Data to accompany: Seedling responses to soil moisture amount versus pulse frequency in a dominant semi-arid shrub

The timing, frequency and quantity of rainfall is rapidly changing in dryland regions, leading to profound alterations to dryland plant communities. Understanding dryland plant responses to future rainfall scenarios is crucial for implementing proactive management strategies, particularly in light of intensive changes to land cover concurrent with climate change. One such change is woody plant encroachment, an increasing abundance of woody plant species in areas formerly dominated by grasslands or savannas. The continued encroachment of P. velutina will depend, in part, on seedling capacity to establish and thrive under future climate conditions. Seedling performance is primarily impacted by soil moisture conditions that are governed by precipitation amount (quantity) and frequency. We hypothesized that H1) seedling performance would be enhanced by both greater soil moisture and greater pulse frequency, such that seedlings with similar mean soil moisture would perform best under high moisture pulse frequency. Alternatively, H2) mean soil moisture would have greater influence than pulse frequency, such that at a given pulse frequency would have little influence on seedling performance. The hypotheses were tested by growing 256 P. velutina seedlings under two distinct soil moisture treatments, each of which was maintained by two different pulse frequency treatments. Contrary to H1, mean soil moisture had far greater impact than pulse frequency on seedling growth, photosynthetic gas exchange, leaf chemistry and biomass allocation. These results indicate that P. velutina seedling establishment may be more responsive to rainfall amount than rainfall frequency.