Fine-scale trait variation of five native forbs along environmental gradients

Seed transfer zones attempt to match seed source and habitat, but the extent of environmental variation within climate-based zones is substantial in some regions and potentially relevant to seed transfer guidelines. Here we surveyed abiotic and biotic soil properties across elevation and insolation (amount of solar radiation) gradients within a 5 km2 area on a Montana property and assessed relationships with selected plant traits in five native species. We detected strong relationships among soil physical properties and elevation and insolation, and similarly large variations in nutrient availabilities and fungal guild abundances. Differences in insolation due to topographical features predicted variation in soil chemical and physical properties, notably moisture and maximum temperature. Elevation was a predictor of minimum soil temperature. Yet, neither elevation nor insolation consistently correlated with variation in plant traits across species. Specific leaf area and seed weight, both heritable traits, correlated with changes in elevation and insolation in some but not all species. We do not know if this trait variation is due to local adaptation or plasticity as it requires reciprocal transplant experiments and longer-term monitoring of the survival and fitness of plants. However, because these gradients were effective predictors of the soil environment, we suggest our sampling strategy to collect seed and select garden sites capable of resolving fine-scale trait-by-environment interactions. Fine-scale transplant studies could reveal if there are benefits of matching heritable traits to environments within a climatic seed zone.