Research
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Changes in the growth rates of trees in Eastern North America Accounting for the fitness–suitability hypothesis
Using tree-ring data, we calculated > 1.5 million annual stem growth rate estimates (standardized for tree size) for 15,677 trees representing 37 species from 558 populations throughout eastern North America. We used collection data and species distribution models to estimate each population’s climatic suitability from 1900 to 2010. We then assessed the relationships between growth, suitability, and time using linear mixed-effects models.
We found that stem growth rates decreased significantly through time independent of changes in climate suitability and that relationships between growth rates and climate suitability were highly variable across species. Contrary to expectations, we found that growth rates were negatively correlated with species’ climate suitability, a relationship that was consistent over time for gymnosperms and became more negative through time for angiosperms.
Link to the paper in Ecography here.
Long-term effects of climate change on tree growth along an elevational gradient in the northern Andes of Colombia
The long-term effects of climate change on tropical trees remain unknown. I use dendroecology to investigate changes in the growth rates of tropical trees across their elevational and thermal ranges.
Specifically, I use tree-ring measurements of wood samples collected from multiple elevations (100 to 1100 m asl) in the northern Colombian Andes Mountains to assess tree growth patterns in two tropical tree species, Jacaranda copaia and Virola sebifera. Changes in growth will be analyzed in relation to the location of sample populations in relation to the species’ thermal optima, estimated through distribution models.
Using these data, I will test how growth rates change through time and in relation to a sample population’s position within its range. Together these tests will transform our knowledge about the effects of climate change on tropical forests and will help to resolve standing controversies about the future role of tropical forests as carbon sinks or carbon sources.
Growth rates of three common South Florida tree species are being affected by climate change and urbanization
South Florida’s natural forest ecosystems, including pine rocklands and hardwood hammocks, are threatened by land use change, invasive species, and climate change.
Using dendrochronology, we characterized long-term growth patterns in three dominant native tree species: Bursera simaruba, Swietenia mahagoni, and Pinus elliottii. We assessed relationships between annual tree growth rates and climatic variables to address three questions. Q1. What are the climatic drivers of tree growth in these three iconic South Florida tree species? Q2. Are growth rates of these species stable or changing through time? And Q3. Are tree growth rates affected by urbanization?
We found significant negative correlations between tree growth and Spring precipitation in P. elliottii and B. simaruba, whereas growth rates of S. mahagoni were positively correlated with Fall precipitation. There were weak negative relationships between temperature and growth for P. elliottii and S. mahagoni but no discernable effects of temperature on the growth rates of B simaruba. Moreover, S. mahagoni and B. simaruba grew faster in urbanized parks, whereas P elliottii grew slower in urban parks. Standardized growth rates of the three species have changed through time, with small young trees showing accelerating growth through time, whereas larger older trees showed decelerating growth rates.
A dendrochronological and stable isotope assessment of a dominant tree species across the Big Cypress National Preserve
Big Cypress National Preserve (BICY) is a 295,000-hectare freshwater swamp ecosystem in southwest Florida that spans three counties and hosts both tropical and temperate plant species. Over 25% of vegetation cover in BICY consists of dwarf cypress (Taxodium ascendens), and BICY supports the largest population of this species. Even within the protected areas of BICY, T. ascendens is being exposed to pressures such as climate variation, alterations in hydrological and fire patterns, and off-road vehicle disturbances.
We measured annual growth rates from wood samples collected from 25 T. ascendens trees growing in BICY to determine the age distributions of T. ascendens and to assess how climate, hydrology, and fire are affecting tree growth through time and across space. Overall, this ongoing research aims to answer three questions. 1. What are the patterns of tree age and growth rates of T. ascendens trees across the BICY landscape? 2. How are growth rates of T. ascendens related to environmental variables, fire, and hydrology? and 3. Is T. ascendens vulnerable to changing environmental factors and disturbances?.
Our preliminary results show that T. ascendens is an extremely slow-growing species with a mean radial growth rate of approximately 0.75 mm/year (ranging from 0.45 to 1.88 mm/year). The oldest tree that we have sampled so far is 317 years old despite having a diameter of just 32.5 cm (12.8 inches).
Annual growth rings and climate in Rhizophora mangle L. from the Cispatá Bay, Colombia
Because of its location in the land-sea ecotone, Rhizophora mangle is an organism with great sensitivity to climate change. The existence of climate-sensitive annual rings in this species highlights its potential relevance for tropical dendroclimatology.
Even though had been previously established the existence of annual rings, delimited by changes in pore density, in the Rhizophora genus, using computed tomographies, is also possible to demonstrate, that the rings in R. mangle can also be defined by changes in wood density.
Comparing wood density maxima (DM) and pore density maxima (PD) in tree cross-sections reveals the annual nature of R. mangle tree rings. With increased rainfall PD increases and DM decreases, and vice versa. PD and DM are interpreted as adaptive traits that allow R. mangle to adapt to the conditions produced by annual pulses in salinity in the bay of Cispatá related to high and low discharges of the rivers. Link to the paper here.
Dendroecological study of forest dynamics in a tropical altitudinal gradient
Through dendrochronology we studied the growth dynamics of three tree species [Carapa guianensis Aubl. (Meliaceae), Cedrela tonduzii C. DC (Meliaceae) and Quercus costaricensis Liemb. (Fagaceae)] in the tropical altitudinal gradient “Caribe -Villa Mills” located between 300 – 3000 m asl on the eastern slope of the Talamanca mountain range, Costa Rica.
We drilled trees with a Diameter at Breast Height ≥ 10 cm, and when fallen trees were found we collected cross sections of the trunk with a chainsaw. We measured growth rings and constructed an average chronology per species. Subsequently, we evaluated for each species the relationship with climatic variables and determined the factors that most influence the growth dynamics of each species in the last 80 years.
All three species presented annual growth rings. In the three species, relationships were found between the average chronologies of each species and the precipitation of any month. We found that at the beginning of the 20th century, trees near the lower limit of the species' range grew on average less than those located near the upper limit, a trend that was reversed around 1976 in C. tonduzii and Q. costaricensis.
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