Effects of climate, atmospheric deposition, and competition on canopy recruitment in eastern United States Forests

To accurately predict the effects of climate and atmospheric pollutants on the abundance and distribution of tree species, we need to understand how these environmental factors influence key demographic processes of growth, survival, and recruitment.  Adult tree growth and survival rates are impacted by temperature, precipitation, nitrogen (N), and sulfur (S) deposition among other abiotic and biotic influences.  Substantially less is known about how these drivers affect canopy recruitment, which is an important process in tree range dynamics.  Here, we examined the effects of climate (temperature and precipitation), atmospheric N and S deposition, and competition on canopy recruitment rates of 50 tree species in the eastern United States from 2004 - 2022.  We combined canopy recruitment rates estimated from Forest Inventory and Analysis censuses, temperature and precipitation data from PRISM, and N and S deposition from the National Atmospheric Deposition Program.  The presence of at least one recruit was highest in an optimal temperature range for 82% of species, while seasonal precipitation was positively correlated to the presence of recruits for 44% of species and negatively correlated for 38% of species.  For most species (90%), low levels of total plot basal area were positively associated with the number of recruits, while medium to higher levels of plot basal area were negatively associated with the number of recruits for 90% of species.  Additionally, we found that for many species, recruitment rates were negatively correlated to S deposition (43.3%), while recruitment was either positively or negatively impacted by N deposition (39% and 37%, respectively).  This work is ongoing, and we are exploring additional environmental covariates as most of the variation remains unexplained by these preliminary models.

Impact/Purpose

In this work, we examine the impact of atmospheric deposition and climate on tree canopy recruitment, or the number of new trees in a population.  We used publicly available data from the U.S. Forest Service on to understand how nitrogen (N) deposition, sulfur (S) deposition, temperature, and precipitation affect the number of new trees in for 50 species in the eastern United States.  In a preliminary analysis, we found that most tree species have an optimal temperature range for maximum recruitment rate, while precipitation had mixed effects.  For example, recruitment was higher for some species in wetter conditions, while drier conditions were better for other species.  Nitrogen deposition had variable effects on recruitment, and S deposition largely negatively impacted recruitment.  This work has long-term significance, as there has been an abundance of work on tree species growth and survival responses to climate and deposition, yet few studies on recruitment, which is an important life-history stage.  We can ultimately combine results from this study with other work at the EPA, particularly other subproducts from ACE.405.2, to determine overall population impacts of deposition and climate on tree species in the U.S. Finally, land managers interested in understanding how species in their parks or forest tracts could use critical load values from our study.

Citation

Dalton, R., C. Clark, L. Murphy, AND C. Canham. Effects of climate, atmospheric deposition, and competition on canopy recruitment in eastern United States Forests. Forest Inventory and Analysis Science Symposium, Virtual meeting (no location), NC, November 19 - 21, 2024.