Exotic Tree Species Research Articles

Aspects of Habitat Use by Birds during Spring in Natural Forests and Non-Native Plantation Forests in the Lower Siret Meadow (Eastern Romania)

Abstract The Lower Siret Meadow forest habitats have been altered from natural structure because of commercial forestry operations, activities that are defining the forest management from previous decades. Afforestation programs aimed to test the introduction of exotic tree species in order to increase wood production and to reduce harvest time intervals. These commercial influences reflect in the decrease of natural forest areas, aspect that could influence the birds presence. Studies on the ecological impact of plantations on birds are scarce, and no studies were found regarding this aspect in the region. Using six different sample areas both in native and non-native tree plantations, we investigated how bird presence is influenced by the support capacity offered by both natural or non-native plantations and which vegetation variables are related to our results. We compared the data from the surveyed areas to relate birds presence and dependence on certain characteristics of the habitats. Our results pointed out that species diversity is higher in natural forests with local tree species and vegetation characteristics like forest canopy density, shrub coverage, and herbaceous layer.

Black walnut as a valuable stand-forming tree species in Hungary – a growing technology review

In Hungary black walnut (Juglans nigra L.) is one of the most valuable exotic tree species, mainly because of its excessively liked wood for furniture industry, that has fine tissue and singular colour. Generally it is established by seeding, it can be regenerated by coopice shoot well, but not by seeding in natural way. Black walnut crops regurarly from the age of 25–30 years and its rotation age is 75–85 years. Prosperous decorative shape of stem allows its using in tree plantings out of forests, too. In the future its role can increase mainly on good.

Damage assessment to subtropical forests following the 2008 Chinese ice storm

Abstract: Ice storm is a major form of extreme climatic event and may occur more frequently in the future under a changing climate. The 2008 Chinese ice storm provided a natural laboratory to study ecosystem responses and feedbacks to climate variability and extreme events. Four typical subtropical forests (Chinese fir plantation, pine plantation, moso bamboo plantation, and secondary mixed broadleaved forest) were selected to assess the damage caused by the ice storm. The ice damage rate of typical subtropical forests varied between 25% and 81%. The secondary broadleaved forest had most extensive damage while the Chinese fir plantation experienced the most severe damage. Exotic pine species (Pinus elliottii Engelm. and Pinus taeda Linn.) were more severely damaged than the native species, Pinus massoniana Lamb. Ice damage was also affected by tree/culm size, age, stand density, site altitude, and management practices. Large-sized trees/culms were more vulnerable to stem breakage, decapitation, and uprooting, while small-sized trees/culms were more vulnerable to bending and leaning. Younger trees/culms had the highest damage rate, and were more susceptible to bending damage. Ice damage rate increased linearly with the stand density, and higher altitude led to a significant increase of stem breakage. Oleoresin tapping aggravated the damage to pine trees. Resistance of trees to ice damage is an emergent consequence of tree attributes, species origin, site conditions, and human disturbance. Forest silviculture and management practices can play significant roles in controlling forest susceptibility to extreme events. Inappropriate utilization of non-timber forest products can reduce trees’ resistance to extreme events. For sustainable forest development, balance needs to be achieved between the high productivity of introduced exotic tree species and the resistance of native species to extreme climatic events.

Key plant indicators for monitoring areas undergoing restoration: A case study at the Das Velhas River, southeast Brazil

In restoration ecology, the search for key variables which allows an informative and concise diagnosis on areas undergoing restoration is still a challenge. Choosing which indicators to use is a fundamental decision when proposing monitoring of any restored area. Here, we have aimed to contribute with the selection of key indicators by identifying plant parameters that are useful to assess restored areas in using a 5-year-old rehabilitated riparian forest as a case study. Initially, we used 14 descriptors to assess the ecosystem attributes of structure, diversity and ecological processes, and then we conducted a model selection to identify variables that best explained the restoration success (defined as the richness of native tree species). Our final model contained six parameters: native tree species (the response variable), native and exotic species of other life forms, basal area, tree density, and canopy openness) and an adjusted R2 of 92%. As the predictive model doesn’t contain variables related to ecological processes, we included seedling recruitment or litterfall production to evaluate this attribute. The selected indicators evidenced that the tree layer has yet to develop and accumulate biomass, the forest has been enriched by species of other life forms (although many of them were exotic and invasive), and exotic tree and shrub species were dominating seedling recruitment. Such a scenario is likely to occur because the forest is located in an anthropogenic region, and highlights the importance of conserving remnant areas as propagule sources. We suggest some managing actions for the area, and conclude that not all measured indicators were necessary to facilitate good vision about the studied forest (because many had collinear responses), which may be important for directing other monitoring projects and save time and money.

Changes in community perspectives on the roles and rules of church forests in northern Ethiopia: evidence from a panel survey of four Ethiopian Orthodox communities

Some of the only Afromontane forest in northern Ethiopia today is on lands managed by followers of the Ethiopian Orthodox Church, where for centuries priests and communities have conserved forest groves around church buildings. The ecological value of the thousands of church forests in Ethiopia has been widely acknowledged, but little is known about the diverse local institutions that govern these resources, or how such institutions might be changing in response to Ethiopia’s rapid recent economic development. This study uses a unique panel survey to explore changes in community perspectives on the social and ecological roles of church forests, and rules governing church forest use, in four Orthodox communities over time. Our sample consists of 122 household surveys conducted in 2002 and a further 122 surveys from 2014, with 71 households interviewed in both periods. We find that reported uses of church forests vary across forests and over time, with larger forests more likely to be used for extractive purposes such as firewood and construction timber, while smaller forests have become more restricted to renewable or non-extractive uses such as natural medicines, honey, and prayer. Results of logistic regression suggest church followers’ support for preserving church forests increases with age and access to alternative sources of firewood – including exotic Eucalyptus spp. plantations which are increasingly widespread in northern Ethiopia. We also observe a shift since 2002 away from an expectation that church followers themselves hold responsibility for rule enforcement in church forests to a perceived sharing of responsibility by church authorities (i.e. priests) and government (i.e. police) in 2014. Together the progressive introduction of exotic tree species in church forests combined with the erosion of religious norms surrounding local forest governance may threaten the integrity and diversity of these unique social-ecological systems.

Birds girdling activity on exotic tree species as a form of adaptive behavior?

Four tree species in the Kostelec n. C. l. arboretum (Czech Republic) have been repeatedly damaged by Dendrocopos medius. The unique aspect of this otherwise common behavior called girdling consists in regularly visiting the same trees every spring, although there are more than 1.200 tree species within the arboretum. We monitored transpiration, leaf phenology and the chemical composition of the xylem sap of girdled and nongirdled trees. Spectral analysis revealed slightly higher amounts of sugars, especially saccharose, in Cladrastis Raf. as the most regularly girdled tree among other conditions, comparing girdled to non-girdled trees. Higher transpiration rates were not confirmed in connection with girdling—quite the opposite—Cladrastis Raf. as the most highly favored tree for girdling showed the lowest transpiration rates (in average 6 kg water per day within spring months) compared to other non-girdled trees. We presume that the birds do not choose a particular tree on the basis of any visible or chemical traits but they examine many trees within their territory. Afterwards they probably remember the position of trees whose xylem sap starts to flow early in the spring compared to other trees, as their transpiration stream is enriched with sweet organic substances that represent an advantage for the forthcoming nesting period.

Allelopathic potentials of exotic invasive and native trees over coexisting understory species: the soil as modulator

Ailanthus altissima and Robinia pseudoacacia are two aggressive exotic tree species invading riparian ecosystems in Central Spain. We explored their allelopathic potentials as a possible mechanism explaining their success in these ecosystems. Specifically, we aimed (1) to compare the phytotoxic effects of the exotic and native (Fraxinus angustifolia and Populus alba) trees on the fitness of several understory plants coexisting in riparian ecosystems, and (2) to assess the capacity of the riparian soil to modulate the phytotoxic effects. In laboratory bioassays, aqueous leaf litter extracts from the donor tree species at field-realistic concentrations were tested on different fitness indicators of 13 understory target species, using germination paper and soil as substrates in petri dishes. Using germination paper, we found species-specific effects between donor and target species, but the phytotoxicity of the exotic trees as a group was not greater than that of the natives. Nevertheless, the exotic R. pseudoacacia was the most effective donor species reducing the radicle growth of the target species. Over riparian soil substrate, the aqueous leaf litter extracts did not produce any phytotoxic effect on the target species, except in one case. Altogether, our results highlight the importance of using both a native control when assessing the phytotoxicity of nonnative plants and also the natural soil in the modulation of phytotoxic effects. Ignoring both factors in laboratory bioassays would have led to the overestimation of the phytotoxicity of the exotic species as a mechanism contributing to their invasion success.

Water transport of native and exotic tree species in relation to xylem anatomical characteristics in low subtropical China

Exotic fast-growing tree species have been commonly planted as pioneer species to facilitate ecological restoration in South China. Their growth and resource utilization behavior related to intrinsic physiology and structural properties have profound influences on forest ecosystem. However, the contrastive research focusing on water utilization features along with xylem anatomical properties between native and exotic species is scarce in South China. The objective of this study is to investigate the sapwood anatomical characteristics and water utilization conditions of native and exotic fast-growing species, and to elucidate the relationship between sap-flux density and conduit features. We measured sap-flux density, conduit length, diameter and density of four native species (Schima superba, Michelia macclurei, Castanopsis hystrix and Castanopsis fissa) and four exotic species (Eucalyptus citriodora, Eucalyptus urophylla × grandis, Acacia auriculaeformis and Acacia mangium). Sap flux density was measured based on the Granier’s thermal dissipation probe method. The whole-tree water transport was quantified by multiplying sap-flux density by sapwood area. The measurements of conduit characteristics were conducted by using segregation and slice method. Sapwood area increased with the growing diameter at breast height (DBH) as a power function. Native species had a larger water-conducting tissue area than exotic species at the same DBH value when trees grew to a size with a certain value of DBH. The conduit diameter of exotic species was significantly larger than that of native species. Conversely, native species, such as S. superba and M. macclurei, had longer conduit length and higher conduit density than other tree species. Based on a physiological interpretation of the measured conduit characteristics, native tree species developed a safe water transport system while exotic fast-growing tree species come into being an efficient system instead. Water transport increased with the growing DBH as a power function, and the exponent for native species (1.60) was higher than that for exotic species (1.22). Under the combined impact of sap-flux density and sapwood area, native species presented a larger water transport at a larger DBH value, indicating that growth advantage of exotic fast-growing species might weaken as DBH increased.

Exotic trees contribute to urban forest diversity and ecosystem services in inner-city Cleveland, OH

Vacant land, a product of population and economic decline resulting in abandonment of infrastructure, has increased substantially in shrinking cities around the world. In Cleveland, Ohio, vacant lots are minimally managed, concentrated within low-income neighborhoods, and support a large proportion of the city’s urban forest. We quantified abundance, richness, diversity, and size class of native and exotic tree species on inner-city vacant lots, inner-city residential lots, and suburban residential lots, and used i-Tree Eco to model the quantity and economic value of regulating ecosystem services provided by their respective forest assemblages. Inner-city vacant lots supported three times as many trees, more exotic than native trees, and greater tree diversity than inner-city and suburban residential lots, with the plurality of trees being naturally-regenerated saplings. The urban forest on inner-city vacant lots also had two times as much leaf area and leaf biomass, and more tree canopy cover. The quantity and monetary value of ecosystem services provided by the urban forest was greatest on inner-city vacant lots, with exotic species contributing most of that value, while native taxa provided more monetary value on residential lots. The predominately naturally-regenerated, minimally managed exotic species on vacant land provide valuable ecosystem services to inner-city neighborhoods of Cleveland, OH.

Soil moisture decline due to afforestation across the Loess Plateau, China

The Loess Plateau of China is a region with one of the most severe cases of soil erosion in the world. Since the 1950s, there has been afforestation measure to control soil erosion and improve ecosystem services on the plateau. However, the introduction of exotic tree species (e.g., R. pseudoacacia, P. tabulaeformis and C. korshinskii) and high-density planting has had a negative effect on soil moisture content (SMC) in the region. Any decrease in SMC could worsen soil water shortage in both the top and deep soil layers, further endangering the sustainability of the fragile ecosystem. This study analyzed the variations in SMC following the conversion of croplands into forests in the Loess Plateau. SMC data within the 5-m soil profile were collected at 50 sites in the plateau region via field survey, long-term in-situ observations and documented literature. The study showed that for the 50 sites, the depth-averaged SMC was much lower under forest than under cropland. Based on in-situ measurements of SMC in agricultural plots and C. korshinskii plots in 2004–2014, SMC in the 0–4m soil profile in both plots declined significantly (p<0.01) during the growing season. The rate of decline in SMC in various soil layers under C. korshinskii plots (−0.008 to −0.016cm3cm−3yr−1) was much higher than those under agricultural plots (−0.004 to −0.005 cm3cm−3yr−1). This suggested that planting C. korshinskii intensified soil moisture decline in China’s Loess Plateau. In the first 20–25yr of growth, the depth-averaged SMC gradually decreased with stand age in R. pseudoacacia plantation, but SMC somehow recovered with increasing tree age over the 25-year period. Irrespectively, artificial forests consumed more deep soil moisture than cultivated crops in the study area, inducing soil desiccation and dry soil layer formation. Thus future afforestation should consider those species that use less water and require less thinning for sustainable soil conservation without compromising future water resources demands in the Loess Plateau.

Canopy manipulations of exotic Bitter Willow (Salix elaeagnos) forest for indigenous seedling recruitment: A pilot study

SummaryThe invasive exotic tree species Bitter Willow (Salix elaeagnos; Salicaceae) has colonised areas of rank exotic grassland and has been found to contain indigenous seed, dispersed by frugivorous birds into the monospecific stands. This small pilot study examined whether indigenous seedlings that have germinated in the understorey of exotic Bitter Willow stands could be stimulated to establish through the creation of small‐scale canopy gaps. In Bitter Willow forest, four single Bitter Willow trees were poisoned to create canopy gaps. Light transmission and seedling regeneration of tree and shrub species were assessed beneath both the four manipulated and three comparable intact Bitter Willow canopies. Over 3 years, seedling height and density increased more beneath opened compared to intact Bitter Willow canopies. These results suggest that Bitter Willow can fill the roles of both a facilitative nurse and a perch tree. Larger‐scale canopy manipulation experiments of both Bitter Willow and other Salix species are needed to determine the full potential of canopy manipulations for forest restoration.

INFLUENCE OF ECOLOGICAL GROUP COMPOSITION, PLANTATION SPACING AND ARRANGEMENT IN THE RESTORATION OF RIPARIAN FOREST ON RESERVOIR SHORES

This work aimed to assess the effect of spacing, arrangement and ecological group composition of planted seedlings on the restoration process of artificial reservoir shores in southeastern Brazil. The assessments were performed 12 years after the settlement of the experiment in which five mixed stand models were tested. First, a general evaluation of the stand was performed when we surveyed the overstory and understory, seed bank and soil for chemical analysis. Then, the survival restoration indicators of planted trees, basal area and density of the tree community, litter accumulated on the soil and canopy closure index were utilized to compare the plantation models and to assess the influence the experimental factors on these parameters. In the general analysis, we found that the studied stand presents low diversity, poor regeneration, and seed bank dominated mostly by one planted exotic tree species and weeds, which may jeopardize the self-maintenance of the stand in the future. The factor that most influenced the models was the ecological group composition with the best performance found for models in which both pioneer and non-pioneer groups were used. Probably, the plantation arrangement and spacing do not have greater influence due to both plant mortality and natural regeneration that has developed to this age. Hence, it is not recommended the use of only pioneer species in the implantation of riparian forest and the proportion of 50% pioneers and 50% non-pioneers using as much species as possible is indicated for areas that might present constraints for the natural regeneration.

Tree Species Richness Promotes Invertebrate Herbivory on Congeneric Native and Exotic Tree Saplings in a Young Diversity Experiment.

Tree diversity in forests is an important driver of ecological processes including herbivory. Empirical evidence suggests both negative and positive effects of tree diversity on herbivory, which can be, respectively, attributed to associational resistance or associational susceptibility. Tree diversity experiments allow testing for associational effects, but evidence regarding which pattern predominates is mixed. Furthermore, it is unknown if herbivory on tree species of native vs. exotic origin is influenced by changing tree diversity in a similar way, or if exotic tree species escape natural enemies, resulting in lower damage that is unrelated to tree diversity. To address these questions, we established a young tree diversity experiment in temperate southwestern Germany that uses high planting density (49 trees per plot; plot size 13 m2). The species pool consists of six congeneric species pairs of European and North American origin (12 species in total) planted in monocultures and mixtures (1, 2, 4, 6 species). We assessed leaf damage by leaf-chewing insects on more than 5,000 saplings of six broadleaved tree species. Plot-level tree species richness increased leaf damage, which more than doubled from monocultures to six-species mixtures, strongly supporting associational susceptibility. However, leaf damage among congeneric native and exotic species pairs was similar. There were marked differences in patterns of leaf damage across tree genera, and only the genera likely having a predominately generalist herbivore community showed associational susceptibility, irrespective of the geographical origin of a tree species. In conclusion, an increase in tree species richness in young temperate forests may result in associational susceptibility to feeding by generalist herbivores.

Photosynthetic CO2 uptake and carbon sequestration potential of deciduous and evergreen tree species in an urban environment

Urban tree planting programmes are increasingly promoted as a way to reduce atmospheric carbon dioxide (CO2) mixing ratios. However, few studies have investigated the photosynthetic CO2 uptake potential of different urban tree species across seasons. In particular little is known about photosynthetic CO2 uptake in cities with a subtropical, oceanic climate where evergreen species are dominant. We addressed this shortcoming by measuring net photosynthetic rates of ten native and exotic tree species during different seasons and times of the day in Auckland, New Zealand. We also assessed the potential of leaf nitrogen (N) concentration as a proxy for net photosynthetic capacities of urban trees, which is of particular importance to upscale leaf-level photosynthetic CO2 uptake to local and regional scales. In addition, we compared measured net photosynthetic capacities (light-saturated net photosynthetic rates) with carbon (C) sequestration rates estimated using tree growth measurements and allometric equations. Mean net photosynthetic capacities ranged between 2.37 and 10.48 μmol m−2 s−1 across all seasons and were closely related to tree C sequestration rates, suggesting that increased photosynthesis enhances growth rates and therefore tree C sequestration rates. Given that winter net photosynthetic capacities remained high in evergreen species (3.38–13.96 μmol m−2 s−1), with almost 50% higher mean net photosynthetic capacity compared to summer across all species, we suggest that tree planting programmes for CO2 mitigation should favour long living evergreen tree species with high basal area increments (BAI). Leaf N explained 43% and 57% of the variability of photosynthetic capacities across species in summer and winter, respectively. These results indicate that leaf N may be used as a proxy for net photosynthetic capacities of commonly planted urban trees in Auckland. However, further research is required to provide robust models that may be used to estimate photosynthetic CO2 uptake at a local and urban scale.

Concerning the prospects of quantitative valuing of leaf surface functional activity for different plants

The following paper discusses the problem of ecophysiological indicators evaluation and comparison for trees foliage formed in dynamic environment conditions. In addition to the already used methods of leaf parameters screening we propose to use one more indicator, characterizing foliage functional activity. In these aims, after performing some analytical procedures with leaf mass samples, some calculations must be made allowing to determine the quantity of active components (for instance, photosynthetic pigments, ash, etc.), per unit of leaf surface area. The prospects of proposing parameter use seem to be fruitful for a variety of purposes, including: - analysis of the seasonal dynamics features of the leaf metabolic activity; - comparison of ecophysiological characteristics of various plants (species and varieties, local and introduced objects); - reactions to stress factors, a comparison of various objects in resistance to stress. The article bases on the original data relating to the vegetation period of 2013-2015. The leaf mass samples were taken: for wild tree or shrub species - in the Krasnosamarsky forests, for fruit crops - in the gardens of Samara regional research institute Zhiguliovskye Sady, for exotic tree and shrub species - in the dendrarium of the Botanical Garden of the Samara University. The leaf samples treatment mass procedure was performed according to the algorithm previously developed. In general, all aforementioned objects demonstrated more smooth dynamics of pigments component content per surface area unit than per mass unit. This situation seems to be connected with age-related changes of the leaf blades, saturated during the vegetative period with a certain amount of ballast substances or osmotically active compounds during stress periods, and so forth. The screening of photosynthetic surface unit quality allows us to note that the plants maintain a certain level of the metabolic activity of the leaf during variable weather conditions, producing a rapid adjustment pool of photosynthetic pigments on the basis of specific and varietal characteristics of their ecological plasticity.

Plant diversity and determinant factors across smallholder agricultural management units in Central Ethiopia

Forests in the highlands of Ethiopia have declined considerably, and the supply of forest-based ecosystem services is eroding. Managing agricultural landscapes as well as enhancing plant biodiversity in agro-ecosystems is and will continue to be one possible strategy to preserve biodiversity, ensure an ecosystem service supply and sustain agricultural productivity. This study investigated the current status and prospects of plant diversity and its determinants in an agricultural landscape dominated by smallholder farmers in Southern Ethiopia. Specifically, the study investigated effects of land use, altitudinal gradient, wealth status and household attributes on plant diversity in agricultural landscapes. A complete count, Y-frame transect sampling method and household interviews were used for the study involving 39 households and 115 sample plots. A total of 166 plant species belonging to 134 genera and 56 families were recorded in all land use types. Of these, 101 were woody plant species (51 trees and 50 shrubs), while 65 were cultivated herbs and grasses. Land use, altitude and household wealth status significantly influenced tree and shrub species richness. Among land uses, home gardens hosted the highest number of tree and shrub species. Upper altitudes and rich households also had the highest tree and shrub species richness compared to others. Plant diversity indices (Shannon, Simpson and Margalef) were affected by altitude, wealth status and land use types. Household location, wealth status, the household attributes of landholding and family size had strong and positive influences on the tree species diversity and woody stem density of households, while educational background and off-farm income were negatively related with household-owned tree stem density. Species preference ranking, seedling demand and importance value index computations indicated the dominance of exotic tree species, which may suggest their economic importance over indigenous tree species. In the long term, this might lead to dominance of exotic tree species in the landscapes, which could cause a potential future threat to the remnant indigenous plant diversity that is currently finding refuge in the agricultural landscapes.

Nest success of the Indian House Crow Corvus splendens: an urban invasive bird species in Dar es Salaam, Tanzania

Nest success of the Indian House Crow Corvus splendens was studied in the urban area of Dar es Salaam, Tanzania, in late March to early May 2011. The study investigated nest success of the Indian House Crow in different tree species with varying canopy covers and heights. Fifty-five active nests and 38 inactive nests were observed and inspected from six species of trees. Details of tree species, heights and canopy covers are provided. Apparent repeat clutches were found but there was no evidence of double brooding. Chi-square analysis of the distribution of the observed nests on trees with different characteristics revealed that nest success of the Indian House Crow was not significant with the selected nesting trees of particular species and height. Bonferroni simultaneous confidence intervals revealed that two exotic tree species, mango Mangifera indica and madras thorn Pithecellobium dulce, were the preferred tree species for nesting. The findings of this study showed that despite the selective behaviour of the House Crow, their nest success does not depend on the height, crown cover or type of tree species selected.

Water use strategy of Eucalyptus urophylla ×E. grandis on karst hillslope based on isotope analysis.

Using stable isotope techniques, water sources and water use efficiencies of Eucalyptus urophylla ×E. grandis (exotic tree species) and Liquidambar formosana (native tree species, as a reference) were studied in a typical karst artificial forest, and the risk of drought stress of the plantation was discussed. The results showed that the isotope value of shallow soil water (0-50 cm) had obvious gradient features and was similar to the recent rain, while that of deep water was more stable and different from the shallow soil water. The soil water content in wet season (May and September) was higher than in dry season (October), and was higher in upslope than in downslope segment. The main water source of L. formosana was shallow soil water, which corresponded to high water use efficiency in different seasons. The main water sources for E. urophylla ×E. grandis on the upper slope and downslope segments were both shallow soil water in wet season, however, the sum of average water using the proportion of deep soil water increased for the downslope segment in the end of wet season. In dry season, E. urophylla ×E. grandis on the downslope segment mainly used shallow soil water, while it used deeper soil water on the upslope segment when soil water was relatively low. Meanwhile, the water use efficiency of E. urophylla ×E. grandis was lower compared with L. formosana, which revealed E. urophylla ×E. grandis did not get enough water supply under drought stress. The above results indicated that E. urophylla ×E. grandis would encounter high risk of water stress if extreme drought events happened in karst regions in the coming future.

Effects of vegetation structure on the diversity of breeding bird communities in forest stands of non-native black pine (Pinus nigra A.) and black locust (Robinia pseudoacacia L.) in the Czech Republic

Forest management affects stands’ vegetation structure, which influences bird communities. Since the effects of forest practices are usually more pronounced if the exotic tree species are planted, we surveyed bird communities and mapped the vegetation structure in stands of non-native broad-leaved and coniferous trees, black locust and black pine, in a central European country, the Czech Republic. By means of spatial analysis – generalized least squares models – we investigated whether the positive relationship between bird species richness in various ecological groups and vegetation heterogeneity is weakened by an assumed negative effect of the exotic tree origin. Further, we tested whether the bird community composition is more impacted by tree origin (native and non-native) than forest type (coniferous and broad-leaved) using multivariate direct gradient redundancy analyses. We found that total bird species richness, species richness of habitat specialists, ground foragers and foliage gleaners significantly increased with increasing vegetation heterogeneity after taking tree origin into account. Since there was higher vegetation heterogeneity in non-native tree stands, we suggest that the potential benefits of this higher heterogeneity were suppressed by some other (unmeasured) characteristics (e.g. limited food supply) of these stands, which might also be the reason for lower richness of habitat specialists and canopy foragers. The most important gradient in the bird community composition was from broad-leaved to coniferous stands irrespective of tree origin. The effect of tree origin was expressed as the secondary gradient, albeit still significant. It seems that the birds’ adaptations to different leaf morphology play more important role in structuring bird communities than the influence of tree origin. Our results indicate that the forest management should focus on the increase of the vegetation heterogeneity in native tree stands to maximize total bird species richness, and on avoiding establishment of non-native tree plantations to prevent loss of habitat specialist birds.

Restoration of degraded sites with suitable tree species in the Mid-hills of Nepal

Land degradation is a major challenge in Nepal. A lot of degraded land is available within the Community Forests in the Mid-hills which are being aimed to be utilized for ecological restoration as well as supporting livelihoods of the local people. In this context, the study was conducted in the Chautaradanda Community Forest (27°44’05’’ N and 85o04’60’’ E) of Thakre Village Development Committee of Dhading District in the lower Mid-hills of Central Nepal to test the survival capacity and growth performance of different tree species (native, naturalized as well as exotic) that can be used for the rehabilitation of degraded sites. Firstly, Stylo (Stylosanthes spp.), a leguminous grass, was introduced on a degraded site for enriching nutrients in June 2008. Secondly, six different native, naturalized as well as exotic tree species (Sapindus mukorossi, Prunus cerasoides, Choerospondias axillaris, Melia azedarach, Pinus patula and Robinia pseudoacacia) were planted in a randomized complete block design with 4 blocks (6 species × 4 blocks) in July 2008. The results showed that the growth and survival rate of exotic species, P. patula was outstanding; however, the performance of its native and naturalised counterparts P. cerasoides, C. axillaris and M. azedarach was found to be satisfactory. R. pseudoacacia was not found to be a suitable species for rehabilitating degraded sites in the lower Mid-hills of Nepal. Therefore, it would be wise to select the native or naturalized species for the rehabilitation of degraded sites in the Mid-hills, as sometimes the introduction of exotic species may have pessimistic ecological consequences; however, P. patula can be used as it has not shown any invasive nature since its introduction (around 1980s) in the Mid-hills of Nepal. Hence, the study shows the possibility of introducing the tree species such as P. cerasoides, M. azedarach and C. axillaris for ecological restoration of degraded sites in the Community Forests in the Mid-hills of Nepal.Banko Janakari, Vol. 23, No. 2