The island of Rotuma lies about 580 km north of the main archipelago of Fiji, and while politically part of that country, it differs culturally and floristically. It has not typically been included in botanical treatments for Fiji as a whole despite visits from several botanists. Pteridophytes of Rotuma were described by St. John in 1954 based on a visit there in 1938, but little additional information is available since then. Much of the original Rotuman forest has been altered by human activity, but pockets of original vegetation persist and substantial areas of secondary forest currently occur there. In June 2019, the first two authors of this report visited Rotuma to study ferns and lycophytes. We added six native species to the total of 31 found by St. John, and we found three species that have become naturalised since St. John was there. We revise the identification of several of those that he found, based on studying his specimens as well as our own, and we update nomenclature for many others to reflect current taxonomy. We conclude that 37 native and three naturalised pteridophyte species are confirmed for Rotuma, and two others may be present as natives based on unconfirmed reports. We discuss geographic relationships of the pteridophyte flora and note that at least four native species on Rotuma are not known from elsewhere in Fiji, but almost all Rotuman pteridophytes are known from Samoa. We speculate that additional pteridophytes remain to be found on Rotuma, and we note that declining coconut cultivation is leading to increased recovery of secondary forest on the island. Additionally, we confirm that the endemic angiosperm Cyrtandra rotumaensis H. St.John [Gesneriaceae] persists on Rotuma.

Understanding plant physiological response to a rising atmospheric CO₂ concentration (c_a) is key in predicting Earth system plant–climate feedbacks; however, the effects of long-term rising c_a on plant gas-exchange characteristics in the tropics are largely unknown. Studying this long-term trend using herbarium records is challenging due to specimen trait variation. We assessed the impact of a c_a rise of ~95 ppm (1927–2015) on the intrinsic water-use efficiency (iWUE) and maximum stomatal conductance (g_smax) of five tropical tree species in Fiji using the isotopic composition and stomatal traits of herbarium leaves. Empirical results were compared with simulated values using models that uniquely incorporated the variation in the empirical g_smax responses and species-specific parameterisation. The magnitude of the empirical iWUE and g_smax response was species-specific, ranging from strong to negligible. Stomatal density was more influential than the pore size in determining the g_smax response to c_a. While our simulation results indicated that photosynthesis is the main factor contributing to the iWUE gain, stomata were driving the iWUE trend across the tree species. Generally, a stronger increase in the iWUE was accompanied by a stronger decline in stomatal response. This study demonstrates that the incorporation of variation in the g_smax in simulations is necessary for assessing an individual species’ iWUE response to changing c_a.

Mangrove ecosystems have attracted increasing global attention for their vital ecosystem services and exceptional carbon storage capacity. This study assessed and updated the species composition and population structure of two mangrove forests in the Marau Sound region of Guadalcanal, Solomon Islands. Circular plots (7 m radius) were established at 25-meter intervals along transects running from the seaward to the landward edge of the forests to capture representative ecological data. The primary aim was to determine the current diversity of true mangrove species in the region. A total of 12 true mangrove species were recorded within the study plots, though observations outside the plots suggest the number could reach up to 26. The Rhizophoraceaefamily was found to be the most dominant, with Bruguiera gymnorrhiza and Rhizophora apiculataidentified as the most ecologically significant species. Notably, the study confirmed the presence of Sonneratia alba and Heritiera littoralis, two species not previously documented in Marau, thus contributing a valuable update to the regional mangrove inventory. These findings highlight Marau as a critical mangrove habitat with species that offer significant potential for blue carbon sequestration, emphasizing the need for continued research and conservation efforts in the region.