North American boreal trees show a decline in the survival of saplings in response to warming or reduced rainfall.

Nature 

Four separate papers exploring how forests and tree species respond to global changes — such as rising temperatures — are published in Nature this week. The studies highlight some of the challenges forests in North America and the Amazon may face in response to climate change.

Temperate deciduous tree with a dendrometer band, of the type used in the study, in the ForestGEO plot at the Smithsonian Conservation Biology Institute in Front Royal, VA.

Credit: Kristina J. Anderson-Teixeira

A study of nine North American boreal tree species, including maples, firs, spruces and pines, shows a decline for all species in the survival of saplings in response to warming or reduced rainfall. In a five-year open-air field experiment, Peter Reich and colleagues found that fir, spruce and pine species abundant in southern boreal forests had the largest reductions in growth and survival due to changes in climate. 

Temperate deciduous tree with a dendrometer band, of the type used in the study, in the ForestGEO plot at the Smithsonian Conservation Biology Institute in Front Royal, VA.Credit: Kristina J. Anderson-Teixeira

However, the species that experienced lower rates of mortality and were more likely to experience growth in response to warming, such as maples, are rarer in southern boreal forests and are unlikely to expand their distribution in this region fast enough to compensate for regeneration failure of the current dominant species.

 An otherwise barren, unnamed valley in the west-central Brooks Range of Alaska, USA, supports a population of boreal white spruce that likely provides the seeds carried many kilometers away by winter wind to germinate in Arctic tundra. Credit: Roman Dial

In another paper, Roman Dial and colleagues describe the northward migration of a North American population of white spruce (Picea glauca) into the Arctic tundra, unoccupied by this species for millennia, at a rate of more than 4 km per decade. The authors found that increasing temperatures together with winter winds, deeper snowpack and increased soil nutrient availability have supported this treeline advance. They argue that increasing Arctic tree cover could lead to a decrease in the habitat available for migratory species and a redistribution of carbon stores.

Two white spruce trees, each probably under 30 years old, overlook a remote tundra valley in northwest Alaska, USA. Recent climate warming, winter winds, and an increasing deep snowpack are facilitating the colonization of Arctic tundra by this boreal species. The trekking pole is one meter long. Credit: Roman Dial

Kristina Anderson-Teixeira and colleagues paired dendrometer band measurements with 207 tree-ring chronologies from 108 forests across temperate deciduous forests of eastern North America. They found that warmer spring temperatures advance the timing of stem growth but have little effect on total annual stem growth. The authors suggest that barring rapid acclimation of these forests to warming conditions, they are unlikely to sequester increasing amounts of carbon as temperatures rise.

In this picture at the Ely site (one of two of the experiment) we see one of the ambient plot in the foreground and some heated plots in the background.  All plants are in the process of fall senescence with slowly developing differentiation in plant senescence between ambient (and the research plots surrounding vegetation) and warmed plots due to the effect warming has on plant phenology.

Finally, Hellen Fernanda Viana Cunha and colleagues show that limitations in the availability of phosphorous directly impact the productivity of the Amazon forest by restricting its responses to CO2 fertilization. This may potentially affect forest resilience to climate change.