Southern Aspect Research Articles

What determines tree mortality in dry environments? A multi-perspective approach.

Forest ecosystems function under increasing pressure due to global climate changes, while factors determining when and where mortality events will take place within the wider landscape are poorly understood. Observational studies are essential for documenting forest decline events, understanding their determinants, and developing sustainable management plans. A central obstacle towards achieving this goal is that mortality is often patchy across a range of spatial scales, and characterized by long-term temporal dynamics. Research must therefore integrate different methods, from several scientific disciplines, to capture as many relevant informative patterns as possible. We performed a landscape-scale assessment of mortality and its determinants in two representative Pinus halepensis planted forests from a dry environment (~300 mm), recently experiencing an unprecedented sequence of two severe drought periods. Three data sources were integrated to analyze the spatiotemporal variation in forest performance: (1) Normalized Difference Vegetation Index (NDVI) time-series, from 18 Landsat satellite images; (2) individual dead trees point-pattern, based on a high-resolution aerial photograph; and (3) Basal Area Increment (BAI) time-series, from dendrochronological sampling in three sites. Mortality risk was higher in older-aged sparse stands, on southern aspects, and on deeper soils. However, mortality was patchy across all spatial scales, and the locations of patches within "high-risk" areas could not be fully explained by the examined environmental factors. Moreover, the analysis of past forest performance based on NDVI and tree rings has indicated that the areas affected by each of the two recent droughts do not coincide. The association of mortality with lower tree densities did not support the notion that thinning semiarid forests will increase survival probability of the remaining trees when facing extreme drought. Unique information was obtained when merging dendrochronological and remotely sensed performance indicators, in contrast to potential bias when using a single approach. For example, dendrochronological data suggested highly resilient tree growth, since it was based only on the "surviving" portion of the population, thus failing to identify past demographic changes evident through remote sensing. We therefore suggest that evaluation of forest resilience should be based on several metrics, each suited for detecting transitions at a different level of organization.

Stable carbon isotope analysis reveals widespread drought stress in boreal black spruce forests.

Unprecedented rates of climate warming over the past century have resulted in increased forest stress and mortality worldwide. Decreased tree growth in association with increasing temperatures is generally accepted as a signal of temperature-induced drought stress. However, variations in tree growth alone do not reveal the physiological mechanisms behind recent changes in tree growth. Examining stable carbon isotope composition of tree rings in addition to tree growth can provide a secondary line of evidence for physiological drought stress. In this study, we examined patterns of black spruce growth and carbon isotopic composition in tree rings in response to climate warming and drying in the boreal forest of interior Alaska. We examined trees at three nested scales: landscape, toposequence, and a subsample of trees within the toposequence. At each scale, we studied the potential effects of differences in microclimate and moisture availability by sampling on northern and southern aspects. We found that black spruce radial growth responded negatively to monthly metrics of temperature at all examined scales, and we examined ∆(13)C responses on a subsample of trees as representative of the wider region. The negative ∆(13)C responses to temperature reveal that black spruce trees are experiencing moisture stress on both northern and southern aspects. Contrary to our expectations, ∆(13)C from trees on the northern aspect exhibited the strongest drought signal. Our results highlight the prominence of drought stress in the boreal forest of interior Alaska. We conclude that if temperatures continue to warm, we can expect drought-induced productivity declines across large regions of the boreal forest, even for trees located in cool and moist landscape positions.

Survival problem in regeneration of high altitude Kharsu oak (Quercus semecarpifolia Smith.) forests in central Himalaya, India.

The high altitudinal (2200-2600m) viviparous kharsu oak ( Quercus semecarpifolia Smith .) is a late successional evergreen tree species. The species is showing failure to regenerate in the Himalayan region. The present study was undertaken to analyze the seed fall density, seedling recruitment and population dynamic of this species on two different aspects over a six-year period (2004-2009). During the study period from 2004 to 2009 only one good seed crop occurred in 2005. In this year at northern aspect, the average seed fall density was 22.8 ±1.24 seeds m -2 and at southern aspect it was 26.02 ± 0.90 seed m -2 . In 2008 the seed fall density on the northern aspect was 8.5±0.73 seeds m -2 and on the southern aspect it was 8.2 ±0.73 seed m -2 . In the years 2004, 2007 and 2009 a negligible seed crop was produced and did not play a significant role in seedling recruitment. In year 2005, new recruitment of seedling from fallen seeds occurred in August and it ranged from 60-75% at both the aspects. Maximum seedling mortality was in the 1 st year of recruitment thereafter, rate of mortality declined. At the end of observation after six years the total mean seedling density at northern aspects was 1.41 seedling m -2 and at southern aspect; it was only 0.67 seedling m -2. The seedling survival between the two aspects did not vary significantly.

Slope-related variations in twig and leaf traits of Robinia pseudoacacia in the northern mountains of Lanzhou

Aims The growth relationship between twigs and leaves is a strategy that plants enhance the ability to use space resources under environmental stresses, and elucidation of this characteristics is important for understanding the phenotypic plasticity of plants in coping with environmental heterogeneity. Our objective was to examine how Robinia pseudoacacia would vary in twig and leaf configuration in response to changes in slope aspect. Methods In the northern mountains of Lanzhou in Gansu Province, China, 20 transects were laid out horizontally along the contour at intervals of 50 m from an elevation of 1 550 m upward in four different slope aspects, and 12 plots were set up along each transect at intervals of 5 m. A handheld GPS was used to measure latitude, longitude and altitude of each plot. Community traits were investigated and all individuals of R. pseudoacacia were used for measurements of the cross-sectional area of twigs, total leaf area, leafing intensity, and average area of a single leaf on each twig. Arc GIS was used to construct the digital elevation model(DEM). The 240 plots were categorized into groups of northern, eastern, western and southern aspects, and the standardized major axis(SMA) estimation method was then used to examine the allometric relationship between the cross-sectional area of twigs, total leaf area, leafing intensity and average area of a single leaf. Important findings With changes in the slope aspect from north to east, south and west, the crown density, average tree height and soil moisture of the plant community displayed a pattern of decrease—increase, and the cross-sectional area of twigs, total leaf area and average area of a single leaf of R. pseudoacacia displayed a pattern of decrease—increase and the leafing intensity displayed a pattern of increase—decrease. Significant positive relationships between the cross-sectional area of twigs and total leaf area were found in R. pseudoacacia in all slope aspects(p 0.05), and the common slope of the regressions was significantly greater than 1; significant negative relationships between leafing intensity and average area of a single leaf were found in all slope aspects(p 0.05), and the common slope of the regressions was significantly close to –1. In addition, when the slope aspect changed from north to east, south and west, the y-intercepts in the scaling relationships of the cross-sectional area of twigs vs. total leaf area and the leafing intensity vs. individual leaf area both displayed a pattern of decrease—increase. The allometric relationship between twig and leaf with changes in slope aspect of the habitat reflected the response and adaption of plant functional traits to their biotic and abiotic environments and the investment balance mechanism of plant architecture construction.

Effects of slope position, aspect and cropping system on soil nutrient variability in hilly areas

Human activities and topography are main factors affecting soil nutrient variation. However, the relationships between these factors are both site- and scale-specific. In hilly areas of south-western China, the dominant cropping systems are rice, vegetables, oranges, Chinese red pepper and maize–sweet potato intercropping. In the present study, slope position (valley, low slope, flat slope, middle slope, upper slope, ridge) and aspect (north, east, south, west) were derived to investigate the relationships among cropping system, terrain, and soil nutrients at county scale. Crops were mainly planted at middle or flat slope positions. Rice and orange plants were evenly distributed across the aspects whereas vegetables were mostly planted on the northern aspect. Red pepper and maize–sweet potato plants were mainly grown on the western and southern aspects. Rice sites had higher contents of organic matter and available nitrogen (N) and lower contents of available phosphorus (P) and available potassium (K). For dryland cropping systems, vegetable sites had higher contents of organic matter, available N, and available P. Red pepper sites had higher contents of available K. Contents of organic matter and available N were generally higher at lower landscape positions. Contents of available K were higher at lower and flat slope positions. Contents of available P were higher at higher landscape positions. Contents of organic matter and available N were higher on the northern and eastern, and lower on the western aspects. Contents of available P were higher on the western and lower on the northern aspects. No significant differences were found for available K across the aspects. Classification tree algorithms indicated that relative importance of the variables on soil nutrient variation was in the order: (i) cropping system, (ii) slope position, and (iii) aspect.

Productivity of Wheat (<i>Triticum Aestivum</i>) as Intercrop in <i>Grewia Optiva</i> Based Traditional Agroforestry System along Altitudinal Gradient and Aspect in Mid Hills of Garhwal Himalaya, India

Grewia optiva, wonder tree of western Himalaya locally known as Bhimal is the most common multipurpose tree is a boon for the inhabitants of Garhwal Himalayan region. About 2/3rd of the cultivated area of Garhwal is rainfed and Wheat (Triticum aestivum) is the predominant food grain crop cultivated on the sloppy terraces in combination of G. optiva trees on terrace bunds. In Present study the productivity of wheat (Triticum aestivum) as intercrop in Grewia optiva based traditional agroforestry system along altitudinal gradient and aspect in mid hills of Garhwal Himalaya, India revels that G. optiva occupied average highest frequency (85%), stem density (145 trees/ha), TBC (7.68 m<SUP>2</SUP>/ha), IVI (86.51), tree height (7.38 m), Crown spread (5.34 m) in the elevation 1000-1500 m of Northern aspect (E1/N site). In the elevation 1000-1500 m, it was observed that there is a reduction in grain, straw and biological yield of wheat as 17.59%, 17.77% and 17.71% respectively on the southern aspect compared to northern aspect. Further elevation 1500-2000 m, the reduction in the average grain yield was recorded 37.31% under G. optiva based traditional agroforestry system in E2/S site. The phenophases of the wheat crop is sown in the month of December which emerges to crown root initiation (CRI) in January followed by tillering, milking, maturity and final harvest during May while G. optiva remain dormant from December to February, leafless in March and new flush of shoots in May. This reversal phenopases of two components are complimentary in tree crop interaction to enhance productivity.

Forest Carbon Stocks in Woody Plants of Arba Minch Ground Water Forest and its Variations along Environmental Gradients

The role of forests in mitigating the effect of climate change depends on the carbon sequestration potential and management. This study was conducted to estimate the carbon stock and its variation along environmental gradients in Arba Minch Ground Water Forest. The data was collected from the field by measuring plants with a DBH of >5cm in quadrat plots of 10 X 20 m and the carbon stocks of each plant were analyzed by using allometric equations. From this study the mean total carbon stock density of Arba Minch Ground Water Forest was found to be 583.27 t ha-1, of which 829.12 t ha-1, 165.88 t ha-1, 1.28 t ha-1, 83.80 t ha-1 was contained in the above ground carbon, belowground carbon, litter carbon and soil organic carbon (0-30 cm depth) 0respectively. Similarly, the analysis of carbon stock variation of different carbon pools on eight different aspects of the forest area showed a significant variation with the exception of litter carbon stock and this is due to fast decomposition rate of litters and low amount of litter fall in the forest. The amount of carbon stock in above and belowground biomass, soil organic carbon and the total carbon stock was higher on the southern aspect as compared to other aspects. This study concluded that the carbon stock value of Arba Minch Ground Water Forest is large, and this will serve as a potential entry point for the engagement of the forest in REDD project. Keywords : Environmental variables; Ground Water Forest; Climate change; Biomass; Forest carbon stock

Non-equilibrium hillslope dynamics and irreversible landscape changes at a shifting pinyon–juniper woodland ecotone

Pinyon–juniper woodlands of the western United States frequently exist within topographically complex landscapes where varied slope aspect yields substantial, local microclimate variation. Vegetation composition and cover typically change markedly along the gradient of relatively mesic northern aspects to more xeric southern aspects. Ecohydrological processes including precipitation runoff, soil moisture storage, and erosion are strongly influenced by vegetation. In certain cases, reduction of plant cover may set self-enhancing feedbacks in motion that lead to further declines of both vegetation and soils, and in some cases, replacement of woodlands with more xerophytic vegetation. The first place such change is likely to occur is in the ecotone between the drier southern aspects and moister north aspects. We studied vegetation, soils, and soil erosion in two small (1–2ha) drainage basins in northeastern Arizona where pinyon–juniper woodlands occupy northern aspects, grading to shrub-dominated vegetation on more xeric southern aspects. Mapping of soil thickness, use of tree-root exposure to measure long-term soil erosion rates, and data on tree mortality and establishment indicate that the ecotone between woodland and more xerophytic vegetation has apparently been shifting for centuries, with a reduction in woodland vegetation. Erosion rates on xeric aspects ranged from 14 to 23cm per century in one basin and as much as 60cm per century in the other basin. In contrast, mesic aspects showed either no net soil losses over the last several centuries or rates significantly less than on the xeric aspects. Exposure of small roots (<5mm diameter) of cliff rose (Purshia stansburiana) directly overlying bare bedrock surfaces indicates that the process of denudation is ongoing and probably expanding in ecotonal areas. Mesic and xeric aspects exemplify “conserving” vs. “non-conserving” ecohydrologic systems in terms of their capacities to retain water and soils. The contrasting sets of self-enhancing feedback dynamics on xeric vs. mesic aspects not only produce different states in vegetation and soils, they also set in motion the production of pronounced geomorphic contrasts that probably require centuries to millennia to develop. The ongoing ecohydrological transitions in the more xeric aspects are in the process of transforming those hillslopes from smooth, curvilinear, soil-mantled, sediment transport-limited slopes to detachment-limited slopes characterized by an expanding area of bare bedrock steps and cliffs, and this transition is probably irreversible. Predicted temperature increases over the next century for the region are comparable to the present-day soil temperature differential on xeric vs. mesic aspects at the site. Soil temperature is the principal driver of soil water evapotranspirative losses, and because of the interdependent linkages between soil temperature, soil moisture, weathering, production and retention of soil, vegetation, and hydrological response, relatively small temperature increases will likely accelerate the ongoing environmental changes in this and similar areas.

Carbon Sequestration Potential of Chir Pine (&lt;i&gt;Pinus&lt;/i&gt;&lt;i&gt; &lt;/i&gt;&lt;i&gt;roxburghii&lt;/i&gt;. Sarg) Forest on Two Contrasting Aspects in Kumaun Central Himalaya between 1650-1860 m Elevation

The tree density for Chir Pine forests on the southern aspect was 1676.66 indi. /ha and on northern aspect 1026.66 indi. /ha. The tree biomass on southern aspect was 252.65 t ha<SUP>-1</SUP> and on northern aspect it was 453.58 t ha<SUP>-1</SUP>. The tree biomass accumulation rate on the southern aspect was lower than the northern aspect. The forest carbon stock on the southern aspect was 120.0 t ha<SUP>-1</SUP> compared to 215.45 t ha<SUP>-1</SUP> on the northern aspect. The carbon sequestration rate on the northern aspect was also lower than southern aspect.

Distribution and growth of autumn olive in a managed forest landscape

Autumn olive (Elaeagnus umbellata) poses significant challenges for forest managers. The ability to predict when and where this species will become a problem would allow managers to more effectively prioritize control efforts and implement the most efficient management practices available. Several studies have sought to determine which key factors lead to greater abundance of exotic, invasive plants on certain sites and their spread at multiple scales. Previous research suggests that disturbances and increased light can be important. The overall goal of this research was to identify factors associated with forest road edges that are most important in facilitating autumn olive. Specific objectives were to: (1) document site factors significantly related to the presence and success of autumn olive, (2) investigate the hypothesis that southern aspects have greater abundance, patch depth and growth of autumn olive than other aspects, (3) examine the hypothesis that there is a negative relationship between the abundance and height of autumn olive and the abundance and height of native species, and (4) determine if the relationship between autumn olive abundance and height and the abundance and height of other invasive species is positive. Densities of autumn olive, native woody species, and other woody exotic, invasive species in different size classes were quantified in plots located along forest-road edges having northern, southern, eastern, and western aspects. Slopes, elevation, road opening width, canopy cover, and basal area were also quantified at each plot location. In addition, presence and absence of autumn olive, slope, elevation, canopy cover, and road canopy closure were quantified at randomly selected points along major and minor gravel roads within the study area. Larger autumn olive were most abundant along edges with southern aspects and patches of autumn olive were deepest on edges with northern and southern aspects. Autumn olive height and abundance were positively related to the height and abundance of both native and exotic, invasive woody plants. Slope, elevation, road canopy cover, road opening width, and road type were found to be important factors influencing autumn olive establishment and success. As a result, these factors may prove useful in the development of habitat suitability models and GIS-based risk maps that managers could use to more effectively address this invasive species.

Homogenization in forest performance across an environmental gradient – The interplay between rainfall and topographic aspect

This study aimed to investigate the interaction between local and regional environmental factors that affect forest performance during drought periods. In previous studies, contradictory results regarding the effect of aspect on forests performance, under different settings, were reported. However, each study focused on a different forest ecosystem at a different time frame, making synthesis inadequate. Monoculture planted Pinus halepensis forests in Israel, covering a broad climatic gradient (200–850mm annual rainfall), form a suitable study system to address this question.We used remote sensing and GIS methods to observe a large number of afforested stands over a wide area at high resolution. Normalized Difference Vegetation Index (NDVI), obtained from Landsat satellite images for 14years between 1994 and 2011, served as an inclusive measure of forest performance. Data on the examined environmental factors were obtained from spatially interpolated annual rainfall maps and a topographic aspects map. The effects of aspect on NDVI were evaluated separately for three regions along the rainfall gradient: arid (200–350mm), intermediate (350–500mm), and humid (500–850mm).During the studied period, NDVI declined in the arid region but remained constant in the intermediate and humid regions. NDVI was positively related to annual rainfall in all three regions. The effect of aspect on NDVI was positively associated with rainfall in the arid region, but not in the intermediate and humid regions. In other words, forest performance homogenization across local habitats occurred in the arid region under drought stress. Relatively wet years were characterized by high NDVI values (∼0.4), with large differences (∼0.025) between northern and southern aspects, whereas dry years were characterized by low NDVI values (∼0.3) and small differences (∼0.01).The present study supports the concept that under severe drought stress forest performance becomes more homogeneous across local habitats, both temporally (in drought years) and spatially (towards the arid forest boundary). Performance homogenization may occur when low soil water levels are reached, and climatic conditions become the dominant limiting factor. When water availability is high enough, differential performance responses among local habitats are maintained. We evaluated the trends and relations among local and regional environmental factors on performance, and assessed their relative effect sizes. Such an evaluation is essential to link local and global studies aimed at predicting the fate of forests facing global climate change.

Post-fire survival and regeneration of Eucalyptus globulus in forest plantations in Portugal

Eucalyptus globulus is one of the most important pulpwood plantation species in the world, and nowadays it is present in most continents. Some of the regions where E. globulus plantations have been expanding have a high incidence of wildfires; therefore, knowing the factors affecting the fire resistance and resilience of this species is particularly important for forest management. This is the case of Portugal, where nearly 1.4million ha of land burned in the last decade and where E. globulus has become the most widespread tree species. In this paper we assessed the short-term post-fire responses of E. globulus trees in four sites affected by wildfires, and investigated their potential relationships with fire severity descriptors and with tree and stand characteristics. One year after fire, individual tree mortality was low (3.9%) but most trees (79.2%) were top-killed (i.e. had stem mortality). Both post-fire tree mortality and top-kill increased with fire severity (expressed by maximum char height and/or char severity rating). Moreover, top-kill was positively related with vegetation cover and the proportion of pine trees in the stand, and was negatively related with tree diameter and the proportion of other broadleaved trees in the stand. The most common post-fire regeneration type among the sampled trees was basal resprouting (89.2%), though 20.9% had epicormic resprouting. The number of basal resprouts increased with char height, top-kill and diameter of the parent tree, and decreased with slope. In terms of post-fire growth, the height of the dominant resprout increased with the number of resprouts and with char severity, while it decreased in drier southern aspects. Results showed that E. globulus is a fire-resilient species with a very high probability of surviving fire; however, in forest plantations where trees are usually felled in short rotations (thus with limited size), individuals have a high probability of being top-killed. The presented models may be useful to help managers on the assessment of post-fire production losses and regeneration potential in E. globulus plantations.

Habitat Interaction Between Two Species of Chipmunk in the Basin and Range Province of Nevada

Interspecies interactions can affect how species are distributed, put constraints on habitat expansion, and reduce the fundamental niche of the affected species. Using logistic regression, we analyzed and compared 174 Tamias palmeri and 94 Tamias panamintinus within an isolated mountain range of the Basin and Range Province of southern Nevada. Tamias panamintinus was more likely to use pinyon/ponderosa/fir mixed forests than pinyon alone, compared to random sites. In the presence of T palmeri, however, interaction analyses indicated T. panamintinus was less likely to occupy the mixed forests and more likely near large rocks on southern aspects. This specie s-by-habitat interaction data suggest that T. palmeri excludes T panamintinus from areas of potentially suitable habitat. Climate change may adversely affect species of restricted distribution. Habitat isolation and species interactions in this region may thus increase survival risks as climate temperatures rise.

Discussion of “Learning from Failure of a Long Curved Veneer Wall: Structural Analysis and Repair” by Paulo B. Lourenço and Pedro Medeiros

Discussion of “Learning from Failure of a Long Curved Veneer Wall: Structural Analysis and Repair” by Paulo B. Lourenço and Pedro Medeiros

GIS를 이용한 울산지역 선사유적 입지분석 및 분포예측

본 논문은 울산광역시를 대상으로 선사시대 최적의 입지를 GIS를 통한 분위수방법과 자연결점법으로 조사하였고, 등급화 통계분석방법으로 선사유적의 존재가능성을 분석하여 선사유적의 정착 패턴을 규명하였다. 연구에 사용된 변수는 고도, 사면 경사도, 수계 최소거리, 사면방향, 지질, 토양배수등급, 심토토성, 토지이용추천 등이며, 이를 이용하여 입지분석 및 분포예측을 실시하였다. 입지분석결과, 선사유적의 최적 입지환경 중 지형적 환경은 저지대 완경사지의 남향인 지역에 수계를 포함하는 곳이며, 지질 토양환경은 제4계 충적층의 배수상태가 양호하고, 심토토성은 식양질, 토지이용추천은 밭인 곳이 최적의 등급으로 분석되었다. 유적분포 예측결과, 태화강과 동천강이 합류하는 하류지역은 하천과 근접하여 식수이용이 용이하며, 경사도 및 고도가 낮은 지역으로 강 상류로부터 운반 퇴적된 충적층이 넓게 형성되어 농경생활에 적합하여 유적존재 가능성이 높은 것으로 나타났다. The optimum location of the prehistoric sites of Ulsan Metropolitan City are investigated by both quantile and natural breaks methods through GIS, and the settlement pattern is studied based on the possibility of presence of the prehistoric sites which are also analyzed with these methods. Such factors including elevation, slope, distance from the nearest water, aspect, geological features, soil drainage classes, subsoil and land use recommended are employed in the analysis. The optimum geographical environment is the place where it includes the water-base in the area that is the southern aspect of the gentle slope land of lowland. The geology is the Quaternary alluvium. The drainage class is fine and the deep soil saturn is the fine loamy soil and the recommendation of land use is the area that is the field. As a result of the forecast of distribution, the prehistoric sites showed the higher possibility of presence in the downstream region where the Taehwa river and Dongcheon river join because the region come close to the watercourse and the drinking water use is easy. And the aspect and elevation is the low area. The alluvium accumulated from the upper stream of the Taehwa river and Dongheon river was made roomily, the area where is suitable for the farming life. Therefore, this region is judged that the possibility of presence of the prehistoric sites is high.

Allergen of the Month—European Aspen

European aspen's scientific name, Populus tremula, like its North American counterpart, Populus tremuloides, describes the propensity for the leaves to flutter with the faintest breeze. This is due to thin, flattened, pliable leafstalks. P. tremula is prevalent through all of Europe, from Britain to North Africa throughout Asia. 1 Phillips R. Trees of North America and Europe. in: Random House, New York1978: 167-169 Google Scholar , 2 Polunin O. Flowers of Europe: A Field Guide. in: Oxford University Press, London1969: 43-47 Google Scholar It has become established in areas of northeastern United States. [3] Sibley D.A. The Sibley Guide to Trees. in: Alfred A. Knopf, New York2009: 228-237 Google Scholar In the northern portion of its range, aspen grows from sea level up to 3500 feet. In the southern aspect of its range, it may be found at higher elevations. European aspen are freely suckering, forming thickets, and are forest-forming trees, covering large areas with dense, pure stands. It is frequently a temporary forest occupant, but it may be dominant for a longer periods following fire destruction of conifers. Aspen are good foliage for both livestock such as cattle and sheep, but also for deer and elk. The wood is used especially for match-making and for high-quality paper.

Mesoscale Variation in Snag and Hardwood Densities and Sizes in Old-Growth Forests in Western Oregon

Abstract Snags and hardwoods contribute to biological, structural, and functional diversity in old-growth forests. In the US Pacific Northwest, only general knowledge about regional patterns is available to determine target density of snags and hardwood trees. To investigate their variability at relevant scales for silviculture, we examined snag and hardwood densities and sizes in 20 old-growth units in northern and southern aspects in the Coast Range and the Willamette Valley foothills of Oregon. Snag densities varied largely between subregions and aspects, with aspect affecting densities more than subregion. In the Coast Range, snag density was 2.8 times greater on northern aspects than on southern aspects, whereas in the Willamette Valley foothills snag density was 1.4 times greater on northern aspects than on southern aspects. Density of snags larger than 101.6 cm in diameter was very low. Hardwood densities were also greater on northern aspects than on southern aspects. The negative exponential distribution of hardwood density frequency by size classes could be explained by cohort growth under a wide range of competitive pressures or repeated-recruitment events. Aspect and subregion should be taken into account when defining management targets. Allowing for flexibility at these smaller spatial scales would better reflect the variability in ecological conditions and land use history that led to the development of old-growth stands.

Structure, Composition and Diversity of Horticulture Trees and Agricultural Crops Productivity under Traditional Agri-Horticulture System in Mid Hill Situation of Garhwal Himalaya, India

Productivity of agricultural crops under traditional agri-hortculture system alongwith structure, composition and diversity of fruit trees and shrub species in mid hill situation of Garhwal Himalaya, India between 1000 to 2000 m asl during summer and winter seasons on northern and southern aspect were studied. The tree density, composition and diversity in the system varied depending upon aspect, landholding and requirements of the farmers. A total of 12 fruit tree species were recorded in agri-horticulture system; of which 4 trees were common in northern and southern aspect and 6 trees were only noticed in northern aspect while 2 in the southern. The apple tree (Malus domestica) was recorded to be dominant fruit tree species with highest IVI values on both northern and southern aspect with prime preference by the farmers for high additional economic return in agri-horticulture system. Among the shrubs, the 6 shrub species were recorded on the northern aspect whereas there number was 16 on southern aspect. The agricultural crop diversity was higher on the northern aspect in summer and winter season. The average annual productivity of grain under agri-horticulture system recorded 1106 kg·ha–1·year–1 on northern aspect and 1122 kg·ha–1·year–1 on southern with a reduction of 34.56% and 38.29% compared to the sole agriculture crops. The aspect and season also played significantly role in grain, straw and biological productivity of agricultural crops present in agri-horticulture and sole cropping systems. In general there was reduction in yield of agricultural crops under fruit trees but this reduction is supplemented by fruit production which support and sustain the rural community of this hilly region.

Site Characteristics for Sibbaldia procumbens (Rosaceae) on the Uapishka Plateau (Monts Groulx), Québec, with Notes on the Alpine Flora

Abstract Sibbaldia procumbens occurs in arctic and alpine environments in widely disjunct locations in North America, Europe, and Asia. It is one of the rarest native plants in New England, with only a single station in New Hampshire. To inform conservation efforts for this species near the southeastern periphery of its North American range, we studied S. procumbens in alpine snowbeds on the Uapishka Plateau (Monts Groulx) in central Quebec, a relatively poorly known mountain range in the Grenville geologic province where the species is abundant enough to evaluate associated site characteristics. Sibbaldia procumbens was positively correlated with slope, southern aspect, and elevation, with the highest abundances associated with 22–26° slopes, 100–230° aspect, and elevations of 1024–1039 m. At our site in Quebec, S. procumbens was more abundant in association with bare rock, supporting the findings of previous authors that S. procumbens may benefit from some level of disturbance. We also quantified the do...

Spatial and temporal variability of ground surface temperature and active layer thickness at the margin of maritime Antarctica, Signy Island

A CALM grid with a data logger system to monitor the active layer thermal regime was established on Signy Island (60°43′S, 45°38′W at 80m a.s.l.) in December 2005. The active layer at each of the 36 nodes of the grid was monitored measuring the ground temperature at least at 4 different depths between 0.02 and 0.4m at the end of the summer season. In addition, within the grid, we selected four sites closely spaced (in a ray of 25m) three of which with the same topographical characteristics (north facing aspect) but different vegetation coverage (one bare ground, BG1 and two sites with different vegetation: Andreaea sp. and Sanionia uncinata) and the fourth (BG2) it is as BG1 a bare ground but with south facing aspect. In particular, 4 thermistors were located at depths of 0.02, 0.3, 0.6, and 0.9m at BG2 and at the Andreaea sp site, 9 thermistors at 0.02, 0.3, 0.6, 1, 1.2, 1.4, 1.6, 2, and 2.5m at BG1 and at 0.02 and 0.6m of depth at Sanionia site. Generally, with the same aspect, a thick vegetation cover (as in Sanionia site) provides a greater insulative effect than a thinner vegetation cover (as in Andreaea site) or bare ground (BG1) because vegetation both shades and insulates the ground resulting in a reduction in summer heat flux.Ground Surface Temperature (GST) was colder and more buffered in spring and summer under the vegetated ground than in BG1, although the coldest GST and lowest Thawing Degree Days (TDD) were recorded at BG2 and related to its southern aspect. Our data confirm that air temperature is the main driver of GST, as already reported both in the Arctic and Antarctic. We also found that the effect of air temperature changes seasonally, being drastically reduced in winter and, to a lesser extent, in fall and spring, when there is generally thin snow cover (<30cm). During the summer, when snow cover is usually absent, the air temperature is the dominant driver, although incoming radiation also had an effect on the northern exposed bare ground and to a lesser extent on the vegetated and southerly exposed bare ground.The active layer ranges between 81 and 185cm on the 4 continuously monitored sites and, considering the sites with the same aspect, it is thicker under bare ground (between 10% up to more than 100%) than under vegetated ground, confirming previous observations in the Arctic and Antarctic. However at our sites, climate forcing has no effect on the active layer thickness, enhancing the role of soil properties including the periods of high moisture content and lateral flow of water.The lack of a statistically significant regressions between GST and active layer thickness could be due to the limited study period (four years) and/or to the variation with time of changes in soil characteristics such as soil moisture, and the possible occurrence of non-conductive heat transfer processes including the lateral flow of water.Further data are required to understand the role of moisture and possible ground water circulation within the active layer to explain the unexpected strong dichotomy between the GST regime and active layer thickness.