Davidsonia

Brazilian pepper (Schinus terebinthefolia) is an aggressive exotic shrub in South Florida, which invades disturbed areas and often creates dense monocultures. As part of management efforts at Montgomery Botanical Center, we investigated a disturbed habitat with both Schinus terebinthefolia and native mangrove vegetation, on a 12 hectare landsite that was initially cleared and has been left fallow since at least the 1950s. We examined relative density and spatial distribution of mangrove and S. terebinthefolia, in order to explore hypotheses about competition between mangroves and S. terebinthefolia. We reviewed archived aerial photographs and conducted a targeted field survey of the interface between the mangrove and Brazilian pepper. Results of the survey and modeling demonstrate that mangroves may sometimes compete successfully with S. terebinthefolia. Intermediate age S. terebinthefolia were not observed at any transect point and seedlings did not produce typical allelopathic effects. In this case mangrove vegetation may compete when dispersed into open areas proximal to Schinus stands. Areas first colonized by mangrove did not support recruitment of Schinus and dense monospecific stands of S. terebinthefolia did not support further seedling recruitment of that species. This may be due to the specific hydrolic conditions and soil dynamics observed in this area. Marl soil, low elevation and constant flux in water level hindered the ability of Schinus to dominate the entire area of the study. Our observations are consistent with observations that early phases of mangrove restoration work are critical to establishing healthy mangrove systems, which are less likely to be invaded by Schinus as mature stands.

Davidsonia - A Journal of Botanical Garden Science

Davidsonia - A Journal of Botanical Garden Science

Editor, Iain Taylor writes about man-made and natural disturbances to ecosystems and the need to understand the impacts of these disturbances.

During over 15 years of plant ecological research in the Kluane region of southwestern Yukon, our studies required us to grow, propagate, and sometimes kill, native plants for experimental purposes. Here we present observations on germinating, growing, propagating and transplanting some of the common native plant species in the Kluane region.

The 1997 Red River flood afforded a valuable opportunity for studying the impact of an infrequent severe disturbance on gallery forests. In 1997 and 2002 we sampled two sites protected and two sites unprotected by a flood control structure near Winnipeg, Manitoba, Canada using three 150 m transects in the lower floodplain (n = 45 quadrats per site). The mature canopy of unprotected sites consisted of Fraxinus pennsylvanica Marsh. and Ulmus americana L. at low cover whereas protected sites contained five tree species. Regeneration data suggest F. pennsylvanica will continue to dominate in unprotected sites, with treefall providing opportunities for pioneer flood specialists like Salix amygdaloides Anderss. Fewer gap openings occurred in protected sites, in which Acer negundo L. and F. pennsylvanica will likely become co-dominants.

Understorey taxa normally able to survive the moderate disturbance associated with seasonal inundation of the lower floodplain of protected sites succumbed to the harsh conditions in the unprotected sites. Many were knocked back or eliminated by 2002, with greater reductions in richness and diversity in unprotected sites. Ruderals were promoted in unprotected sites but most were less prominent by 2002. Although several taxa, e.g., Vitis riparia Michx. and Bidens frondosa L. had significantly higher cover in protected sites by 2002, Xanthium strumarium L. and Polygonum amphibium L. were the only understorey species with significantly higher cover in the unprotected sites. Correspondence analysis indicated flood protection generated differing trajectories, with site differences contributing to variable successional outcomes.