Canopy Gap Characteristics Research Articles

Relation between Topography and Gap Characteristics in a Mixed Sessile Oak–Beech Old-Growth Forest

The interest to assess the relationship between forest gap characteristics and topography features has been growing in the last decades. However, such an approach has not been studied in undisturbed mixed sessile oak–beech old-growth forests. Therefore, the present study carried out in one of the best-preserved sessile oak–beech old-growth forests in Europe, aims to assess the influence of topographic features (slope, altitude and aspect) on (i) some characteristics of canopies and expanded gaps (surface, diameter and perimeter) and (ii) the proportion of beech and sessile oak as bordering trees, gap fillers and gap makers. Through a complete gap survey on an area of 32 ha, 321 gaps were identified and mapped. The largest gaps and also the highest gap frequency (140) was found in the slope class (15.1–20°), while the gap frequency increased with altitude, with 99 gaps being recorded at 601–650 m a.s.l. The size and perimeter of the canopy and expanded gaps, as well as the number of gap makers, were negatively related to the slope and altitude. The expanded gap to canopy gap size ratio decreased with the slope and was positively related to the altitude, while a significant negative decrease in gap filler density with altitude was encountered. The sessile oak participation ratio as bordering trees forming the gap increased not only with the altitude but also with the slope. The topography plays an important role in the formation of gaps as well as in the characteristics of the future stand. This study provides valuable insights into the relationship between canopy gap characteristics and topography, which is useful information for forest owners that pursue the design of forest management toward nature-based solutions.

Canopy gap characteristics and regeneration patterns in the Białowieża forest based on remote sensing data and field measurements

Forest dynamics is driven by the formation of gaps, especially in temperate forests. A potentially useful tool for identifying canopy gaps at different spatial scales is remote sensing. Our study used two types of data: (1) high spatial resolution Canopy Height Model (CHM) to detect canopy gaps in the forest and (2) field data to quantify natural and artificial regeneration within the gaps. The study aimed to: (i) measure the characteristics of canopy gaps; (ii) identify the regeneration patterns within gaps; (iii) identify the factors influencing tree species regeneration within gaps. We analysed 313 tree canopy gaps in the Polish part of Białowieża Forest (ca. 620 km2), east Poland. Variability in the mean gap area was very high, ranging from 20.2 to 8693.8 m2. The number of gaps with an area>1000 m2 was the largest. The total area of gaps was highest in coniferous stands, where the biggest median area was also found. Gap size did not affect regeneration density in the Białowieża Forest, except for birch and hornbeam. The density of less light-demanding tree species in the gaps was greater than light-demanding ones. Birch regenerated in all gap sizes, and its density increased with gap area. Oak seedlings dominated in small gaps but conditions in the 'matrix of small gaps' was sufficient for short oak saplings. Hornbeam regeneration was highest in the gaps surveyed, especially the density of short saplings. Seedlings of hornbeam were present in 32% of gaps, but saplings were present in as many as 56% of gaps. Spruce regeneration was less numerous than hornbeam regeneration. Birch regeneration was the most numerous in short sapling stage. We analyzed 31 variables from different categories to identify the factors influencing tree species regeneration within gaps. The most essential variables for the birch and hornbeam regeneration were those containing supporting information, especially the percentage of the specific tree species covering the land around the gap. The variables based on gap geometry (size, shape, direction, elongation) were less important than variables from other categories. We found the positive influence of browsing on the density of hornbeam saplings. However, the high density of ungulates and their browsing pressure hinder birch regeneration. Intensive browsing by ungulates seems to be the most important factor in changing species composition and forest regeneration structure in gaps.

UAVs as remote sensing platforms in plant ecology: review of applications and challenges

AbstractAimsUnmanned aerial vehicles (UAVs), i.e. drones, have recently emerged as cost-effective and flexible tools for acquiring remote sensing data with fine spatial and temporal resolution. It provides a new method and opportunity for plant ecologists to study issues from individual to regional scales. However, as a new method, UAVs remote sensing applications in plant ecology are still challenged. The needs of plant ecology research and the application development of UAVs remote sensing should be better integrated.MethodsThis report provides a comprehensive review of UAV-based remote sensing applications in plant ecology to synthesize prospects of applying drones to advance plant ecology research.Important FindingsOf the 400 references, 59% were published in remote sensing journals rather than in plant ecology journals, reflecting a substantial gap between the interests of remote sensing experts and plant ecologists. Most of the studies focused on UAV remote sensing’s technical aspects, such as data processing and remote sensing inversion, with little attention on answering ecological questions. There were 61% of studies involved community-scale research. RGB and multispectral cameras were the most used sensors (75%). More ecologically meaningful parameters can be extracted from UAV data to better understand the canopy surface irregularity and community heterogeneity, identify geometrical characteristics of canopy gaps and construct canopy chemical assemblies from living vegetation volumes. More cooperation between plant ecologists and remote sensing experts is needed to promote UAV remote sensing in advancing plant ecology research.

Gap and stand structural characteristics in a managed and an unmanaged old-growth oriental beech (Fagus orientalisLipsky) forest

AbstractSimplified forest structures following even-age management have been associated with the loss of biodiversity, which may be avoided through disturbance-inspired silviculture. Here, we ask how much do gap characteristics in a managed old-growth differ from those in unmanaged old-growth subject only to natural dynamics? In this study, we compared important characteristics of gaps (e.g. canopy gap fraction, distribution of gap sizes) and gapmakers (e.g. size classes, frequency, decay classes) between a managed and an adjacent unmanaged old-growth Oriental beech (Fagus orientalis Lipsky) compartment in the Keladarsht region of northern Iran 10 years after a single harvest entry using single-tree selection. Canopy openings >100 m2 with visible remnants of gapmakers (i.e. stumps) were included in this study. Gap characteristics of both compartments were within typical ranges for old-growth beech. Nonetheless, small but potentially important differences between the two areas were observed. In the managed compartment, harvesting poor quality trees with structural defects and typical diameters at breast height >52.5 cm plus natural mortality resulted in 102 canopy gaps (1–6 gapmakers, averaging 3.5 gaps/ha, gap fraction 9.8 per cent) compared with 59 natural canopy gaps (1–7 gapmakers, averaging 2.6 gaps/ha, gap fraction 13.7 per cent) in the unmanaged compartment. In both compartments, medium-sized gaps (200–500 m2) were most prevalent. In the managed compartment, 60 per cent of gapmakers were large or very large (typically cut) compared with 39 per cent in the unmanaged compartment where large trees typically snapped and became snags. Uprooting, particularly of small and medium sized gapmakers, was less common in the managed than the unmanaged compartment. Our results indicate that even one single-tree selection harvest may lead to a short-term divergence in stand structure compared with the unmanaged forest. While such managed forests may no longer be considered as old-growth, divergences in canopy gap characteristics indicate that a more nuanced harvesting scheme that includes cutting some larger gaps may more closely mimic the canopy dynamics of this old-growth forest.

Regeneration growth and crown architecture of European beech and silver fir depend on gap characteristics and light gradient in the mixed montane old-growth stands

Light is a vital factor affecting tree growth, survival and reproduction. In forests, natural and anthropogenic disturbances are the main drivers of abrupt changes in environmental conditions, including solar irradiance. We examined interspecific differences in the responses of European beech and silver fir to canopy gap characteristics and positions within gaps across various life stages (small seedlings, tall seedlings and saplings) in old-growth stands in Świętokrzyski National Park, Central Poland. Additionally, we analyzed sapling architectural responses to light. Regeneration densities were strongly affected by gap characteristics. The largest interspecific differences in responses to gap characteristics were found for small seedlings, which indicated their different preferences not only for light conditions created within gaps, but also toward various microsites distributed on a fine-scale after gap creation. Small beech seedlings responded only to the position within the gap, but small fir seedlings reacted in a more complex way, including such variables as gap size, shape and distance from a gap border. Gap size and the distance from its border had the most noticeable positive effect on tall seedlings and saplings, indicating that successful transition of regeneration to taller life stages may be possible only in larger gaps and in places further from a canopy border. Light conditions did not affect sapling length to diameter ratio. However, both direct and diffuse light had a negative effect on beech and fir crown area and length. Fir had wider but shorter crowns compared with beech in the whole light spectrum. This result indicates that these two species might have contrasting strategies regarding light interception, with fir being better adapted to increase a crown laterally, and with beech either being more tolerant to self-shading than fir or able to keep a favorable spatial leaf arrangement to avoid self-shading. Beech had the highest height growth increments in low levels of direct light, but its height growth was positively affected by diffuse light. Fir height growth rates showed no response to direct light, but were highest in medium levels of diffuse light. No effect of light on beech height to lateral growth rate ratio was found. The effect of direct light on this parameter for fir was negative, and nonlinear in the case of diffuse light, with the highest ratios observed in medium light levels. Our results stress the need of using both direct and diffuse light when analyzing light effects on sapling architecture.

Canopy gap characteristics and spatial patterns in a subtropical forest of South China after ice storm damage

The divergent gap characteristics and spatial patterns of canopy gaps created by natural or artificial disturbances can exert a dominant influence on forest structure and composition. However, little research has been conducted on the effects of ice storm damage on canopy gaps in subtropical mature forests of South China. In this study, one semi-natural site was dominated by a broad-leaf forest and two managed sites were representative of plantations with coniferous forests. Based on airborne laser scanning data and field evidence across sites, statistical analyses were used to examine gap characteristics following ice storms of moderate severity. Generalized Ripley’s K-function analysis was applied to test gap spatial patterns at a range of scales, and spatial point pattern analysis was used to quantitate the relative importance of specific influences on patterns of gap occurrence. The results revealed that the average gap size was 75.7 m2 and that 12.2 gaps occurred per hectare. Most gaps were single-tree fall events. In addition to more gaps, the mean gap size was smaller and the shape was more complex in the semi-natural site than in two managed sites. Large differences in gap characteristics were observed among snapped, uprooted, snag, and artificial gap damage types. Gaps generally showed a clustered distribution at large scales (e.g. 70m), whereas spatial patterns varied with gap damage types at different sites. The occurrence of gaps was strongly related to slope and topographic position at the semi-natural site, whereas slope, stem density, and human accessibility (proximity to pathways) were the most important factors affecting gap occurrence at the managed sites. We suggest that gap-based silvicultural treatments and natural disturbances regimes conjoin, highlighting interactions with other factors such as microsite conditions, non-tree vegetation and more.

Canopy gaps characteristics of pure and mixed stands in the Hyrcanian forests of north Iran

Canopy gaps play an important role in forest ecology helping to preserve biodiversity, influence nutrient cycles, maintain the complex stand structure, and also they substantially contribute to regeneration of forests. To survey the characteristics of canopy gaps in the Hyrcanian forests of Iran, three main old-growth and intact stands were studied. For each canopy gap, two parameters were measured: the length (L) as the longest distance within the gap and the width (W) as the largest distance perpendicular to the length. The gap maker (DBH≥20 cm) was considered to be a tree from the upper tree layer whose death caused an opening in the canopy. A total of 89 canopy gaps were studied in three old-growth stands (48 gaps in hornbeam-ironwood, 21 in hornbeam, and 19 in beech-hornbeam stands). The given canopy gaps cover 5.4% of the land area with an average of eight gaps per hectare. The mean size of the canopy gaps were 291, 353 and 565m 2 for hornbeam-ironwood, hornbeam, and beech-hornbeam stands, respectively. Frequency distribution of the gap sizes the mentioned three forest stands showed a lognormal distribution. The number of gap makers ranged from one to eight with a median of 4.5. Amongst the studied 261 gap makers in all canopy gaps, 61.2% belonged to hornbeam-ironwood stand. Also, there were canopy gaps formed by one to four gap makers within the three forest types, while gaps formed by five, six and eight gap makers were only observed within hornbeam stand. The results showed that the characteristics of the canopy gaps were different in terms of the composition, complexly of structure, environmental characteristics, size, number and species of gap makers in different forests. As a whole, hornbeam-ironwood stands present in lower altitudes, are more susceptible to wind-throw and create smaller gaps but more gap makers.

Distinct characteristics of canopy gaps in the subtropical mangroves of Moreton Bay, Australia

Mangroves often form extensive closed forests characterised by the occurrence of canopy gaps consisting of a group of standing dead trees. This article describes the physical characteristics, micro-environmental changes and the regrowth pattern of the naturally created unique circular canopy gaps in the subtropical Avicennia marina mangroves of Moreton Bay, Southeast Queensland, Australia. A survey on 52 canopy gaps was carried out to quantify the size and shape of canopy openings. We found that gap size ranged from a minimum area of 27 m2 to a maximum area of 474 m2 with an average (±standard deviation) of 134 ± 102 m2. All of the gaps surveyed were circular in shape with the eccentricity of length and width between 0.7 and 1.3. Once a canopy gap is created, the forest physical and biological processes are altered compared with the surrounding forest, such as in an increase in the potential photosynthetic active radiation (PPAR) and canopy openness, and a decrease in leaf area index (LAI). We found that canopy openings also had a significant effect on sediment pore water temperature but not on salinity and pH. The sudden increase in the amount of light following canopy opening stimulated rapid growth of seedlings which were available for the opportunity to take the place of the dead trees. Gap Closure Index (GCI) is introduced to illustrate surveyed gaps in the context of vertical growth of seedlings to fill up gap space to reach the site maximal canopy height, thus demonstrating the phases of gap dynamics in the natural regeneration of the subtropical monospecific mangrove forest.

流域水文变化对胡杨荒漠河岸林林窗及形成木特征的影响

流域水文变化对胡杨荒漠河岸林林窗及形成木特征的影响

Determinants of canopy gap characteristics in rehabilitating coastal dune forests

AbstractQuestionsWhat drives canopy gap formation in regenerating coastal dune forest? Does canopy gap size frequency distribution differ between new and old‐growth forests? Can canopy gaps divert regenerating trajectories?LocationRehabilitating coastal dune forest, KwaZulu‐Natal, South Africa.MethodsWe mapped canopy gaps in regenerating dune forest patches of varying age, which develop after seeding of the pioneer Vachellia kosiensis, and a reference forest by means of unsupervised classification of multi‐spectral satellite images. We tested if gap formation can be explained by abiotic (exposure to winds) and/or biotic (tree density at early stages) variables. We calculated the scaling exponent of a power‐law model to quantify if gap size frequency differed between new and old‐growth forests. Finally, we measured canopy openness, tree height and number of stems to validate canopy gap classification and assess the consequences of canopy gaps on regenerating trajectories.ResultsExposure to winds and tree density at early stages were both significant predictors of gap presence. Gaps were more likely to be present along dune ridges and areas with low tree density than valleys and areas with high tree density at early stages. Large gaps were common in both new and old‐growth forests. The scaling exponent was positively related to regeneration age, indicating a reduction in gap size as the forest aged. Areas with open canopies had shorter individual trees that were more likely to be multi‐stemmed than areas with closed canopies.ConclusionCanopy gaps are an important component of new and old‐growth coastal dune forests dynamics. Although gaps are filled during forest development, changes in individual life‐history strategies and morphology may alter regeneration trajectories. However, because their effect is partly controlled by the exposure to wind and tree density at early stages, it can also be manipulated by management to ensure nucleation, which could accelerate forest recovery.

Simultaneous influence of canopy decline and deer herbivory on regeneration in a conifer–broadleaf forest

Understanding how forests respond to multiple disturbances is becoming increasingly important under global change. We examined the simultaneous influence of canopy decline and deer browsing on regeneration in an old-growth reserve and surrounding managed forest dominated by Fagus sylvatica L. and Abies alba Mill. in Slovenia. We quantified both disturbance processes by measuring characteristics of canopy gaps and reconstructing historical deer densities. Forest response was assessed with repeated measurements of tree regeneration and regeneration patterns within deer exclosures. Most gaps were formed by mortality of A. alba (71%), and gapmaker characteristics suggest that gaps formed slowly and often expanded, resulting in a mosaic of openings covering 17% of the old-growth reserve. Fagus sylvatica dominated the regeneration layer throughout the reserve and recruited to taller height classes over the past 26 years. The recruitment failure of preferred browse species (A. alba and Acer pseudoplatanus L.) in the reserve and the successful recruitment of these species within exclosures indicate that selective browsing by deer has altered the successional response to A. alba decline, facilitating the dominance of F. sylvatica. Given that global change may increase forest decline worldwide and the ubiquitous nature of deer browsing in many temperate forests, understanding their combined effects on forests will become increasingly important.

Gap Dynamics and Structure of Two Old-Growth Beech Forest Remnants in Slovenia

ContextDue to a long history of intensive forest exploitation, few European beech (Fagus sylvatica L.) old-growth forests have been preserved in Europe.Material and MethodsWe studied two beech forest reserves in southern Slovenia. We examined the structural characteristics of the two forest reserves based on data from sample plots and complete inventory obtained from four previous forest management plans. To gain a better understanding of disturbance dynamics, we used aerial imagery to study the characteristics of canopy gaps over an 11-year period in the Kopa forest reserve and a 20-year period in the Gorjanci forest reserve.ResultsThe results suggest that these forests are structurally heterogeneous over small spatial scales. Gap size analysis showed that gaps smaller than 500 m2 are the dominant driving force of stand development. The percentage of forest area in canopy gaps ranged from 3.2 to 4.5% in the Kopa forest reserve and from 9.1 to 10.6% in the Gorjanci forest reserve. These forests exhibit relatively high annual rates of coverage by newly established (0.15 and 0.25%) and closed (0.08 and 0.16%) canopy gaps. New gap formation is dependant on senescent trees located throughout the reserve.ConclusionWe conclude that these stands are not even-sized, but rather unevenly structured. This is due to the fact that the disturbance regime is characterized by low intensity, small-scale disturbances.

Canopy Gap Characteristics and Disturbance Dynamics in Old-GrowthPicea abiesStands in Northern Fennoscandia: Is the Forest in Quasi-Equilibrium?

Emulating natural disturbances in managed forests has been suggested as a potential solution to maintain habitat conditions similar to those observed in old-growth forests. We examined the gap attributes and disturbance history of old-growth Picea abies-dominated stands in the northern boreal vegetation zone of the Pallas-Yllästunturi National Park in northwestern Finland to evaluate the influence of gaps on forest dynamics and the temporal patterns of gap creation. Six stands located at two sites were sampled along 400-m-long linear transects so that all intersected gaps were measured and dated. The average proportion of the forest area in the gaps was 43.1% ± 7.5%. An average gap size was estimated to be 221 m2 ± 198 m2, whereas the median gap size was 170.2 m2. While only 20% of the gaps were smaller than 100 m2, nearly 85% of them were smaller than 300 m2. Gap creation was constant with no distinct peaks from 1965 to 2005. Thus, forest dynamics were driven by continuous small-scale disturbances and were characterized by quasi-equilibrium structure. However, the results of the growth release analysis indicated that more severe disturbance(s) may have occurred almost two centuries ago. Emulating this type of forest dynamics would imply selective or group harvesting of trees as the predominant methods, but larger-scale, more intensive cuttings could also be carried out periodically.

Gap characteristics and their effects on regeneration, dominance and early growth of woody species

Aims We aim to examine the canopy gap characteristics and evaluate their influence on regeneration, dominance and the early growth of woody species in seasonally dry Shorea robusta forests (Sal forests).

Woody regeneration in and around aging southern bottomland hardwood forest gaps: Effects of herbivory and gap size

We examined long-term impacts of mammalian herbivores and canopy gap characteristics on woody plant establishment and growth within six size classes of canopy gaps created in 1994 in a southern bottomland hardwood forest. Woody stem composition (1996, 2004) and height (2004) were assessed in and out of white-tailed deer ( Odocoileus virginianus) and swamp rabbit ( Sylvilagus aquaticus aquaticus) exclosures in gap centers, and in additional plots in gap centers, edges, and beneath adjacent forest canopy. Herbivory did not influence vegetation patterns. Composition was more homogenous in 1996 than in 2004, both in gap centers, and along the gap center—forest understory gradient. Composition differed among gap sizes (oaks were more prevalent in larger gaps) and with distance from gap centers (wind-dispersed trees, wind- and animal-dispersed trees, and oaks typified gap centers, gap edges, and forest understory, respectively). Seedlings and saplings were tallest in the smallest gaps and gap centers, intermediate on gap edges, and shortest in the forest. Maintaining low deer densities could continue to minimize mammalian herbivore effects on woody regeneration in this bottomland hardwood forest system. In addition, management for canopy openings in a variety of sizes could promote woody vegetation heterogeneity and regeneration of desirable tree species.

CHARACTERISTICS OF CANOPY GAP DISTURBANCE IN WOLONG NATURE RESERVE

Canopy gap disturbances are important processes that maintain forest structure and diversity. We investigated the distribution and characteristics of canopy gaps in Wolong Nature Reserve around Wuyipeng, Sichuan. The results showed that small-scale gaps were the predominant types of disturbance. The average gap density was 12.5 km -1 . The distribution pattern of gaps was aggregated on south facing slopes and was approximately homogeneous on north facing slopes. Conifer trees were the primary gap-makers in this forest that was dominated by Abies faxoniana, Tsuga chinensis, Betula utilis, both in abundance and diameter rank. The decay class distribution of gap-makers indicated that the mode of gap formation and gap-maker species changed with age of the forest; the contribution of conifer species to gap formation decreased with time and broadleaf species increased. Moreover, the proportion of gaps caused by cutting and tree falls decreased while the proportion caused by standing dead and broken trunks increased. Association analysis of the mode of gap formation showed that there were significant negative associations between trees that were cut and tree falls and between snapped trunks and tree falls. Association coefficients for trees that were cut were relatively high with all other modes of gap formation, but there were no other significant associations between other modes of gap formation.

Canopy gap characteristics and their implications for management in the temperate rainforests of southeast Alaska

In the coastal temperate rainforests of southeast Alaska, much progress has been made in describing landscape-level natural disturbances and formulating management systems that emulate those disturbances. Little is known, however, concerning canopy gaps, the dominant form of natural disturbance in the region. During June–August, 1991–1993, we characterized canopy gap patterns and dynamics at three sites in the western hemlock/blueberry/shield fern plant association in the northern portion of the Tongass National Forest. Forest area in canopy gaps ranged from 5.8 to 12.6% and averaged 8.7%. The proportion of forest area in expanded gaps ranged from 18.1 to 43.9% and averaged 27.4%. Gap and gapmaker (tree whose death or crown displacement results in the creation or expansion of a canopy gap) characteristics were generally similar among sites. The majority of canopy gaps were <50 m 2 in area, had a D/ H ratio <0.50, were created from the death of one or two gapmakers, and had experienced gap expansion. The majority of expanded gap areas were <200 m 2. Gapmakers were usually snapped, had recently died (<20 years ago), and tended to be larger in diameter than surrounding overstory trees. Species composition of gapmakers was similar to surrounding overstory trees. A substantial amount of gap infilling takes place between 20 and 80 years following tree death, but gaps, or portions of gaps, can persist for >80 years. Forest turnover time was estimated to range from 230 to 920 years, and average 575 years. Canopy residence time was estimated to range between 210 and 840 years, and averaged 525 years. To emulate canopy gap dynamics in the plant association studied, forest managers should: (1) maintain a small proportion of a stand in openings within an otherwise undisturbed canopy; (2) use a combination of single tree selection and small group selection systems; (3) re-enter stands every 20–80 years; (4) select larger than average diameter crop trees in proportion to the species composition of the stand; (5) minimize soil disturbance and (6) select crop trees during re-entry so that the creation of new gaps and the expansion of old gaps is accomplished in approximately equal proportions.

Canopy gap characteristics and its influence on the regeneration of broad-leaved Korean pine forests in Changbai Mountain

With the concern of regeneration, characteristics of canopy gaps in broad-leaved Korean pine forest were studied. The areas of actual gap, expanded gap and maximum gap were analyzed respectively. The species composition, number, origin, decayed class and sizes of gap makers were studied comprehensively. The comparative studies of regeneration inside and outside of canopy gap showed that the density of regeneration inside canopy gaps was 30% higher than that outside canopy gaps. The specific species regeneration response to canopy gap varied greatly.Pinus koraiensis, Picea jezoensis Fraxinus mandshurica, Juglans mandshurica andAcer mono generally did not response to canopy gap disturbance. The Regeneration Importanice Value (RIV) ofAbies nephrolepis, Ulmus Japonica increased with canopy gap disturbance. RIV ofTilia amurensis, Acer madshurica and Ulmus laciniata decreased with canopy gap disturbance. Canopy gap disturbance was not strong enough to result in the regeneration of some species of shade intolerance such asLarix olgensis, Betula platyphylla.

Canopy Gap Characteristics and Tree Replacement in the Southeastern Boreal Forest

This study identifies patterns in the gap disturbance regime along a successional gradient in the southern boreal forest and uses this information to investigate canopy composition changes. Gaps were characterized in hardwood, mixed-forest, and conifer stands surrounding Lake Duparquet in northwestern Quebec. From 39 to 80 gaps were evaluated along transects established in each of these stands. The abundance of gap makers and gap fillers and total regeneration was evaluated by species, as well as the size of each gap encountered along the transects. The percentage of the forest in canopy gap was calculated directly from the proportion of the transect in gap and by using gap area and line-intercept techniques. Changes in composition were evaluated from gap-maker and gap-filler distributions and by using transition matrices based on species mortality and regeneration in canopy gaps. The percentage of the forest in canopy gap ranges from 7.1% in a 50-yr-old forest dominated primarily by aspen to 40.4% in a 234-yr-old fir-dominated forest. Gap events are due to individual or small-group tree mortality in the early successional forest but become species-specific events controlled by spruce budworm outbreaks in the later stages of succession. Due to the high latitude, direct light only reaches the forest floor in the very largest gaps of the conifer-dominated stands. However, these gaps form slowly as budworm-caused mortality occurs over a number of years, whereas in aspen-dominated stands gaps are formed quickly by the snapping of tree stems. Balsam fir is the most abundant gap-filling species; however, its abundance is negatively correlated to gap size in all stand types. Markovian transition matrices suggest that in the young aspen-dominated forests small gaps lead to species replacment by more shade-tolerant conifers but that in the oldest forests the larger gaps will result in maintenance of the intolerant species and an increase in the abundance of cedar.

Filling the Gaps: Remote Sensing Meets Woodland Ecology

Natural disturbance has considerable ecological significance, and within woodlands tree-falls significantly change environmental conditions. The spatial characteristics of canopy gaps influence regeneration dynamics, and species diversity and distribution. In this study imagery from a Compact Airborne Spectrographic Imager (CASI) was analysed to produce a vegetation cover map for a range of types of deciduous woodlands. This map was used to delineate canopy gaps in these areas. A raster-based GIS was used to derive a range of measures to describe he spatial characteristics of canopy gaps, in order to infer the relative ecological status of different types of deciduous woodland. For the study sites, spatial characteristics have been used to derive information on: (1) gap creation mechanisms: large gaps are created by progressive enlargement rather than instantaneously by a catastrophic event; (2) regeneration dynamics: