Uncertainties in the response of a forest landscape to global climatic change

Many studies have been conducted to quantify the possible ecosystem/landscape response to the anticipated global warming. However, there is a large amount of uncertainty in the future climate predictions used for these studies. Specifically, the climate predictions can be very different based on a variety of global climate models and alternative greenhouse emission scenarios. In this study, we coupled a forest landscape model, LANDIS-II, and a forest process model, PnET-II, to examine the uncertainty (that results from the uncertainty in the future climate predictions) in the forest-type composition prediction for a transitional forest landscape [the Boundary Water Canoe Area]. Using an improved global-sensitivity analysis technique [Fourier amplitude sensitivity test], we also quantified the amount of uncertainty in the forest-type composition prediction contributed by different climate variables including temperature, CO₂, precipitation and photosynthetic active radiation (PAR). The forest landscape response was simulated for the period 2000–2400 ad based on the differential responses of 13 tree species under an ensemble of 27 possible climate prediction profiles (monthly time series of climate variables). Our simulations indicate that the uncertainty in the forest-type composition becomes very high after 2200 ad , which is close to the time when the current forests are largely removed by windthrow disturbances and natural mortality. The most important source of uncertainty in the forest-type composition prediction is from the uncertainty in temperature predictions. The second most important source is PAR, the third is CO₂ and the least important is precipitation. Our results also show that if the optimum photosynthetic temperature rises due to CO₂ enrichment, the forest landscape response to climatic change measured by forest-type composition may be substantially reduced.     

Ovarian polarity and cell shape determination by Btk29A in Drosophila

Drosophila Btk29A is a Tec family nonreceptor tyrosine kinase, the ortholog of which causes X‐linked agammaglobulinemia in humans when mutant. In Btk29A^ficP mutant ovaries, multiple defects are observed: extrapolar cells form ectopically; osk mRNA fails to accumulate posteriorly in mature oocytes; the shape and alignment of follicle cells are grossly distorted. All these phenotypes are rescued by selectively overexpressing the type 2 isoform of wild‐type Btk29A in follicle cells. Expression of certain proteins enriched in adherens junctions is markedly affected in Btk29A^ficP mutants; the anterior–posterior gradient normally observed in the expression of DE‐Cadherin and Armadillo are lost and Canoe is sequestered from adherens junctions. Intriguingly, tyrosine phosphorylation of Canoe is reduced in Btk29A^ficP mutants. It is proposed that Btk29A is required for the establishment of egg chamber polarity presumably through the regulation of subcellular localization of its downstream proteins, including Cno.     

Rap1 maintains adhesion between cells to affect Egfr signaling and planar cell polarity in Drosophila

The small GTPase Rap1 affects cell adhesion and cell motility in numerous developmental contexts. Loss of Rap1 in the Drosophila wing epithelium disrupts adherens junction localization, causing mutant cells to disperse, and dramatically alters epithelial cell shape. While the adhesive consequences of Rap1 inactivation have been well described in this system, the effects on cell signaling, cell fate specification, and tissue differentiation are not known. Here we demonstrate that Egfr-dependent cell types are lost from Rap1 mutant tissue as an indirect consequence of DE-cadherin mislocalization. Cells lacking Rap1 in the developing wing and eye are capable of responding to an Egfr signal, indicating that Rap1 is not required for Egfr/Ras/MAPK signal transduction. Instead, Rap1 regulates adhesive contacts necessary for maintenance of Egfr signaling between cells, and differentiation of wing veins and photoreceptors. Rap1 is also necessary for planar cell polarity in these tissues. Wing hair alignment and ommatidial rotation, functional readouts of planar cell polarity in the wing and eye respectively, are both affected in Rap1 mutant tissue. Finally, we show that Rap1 acts through the effector Canoe to regulate these developmental processes.     

Tahitala's Revenge: Monumental Architecture and the Great Canoe,Lomipeau

In discussing ways that monumental architecture symbolises political power, I suggest that vehicles are a unique category of monument construction. Their ability to travel, and to be used for politically momentous tasks, increases the prestige of the rulers who make use of them. The Lomipeau, a large double‐hulled canoe used by Tongan rulers in the sixteenth century, exemplifies the concept of a monumental vehicle. To demonstrate the concept, I examine the origins of the canoe, the archaeology of sites associated with its exploits, and its use in ceremonial voyages of national importance. Identifying vehicles as a distinctive class of monumental architecture in future studies will help us to comprehend the complex variety of ways leaders express power across cultures.     

Ras target protein canoe is a substrate for Cdc2 and Cdk5 kinases

Mutations in the canoe locus of Drosophila lead to failure in the dorsal closure of the embryonic epidermis and pattern formation defects in imaginal eyes and wings. In the wing, the canoe mutants develop extra veins when they are heterozygous for shaggy, a mutation in the locus encoding the glycogen synthase kinase 3 beta (Gsk3 beta), which has been known to phosphorylate the Armadillo protein. Although Canoe has a putative target sequence for phosphorylation by Gsk3 beta similar to that found in Armadillo, in vitro experiments indicate that Canoe is not phosphorylated by Gsk3 beta . Instead, Canoe is demonstrated to be a good substrate of Cdc2 and Cdk5 kinases. Thus, Cdc2 and Cdk5 kinases are the potential regulators of the function of Canoe in morphogenesis. Arch.     

Simulating the Effects of Fire Reintroduction Versus Continued Fire Absence on Forest Composition and Landscape Structure in the Boundary Waters Canoe Area, Northern Minnesota, USA

The Boundary Waters Canoe Area (BWCA) Wilderness of northern Minnesota, USA, ememplifies how fire management and natural disturbance determine forest composition and landscape structure at a broad scale. Historically, the BWCA (>400,000 ha) was subject to crown fires with a mean rotation period of 50–100 y. Fires often overlapped, creating a mosaic of differently aged stands with many stands burning frequently or, alternatively, escaping fire for several centuries. The BWCA may never have reached a steady-state (defined as a stable landscape age-class structure). In the early 1900s, a diminished fire regime began creating a more demographically diverse forest, characterized by increasingly uneven-aged stands. Shade-tolerant species typical of the region began replacing the shade-intolerant species that composed the fire-generated even-aged stands. Red pine (Pinus resinosa) stands are relatively uncommon in the BWCA today and are of special concern. The replacement of early-to-midsuccessional species is occurring at the scale of individual gaps, producing mixed-species multiaged forests. We used LANDIS, a spatially explicit forest landscape model, to investigate the long-term consequences of fire reintroduction or continuing fire absence on forest composition and landscape structure. Fire reintroduction was evaluated at three potential mean fire rotation periods (FRP): 50,100, and 300 y. Our model scenarios predict that if fire reintroduction mimics the natural fire regime (bracketed by FRP = 50 and 100 y), it will be most successful at preserving the original species composition and landscape structure, although jack pine (Pinus banksiana) may require special management. With limited fire reintroduction, all of the extant species are retained although species dominance and landscape structure will be substantially altered. If fire remains absent, many fire-dependent species will be lost as local dominants, including red pine. The landscape appears to be in a state of rapid change and a shift in management to promote fire may need to be implemented soon to prevent further deviation from historic, presettlement conditions.