Responses of decomposition of green leaves and leaf litter to stand density,N and P additions in <Emphasis Type="Italic">Acacia auriculaeformis</Emphasis> stands

The effects of nitrogen (N), phosphorus (P) and N?+?P additions on the decomposition of green leaves and leaf litter were studied over 2 years using the litterbag technique in Acacia auriculaeformis stands with different densities in southern China. The green leaves and leaf litter were treated with four fertility treatments: control, N addition, P addition and N?+?P addition to test the effect of stand density and fertility on the decomposition of green leaves and leaf litter. The mean percentage of mass remaining (PMR) of green leaves and leaf litter significantly decreased with increasing density. Nitrogen and N?+?P additions had a negative effect on PMR, whereas the addition of P had a positive effect. The rapid decomposition of green leaves was associated with a higher N and P content and a lower N/P ratio, indicating a likely P limitation for A. auriculaeformis stands. Our results imply that stand density associated with canopy openness can impact litter decomposition, and P is an important control factor on litter decomposition in A. auriculaeformis stands.     

Litterfall,decomposition and nutrient release of <Emphasis Type="Italic">Shorea robusta</Emphasis> and <Emphasis Type="Italic">Tectona grandis</Emphasis> in a sub-tropical forest of West Bengal,Eastern India

We studied leaf litter fall, decomposition and nutrient release patterns of Shorea robusta and Tectona grandis by using a litter bag technique to better understand the release pattern of nutrients to soil from leaf litter. Annual litterfall varied from 13.40 ± 2.56 t ha^?1 a^?1 for S. robusta to 11.03 ± 3.72 t ha^?1 a^?1 for T. grandis and the decay constant (k) of decomposed leaf litter was distinctly higher for T. grandis (2.70 ± 0.50 a^?1) compared to S. robusta (2.41 ± 0.30 a^?1). Biomass loss was positively correlated with the initial litter C, WSC, C/N and ash content in S. robusta and N, P and K concentration for T. grandis. Biomass was negatively correlated with lignin and L/N ratio for S. robusta and L, WSC, L/N and C/N ratio for T. grandis (P < 0.01). Nutrient use efficiency (NUE) and nutrient accumulation index (NAI) of S. robusta was higher than for T. grandis. The retranslocation of bioelements from senescent leaves ranked as P > N > K. Annual N, P and K input to soil through litterfall differed significantly between the two species in the following order: N>K>P. S. robusta was superior in terms of K and P return and T. grandis was superior in terms of N return. The two tree species showed a similar patterns of nutrient release (K > P > N) during decomposition of their leaf litter. Nutrients of N, K and P were the primary limiting nutrients returned to soil through litterfall with important roles in soil fertility and forest productivity.     

Impacts of mixed litter decomposition from <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> and other tree species on C loss and nutrient release in the Loess Plateau of China

The productivity of Robinia pseudoacacia (R.p.) pure forest usually declines at the late growth stage, and reforming it into mixed forests could be a promising way to resolve this problem. When choosing a suitable tree species that can be mixed with R.p., the interspecific relationship is an important issue. Therefore, we gathered the autumn litter fall from R.p. and 10 other species from the Loess Plateau of China were mixed in dual species litterbags (R.p. + each other species) and buried them in soil for a 345 days lab decay incubation. We measured the litter mass loss and nutrient contents to determine whether the nutrient release was affected by mixed species litter decomposition. The impacts of mixed litter decomposition on macro-elements release were more obvious than on micro-elements. The litters with similar substrate quality might show variable impacts on nutrients release in mixed decomposition. The C loss and release of nutrient was improved by descending order when R.p. litter was mixed with Hippophae rhamnoides, Ulmus pumila, Populus simonii, Larix principis-rupprechtii and Quercus liaotungensis (Q.l.). But, except for Q.l., only the other species were recommended as suitable mix-plants for R.p. since promoting a high turnover of the nutrient in the litter compartment and a rapid availability for tree.     

紫金山两种主要林型有机物层中丝状真菌多样性

本文对紫金山两种主要林型,栓皮栎林(Quercus variabilis)和马尾松-枫香(Pinus massoniana-Liguidam barformasana)混交林的有机物层(L, F, H层及土壤淋溶A层)可培养丝状真菌多样性进行了研究。通过分离鉴定,共得到真菌67种,其中接合菌3种、子囊菌5种、半知菌类56种和未确定种3种,半知菌类最为丰富。两种林型分解真菌优势种群为链格孢(Alternaria sp.)、曲霉(Aspergillus spp.)、枝孢(Cladosporium sp.)、毛霉(Mucor sp.)、青霉(Penicillium sp.)、木霉(Trichoderma spp.)、根霉(Rhizopus sp.)、粘帚霉(Gliocladium sp.)。混交林型中真菌的种类和数量明显高于栓皮栎林。两个林型均以F层真菌种类最多,但F层之间和L层之间真菌多样性差异较大。在混交林型中从马尾松针叶上分离的真菌种类和数量比从枫香上分离得到的少; 从马尾松针叶上分离的真菌丰富度随着有机物层深度增加而增加,枫香则反之。比较两个林型以及混交林的两种落叶上真菌种类发现,随着有机物层深度的增加,真菌的种类差异性却随之减少,即同时出现在两个林型或两种针叶上的真菌种类增多。真菌种类随着分解过程的进行具有明显的演替现象。混交林型中同一层内不同落叶上分解真菌多样性的差异,表明凋落物基质的差异是决定真菌种类和数量的重要因素     

Geometric morphometric analyses of leaf shapes in two sympatric Chinese oaks: <Emphasis Type="Italic">Quercus dentata</Emphasis> Thunberg <Emphasis Type="Italic">and Quercus aliena</Emphasis> Blume (Fagaceae)

Key message

Geometric morphometric analyses (GMMs) of the leaf shape can distinguish two congeneric oak species Quercus dentata Thunberg and Quercus aliena Blume in sympatric areas.

Contexts

High genetic and morphological variation in different Quercus species hinder efforts to distinguish them. In China, Q. dentata and Q. aliena are generally sympatrically distributed in warm temperate forests, and share some leaf morphological characteristics.

Aims

The aim of this study was to use the morphometric methods to discriminate these sympatric Chinese oaks preliminarily identified from molecular markers.

Methods

Three hundred sixty-seven trees of seven sympatric Q. dentata and Q. aliena populations were genetically assigned to one of the two species or hybrids using Bayesian clustering analysis based on nSSR. This grouping served as a priori classification of the trees. Shapes of 1835 leaves from the 367 trees were analyzed in terms of 13 characters (landmarks) by GMMs. Correlations between environmental and leaf morphology parameters were studied using linear regression analyses.

Results

The two species were efficiently discriminated by the leaf morphology analyses (96.9 and 95.9% of sampled Q. aliena trees and Q. dentata trees were correctly identified), while putative hybrids between the two species were found to be morphologically intermediate. Moreover, we demonstrated that the leaf morphological variations of Q. aliena, Q. dentata, and their putative hybrids are correlated with environmental factors, possibly because the variation of leaf morphology is part of the response to different habitats and environmental disturbances.

Conclusion

GMMs were able to correctly classify individuals from the two species preliminary identified as Q. dentata or Q. aliena by nSSR. The high degree of classification accuracy provided by this approach may be exploited to discriminate other problematic species and highlight its utility in plant ecology and evolution studies.

     

Trees enhance soil carbon sequestration and nutrient cycling in a silvopastoral system in south-western Nicaragua

Tree occurrence in silvopastoral systems of Central America has been under pressure for various reasons including attempts to improve grassland productivity and the need for wood. However, scattered isolated trees are also recognized to provide ecosystem services like shade, fodder and fruits that are important to cattle in the dry season. In addition, trees may enhance the climate change mitigation potential of silvopastoral systems through increased carbon (C) uptake and subsequent soil carbon sequestration. Through differences in plant traits like nutrient uptake, canopy structure and litter quality, tree species may have an effect on C and nutrient cycling. Due to a prevailing north-easterly wind in the study area, three distinct areas associated with the impact of tree litter deposition were identified: (1) open pasture—no tree litter deposition; (2) tree canopy—above and belowground tree litter; and (3) leaf litter cone—aboveground tree litter deposition. Furthermore, the effect of tree species, Guazuma ulmifolia and Crescentia alata, were considered. The presence of trees, as compared to pasture, caused larger topsoil C, N and P contents. In the subsoil, C content was also larger due to tree presence. Soil fractionation showed that tree-induced larger litter input subsequently increased free and occluded OM fractions and ultimately increased stabilized SOM fractions. Therefore, trees were found to enhance soil C sequestration in these silvopastoral systems. This is also supported by the soil respiration data. Although the respiration rates in the pasture subplots were lower than in the leaf litter subplots, the difference was not significant, which suggests that part of the extra C input to the leaf litter subplots stayed in the soil. Nutrient cycling was also enhanced by tree presence, but with a clear differentiation between species. C. alata (Jícaro) enhanced available and stabilized forms of organic N, while G. ulmifolia (Guácimo) enhanced available soil P and stabilized organic P.     

Communities of saprobic fungi on leaf litter of <Emphasis Type="Italic">Vismia guianensis</Emphasis> in remnants of the Brazilian Atlantic Forest

We examined the mycobiota associated with Vismia guianensis leaf litter in three Atlantic Forest remnants of Brazil’s semiarid region. Among the study sites, two remnants were protected forest reserves, whereas the third was influenced by major anthropogenic activities. Eighteen litter samples were collected in wet and dry seasons and were processed by particle filtration technique. A total of 4750 fungal isolates of 142 taxa were identified. Species richness was higher in litter samples collected during wet season. Nonmetric multidimensional scaling multivariate analysis showed differences in the composition of fungal communities among the sampling sites and the seasons. Analysis of similarity showed that the differences were statistically significant (R = 0.85; P = 0.0001). Our findings revealed that spatial and temporal heterogeneity, and human activities had significant impacts on the saprobic fungi of V. guianensis leaf litter.     

Periodicity of different phenophases in selected trees from Himalayan Terai of India

The temporal phenology of leaf bud bursting, leaf initiation, leaf maturation, leaf fall, flower initiation, fruit initiation and fruit fall was recorded for eight tree species (Ficus hispida, F. squamosa, Mallotus nudiflorus, M. philippensis, Shorea robusta, Schleichera oleosa, Pongamia pinnata and Terminalia arjuna) in the tropical moist deciduous forest of Himalayan Terai region from November 2009 to October 2012. The study revealed that a short low temperature dry period, sufficient winter rain and temperature rise are the triggering factors for summer leaf flushing and, the increased soil water availability for second leaf flushing in rains. Initiation of flowering with leaf emergence in the dry period supports higher rate of fruit setting due to maximum availability and activities of pollinators. The dispersal and post dispersal success of fruits increased by their ripening before and/or in the rainy season. In T. arjuna, no correlation has been found between the fruiting and rains. M. nudiflorus and M. philippensis initiate leaves and flowers with the first significant increase in temperature and photoperiod and are thus suggested as the potential tree species for climate change studies in tropics.     

Soil N mineralization profiles of co-existing woody vegetation islands at the alpine tree line

Tree lines form a transition ecotone from forest to tundra both at high elevation and high latitude and occur in a number of different forms. Nitrogen (N) deficiency is considered to be a factor involved in tree line formation, and also N dynamics are considered to differ between the trees and the ericaceous vegetation of the tundra. In the Austrian Alps at the tree line, N availability and N mineralization in soils of different vegetation types (Picea abies, Pinus mugo and Rhododendron ferrugineum) as well as total phenols were determined. Soil from under P. abies was taken from two different tree line forms, an island type and a diffuse type, as well as from P. abies growing at a lower elevation. N mineralization was measured in situ using a covered PVC tube incubation method and in a laboratory incubation under controlled conditions. Ion exchange resin capsules were installed at the interface of humus and mineral soil for estimating N in the soil solution. Net N mineralization showed a similar pattern for the vegetation types for both the in situ and laboratory incubation. The soil humus layer had the highest levels of N mineralization compared to the other soil layers. N mineralization rates were similar in P. abies and P. mugo at the tree line regardless of tree line form. Rates of N mineralization were lower under R. ferrugineum than the tree species, but this lower rate was not related to the occurrence of high levels of total phenols in the soil. Nitrogen deficiency was not evident in the island-type tree line, but was evident in the diffuse tree line type.     

Effects of litter quality and climate change along an elevational gradient on litter decomposition of subalpine forests,Eastern Tibetan Plateau,China

Temperature and freeze-thaw events are two key factors controlling litter decomposition in cold biomes.Predicted global warming and changes in freeze-thaw cycles therefore may directly or indirectly impact litter decomposition in those ecosystems. Here, we conducted a2-year-long litter decomposition experiment along an elevational gradient from 3000 to 3600 m to determine the potential effects of litter quality, climate warming and freeze-thaw on the mass losses of three litter types [dragon spruce(Picea asperata Mast.), red birch(Betula albosinensis Burk.), and minjiang fir(Abies faxoniana Rehd. et Wild)]. Marked differences in mass loss were observed among the litter types and sampling dates. Decay constant(k) values of red birch were significantly higher than those of the needle litters. However, mass losses between elevations did not differ significantly for any litter type.During the winter, lost mass contributed 18.3–28.8 % of the net loss rates of the first year. Statistical analysis showed that the relationships between mass loss and litter chemistry or their ratios varied with decomposition periods. Our results indicated that short-term field incubations could overestimate the k value of litter decomposition.Considerable mass was lost from subalpine forest litters during the wintertime. Potential future warming may not affect the litter decomposition in the subalpine forest ecosystems of eastern Tibetan Plateau.     

Assaying the allelopathic effects of <Emphasis Type="Italic">Eucalyptus camaldulensis</Emphasis> in a nursery bed incorporated with leaf litter

Allelopathic effects of Eucalyptus camaldulensis Dehnh. were confirmed in Petri dish and pot experiments in our previous studies. However, the degree to which such effects under controlled experiments exist in more complex ecological settings remains to be tested. Thus, the present study was carried out by incorporating different proportions of ground litter of E. camaldulensis in soil. The growth of three agricultural crops: falen (Vigna unguiculata (L.) Walp.), chickpea (Cicer arietinum L.), and arhor (Cajanus cajan (L.) Millsp.), and two tree species, kala koroi (Albizia procera (Roxb.) Benth.) and ipil ipil (Leucaena leucocephala (Lam.) de Wit) were tested. There were inhibitory effects of leaf litter on germination, shoot and root growth, leaf number, and collar diameter as well as a reduction of nodulation by legume crops (25–80% reduction). The extent of the effects was dependent on the proportion of leaf litter, the species and the type of traits. In contrast to shoot growth, the effect on root growth was more severe. No effect on germination was found with the agriculture crops while the two tree species showed reduced germination. The effect was greater in the presence of higher proportions of leaf litter mixed in soil while in some cases lower proportions stimulated growth. Not all species were suppressed; A. procera, C. cajan, V. unguiculata showed compatible growth while C. arietinum and L. leucocephala were found incompatible. This study provides evidence that E. camaldulensis has allelopathic potential under field conditions and a careful selection of associated crops in agroforestry systems is highly recommended.     

Conversion of conifer plantations to native hardwoods: influences of overstory and fertilization on artificial regeneration

Forest tree species in the eastern US such as American chestnut (Castanea dentata (Marsh.) Borkh) and oaks (Quercus spp.) have been negatively impacted by forest changes over the past century. Many mature, introduced pine (Pinus spp.) plantations exist in the Midwest US following establishment 50–60 years ago yet have little economic and ecological value. As oak and chestnut have similar site preferences to pines, these stands may be ideal sites for hardwood restoration plantings. We sought to determine optimal management strategies for converting pine plantations by manipulating their canopies. We underplanted hybrid American chestnut and northern red oak (Quercus rubra L.) seedlings into three canopy treatments (control, shelterwood, clearcut) and included an open field treatment. For each of two growing seasons, 0, 30, or 60 g 19N–6P–12K of controlled-release fertilizer (CRF) were also applied to seedlings. Soil chemical parameters and leaf nutrients were analyzed throughout the study. Chestnut and oak seedlings had significantly greater height after two growing seasons in the clearcut and shelterwood than the control and open field, and chestnut had significantly greater diameter as well. Chestnut height and RCD growth were threefold that of oak after two growing seasons. In general, fertilization increased seedling growth more in the clearcut and open field than shelterwood and control for both species. Soils had significantly higher pH, K, and S in the open field than in pine stands. Results suggest that pine plantations may serve as target sites for restoration of these hardwood species. Shelterwoods and clearcuts are both favorable conversion options for oak and chestnut, and addition of CRF may augment further growth increase, especially in open environments.     

Quantification of organic carbon and primary nutrients in litter and soil in a foothill forest plantation of eastern Himalaya

The present study was an effort to understand the amount of litter fall and its subsequent decomposition and quantify the release of available nutrients and soil physicochemical characteristics in plantations of four forest tree species(Lagerstroemia parviflora, Tectona grandis, Shorea robusta and Michelia champaca) in the Chilapatta Reserve Forest of the Cooch Behar Wildlife Division in the Terai zone of West Bengal, India. The most litter(5.61 Mg ha~(-1))was produced by T. grandis plantation and the least(4.72 Mg ha~(-1)) by L. parviflora. The material turnover rate to the soil through decomposition from total litter was fastest during the first quarter of the year and subsequently decreased during the next two quarters. The material turnover rate was only 1 year, which indicates that more than90% of the total litter produced decomposed within a year.The available primary nutrient content in litter varied across the four plantations over the year. The plantations generally did not significantly influence the soil physical characteristics but did significantly influence the availability of primary nutrients and organic carbon at two depths(1–15 and16–30 cm) over the year. The availability of soil primary nutrients in the four plantations also increased gradually from the first quarter of the year to the third quarter and then decreased during the last quarter to the same level as in the first quarter of the year at both depths. The availability for soil organic carbon in the plantations followed a similar trend. The amount of litter produced and the material turnover in the soil in the different plantations differed, influencing the nutrient availability and organic carbon at the plantations. The amount of soil organic carbon was highest for T. grandis(2.52 Mg ha~(-1)) and lowest for L. parviflora(2.12 Mg ha~(-1)). Litter is the source of soil organic matter,and more the litter that is produced by the plantations, the higher will be the content and amount of soil organic carbon in the plantation.     

Ozone fumigation of Quercus ilex L. slows down leaf litter decomposition with no detectable change in leaf composition

Context

The evaluation of changes in litter decomposition rate due to increasing trend in tropospheric ozone is an emerging field of investigation, providing relevant information on long-term forest ecosystem sustainability.

Aims

This research aims to clarify the effects of ozone exposure on Quercus ilex leaf chemical composition and decomposition slow down.

Methods

Young plants were fumigated in growth chambers at a cumulative dose of 17.15 ppm h. To assess the fumigation effectiveness, stomatal conductance and net photosynthesis were monitored. Leaves were analysed for C, N, S, Ca, Mg, K, Fe, Zn, Mn, total soluble sugars, starch, acid-detergent fibre (ADF), lignin and cellulose prior to the incubation in litter bags in mesocosms, and during decomposition along 395 days.

Results

Ozone-exposed leaves showed a significant reduction in net photosynthesis and stomatal conductance but did not differ from control leaves in all the chemical parameters analysed. Nevertheless, leaf decomposition rate was lower in treated leaves. The main differences between the models describing the mass loss in exposed and control leaves were played by ADF for exposed leaves and by lignin for control leaves, as well as by N, that showed a greater contribution in the model for the exposed leaves.

Conclusion

Ozone fumigation of Q. ilex results in leaf litter decomposition slowing down, mainly due to ADF joint dynamics with the other variables describing mass decay, even if no detectable changes in initial leaf composition occur.     

Nutrients leaching from green leaves of three potential agroforestry tree species

Nutrient (NH₄, PO₄ and K) leaching from oven dried green leaves of Emblica officinalis Gaerten, Sesbania grandiflora (L.) Pers. and Moringa oleifera Lam.were investigated in laboratory condition. Oven-dried green leaves were immersed in demineralized distilled water for 8 days. Electrical conductivity (EC), Total dissolved solids (TDS) and nutrients (NH₄, PO₄ and K) of leaching water samples were measured at 0.25, 0.5, 1, 2, 3, 4, 6, 8, 12, 24, 48, 72, 96, 144, and 192 h of intervals. All these species showed an increasing trend for EC and TDS in leachate and comparatively higher EC and TDS were observed in E. officinalis, which is followed, by S. grandiflora and M. oleifera. Significantly high amount (P < 0.05) of NH₄ was leached from S. grandiflora and PO₄ from M. oleifera. But, both S. grandiflora and M. oleifera leached significantly higher (P < 0.05) K than E. officinalis. Within the first 0.25 h, 100 % and 82 % of NH₄ and 68 % and 74 % of K were leached from leaves of S. grandiflora and M. oleifera respectively. S. grandiflora and M. oleifera leached 100 % of PO₄ within 6 h. The concentrtions of NH₄, PO₄ and K in the leachate from E. officinalis, S. grandiflora and M. oleifera were not significantly different (P > 0.05). The green leaves of S. grandiflora and M.oleifera can be a potential source of NH₄, PO₄ and K for a quick nutrient supplement to the agricultural crops in agroforestry practices.     

Carbon storage in biomass,litter, and soil of different native and introduced fast-growing tree plantations in the South Caspian Sea

Replantation of degraded forest using rapidgrowth trees can play a significant role in global carbon budget by storing large quantities of carbon in live biomass,forest floor,and soil organic matter.We assessed the potential of 20-year old stands of three rapid-growth tree species,including Alnus subcordata,Populus deltoides and Taxodium distichum,for carbon(C) storage at ecosystem level.In September 2013,48 replicate plots(16 m × 16 m) in 8 stands of three plantations were established.36 trees were felled down and fresh biomass of different components was weighed in the field.Biomass equations were fitted using data based on the 36 felled trees.The biomass of understory vegetation and litter were measured by harvesting all the components.The C fraction of understory,litter,and soil were measured.The ecosystem C storage was as follows: A.subcordata(626.5 Mg ha~(-1)) [ P.deltoides(542.9Mg ha~(-1)) [ T.distichum(486.8 Mg ha~(-1))(P \ 0.001),of which78.1–87.4% was in the soil.P.deltoides plantation reached the highest tree biomass(206.6 Mg ha~(-1)),followed by A.subcordata(134.5 Mg ha~(-1)) and T.distichum(123.3 Mg ha~(-1)).The highest soil C was stored in theplantation of A.subcordata(555.5 Mg ha~(-1)).The C storage and sequestration of the plantations after 20 years were considerable(25–30 Mg ha~(-1) year~(-1)) and broadleaves species had higher potential.Native species had a higher soil C storage while the potential of introduced species for live biomass production was higher.     

小陇山不同经营措施下次生锐齿栎天然林物种多样性研究

采用固定样地和样方法调查了小陇山林区百花林场3个实施不同经营措施的锐齿栎天然林林分特征和物种组成,运用4种常用的物种多样性指数对调查林分的乔木层、灌木层和草本层的物种多样性进行对比分析,结果表明:3种类型锐齿天然林的灌木层相对于其乔木层和草本物种组成丰富,多样性高;长期封育后的锐齿栎天然林群落在3种天然林类型中物种组成最丰富,乔木层、灌木层和草本层的Shannon-Wiener指数、Pielou指数和Margalef指数值在3个林分中最高;近自然技术单株经营后的锐齿栎天然林各层次的物种组成相对较少,多样性较低,但其林分中保留的乔木树种个体较大;结构优化抚育后的锐齿栎天然林的物种组成和多样性介于二者之间.抚育经营措施对林分的影响与抚育经营强度密切相关,适当的抚育经营强度能够促进林分多样性提高,否则会带来不利的影响,结构化森林经营技术是一种有效的经营方法.     

Young conifer stands form a deer browsing refuge for an oak admixture: silvicultural implications for forest regeneration under herbivore pressure

There is little knowledge how ungulate pressure on forest regeneration may be mitigated by silvicultural methods. The knowledge is especially needed for artificially regenerated, deciduous tree species. We studied factors affecting browsing incidence by deer in the Pisz Forest District in Poland, an area where 10,000 ha of forest was damaged by a 2002 hurricane. In 2006, we established three experimental plots (in total, 22.6 ha), in which the main species was Scots pine (Pinus sylvestris) admixed with pedunculate oak (Quercus robur). The data on browsing were collected in 2008–2015. In general, oak browsing incidence was unrelated to oak planting density. On a plantation scale, it was significantly affected by the pine age. Although in each variant all the oaks were browsed for four consecutive years (2009–2012), in 2013 browsing incidence began to decrease. When the pines grew higher and formed a physical barrier, it was harder for deer—roe deer (Capreolus capreolus), red deer (Cervus elaphus) and moose (Alces alces)—to move through and locate the oaks. Moreover, within plantations, oak browsing incidence was higher in the patches with shorter pines. Browsing of individual saplings or small groups of saplings was also negatively affected by the height of neighbouring pine saplings. Oak density influenced deer selectivity depending on the tree height. In a low oak tree density, browsing incidence was unrelated to oak height, while in higher tree density, deer selected oaks of the height between 40 and 100 cm. We postulate that deciduous admixture in a coniferous (unattractive) stand can be planted with a few year delay. Older coniferous trees should impede locating of attractive tree species by deer and the browsing incidence.     

Decomposition of Mongolian pine litter in the presence of understory species in semi-arid northeast China

The effects of understory plant litter on dominant tree litter decomposition are not well documented especially in semi-arid forests. In this study, we used a microcosm experiment to examine the effects of two understory species (Artemisia scoparia and Setaria viridis) litter on the mass loss and N release of Mongolian pine (Pinus sylvestris var. mongolica) litter in Keerqin Sandy Lands, northeast China, and identified the influencing mechanism from the chemical quality of decomposing litter. Four litter combinations were set up: one monoculture of Mongolian pine and three mixtures of Mongolian pine and one or two understory species in equal mass proportions of each species. Total C, total N, lignin, cellulose and polyphenol concentrations, and mass loss of pine litter were analyzed at days 84 and 182 of incubation. The chemistry of pine litter not only changed with the stages of decomposition, but was also strongly influenced by the presence of understory species during decomposition. Both understory species promoted mass loss of pine litter at 84 days, while only the simultaneous presence of two understory species promoted mass loss of pine litter at 182 days. Mass loss of pine litter was negatively correlated with initial ratios of C/N, lignin/N and polyphenol/N of litter combinations during the entire incubation period; at 182 days it was negatively correlated with polyphenol concentration and ratios of C/N and polyphenol/N of litter combinations at 84 days of incubation. Nitrogen release of pine litter was promoted in the presence of understory species. Nitrogen release at 84 days was negatively correlated with initial N concentration; at 182 days it was negatively correlated with initial polyphenol concentration of litter combinations and positively correlated with lignin concentration of litter combinations at 84 days of incubation. Our results suggest that the presence of understory species causes substantial changes in chemical components of pine litter that can exert strong influences on subsequent decomposition of pine litter.     

Influence of tree shelters on seedling success in an afforested riparian zone

The restoration of a natural riparian ecosystem is a key component to improving water quality and restoring stream health in a disturbed watershed. The rate and degree of riparian restoration, and hence stream restoration, depends in part upon afforestation practices. Successful afforestation is determined largely by the rates of survivorship and growth of the tree species planted or recruited in a riparian zone. This study was part of a project involving the restoration of a channelized section of Wilson Creek located in the Bernheim Arboretum and Research Forest, Nelson County, Kentucky. Riparian restoration activities focused on reestablishing a native riparian corridor using American sycamore (Platanus occidentalis), green ash (Fraxinus pennsylvanica var. subintegerrima), and pin oak (Quercus palustris). This study evaluated techniques for improving the growth and survivorship of planted seedlings along Wilson Creek. Specifically, two tree shelter types (Tubex^® vs. continental mesh), with or without herbicide treatments, were compared. Additionally, the influence of these techniques on debris retention within the riparian zone was also examined. Results showed that use of tree shelters significantly increased the growth of seedlings (but not survivorship), provided physical protection especially during heavy flooding events, and accelerated woody debris retention. Both Tubex^® and continental mesh tree shelters were effective in enhancing seedling growth, with Tubex^® shelters yielding significantly better growth when combined with herbicide to control competing vegetation. Thus, the most cost effective choice may depend on the environmental setting and ability to combine the shelters with other growth enhancing treatments.