Linking vines to woody hosts: Untangling the biotic influences in a physically dominated environment

Background/Question/Methods

Vines and lianas play important roles in plant communities, particularly with regard to successional processes.  Associations of vines with supporting woody vegetation affect establishment patterns as well as success of woody species colonization and expansion.  In mid-Atlantic coastal communities, these patterns and processes are particularly apparent due to relatively simple species assemblages, which are limited in complexity by harsh physical factors.  We investigated associations among species and functional groups at two Atlantic coastal barrier sites representing natural and managed conditions.  We measured vine and woody species community composition, abundance, cover, and density to investigate linkages between vine colonizers and woody plants.  These were compared to environmental variables including distance to shoreline, elevation, total soil chlorides and soil pH. Geomorphology of sites and physical structure of plant communities were evaluated using remotely-sensed data including aerial photography, hyperspectral imagery, and LIDAR scans.  Using relationships between LAI and woody cover derived from LIDAR data, we investigated how vine infiltration impacted shrub thickets of different ages.  Presence / absence data and stem counts were used to relate vine and woody abundance to environmental variables, to relate vine functional group abundance to woody functional group presence and abundance, and to test for associations among species.

Results/Conclusions

Woody communities were largely dominated by two congeneric (Morella) nitrogen-fixing shrubs.  Vine communities were dominated by the generalist species, Parthenocissus quinquefolia, Toxicodendron radicans, Smilax bona-nox, and two Vitis species.  Significant functional group associations existed, linking environmental variables to woody vegetation occurrence, and to abundance of vines when considered as one functional group.  At the managed site, vine cover and vine species richness were significantly related to woody cover and richness (p < 0.01).  At the natural site, the relationship between vine cover and woody cover was significant (p < 0.05), as was the relationship between vine richness and woody species richness (p < 0.01).  LIDAR analysis results demonstrated that canopy density did not increase significantly with vine presence, indicating that canopy replacement has occurred.  Hyperspectral indices also indicated a negative physiological impact of vines on woody vegetation.  Little evidence of species-specific interactions at these sites was observed.  We attribute this to overwhelming dominance of climber-accommodating Morella species and the generalist habits of the most abundant vines.  We support the hypothesis that vines play a linking role in the expansion and decline of woody shrub thickets, and in the transition to maritime forest at coastal barrier sites.