Forest Resilience & Long-Term Stand Dynamics

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Coast redwood legacy tree at Swanton Pacific Ranch.

Coast redwood regeneration & forest resilience under multiple, interacting disturbances

Forest ecosystems are invaluable ecological and sociocultural resources, which are shaped by historical disturbance regimes. While disturbance is a natural process in all ecosystems, climate change will affect the frequency and intensity of disturbances in the future, potentially leading to unpredictable disturbance regimes. One quality of new disturbance regimes could be an increase in compounding disturbances – multiple disturbances whose effects (or legacies) in the local ecosystem overlap in space and time. Compounding disturbances exert unpredicted stresses on ecosystems, leading to novel conditions that may exceed the capacity for recovery. We hypothesize that alterations to the frequency of disturbance, or an increase in compounding disturbances, could uniquely affect forest composition and structure in forests for years following disturbance.

In this research we are asking the following questions: 1) How do compounding disturbances influence the trajectories of coast redwood forests and their long-term resilience? 2) How do belowground (soil) legacies of single and compounding fire disturbances vary over time? 3) Do soil legacies of fire disturbances have measurable effects on coast redwood regeneration? To answer these questions, we are mapping post-fire forests and local above- and belowground conditions across four burn years spanning 1985-2013 in Big Sur, California.

Improved understanding of the effects of fires is important in coast redwood forests, which will see increased fire frequency in the future. Research into variation in disturbance legacies over time will help to fill gaps in the basic knowledge about coast redwood regeneration and may address how controls on regeneration vary under differing disturbance regimes. This research will contribute to our understanding of influences on forest regeneration following novel disturbance patterns under climate change for coast redwood forests, and provide information relevant in forest ecosystems outside of the coast redwood range.

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High severity burn within Rim Fire boundary of Stanislaus National Forest.

Interacting effects of wildfire & salvage logging on conifer regeneration following the King Fire

Disturbances are vital processes for the composition, structure, and function of all forest ecosystems. Although both natural and often common to forest ecosystems, disturbance frequency and severity are predicted to increase across western forests and interacting disturbances will become more likely. Multiple disturbances may generate novel responses and differential recovery of forest ecosystems, and little is known on the effects of these interactions. The 2014 King Fire burned ~97,000 acres on the El Dorado National Forest and adjacent lands. A subset of areas impacted by high severity fire will be salvage logged in Fall 2015. Led by Pacific Southwest Research Station forest and fire ecologists, we initiated a study to evaluate the long-term impacts of varying degrees of salvage on regeneration and long-term stand dynamics. This study will assess the interactions between mixed-severity wildfire and post- fire salvage logging on regeneration by addressing the following questions: 1) Does salvage logging have different and/or additional ecological effects than wildfire alone? 2) What is the combined effect of wildfire and subsequent salvage logging on conifer regeneration? and 3) How do variations in intensity of natural and anthropogenic disturbances alter post-disturbance regeneration and long-term stand dynamics? We are working with the PSW Research Station to establish plots across a gradient of salvage intensities and including blocked areas to assess replanting and shrub removal. Research will follow regeneration and stand development over time in order to adequately address these questions of interest.

Collaborator: Dr. Eric Knapp (USDA Pacific Southwest Research Station), Dr. Morris Johnson (USDA Pacific Northwest Research Station), Dr. Malcolm North (USDA Pacific Southwest Research Station), and Dr. Jen Stevens (USDA Pacific Southwest Research Station)

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Gap harvest unit on variable density thinning study at Stanislaus-Tuolumne Experimental Forest.

Conifer regeneration and survival under historic, current, and predicted future conditions in Sierra Nevada Mixed-Conifer forests

We are collaborating with the Pacific Southeast Research Station to evaluate the response of historically-dominant conifers to altered past, present, and future climate and local environmental conditions. Our lab established experiemntal and observational plots across the Stanislaus-Experimental Forest and within Yosemite National Park to examine the influence of local climate, interspecies competition, and historic management practices on conifer regeneration over the last century. Masters students Emily O’Dean and Marissa Vossmer will take lead on this study.

Historic Drivers of Composition in Sierra Nevada Mixed-Conifer Forests: Changes to the composition of western forests due to forest management, fire suppression, and altered disturbance regimes influence seedling establishment and survival through alterations to the regeneration environment, which can modify the type and suitability of seedling establishment sites. Although historic datasets are frequently used to identify such changes, no studies have tracked seedling survival or followed seedlings through to current Sierra Nevada forests. The objectives of this study are to: (1) track and identify survival differences of dominant Sierran conifers across different establishment conditions, (2) quantify and track seedling survival under different understory compositions, and (3) identify abiotic and biotic factors that influence seedling survival. I will use a historical dataset (circa 1929) and a 2016 re-measurement to track seedling survival from historic to current forests and examine the relationship between survival, abiotic site factors, and biotic competition of shrub species. Tracking historic seedling survival and examining the site conditions and understory compositions that influence survival can provide useful information for forest managers as to how current forest structure and composition will influence seedling survival and future forest community composition.

Ecotone shifts under current & predicted future climate change: Increasing temperatures, fluctuating precipitation, and longer growing seasons associated with climate change may pose a severe threat to the sustainability of certain tree species, either through interspecific competition or stress due to lack of suitable habitat. Our research will bridge some of the gaps in knowledge that exist in the mechanisms of survival in two conifer seedlings in a major California ecotone – Abies concolor and Abies magnifica. Previous research in this ecotone includes an observational study conducted by Albert Parker between 1984-1988, which sampled overstory and understory composition in this ecotone in Yosemite National Park. Parker’s research determined that the ecotone was stable, but after 30 years of a changing climate, returning to these sites may present evidence of instability and significant compositional shifts. By re-sampling this ecotone and supporting our results with an ex-situ factorial climate manipulation of these conifer species, we will be able to quantify shifts in range, and determine if abiotic climatic factors are the driving force behind shifts. Abies magnifica may be at particular risk from climate change, due to its limited upper-montane range. Interspecific competition and rapidly changing climatic conditions may drive this species toward higher elevations, which in some cases may not exist.

Collaborator: Dr. Eric Knapp (USDA Pacific Southwest Research Station)

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