Eastern lilaeopsis (Lilaeopsis chinensis) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Keddy (1987) found the species to be abundant at sites in the Medway and Tusket river estuaries, estimating that L. chinensis extended for several kilometres of coastline wherever suitable habitat (gently sloping muddy or gravel shoreline) existed. Keddy (1987) reported very high densities of plants (1,250 / 25 cm²) at these two sites, although how she determined individuals is unclear (presumably individual leaves). Extrapolating from this value, an estimate of 2.2 billion plants or more (sensu stricto per Keddy 1987) may be found along Nova Scotia’s south shore, localized at several sites in the Tusket and Medway river estuaries. This is based on a band of growth with an estimated length equal to the extent to which Keddy successfully found L. chinensis (Keddy 1987), with a conservative width of two metres. However, A. Kingsley (pers. comm., 2002) estimated in one stretch of the Tusket population a density ranging from 5-50 clumps per during a 1998 site visit, indicating a discontinuous and patchy distribution. It is very doubtful the simple extrapolation based on Keddy’s observation gives an accurate estimate of population size.

Field investigations in 2002 were conducted by Holder over a period of 6 days, with a total of 10 areas searched (supplementary maps of search areas were provided to COSEWIC), including the three estuaries where the species was confirmed to be extant. Two Nova Scotia government employees searched the LaHave site, also in 2002, but found no new sites beyond that reported in this report by Holder. Field investigations by Holder in 2002 confirmed the extent of L. chinensis at the Tusket River estuary reported by Keddy (1987). Indeed, the population was found along a greater length of shoreline during 2002 than was found earlier, but this certainly reflected greater search effort rather than a range extension.

In agreement with Kingsley’s 1998 observation, distribution was patchy and discontinuous at Tusket, with L. chinensis absent from some large sections of shoreline. Along a 450 m stretch of shoreline at the mouth of the Tusket, a total of 110m of shoreline hosted L. chinensis plants. Where leaves were present, two types of quadrats were thrown to help estimate density. Leaf density as measured by 10 cm x 10 cm quadrats ranged from 20 to 81 leaves/ 100 cm², the average being 57 leaves/ 100 cm². However, five 1m x 1m quadrats showed that extrapolation from these data was inappropriate since densities measured at this scale were far lower than extrapolated values, ranging from 440 to 870 leaves/m², with an average of 605 leaves/m².  Nowhere was density as high as that reported by Keddy (1987), even in small quadrats with dense rhizome growth.

All patches of L. chinensis had flowering plants, with densities that similarly ranged with scale. Within 100cm² quadrats, flower density ranged from 5 to 24 flowers (average 14 flowers/100 cm²). At a larger spatial scale, density was lower, ranging from 56 to 73 flowers/m² (average of 64 flowers/m²). The size of the population at Tusket is estimated to be between 660,000 and 1,300,000 leaves, or between 84,000 and 110,000 flowers.

The presence of L. chinensis at the Medway River estuary was confirmed during 2002. Its distribution was widely scattered along the estuary, occurring in discrete clumps of 1 m² up to 100 m², up to a hundred or more metres apart. At this location, L. chinensis grew in association with S. alterniflora and P. maritima, almost always within dense stands of the grass. Rarely was it found in open patches within dense Spartina stands, and it was not found in the open mudflats further down the intertidal zone. Of the approximately 15,000m² searched in one area near the mouth of the Medway River, L. chinensis populated approximately 320 m² (~2% of the area).

Where it was found, L. chinensis grew in densities greater than those found at Tusket. Within 10 quadrats measuring 10cm x 10cm, densities ranged from 93 to 213 leaves/100cm², with an average of 156/100 cm². At a large scale, densities were lower than expected from a straight extrapolation of the 100 cm² data, but were higher than densities at Tusket. Five 1m² quadrats had a range of 1430 to 1950 leaves/m², with an average of 1720/m².

Densities of flowers were smaller than at Tusket, somewhat surprising considering the higher densities of leaves within clumps at the Medway estuary. All clumps had flowers, but with a range of 3 to 10 flowers /100 cm² (average of 6/100 cm²), or 38 to 64 flowers/m² (average 52/m²), depending on the scale of measurement. Higher densities of leaves but lower densities of flowers seen at the Medway estuary suggests that vegetative reproduction predominates sexual reproduction to a greater degree than seen in the Tusket population. The size of the population at the Medway River is estimated to be between 1.7 and 2.3 million leaves, or between 46,000 and 77,000 flowers.

No information regarding past population size or extent is available for the LaHave River estuary, since Keddy (1987) did not visit the site. However, the species was first recorded at this site in 1992, and its presence was confirmed during 2002. There is no reason to believe that this population has been established recently considering that it is present as scattered colonies within the estuary as compared to perhaps just a single colony of restricted area of occurrence if only recently established.

The population at the LaHave River estuary is scattered and found in much lower densities than seen at either the Tusket or Medway river estuaries. Growth was sparse, with densities of leaves ranging from 10 to 20 leaves /100 cm². Very few flowers were noted; only one or two occurred within clumps of leaves, and some clumps had not produced flowers. However, scattered clumps were found well along the estuary, associated with stands of S. alterniflora. The size of the population at the LaHave River is estimated to be between 56,000 and 110,000 leaves, or up to 300 flowers.

Other sites along Nova Scotia’s southern coast were surveyed, including superficially similar habitats between known occurrences, but no other population was located.

Although densities observed during 2002 were much lower than those very high densities reported by Keddy (1987), the distribution of extant populations does not appear to have changed. Indeed, data from the Tusket and Medway populations show that measures of density do not remain consistent across spatial scales. These data indicate that L. chinensis populations have structure at several spatial scales, where within a populated stretch of shoreline plants grow in clumps between 100cm² and 1m² in size. This probably reflects colonization events at a fine spatial scale, and subsequent growth of individual rhizomes. Although this may appear to be a way one can identify individual plants, identifying discrete clumps of L. chinensis was very difficult. Patches of leaves varied in size, and large patches may represent either rhizomes that have been established for a greater length of time, or they may represent clusters of rhizomes that were established in close proximity to each other. It is probably best to use as indices of population size several measures of density, such as the number of leaves and flowers per unit area. Density measurements should be done at a scale of 100 cm² and 1 m² so as to facilitate future comparisons of density over time.

Population size is expected to fluctuate with local conditions (e.g. occasional storm events, localized disturbance), but the extent is unknown. L. chinensis is naturally rare in Canada, reaching the northernmost edge of its range in southern Nova Scotia, the southernmost part of Canada on the Atlantic Coast. Although certain specific and localized sites have been destroyed (Keddy 1987), no changes in population size, health or distribution have been documented for Nova Scotian populations. American populations in the northern Atlantic states are rare, and some localized populations may have been destroyed, such as in Rhode Island. However, it is apparent that it is naturally rare in the northern states for the same reasons L. chinensis is rare in Nova Scotia, and at least Delaware and New Jersey harbour common and stable populations of this plant. The likelihood of this species naturally repopulating Canadian shores if it becomes extirpated is very low, due to the apparent rarity of potential sources in the northern Atlantic states with the closest populations occurring in southern Maine about 500 km distant.

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