Adding tree rings to North America's National Forest Inventories: an essential tool to guide drawdown of atmospheric CO2

Tree-ring time series provide long-term, annually resolved information on the growth of trees. When sampled in a systematic context, tree-ring data can be scaled to estimate the forest carbon capture and storage of landscapes, biomes, and-ultimately-the globe. A systematic effort to sample tree rings in national forest inventories would yield unprecedented temporal and spatial resolution of forest carbon dynamics and help resolve key scientific uncertainties, which we highlight in terms of evidence for forest greening (enhanced growth) versus browning (reduced growth, increased mortality). We describe jump-starting a tree-ring collection across the continent of North America, given the commitments of Canada, the United States, and Mexico to visit forest inventory plots, along with existing legacy collections. Failing to do so would be a missed opportunity to help chart an evidence-based path toward meeting national commitments to reduce net greenhouse gas emissions, urgently needed for climate stabilization and repair.Published versio

Growth variable-specific moisture and temperature limitations in co-occuring alpine tree and shrub species, central Himalayas, Nepal

Trees and shrubs found in the forest-tundra ecotone (FTE) are considered to be highly sensitive to climate change, but their response to climatic drivers is only partially understood. We use dendrochronological techniques to develop growth chronologies for co-occuning tree (Abies spectabilis, radial growth and height) and dwarf shrub ( Cassiope frutigiata, stem elongation and leaf number) species in central Himalaya, Nepal, in order to identify and compare climate drivers of growth (temperature, precipitation, moisture (SPEI)). Our results reveal growth variable-specific responses characterized by a predominant response to previous year and non-growing season climate, and to length of the monsoon season. Tree radial growth was significantly correlated with temperature during previous summer and non-growing season months, and moisture in the late monsoon (September). Tree height increment correlated with late-monsoon temperature and moisture in the previous post-monsoon. Shrub stem elongation mainly correlated with temperature and moisture conditions in previous year pre-monsoon (May), while leaf production correlated with moisture in previous pre-monsoon and monsoon periods, and precipitation in the late-monsoon. These results contribute new evidence that mid-latitude FTE tree and shrub species and individual growth variables are limited by unique climate drivers operational at different periods during and outside the monsoon season. Within the context of rising temperatures and increased precipitation variability in the Himalayas, moisture may become a more frequent stressor on tree and shrub growth. Consideration of climate and site variable interactions at alpine sites is important to detecting subtleties of growth response. Dendroecological studies of co-occurring tree and shrub species help to identify concomitant and disparate growth responses to climate drivers and in turn, provide information and insight into FTE changes in the Himalayas and elsewhere.acceptedVersio

Methods for measuring arctic and alpine shrub growth: A review

Shrubs have increased in abundance and dominance in arctic and alpine regions in recent decades. This often dramatic change, likely due to climate warming, has the potential to alter both the structure and function of tundra ecosystems. The analysis of shrub growth is improving our understanding of tundra vegetation dynamics and environmental changes. However, dendrochronological methods developed for trees, need to be adapted for the morphology and growth eccentricity of shrubs. Here, we review current and developing methods to measure radial and axial growth, estimate age, and assess growth dynamics in relation to environmental variables. Recent advances in sampling methods, analysis and applications have improved our ability to investigate growth and recruitment dynamics of shrubs. However, to extrapolate findings to the biome scale, future dendroecological work will require improved approaches that better address variation in growth within parts of the plant, among individuals within populations and between species