Save the Redwoods League

Abstract Background. Pitch pine is a globally rare tree species that occurs on xeric sites in the largely mesic landscape of eastern North America. Supporting a rich assemblage of rare species, pitch pine communities are threatened by succession to more mesophytic species in the absence of natural and anthropogenic disturbance. We examined multi-millennial dynamics of pitch pine woodland in relation to fire and land use across a local moisture gradient in coastal Maine, USA. Results. Fossil pollen from a forest hollow revealed that pitch pine has been a long-time inhabitant of the land that today is called The Basin Preserve, extending back at least seven millennia before present. Fossil charcoal demonstrated the long historical importance of fire in these pitch pine stands. Euro-American settlement left a pronounced imprint on sediment records and current forest patterns, including an expansion of pitch pine populations in response to land clearing. Age structure and current regeneration patterns of tree species across the moisture gradient revealed ongoing succession of pitch pine to more mesophytic species, such as red oak and red maple, except on the most xeric sites, where the species appears to be self-perpetuating. Conclusions. The results reveal succession, mesophication, and contraction of pitch pine woodland in the Basin Preserve, a pattern also found in more southern parts of this species range. Given the importance of these rare xeric ecosystems as biodiversity hotspots in a largely mesic landscape, active management to reduce vegetation in this preserve cover should be considered.

ABSTRACTThe giant sequoia (Sequoiadendron giganteum) of California are massive, long-lived trees that grow along the U.S. Sierra Nevada mountains. As they grow primarily in isolated groves within a narrow range, conservation of existing trees has been a national goal for over 150 years. Genomic data are limited in giant sequoia, and the assembly and annotation of the first giant sequoia genome has been an important goal to allow marker development for restoration and management. Using Illumina and Oxford Nanopore sequencing combined with Dovetail chromosome conformation capture libraries, 8.125 Gbp of sequence was assembled into eleven chromosome-scale scaffolds. This giant sequoia assembly represents the first genome sequenced in the Cupressaceae family, and lays a foundation for using genomic tools to aid in giant sequoia conservation and management. Beyond conservation and management applications, the giant sequoia assembly is a resource for answering questions about the life history of this enigmatic and robust species. Here we provide an example by taking an inventory of the large and complex family of NLR type disease resistance genes.

Abstract The understory of California's coast redwood forests boasts an abundance of ferns, half of which are drought deciduous. Despite their ecological importance, little is known about the functional differences between deciduous and perennial ferns. This study explored morphological and physiological leaf traits of an assortment of coast redwood forest fern species sampled from the southern, drier extent of the ecosystem, to determine if deciduous species are less drought tolerant than co-occurring evergreen species because of their shorter leaf lifespan. In mid-summer, all ferns were well hydrated with water potentials above −1 MPa. Although the deciduous ferns were more vulnerable to hydraulic dysfunction by embolism, it is likely that all species experienced similarly low degrees of embolism in situ, as inferred from mid-day water potential measurements. Despite their similar water relations when water was not limiting, we observed that deciduous ferns had thinner pinnae because they avoid the late...

Leaf hydraulic conductance (k leaf) is a central element in the regulation of leaf water balance but the properties of k leaf remain uncertain. Here, the evidence for the following two models for k leaf in well-hydrated plants is evaluated: (i) k leaf is constant or (ii) k leaf increases as transpiration rate (E) increases. The difference between stem and leaf water potential (ΔΨstem-leaf), stomatal conductance (g s), k leaf, and E over a diurnal cycle for three angiosperm and gymnosperm tree species growing in a common garden, and for Helianthus annuus plants grown under sub-ambient, ambient, and elevated atmospheric CO₂ concentration were evaluated. Results show that for well-watered plants k leaf is positively dependent on E. Here, this property is termed the dynamic conductance, k leaf(E), which incorporates the inherent k leaf at zero E, which is distinguished as the static conductance, k leaf(0). Growth under different CO₂ concentrations maintained the same relationship between k leaf and E, resulting in similar k leaf(0), while operating along different regions of the curve owing to the influence of CO₂ on g s. The positive relationship between k leaf and E minimized variation in ΔΨstem-leaf. This enables leaves to minimize variation in Ψleaf and maximize g s and CO₂ assimilation rate over the diurnal course of evaporative demand.