Abstract

Abstract:

Between 1958 and 2018, multiple roadside surveys were conducted on the upper altitudinal limits of the alpine Maunaloa (now preferred Hawaiian language spelling of Mauna Loa) vascular flora from near tree line (2,525 m) to the NOAA Mauna Loa Observatory (MLO) at 3,397 m. Five native plant species were encountered in 1958 on numerous sparsely vegetated historic and prehistoric basaltic lava flows. A resurvey of the roadside 50 years later (2008) yielded 22 species including nine new native species and eight aliens. The aliens were limited to a few individuals at sites disturbed by human activity. Here, floristic change along the transect was reassessed after 60 years (2018), recording a total of 30 species with 15 natives and 15 aliens. Floristic diversity and shifts in altitudinal limits are evaluated in relation to well documented and dramatic local climate change over recent decades, along with the competing influences of substrate-control and increasing human disturbance. The results indicate that lava substrate age and textural variation, along with human mediated propagule pressure, and associated disturbance exert greater impact than rapid climate change in explaining current patterns of plant distribution and diversity in this hyper-arid, alpine environment. This long-term monitoring effort of alpine lava flows has also informed and reinforced a more general moisture/substrate-control model for early primary succession extending to lower subalpine mountain elevations involving the two dominant lava flow textural classes: 'a 'ā and pāhoehoe.

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