Tree Growth Dynamics, Fire History, and Fire-Climate Relationships in Pine Rocklands of the Florida Keys, U.S.A.

Pine rocklands are globally endangered, fire-maintained communities currently restricted to small habitat areas in southern Florida, Cuba, and the Bahamas. The purpose of this dissertation research was to identify the long-term ecological disturbance regimes and climatic trends responsible for the persistence of pine rocklands, and examine how human-induced changes during the 20th century contributed to decline of these communities. This research applied techniques of dendrochronology in extreme southern Florida, in a subtropical region where tree‐ring science has never been applied, to increase the understanding of how anthropogenic and natural disturbance events have decreased the spatial distribution of South Florida slash pine (Pinus elliottii Engelm. var. densa Little and Dorman; hereafter slash pine), the foundation species of pine rocklands. To investigate the complex dynamics of declining pine rockland communities, I analyzed (1) the dendrochronological potential and climate response of slash pine, (2) the intra-annual ring formation characteristics and relationships to monthly climatic conditions, (3) the influence of historical fire regimes and varied fire management practices since the 1950s on the structure of slash pine savannas on adjacent islands in the Lower Florida Keys, and (4) the control of global-scale oceanic/atmospheric oscillations on historical wildfire occurrence. The analyses presented here demonstrate that slash pine forms anatomically distinct, annual growth rings with the consistent year-to-year variability necessary for rigorous dendrochronological studies. Annual radial growth of slash pine is primarily influenced by water availability during the growing season; however intra-annual cellular growth is driven by daily insolation. In the Lower Florida Keys, the growing season of slash pine occurs between February and November, with trees experiencing dormancy between November and January. Reconstructions of fire history and savanna structure revealed that, over the past 150 years, frequent fires occurring every ca. 6 years promoted pine recruitment and ensured the persistence of pine rockland habitat. However, the recent lack of fire in some areas could result in the loss of pine rockland habitat, as pine savannas are currently succeeding to tropical hardwood hammock. Over the past several centuries, interacting effects of two Pacific climatic forcing mechanisms (El Niño-Southern Oscillation, Pacific Decadal Oscillation) drove wildfire occurrence in the Lower Florida Keys

Mutations in DONSON disrupt replication fork stability and cause microcephalic dwarfism

To ensure efficient genome duplication, cells have evolved numerous factors that promote unperturbed DNA replication and protect, repair and restart damaged forks. Here we identify downstream neighbor of SON (DONSON) as a novel fork protection factor and report biallelic DONSON mutations in 29 individuals with microcephalic dwarfism. We demonstrate that DONSON is a replisome component that stabilizes forks during genome replication. Loss of DONSON leads to severe replication-associated DNA damage arising from nucleolytic cleavage of stalled replication forks. Furthermore, ATM- and Rad3-related (ATR)-dependent signaling in response to replication stress is impaired in DONSON-deficient cells, resulting in decreased checkpoint activity and the potentiation of chromosomal instability. Hypomorphic mutations in DONSON substantially reduce DONSON protein levels and impair fork stability in cells from patients, consistent with defective DNA replication underlying the disease phenotype. In summary, we have identified mutations in DONSON as a common cause of microcephalic dwarfism and established DONSON as a critical replication fork protein required for mammalian DNA replication and genome stability

Tropical tree growth driven by dry-season climate variability

Interannual variability in the global land carbon sink is strongly related to variations in tropical temperature and rainfall. This association suggests an important role for moisture-driven fluctuations in tropical vegetation productivity, but empirical evidence to quantify the responsible ecological processes is missing. Such evidence can be obtained from tree-ring data that quantify variability in a major vegetation productivity component: woody biomass growth. Here we compile a pantropical tree-ring network to show that annual woody biomass growth increases primarily with dry-season precipitation and decreases with dry-season maximum temperature. The strength of these dry-season climate responses varies among sites, as reflected in four robust and distinct climate response groups of tropical tree growth derived from clustering. Using cluster and regression analyses, we find that dry-season climate responses are amplified in regions that are drier, hotter and more climatically variable. These amplification patterns suggest that projected global warming will probably aggravate drought-induced declines in annual tropical vegetation productivity. Our study reveals a previously underappreciated role of dry-season climate variability in driving the dynamics of tropical vegetation productivity and consequently in influencing the land carbon sink.We acknowledge financial support to the co-authors provided by Agencia Nacional de Promoción Científica y Tecnológica, Argentina (PICT 2014-2797) to M.E.F.; Alberta Mennega Stichting to P.G.; BBVA Foundation to H.A.M. and J.J.C.; Belspo BRAIN project: BR/143/A3/HERBAXYLAREDD to H.B.; Confederação da Agricultura e Pecuária do Brasil - CNA to C.F.; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES, Brazil (PDSE 15011/13-5 to M.A.P.; 88881.135931/2016-01 to C.F.; 88887.199858/2018-00 to G.A.-P.; Finance Code 001 for all Brazilian collaborators); Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq, Brazil (ENV 42 to O.D.; 1009/4785031-2 to G.C.; 311874/2017-7 to J.S.); CONACYT-CB-2016-283134 to J.V.-D.; CONICET to F.A.R.; CUOMO FOUNDATION (IPCC scholarship) to M.M.; Deutsche Forschungsgemeinschaft - DFG (BR 1895/15-1 to A.B.; BR 1895/23-1 to A.B.; BR 1895/29-1 to A.B.; BR 1895/24-1 to M.M.); DGD-RMCA PilotMAB to B.T.; Dirección General de Asuntos del Personal Académico of the UNAM (Mexico) to R.B.; Elsa-Neumann-Scholarship of the Federal State of Berlin to F.S.; EMBRAPA Brazilian Agricultural Research Corporation to C.F.; Equatorian Dirección de Investigación UNL (21-DI-FARNR-2019) to D.P.-C.; São Paulo Research Foundation FAPESP (2009/53951-7 to M.T.-F.; 2012/50457-4 to G.C.; 2018/01847‐0 to P.G.; 2018/24514-7 to J.R.V.A.; 2019/08783-0 to G.M.L.; 2019/27110-7 to C.F.); FAPESP-NERC 18/50080-4 to G.C.; FAPITEC/SE/FUNTEC no. 01/2011 to M.A.P.; Fulbright Fellowship to B.J.E.; German Academic Exchange Service (DAAD) to M.I. and M.R.; German Ministry of Education, Science, Research, and Technology (FRG 0339638) to O.D.; ICRAF through the Forests, Trees, and Agroforestry research programme of the CGIAR to M.M.; Inter-American Institute for Global Change Research (IAI-SGP-CRA 2047) to J.V.-D.; International Foundation for Science (D/5466-1) to M.I.; Lamont Climate Center to B.M.B.; Miquelfonds to P.G.; National Geographic Global Exploration Fund (GEFNE80-13) to I.R.; USA’s National Science Foundation NSF (IBN-9801287 to A.J.L.; GER 9553623 and a postdoctoral fellowship to B.J.E.); NSF P2C2 (AGS-1501321) to A.C.B., D.G.-S. and G.A.-P.; NSF-FAPESP PIRE 2017/50085-3 to M.T.-F., G.C. and G.M.L.; NUFFIC-NICHE programme (HEART project) to B.K., E.M., J.H.S., J.N. and R. Vinya; Peru ‘s CONCYTEC and World Bank (043-2019-FONDECYT-BM-INC.INV.) to J.G.I.; Peru’s Fondo Nacional de Desarrollo Científico, Tecnológico y de Innovación Tecnológica (FONDECYT-BM-INC.INV 039-2019) to E.J.R.-R. and M.E.F.; Programa Bosques Andinos - HELVETAS Swiss Intercooperation to M.E.F.; Programa Nacional de Becas y Crédito Educativo - PRONABEC to J.G.I.; Schlumberger Foundation Faculty for the Future to J.N.; Sigma Xi to A.J.L.; Smithsonian Tropical Research Institute to R. Alfaro-Sánchez.; Spanish Ministry of Foreign Affairs AECID (11-CAP2-1730) to H.A.M. and J.J.C.; UK NERC grant NE/K01353X/1 to E.G.Peer reviewe

Implications of climate change on the habitat shifts of tropical lizards

The effect of temperature on the distributions of ectothermic vertebrates is well documented. Despite the increase of 6°C expected in the next 60 years in South America, numerous vertebrates are still considered as ‘Least Concern’ species by the IUCN due to their large distribution, insufficient widespread threats and insignificant population decline. One example is the lizard Tropidurus torquatus (Squamata: Tropiduridae), commonly found thermoregulating in anthropic environments throughout the Brazilian Cerrado, but restricted to gallery forests in the equator-ward localities. The urban areas in this warmer region have been colonised by other closely related congeners (e.g. Tropidurus oreadicus). This study aimed to understand this divergence of habitat selection by these tropirudids that may explain some of the species responses to past and future climate warming. We collected body temperatures (Tb), micro-environmental temperatures (Ta) and operative (Te) temperatures in four sites along a latitudinal gradient: a pole-ward and two central sites where T. torquatus inhabit urban areas and one equator-ward site where T. torquatus and T. oreadicus occur in the gallery forest and in urban microhabitats, respectively. All three populations of T. torquatus present similar Tb (35.5–36°C) and shared microhabitats with a similar Ta (34–37.3°C). The Te in the equator-ward urban site was considerably higher than in the gallery forest. Tropidurus oreadicus Tb was 38.2 °C (30.1–41.3°C) and was active at a Ta of 30.5–42.3°C. The overlap between the genus Tb, Ta and Te highlights a decrease in the hours of activity that lizards would experience under climate warming. The reduction of hours of activity together with the devastation of natural habitats represents threats and an alarming scenario especially for the equator-ward populations.Fil: Piantoni, Carla. University of Hawaii at Manoa; Estados Unidos. Universidade de Sao Paulo. Departamento de Fisiología; BrasilFil: Curcio, Felipe F.. Universidade Federal do Mato Grosso do Sul; BrasilFil: Ibarguengoytía, Nora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Departamento de Zoología; ArgentinaFil: Navas, Carlos Arturo. Universidade de Sao Paulo. Departamento de Fisiología; Brasi

Tropical tree growth driven by dry-season climate variability

Interannual variability in the global land carbon sink is strongly related to variations in tropical temperature and rainfall. This association suggests an important role for moisture-driven fluctuations in tropical vegetation productivity, but empirical evidence to quantify the responsible ecological processes is missing. Such evidence can be obtained from tree-ring data that quantify variability in a major vegetation productivity component: woody biomass growth. Here we compile a pantropical tree-ring network to show that annual woody biomass growth increases primarily with dry-season precipitation and decreases with dry-season maximum temperature. The strength of these dry-season climate responses varies among sites, as reflected in four robust and distinct climate response groups of tropical tree growth derived from clustering. Using cluster and regression analyses, we find that dry-season climate responses are amplified in regions that are drier, hotter and more climatically variable. These amplification patterns suggest that projected global warming will probably aggravate drought-induced declines in annual tropical vegetation productivity. Our study reveals a previously underappreciated role of dry-season climate variability in driving the dynamics of tropical vegetation productivity and consequently in influencing the land carbon sink

Tropical tree growth driven by dry-season climate variability

Interannual variability in the global land carbon sink is strongly related to variations in tropical temperature and rainfall. This association suggests an important role for moisture-driven fluctuations in tropical vegetation productivity, but empirical evidence to quantify the responsible ecological processes is missing. Such evidence can be obtained from tree-ring data that quantify variability in a major vegetation productivity component: woody biomass growth. Here we compile a pantropical tree-ring network to show that annual woody biomass growth increases primarily with dry-season precipitation and decreases with dry-season maximum temperature. The strength of these dry-season climate responses varies among sites, as reflected in four robust and distinct climate response groups of tropical tree growth derived from clustering. Using cluster and regression analyses, we find that dry-season climate responses are amplified in regions that are drier, hotter and more climatically variable. These amplification patterns suggest that projected global warming will probably aggravate drought-induced declines in annual tropical vegetation productivity. Our study reveals a previously underappreciated role of dry-season climate variability in driving the dynamics of tropical vegetation productivity and consequently in influencing the land carbon sink