Survivorship and productivity of invasive plant species in response to different forest management regimes across regional and local environmental gradients

Background/Question/Methods

Oak regeneration in Eastern U.S. forests is associated with disturbances, such as fire and shelterwood harvests, which increase the amount of light reaching the forest floor.  In contrast, diameter-limit cutting (DLC; removal of the largest, most merchantable trees) is primarily used by private land owners.   Forest canopy openings by any of these methods may result in invasion by exotic plant species.  Invasive plant establishment is also dependent on available resources, with mesic and nutrient-rich sites often more prone to invasion than more xeric, less fertile, sites. 

Garlic mustard (Alliaria petiolata, GM), Japanese stiltgrass (Microstegium vimineum, JSG), and tree of heaven (Ailanthus altissima, TOH) survivorship and productivity were compared.  Fifty-six sites were selected from two regions (Allegheny Plateau (AP) and Ridge and Valley (RV) Provinces), two topography-types (north-northeastern-east (NE), and south-southwestern-west (SW) slopes), and five management regimes (control, single burn, repeat burn, shelterwood, and DLC) in OH, WV, and VA.   In early spring 2011, GM was planted as seedlings (cotyledons).  JSG and TOH were transplanted with their first leaves, in late spring.  After three months, shoot biomass was determined for all species and root biomass was determined for TOH.  Light and soil temperature were measured for each site.

Results/Conclusions

All three species had more biomass in the shelterwoods.  Productivity decreased in the following order:  DLCs, repeat burns, single burns, and controls, except for GM, in which the burns had greater productivity than the DLCs and controls.  JSG was more productive in the RV, while GM was more productive on NE slopes.  TOH’s shoot biomass did not differ among region or slope, but its root biomass was greater in the RV.  GM survival was greater in the AP and in the burns, but survival did not differ among treatment, region, or topography for TOH or JSG.  Shelterwoods had the highest light and soil temperature, followed by the DLCs, two burns, and controls.  The RV and SW slopes had higher light and soil temperature than the AP and NE slopes, respectively. 

Invasive plant response varied among the species, but the most disturbed treatment (shelterwood) showed the greatest productivity for all three species.  A wet spring/summer may explain the high productivity of JSG and TOH in the RV.  No difference in survival of JSG and TOH suggests young plants can become established (though not prosper) under variable conditions.  GM’s response indicates that younger developmental stages may be more sensitive to existing conditions.