Mist rising above a forest.

Understanding carbon life cycles and climate impacts unfolding deep in the woods.

The forest-climate connection is simple, isn’t it? When trees grow, they absorb carbon dioxide; when they die, they slowly release it.

But forest-carbon estimation and forecasting—the gritty, technical work that underlies greenhouse gas accounting? That is wickedly complex stuff, demanding knowledge from a broad spectrum of natural sciences.

Just ask Robert Hember. The PICS postdoctoral fellow worked on the PICS Forest Carbon Management Project, under the leadership of Natural Resources Canada’s Dr. Werner Kurz (see: “Woodsy Solutions”). His team’s research has helped provincial and federal governments get a better fix on how environmental changes such as hotter, drier summers impact forest productivity.  

To inform this work, Hember and his colleagues:

  • Worked with climatologists to understand how influential hydrological conditions have changed. Published in the journal Hydrology.

  • Compiled data from national monitoring networks and satellites to map the annual rate of nitrogen deposition—another influential changing environmental factor. Published in the journal Data In Brief.

  • Compiled more than 10,000 historical observations of forest growth and mortality. Published in the journal Global Biogeochemical Cycles.

  • Applied advanced models of tree growth and mortality to assess how overall landscapes of forest biomass production should be responding to gradual changes in climate and atmospheric carbon dioxide concentration. Published in the journal Forests.

  • And looked to tree-ring records to further understand how tree growth has changed. Published in the journal JGR Biogeosciences.

“It was much like a hospital visit,” recalls Hember, thinking back about how the team proceeded. “If something doesn’t feel right, start monitoring vital rates. If forests seem to be in abnormally poor health, look at BC’s extensive database of ground plot measurements to help make a diagnosis.” The work marked the first time that a national-scale study of annual forest biomass production would be based on statistical analysis of observations, rather than theory, simulation, or average historical yields. 

The results were not all doom and gloom. Although forest biomass production has decreased slightly due to higher tree mortality in dry regions of western Canada, wet regions appear to be thriving, where trees likely grow much faster today than they did 100 years ago as a result of beneficial environmental changes, including increasing levels of nitrogen and carbon dioxide in the atmosphere. 

Six published papers later, Hember’s team has enriched the science of estimating the role of environmental impacts on forest productivity.

Water balance variable illustrations
These excerpts from Robert Hember’s 2017 paper illustrate the change in forest water-balance variables across North America between 1951 and 2014. (A) depicts warm-season mean reference evapotranspiration, (b) shows warm-season mean actual evapotranspiration, (c) reveals spring snowmelt, while (d) depicts warm-season soil-water content

The work contributes to a larger effort in BC and elsewhere to incorporate climate change into our daily business. This means accounting for ongoing climate change impacts in future projections of timber supply and carbon sequestration--which under current practices typically assume that trees are growing and dying at rates that haven’t changed over the last century.

“Much public attention and research focuses on visible impacts, such as wildfires and insect outbreaks,” says Hember, who now works for the province as a forest carbon modeling professional. 

“But anyone concerned about the state of our forests, and the role they play in addressing climate change, needs to equally consider the trends that unfold over decades in the vast expanses of the province that are not being disturbed by severe wildfire.”

Climate change impacts infographic



Link  Hember, Robbie A. and Kurz, Werner A. and Coops, Nicholas C. Relationships between individual-tree mortality and water-balance variables indicate positive trends in water stress-induced tree mortality across North AmericaGlob Chang Biol vol. 23, 4, 2017