Markedly divergent estimates of Amazon forest carbon density from ground plots and satellites

AIM

The accurate mapping of forest carbon stocks is essential for understanding the global carbon cycle, for assessing emissions from deforestation, and for rational land-use planning. Remote sensing (RS) is currently the key tool for this purpose, but RS does not estimate vegetation biomass directly, and thus may miss significant spatial variations in forest structure. We test the stated accuracy of pantropical carbon maps using a large independent field dataset.

LOCATION

Tropical forests of the Amazon basin. The permanent archive of the field plot data can be accessed at: http://dx.doi.org/10.5521/FORESTPLOTS.NET/2014_1.

METHODS

Two recent pantropical RS maps of vegetation carbon are compared to a unique ground-plot dataset, involving tree measurements in 413 large inventory plots located in nine countries. The RS maps were compared directly to field plots, and kriging of the field data was used to allow area-based comparisons.

RESULTS

The two RS carbon maps fail to capture the main gradient in Amazon forest carbon detected using 413 ground plots, from the densely wooded tall forests of the north-east, to the light-wooded, shorter forests of the south-west. The differences between plots and RS maps far exceed the uncertainties given in these studies, with whole regions over- or under-estimated by > 25%, whereas regional uncertainties for the maps were reported to be < 5%.

MAIN CONCLUSIONS

Pantropical biomass maps are widely used by governments and by projects aiming to reduce deforestation using carbon offsets, but may have significant regional biases. Carbon-mapping techniques must be revised to account for the known ecological variation in tree wood density and allometry to create maps suitable for carbon accounting. The use of single relationships between tree canopy height and above-ground biomass inevitably yields large, spatially correlated errors. This presents a significant challenge to both the forest conservation and remote sensing communities, because neither wood density nor species assemblages can be reliably mapped from space.

Patterns of angiogenic response to mast cell granule constituents

Agents derived from mast cell granule constituents, and compound 48/80 which stimulates release of mast cell granules, have been used by us to develop new methods for quantitating angiogenesis in the chick chorioallantoic membrane. Two of these methods provide different insights, demonstrating different patterns of response to dosage and over time, produced by different agents. Counting mesenchymal blood vessels is convenient for obtaining dose-response data. Histamine and compound 48/80 have been shown previously to give a sigmoid dose-response curve resulting in a plateau before the lethal dose. This contrasts with the effect of porcine sodium heparin (Evans Biologicals) which results in a minor increase then a relative decline in vessel number due to a failure of growth. Here, the ability to produce angiogenesis or antiangiogenesis appears to be dose-dependent. Measurement of the changes in DNA synthesis, leading to visible angiogenesis, may be performed once the optimal angiogenic dose is known, and again distinctive patterns of response with different agents have been found. Histamine results in a fall then rise to a peak at 36 hr. We now show that two types of heparin each produce a peak at 12 hr. Compound 48/80 results in a distinctive pattern that looks like a composite of the histamine and especially the heparin effects, and this suggests that both are relevant to induction of angiogenesis by mast cells. The elicitation of this pattern of response also provides a method, additional to electron microscopy, for discovering whether or not an angiogenic substance is likely to operate via mast cell stimulation. Such characteristic patterns offer a new way of classifying angiogenic substances.

Quantitation of histamine-induced angiogenesis in the chick chorioallantoic membrane: mode of action of histamine is indirect

Histamine was chosen as a standard chemical suitable for the development of new methods of assessing vascularity in the chick chorioallantoic membrane (CAM). When applied in liquid form to the entire 'dropped' area of CAM at day 10 of growth, a sublethal dose was required before a convincing appearance of increased vascularity was produced by day 15. Computer-assisted morphometry, using osmium-stained CAMs viewed en face, demonstrated a progressive increase in both length (21%) and number (59%) of arterial branches over 5 days relative to buffer only controls. A 56% increase in number of mesenchymal vessels seen in cross-section was also detected and this method is the quickest and easiest. No increase in the number of capillaries in the surface plexus of the ectoderm was found but this may be attributable to inadequate technique due to the already high density of capillaries present even in control CAMs using thin resin sections. However a 21% increase in the haemoglobin content of the CAM 4 days after histamine is consistent with an overall increase in the vascular bed. A rapid fall in DNA synthesis by 6 h (-48%) was produced by histamine, followed by a slow rebound to a peak at 36 h (74%). This contrasts with the growth factor type of pattern seen previously with fibrin degradation products giving a progressive rise to a major peak of DNA synthesis at 18 h. These effects indicate two mechanisms of induction of angiogenesis, and that the action of histamine is indirect.

Optical properties of spray-deposited tin oxide films

Optical properties of spray-deposited tin oxide (TO) films are studied here. Optical grade TO films were deposited using monobutyl tin chloride and dibutyl tin diacetate solutions. The refractive index and extinction coefficient, n(lambda) and k(lambda), respectively, and film thickness of TO films are evaluated from spectrophotometric transmittance characteristics examined in the visible and UV regions. Since the interference effects are suppressed by the optical absorption in the near-IR region, both reflectance and transmittance spectra are used to evaluate n(lambda) and k(lambda) values. Spray-deposited TO films are found to be an indirect band gap material exhibiting an absorption minimum at ~1.0 microm (k less, similar 10(-3)), an energy gap at ~3.7 eV. A transition from a bounded electron model to a free electron model occurs at lambda approximately 1.4 microm.