The responses of three riparian cottonwood species to water table decline

The influence of rate of water table decline was studied with three North American cottonwood (poplar) species: the prairie cottonwood, Populus deltoides; the narrowleaf cottonwood, P. angustifolia; and the balsam poplar, P. balsamifera. Shoot cuttings were rooted and transplanted into rhizopods, experimental devices that permit the controlled manipulation of water table depth. Three rates of water table decline were applied, 0, 4 and 10 cm day⁻¹, and growth and transpiration were studied.

Two clones of each species performed relatively similarly; the P. balsamifera clones grew fastest under all three treatments, followed by P. deltoides under 0 and 4 cm day⁻¹ conditions. Under the 10 cm day⁻¹ treatment, the P. deltoides grew as slowly as P. angustifolia. In all genotypes, shoot growth and apparent transpiration were progressively reduced with increasing rate of water table decline. Conversely, root growth was promoted by water table decline and root elongation was most rapid under the gradual 4 cm day⁻¹ treatment; root elongation was insufficient for the abrupt 10 cm day⁻¹ decline and some P. angustifolia and P. deltoides saplings died under that treatment.

The present study demonstrates that tolerance to water table decline varies across cottonwood genotypes and that P. balsamifera saplings were the most vigorous. This is relevant to the natural distribution in which P. balsamifera occurs in mountain regions where stream stages and riparian water table depths often change abruptly. The vigor of P. balsamifera is also consistent with the reproductive mechanism of ‘branch propagation', a process of clonal recruitment in which browsed or broken branch fragments root along stream edges, enabling dispersive propagation, particularly of P. balsamifera and P. trichocarpa.     

Water table decline alters growth and survival of Salix gooddingii and Tamarix chinensis seedlings

In the western United States, many native riparian forests are declining downstream from dams and diversions, primarily due to a lack of successful regeneration of native species. Conceptual models have been described that incorporate stream flow characteristics that promote successful regeneration of western riparian Populus seedlings. However, these models need to be calibrated for additional species and specific stream characteristics. In this study, we examined the growth and survival of two dominant Sonoran desert riparian tree species, a native Salix gooddingii, and an exotic, Tamarix chinensis, to simulated water table declines at rates of 0, 1, 2, and 4 cm/day. Salix seedlings performed best in the 0 cm/day treatment in which the soil was saturated and showed decreasing survival and growth with increasing rates of water table decline. Root-to-shoot ratios were high for Salix, but root elongation rates were low with an emphasis on lateral root development. This root growth pattern may be an adaptation to habitat where Salix typically grows, near the stream channel where the water table is shallow but the likelihood of flood scour is high. Lateral root development may help to protect Salix seedlings from late season flood scour. Tamarix seedlings showed consistently high survival across all treatments and had the greatest growth in the 0 and 1 cm/day treatments. Tamarix seedlings had greater root elongation rates in response to water table decline relative to the control, with the greatest elongation in the 1 cm/day treatment. Greater root elongation rates and higher drought tolerance allowed Tamarix seedlings to persist in dry soils where Salix seedlings died. Differences in growth and survival of these two species in response to water table decline will need to be incorporated into management practices to promote successful native riparian tree regeneration.     

An economic and ecological multi-criteria evaluation of reforestation methods to recover burned Pinus nigra forests in NE Spain

Recurrence of recent large wildfires is threatening the permanence of Pinus nigra Arnold (Black pine) forests in central Catalonia (NE Spain), due to the almost nil post-fire regeneration of this non-serotinous pine. Potential practices to carry out extensive reforestation programs with P. nigra may differ widely in terms of their final success, economic cost and undesired ecological impact. In this framework, we have analysed different types of vegetation clearing (mechanical, controlled burning or grazing), soil preparation (ripping or planting holes) and reforestation methods (broadcast seeding, spot seeding and planting) to restore P. nigra forests. We have compared these practices in terms of seedling establishment, but also in the light of their economic costs and ecological impact, through a new multi-criteria analysis. Seedling establishment after sowing was very poor and not influenced by vegetation clearing. In plantations, seedling survival was higher in the ripper treatment than in planting holes for all vegetation clearing treatments except the control one. Nevertheless, the higher economic cost of the planting holes treatment and the negative impact of mechanical clearing and burning on the small mammals community made the stated differences in seedling survival irrelevant. Thus, the multi-criteria analysis revealed that the two most preferred options were planting in uncleared or lightly grazed areas with soil preparation through ripping. This study gives some valuable insights about the use of new decision-support tools in restoration programs and provides practical guidelines concerning the restoration of extensive burned P. nigra forests.     

Impact of bark stripping by sika deer, Cervus nippon, on subalpine coniferous forests in central Japan

We investigated the effect of bark stripping by sika deer, Cervus nippon, on forest regeneration in subalpine coniferous forests on Mt. Ohdaigahara and in the Ohmine Mountains of central Japan. Bark stripping by sika deer occurred in five major tree species: Abies homolepis; Abies Veitchii; Tsuga diversifolia; Picea jezoensis var. hondoensis; and Chamaecyparis obtusa. The percentage of damaged trees on Mt. Ohdaigahara was higher than in the Ohmine Mountains, probably because of the higher deer density. On Mt. Ohdaigahara, the DBH distributions of stems for P. jezoensis var. hondoensis, A. homolepis, T. diversifolia andC. obtusa were bell-shaped with fewer smaller and larger trees. On the other hand, in the Ohmine Mountains the distributions for P. jezoensis var. hondoensis and A. Veitchii showed a reverse-J shaped with more smaller trees. Larger overstory conifers on Mt. Ohdaigahara were killed by bark stripping when 100% barked, although in the Ohmine Mountains ca. 50% of the trees survived even when 100% barked. After the disappearance of the overstory conifers on Mt. Ohdaigahara, the dwarf bamboo, Sasa nipponica, expanded into the forest floor due to changes in light reaching the forest floor. Since S. nipponica is the main forage of deer in this area, this increase caused a corresponding increase in the deer population, which in turn, could cause a further decline in the coniferous forests.     

The regeneration characteristics of Picea jezoensis and Abies sachalinensis on cut stumps in the sub-boreal forests of Hokkaido Tokyo University Forest

The regeneration characteristics of Picea jezoensis Carr. and Abies sachalinensis Masters on cut stumps in natural forest under selection cutting and natural regeneration were studied in a sub-boreal forest of the Hokkaido Tokyo University Forest. The following points were investigated: (1) what decay class of cut stumps are suitable for regeneration of the two conifer species; (2) what part, either a root collar or a cut surface, of a cut stump is suitable for regeneration; and (3) what percentages of cut stumps support conifer seedlings. The percentages of cut stumps that supported conifer seedlings increased as the decay class advanced, but slightly decreased in the latest stage of decay class, V. Both P. jezoensis and A. sachalinensis seedling densities per cut stump and per square meter of cut stumps increased as the decay class advanced. Some root collars in decay class IV supported A. sachalinensis seedlings, but few supported P. jezoensis. Densities of P. jezoensis per cut surface and per square meter of cut surface in decay class IV were higher than those of A. sachalinensis. On the other hand, densities of A. sachalinensis per root collar and per square meter of root collar in decay class IV were higher than those of P. jezoensis. Cut stumps in advanced decay classes are more suitable for regeneration of P. jezoensis and A. sachalinensis than those in early decay classes. Whereas a cut surface is more suitable for regeneration of P. jezoensis, a root collar is more suitable for regeneration of A. sachalinensis. Cut stumps are not sufficient to ensure enough conifer regeneration because not all conifer cut stumps in advanced decay classes support conifer seedlings.     

5种引种地被竹在山东的耐旱与耐寒性分析

以引自江苏扬州大禹观赏竹园的2年生鹅毛竹(Shibataea chinensis)、黄条金刚竹(Sasaella masamuneana f. aureostriata)、菲白竹(Pleioblastus fortunei)、菲黄竹(Pleioblastus viridistriatus)、铺地竹(Pleioblastus argenteostriatus)等5种地被竹为研究材料,研究了干旱和低温胁迫处理对地被竹超氧化物歧化酶(SOD)、过氧化物酶(POD)、可溶性蛋白质等生理指标的影响,并对地被竹的耐旱、耐寒性进行综合评价。结果表明,5种引种地被竹的耐旱性从大到小的排序为鹅毛竹＞黄条金刚竹＞铺地竹＞菲白竹＞菲黄竹,耐寒性从大到小的排序为鹅毛竹﹥黄条金刚竹﹥菲黄竹﹥菲白竹﹥铺地竹。     

紫竹和灰金竹在西藏拉萨的引种栽培试验

紫竹（Phyllostachys nigra）和灰金竹（Ph.nigra var.henonis）是重要的观赏竹种，为丰富西藏的城市绿化树种种类，在拉萨市开展了紫竹和灰金竹引种栽培试验。试验采用3因素（基质、复合肥和生根粉）3水平的正交试验设计，分析不同因素和水平对引种竹种生长的影响。结果表明：引种自云南昆明的紫竹和灰金竹在西藏拉萨栽植2年后，2个竹种的成活率分别达到68.0%和47.0%，发笋率分别为36.8%和35.8%，显示出紫竹在拉萨的适应性要强于灰金竹；在各因素中，复合肥对于紫竹成活率影响最大，而生根粉对灰金竹成活率影响最大。各因素对于2个竹种生长指标影响程度的排序是一致的，即基质>生根粉浓度>复合肥施肥量；3因素最优水平组合均为：以牛粪为基质、复合肥施用量为10 g/丛、用0.02%的生根粉溶液浸泡竹篼。研究结果为紫竹和灰金竹在西藏拉萨市等高寒地区的引种及苗木繁育提供了重要的技术依据。     

Effect of drought on diameter increment of Quercus ilex, Phillyrea latifolia, and Arbutus unedo in a holm oak forest of NE Spain

The present study was carried out to elucidate the drought growth responses of Quercus ilex L., Phillyrea latifolia L., Arbutus unedo L., and other accompanying woody species of the Mediterranean holm oak forest. We submitted holm oak forest stands in Prades mountains (NE Spain) to a 2-year experimental drought. We reduced soil water availability about 15% by plastic strips and funnels that partially excluded rain throughfall and by ditch interception of water runoff. Mean stem diameter increment showed a great variation depending on the species. A. unedo had larger growth rates than Q. ilex and P. latifolia, but it was also the species that experimented the highest growth reduction in the drought plots (77%), suggesting a higher drought sensitivity than Q. ilex (55%) and P. latifolia (no drought effect). The growth reduction was specially marked in the larger trees. Aboveground stand biomass increment, estimated from stem diameter by allometric relationships, was 1.9 Mg ha⁻¹ per year in the control plots. The 15% reduction in the upper soil moisture produced 42% reduction in this biomass increment. In the drier conditions predicted in this Mediterranean area in the frame of climate change, an important reduction of growth rates can be hence expected, accompanied by a gain of dominance of drought-tolerant species such as P. latifolia in detriment of more mesic species such as Q. ilex.     

Growth potential of twelve Acacia species on acid soils in Hawaii

Reforestation of degraded tropical sites is often hampered by soils of high acidity, high aluminum saturation, and low fertility. To evaluate the possibility of cultivating Acacia species on such soils, a study was conducted at Waiawa, HI, to test growth under conditions of (1) high acidity (primarily aluminum) and nutrient stress, and (2) no acidity stress and high nutrient availability. Twelve Acacia species, including the important native Hawaiian species Acacia koa, were established on a Ustic Kanhaplohumult soil. The experimental design was a split plot with two fertility treatments as the main plots and the 12 Acacia species as subplots. The treatments were: low fertility (F₀; 143 kg ha⁻¹ 14-14-14 plus micronutrients) and high fertility (F₁; 8 Mg ha⁻¹ lime, 143 kg ha⁻¹ 14-14-14 plus micronutrients, 200 kg P ha⁻¹, and 77 kg K ha⁻¹). Acacia angustissima, Acacia aulacocarpa, Acacia auriculiformis, Acacia cincinnata, Acacia crassicarpa, Acacia implexa, Acacia koa, and Acacia mangium grew significantly faster under the high fertility treatment. Three species, A. cincinnata, A. crassicarpa, and A. mangium, are recommended for planting on infertile acid soils. The volume of A. koa was increased ten-fold by the high fertility treatment. Additional study on koa's nutritional requirements is suggested in order to identify the nutrients contributing to this increased growth.     

4种观赏地被竹的生长及扩展能力比较

对山东东平县第二苗圃4种3年生地被竹生长进行了调查,并探讨和比较了其扩展能力差异。结果表明：4种观赏地被竹高生长排序为菲白竹 > 黄条金刚竹 > 铺地竹 > 鹅毛竹,地径生长的排序为鹅毛竹 > 铺地竹 > 菲白竹 > 黄条金刚竹,菲白竹与黄条金刚竹的高径比较大,鹅毛竹与铺地竹的高径比相对较小;单位面积株数的排序是菲白竹 > 铺地竹 > 鹅毛竹 > 黄条金刚竹,菲白竹和铺地竹生长较为密集,鹅毛竹和黄条金刚竹相对稀疏;4种地被观赏竹扩展距离从大到小的排序为鹅毛竹 > 黄条金刚竹 > 铺地竹 > 菲白竹;不同竹种之间相遇时竞争能力不同,其排序为鹅毛竹 > 菲白竹 > 黄条金刚竹 > 铺地竹。     

Natural regeneration status of commercial mangrove species (Rhizophora apiculata and Bruguiera gymnorrhiza) in the mangrove forest of Tanjung Bungin, Banyuasin District, South Sumatra

In the mangrove forest areas of Sumatra, Rhizophora apiculata (Bl.) and Bruguiera gymnorrhiza (L.) Lmk., the two most economically important commercial species of mangrove trees, have been intensively exploited for their valuable wood and tannin since the Dutch colonization in the 16th century. The mangrove forest areas of Tanjung Bungin, Banyuasin District, South Sumatra belong to the production forest. Typical Rhizophora-dominated stands were sampled from two inundation classes (Watson, 1928, III and IV) of the virgin mangrove forest of Tanjung Bungin. The sampling method used a 20 × 10-m quadrat for tress. A 5 × 5-m subplot and a 1 × 1-m sublot, for saplings and seedlings respectively, were made in each of the main plots at 10-m intervals. The distribution pattern of R. apiculata and B. gymnorrhiza seedlings studied indicates that regeneration of R. apiculata by seedling establishment is generally sufficient to ensure local propagation in inundation III subplots where Acrostichum aureum is absent. Due to the abundance of A. aureum as a weed in inundation IV zones, the regeneration of both commercial mangrove species is inadequate. This has given rise to considerable concern for their survival. Finally, the presence of regenerating virgin mangrove forest in Tanjung Bungin provides strong argument for this area to be set aside as a conservation area.     

毛金竹在江西地区的生物学特性

毛金竹是江西优良的乡土笋材两用竹种,但长期处于野生状态,资源面临衰退的局面,亟需开展科学经营研究和技术推广。在江西省毛金竹林分内设立固定样地,进行了连续3年的生物学、生态学特性研究。结果表明:毛金竹笋期为4月中下旬至5月上旬、历时30~35d,笋期前25d的出笋数约占总数的75%,笋期高生长具有"慢-快-慢-停"的生长规律,幼竹高生长于6月20日左右完成,且新竹地径决定立竹全高。     

坝竹和小篷竹花果特征及种子营养成分

坝竹和小篷竹均为藤蔓型、灌木状竹种,具有较高的观赏价值。已有文献中对2个竹种花和果实特征的记载不全面,造成了它们在植物分类上存在争议。在2个竹种的原产地于开花结实期细致观察并记录了竹种的花和果实特征,并采集种子测定分析了种子的营养成分。结果表明：1）坝竹和小蓬竹的花、果形态相似,主要区别是坝竹外稃上的脉较小蓬竹多,而果实上紧贴內稃背面宿存的梗长则小于小蓬竹;2）坝竹和小蓬竹种子均含有丰富的蛋白质、多糖、碳水化合物及矿质元素,其中钙、镁、钾、铜、铁、锌、锰等元素含量尤为丰富,可作为食源植物;坝竹种子中的硒含量达到了富硒食品的要求,可作为富硒食品。     

Differentiation of Prosopis juliflora (Sw.) DC. and P. pallida (H. & B. ex. Willd.) H.B.K. using foliar characters and ploidy

Two species of Prosopis, Prosopis juliflora and Prosopis pallida, native to Central America and northern South America, have been widely introduced and are now found throughout the world’s hot arid and semi-arid zones. However, these species are frequently misidentified, especially where introduced, hampering genetic improvement and effective management. Samples from trees previously identified as either P. juliflora or P. pallida were divided into two groups by multivariate analysis using selected foliar characters. One group contained known tetraploids and the other contained known diploids. It was concluded that the tetraploid and diploid groups correspond to P. juliflora and P. pallida, respectively. Triploid individuals were also identified, the first report of these in the genus Prosopis. A dichotomous key was developed to differentiate the species, using number of interfoliar glands per rachis, number of leaflet pairs per pinna and leaflet length. P. juliflora and P. pallida grown from seed collected within their respective native ranges were correctly identified using the key. Where introduced, samples from Burkina Faso, Jordan and India were confirmed as P. juliflora, but those from Brazil, Cape Verde and Senegal were identified as P. pallida, rather than P. juliflora, the species assumed to be naturalized in these countries. The correct identification of these two species will facilitate the genetic improvement and management of P. juliflora and P. pallida. There is a strong case for basing future selection and genetic improvement programs on P. pallida rather than P. juliflora. Further collection and evaluation of P. pallida is therefore required, together with conservation programs in the native range.     

Canopy tree development and undergrowth bamboo dynamics in old-growth Abies–Betula forests in southwestern China: a 12-year study

Interactions between forest canopy characteristics and plants in the forest understory are important determinants of forest community structure and dynamics. In the highlands of southwestern, China the dwarf bamboo Bashania fangiana Yi is an understory dominant beneath a mixed canopy of the evergreen Abies faxoniana (Rheder & Wilson) and the deciduous Betula utilis (D. Don). The goal of this study was to better understand the role of bamboo dominance, canopy characteristics, and periodic bamboo dieback on forest development. To achieve this goal, we measured tree seedling, tree saplings, and trees, forest canopy characteristics, and bamboo cover in permanent forest (n = 4) and gap plots (n = 31) in a mixed A. faxoniana and B. utilis forest in Sichuan, China. Dwarf bamboos died off in 1983 in the gap plots, and in three of the four forest plots. Forest development was assessed for the period 1984–1996. The seedling bank in forest and gap plots increased after bamboo die-off. A. faxoniana seedlings increased more than B. utilis in forest plots; the opposite pattern characterized gap plots. The proportion of seedlings on raised micro-sites on the forest floor also changed and new seedling were more abundant on the forest floor. By 1996, bamboo seedling cover and biomass had recovered to ca. 45% or their pre-flowering values. Rates of bamboo seedling recovery were faster beneath canopy gaps and deciduous trees than beneath forest or evergreen trees. Tree mortality exceeded recruitment in plots with dense bamboo; the opposite pattern was found in the plot with little bamboo. The mortality rate for B. utilis trees (2.4% year⁻¹) was higher than that for A. faxoniana (0.8% year⁻¹) and forests with dense bamboos became more open over the census period. Tree mortality was size-dependent and intermediate sized trees had the lowest rates of mortality. Stand basal area increased mainly due to greater basal area gain than loss for A. faxoniana. Interactions between tree species life history, canopy type, and bamboo life-cycles create heterogeneous conditions that influence tree and bamboo regeneration and contribute to the coexistence of A. faxoniana and B. utilis in old-growth forests in southwestern China.     

Seasonality in rooting of Prosopis chilensis cuttings and in-vitro micropropagation

Seasonality in rooting of cuttings and its relationship with some environmental conditions and growth parameters of Prosopis chilensis (Mol. Stunz) were studied. It was observed that rooting could be induced in cuttings taken from field collections only during the dry season, the period corresponding to the highest vegetative growth and reproductive activity (September to March); however, percentages did not exceed 15%. The rooting response does not occur during the dormant period (May to September). When using cuttings from clonal material growing in the glasshouse, rootings exceeding 80% were obtained in liquid aerated media.

In-vitro micropropagation was assessed in P. chilensis using nodal and apical segments collected both from the field and from clonal material and plantlets grown from seed in the glasshouse. Juvenile material gave an 80% regeneration rate of complete plants in Murashige-Skoog medium fortified with 5 mg naphtaleneacetic acid 1⁻¹ and 10 mg cysteine 1⁻¹. In this same medium, the regenerative response of segments obtained from rooted cuttings was 60%. The material collected from the field showed no rooting responses.     

坝竹和小篷竹景观效果及实生苗培育

实地调查了黔北坝竹和黔南小蓬竹天然林景观效果，并进行了引种及实生苗培育试验。结果表明：2个竹种在喀斯特石山地沿岩壁下垂如帘，形态飘逸，颇为美观。坝竹实生苗人工培育1年时，每株苗分蘖11个左右，苗高50 cm左右，培育15个月时苗高74 cm左右；小蓬竹实生苗人工培育1年时，每株苗分蘖7个左右，苗高72 cm左右，培育15个月时苗高77 cm左右。研究结果可为坝竹和小篷竹的边坡绿化及盆栽观赏提供参考。     

High diversity of ectomycorrhizal fungi associated with Arctostaphylos uva-ursi in subalpine and alpine zones: Potential inoculum for afforestation

Arctostaphylos uva-ursi plant associations have long been suggested to be a suitable location for afforestations, but systematic studies on the observed beneficial effect are still missing in Alpine areas. In this study we address the question which ectomycorrhizal (ECM) fungal communities exist in Austrian alpine and subalpine Arctostaphylos habitats, and if they persist in A. uva-ursi stands even hundred of years after disappearance of trees in these areas. The diversity of fungal communities associated with A. uva-ursi was assessed in four study sites (1800–2450 m a.s.l.) in the Central European Alps of Tyrol (Austria). Three approaches were applied: (i) collecting and identifying fungal fruit bodies; (ii) studying the arbutoid mycorrhiza morphotypes of A. uva-ursi; (iii) molecular identification of the most common arbutoid morphotypes. The detected diversity of ECM fungal species was very high (99 taxa), and the occurrence of e.g. Boletus, Cantharellus, Suillus, Tricholoma, Russula spp. in sites that have been treeless for centuries is especially remarkable. Fruit bodies of 82 fungal species were found in association with A. uva-ursi, 63 of them were ECM. Seventy arbutoid morphotypes were detected on 2072 mycorrhized root tips, and 39 taxa of basidiomycete mycobionts were identified with molecular methods. Twelve Cortinarius spp. clearly dominated the mycobiont species richness, followed by nine spp. of Thelephoraceae and four spp. of Boletaceae. Most mycobionts of A. uva-ursi were generalists, but fungal taxa (e.g. Lactarius deterrimus and Suillus spp.) known to be specifically associated with other host plants were also detected. We therefore consider A. uva-ursi as a “non-selective” host, providing mycorrhizal inoculum of highly specialized and effective mycorrhizal fungi for afforestation. This explains why A. uva-ursi plant associations represent suitable locations for forest regeneration and afforestation, especially in the harsh environmental conditions of subalpine and alpine sites.     

Relationships between soil and foliar nutrients in young densely planted mini-plots of Pinus radiata and Cupressus lusitanica

The long-term nature of forest crop rotations makes it difficult to determine impacts of forestry on soil nutrients that might be depleted by forest growth. We used small scale, highly stocked plots to compress the length of the rotation and rapidly induce nutrient depletion. In the study, two species (Pinus radiata D. Don and Cupressus lusitanica Miller) are compared under two disturbance regimes (soil undisturbed and compacted), and two fertiliser treatments (nil and plus fertiliser), applied in factorial combination at 33 sites, covering the range of climatic and edaphic variation found in plantation forests across New Zealand. To assess our ability to rapidly highlight important soil properties, foliar nutrient concentrations were determined 20 months after planting. It was hypothesised that the densely planted plots, even at a young age, would create sufficient pressure on nutrient resources to allow development of relationships between properties used as indicies of soil nutrient availability and foliar nutrient concentrations. For both species significant relationships between foliar nutrients and 0–10 cm layer soil properties from unfertilised plots were evident for N (total and mineralisable N) and P (total, acid extractable, organic, Bray-2 and Olsen P). With the exception of Ca in C. lusitanica, foliar K, Ca and Mg were correlated with their respective soil exchangeable cation measures. The results thus confirm the utility of the experimental approach and the relevance of the measured soil properties for forest productivity.

In unfertilised plots foliar N and P concentrations in P. radiata exceeded those in C. lusitanica, the differences being eliminated by fertiliser application. Foliar N/P ratios in P. radiata also exceeded those in C. lusitanica. In contrast to N and P, foliar K, Ca and Mg concentrations were all higher in C. lusitanica, the difference being particularly marked for Ca and Mg. P. radiata contained substantially higher concentrations of the metals Zn, Mn and Al than C. lusitanica, whereas the latter contained higher B concentrations. Possible reasons for differences between species in foliar nutrient concentrations are discussed.     

Regeneration of Polylepis australis Bitt. in the mountains of central Argentina

Polylepis australis woodlands range from northern to central Argentina. They support a high number of endemisms (both plants and animals) and constitute the main cover type in watersheds contributing to retain soil and catch water. Natural regeneration of P. australis in the Córdoba mountains, Argentina, was studied in two communities dominated by P. australis: shrublands and woodlands. The main objectives of the study were: (1) to characterize shrublands and woodlands in terms of physical (physical and chemical soil properties) and biological (Polylepis’ growth form, fern and moss cover) characteristics; (2) to describe P. australis’ soil seed bank and compare seedling and sapling establishment between both communities. The presence of seedlings as well as saplings was quantified, and soil samples were taken so as to characterize the seed bank.

Results showed significant differences in habitat conditions between shrublands and woodlands. Seedlings’ density was higher in the shrublands, while no differences appeared regarding the sapling numbers. A negative correlation was found between seedling numbers and total community cover as well as mosses and ferns cover. Seed density in the soil bank was higher in the woodlands, but overall seed viability was less than 5%. In the shrublands, the most critical stage of the species regeneration cycle was the transition from seedling to sapling, while in the woodlands the main “filter” occurred during seed germination. The low number of saplings observed in both units suggests a stagnation of P. australis regeneration, which could be translated into an unlikely expansion of the species throughout the Córdoba mountains.