Formation of xylem tissues and secondary cell walls is diminished by severe and consecutive insect defoliation.

PREMISE: Insect defoliation of trees causes unusual changes to wood anatomy and slows radial growth that decreases tree value; however, the characteristics of these anatomical changes in hardwoods remain unclear. The aim of this study was to characterize the anatomy and histochemistry of the wood in trunks of Betula maximowicziana trees after severe insect defoliation. METHODS: Secondary xylem tissues were sampled from trunks that had been defoliated by Caligula japonica at Naie and Furano in central Hokkaido during 2006-2012, then cross-dated and examined microscopically and stained histochemically to characterize anatomical and chemical changes in the cells. RESULTS: White rings with thin-walled wood fibers and greatly reduced annual ring width in the subsequent year were observed in samples from both sites. From these results, the year that the white rings formed was determined, and severe defoliation was confirmed to trigger white ring formation. The characteristics may prove useful to detect the formation year of white rings. Scanning electron microscopy and histochemical analyses of the white rings indicated that the thickness of the S2 layer in the wall of wood fiber cells decreased, but xylan and lignin were still deposited in the cell walls of wood fibers. However, the walls of the fibers rethickened after the defoliation. CONCLUSIONS: Our results suggest that B. maximowicziana responds to a temporary lack of carbon inputs due to insect defoliation by regulating the thickness of the S2 layer of the cell wall of wood fibers. For B. maximowicziana, insect defoliation late in the growing season has serious deleterious effects on wood formation and radial growth.

Tree ring evidence of rapid development of drunken forest induced by permafrost warming.

Black spruce trees growing on warming permafrost lean in all directions due to soil movement, forming a "drunken" forest. Two hypothetical drivers of drunken forest development are (i) loosening of the soil foundation induced by permafrost degradation in warm summers and (ii) mound rising induced by freezing soil in winter. However, no evidence has previously clarified whether recent tree leaning is related to climate warming or is part of a natural hummock formation process. Here, we provide evidence that tree leaning and soil hummock formation have accelerated due to climate warming. We find that trees' leaning events synchronize with the development of soil hummocks as recorded in tree rings with lignin-rich cells. Tree leaning is caused by mound rising in winter due to refreezing of soil following deep thaws in summer, rather than by loosening of the soil foundation in summer. Hummock formation shifted from periodic events before 1960 to continuous mound rising in the warmer succeeding 50 years. Although soil change is generally a slow process, recent permafrost warming has induced rapid hummock formation, which threatens the stability of drunken forests and organic carbon in soil hummocks based on shallow permafrost table.

The effects of localized heating and disbudding on cambial reactivation and formation of earlywood vessels in seedlings of the deciduous ring-porous hardwood, Quercus serrata.

BACKGROUND AND AIMS: The networks of vessel elements play a vital role in the transport of water from roots to leaves, and the continuous formation of earlywood vessels is crucial for the growth of ring-porous hardwoods. The differentiation of earlywood vessels is controlled by external and internal factors. The present study was designed to identify the limiting factors in the induction of cambial reactivation and the differentiation of earlywood vessels, using localized heating and disbudding of dormant stems of seedlings of a deciduous ring-porous hardwood, Quercus serrata. METHODS: Localized heating was achieved by wrapping an electric heating ribbon around stems. Disbudding involved removal of all buds. Three treatments were initiated on 1 February 2012, namely heating, disbudding and a combination of heating and disbudding, with untreated dormant stems as controls. Cambial reactivation and differentiation of vessel elements were monitored by light and polarized-light microscopy, and the growth of buds was followed. KEY RESULTS: Cambial reactivation and differentiation of vessel elements occurred sooner in heated seedlings than in non-heated seedlings before bud break. The combination of heating and disbudding of seedlings also resulted in earlier cambial reactivation and differentiation of first vessel elements than in non-heated seedlings. A few narrow vessel elements were formed during heating after disbudding, while many large earlywood vessel elements were formed in heated seedlings with buds. CONCLUSIONS: The results suggested that, in seedlings of the deciduous ring-porous hardwood Quercus serrata, elevated temperature was a direct trigger for cambial reactivation and differentiation of first vessel elements. Bud growth was not essential for cambial reactivation and differentiation of first vessel elements, but might be important for the continuous formation of wide vessel elements.