Ectomycorrhizal Fungal Succession in a Native Monterey Pine Forest and Its Potential Influence Upon Forest Population Dynamics

Ectomycorrhizal fungi are plant symbionts influential to the growth and survival of many plant species found within forest ecosystems throughout the globe. The succession of ectomycorrhizal communities during forest maturation has been observed in a number of systems; however, though it is generally assumed that this process is important for forest dynamics, we do not fully understand the causes of succession and whether it strongly influences metrics of plant population dynamics such as population growth rates or size class structure. I studied a secondary successional chronosequence to test the hypothesis that ectomycorrhizal fungal succession occurs within a native Monterey pine forest and parallels the trajectory observed in the well-studied bishop pine system. I also characterized the abiotic environmental factors strongly associated with successional changes in community composition. The hypothesis was partially confirmed by the increase in abundance of Russula spp. with increasing tree size and by the lack of association to environmental factors with the genus Tomentella. Furthermore, factors influential in describing the distribution of genera differed between species within these genera. Additionally, I utilized recent findings that mature forest ectomycorrhizal fungal networks, or commycorrhizal networks (CMN\u27s), reduce seedling mortality and pine demographic data in the same forest type to model the potential influence of these mature forest ectomycorrhizal fungal communities on pine population growth rates and stable size class structure. I hypothesized that removal of beneficial CMN effects from forest seedlings would significantly decrease pine population growth rates. Comparisons between the projected population growth rates from the observed demographic data and the adjusted model removing CMN benefits from seedlings indicated little difference between population growth rates or stable size class structure, thereby rejecting my hypothesis. A model scenario in which CMNs increase survivorship throughout the lifetime of this species, however, suggests that if CMNs influence the trees\u27 entire life cycle, they are extremely important for the persistence of these forest populations. Altogether, these results suggest that ectomycorrhizal succession is occurring in this native Monterey pine forest, but its influence on plant population dynamics may depend on the extent to which CMNs influence forest trees