In the current study, I chose to transplant seedlings into the plots in order to maintain a uniform number and initial size of seedlings in the plots. However, in future experiments it would also be useful to sow seeds of early successional woody species directly inside the plots receiving warming and N addition treatments, in order to assess how treatment effects on the timing of germination influence seedling growth and survival, and also to avoid the effects of transplant shock. Likewise, it would be informative to leave the seedlings in the plots for multiple years, so that responses to treatment effects on winter conditions (e.g. reductions in snow cover and increased soil freezing) could be assessed (Drescher and Thomas 2013).
Future studies could also examine the responses of a wider range of early successional woody species, focusing on how differences in the timing of seed dispersal might affect treatment responses. For example, all of the species used in my experiment had fruit that matured and dispersed in the fall, with seeds that remained dormant over winter and germinated in the spring and early summer (Kock et al. 2008;Voss & Reznicek 2012). However, as observed by Classen et al. (2010), species such as silver maple (Acer saccharinum), in which keys mature, disperse, and germinate in the spring, may respond differently to changes in temperature and water availability than those that disperse in the fall. Not only is timing of germination important, seed size may also affect the responses of plants to future conditions. Larger seeds are prone to desiccation stress may and be more visible to predators (Donath and Eckstein 2010, Loydi et al. 2013), but smaller seeds may not successfully germinate through dense litter cover due to smaller reserves (Facelli 1994, Laborde and Thompson 2013). Overall, including more species to compare a wider range of germination times and strategies, functional groups or native vs. exotics may provide a better idea of how changing environmental conditions may impact the establishment by woody species in early successional habitats as a whole.
An important component of future environmental change not included in my study was that of elevated atmospheric carbon dioxide, which is linked with increases in global temperatures. In experiments featuring increased carbon dioxide applied at the ground level through free air CO2 enrichment (FACE), seedling survival and establishment have
increased as a result of decreased transpiration and water stress since higher CO2
concentrations allow seedlings to close their stomata for longer periods of time (Picon et al. 1996, Polley et al. 1996, Dermody et al. 2007, Davis et al. 2007). Since desiccation played such a critical role in the survival and establishment of seedlings in my study, it would be valuable to explore the extent to which elevated CO2 might ameliorate water
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