Influence of woody invader control methods and seed availability on native and invasive species establishment in a Hawaiian forest

  • Published source details Loh R.K. & Daehler C.C. (2008) Influence of woody invader control methods and seed availability on native and invasive species establishment in a Hawaiian forest. Biological Invasions, 10, 805-819.


The invasive fire tree Morella faya, occurs in large, nearly monospecific stands in moist forests on Hawai'i island. Logging, girdling (i.e. stripping a ring of bark around the trunk) and incremental girdling to kill fire tree stands at different rates were trialled. The aim was to deduce which method best promotes native forest re-establishment. It was considered that logging (i.e. rapid canopy opening) would lead to preferential establishment of fast-growing non-natives, but that slower canopy opening by girdling techniques might enhance native plants able to growing in partial shade.

Study area: The study was undertaken in a 270 ha forest block (fenced to exclude feral pigs Sus scrofa) located in Hawai'i Volcanoes National Park (19˚20'N, 155˚15'E). Here, M.faya has replaced much of the native forest formerly dominated by Metrosideros polymorpha.

Fire tree treatments: In summer 1999, five replicate 30 x 30 m M.faya-dominated plots were randomly assigned to one of three treatments or an untreated control, in each of two sites. The treatments (selected to kill M.faya trees at different rates) were:

i) logging - clear-cutting followed by stump application of 50% Garlon 3A (Dow AgroSciences LLC);

ii) girdling - bark girdling of all M.faya trees, herbicide applied to the girdle;

iii) incremental girdling - girdling and herbicide application to 33% of M.faya trees, girdling of another 33% of trees at 12 months, and of the final 33% after 20 months.

Dead trees, cut and fallen wood were left in situ. Any treated trees resprouting were treated with herbicide a second time within 1 month.

Environmental variables: Soils were analyzed for pH, organic C, P, K, Ca, B, Mg and total N content, before treatment and at the end of the third year. Soil moisture, humidity, air temperature 5 cm above the soil surface, and light availability were measured at intervals throughout the study period.

Plant monitoring: After applying the treatments, seed banks, seed rain and plant recruitment were monitored over 3 years.

Logged plots: The logged plots exhibited invasion by non-native species, as predicted. These plots were characterized by high light intensity, an initial increase in available nitrogen, and wide temperature fluctuations, all of which may have promoted germination and establishment of fast-growing herbs present in the soil seed bank and derived from seed rain.

Girdled plots: Native species, including importantly the dominant native tree M.polymorpha and tree fern Cibotium glaucum, established most frequently in the girdle and incremental girdle plots, but short-lived non-natives were more abundant than native species.

Whilst girdling and incremental girdling both promoted establishment of major components of native forest, the authors consider that a diverse native forest is unlikely to regenerate under these treatments alone due to seed limitation for many native species.

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