By Kat Kerlin
CCalifornia’s drought and bark-beetle infestation killed more than 129 million trees between 2012 and 2016 in the Sierra Nevada. But amid the devastation stood some survivors.
At the time, UC Davis biologist Patricia Maloney and a team of researchers entered the forest to collect seeds from 100 surviving sugar pine trees. Alongside other parched sugar pines etched with the tell-tale tunnel marks of bark beetles, were green, healthy trees. The researchers spent the past two years raising 10,000 seedlings from 100 surviving mother trees around the Lake Tahoe Basin. They were first cultivated at the USDA Forest Service’s Placerville Nursery and then moved to the UC Davis Tahoe City Field Station.
This week, between 4,000 and 5,000 of the seedlings are being planted around Lake Tahoe’s North Shore as part of a restoration project funded by the Tahoe Fund and the California Tahoe Conservancy. About 1,500 will be used to study and identify important adaptive traits, and the remainder will be given to private landowners to plant.
f the seedlings turn out to be as genetically resilient as Maloney thinks and hopes they will be, these trees could represent the future forest, one better able to withstand the threats of climate change, including more droughts and bark beetle outbreaks.
“These survivors matter,” said Maloney, a scientist in the UC Davis Department of Plant Pathology and Tahoe Environmental Research Center. “Essentially, these are the offspring of drought survivors. This is hopefully the genetic stock of the future.”
By Andy Eckardt and Yuliya Talmazan
HAINICH, Germany — As forester Dirk Fritzlar walks through thick woodland on a sunny September morning, it starts to “rain” spruce needles.
“It is not normal for the trees to shed so many needles. It is far too dry. Many spruce trees are dying,” Fritzlar said as he peeled off a piece of bark. He quickly finds a colony of bark beetles that are a major threat to the spruce — a common species in German forests.
In the last two years, Germany has experienced long summer droughts and rising temperatures, both of which are putting the country’s woodlands in peril.
The potential fate of this forest and millions of German trees shows the danger climate change and changing weather patterns pose to biodiversity and raises questions of how states and citizens should protect their local green spaces.
In 2018 alone, 110,000 hectares (about 272,000 acres) of forest area in Germany were damaged and 33 million cubic meters of wood — equivalent in volume to 12 Great Pyramids of Giza — were declared dead, researchers at the country’s Thünen Institute of Forest Ecosystems said.
A preliminary assessment for 2019 shows at least the same amount of damage.
German researchers and foresters have told NBC News the damage is the result of high temperatures and lack of rain drying out the trees, and in the case of the spruce, weakening its defenses against pests such as the bark beetle.
During a heat wave that hit much of Europe in July, Germany was one of several countries to break records, recording temperatures as high as 42.6 degrees Celsius (108.7 F).
Hygroscopic aerosols — particles in the air that attract water — could be causing forest decline around the world, according to experiments performed in Germany. Researchers believe that aerosol accumulation on trees enables thin bridges of liquid to form between the leaf interior and the leaf surface, causing the plants to dry out much more rapidly.
“In the atmosphere, aerosols act as cloud condensation nuclei,” says Juergen Burkhardt of the University of Bonn, Germany. “Deposited aerosols on leaf surfaces act almost the same way but attract water from inside the plant.”
Plants have developed sophisticated mechanisms for taking up carbon dioxide from the air for photosynthesis without losing too much water but, as the scientists note, it’s a delicate balance. And one that appears to be upset by rising levels of airborne particles.
“Global aerosol concentrations have roughly doubled compared with natural conditions, and the concentration increase over the continents is even higher,” says Burkhardt. “Our results show that aerosols deposited on leaves interfere with this delicate balance, pointing to a direct mechanism by which air pollution can reduce the drought tolerance of plants.”
Burkhardt and colleagues grew three species of tree — Scots pine, silver fir and common oak — for two years in two greenhouses, one ventilated with ambient air and the other fed with air filtered to remove 99% of aerosols. Seedlings grown under filtered conditions had superior drought tolerance to those raised in ambient air, the team found.
Diversity is strength, even among forests. In a paper published in Nature, researchers led by University of Utah biologist William Anderegg report that forests with trees that employ a high diversity of traits related to water use suffer less of an impact from drought. The results, which expand on previous work that looked at individual tree species’ resilience based on hydraulic traits, lead to new research directions on forest resilience and inform forest managers working to rebuild forests after logging or wildfire.
Surprisingly, says Anderegg, a forest’s hydraulic diversity is the predominant predictor of how well it can handle a drought.
“We expected that hydraulic traits should matter,” he says, “but we were surprised that other traits that a lot of the scientific community have focused on weren’t very explanatory or predictive at all.”
After a record low winter run-off, some water experts are now calling this Arizona’s worst mega-drought in recorded history, even when compared to tree-ring data that goes all the way back to the 1300s.