Leaf phloem alterations in two provenances ofAbies alba Miller (silver fir) during ageing

The phenomenon of premature needle senescence in two Italian provenances of silver fir was studied as part of a more general research project on decliningAbies alba. The two provenances showed a different degree of sensitivity to atmospheric pollutants. Comparative observations on 1-, 3-, 5-, 7- and 9-year-old needles from both provenances highlighted a faster loss of function in the phloem of needles from the Vallombrosa provenance. This fact appears to be related more to a loss of function in the cambium, than to a different rate of degeneration of sieve cells. This phenomenon may help explain why needles of the Vallombrosa provenance tend to be shed sooner than those of the Serra San Bruno provenance.     

Climate–growth relationship of tree species from a mixed stand of Apuseni Mts., Romania

We present the first results of a dendroecological investigation on three prevailing species growing in the Apuseni Mountains. In this study we succeeded in building up about 200-year long local master chronologies for spruce, fir and beech. These chronologies will serve as a reference for crossdating of (sub-fossil) logs that were preserved in ice caves at the Apuseni Mts.

The analysis of climate–growth relationship provided interesting and different results for the three studied species: we found significant correlations between the beech chronology and the mean temperature of the prior July, autumn and January of the actual year as well as the weather conditions at the beginning of the vegetation period. Conifers yielded coherent results for the mean temperature of prior July and sum of precipitation in April. In addition, fir seems to be favouring above-average temperatures in January and February. The coherent and significant correlations with the April precipitation suggest a common coniferous phenomenon. Finally, beech index showed negative correlation with April temperature.     

Short-Term Effects of Cattle Browsing on Tree Sapling Growth in Mountain Wooded Pastures

Browsing by livestock has been identified as an important factor preventing tree regeneration in wooded pastures. Two field experiments were performed to investigate the effects of cattle browsing on tree sapling growth in a mountain-wooded pasture. Two size classes (ca. 12–17 cm and 41–59 cm) of each of 4 species (Picea abies, Abies alba, Acer pseudoplatanus and Fagus sylvatica) were exposed to zero, low and high grazing intensities. We measured the proportion of saplings browsed and the effect of browsing on growth. A mowing treatment within the zero grazing intensity treatment showed no significant effect on sapling growth. One percent of the large saplings but 25% of the small saplings escaped browsing. Saplings were better protected when surrounded by taller vegetation. The proportion of saplings browsed was not significantly different among species although evergreen tree saplings lost a larger proportion of biomass than deciduous species when browsed. Under grazing, average current-year shoot production and total aboveground biomass of all species were significantly reduced. Browsing effects tended to be smaller at the lower grazing intensity. Because the deciduous species were least reduced in aboveground growth, especially under the low grazing intensity, we conclude that at least in short-term, deciduous species are less affected by cattle browsing.     

雅致玉凤花——陕西省兰科一新分布种

报道了陕西省兰科(Orchidaceae)玉凤花属(Habenaria)一新分布种——雅致玉凤花(Habenaria fargesii)。     

濒危植物秦岭冷杉补光育苗技术研究

秦岭冷杉种子生活力差、成苗率低(2.2%)是制约种群恢复的薄弱环节。通过对播种后苗期2年连续补光处理,幼苗表现出良好的生长效应,苗高10.5 cm(对照为7.3 cm),地径4.5 mm(对照为2.7 mm),保存率88.6%(对照66.4%),延长了幼苗生长期,增加了苗木生物量积累,加快了苗木培育进程。     

The mid-Holocene extinction of silver fir (Abies alba) in the Southern Alps: a consequence of forest fires? Palaeobotanical records and forest simulations

Pollen records suggest that Abies alba played a dominating role in both the montane and lowland forests at the border of the Southern Alps between ca. 8500 and 5700 years ago. Two major declines in fir, at about 7300–7000 cal b.p. and at ca. 6000 cal b.p., followed by the local extinction of the species are characteristic of the area below ca. 1000 m a.s.l. In order to test the impact of fire on the population dynamics of silver fir, a dynamic model (DisCForm) with a fire module was applied to simulate the early- and mid-Holocene forest development. Simulation outputs based on different fire scenarios were compared with the pollen record from Lago di Annone (226 m a.s.l.). The marked Abies decreases shown in the pollen record can be simulated with very intensive fire scenarios, but they do not result in an extinction of silver fir in the model. Low charcoal influx values related to the Abies declines in the palaeobotanical record suggest that fire was not the only reason for the extinction of silver fir. Human impact, as well as Holocene climatic changes leading to temporary moisture deficits and reduced adaptability due to low genetic variation may have had a significant impact on the Abies forests.     

The effects of enhanced ultraviolet-B and nitrogen supply on growth,photosynthesis and nutrient status of <Emphasis Type="Italic">Abies faxoniana</Emphasis> seedlings

Abies faxoniana is a key species in reforestation processes in the southeast of the Qinghai-Tibetan Plateau of China. The changes in growth, photosynthesis and nutrient status of A. faxoniana seedlings exposed to enhanced ultraviolet-B (UV-B), nitrogen supply and their combination were investigated. The experimental design included two levels of UV-B treatments (ambient UV-B, 11.02 KJ m⁻² day⁻¹; enhanced UV-B, 14.33 KJ m⁻² day⁻¹) and two nitrogen levels (0; 20 g N m⁻²). The results indicated that: (1) enhanced UV-B significantly caused a marked decline in growth parameters, net photosynthetic rate (Pn), photosynthetic pigments and F _v/F _m, (2) supplemental nitrogen supply increased the accumulation of total biomass, Pn, photosynthetic pigments and F _v/F _m under ambient UV-B, whereas supplemental nitrogen supply reduced Pn, and not affect biomass under enhanced UV-B, (3) enhanced UV-B or nitrogen supply changed the concentration of nutrient elements of various organs.     

竹子新害虫——木竹泰广肩小蜂

木竹泰广肩小蜂Tetramesa cereipes Erds为我国1新记录种,在北京市紫竹院公园发现危害巴山木竹的嫩竹枝,受害竹枝形成多室虫瘿。该小蜂在北京1年发生1代,11月下旬以老熟幼虫在寄主虫瘿内过冬,翌年3月下旬起化蛹,4月初为化蛹高峰期。4月中旬开始羽化,5月初盛发,5月下旬终止。幼虫为害期从6月中旬到11月下旬止。此外,还描述各虫态的形态特征。     

The Strait of Gibraltar as a major biogeographic barrier in Mediterranean conifers: a comparative phylogeographic survey

The Strait of Gibraltar (SG) is reputed for being both a bridge and a geographic barrier to biological exchanges between Europe and Africa. Major genetic breaks associated with this strait have been identified in various taxa, but it is unknown whether these disjunctions have been produced simultaneously or by independent biogeographic processes. Here, the genetic structure of five conifers distributed on both sides of the SG was investigated using mitochondrial (nad1 b/c, nad5-1, nad5-4 and nad7-1) and chloroplast (Pt1254, Pt15169, Pt30204, Pt36480, Pt71936 and Pt87268) DNA markers. The distribution of genetic variation was partially congruent between types of markers within the same species. Across taxa, there was a significant overlapping between the SG and the genetic breaks detected, especially for the four Tertiary species surveyed (Abies pinsapo complex, Pinus nigra, Pinus pinaster and Taxus baccata). For most of these taxa, the divergence of populations across the SG could date back to long before the Pleistocene glaciations. However, their strongly different cpDNA G(ST) and R(ST) values point out that they have had dissimilar population histories, which might include contrasting amounts of pollen-driven gene flow since their initial establishment in the region. The fifth species, Pinus halepensis, was genetically depauperated and homogenous on both sides of the SG. A further analysis of nuclear DNA sequences with coalescent-based isolation with migration models suggests a Pleistocene divergence of P. halepensis populations across the SG, which is in sharp contrast with the pre-Pleistocene divergence dates obtained for P. pinaster. Altogether, these results indicate that the genetic breaks observed across this putative biogeographical barrier have been produced by independent evolutionary processes related to the biological history of each individual species instead of a common vicariant phenomenon.     

Altitudinal variations in seedling and sapling density and age structure of timberline tree species in the Sergyemla Mountains, southeast Tibet

The growth situation of seedlings of treeline species can be used as an indicator for the upper or lower shift of treeline under global climate change, since any advance of a treeline would require seedling survival above the current treeline elevation. We investigated seedling and sapling density of two dominant conifers Abies georgei var. smithii and Sabina saltuaria at lower, middle and upper altitude of two contrasting slopes in Sergyemla Mountain, southeast Tibet. Seedling and sapling age structure of A. georgei var. smithii was analyzed further. Seedling density of both species, as well as sapling density of S. saltuaria, showed a declining trend as elevation increased. Sapling density of A. georgei var. smithii was somewhat higher at middle altitude than other positions. The frequency of old-aged A. georgei var. smithii seedlings/saplings (age >10 year) was the lowest at the highest altitude and tended to increase with the declining elevation. The results indicate that the higher density of seedling and sapling in high-altitude might be attributed to better soil moisture availability and solar insolation than in the mid- and low-altitudes during the growth season. Yet confined by other environmental factors, A. georgei var. smithii seedlings in high-altitude suffer from lower survival rate and lower possibility to grow tall compared with those in mid- and low-altitudes.