Epiphytic and epixylic lichen species diversity in Estonian natural forests

The epiphytic and epixylic lichen flora of natural forests was recorded in different parts of Estonia. Altogether 232 taxa of lichens, lichenicolous fungi, or non-lichenized fungi were recorded, 10 of them listed in the Estonian Red Data Book. We found regional differences in lichen species composition and diversity caused by differences in the forest types. The tree-species-rich boreo-nemoral forests had the most diverse lichen flora, while the boreal forest dominated by coniferous trees or birch had the lowest diversity. The stand age proved to be significant in regard to the number of lichen species in a forest. The most remarkable effect on the diversity of forest lichen species was caused by the presence of Populus tremula. Aspen had the highest number of lichen species on the basal trunk and twigs, and also the highest number of host-specific lichen species.     

A method for studying dead bole dynamics in Pinus contorta var. latifolia - Picea engelmannii forests

Rates of decomposition were determined for the boles of Pinus contorta var. latifolia Engelm. and Picea engelmannii Parry ex. Engelm. in five lower subalpine forest stands in the Southern Canadian Rocky Mountains. Stands ranged in age from 58 to 222 yr since last fire. The date of death of standing dead and fallen boles was determined by cross-dating their ring-width patterns to stand master ring- width chronologies. Boles could be dated which had been dead for up to 35 years in a 58-yr old stand and 100 yr in a 222-yr old stand. An empirical relationship between mass density and diameter of live trees was used to predict the mass density at death for trees already dead. The falling rate of dead standing boles was estimated from the dead bole's time of death and whether it was standing or on the ground at the time of observation. The falling rates for both Pinus contorta and Picea engelmannii ranged from 0.020 to 0.064/yr falling with most stands in the 0.050 range. No effect of size was found on the falling rate probably as a result of the small size of the boles (< 20 cm). Because of their dry condition standing dead boles do not decompose. An equation was developed which estimates the time a dead bole has been on the ground, given that it would have stood for some time before falling over and been subject to little decomposition during this time. Decomposition rates, using a negative exponential model, gave only marginally better r² than linear models. Pinus contorta had exponential decay rates from 0.0299 and 0.0171 mass density loss/yr for the most recent 15 and 25 yr in stands 58 yr old, to 0.0045 and 0.0035 mass loss/yr for the most recent 65 and 80 yr in stands 215 and 222 yr old. Picea engelmannii had exponential decay rates of 0.0054 and 0.0025 mass loss/yr for the most recent 20 and 65 yr in stands 99 and 215 yr old.     

红松人工幼林透光伐效果的分析

红松人工幼林透光伐分别采取清除红松林冠上方全部(全透林)和50％(半透林)阔叶树的抚育方式。半透林生长快,蓄积是全透林的1.5倍;叶面积指数、叶面积密度和森林生产力分别是全透林的1.3、0.8和1.3倍。全林营养元素积累量大,吸收的太阳辐射比全透林多100.3×10~6J/m~2,光能利用率高0.06％。最后,根据乌道特公式证明,幼林半透抚育效果良好,有利于形成复层结构的林分,充分利用环境资源,减少竞争,提高森林生产力。     

A fifty-year reconstruction of annual changes in the spatial distribution of Pinus banksiana stands: does pattern fit competition theory?

We used tree-ring reconstruction data to study changes in the spatial pattern of live and dead trees at an annual resolution over a 50-year period at four unmanaged, even-aged fire origin jack pine (Pinus banksiana Lamb.) stands in Saskatchewan and Manitoba, Canada. Previous studies of the spatial pattern in P. banksiana have either looked at only a snapshot from a survey done at a single point in time, or repeated measurements of permanent plots taken at 10-year intervals. With annual data, we could examine detailed changes in spatial patterns and relate these to events during stand development and external disturbances. Trees were initially clustered at all sites, but at different distances at each site, most likely because of variability in seedbed distribution at stand initiation. Clustering disappeared over time at all sites, and at a similar mean tree spacing at each site. However, significant regularity only appeared sporadically at one site, indicating that competition with neighbours was not the only factor influencing changes in spatial pattern. At two of the four sites, clustering disappeared suddenly at the same time that mortality rate reached a peak, in one case also coinciding with a jack pine budworm (Choristoneura pinus pinus Freeman) defoliation event. Dead trees were also initially more clustered than the distribution of all trees, but at different distances than the clustering of live trees. This also disappeared over time so that dead trees were eventually a random sample from the distribution of all trees. After the peak of mortality had passed, factors other than competition were determining the dynamics of these forests.     

Transpiration and canopy conductance in an inner alpine Scots pine (Pinus sylvestris L.) forest

Canopy transpiration (E_c) of a 150-year-old Pinus sylvestris L. stand in an inner Alpine dry valley, Tyrol, Austria was estimated throughout two growing seasons 2011 and 2012 by means of xylem sap flow measurements. Although there were prolonged periods of limited soil water availability, E_c did not show a clear trend with respect to soil water availability and averaged 0.4 ± 0.19 mm day⁻¹ under conditions of non-limiting soil water availability and 0.37 ± 0.17 mm day⁻¹ when soil water availability was limited. This is because canopy conductance declined significantly with increasing evaporative demand and thus significantly reduced tree water loss. The growing season total of E_c was 74 mm and 88 mm in 2011 and 2012, respectively, which is significantly below the values estimated for other P. sylvestris forest ecosystems in Central Europe, and thus reflecting a strong adaptation to soil drought during periods of high evaporative demands.     

Understory vegetation response to thinning disturbance of varying complexity in coniferous stands

Question: Can augmented forest stand complexity increase understory vegetation richness and cover and accelerate the development of late‐successional features? Does within‐stand understory vegetation variability increase after imposing treatments that increase stand structural complexity of the overstory? What is the relative contribution of individual stand structural components (i.e. forest matrix, gaps, and leave island reserves) to changes in understory vegetation richness? Location: Seven study sites in the Coastal Range and Cascades regions of Oregon, USA. Methods: We examined the effects of thinning six years after harvest on understory plant vascular richness and cover in 40‐ to 60‐year‐old forest stands dominated by Douglas‐fir (Pseudotsuga menziesii). At each site, one unthinned control was preserved and three thinning treatments were implemented: low complexity (LC, 300 trees ha^?1), moderate complexity (MC, 200 trees ha^?1), and high complexity (HC, variable densities from 100 to 300 trees ha^?1). Gaps openings and leave island reserves were established in MC and HC. Results: Richness of all herbs, forest herbs, early seral herbs and shrubs, and introduced species increased in all thinning treatments, although early seral herbs and introduced species remained a small component. Only cover of early seral herbs and shrubs increased in all thinning treatments whereas forest shrub cover increased in MC and HC. In the understory, we found 284 vascular plant species. After accounting for site‐level differences, the richness of understory communities in thinned stands differed from those in control stands. Within‐treatment variability of herb and shrub richness was reduced by thinning. Matrix areas and gap openings in thinned treatments appeared to contribute to the recruitment of early seral herbs and shrubs. Conclusions: Understory vegetation richness increased 6 years after imposing treatments, with increasing stand complexity mainly because of the recruitment of early seral and forest herbs, and both low and tall shrubs. Changes in stand density did not likely lead to competitive species exclusion. The abundance of potentially invasive introduced species was much lower compared to other plant groups. Post‐thinning reductions in within‐treatment variability was caused by greater abundance of early seral herbs and shrubs in thinned stands compared with the control. Gaps and low‐density forest matrix areas created as part of spatially variably thinning had greater overall species richness. Increased overstory variability encouraged development of multiple layers of understory vegetation.     

Stand structure and woody species diversity in relation to stand stratification in a subtropical evergreen broadleaf forest, Okinawa Island

Stand structure and woody species diversity in a subtropical evergreen broadleaf forest grown in a silicate habitat, Okinawa Island, have been investigated on the basis of stand stratification. The forest stand consisted of four layers. The floristic composition of the top and the lower three layers was only slightly similar, although approximately one-third of the species were common to them. Mean tree weight decreased from the top toward the bottom layer whereas tree density increased from the top downward. This trend resembled the mean weight–density trajectory of self-thinning plant populations. The relationship between mean tree height and tree density for the upper two layers supported Yamakuras quasi –1/2 power law of tree height. The values of the Shannon–Wiener index, H, and the equitability index, J, tended to increase from the top layer downward except for the bottom layer. The values of H and J were, respectively, 4.83 bit and 0.82 for trees taller than 0.10 m. The lower layers contained many species of smaller height. High species diversity of the forest depended on small trees in the lower layers. Conservation of small trees in the lower layers, especially the bottom layer, is indispensable for sound maintenance of Okinawan evergreen broadleaf forests.     

Variation in leaf area index and stand leaf mass of European beech across gradients of soil acidity and precipitation

Leaf area index (LAI, the one-sided foliage area per unit ground surface area) is a key determinant of plant productivity which has a large influence on water and energy exchange between vegetation and the atmosphere. The variation in forest LAI across landscapes and environmental gradients and its causes are not sufficiently understood. We measured the LAI of European beech (Fagus sylvatica) by litter trapping in 23 closed, mature stands across gradients of rainfall and soil acidity or fertility. With a mean LAI of 7.4 m² m⁻² (minimum: 5.6, maximum: 9.5 m² m⁻²), beech stands maintained a comparably high leaf area index with relatively small variation along steep environmental gradients. Contrary to expectation, decreasing water availability (rainfall gradient from 1030 to 520 mm yr⁻¹) or increasing soil acidity (pH 3–7) had no significant effect on LAI. Stand leaf mass (M _l) increased slightly with soil fertility (C/N ratio, base saturation). We regressed parameters of site water availability (rainfall), soil fertility or acidity (pH, base saturation, C/N ratio, exchangeable Mg and Al content), and stand structure (stand age and stem density) against LAI and M _l in order to detect environmental controls of stand leaf area. Stand age was the most influential factor for both LAI and M _l (negative relationship). Stem density and the base saturation of the soil affected M _l significantly, but had a weak influence on LAI. We conclude that the leaf area index of beech is mainly under control of age-related physiological factors, whereas the influence of soil chemistry and rainfall is comparably low.     

Effects of abiotic conditions on Phragmites australis along geographic gradients in Lake Burullus, Egypt

Stand structure and biomass production of Phragmites australis (Cav.) Trin. ex Steud. were analyzed along north-south and east-west transects in the Burullus coastal lagoon (N Egypt, 410 km²) at monthly intervals over a period of 1 year (February 2003 until January 2004). For this purpose, young and old stands were selected at eight different locations in the lagoon. It was found that the north-south transect mainly represented a fertility gradient (207-286 mg l⁻¹ TN, 30-106 mg l⁻¹ TP), while the east-west transect was associated with significantly decreasing salinity (7-4 ppt). All morphological and biomass variables of P. australis were significantly different between young and old stands. On average, the old (7.3 ± 0.2 kg DW m⁻²) accumulated three times more total above-ground biomass than the young stands (2.5 ± 0.1 kg DW m⁻²). Shoot height, diameter and shoot dry weight significantly increased by 25-50% with increasing fertility along the north-south transect. Shoot density significantly decreased from north to south, while it almost doubled in the north sites from 109 ± 6 to 216 ± 7 shoots m⁻² along the west-east transect. In separate stepwise multiple regressions, variation in water quality explained 34-63% of the variation in morphology and total above-ground biomass in the old stands (salinity and water level were most important for biomass, transparency also for height and density) while it explained 16-42% of variation in young stands (mainly transparency).     

Foliar chemical concentrations in red alder stands of various ages

Summary Six stands of red alder (Alnus rubra Bong.) were sampled to assess the relationship between stand age and foliar chemical concentrations. The stands ranged in age from 9 to 45 years, and were located near Olympia, Washington, on sites of similar soil, aspect, and slope. Foliage was collected in July, and concentrations of most essential nutrients and aluminum were determined. Foliar concentrations of these elements varied among the different stands. Highest concentrations of N, P, Ca, S, Fe, and Al were found in trees of the youngest stand. Concentrations of N, P, S, and Fe were negatively correlated with stand age. The strongest correlation was obtained with P (r=–0.96,P<0.01), followed by N (r=–0.85,P=0.03). Results suggest that declining growth and deterioration of red alder stands with age may be related, at least in part, to limiting supplies of essential nutrients, especially P, N, and S.