Dynamics of wetland and upland subshrubs at the salt marsh-coastal sage scrub ecotone

We asked: Is Lycium californicum an ecotone species and what factors restri ct it from overlapping more broadly with dominant plants of the salt marsh (downslope) and the coastal sage scrub (upslope)? Field sampling at Tijuana Estuary revealed that Lycium grows within a 1.1-m elevation range intermed iate between that of Eriogonum fasciculatum (a subshrub of the coastal sage scrub) and Salicornia subterminalis (an obligate wetland subshrub of tidal marshes). Hence, Lycium was confined to the wetland-upland ecotone. In gre enhouse experiments salt water wetting and soil moisture influenced these t hree species as follows: Salicornia required saturated soil to establish, r estricting it to the wetland. Eriogonum failed to tolerate salt water wetti ng of the soil, both as seedlings (100% mortality) and as adults (100% mort ality), likely restricting it to the upland. Lycium adults tolerated seawat er wetting of the soil (100% survival) but seedlings did not (100% mortalit y). Both Lycium and Eriogonum should be able to establish seedlings near th e wetland when soil salinity is low, but only Lycium would survive subseque nt tidal surges (seawater wetting). Lycium showed evidence of drought toler ance but no requirement for groundwater (which would restrict it to the low land); hence, its absence from the coastal sage scrub community may be due to competition with less salt-tolerant species. The few remaining populatio ns of Lycium are restricted by the narrow range of suitable habitat and con tinuing pressure fbr coastal development. Thus, the transition from salt ma rsh to coastal sage scrub should be protected and restored to support this rare ecotone species.