Coastal strand plant community monitoring: Kaloko-Honokōhau National Historical Park

Ainsworth, Alison; Phifer, Colin; Simon, Melissa; Yanger, Corie

A critical mission of the Pacific Island Network Inventory and Monitoring program is to monitor park ecosystems to better understand their dynamic nature and provide park managers with current data to inform management actions. The coastal strand plant community at Kaloko-Honokōhau (KAHO) is a narrow band of vegetation consisting of plant species adapted to salt spray, waves, wind, and poor soils. This community at KAHO is significant despite its small size because it is protected from shoreline development, unlike much of state’s coastal strand. By establishing baseline vegetation information, we can determine if and to what extent these coastal strand plant communities are changing. In July 2011, ten permanent and three rotational or temporary monitoring plots (200 m2) were established in the coastal strand at KAHO. Thirty-one plant species were recorded including 11 native, 19 non-native, and one Polynesian-introduced species. Species richness ranged widely among plots (3-13 species/plot) with nearly twice as many non-native species as native species per plot. Species diversity and evenness were relatively high due to this variance among plots, with 13 species only found in one plot. One of these species was the native endemic shrub, maiapilo (Capparis sandwichiana), which is currently listed as a species of concern. The most frequently encountered species were woody, disturbance tolerant species including native naupaka kahakai (Scaevola taccada), and non-native tree heliotrope (Tournefortia argentea) and Christmas berry (Schinus terebinthifolius). The understory of the coastal strand was mostly vegetated (73% cover) with non-native species accounting for 67% of the relative vegetated cover. Similar to species richness, woody species cover was more abundant than herbaceous species cover. High non-native woody cover was primarily due to the non-native coastal tree heliotrope and native woody cover was due to naupaka kahakai and milo (Thespesia populnea). Tree distribution is clumped across the coastal strand with tree heliotropes dominating the large (> 10 cm diameter) live and dead trees, but encouragingly native milo was common in the small tree and seedling categories. Despite the abundance of tree heliotropes, few large downed logs were encountered and all but one were sound wood. Considering the dry windswept climate of the strand, decomposition of large logs is likely to be slow and they rarely seem to serve as nurse logs in this environment. Currently, the coastal strand at KAHO is an assortment of microhabitats and plant associations with varing levels of invasion and few consistently dominant species. Long-term, the coastal strand is likely to be impacted by sea level rise, subsidence, drought, and as a result of growing visitor use, increased human disturbance and non-native species invasion. We expect to return to KAHO and re-measure the coastal strand plant community in 2016 to gain a greater understanding of the variance within this community and to quantify any species and population changes.

Coastal strand plant community monitoring: Kaloko-Honokōhau National Historical Park

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