Browsing by Author "Rapson GL"

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Changing methodology results in operational drift in the meaning of leaf area index, necessitating implementation of foliage layer index
(John Wiley and Sons Ltd, 2018-01-08) Rapson GL
Leaf area index (LAI) was developed to describe the number of layers of foliage in a monoculture. Subsequent expansion into measurement by remote-sensing methods has resulted in misrepresentation of LAI. The new name foliage layer index (FLI) is applied to a more simply estimated version of Goodall's "cover repetition," that is, the number of layers of foliage a single species has, either within a community or in monoculture. The relationship of FLI with cover is demonstrated in model communities, and some potential relationships between FLI and species' habit are suggested. FLIcomm is a new formulation for the number of layers of foliage in a mixed-species' community. LAI should now be reserved for remote-sensing applications in mixed communities, where it is probably a nonlinear measure of the density of light-absorbing pigments.
Coastal Dynamics Initiate, Relocate and Terminate Short-Lived Wetlands of Dune Slacks, Manawatū, New Zealand
(MDPI (Basel, Switzerland), 2022-07) Villacís Lozada SP; Rapson GL; Prisco I; Roscioni F; Marzialetti F
Dunelands are one of the most dynamic environments on Earth, which greatly hinders their conservation and management. In the dune slacks along the Manawatū coast, New Zealand, lies a zone of small, temporary, freshwater wetlands that host early seral communities of rare turf plants. Analysis of historical aerial photos allowed determination of coastline movement, distance of the wetlands from the coast, and wetland movements through time. Study sites were around the coastal settlements of Tangimoana and Foxton Beach, both having major rivers debouching nearby, and Himatangi, amongst stabilising exotic pine plantations. The coastline is prograding (with seaward movement) generally by 0.7–1 m yr−1, but is more variable closer to river mouths, with episodes of movement of up to 15 m yr−1. Wetlands occur 200–400 m behind the strandline, are closer to the coast at Foxton Beach, and furthest away at Himatangi. Wetlands wobble in their position at 5.2 m yr−1 but migrate inland at an average of 2.7 m yr−1. Wetland size appears unrelated to rainfall, but may be related positively to coastal progradation rate, to which wetland movement is negatively related. Near the major rivers, dunes are less stable, and wetlands can be impacted both positively and negatively. Wetland existence and movement is balanced between stability and dynamism on the coast, and management will need to be proactive to maintain environments for early successional turfs.
Invasive species over-stabilise the vegetation of a mobile dunefield, Manawatū, New Zealand, disrupting natural succession
(Pensoft Publishers, 2023-12-22) Rapson GL; Murphy AL; Smith AR
Aims: Mobile, coastal dunefields around the world are under threat from invasive plants, which may out-compete native plant species. These aliens may also accelerate stabilisation of the dunes, to the complete exclusion of early successional native flora. In a mobile dunefield we examine the impact of the increasing abundance of alien species on substrate stability and successional trends of the native vegetation. Study area: Tawhirihoe Scientific Reserve, Manawatū, New Zealand. Methods: We recorded species' covers and environmental factors in quadrats placed randomly over the mobile dunefield, and analysed the vegetation and its successional patterns via multivariate analysis. We explored the degrees of stabilisation and nativeness, referencing changes over the last three decades. Results: Our analysis reveals seven vegetation types, three with a high native component and following an established successional trend, and the others becoming dominated by alien grasses and herbs, and associated with increasing dune stability. Biodiversity is trending towards aliens, especially behind the foredunes, and aliens occupy nearly double the area of the mobile dunefield as do natives. Coverage of unvegetated or mobile sand has declined to 21 % and is projected to decline further. Conclusions: Only the foredunes and dune-slack wetlands are now in a mostly natural state, while native rear dune vegetation is becoming rare, and natural succession appears to be interrupted. Alien species over-stabilise the dunefield, facilitating further alien invasion, the longer-term implications of which are unknown. Intervention to destabilise the dunefield seems the most viable management option.