About This Project

Billions of tree seedlings are produced annually in the USA to replace trees lost due to timber harvesting and disturbances such as wildfire. In addition to an historic lack of precipitation across the western US, increased temperatures due to climate warming are further reducing the water available to seedlings, posing challenges to forest regeneration. Our research project seeks to determine how best to enhance the resilience of seedlings to drought conditions.

Ask the Scientists

What is the context of this research?

Climate change is increasing the frequency and intensity of drought in the western USA, consequently subjecting plants to levels of drought stress beyond which they are adapted (USGCRP 2018). The probability of seedling survival, whether natural or planted, is related to the ability of roots to contact plant-available water in the soil (Grossnickle 2005, Day et al. 1975). Drought conditioning has been shown to increase seedling drought tolerance and survival for some tree species (Driessche 1992, Valliere et al. 2019). However, it is unknown whether drought preconditioning promotes desirable root growth patterns in western larch (Larix occidentalis) seedlings, an important timber species in the western USA.

What is the significance of this project?

In this project, we investigated whether successive exposure to drought prepares western larch seedlings for subsequent extreme drought. This is significant because the frequency and intensity of drought conditions in the western USA are increasing as regional mean air temperatures rise and precipitation patterns become more erratic (USGCRP 2018). Western larch is an important North American timber species and could become more vulnerable to drought as drought conditions intensify in the western USA, as climate reports suggest. Forest nurseries could achieve enhanced drought hardiness through successive drought exposure in their operations if desirable root growth patterns occur as a result of successive drought exposure.

What are the goals of the project?

In May of 2021, 96 western larch seedlings were planted in five gallon pots and were exposed to various levels of drought over a three month period. Drought was measured by volumetric water percentage of the soil. Half of the seedlings were drought stressed to 75% of their volumetric weight, while the other half were drought stressed to 50%. When the seedlings reached their respective volumetric weight percentage, they were watered for 45 minutes using an overhead irrigation system. In August of 2021, seedlings were harvested, roots were separated from soil media, and leaves were separated from branches. All plant material will be separately weighed and foliar tissue will be sent to UC Davis for carbon isotope discrimination analysis. Root architecture will also be analyzed.