tarns classified in species rich, mesotrophic and eutrophic groups.

13. Change in upland tarns Dramatic decline in species richness, particularly of fully aquatic species No significant change in any of the ecological scores – unlikely to be a consequence of eutrophication or acidification Changing uplands- decline in grazing, especially since F&M in 2000 – though unlikely to impact aquatic vegetation. Climate change? Cumbria had some of its warmest summers on record recently

14. Conclusions Many of Cumbria’s tarns have changed in the last 30 years to varying degrees, and often in differing ways. More complete study would have been possible if abundance data had been available for Stokoe’s surveys – giving a more accurate picture of change Tarns project has yielded excellent data – providing a good baseline for comparison with surveys in another 30 years time!

15. Thank-you for the data! Photo credits Claire Cornish Heather & Tony Marshall Interactive flora of NW Europe nlbif.eti.uva.nl/bis/flora.php