Modeling FoRTE, the Forest Resilience Threshold Experiment

<p>Forested ecosystems represent a large yet uncertain fraction of the global terrestrial carbon sink. Their future state depends on a number of natural and anthropogenic influences; a particularly large uncertainty is how disturbance affects vegetation structure and ecosystem biogeochemistry.  We used the Ecosystem Demography model to explore the ecological and biogeochemical consequences of disturbance as part of the Forest Resilience Threshold Experiment (FoRTE), a dual modeling and manipulative field experiment investigating the effects of disturbance at different severities on a century-old deciduous forest. The field component was conducted at the University of Michigan Biological Station (UMBS), where stem girdling was applied to achieve four different severity levels of disturbance (0, 45, 65, and 85% gross defoliation) before the 2019 growing season. Since then, we have tracked the subsequent changes in vegetation and biogeochemistry. The modeling component attempted to simulate the FoRTE disturbance treatments within its framework. While we were able to instantiate a forest in ED with a similar climatology, soil characteristics, disturbance history, and vegetation of UMBS,  baseline ED is ultimately unable to reproduce the vegetation dynamics and carbon fluxes observed at the UMBS control plots. This is consistent with previous work where the model is not capable of matching observed carbon and vegetation dynamics. However, ED’s response to the disturbance treatments is consistent with observations from UMBS: in both the model and UMBS experimental results, we observed different resiliences and carbon cycle responses with respect to disturbance severity. These intriguing results point to both weaknesses and new possibilities in the modeling of ecosystems facing rising disturbances and climate change.</p>

Characterizing Ectomycorrhizal Fungal Community Structure and Function of Two Varieties of Pinus clausa That Differ in Disturbance History

Despite the immense amount of diversity present in the soil biota, the ecological and evolutionary processes that regulate species diversity and abundance of ectomycorrhizal (ECM) fungi across space and time remain elusive. In forest ecosystems, ECM fungal diversity may be maintained by periodic disturbances which operate at different time scales due to their effects on host genetic and phenotypic characteristics and the associated environment. To investigate the degree to which these factors shape ECM fungal community composition and function, I sampled 10 independent sites for a pine species indicative of an endangered ecosystem, the Florida scrub, where disturbance history has driven the divergence of a single species into two genetically distinct varieties (Pinus clausa var. immuginata and var. clausa). A total of 300 ECM fungal species were identified based on rDNA ITS sequences, but each variety harbors different ECM species composition and function. A follow-up greenhouse experiment, in which the seed from each variety was grown in its own soil (“home”) and in the soil of the other variety (“away”), suggests these communities differentially impact the growth of their host seedlings. While var. clausa seedlings had the same total biomass regardless of soil origin, var. immuginata had higher biomass in their own soil compared to var. clausa. This is likely due to an increased number of ECM colonized tips in the home soil compared to in away soil. Taken together, these results may suggest different evolutionary histories where structure host genetic and phenotypic characteristics may be important for structuring their dynamics with ECM fungi.

A collaborative typology of boreal Indigenous landscapes

Climate change and natural resource extraction are transforming boreal forest landscapes, with effects on Indigenous people’s relationship with the land. Collaborative management could enhance the consideration of Indigenous perspectives and limit negative outcomes of environmental change, but it remains the exception rather than the norm. We addressed barriers to involvement of Indigenous people in land management by developing a method to enhance communication and trust, while favouring bottom-up decision-making. We partnered with the Abitibiwinni and Ouje-Bougoumou First Nations (boreal Quebec, Canada) (1) to develop indicators of Indigenous landscape state, (2) to create a typology of Indigenous hunting grounds, and 3) to suggest guidelines for sustainable land management in Indigenous contexts. Through participatory mapping and semi-directed interviews with 23 local experts, we identified factors influencing Indigenous landscape value. Using open-access data, we developed indicators to measure landscape state according to those values. We identified four types of hunting grounds with k-means clustering, based upon biophysical factors and disturbance history. Our results suggest that land management should aim to reduce differences between hunting ground states and consider the risk of rapid shifts from one state to another.