1. Effects of garlic mustard removal and deer exclusion on native plants in suburban forests Janet A. Morrison Department of Biology, The College of New Jersey and The New York Botanical Garden

3. Alliaria stand – Westchester County

4. How does a non-native invasive plant species affect native plant abundance and diversity? How do deer affect native plants? Do non-natives and deer interact in their effect on natives?

5. Northern Westchester County, NY Suburban / forested landscape Abundant Alliaria petiolata White-tailed deer density = 40 / km 2 Photo: PA State Parks

6. Experimental approach 8 stands of Alliaria ; 4 treatments / stand, 4m 2 plots: No removal, no caging No removal, caging Alliaria removal, caging Alliaria removal, no caging

7. Alliaria seedlings – removed 2x / year

8. Deer exclosure caging

9. Carya ovata shagbark hickory Quercus alba white oak

10. time x caging, F = 8.99, P= 0.0005 time x removal, F = 1.56, P = 0.23 * * *

12. RESULTS - WOODY NATIVES Cover and species richness did not increase with release from Alliaria competition. Cover and species richness did increase with protection from herbivory. Initial percent cover after 4 yr caging Acer saccharum (sugar maple): 2.27 %6.95 % Euonymus americana0.12 %1.13 % Lindera benzoin (spicebush)0.53 %1.62 % (means) Species colonizing caged plots: Acer rubrumCornus floridaLiriodendron tulipifera Acer saccharumEuonymus americanus Prunus serotina Betula sp. Fagus grandifolia Quercus alba Carpinus carolinianaFraxinus sp Vibernum acerifolium

13. Impatiens capensis spotted touch-me-not

14. time x caging, F = 2.13, p = 0.13 time x removal, F = 3.02, P = 0.05 *

16. RESULTS - NATIVE HERBS Cover (but not species richness) increased with release from Alliaria competition, but only after four years, and mostly when also protected from herbivory (but ns interaction). Species richness did not increase with protection from herbivory.

17. Celastrus orbiculatus Japanese bittersweet Photo: U. of CT.

18. time x caging, F = 1.59, P = 0.22 time x removal, F = 0.36, P = 0.78 *

21. RESULTS - NON-NATIVES Cover and species richness increased when release from Alliaria competition was combined with protection from herbivory. After 4 yr Initial percent cover Alliaria removal + caging Celastrus orbiculatus0.27 %3.61 % Species colonizing removal + caged plots: Berberis thunbergii Celastrus orbiculatus Microstegium vimineum Rosa multiflora

23. *

24. Alliaria petiolata no cagingcaging

25. Herbivory on Alliaria petiolata

26. SIGNIFICANT RESULTS - SUMMARY Woody natives -- cover and species richness -- increased with caging, regardless of Alliaria removal -- cover response in 2 years -- no response to Alliaria removal Herbaceous natives -- cover -- increased with Alliaria removal (mostly in caged plots); response took 4 years -- no response to caging alone no effects on species richness Other non-natives - cover and species richness -- increased only with combination of caging + Alliaria removal -- cover response in 2 years Alliaria cover : - increased w/ caging in 2 years - evidence for herbivory

27. CONCLUSIONS

28. Conclusions and Predictions For metro forests with both dense Alliaria and deer populations : herbivory stronger than competition if reduce Alliaria without reducing deer, unlikely to influence native plant community if reduce deer without reducing Alliaria, then Alliaria may increase before natives do

29. Caution ! Alliaria petiolata responded strongly and quickly to protection from deer, compared to native herbs Alliaria: mean cover 19% outside cages, 43% inside cages native herbs: 13% outside cages, 15% inside cages Non-native plants and native plants responded similarly to the combination of release from Alliaria competition and protection from deer non-natives: no-rem/no-caging mean cover 3.5%, rem/caging 8.4% native herbs: no-rem/no-caging 12.9%, rem/caging 19.3%