Small Groups Of Trees Research Articles

Assessment of regulatory ecosystem services of green plants in urban ecosystems

The article presents the results of research on the assessment of ecosystem services of green tree stands on the territory of the first academic campus of the National University of Kyiv-Mohyla Academy using the MyTree tool. It is a part of the i-Tree tool set developed by the Forest Service of the United States Department of Agriculture (USDA) of the comprehensive program, designed to assess the ecosystem services provided by individual trees or small groups of trees. Research has established that the most important regulatory services were carbon dioxide absorption, microclimate regulation, energy saving, air purification from ozone and sulfur dioxide. Calculations by the MyTree tool show the annual cost of tree planting services on campus and its projected cumulative growth after 20 years. According to the calculations of the MyTree tool, this year’s cost of tree plantation services of the first academic campus of the National University of Kyiv-Mohyla Academy was $847.29, and according to forecasts, after 20 years it will cumulatively increase to $18,895.36. Estimates of the cost of individual components of regulatory ecosystem services are provided. The cumulative estimate over the next 20 years for CO2 sequestration was $4,129.15, which includes the sequestration of 21,963.55 kg of carbon. Air purification for 20 years is estimated at $1,342.66, which includes absorption and neutralization of 656.24 kg of O3, 117.47 kg of SO2, 54.45 kg of NO2, and 34.26 kg of solid dust particles PM2.5. Energy savings are estimated at $10,791.14, which includes energy savings of 100,448.21 kW. The tree species Aesculus hippocastanum (Bitter chestnut), Picea abies (European spruce), Picea pungens (Blue spruce), Betula pendula (Hanging birch) and Ulmus laevis (Smooth elm) provide the highest value of services. The results of this study can be used in the future to improve the planning and management of green areas of the university campus, taking into account the value of their ecosystem services.In general, the study confirmed the importance of monitoring and evaluating the ecosystem services of green spaces in urban ecosystems for making sustainable decisions regarding the development of urban areas, supporting the well-being and health of the population.

Recent Advance on Chemistry and Bioactivities of Secondary Metabolites from Viburnum Plants: An Update.

Viburnum species are a group of small trees or shrubs that are of great ornamental and medicinal values. Some of them have been used for a long time both as conventional and ethnic medicine. Viburnum fruits, eaten in fresh and processed forms, have been revealed to contain various health-promoting nutrients. With the increasing research on Viburnum plants, they are considered to be an abundant resource of bioactive natural products possessing diverse pharmacological properties and unique chemical structures, that is powerfully proved by the existence of structurally novel vibsane-type diterpenoids which only occur in Viburnum species, newly discovered lignan constituents with unusual side chains and other noteworthy natural components. This review describes 185 new and 228 known secondary metabolites from Viburnum genus between 2008 and 2020, including their chemical structures, sources and bioactivities, and highlights the corresponding structure-activity relationships.

Genetic diversity and spatial structure of the imperiled European population of Malus trilobata in Greece

Malus trilobata, is a rare tree species occurring in several small and disjunct populations in the eastern part of the Mediterranean basin. The main European population is found in the region of Evros (NE Greece) and is divided in five distinct subpopulations following the species geographical pattern. The genetic diversity of approximately the entire population (69 trees) was analyzed using nuclear microsatellite and random genomic markers. Polymorphism was discovered in 29 out of 45 genomic marker loci (64.44%), while for nuclear microsatellite markers, all three loci were polymorphic with an average of 3.75 alleles per locus. Our results unraveled a specific grouping pattern for both markers. Both genetic markers exhibited relatively low genetic diversity which is in accordance with the prevalent perception that species with fragmented distributions tend to have low genetic diversity, while the differentiation among individuals, revealed a patchy pattern among small groups of trees separated by roads, firebreaks or distance. These results indicate a high genetic fragmentation level for the main European population of M. trilobata, while the presence of roads, firebreaks, conifer plantations and agricultural land, seem to function as potential barriers to gene flow. Consequently, and since it is well-documented that bees hesitate to change foraging patches, as long as their food is abundant, the observed genetic differentiation patterns could be partially attributed to the foraging and flight behavior of bees, which are the main pollinators of the species. The low levels of available genetic diversity combined with the small overall population and repeated events of forest fires inside the M. trilobata distribution, perils the survival of the species and imposes the necessity for a thoroughly organized conservation strategy.

CRATAEGUS GENUS: PRESERVED PLANTS

Crataegus Genus is a complex group of small trees with more than 1000 species being native to northern temperate zones. The Herbarium hosts 200 plates that contain 30 Crataegus Genus species. Most plates belong to C. monogyna, C. pentagyna and C. oxyacantha. The majority of Crataegus species were gathered between the years 1934 and 1943. A large number of plates are signed by Al. Beldie, S. Pașcovski, Al. Borza, C.C.Georgescu and were gathered from Texas, Pensylvania (USA), and from Romania (Bucharest, Argeș). The herbarium offers a unique perspective for the Crataegus genus species in regard to their locationtemporal dynamic.

Bark beetle infestation spots as biodiversity hotspots: Canopy gaps resulting from insect outbreaks enhance the species richness, diversity and abundance of birds breeding in coniferous forests

Natural disturbances are a major source of spatial stand heterogeneity, initiating forest community turnover. Besides large-scale events like fires, landslides or windthrows, small-scale canopy gaps resulting from the mortality of a single tree or a group of trees represent a distinct structure within a stand. Although the role of canopy gaps is well recognized in tropical ecosystems, the effect of small-scale openings on species richness, diversity and abundance has not been satisfactorily addressed in temperate forests. A specific example of a canopy gap is the bark beetle infestation spot, that is, a small group of trees that have died as a result of insect activity. We studied the effect of canopy gaps on the breeding bird assemblage in old-growth coniferous forests in the Tatra Mts. and Gorce Mts. (Carpathians, S Poland). Our hypothesis was that the gaps and the nearby closed-canopy forest would differ in species richness, diversity and relative abundance. We censused the breeding bird assemblages in 50 such gaps (median size 0.85 ha, quartile range 0.30–2.34 ha, range 0.03–10.0 ha) and 50 nearby closed-canopy reference plots using point counts. Almost 25% more bird species were recorded in the gaps than in the closed-canopy forest, and species richness correlated positively with the number of snags. The number of individual birds recorded in the gaps was 40% higher than in the closed-canopy forest and correlated positively with the number of fallen logs. Gap size was not correlated with the richness, diversity or relative abundance of species. Our results show that canopy gaps resulting from bark beetle outbreaks increase species richness, diversity and abundance by providing suitable habitats for cavity-nesting, ground-nesting and insectivorous birds. We suggest that by increasing habitat heterogeneity and enhancing food resources, even relatively small-scale canopy gaps improve the overall biodiversity of coniferous forests.

THE COMPLEX OF ARTHROPOD-PESTS OF THE GENUS SORBUS L. PLANTS

The article represents research findings as for the species composition identification of the arthropod-pests of the genus Sorbus. The study was conducted in the period from April to October during several years in greenery on the territory of Kyiv and the Kyiv region. Four groups of pests were distinguished: pests of root system (6 species), pests of leaves (18 species), pests of fruits (2 species), pests of sprouts (4 species). Twenty-nine species of arthropods of the hexapods (Insecta) which belong to the 6 numbers of plant groups and 1 species of acariform mites (Acariformes, Arachnida) were found and identified. The most numerous species were arthropod pests, the representatives of the order Coleoptera – 10 species – and Lepidoptera – 8 species. The greatest damage caused by pests at different stages of their biological development was inflicted on the leaf cover of rowan – 60%, and its root system – 20%. Significant damage to rowan plants was caused by pests – polyphagous: Gryllotalpa gryllotalpa L., Psylla mali Schm., Aphis pomi De Green, Rhopalosiphum insertum Wal., Edwardsiana rosae L., Lepidosaphes ulmi L., Operophtera brumata L., Мelolontha melolontha L., Selatosomus aeneus L., Scolytus mali Bech., Phyllobius argentatus L., Agrotis segetum Den.et Schiff., Yponomeuta melinellus L., Simaethis pariana L., Argyresthia conjugella Zell., Pentatrichopus sp. The thorough analysis of damage to various parts of plants was carried out. In most instances, the greatest damage by pests to plants was observed on densely clustered plantations of rowan compared to single and small groups of trees and the presence of plants of the family Rosaceae as an additional forage base. The physiological condition of plants was significantly worsened by the adverse impacts of critical environmental factors. The damage to rowan by pests had a clear mosaic character and depended on various biotic and abiotic environmental factors.

Phenotypic plasticity of two invasive alien plant species inside a deciduous forest in a strict nature reserve in Italy

ABSTRACTInvasive alien plant species (IAPs) represent one of the main biological threats to biodiversity worldwide. Information about their phenotypic plasticity are needed to increase awareness about their future invasive potential. A study about phenotypic plasticity in response to contrasting light regimes and its quantification by a plasticity index (PI) of two IAPs (Ailanthus altissima and Robinia pseudoacacia) inside a Strict Nature Reserve was conducted. R. pseudoacacia showed a 70% higher PI, with a strongly greater value at morphological leaf level, associated with a greater ability to survive and grow in forest understory, explaining its greater widespread. Otherwise, A. altissima showed its highest PI at physiological level, which was associated with the ability to colonize and grow in environments with high-light regimes. Based on these results, the conservative management has limited the presence of A. altissima by its lower ability to grow in forest understory. In fact, the small-scale gaps in the forest infrastructure, that could allow its recruitment, are originated only from the death of a single tree or small group of trees. Regarding R. pseudoacacia, it is critical to maintain this type of management because any disturbances resulting in large openings could further promote its presence inside the Reserve.

Determining the extent and drivers of attrition losses from wind using long-term datasets and machine learning techniques

Abstract In addition to causing large-scale catastrophic damage to forests, wind can also cause damage to individual trees or small groups of trees. Over time, the cumulative effect of this wind-induced attrition can result in a significant reduction in yield in managed forests. Better understanding of the extent of these losses and the factors associated with them can aid better forest management. Information on wind damage attrition is often captured in long-term growth monitoring plots but analysing these large datasets to identify factors associated with the damage can be problematic. Machine learning techniques offer the potential to overcome some of the challenges with analysing these datasets. In this study, we applied two commonly-available machine learning algorithms (Random Forests and Gradient Boosting Trees) to a large, long-term dataset of tree growth for radiata pine (Pinus radiata D. Don) in New Zealand containing more than 157 000 observations. Both algorithms identified stand density and height-to-diameter ratio as being the two most important variables associated with the proportion of basal area lost to wind. The algorithms differed in their ease of parameterization and processing time as well as their overall ability to predict wind damage loss. The Random Forest model was able to predict ~43 per cent of the variation in the proportion of basal area lost to wind damage in the training dataset (a random sample of 80 per cent of the original data) and 45 per cent of the validation dataset (the remaining 20 per cent of the data). Conversely, the Gradient Boosting Tree model was able to predict more than 99 per cent of the variation in wind damage loss in the training dataset, but only ~49 per cent of the variation in the validation dataset, which highlights the potential for overfitting models to specific datasets. When applying these techniques to long-term datasets, it is also important to be aware of potential issues with the underlying data such as missing observations resulting from plots being abandoned without measurement when damage levels have been very high.

Microhabitat Selection of the Virginia Northern Flying Squirrel (Glaucomys sabrinus fuscusMiller) in the Central Appalachians

Glaucomys sabrinus fuscus (Virginia Northern Flying Squirrel; VNFS) is a rare Sciurid that occurrs in the Allegheny Mountains of eastern West Virginia and northwest Virginia. Previous work on this subspecies has confirmed close associations with Picea rubens (Red Spruce) at the landscape and stand levels in the region. However, ongoing Red Spruce restoration actions using canopy-gap creation to release single or small groups of trees requires a better understanding of within-stand habitat selection of VNFS to assess potential short- and medium-term impacts. To address these questions, we conducted a microhabitat study using radio-collared squirrels in montane conifer and mixed conifer—hardwood stands. We used points obtained from telemetry surveys and randomly generated points within each squirrel's home range to compare microhabitat variables for 13 individuals. We found that VNFS preferentially selected plots with conifer-dominant overstories and deep organic-soil horizons. VNFS avoided plots with dense Red Spruce regeneration in the understory in stands with hardwood-dominated overstories—the types of areas targeted for Red Spruce restoration. We also opportunistically searched for hypogeal fungi at telemetry points and found 3 species of Elaphomyces during our surveys. Our results indicate that microhabitat selection is associated with Red Spruce-dominant forests. Efforts to restore Red Spruce where hardwoods dominate in the central Appalachians may improve the connectivity and extent of habitat of VNFS.

Beetle community response to residual forest patch size in managed boreal forest landscapes: Feeding habits matter

Forest fragmentation by management activities has been implicated in the decline of forest biodiversity. Even though boreal ecosystems are generally deemed quite resilient to disturbance effects, high contemporary levels of disturbance might push forest-interior species toward decline or extinction. In this study, we examined beetle communities in forest patches of different sizes, including clearcuts, residual postharvest patches from 0.03 to 50ha in size, and large mature forest tracts (>1000ha). Overall, community structure follows a gradient between clearcuts and large mature forest tracts, even if patch size effects were more difficult to detect among patches >2.5ha. Beetles were most abundant in clearcuts, and species richness was highest in small tree groups (0.03–0.05ha). The effects of fragmentation were strongly conditioned by beetle feeding habits. Predators and xylophagous beetles were mostly associated with clearcuts or smaller patches (i.e., small tree groups or large tree groups [0.3–0.5ha]), whereas fungivorous beetles were associated with forest-interior habitats. Although many forest-interior species were still present in relatively small patches 1–5years after harvesting, negative effects of habitat fragmentation on these species might increase in the long-term.

3D Tree Dimensionality Assessment Using Photogrammetry and Small Unmanned Aerial Vehicles.

Detailed, precise, three-dimensional (3D) representations of individual trees are a prerequisite for an accurate assessment of tree competition, growth, and morphological plasticity. Until recently, our ability to measure the dimensionality, spatial arrangement, shape of trees, and shape of tree components with precision has been constrained by technological and logistical limitations and cost. Traditional methods of forest biometrics provide only partial measurements and are labor intensive. Active remote technologies such as LiDAR operated from airborne platforms provide only partial crown reconstructions. The use of terrestrial LiDAR is laborious, has portability limitations and high cost. In this work we capitalized on recent improvements in the capabilities and availability of small unmanned aerial vehicles (UAVs), light and inexpensive cameras, and developed an affordable method for obtaining precise and comprehensive 3D models of trees and small groups of trees. The method employs slow-moving UAVs that acquire images along predefined trajectories near and around targeted trees, and computer vision-based approaches that process the images to obtain detailed tree reconstructions. After we confirmed the potential of the methodology via simulation we evaluated several UAV platforms, strategies for image acquisition, and image processing algorithms. We present an original, step-by-step workflow which utilizes open source programs and original software. We anticipate that future development and applications of our method will improve our understanding of forest self-organization emerging from the competition among trees, and will lead to a refined generation of individual-tree-based forest models.

Selection cutting in a yellow birch–conifer stand, in Quebec, Canada: Comparing the single-tree and two hybrid methods using different sizes of canopy opening

We experimented three selection cutting patterns using different sizes of canopy opening, including single-tree (SIN, <100m2 in area), hybrid single-tree and small groups of trees (HGR, 100–300m2), hybrid single-tree and one larger gap (HGA, 700m2), and an uncut control (CON) to regenerate tree species with a range of shade tolerance in a yellow birch (Betula alleghaniensis Britt.)–conifer stand, in Quebec, Canada. In this paper, we are presenting the 10-year effects on regeneration dynamics, seedbed coverage and light availability. During the six summers of monitoring, incoming solar radiation increased with canopy opening at a rate of 1.5, 3.9, 4.9 and 8.9MJ/m2/day in microsites distinctive of the CON, SIN, HGR and HGA, respectively. Yellow birch established well in the three cutting patterns (including the matrix and openings), which contained 5–6 times more seedlings >5cm in height than the control (2400/ha) after 10years (all p<0.001). Raspberry (Rubus idaeus L.) coverage was also higher in the three cuts (9–15% at year 10) than in the CON (<1%, p⩽0.001). Pin cherry (Prunus pensylvanica L. f.) rapidly emerged independently from the cutting pattern (6000–7000stems/ha, year 2), but had almost disappeared by year 10 (100–300stems/ha). The 100–300m2 groups and 700m2 gap were favourable niches for yellow birch development. The gap, where light blade scarification was carried out in areas without conifer advance growth, was by far the worst niche for both red spruce and balsam fir (Abies balsamea [L.] Mill.). Therefore, the hybrid method that removed small groups of trees revealed the best option to maintain yellow birch and conifer species in the study site.

Inventory of Green Spaces and Woody Plants in the Urban Landscape in Ariogala

Background and purpose: Regulation of urban greenery design, management and protection was approved in 2008 in Lithuania after the Green Space Law was passed, allowing protection of public green spaces and woody plants. Protection of these resources first requires an inventory, and we have created a digital database that will help in management of urban green spaces. Materials and methods: An inventory of green spaces and woody plants was conducted in the public urban territory of Ariogala, using GIS technology. A digital cartographic database was created using ArcGis 9.1 software. Results and conclusions: Most of the woody plants in the survey area are deciduous trees, and the survey reenvironmental condition of the green spaces and to ensure that the size of the green spaces conforms to valid standards [1]. The inventory of green spaces in Lithuanian towns using GIS technology was launched in 2005. An upgraded methodology of forest inventory, which is more appropriate for individual trees, small tree groups and alleys, was used for inventory of green spaces in towns. This article analyses the results of the green space inventory of the town of Ariogala. MATERIALS AND METHODS

Mapping trees outside forests using high-resolution aerial imagery: a comparison of pixel- and object-based classification approaches

Discrete trees and small groups of trees in nonforest settings are considered an essential resource around the world and are collectively referred to as trees outside forests (ToF). ToF provide important functions across the landscape, such as protecting soil and water resources, providing wildlife habitat, and improving farmstead energy efficiency and aesthetics. Despite the significance of ToF, forest and other natural resource inventory programs and geospatial land cover datasets that are available at a national scale do not include comprehensive information regarding ToF in the United States. Additional ground-based data collection and acquisition of specialized imagery to inventory these resources are expensive alternatives. As a potential solution, we identified two remote sensing-based approaches that use free high-resolution aerial imagery from the National Agriculture Imagery Program (NAIP) to map all tree cover in an agriculturally dominant landscape. We compared the results obtained using an unsupervised per-pixel classifier (independent component analysis-[ICA]) and an object-based image analysis (OBIA) procedure in Steele County, Minnesota, USA. Three types of accuracy assessments were used to evaluate how each method performed in terms of: (1) producing a county-level estimate of total tree-covered area, (2) correctly locating tree cover on the ground, and (3) how tree cover patch metrics computed from the classified outputs compared to those delineated by a human photo interpreter. Both approaches were found to be viable for mapping tree cover over a broad spatial extent and could serve to supplement ground-based inventory data. The ICA approach produced an estimate of total tree cover more similar to the photo-interpreted result, but the output from the OBIA method was more realistic in terms of describing the actual observed spatial pattern of tree cover.

Even-Aged and Uneven-Aged Forest Management in Boreal Fennoscandia: A Review

Since WWII, forest management in Fennoscandia has primarily been based on even-aged stand management, clear cut harvesting and thinning from below. As an alternative, uneven-aged management, based on selection cutting of individual trees or small groups of trees, has been proposed. In this review we discuss the theoretical aspects of ecology and economics of the two management approaches. We also review peer-reviewed studies from boreal Fennoscandia, which have aimed at comparing the outcomes of uneven-aged and the conventional even-aged forest management. According to a common view the main obstacle of practicing uneven-aged forestry is its low economic performance. However, the reviewed studies did not offer any straightforward support for this view and several studies have found uneven-aged management to be fully competitive with existing even-aged management. Studies on the ecological aspects indicated that selection cuttings maintain mature or late-successional forest characteristics and species assemblages better than even-aged management, at least at the stand scale and in the short term. We conclude that although the number of relevant studies has increased in recent years, the ecological and economic performance of alternative management methods still remains poorly examined, especially for those stands with multiple tree species and also at wider spatial and temporal scales. For future research we advocate a strategy that fully takes into consideration the interdisciplinary nature of forest management and is better connected to social goals and latest theoretical and methodological developments in ecology and economics.

Permian vegetational Pompeii from Inner Mongolia and its implications for landscape paleoecology and paleobiogeography of Cathaysia

Plant communities of the geologic past can be reconstructed with high fidelity only if they were preserved in place in an instant in time. Here we report such a flora from an early Permian (ca. 298 Ma) ash-fall tuff in Inner Mongolia, a time interval and area where such information is filling a large gap of knowledge. About 1,000 m(2) of forest growing on peat could be reconstructed based on the actual location of individual plants. Tree ferns formed a lower canopy and either Cordaites, a coniferophyte, or Sigillaria, a lycopsid, were present as taller trees. Noeggerathiales, an enigmatic and extinct spore-bearing plant group of small trees, is represented by three species that have been found as nearly complete specimens and are presented in reconstructions in their plant community. Landscape heterogenity is apparent, including one site where Noeggerathiales are dominant. This peat-forming flora is also taxonomically distinct from those growing on clastic soils in the same area and during the same time interval. This Permian flora demonstrates both similarities and differences to floras of the same age in Europe and North America and confirms the distinct character of the Cathaysian floral realm. Therefore, this flora will serve as a baseline for the study of other fossil floras in East Asia and the early Permian globally that will be needed for a better understanding of paleoclimate evolution through time.

Cost-effective strategies to conserve boreal forest biodiversity and long-term landscape-level maintenance of habitats

Setting aside parcels of land is the main conservation strategy to reduce the rate of biodiversity loss worldwide. Because funding for biological conservation is limited, it is important to distinguish the most efficient ways to use it. Here, we assess implications of alternative measures to conserve biodiversity in managed boreal forest landscapes. We calculated four alternative spatio-temporal scenarios and compared these to the current management regime over 100-year time period. In the alternative scenarios, a fixed amount of funding was invested in (1) permanent large reserves (each tens of ha in size), (2) permanent small reserves (each a few ha in size), (3) temporary small reserves (based on 10-year contracts with private land owners), and (4) green-tree retention (small groups of trees retained on clear-cuts). To assess biodiversity implications, we used habitat suitability indices to calculate overall habitat availability for five groups of red-listed and habitat-specific species associated with decaying spruce logs. The possibilities for timber harvests did not differ among the scenarios, but biodiversity performance was different. The scenarios with permanent reserves tended to outperform other scenarios, suggesting that conservation policies based on permanent reserves are the most cost-efficient in the long term. Results, however, varied among time scales and species groups. In the short term, a strategy of investment in temporary small reserves was the most efficient. Habitat for species associated with old spruce dead-wood and preferring shade was rare throughout all simulations, and therefore, it is likely that these species cannot be sustained in managed forests. Species that live on fresh dead-wood and are associated with forest edges coped well in all scenarios suggesting that such species will persist in managed landscapes without additional conservation efforts. Explicit definition of conservation objectives and time frames for conservation action are thus prerequisites for successful conservation planning.

Changes in soil fauna 10 years after forest harvestings: Comparison between clear felling and green-tree retention methods

We studied the responses of soil decomposer animals to clear felling and alternative, green-tree retention harvesting methods (GRT) in Norway spruce forests in Finland. The study plots which were sampled for immediate treatment effects (up to three years) were resampled after 10 years. We hypothesized that responses of decomposers still depends on the level of GTR. The treatments, in addition to untreated controls (100% retained), were: (1) selection felling (70% dispersed tree retention), (2) and (3) gap felling with and without site preparation, respectively (three small gaps were felled in a 1-ha area and 50% of the stand volume was retained), (4) retention felling (10% of the stand volume was retained in three small tree groups) and (5) traditional clear felling (0% retention). Ten years after the treatments the strong increase of enchytraeids immediately after the harvestings was leveled out and the numbers on all treated plots were at the control level. Total numbers or community structure of soil dwelling collembolans were not affected either. The abundance of macroarthropods on the harvested plots, except selection felling, was ca. 50% lower compared to the control forest. Their community structure was also changed due to the harvestings. The most sensitive animal groups were herbivores, microbivores and some detritivores. After 10 years, predators (mainly spiders and certain coleopterans) were decreased only under retention tree groups, while microbidetritivores (dipteran and coleopteran larvae) were unaffected. Our study showed that dispersed tree retention, at least when only 30% of the stand volume was harvested, induced no significant changes in soil decomposer animal community in boreal coniferous forest. On the other hand, decomposer community in clear-felled areas (either large or small) and in small aggregated retention tree groups is still different from that in unfelled forest 10 years after the harvestings. Mesofauna living in the soil organic layer (humus) seem to be better buffered against environmental changes induced by the harvesting compared to animals dwelling close to or on the soil surface. These animals are affected long after harvestings.

Performance of Siberian elm ( Ulmus pumila) on steppe slopes of the northern Mongolian mountain taiga: Drought stress and herbivory in mature trees

Vegetation, soil conditions, age structure, water relations, light response of the chlorophyll fluorescence yield, and herbivore damage were studied in native savanna-like stands of Siberian elm ( Ulmus pumila) on south-facing slopes in the mountain taiga of the western Khentey Mountains in northern Mongolia. These stands limited to the middle and lower parts of the slopes consist of single trees or small groups of trees of up to 5 m height. Parts of the tree crowns are characteristically dead. The stands have a marked shrub layer of, e.g., small individuals of U. pumila as well as Spiraea aquilegifolia, Padus asiatica, and Ribes diacantha, and a diverse, but patchy ground vegetation. U. pumila is limited to loose, deep, stony soils on the slopes, which preferably occur near rock outcrops, mostly in contact to mountain steppe. Fine-grained, non-skeletal soils are avoided by U. pumila, but inhabited by meadow steppe. The preference for stony soils is attributable to the high water requirements of U. pumila, as rock cracks are known to form a reservoir for rain and dew water. The high demand for water is a partly a consequence of a low VPD sensitivity of the stomata regulation known for U. pumila. High transpiration rates may help U. pumila to avoid elevated leaf temperatures under high solar irradiation on the exposed steppe slopes. Increasing non-photochemical quenching at a PPFD > 2000 μmol m −2 s −1 gives additional evidence of the good adaptation of U. pumila to sunlit environments. Minimum shoot water potentials far above the point of zero turgor throughout the growing season suggest sufficient water supply in summer in years with average rainfall. Literature data indicate that U. pumila can also suffer lethal damage on the rocky slopes during exceptionally dry summers. Insect herbivory was of subordinate significance for the elm trees. Therefore, desiccation is thought to be the main cause of the frequent occurrence of dead crown parts and the early death of the elm trees on the sun-exposed slopes. Mean age of the sample trees was as low as 17 years. At this age, the trees are not fertile, but proliferate vegetatively. The low lifespan of U. pumila on the sun-exposed slopes suggests that these slopes are a suboptimal habitat for this tree species. The dependence on loose, stony soils alone explains the irregular distribution of U. pumila on the sun-exposed slopes and rules out the formation of closed elm forest at these sites.

Impact of sun-surface-sensor geometry upon multitemporal high spatial resolution satellite imagery

Agile high spatial resolution satellites, such as QuickBird, are capable of varying their in-track and cross-track view angles, thereby reducing the time required for the satellite to revisit the same location. However, variation in these view angles can impact the structural representation of image objects, with implications for multitemporal analyses of high spatial resolution imagery. To demonstrate this, we used four QuickBird images collected annually between 2003 and 2006 over a managed forest location near Merritt, British Columbia, Canada. Selected linear features (i.e., roads) were used to assess the geometric fidelity of the images, while forest structure, characterized with image segments and local maxima stem counts, was used to assess the impact of variability in viewing geometry. Using the 2003 QuickBird panchromatic image as a base, over 80% of the selected linear features in the 2004, 2005, and 2006 images were within less than 1 m of the 2003 control, and more than 96% were within 2m. Using pairwise t tests of the stem counts per segment (image-derived spatial units analogous to small groups of trees) for each year of imagery, we identified a significant difference between the stem count generated from the 2005 imagery and stem counts generated from each of the other images. The 2005 image had a markedly different in-track view angle and satellite azimuth relative to the other images considered, and therefore, although our time series of QuickBird imagery had demonstrated geometric fidelity, the forest structural information extracted from our time series was not consistent. We conclude that careful attention should be paid to these image acquisition parameters when selecting high spatial resolution images for multitemporal analyses in forested environments.