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Establishing Gliricidia Trees

Pre-treated gliricidia cuttings.  The cuttings were pre-soaked in sphagnum moss for 2 weeks before planiting.The USDA-NRCS Hoolehua Plant Materials Center is evaluating factors that impact the establishment of Gliricidia trees, a highly adaptable tree species for natural resource conservation practices across the Pacific Islands Area (PIA). The study will look at the establishment of the tree species Gliricidia sepium (gliricidia) and effects of pre-treated stem cuttings versus direct-planted stem cuttings, soil moisture regimes, the incorporation of superabsorbent hydrogel into soil, and stem size on the establishment of Gliricidia in a low rainfall environment.

Tree Establishment is a fundamental practice to control soil erosion primarily because the impact of falling rain is dramatically reduced by leaves and branches. Trees also create microclimates to enhance seed germination, seedling establishment, and forest regeneration. In very dry areas, establishing trees will be more difficult as climate change is expected to reduce rain, up to 60% less, in parts of Hawaii and Micronesia by the end of the century. The change in climate is expected to increase both the frequency of drought and flood, i.e., rains will be less frequent, but heavier. Gliricidia is known to grow well in a wide range of soils and climates and is one candidate that may be able to meet the challenge.

GliricidPre-treated gliricidia cutting showing initial root growth after being pre-soaked in sphagnum moss for 2 weeks before planting.ia sepium is a small to medium size deciduous tree that originates from northwestern Mexico to Panama. It is drought tolerant, able to fix nitrogen, and may reach a height of 10 to 12 m. This tree grows well where annual rain ranges 30-60 inches (900-1500 mm) and survives in areas where annual rain is as high as 135 inches (3500 mm). In addition, Gliricidia also grows well where mean annual temperature is 70 to 82 F (22 to 28 C). Gliricidia is found widely across the tropics. In the Pacific Islands Area, Gliricidia is found in American Samoa, Federated States of Micronesia, Guam, and Hawaii.  Although Gliricidia is not native to the Pacific Islands, the species has shown the ability to establish in very harsh landscapes where native trees do not establish well Gliricidia provides an ecological and successional bridge to enable future establishment of even more desirable forest species (including native species) in the future. Hawaii-Pacific Weed Risk Assessments have characterized Gliricidia as a low risk for invasiveness.

NRCS recommends Gliricidia for multiple conservation practices, particularly in lower rainfall areas in PIA. Studies have shown that planting-material quality and root environment affect plant establishment. The current recommended minimum annual rainfall for Gliricidia is 25 inches (635 mm) according to the PIA Vegetation Specification and Implementation Requirements. The results from this study could potentially expand the environmental limits of this drought tolerant tree species to further promote soil conservation under changing climate conditions.