Leaf litter and understory canopy shade limit the establishment, growth and reproduction of Microstegium vimineum

Abstract

The invasive grass Microstegium vimineum is widely distributed in closed-canopy forests, but often is patchily distributed under uniform canopy conditions. We hypothesized that the occurrence of patches of invasion may be related to two interacting factors, the presence of dense understory shrub layers and the presence of thick litter layers on the forest floor. Seeds of M. vimineum were sown in plots located under or distant from Lindera benzoin (spicebush) shrubs, and with or without litter manipulations (none, half of natural amount, naturally occurring amount, double the natural amount) in a mature forest in central New Jersey, USA. Populations were monitored for germination and survivorship, as well as growth and fecundity of surviving plants. Neither shrub-associated shade nor litter depth affected seed germination, but both factors affected survivorship, growth and reproduction. The presence of shade from the shrubs reduced survivorship and seed set. Seeds germinating on top of the litter layer also experience higher mortality than seeds germinating under litter and in contact with soil. These results suggest that the interacting effects of shade from understory strata and deep litter layers may limit the spread of M. vimineum. The loss of shrub layers due to intense deer browse and other factors may thus accelerate the spread of this highly invasive species.

Performance and reproduction of an exotic invader across temperate forest gradients

“…5). These results are consistent with other researchers that report decreased M. vimineum growth and reproduction in drought and shade (Claridge and Franklin 2002, Cole and Weltzin 2004, 2005, Glasgow and Matlack 2007, Marshall and Buckley 2008a, Eschtruth and Battles 2009a, Flory and Clay 2009a v www.esajournals.org 2010, Droste et al 2010, Flory 2010, Huebner 2010a, Schramm and Ehrenfeld 2010). Yet, as noted, these associations cannot fully decouple cause and effect in M. vimineum establishment.…”

“…Our results indicate a significant increase in M. vimineum recruitment with litter disturbance, but recruitment occurred, even if to a lesser extent, in undisturbed patches. Moreover, other workers have found mixed to marginal M. vimineum resistance to litter cover (Marshall and Buckley 2008b, Miller and Matlack 2010, Schramm and Ehrenfeld 2010. The efficacy for leaf litter to prevent M. vimineum invasion may depend on the level of seed input, and here again we find the need to know the plant's niche requirements.…”

Habitat, dispersal and propagule pressure control exotic plant infilling within an invaded range

“…Many researchers report that light limits M. vimineum seed production (Barden 1987, Cole and Weltzin 2005, Droste et al 2010, Schramm and Ehrenfeld 2010, Flory et al 2011a, but we find temperature and soil moisture mainly limiting and this may be because we had lower light availabilities across our plots than are commonly investigated. The interaction between temperature and soil moisture indicates that M. vimineum growth (and hence reproduction) responded positively to increased temperature and soil moisture, and it increased dramatically where both environmental drivers were high.…”

Extreme drought stress shifts net facilitation to neutral interactions between shrubs and sub‐canopy plants in an arid desert

“…However, some of the abiotic factors modulated by shrubs can also affect understory plants negatively. For example, heavy shading by canopies has been reported to limit the photosynthetic activity of understory species (Hautier et al 2009), thereby impairing their establishment, growth, and reproduction (Schramm and Ehrenfeld 2010). Such negative effects are more likely to occur under deep shade, though, and shift to facilitation at intermediate light levels (Holmgren et al 2012).…”