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Ceanothus verrucosus (CEVE) is a globally rare, long-lived, chaparral shrub endemic to coastal southern California (CA) and northern Mexico. There is concern for CEVE persistence because of habitat loss, fire, and climate change, yet little is known about basic features of the plant, including whether it contains annual rings, plant age, and climate–growth response. Growth-ring analysis was challenging because of semi-ring-porous structure, false, and missing rings. We successfully crossdated CEVE annual rings, primarily from Cabrillo National Monument, CA, using a nearby Pinus torreyana chronology. The oldest living individual had 116 rings; the oldest inner-ring date was 1873; and most of the plants established between 1894 and 1905, all older than previous estimates. CEVE mortality occurred during a dry period from the late 1940s through the early 1960s. Correlations between age and stem measurements were weak to moderate (r = 0.10 to 0.56) posing challenges for field-based estimates of plant ages, which are important for population modeling. Variability in CEVE ring width had a strong positive correlation with prior cool-season (October–April) precipitation, yet 2- to 7-day warm-season precipitation events were recorded as rare false rings in multiple years, indicating extreme plasticity in cambial phenology and growth response to moisture.
To investigate drought influences on mixed-severity fire regimes in montane forests of southeastern British Columbia, we developed a Douglas-fir latewood-width chronology and tested its associations with drought records across the fire season. Associations were strong between drought and latewood-widths particularly for June–August. Based on the chronology, we reconstructed the summer Drought Code, an index of moisture content in slow-drying deep compact organics in the soil and coarse woody fuels. Using the summer Drought Code and an existing reconstruction of the summer Palmer Drought Severity Index, representing moisture content in the quick-drying duff layer, we tested fire–drought associations using fire-scar records. Subtle differences in fire–drought associations reflect distinct drying rates and overwintering capacity among forest fuels represented by each summer drought reconstruction. Variable moisture conditions across fuels influence fire occurrence; in particular when the summer Drought Code exceeds 344 and the summer Palmer Drought Severity Index is below 0.08, fire occurrence is more likely. The application of these thresholds with climate change scenarios may provide insights on how mixed-severity fire regimes could be impacted in montane forests of southeastern British Columbia.
Latewood ring widths of longleaf pine (Pinus palustris Mill.) growing on Carolina bay sand rims on the coastal plains of North Carolina are effective recorders of tropical cycone precipitation (TCP). Longleaf pine are hypothesized to be effective recorders of TCP because of their extensive lateral root structure that is exposed to enhanced soil moisture when TCP events raise the water table to root level, but this hypothesis has not been empirically tested. In this study, we used a combination of North Carolina Phase 1 LiDAR and high-precision georeferenced data to investigate the relationship between radial tree growth, TCP, and microelevation. Our findings suggest that the strength of correlations between latewood ring widths and TCP are positively correlated (p < 0.05) with tree elevation on Carolina bay sand rims, resulting in greater sensistivity of trees at higher elevations. These findings suggest that in some environments, microelevational differences (<1 m) may significantly affect climate/radial growth relationships and the use of high-resolution LiDAR technology may be an effective tool for better understanding the role of microtopography on radial growth patterns.
Tree-ring research (TRR) in South America (SA) continues to make important contributions in multiple sub-disciplines, including dendrochemistry and dendrohydrology. This report describes some of the advances in TRR in SA presented in a two-day International Meeting Research entitled “An International Network to Promote Advances in Dendrochronology in South America”, organized by the Laboratory of Dendrochronology and Environmental Studies of the Pontifical Catholic University of Valparaíso in Valparaíso, Chile, on January 21–22, 2019. The objective of the meeting was to communicate recent advances in TRR within a network of laboratories in Argentina, Brazil, Chile, Peru, and Uruguay. Novel methodologies and results in dendrochemistry and wood anatomy were also presented by collaborating researchers from German institutions. This report describes some of the research within the subdisciplines of tree-ring science, including dendrochemistry, anatomy and dendrohydrology, and their application to understanding spatio-temporal variability in heavy metal contamination, climate, hydrology, fire regimes and other critical components of South American forest and woodland ecosystems. The meeting demonstrated expansion and diversification of inquiry and applications of TRR in SA, whereby collaboration across research centers has been critical for the advances made in broad-scale comparative studies as well as multi-proxy approaches and the study of global and hemisphere-scale climate phenomena.