Effects of the Invasive Shrub Lonicera maackii on Soil Water Content in Eastern Deciduous Forest

Abstract

We quantified the fine root length density of Lonicera maackii (Amur honeysuckle) and native trees at two depths on transects away from individuals of this invasive shrub and tested whether the invasive shrub L. maackii reduced water availability for other forest plants by either of two mechanisms: (1) intercepting rainwater during light rain events or (2) absorbing large amounts of water through its fine roots. To test the two hypothesized mechanisms, we selected plots near large L. maackii shrubs and control plots away from any large L. maackii shrubs in the forest understory. Within each plot we placed a trenched and an untrenched subplot and measured soil water content in each. We also measured precipitation above and below L. maackii canopies. We found that within 2 m of large L. maackii shrubs, this shrub accounted for a large fraction (22–25%) of the fine roots in the top 12 cm of soil. Reduced throughfall and soil moisture below shrubs supported the hypothesis that L. maackii competes with tree seedlings by interception. Findings were inconclusive regarding the hypothesis of competition by water uptake.