Total Gap Area Research Articles

Evaluation of Gaps or Voids Occurring in Roots Filled with Three Different Sealers

The purpose of this in vitro study was to evaluate gaps or voids occurring in roots filled with three different sealers. Thirty extracted human single-rooted teeth were decoronated, instrumented using NiTi rotary instruments, divided into three groups (n=10 per group) and obturated with one of the following: Epiphany with Resilon, MetaSEAL with gutta-percha or AH Plus with gutta-percha using the match-taper single-cone technique. After storage for one week in 100% humidity at 37 degrees C, the teeth were horizontally sectioned (n=10). Photographs were taken from the coronal, median and apical parts of the roots using a stereomicroscope at 10X magnification, and the images were then transferred to a computer. The mathematical method known as the 'Affine Transformation' was used for the transformation of pixel coordinates to ground coordinates in the Netcad Software program. The mean areas (mum(2)) of the gaps between the sealer and root dentin or gutta percha/resilon and the gaps between the sealer and/or voids inside the sealer mass were measured, scored on a 0-3 scale and statistically analyzed with the Kruskal-Wallis test. The mean total area of gaps or voids for each sealer was 4631.80 mum(2) for the Epiphany-Resilon, 3826.80 mum(2) for the MetaSEAL-gutta-percha and 31334 mum(2) for the AH Plus-gutta-percha. The MetaSEAL-gutta-percha group showed more gap or void-free interfaces. No significant differences were found among the sealers in the scores for the gap areas (P<.05), and the MetaSEAL showed similar interfaces with Epiphany. No significant differences in the mean areas of gaps or voids were found among the tested resin-based sealers.

LiDAR mapping of canopy gaps in continuous cover forests: A comparison of canopy height model and point cloud based techniques

In continuous cover forest systems, canopy gaps are created by management activities with an aim of encouraging natural regeneration and of increasing structural heterogeneity. Light Detection and Ranging (LiDAR) may provide a more accurate means to assess gap distribution than ground survey, allowing more effective monitoring. This paper presents a new approach to gap delineation, based on identifying gaps directly from the point cloud and avoiding the need for interpolation of returns to a canopy height model (CHM). Areas of canopy are identified through local maxima identification, filtering and clustering of the point cloud, with gaps subsequently delineated in a GIS environment. When compared to field surveyed gap outlines, the algorithm has an overall accuracy of 88% for data with a high LiDAR point density (11.4 returns per m2) and accuracy of up to 77% for lower density data (1.2 returns per m2). The method provides an increase in overall and Producer's accuracy of 4 and 8% respectively, over a method based on the use of a CHM. The estimation of total gap area is improved by, on average, 16% over the CHM based approach. Results indicate that LiDAR data can be used accurately to delineate gaps in managed forests, potentially allowing more accurate and spatially explicit modelling of understorey light conditions.

Reactions of the herb and moss layer, tree saplings and the shrub layer to tree deaths in forests of the Wielkopolska National Park (Western Poland)

This study examines the impact of canopy and canopy gaps on the development of lower forest layers in five protected phytocoenoses of oak-hornbeam habitats (natural and regeneration stands) and oak-pine habitats in the Wielkopolska National Park (WPN). In the studied forests the most common form of dead trees are those which are uprooted (45–59%), while the most frequently dying tree is pine (40–88%). The total area of gaps in relation to the studied forest area ranges from 329 to 2356 m2/ha. The study reaches the following key conclusions. Gaps do not affect bryophyte richness and cover. The impact of gaps on the herb layer is not uniform for the investigated forests. Gaps often, though not in all cases, cause a significant increase in the total herb layer cover, vascular antrophophyte cover, vascular species richness and a greater H′ diversity. Change in the cover of grasses and lianas to the thinning are not statistically significant. The greatest increase was observed in perennial herbs (mainly dicotyledones). In tree stands under regeneration change gaps are characterized by a rising cover of woody perennials and pioneer species of the Rubus genus. The increase in the herb layer cover does not diminish the cover of tree seedlings. To generalize: differences in the herb layer between the canopy and gaps are greater for forests of oak-hornbeam habitats than for oak-pine forest. The strength of the influence of light gaps on the herb layer is determined by such traits of the pytocoenoses as: density, species composition of tree stand, overshadowing abilities of species present in the canopy, domination or co-domination of one or two species in the herb layer.

Colonization of storm gaps by the spruce bark beetle: influence of gap and landscape characteristics

After storm disturbances, there is a risk for degradation of the quality of fallen trees, and for subsequent tree mortality caused by the spruce bark beetle Ips typographus (L.) (Coleoptera: Curculionidae). Models assessing the risk for bark beetle colonization of different kinds of storm gaps would be a valuable tool for management decisions. The present study aimed to determine which gap and landscape characteristics are correlated with the probability of colonization of wind‐felled Norway spruce trees by I. typographus. The study included 36 storm gaps, varying in size from three to 1168 wind‐felled spruces, created by the storm Gudrun in southern Sweden in January 2005. In the first summer, on average, 5% of the wind‐felled spruces were colonized by I. typographus. The percentage of colonized wind‐felled trees per gap was negatively correlated with the total area of storm gaps within 2000 m in the surrounding forest landscape. In the second summer, the proportion of colonized trees increased to 50%. Both gap (mean diameter of wind‐felled trees and basal area of living spruce trees) and landscape variables (amount of spruce forest) were significantly correlated with colonization percentage and explained almost 50% of the variation between gaps. There was no relationship between gap area and colonization percentage. This implies that landscapes with many large storm gaps, where logging resources will be most effectively used, should be salvaged first.

Gap dynamics in a near-natural spruce forest at Mt. Brocken, Germany

We analyzed indices of gap dynamics, i.e. gap formation and gap closure rates as well as turnover rates, in a montane conifer forest in the temperate zone and asked: (1) Are the characteristics of gap dynamics comparable with those of other temperate forests? (2) Do gap dynamics exhibit temporal trends, and (3) if so, are they related to recent climate change? We also addressed methodological issues concerning the differences observed at differing temporal and spatial scales of the used datasets. Thus, we asked further how the indices of gap dynamics are influenced (4) by differences in the length of observation periods and (5) by differences in gap size categories included in the study?The study area was located in the near-natural Picea abies forests in the core zone of the Harz National Park on the north-eastern slopes of Mt. Brocken, Germany. From this area, aerial photographs from the last 60yrs (1945, 1991, 2000, 2003) were analyzed by GIS techniques. Total gap area, number of gaps, gap size and area-based turnover rate, rotation time, gap formation and gap closure rate were calculated and correlated with climate variables.The total gap area varied between 10.9ha and 19.0ha for the study area of 225.2ha between the different years. Similarly, the median of the gap size was 155.6m2 and 87.0m2 in 1945 and 2003, respectively. A rotation time of 228yrs was calculated for the study area. Area-based turnover rates and gap formation rates increased with time, while mean gap size decreased. The most frequently recorded gaps were those in the category <100m2. In particular, small gaps at the level of single trees (≤40m2) became more frequent in the last decade and showed a higher gap formation rate than larger gaps. Temperature was significantly related to both turnover and gap closure rates.In conclusion, for the near-natural spruce stands at Mt. Brocken indices of gap dynamics were of a magnitude comparable to those described from other forest types in the temperate zone. However, the indices of gap dynamics increased with time, which coincided with increasing temperatures over the last few decades.

Natural gap dynamics in a Central European mixed beech—spruce—fir old-growth forest

We provide a study on long-term canopy gap dynamics in the Źofin Virgin Forest (total area 98 ha), which has been strictly protected since 1838. Our aims were i) to describe the size distribution of gaps at a given time; ii) to determine the area where dynamic processes occurred within a given period; and iii) to determine the role of deciduous versus coniferous trees in gap formation. The fate of individual gaps was followed in a 47-ha beech-dominated part of the reserve by analyzing aerial photographs taken in 1971, 1983, 1991, and 2004. The role of individual trees in canopy gap dynamics was studied by combining gap distribution maps with stem position maps of 1975 and 1997 for a 10-ha sample plot. We showed that i) total gap area (9–11%) and average gap size (88–99 m2) was stable during the 33-y study period; ii) canopy dynamics occurred in 0.1% of the area annually; iii) most gaps were created by the simultaneous death of 1–3 canopy trees; iv) death of deciduous trees played a more important role in the creation of gaps than their proportion among dead trees would suggest; and v) tree size and neighbourhood also determined if a dead tree became a gap maker.

Gap disturbance regime in an old-growthFagus–Abiesforest in the Dinaric Mountains, Bosnia-Herzegovina

Due to the scarcity of old-growth forests in much of Europe, there is little quantitative information on disturbance processes that influence forest dynamics. However, this information is crucial for forest management that tries to emulate patterns and processes in natural forests. We quantified the gap disturbance regime in an old-growth forest dominated by European beech ( Fagus sylvatica L.) and silver fir ( Abies alba Miller) in the Dinaric Mountains of Bosnia and Herzegovina. We sampled 87 gaps in four stands using line-intercept sampling. The percentages of forest area in canopy gaps and expanded gaps ranged from 12% to 17.2% and 35.5% to 39.7%, respectively. Although many of the gaps were small (&lt;100 m2) and formed from a single gapmaker, large canopy openings &gt;1000 m2with numerous gapmakers made up a disproportionate amount of the total gap area. More than half the gaps had more than one gapmaker and were often in separate decay classes, indicating gaps had expanded over time during separate disturbance events. Furthermore, 51% of all gapmakers were uprooted or wind-snapped, whereas only 22% died standing. These results suggest that wind disturbance plays an important role in creating intermediate to large canopy openings through both gap formation and gap expansion processes.

Airborne Laser Scanning Quantification of Disturbances from Hurricanes and Lightning Strikes to Mangrove Forests in Everglades National Park, USA.

Airborne light detection and ranging (LIDAR) measurements derived before and after Hurricanes Katrina and Wilma (2005) were used to quantify the impact of hurricanes and lightning strikes on the mangrove forest at two sites in Everglades National Park (ENP). Analysis of LIDAR measurements covering 61 and 68 ha areas of mangrove forest at the Shark River and Broad River sites showed that the proportion of high tree canopy detected by the LIDAR after the 2005 hurricane season decreased significantly due to defoliation and breakage of branches and trunks, while the proportion of low canopy and the ground increased drastically. Tall mangrove forests distant from tidal creeks suffered more damage than lower mangrove forests adjacent to the tidal creeks. The hurricanes created numerous canopy gaps, and the number of gaps per square kilometer increased from about 400~500 to 4000 after Katrina and Wilma. The total area of gaps in the forest increased from about 1~2% of the total forest area to 12%. The relative contribution of hurricanes to mangrove forest disturbance in ENP is at least 2 times more than that from lightning strikes. However, hurricanes and lightning strikes disturb the mangrove forest in a related way. Most seedlings in lightning gaps survived the hurricane impact due to the protection of trees surrounding the gaps, and therefore provide an important resource for forest recovery after the hurricane. This research demonstrated that LIDAR is an effective remote sensing tool to quantify the effects of disturbances such as hurricanes and lightning strikes in the mangrove forest.

Thirty years of gap dynamics in a central european beech forest reserve

Summary Investigation of gap characteristics and tree regeneration patterns is central for our understanding of forest dynamics. By integrating aerial photograph analyses and ground surveys, we provide a study of long-term canopy gap dynamics and tree regeneration patterns in a Hungarian beech forest reserve. We found (1) that in spite of the overall increase of gap area during the investigated 30-years (from 2.5 to 7.7 per cent), total gap area and average gap size (40 – 93 m 2 ) were remarkably similar to those found in other temperate and tropical forests, (2) if the fate of individual gaps was followed, two to three times more intensive canopy dynamics (gap creation, closure and expansion) could be recognized than simple change of gap area indicated, and (3) average seedling density was considered to be suffi cient for natural regeneration. However, it was apparent that recent increased deer browsing had prevented establishment of younger trees of 1 – 2 m in height, as taller saplings were recorded only in old gaps. Our results not only provide useful information on forest dynamics but can also contribute to understanding the potential roles that small forest reserves can play in providing essential reference data for nature-based forest management of this forest type.

Identification of gaps in mangrove forests with airborne LIDAR

Mangrove forests change frequently due to disturbances from tropical storms, frost, lightning, and insects. It has been suggested that the death and regeneration of trees in small gaps due to lightning may play a critical role in mangrove forest turnover; however, the large-scale quantification of spatial pattern and areas of gaps is lacking for investigating this issue. Airborne light detection and ranging (LIDAR) technology provides an effective way for identifying gaps by remotely obtaining direct measurements of ground and canopy elevations. A method based on an alternative sequential filter and black top-hat mathematical morphological transformation was developed to extract gap features. Comparison of identified gap polygons with raw LIDAR measurements and field surveys shows that the proposed method successfully extracted gap features in mangrove forests in Everglades National Park. There are 400–500 lightning gaps per square kilometer in mangrove forests at the study sites. The distribution of gap sizes follows an exponential form and the area of gaps with sizes larger than 100 m2 account for 55–61% of the total area of gaps. The area of gaps in the mangrove forest in Everglades National Park is about 4–5% of the total forest area and the average gap formation rate is about 0.3% of the total forest area per year, indicating that lightning gaps play an important role in mangrove forest dynamics.

Differential Regulation of Pulmonary Endothelial Monolayer Integrity by Varying Degrees of Cyclic Stretch

Ventilator-induced lung injury is a life-threatening complication of mechanical ventilation at high-tidal volumes. Besides activation of proinflammatory cytokine production, excessive lung distension directly affects blood-gas barrier and lung vascular permeability. To investigate whether restoration of pulmonary endothelial cell (EC) monolayer integrity after agonist challenge is dependent on the magnitude of applied cyclic stretch (CS) and how these effects are linked to differential activation of small GTPases Rac and Rho, pulmonary ECs were subjected to physiologically (5% elongation) or pathologically (18% elongation) relevant levels of CS. Pathological CS enhanced thrombin-induced gap formation and delayed monolayer recovery, whereas physiological CS induced nearly complete EC recovery accompanied by peripheral redistribution of focal adhesions and cortactin after 50 minutes of thrombin. Consistent with differential effects on monolayer integrity, 18% CS enhanced thrombin-induced Rho activation, whereas 5% CS promoted Rac activation during the EC recovery phase. Rac inhibition dramatically attenuated restoration of monolayer integrity after thrombin challenge. Physiological CS preconditioning (5% CS, 24 hours) enhanced EC paracellular gap resolution after step-wise increase to 18% CS (30 minutes) and thrombin challenge. These results suggest a critical role for the CS amplitude and the balance between Rac and Rho in mechanochemical regulation of lung EC barrier.

Long-term canopy dynamics analyzed by aerial photographs and digital elevation data in a subalpine old-growth coniferous forest

:We analyzed the long-term canopy dynamics of a 2-ha permanent plot in subalpine old-growth coniferous forest over 43 y using digital surface models (DSMs) and a digital elevation model (DEM). The models contoured canopy and ground surface elevation, respectively. Abies mariesii, A. veitchii, Betula ermanii, Picea jezoensis var. hondoensis, and Tsuga diversifolia were the main species in the forest canopy. Canopy surface DSMs (2.5- × 2.5-m grids) were constructed of the area including the 2-ha plot using aerial photographs from 1959, 1969, 1979, 1989, and 2002, and a DEM was constructed from ground survey data collected in 1991. Canopy height profiles were obtained by calculating the difference between the canopy and the ground surface, and the status of the forest in each grid cell for each year was classified as gap or closed canopy, depending on whether the canopy height was ≤ 25 m or > 25 m, respectively. Tree census data were collected in 2000. The threshold value was decided by comparing the gap from digital elevation data with the result of the field survey. The total gap area in 1959 was greater than 1 ha, indicating that some disturbances had occurred in this plot, probably related to the Isewan Typhoon. A large change occurred during 1969–1989, when mean canopy closure rates were significantly higher than mean gap formation rates. Abies mariesii and B. ermanii tended to occur in the canopy layer in grid cells that contained gaps in 1959 and closed canopy in 2002. The presence of A. veitchii in the canopy layer was also associated with the change from gap to closed canopy, although not significantly so. These results suggest that Abies spp. regenerate more effectively than the other species by establishing seedling or sapling banks before gap formation. Large-scale disturbances, such as the Isewan Typhoon, do not favour the regeneration of spruce over subalpine fir, and species other than spruce are responsible for recovery following such disturbances, according to our analyses of long-term canopy dynamics.

Long‐term canopy dynamics in a large area of temperate old‐growth beech (Fagus crenata) forest: analysis by aerial photographs and digital elevation models

Summary Long‐term canopy dynamics in a large area of temperate old‐growth beech forest in the Daisen Forest Reserve, south‐western Japan (11.56 ha studied over 43 years), were investigated using digital elevation models (DEMs) of the canopy surface, constructed from aerial photographs taken in the growing season (i.e. with foliage) in 1958, 1978, 1992 and 2001. A ground surface DEM at the same resolution (a 2.5 × 2.5 m grid) was constructed using aerial photographs taken when foliage was absent (winter 2002). Canopy height data were obtained by calculating differences in elevation between the canopy and the ground surface, and a canopy height profile was constructed. Topographic data for a 4‐ha plot, located within the 11.56‐ha area, were obtained via a ground survey and used to validate the ground surface DEM derived from aerial photographs. Canopy height class distributions changed significantly over the 43 years. The total number of gaps, defined as areas where canopy height was ≤ 15 m, decreased but total gap area increased over time. Total gap area in 2001 was twice that of 1958. The density of gaps decreased as gap size increased. Gap formation rates increased from 0.47% year−1 (1958–78) to 1.30% year−1 (1992–2001), with a mean of 0.77% year−1, and substantially exceeded closure rates, which fluctuated from 0.28% year−1 (1958–78) to 0.54% year−1 (1978–92), with a mean of 0.39% year−1. Gaps generally expanded and became connected to each other. Temporal variation in gap formation and closure might be correlated with the frequency and severity of typhoon disturbances but, if the observed trends continue, this old‐growth beech stand may become an open stand. The long‐term dynamics of this forest type appear to be far from equilibrium.

Southeastern Anatolia Project (GAP) of Turkey and Regional Development Applications

Southeastern Anatolia Project (GAP: Guneydogu Anadolu Projesi in Turkish) is the largest regional development project in Turkey, and also one of the major projects in the world. There are 13 major projects in the lower Euphrates and Tigris basins that consist of dam's hydropower plants and irrigation schemes and accompanying growth of agriculture, transportation, industry, telecommunications, health and education sectors and services in the region. A total of 22 dams and 19 hydropower plants are to be constructed by DSI. After completion of the project, 1.7 million hectares of land will be irrigated and the ratio of irrigated land to the total GAP area will increase from 2.9 percent to 22.8 percent while that for rain-fed agriculture will decrease from 34.3 percent to 7 percent. The GAP area is bigger than Holland, Denmark, Belgium, Ireland and Luxembourg.

Long‐term canopy dynamics analysed by aerial photographs in a temperate old‐growth evergreen broad‐leaved forest

Summary We used aerial photographs to analyse canopy dynamics over 32 years in a 4‐ha permanent plot of an old‐growth evergreen broad‐leaved forest in the Tatera Forest Reserve, south‐western Japan. We used aerial photographs taken in 1966, 1983, 1993 and 1998 to create digital elevation models (on a 2.5‐m grid) of the canopy surface in a 10‐ha area that included the 4‐ha plot. A topographic map of the ground surface of the 4‐ha plot was also created from ground measurements taken in 1990. The canopy height at each location was calculated and the ‘vegetation height profile technique’ was applied to quantify canopy dynamics. The size distributions of gaps at each observation time showed peaks at both small and intermediate sizes. The total number of gaps and gap density increased over the study period, while total gap area, mean gap size and maximum gap size fluctuated. While the overall mean rates of gap formation and closure (0.58 vs. 0.50% year−1) were nearly balanced, we found large temporal variation. Of the 6400 of 2.5 × 2.5‐m quadrats, 3.4% remained as gaps throughout the 32‐year period. These tended to be in the centres of large, old gaps, whereas those that experienced re‐disturbance (2.5%) were distributed along the edges of old gaps. A large proportion (74.5%) maintained a closed canopy state. Meteorological data suggested that the variation in gap formation and gap closure rates may be related to year‐to‐year variations in the number and severity of typhoons. This study suggests that long‐term and large openings are essential for the establishment of deciduous broad‐leaved and shade intolerant pioneer species in predominantly evergreen broad‐leaved forests.

Computed tomographic assessment of fractures of the posterior wall of the acetabulum after operative treatment.

The purpose of this study was to evaluate the results after operative treatment of fractures of the posterior wall of the acetabulum in relationship to the quality of the fracture reduction as assessed by postoperative two-dimensional computed tomography. The functional results for sixty-seven patients who had open reduction and internal fixation of an unstable fracture of the posterior wall of the acetabulum and the findings of two-dimensional computed tomography performed postoperatively were analyzed. Sixty-one patients were followed for a mean of four years after the injury, and the remaining six patients who had poor early results necessitating reconstructive surgery were followed for less than two years. All patients were evaluated preoperatively and postoperatively with use of three standard plain radiographs (one anteroposterior and two Judet 45 degrees oblique pelvic radiographs) and a two-dimensional computed tomography scan. The functional outcome for the patients was evaluated with use of a modification of the clinical grading system described by Letournel and Judet. The radiographs were graded according to the criteria described by Matta. The two-dimensional computed tomography scans were used to determine fracture gap and offset measurements. The clinical outcome was graded as excellent in thirty-one patients (46%), very good in twenty (30%), good in eight (12%), and poor in eight (12%). The final radiographic results were graded as excellent in fifty-three hips (79%), good in four (6%), fair in three (5%), and poor in seven (10%). There was a strong association between clinical outcome and final radiographic grade. Fracture reductions were graded as anatomic in sixty-five and imperfect in two, as determined with use of plain radiography. However, postoperative computed tomography revealed an incongruency (offset) of >2 mm in eleven hips and fracture gaps of > or = 2 mm in fifty-two. Fracture gaps of > or = 10 mm in any dimension or a total gap area of > or = 35 mm(2) were associated with a poor result. The main risk factors for a poor result were a residual fracture gap width of > or = 10 mm and osteonecrosis of the femoral head. The degree of residual fracture displacement is detected more accurately on postoperative computed tomography scans than on plain radiographs. The accuracy of surgical reduction as assessed on postoperative computed tomography is highly predictive of the clinical outcome. Therapeutic study, Level III-2 (retrospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

Controls of fine root dynamics across a gradient of gap sizes in a pine woodland.

Controls of fine dynamics were investigated in a Pinus palustris Mill. (longleaf pine) woodland subjected to two understory vegetation treatments (control versus removed) and four overstory treatments (no gap control, and canopy gaps of three sizes with constant total gap area per stand). Fine root (<2 mm diameter) dynamics were measured over 11 months using ingrowth cores (all treatments) and minirhizotrons (understory removed in no gap control and large gap treatments only). At the fine (microsite) spatial scale, pine and non-pine root mass production responded negatively to each other (P=0.033). Each life form was significantly (P< or =0.028) related to nearby overstory density, and pine root production compensated for reductions in non-pine roots if understory vegetation was removed. Soil moisture and NO(3) mineralization rate were negatively related to pine root mass production (ingrowth cores; P<0.001 and P=0.052) and positively related to pine root length production, mortality and turnover (minirhizotrons; P from <0.001 to 0.078). Temperature variance was negatively related to pine root lifespan P<0.001) and positively related to pine root turnover (P=0.003). At the ecosystem scale, pattern of overstory disturbance (gap size and number) had no significant effect on non-pine, pine, or total root production. However, the presence of gaps (versus the no-gap control) increased non-pine root mass production (ANOVA, P=0.055) in natural understory conditions, and reduced pine root mass production (P=0.035) where the understory was removed. Ecosystem-wide pine root length production, mortality and turnover were positively related to weekly soil temperature (P< or =0.02). In natural systems, fine root dynamics are highly variable and strongly affected by biotic factors. Roots quickly close belowground gaps because one life form (pine or non-pine) compensates for the absence of the other. When understory vegetation is removed, however, pine roots respond to the local abiotic environment, particularly moisture and NO(3).

Bestandslücken in einem subalpinen Fichtenwald der Westkarpaten

The size, number, and enlargement of gaps as well as the process of gap formation were analyzed in a subalpine spruce forest in the Babia Gora massif, one of the highest in the western Carpathian Mountains. Openings in the forest canopy of up to one hundred square meters are typical structural elements of subalpine spruce forests. Gaps comprised 34% of the studied forest area of 14.4 ha. There were 38 gaps per ha, most of them <100 m2. Average gap size was 92 m2. Most gaps were environmentally heterogeneous as a result of their progressive and ongoing enlargement, which was evidenced in many gaps by snags and logs representing a wide spectrum of decomposition classes. The density of logs and the area covered by them were about two times larger in gaps than under spruce canop. Logs in gaps were of greater diameter. The mean gap size has increased in recent years. At the same time establishment of new gaps became rarer and enlargement of existing gaps took place more often. This suggests that the average area of gaps will further increase in the future. The closure of gaps resulting from the elongation of spruce branches on adjacent trees and through the development of young trees did not keep pace with the process of gap creation. It yielded a 0.3–0.4% increase of total gap area per year.

Canopy gap formation and replacement pattern of major tree species among developmental stages of beech (Fagus crenata) stands, Japan

Gap characteristics and gap phase replacement of major tree species were examined in two primary old-growth (mean DBHs of the canopy trees were 45.2 and 56.1 cm) and four secondary developing (range of mean DBH of the canopy trees was 23.5–39.9 cm) beech (Fagus crenata) stands in the Daisen Forest Reserve, southwestern Japan, and these were analyzed in relation to stand development as expressed by the difference of mean DBH of canopy trees. Percentage gap area (percentage of total gap area to total surveyed area) and mean and maximum gap size varied widely and ranged from 1.7 to 20.0%, from 19.4 to 162.8 m2, and from 35.7 to 585.1 m2, respectively. Mean percentage gap area and mean gap size were significantly greater in old-growth than in developing stands. However, they and maximum gap size might not increase linearly with stand development, and the gap feature of less developed stands was greater than that of later stages in developing stands. The cause was a higher formation rate, in younger developing stands, of gaps formed by simultaneous death (multiple trees falling down in domino fashion) which tends to produce larger gaps. In developing stands mean DBH of gapmakers (canopy trees that formed a gap) was smaller than that of canopy trees, though the inverse trend might be found in old-growth stands. Three typical types of death or injury states of gapmakers such as standing dead, trunk broken and uprooted were found in every study stand and the difference in stand development may not cause stand-to-stand variations for them. Importance of F. crenata (the most dominant species) in the canopy layer increased and its importance in the understory layer decreased with stand development. Shade-intolerant Quercus mongolica in the canopy layer was more important in younger than in old-growth stands, and there was no Quercus regeneration in old-growth stands. Acer mono consistently appeared, though in much less abundance than other species, in both canopy and understory layers of all study stands. Sub-canopy layers, which are mainly formed by sub-canopy tree species such as Acanthopanax sciadophylloides and Acer japonicum, may gradually develop with stand development.p>

A Model of Conductive Heat Flow in Forest Edges and Fragmented Landscapes

Although the creation of edges during forest fragmentation can have important abiotic and biotic impacts, especially under conditions of future climate change, mechanistic models of edge effects have not been forthcoming. A simple numerical model of two-dimensional heat flow is developed and applied to a vertical forest/clearcut edge profile and to simulated fragmented landscapes. Height-specific thermal diffusivity and conductivity in the forest were assumed to vary in proportion to foliage densities measured in the central Amazon. In the edge profile, the clearcut that abutted the edge served as a heat source and its temperature was maintained at a constant value higher than in the initially cooler forest. In the fragmented landscapes, simulated treefall gaps were heat sources whose temperature varied with sun movements during the day. Gap frequency was varied so as to approximate the gap coverage observed in selectively logged forests. In one set of simulations, temperature in the openings was systematically varied; in another, thermal diffusivity of the forest was varied. Along the edge profile, high temperatures in the clearcut were rapidly transmitted into the upper canopy due to additive edge effects. Temperatures in the forest understory were also very sensitive to clearcut temperatures due to relatively sparse understory foliage. An overall increase in forest diffusivity led to markedly higher temperatures close to the edge and a more even temperature distribution among height strata. In fragmented landscapes, total gap coverage and additivity from neighboring gaps strongly influenced forest temperatures. At low conductivities, heat flowed only into the forest close to the gaps and hence forest temperature increased almost linearly with gap area. However, at high conductivities, heat flowed far into the forest and forest temperature varied as a function of gap density in the surrounding neighborhood. Because of these additive effects, slight increases in total gap area led to disproportionate changes in the thermal profile of the landscape. These results have important implications for the conservation of forest ecosystems.