Experimental spring planting and attribution of ponderosa pine seedling survival in a hot and dry subregion of the southwestern United States

Abstract

Artificial regeneration (i.e., seedling planting) will be required to maintain dry coniferous forests in the southwestern United States (SWUS). I conducted a 3-year (2022–2024) spring planting experiment in one burned and three unburned ponderosa pine forests in southern Nevada, USA, a location with notably hot and dry summers. Instrumented experimental sites supported the mechanistic assessment of meteorological and environmental controls on survival. Low precipitation, low soil moisture, and high air and soil temperatures distinguished very low seedling survival ($<$20 %), which occurred in the burned forest and in unburned forests during low precipitation years, often in the first 40 days following planting. Lower (≤40 %) versus higher ($>$65 %) survival was distinguished by precipitation, different forest environments, and 10–30 day variation in planting date. Higher survival (36–100 %) in 2023 continued through 2024, especially for earlier planted seedlings. Thus, alterations to the timing of spring planting may provide benefits to seedling survival. This experiment underscores the influence of meteorological and environmental variation on artificial regeneration, and portends to increasing survival restriction – and reliance on precipitation events – as warm seasons in SWUS forests increasingly resemble those of southern Nevada.