Primary Succession on a Hawaiian Dryland Chronosequence

<div><p>We used measurements from airborne imaging spectroscopy and LiDAR to quantify the biophysical structure and composition of vegetation on a dryland substrate age gradient in Hawaii. Both vertical stature and species composition changed during primary succession, and reveal a progressive increase in vertical stature on younger substrates followed by a collapse on Pleistocene-aged flows. Tall-stature <i>Metrosideros polymorpha</i> woodlands dominated on the youngest substrates (hundreds of years), and were replaced by the tall-stature endemic tree species <i>Myoporum sandwicense</i> and <i>Sophora chrysophylla</i> on intermediate-aged flows (thousands of years). The oldest substrates (tens of thousands of years) were dominated by the short-stature native shrub <i>Dodonaea viscosa</i> and endemic grass <i>Eragrostis atropioides</i>. We excavated 18 macroscopic charcoal fragments from Pleistocene-aged substrates. Mean radiocarbon age was 2,002 years and ranged from < 200 to 7,730. Genus identities from four fragments indicate that <i>Osteomeles spp</i>. or <i>M</i>. <i>polymorpha</i> once occupied the Pleistocene-aged substrates, but neither of these species is found there today. These findings indicate the existence of fires before humans are known to have occupied the Hawaiian archipelago, and demonstrate that a collapse in vertical stature is prevalent on the oldest substrates. This work contributes to our understanding of prehistoric fires in shaping the trajectory of primary succession in Hawaiian drylands.</p></div

Site characteristics of the Pōhakuloa substrate age gradient.

<p>Site characteristics of the Pōhakuloa substrate age gradient.</p

Mean distance (m) 2,000 randomly selected locations on substrates of the Pōhakuloa substrate age gradient and the nearest location with at least 25%, 50% or 75% lateral cover of NPV.

<p>Standard deviation provided in parentheses. Because NPV in this landscape is mainly fine fuels, these numbers demonstrate that a gradient in susceptibility to fire is associated with substrate age.</p><p>Mean distance (m) 2,000 randomly selected locations on substrates of the Pōhakuloa substrate age gradient and the nearest location with at least 25%, 50% or 75% lateral cover of NPV.</p

Airborne imaging spectroscopy and LiDAR can be used to quantify the composition and fractional cover of vegetation.

<p>The top image is a true color composite overlaid on the digital terrain model (DTM). The bottom image is an RGB composite of the same area processed to quantify barren substrate (B, <b>r</b>ed), photosynthetic vegetation (PV; <b>g</b>reen) and non-photosynthetic vegetation (NPV; <b>b</b>lue). Changes in the lateral distribution of PV, NPV, B, and height are apparent across the substrate age gradient. For example, <i>M</i>. <i>polymorpha</i> woodland (MPW) on the 750–1200 year-old substrate is dominated by B and tall-statured NPV, indicated by reds and blues in the bottom panel. In contrast, <i>D</i>.<i>viscosa</i> shrubland (DVS) on a Pleistocene aged substrate is dominated by short-statured NPV and PV, indicated by blues and greens in the bottom panel. The areas shown are a 1 km² sample of the 23.1 km² study area mapped at 2.2 m resolution.</p

Relationships among types of lateral vegetation cover.

<p>PV = photosynthetic vegetation; NPV = non-photosynthetic vegetation; B = barren substrate. The youngest substrates are dominated almost exclusively by B, but accumulate NPV and PV during primary succession and ecosystem development. The rate of development is faster on pāhoehoe (right column) than on aʻa (left column). Pāhoehoe and aʻa lava types are not distinguishable on the 65 ky Pleistocene aged substrates.</p

Distributions of lateral vegetation cover on substrates of the Pōhakuloa substrate age gradient.

<p>Distributions of lateral vegetation cover on substrates of the Pōhakuloa substrate age gradient.</p

¹⁴C age frequency distribution for 18 macroscopic charcoal fragments excavated from Pleistocene- aged soils.

<p>Black vertical lines indicate charcoal ages. Red vertical lines indicate the timing of arrival of Europeans (solid) and Polynesians (dashed) to the Hawaiian archipelago.(Kirch 2010).</p

Supplementary Material for: Thrombolysis for acute wake-up and unclear onset strokes with alteplase at 0.6 mg/kg in clinical practice: THAWS2 Study

Introduction: The aim of this study was to determine the safety and efficacy of intravenous (IV) alteplase at 0.6 mg/kg for patients with acute wake-up or unclear onset strokes in clinical practice. Methods: This multicenter observational study enrolled acute ischemic stroke patients with last-known-well time >4.5 h who had mismatch between DWI and FLAIR and were treated with IV alteplase. The safety outcomes were symptomatic intracranial hemorrhage (sICH) after thrombolysis, all-cause deaths and all adverse events. The efficacy outcomes were favorable outcome defined as an mRS score of 0–1 or recovery to the same mRS score as the premorbid score, complete independence defined as an mRS score of 0–1 at 90 days, and change in NIHSS at 24 h from baseline. Results: Sixty-six patients (35 females; mean age, 74±11 years; premorbid complete independence, 54 [82%]; median NIHSS on admission, 11) were enrolled at 15 hospitals. Two patients (3%) had sICH. Median NIHSS changed from 11 (IQR, 6.75–16.25) at baseline to 5 (3–12.25) at 24 h after alteplase initiation (change, –4.8±8.1). At discharge, 31 patients (47%) had favorable outcome and 29 (44%) had complete independence. None died within 90 days. Twenty-three (35%) also underwent mechanical thrombectomy (no sICH, NIHSS change of –8.5±7.3), of whom 11 (48%) were completely independent at discharge. Conclusions: In real-world clinical practice, IV alteplase for unclear onset stroke patients with DWI-FLAIR mismatch provided safe and efficacious outcomes comparable to those in previous trials. Additional mechanical thrombectomy was performed safely in them