Ecological turnover and megafaunal ghost ranges during the Pleistocene-Holocene transition in central Yukon, Canada as revealed by palaeoenvironmental DNA

<p>The multitude of factors alleged to have contributed to the late Quaternary mass extinction of some two-thirds of Earth’s megafauna is complicated by the coarse record of buried macro-fossils. In response, micro-methods such as ancient DNA have been increasingly able to augment discontinuous palaeontological records to investigate the relative timings of vegetation turnover versus megafaunal extirpations—all in the absence of biological tissues. Here, we present sedimentary ancient DNA data retrieved using the PalaeoChip Arctic-1.0 bait-set diachronically identifying fauna and flora from permafrost cores recovered from the Klondike region of central Yukon, Canada dating between 30,000–6000 calendar years BP. We observe a substantial turnover in ecosystem composition between 13,000–10,000 BP with the rise of woody shrubs and the disappearance of mammoth-steppe vegetation. We also identify a lingering signal of <em>Equus</em> sp. (North American horse) and <em>Mammuthus primigenius</em> (woolly mammoth) from multiple samples thousands of years after their last dated macro-fossils, possibly as late as the mid-Holocene.</p>

Mysterious chokeberries: new data on the diversity and phylogeny of Aronia Medik. (Rosaceae)

Aronia Medik. (chokeberry, Rosaceae) is a genus of woody shrubs with two or three North American species. Species boundaries and relationships between species of Aronia are frequently under question. The only European species in the genus, A. mitschurinii A.K.Skvortsov & Maitul., is suggested to be an inter-generic hybrid. In order to clarify the relationships between species of Aronia, we performed several morphometric and molecular analyses and found that the molecular and morphological diversity within data on American Aronia is low, and species boundaries are mostly not clearly expressed. Whereas morphology is able to separate American species from A. mitschurinii, there is no support for such discrimination from the molecular data; our analyses did not reveal evidence of A. mitschurinii hybrid origin. We believe that higher-resolution markers are needed to resolve species boundaries and putative hybridization events.

Aboveground Biomass Response to Release Treatments in a Young Ponderosa Pine Plantation

Controlling competing vegetation is vital for early plantation establishment and growth. Aboveground biomass (AGB) response to manual grubbing release from shrub competition was compared with no release control in a twelve-year-old ponderosa pine (Pinus ponderosa Lawson & C. Lawson) plantation established after a wildfire in northeastern California. In addition, response to chemical release followed by precommercial thinning in an adjacent plantation was also examined as a growth potential from a more intensively managed regime, where shrub competition was virtually eliminated. We measured AGB in both planted trees and competing woody shrubs to partition the biomass pools in the plantation. The results showed a significant grubbing treatment effect on basal diameter (BD) at 10 cm aboveground (p = 0.02), but not on tree height (p = 0.055). Height and BD were 2.0 m and 7.4 cm in the manual release, respectively, compared to 1.7 m and 5.6 cm in the control. However, chemical release produced much greater rates of tree growth with a height of 3.6 m and BD of 14.7 cm, respectively. Tree AGB was 60% higher with the manual release of shrubs (1.2 Mg ha−1) than with control (0.7 Mg ha−1) (p < 0.05). The planted area without shrub competition yielded a much higher green tree biomass (16.0 Mg ha−1). When woody shrub biomass was included, the total AGB (trees and woody shrubs) appeared slightly higher, but non-significant in the no release control (13.3 Mg ha−1) than in the manual release (11.9 Mg ha−1) (p = 0.66); the chemical release had 17.1 Mg ha−1. Clearly, shrub biomass dominated this young plantation when understory shrubs were not completely controlled. Although the manual release did increase targeted tree growth to some degree, the cost may limit this practice to a smaller scale and the remaining shrub dominance may create long-term reductions in growth and a persistent fuels problem in these fire-prone ecosystems.

Rapid, nondestructive estimation of forest understory biomass using a handheld laser rangefinder

The forest understory is often associated with rapid rates of carbon and nutrient cycling, but cost-efficient quantification of its biomass remains challenging. We tested a new field technique for understory biomass assessment using an off-the-shelf handheld laser rangefinder. We conducted laser sampling in a pine forest with an understory dominated by invasive woody shrubs, especially Rhamnus frangula L. Laser sampling was conducted using a rangefinder, mounted on a monopod to provide a consistent reference height, and pointed vertically downward. Subsequently, the understory biomass was measured with destructive sampling. A series of metrics derived from the airborne LiDAR literature were evaluated alone and in combination for prediction of understory biomass using best-subsets regression. Resulting fits were good (r2 = 0.85 and 0.84 for the best single metric and best additive metric, respectively, and R2 = 0.93 for the best multivariate model). The results indicate that laser sampling could substantially reduce the need for costly destructive sampling within a double-sampling context.