An exploratory study of facilitation in three species of Raoulia

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In order to determine the roles that size, temperature, moisture and pH play in ecological facilitation, we investigated facilitation in two cushion plant species (Raoulia eximia and R. bryoides) and one semi-compact creeping cushion (R. australis) on South Island, New Zealand. We measured canopy moisture, pH and temperature as a function of size to determine if these species might have different microenvironments within their canopies and whether these abiotic factors might correlate to increased facilitation. We found that R. eximia showed increasing canopy moisture and decreasing pH with increasing size, indicating microenvironment changes with canopy of the cushion. Temperature at 2 cm canopy depth did not differ with size in any species, nor did it differ from 2 cm depth in open soil. Only R. eximia exhibited plant facilitation by showing more species within the canopy than in nearby soil. This work supports the importance of cushion microclimate in facilitation.

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