Effects of species interactions on plant topographic realized niche across an elevation gradient

Background/Question/Methods

Cool microclimates created by topographic variation could buffer plant species from climate change. However competition or facilitation by neighboring plant species may affect species occupancy of favorable topographic microclimates. We experimentally tested the effects of interactions with neighbors on realized topographic niche of a model herbaceous species - Trientalis latifolia – at nine sites across an elevation gradient in SW Oregon. Species topographic niche was modeled using fine-scale topographic variables and occurrences from federal lands surrounding the study area. The model was used to define “optimum”, “warm”, or “cool” topographic microclimates for species occurrence. Trientalis bulbs were planted in nine pairs of neighbor removal and control plots in each of the three topographic microclimate categories at nine sites. Temperature, soil moisture, and light were measured to link abiotic variables affected by topography to plant performance. Plant response was quantified by measuring emergence, aboveground biomass, and fitness. We tested for the effects of individual abiotic variables, elevation, and microclimate category on plant responses with generalized linear models. We described the effect of neighbors on fitness and aboveground biomass by calculating “relative interaction intensity” between neighbor removal and control plots.  

 Results/Conclusions

We found that emergence was significantly higher at lower elevations. In addition, the effects of elevation on emergence interacted with microclimate niche. Emergence was highest outside the topographic niche in warm microclimates at low elevations and at optimum microclimates at high elevations. Neighbor presence had a positive effect on plant fitness outside of the modeled topographic niche – in both cool and warm microclimates – and negative effect within the niche. These results suggest that interactions between elevation and understory density could significantly affect herbaceous species colonization of cooler topographic microclimates with climate warming.