Paleoclimate and paleoecology of the latest Eocene Florissant flora of Central Colorado, U.S.A.

The uppermost Eocene Florissant Formation of central Colorado, U.S.A. contains a diverse flora and fauna preserved in lacustrine facies and represents a key episode in Earth history immediately preceding the Eocene-Oligocene boundary. Laminated shales contain impressions of non-monocot angiosperm leaves that were used to estimate paleoecological and paleoclimatic parameters using leaf physiognomic methods including: leaf mass per area (MA), digital leaf physiognomy (DiLP), leaf margin analysis (LMA), and leaf area analysis (LAA). The majority (58%) of the morphotypes analyzed for MA suggested a semi-evergreen leaf lifespan, whereas another 27% indicated a deciduous habit and 15% an evergreen habit. There was no significant relationship between MA and insect damage based on a small subset of Florissant’s leaves. Higher MA values (~73% of leaves ≥ one-year lifespan), coupled with a tendency toward long and narrow leaf shapes and small leaf areas, indicate the existence of sclerophyllous vegetation. Using the global regression for mean annual temperature (MAT), the DiLP estimate of MAT was anomalously cold: 5.5 ± 4 °C. However, using a Northern Hemisphere regression the DiLP MAT estimate of 11.6 ± 3.3 °C was more plausible. Using DiLP, mean annual precipitation (MAP) was estimated at 740 +608/-334 mm∙yr-1, which supports dry conditions. Estimates for MAT and MAP using the univariate LMA and LAA methods overlapped within uncertainty of the DiLP results. In addition, those taxa classified as growing in wet areas (riparian) had significantly more teeth than non-riparian taxa. These paleoclimatic and paleoecological results suggest that outside the riparian forest, the Florissant flora sampled a seasonally dry temperate sclerophyllous shrubland to woodland, perhaps similar to modern chaparral forests, in the western interior of the U.S.A. just before the transition into the cooler Oligocene.

La vegetación escletófila perennifolia del Valle de Tehuacán, Puebla y sus similitudes con la vegetación esclerófila de climas mediterráneos

The evergreen sclerophyllous vegetation of the Tehuacán Valley is described and compared with 4 of the 5 zones with Mediterranean-type climates. In the vegetation description structural aspects such as cover, height, frequency and life forms spectrum were considered. This vegetation type called Mexical has a close similarity in life forms spectrum with annuals predominance with the Mediterranean-type vegetation. Therefore, the evergreen sclerophyllous vegetation distribution within the tropics not only is explained in relation with mediterranean-type climates, and also because by historical factors .

Effects of post-fire logging on fuel dynamics in a mixed-conifer forest, Oregon, USA: a 10-year assessment

Removal of fire-killed trees (i.e. post-fire or salvage logging) is often conducted in part to reduce woody fuel loads and mitigate potential reburn effects. Studies of post-salvage fuel dynamics have primarily used chronosequence or modelling approaches, with associated limitations; longitudinal studies tracking fuels over time have been rare. We resampled a network of post-fire plots, comprising a range of logging intensities, 10 years after the 2002 Biscuit Fire (Oregon, USA). For surface woody fuels, which started from large treatment differences immediately following logging (stepwise increases with harvest intensity), we found converging trends among treatments at 10 years, with convergence nearly complete for fine fuels but not for coarse fuels. Fire-killed snags for the dominant species (Pseudotsuga menziesii) decayed while standing at a statistically significant rate (single-exponential k = 0.011), similar to or only slightly slower than down wood, suggesting that not all snag biomass will reach the forest floor. Live vegetation (largely resprouting sclerophyllous vegetation) is beginning to dominate surface fuel mass and continuity (>100% cover) and likely moderates differences associated with woody fuels. Post-fire logging had little effect on live fuels or their change over time, suggesting high potential for stand-replacing early-seral fire regardless of post-fire harvest treatments.

Fossil leaves of Banksia, Banksieae and pretenders: resolving the fossil genus Banksieaephyllum

The genus Banksieaephyllum, originally erected for cuticle-bearing fossil leaves of subtribe Banksiinae (Proteaceae subfamily Grevilleoideae, tribe Banksieae), is reassessed. Of the 18 described species, nine are accepted within Banksia, including Banksieaephyllum obovatum Cookson & Duigan, which is synonymised with B. laeve Cookson & Duigan on the basis of new cuticular preparations. Two other species are transferred to Banksieaefolia gen. nov., a genus erected for Banksieae of uncertain affinities, and which presently includes only fossils that probably belong to subtribe Musgraveinae. The seven other Banksieaephyllum species lack definitive characters of Proteaceae (i.e. brachyparacytic stomata and annular trichome bases) and do not have Banksieae-type cylindrical trichome bases. These species are, therefore, not accepted as Proteaceae and are transferred to Pseudobanksia gen. nov., together with another fossil Banksia-like leaf species, Phyllites yallournensis Cookson & Duigan. Lectotypes are chosen for Banksia fastigata H.Deane, Banksieaephyllum acuminatum Cookson & Duigan, Banksieaephyllum angustum Cookson & Duigan and Banksieaephyllum laeve Cookson & Duigan. Implications arising from the re-assessment of Banksieaephyllum include clarification of biome conservatism in Banksieae; Banksia has long had an association with relatively open, sclerophyllous vegetation, and Musgraveinae with rainforest. Pseudobanksia and Banksia share convergent traits, but in contrast to Banksia, Pseudobanksia failed to survive the drying climates and increased fire-frequencies of the Neogene.

Croton condorensis: an enigmatic new species of Euphorbiaceae from southern Ecuador

Croton condorensis (Euphorbiaceae), a new species from the Cordillera del Cóndor in southern Ecuador, is here described and illustrated. The new species occurs in sclerophyllous vegetation on sandstone substrate. A detailed examination of its morphology indicates that the species has some characters in common with Croton sect. Cyclostigma, but it also differs from that section in several other key characters. Given its restricted geographic distribution, the particular substrate where it grows, and its unusual morphology, we hypothesize that Croton condorensis might represent a previously unsampled clade of the Croton phylogeny. Se describe e ilustra Croton condorensis (Euphorbiaceae), una nueva especie de la Cordillera del Cóndor en el sur de Ecuador. Esta especie se encuentra en vegetación esclerófila sobre substrato de arenisca. Una examinación detallada de su morfología indica que la especie comparte algunos caracteres morfológicos con miembros de Croton sect. Cyclostigma, pero también posee caracteres clave que no son compatibles con la morfología de dicha sección. Dada su restringida distribución geográfica, el particular substrato en el que crece, y la falta de afinidades morfológicas evidentes con alguna de las secciones de Croton, planteamos la hipótesis de que Croton condorensis podría representar un clado de la filogenia del género aún no muestreado.

Leaf tissue water relations and hydraulic properties of sclerophyllous vegetation on white sands of the upper Rio Negro in the Amazon region

The objective of this study was to explore the leaf tissue water relations in terminal branches, as well as the relations between xylem structure and function of five sclerophyllous species coexisting on white sands within the Amazon region. In these species, which possess costly leaves and thrive in an extremely nutrient-poor habitat, the preservation of leaf survival would be of comparable importance to the preservation of xylem vessels. Three trees per species were tagged in the field for all measurements. Minimum leaf water potential (Ψ) was −1.53 ± 0.61 and −0.94 ± 0.10 MPa during rainless and rainy days, respectively. The Ψ for turgor loss averaged −1.92 ± 0.05 MPa. Therefore, minimum Ψ was maintained within a safety range above the critical value for turgor loss. Xylem (Kx) and leaf (Kl) specific conductivity averaged 1.4 ± 0.22 and 0.00033 ± 0.000045 kg m−1 s−1 MPa−1, respectively. Water supply was favoured in species with higher vessel density, and all species depended on relatively less abundant larger vessels for water transport. This would be advantageous because leaves were unable to develop very negative water potentials in order to maintain transpiration. High transpiration rates may be restricted to a few hours daily so as to prevent cavitation of widest vessels.