The effects of light and nutrients on an invasive, Buddleja davidii, and native, Griselinia littoralis

Buddleja davidii, (Buddlejaceae), an aggressive, highly invasive, ornamental shrub of Asian origin, may be suppressing slower-growing native species (e.g., Griselinia littoralis; Family: Griseliniaceae) on New Zealand floodplains thus altering successional trajectories.  This study sought to learn what affect Buddleja might have on a mid-successional species when different treatments of light and nutrients were applied.  Buddleja and Griselinia shoot relative growth rate and foliar N and P were significantly greater when grown in the 27% light than in the 90 and 10% light levels.  In contrast, both species have reduced growth (Buddleja, 97 and Griselinia 99 % less shoot RGR) and higher mortality in 10% light than those grown in the 27 and 90% light levels.  These results suggest that both species are better suited for growth in a mid-successional stand than at newly disturbed sites or under late-succession forest canopy.  Buddleja growth and foliar N and P were significantly less when grown with another plant of equal or greater biomass regardless of species, while Griselinia growth was adversely affected by the presence of Buddleja.  These results suggest that competition will suppress Buddleja growth.  However, further investigation is needed to determine the response of Buddleja to another like-sized species under field conditions.