New Jersey rush (Juncus caesariensis) COSEWIC assessment and status report: chapter 6
Biology
General
New Jersey Rush is a perennial herb that produces large numbers of seeds. In spite of this, seedlings are rarely found in the field in the United States (Schuyler, 1990) and none have been identified in the field in Nova Scotia. This species also reproduces asexually by means of rhizomes. Plants are wind-pollinated (Knuth, 1909) with flowering occurring in July and August; fruiting begins in August (Kral, 1983).
Reproduction
The relative amount of self- versus cross- pollination remains unknown (Schuyler, 1990).
Germination experiments by Ware (pers. comm., 1991) indicate that seeds germinate easily and quickly (in a few days) when placed on moist sphagnum in a Zip Loc bag and left for a short time in the greenhouse.
Survival
Changes in hydrological regime and succession by woody species affect the species’ survival.
Nine new stations for Juncus caesariensis were reported by Strong and Sheridan (1991) in Virginia. Seven of these new sites were located in power line right-of-ways. Schuyler (1990) reported it from logged sites in New Jersey and Virginia. These findings suggest that Juncus caesariensis is able to persist in vegetative form, for a certain length of time, in areas where canopy closure has rendered the habitat unsuitable for New Jersey Rush. When the canopy is opened up either through natural or unnatural means, these plants resume production of new shoots (Schuyler, 1990).
Physiology
The species is highly dependent on a certain hydrological regime and tolerates limited shade (Schuyler, 1990). This species does well under acidic conditions and is often found growing in sphagnum moss. It is always found in wet areas but does not tolerate steady standing water conditions.
In July of 1991, pH measurements and peat depths were recorded at five sites in the Point Michaud region (Newell and Newell, 1992). The pH at these locations ranged from 4.07 to 5.52.
This species is tolerant of some shade as indicated by its occurrence in Atlantic White Cedar swamps in the United States. In Nova Scotia, it is often slightly shaded by the shrubs in the riparian edges of bogs and fens. Full canopy closure, however, appears to impact New Jersey Rush negatively. Due to its re-appearance in logged sites and on power line-right-of-ways in the United States, it is believed that it can survive shaded conditions in vegetative form, resuming sexual reproduction once the canopy is opened. How long it can persist under these conditions is unknown.
Movements/dispersal
There is no data on seed dispersal although casual observation suggests that seasonal flooding and/or animal movement may assist with movement of propagules.
Nutrition and interspecific interactions
Juncus caesariensis is a member of the Atlantic Coastal Plain Flora. Most of these species are poor competitors but are tolerant of naturally occurring environmental stresses, e.g., flooding, ice scour, wave action and infertile soil (Keddy and Wisheu, 1989). These species are therefore often confined to habitats where more competitive but stress intolerant species cannot survive. New Jersey Rush, at least in Nova Scotia, is generally found in the peripheral zone of relatively infertile bogs and fens. It is in this area where seasonal flooding also occurs.
In August, 2002 a high percentage of the plants of New Jersey Rush occurring in one of the Gracieville sites (Site 4a) were observed to be heavily infected with a rust. This disease was not noticed at any of the other sites visited by the author at this time.
Behaviour/adaptability
New Jersey Rush habitat is susceptible to invasion by woody species. Any natural events or human-related activities that hold succession at an early stage appear to be beneficial to this species. Strong and Sheridan (1991) reported finding several healthy populations of Juncus caesariensis in recently cut power line right-of-ways in Virginia. The annual mowing of these areas was beneficial to New Jersey Rush by reducing woody second-growth vegetation and maintaining an open habitat. Ware (pers. comm., 1991) describes a reduction in plant numbers at one site in Virginia that seemed to be attributable to an invasion of Clethra alnifolia (Sweet Pepper Bush). On Cape Breton Island, Nova Scotia, the frequent occurrence of this species along animal, and in some cases, lightly used ATV trails, suggests a tolerance of, if not a dependence upon, some disturbance to maintain open habitat.
Seedlings grown by Ware (pers. comm., 1991) in the greenhouse were transplanted, when they were 30 cm tall, to a sphagnous pond margin where, J. caesariensis was once known to occur. Within two years, all had died. This was attributed to excessive flooding which kept the young plants covered by shallow water for extended periods.
Anything affecting the hydrologic regime where this species occurs may have a negative impact upon populations.