Forest Ecologist Sarah Bisbing reported on her research in Cambria’s Monterey Pine forest at the Forest Committee’s January meeting. Here is her slide presentation, Bisbing MP Disease slideshow, along with explanatory information:
Slide 1: Title page and authors. Climate and Disease-Induced Demographic Shifts in an Endemic Conifer
Slide 2: In the context of changing climate, Monterey Pine is a model of what the range of possible effects may be. Scientists and forest managers can learn from observing how Monterey Pine is reacting. Trees have a range of tolerance to conditions. Young trees respond differently to temperature than mature trees do.
Slide 3: Monterey Pine forests have expanded and contracted in response to climate changes over millennia. Pollen records show that Monterey Pines historically covered a larger area of California.
As the climate gets warmer and drier in Cambria, Monterey Pines are under stress. The graphic slide shows how plants that no longer match the climate die off. Only a subset can survive. Plants and animals have to migrate, adapt or die.
Slide 4: It’s not happening only in Cambria. It’s happening globally. Species adapted to past conditions are now subjected to new conditions. High temperatures and low moisture are extreme stressors to trees.
Slide 5: California Tree Mortality Viewer: Trees died off in the Sierras during the 2014-2016 period, years of serious drought and high temperatures. Conifers are stress tolerant. It takes them a few years of stress to die, and to fully manifest the effects of drought.
Slide 6: The few locations in which Monterey Pines (Pinus radiata) grow naturally are small: Cambria, Monterey and Santa Cruz. It’s an endemic conifer in those locations, naturally occurring but rare, in a subset of discrete locations. Monterey Pine is classified as Endangered on the IUCN’s Red List of Threatened Species.
Slide 7: Monterey Pine is widely raised commercially, as shown on this world map. The plantatons preserve some genetic diversity, as the trees need to adapt to local conditions. Plantations are watered and cultivated, unlike the trees in Cambria’s forest. They are grown as a crop.
Slide 8: Monterey Pine is one of two major species of trees in Cambria. The other is Coast Live Oak, Quercus agricfolia. They have distinctive silhouettes. They are part of an ecological community, a group of organisms that occur together.
Slide 9: Pitch Pine Canker was feared to kill all the Monterey Pine 20 years ago. It killed some trees, but Monterey Pine has a history of Boom and Bust cycles. More trees are infected at the edges of the community than the interior. In 2001, Don Canestro began gathering data on Cambria’s Monterey Pine at the UC SB Reserve in Cambria. He took photos to compare how the forest was faring over time.
Slide 10: Cal Fire’s maps show the progression of mortality.
Slide 11: Fog Dependency. Fog may be a primary source of moisture for Monterey Pine, although this is not yet established scientifically. One of the changes in climate is a reduction in fog.
Slide 12: There is, however, evidence of bishop pine dependence on fog, which is a species closely related to Monterey pine. Bishop pine mortality is significantly driven by fog dependency.
Slide 13: The three research questions Dr. Bisbing and her students are exploring:
Are forest population dynamics driven more by exogenous or endogenous factors? Exogenous factors are regional climate over months, seasons, and years. Long term data on climate factors are needed to understand this question. It’s bigger than the stand itself. It’s impacting everyone. Endogenous factors are within-stand factors, such as disease, topography and microclimate, and fire.
How does climate influence patterns of mortality and regeneration? The number of trees and the stand density are factors to observe. What is driving mortality? Is the big picture or local conditions more important?
Given these drivers, what response can we anticipate under future conditions?
Slides 14-15: These graphs show the Temperature, Precipitation, Humidity (fog), the Frost-free period(the growing season) and the number of days above18 degrees C for the years from 2001-2015. They show the extended drought we had from 2010-2015.
The Frost-free period is usually 325 days in Cambria. During the drought it extended to 350 days. Every day was stressful for the trees.
The number of days above 18 degrees C is an indicator of how many days of extreme heat. The graph shows an exponential increase in hot days during the drought.
Slide 16: The Climatic Water Deficit combines the factors that stress trees to create a surrogate for tree stress. It’s a way to indicate how trees are not meeting their photosynthetic demands. Trees are not stressed during the months of January through April.
Slide 17: Shows Mortality, how many trees died, in four age ranges. Forest density and pitch canker infection were factors in the 2000s. Density influences mortality, because more trees use more water, making less water available per tree. During the drought, older trees and small trees died, but seedlings regenerated. Trees are always dying, which is called the background mortality. The drought caused a pulse of mortality.
Slide 18: Mature oaks were not affected by the drought. Oaks did not show even background mortality. Monterey Pines have a life expectancy of 80-100 years. Oaks live hundreds of years.
Slide 19: Graphs show the amount of regeneration, new seedlings taking root. Monterey Pines show a big pulse of regeneration during the El Nino of the early 2000s.
Slides 20-21: These graphs show the predicted mortality for Monterey Pines, based on age class. More seedlings sprout, but then die off. There is a threshold of tolerance for tree stress. Fog didn’t make a difference.
Slide 22: More Monterey Pines die when there is less precipitation. The turning point is about 490 mm, about 19 inches, of rain. Average precipitation in Cambria is 16 inches. It’s an arid climate.
Slide 23: Coast Live Oak is the underdog in the story. They survived the drought.
Slide 24-27: The forecast for the future is for less precipitation and a longer growing season. That means more tree stress, more extreme heat days. Trees will need to tolerate these conditions going forward. Cambria’s signature forest could change. Monterey Pine grows under dry conditions, but Cambria Oaks by the Sea could become the dominant silhouette.
Slide 28: The data support these conclusions: Exogenous factors are more influential than endogenous factors. Factors are species specific, affecting pine and oak differently. We can expect population declines and compositional shifts in the forest. How we manage development and urbanization will make a difference to how well the Monterey Pine forest survives. We can’t change climate future, but we can make a difference.
Slide 29: Managing Monterey Pine so that it has sites to grow will help. These permanent plots across Cambria give Monterey Pine a network of sites. Fiscalini Ranch Preserve and Covell Ranch are large stands. Tracking the proportion of infected trees indicates that the forest is responding. The proportion of trees infected is not high.
Slide 30-31: These maps show the annual mortality for 2014, 2015, 2016, by year and cumulatively through 2017. Background mortality is 1-5 percent.