Growth, Leaf Characteristics, and Spore Production in Native and Invasive Tree Ferns in Hawaii

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Abstract
The Australian tree fern Sphaeropteris cooperi is an invasive species in Hawaiian wet forests where it displaces Cibotium, the dominant native Hawaiian tree fern, where they co-occur. This study was undertaken in order to assess the relative growth rates and reproductive potential of S. cooperi and the native Cibotium species. Field measurements of growth rates, fertile frond production and leaf traits were made monthly over the course of one year. Sphaeropteris cooperi had a significantly higher growth rate, both in terms of height increase and frond production, and maintained four times more fronds than the native Cibotium species. The mean annual height increase of the invasive tree fern was 15 cm compared to 2 to 3 cm for the native tree ferns. The leaf mass per area of S. cooperi was significantly lower than that of the native Cibotium species, and the leaf life span was significantly shorter, suggesting that the cost of construction of the invasive species' fronds was relatively low. Sphaer...