Distribution, abundance and conservation management of two calcicolous bittercress species Cardamine integra and C. caesiella, (Brassicaceae) Heenan, in limestone areas of South Canterbury, New Zealand

Abstract
Cardamine (Brassicaceae) supports numerous species (>40) in New Zealand. They are mostly small perennial herbs and grow in diverse habitats, often related to a specific geological substrate or soil type, including limestone outcrops. Two of these calcicolous species Cardamine caesiella Heenan and C. integra Heenan are endemic to South Canterbury, though the areas of occupancy are disjunct. This study investigates the distribution, abundance and ecology of the two species across limestone outcrops in South Canterbury to identify appropriate conservation management for these threatened plants. Surveys between 2019 – 2022 recorded 773 plants of C. integra, comprising 515 mature plants in 13 sub-populations, ten previously unknown. C. caesiella were recorded in one isolated limestone area, a population with 929 plants, 638 mature. As the total area of occupancy for both species is below 1 ha, the current threat ranking of ‘Threatened / Nationally Critical’ should remain. Grazing pressure and competition by introduced weeds and grasses are the main threats for these small herbaceous plants. Experimental conservation work like weed control and enclosures for small sub-sites has been trialled. Control measures for the wide-spread invasive Sedum acre were undertaken in a number of larger limestone areas over successive years.

Cite as
Frank, H. (in press). Distribution, abundance and conservation management of two calcicolous bittercress species Cardamine integra and C. caesiella, (Brassicaceae) Heenan, in limestone areas of South Canterbury, New Zealand. Perspectives in Biodiversity, 4