Forest Canopy Gaps Research Articles

Diurnal variations and gap effects of soil CO2, N2O and CH4 fluxes in a typical tropical montane rainforest in Hainan Island, China

AbstractAccurate estimations of soil greenhouse gas (GHG) fluxes in tropical montane rainforests are critical for assessing the role of tropical forests in influencing global climate change. This research aimed to determine the diurnal variation in soil GHG fluxes and understand the effects of forest canopy gaps on GHG fluxes, and their major controlling factors. The diurnal fluxes of soil carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) inside and outside three forest canopy gaps in a tropical montane rainforest were measured with a closed static chamber system in June 2015. The main results are as follows. (1) There was an obvious single‐peak daily variation of soil GHG fluxes. (2) The averaged soil CO2, N2O and CH4 fluxes of the whole day were closest to the daily average emission fluxes at 9:00 and 12:00 for CO2, 6:00 and 9:00 for N2O, and 9:00 and 12:00 for CH4, respectively. (3) Soil CO2 and N2O emissions (positive values) and CH4 uptake (negative values) were higher inside gaps than outside. (4) There were stronger exponential relationships between soil CO2 and N2O emissions and temperature inside gaps than outside, and there was a stronger quadratic relationship between CH4 uptake and temperature outside gaps than inside. However, significant relationships between soil CO2 (or CH4) and soil moisture only occurred inside gaps (P < 0.01). There were clear diurnal variations and significant effects of gaps on soil CO2, N2O and CH4 fluxes. Our study indicated that understanding the different diurnal variations of soil CO2, N2O and CH4 fluxes inside and outside canopy gaps could improve the accurate evaluation of soil GHG fluxes in tropical montane rainforests under a changing climate.

Episodic Canopy Structural Transformations and Biological Invasion in a Hawaiian Forest.

The remaining native forests on the Hawaiian Islands have been recognized as threatened by changing climate, increasing insect outbreak, new deadly pathogens, and growing populations of canopy structure-altering invasive species. The objective of this study was to assess long-term, net changes to upper canopy structure in sub-montane forests on the eastern slope of Mauna Kea volcano, Hawai‘i, in the context of continuing climate events, insect outbreaks, and biological invasion. We used high-resolution multi-temporal Light Detection and Ranging (LiDAR) data to quantify near-decadal net changes in forest canopy height and gap distributions at a critical transition between alien invaded lowland and native sub-montane forest at the end of a recent drought and host-specific insect (Scotorythra paludicola) outbreak. We found that sub-montane forests have experienced a net loss in average canopy height, and therefore structure and aboveground carbon stock. Additionally, where invasive alien tree species co-dominate with native trees, the upper canopy structure became more homogeneous. Tracking the loss of forest canopy height and spatial variation with airborne LiDAR is a cost-effective way to monitor forest canopy health, and to track and quantify ecological impacts of invasive species through space and time.

Throughfall quantity and carbon input beneath canopy gaps of varying size in degraded tropical peatland forest of West Kalimantan, Indonesia

Astiani D, Curran Lm, Mujiman, Salim R. 2017. Throughfall quantity and carbon input beneath canopy gaps of varying size in degraded tropical peatland forest of West Kalimantan, Indonesia. Biodiversitas 18: 1258-1264. Tropical peatland forest ecology, is mostly determined by peatland hydrological conditions. However, deforestation, forest degradation, or any other environmental disturbance can transform hydrological patterns and processes for peatland water movement, and thus alter carbon flow via water in this type of ecosystem. These changes arise from alteration in the quantity of throughfall (water that falls through plant canopies), in its interception, and in its evaporation to the atmosphere from vegetation surfaces. We have investigated the effects of a gradient of forest degradation levels, represented by canopy gaps (open, intermediate and closed), on throughfall quantity to the peatland forest floor. Nine plots, 50m x 50m in size, were stratified into the three forest canopy gap classes. Nine bucket collectors were used for throughfall, and tipping bucket rain gauges were set up for precipitation monitoring. Results show that annual precipitation in the area was 3,168.8 ± 111.3 mm, with a mean monthly rainfall of 264.0 ± 15.3 mm. Throughfall monitoring demonstrated that closed canopies transferred significantly more water as throughfall than intermediate or open canopies, due to differences in their effect on water movement through the canopies. The proportion of precipitation that passed through the canopies to the forest floor as throughfall was measured to be 76.5%, 77.3% and 89.4 %, or 202, 204 and 236 mm per month, respectively for open, intermediate, and closed canopies. It was found that higher levels of canopy cover resulted in significantly higher amounts of total organic carbon (TOC) content per unit of throughfall; specifically, 2.5 2.8 and 3.4 mg L-1 respectively for the open, intermediate, and closed canopies. When coupled with the higher quantity of throughfall in the closed canopy, the higher concentration of carbon results in a greater amount of carbon brought to the peatland forest floor by the throughfall pathway. This could also have impacts for other nutrients in the peatland soil.

Xylobolus subpileatus, a specialized basidiomycete functionally linked to old canopy gaps

Documenting succession in forest canopy gaps provides insights into the ecological processes governing the temporal dynamics of species within communities. We analyzed the fruiting patterns of a rare but widely distributed saproxylic macromycete, Xylobolus subpileatus, during the ageing of natural canopy gaps in oak forests. In one of the last remaining Quercus ilex L. old-growth forests (on the island of Corsica, western Mediterranean basin), we systematically recorded and conducted molecular analyses of X. subpileatus basidiomes in 80 dated natural canopy gaps representing a 45-year long sequence of residence time of tree logs on the forest floor. Xylobolus subpileatus fruited exclusively on Q. ilex logs. The probability of fruiting of X. subpileatus significantly increases during the process of wood decomposition to reach its maximum in the oldest gaps, approximately 40 years after treefall. In contrast, the abundance and the richness of saprobic and ectomycorrhizal fruitbodies decrease as canopy gaps age. Our results emphasize the high ecological specialization of X. subpileatus. They also highlight the imperative need to conserve the last patches of old-growth Mediterranean forests to secure the persistence of this endangered and functionally unique macromycete whose presence is highly dependent on old wood in advanced stages of decomposition.

Insect herbivores increase mortality and reduce tree seedling growth of some species in temperate forest canopy gaps.

Insect herbivores help maintain forest diversity through selective predation on seedlings of vulnerable tree species. Although the role of natural enemies has been well-studied in tropical systems, relatively few studies have experimentally manipulated insect abundance in temperate forests and tracked impacts over multiple years. We conducted a three-year experiment (2012–2014) deterring insect herbivores from seedlings in new treefall gaps in deciduous hardwood forests in Maryland. During this study, we tracked recruitment of all tree seedlings, as well as survivorship and growth of 889 individual seedlings from five tree species: Acer rubrum, Fagus grandifolia, Fraxinus spp., Liriodendron tulipifera, and Liquidambar styraciflua. Insect herbivores had little effect on recruitment of any tree species, although there was a weak indication that recruitment of A. rubrum was higher in the presence of herbivores. Insect herbivores reduced survivorship of L. tulipifera, but had no significant effects on A. rubrum, Fraxinus spp., F. grandifolia, or L. styraciflua. Additionally, insects reduced growth rates of early pioneer species A. rubrum, L. tulipifera, and L. styraciflua, but had little effect on more shade-tolerant species F. grandifolia and Fraxinus spp. Overall, by negatively impacting growth and survivorship of early pioneer species, forest insects may play an important but relatively cryptic role in forest gap dynamics, with potentially interesting impacts on the overall maintenance of diversity.

Woody plant invasions and restoration in forests of island ecosystems: lessons from Robinson Crusoe Island, Chile

Islands are susceptible to exotic plant invasion, and Robinson Crusoe Island (RCI), Juan Fernandez Archipelago (33°S, 78°7′W, Chile) is no exception. Through a literature review, we assessed plant invasion and compared it to other oceanic islands worldwide. Here, we discuss measures to enhance forest recovery on RCI based on knowledge accumulated from studies on RCI and other islands. Although these findings are designed to halt the progress of invasion on RCI, they could also be applied to other insular ecosystems. We addressed the following questions: (1) What is the plant invasion status on RCI in relation to other islands worldwide? (2) How imminent is biodiversity loss by plant invasion on RCI? (3) How is woody plant invasion taking place on RCI? (4) What methods are effective in controlling invasive woody species on islands worldwide? (5) What is the ability of natural forests to recover after controlling invasive plants on RCI? We found that (1) RCI is globally the fourth most invaded island for woody species. (2) Invasive woody species expansion is estimated at 4.3 ha annually. (3) Some invasive species establish under forest canopy gaps, out-competing native species. (4) Control of invasive plant species should focus on small gaps, and restoration should promote plant cover and soil protection. Mechanical and chemical control of invasive species seemed to be insufficient to prevent biodiversity loss. Developing alternatives like biological control are indispensable on RCI. (5) Six years after invasive species control, floristic composition tended to recover.

Natural Regeneration in a Multi-Layered Pinus sylvestris-Picea abies Forest after Target Diameter Harvest and Soil Scarification

Forest management in Sweden can be characterized by even-aged silviculture heavily relying on three established harvest regimes: clearcutting, the seed-tree method, and the shelterwood system. Less intense, small-scale retention harvest systems such as single tree and group selection harvest are rarely used. In addition, natural regeneration dynamics without enrichment planting have barely been studied. Consequently, this study examined natural regeneration establishment in a multi-layered Pinus sylvestris-Picea abies forest stand in southwest Sweden after target diameter harvesting and soil scarification. The creation of forest canopy gaps had a positive effect on total seedling density five years after harvest, mainly due to a significantly higher number of Betula pendula individuals. Seedling density of more desirable tree species suitable for continuous cover forestry such as Fagus sylvatica, Quercus petraea and Picea abies also increased substantially in gaps when compared to pre-harvest conditions or the unharvested plots. In contrast, soil scarification did not increase the number of seedlings of desired tree species due to a significant decrease in Picea abies abundance. Soil moisture and gap size significantly improved Betula pendula seedling establishment while a larger number of Quercus petraea seedlings were observed in Vaccinium myrtillus patches. We conclude that canopy gaps are beneficial under the encountered stand conditions to initiate forest regeneration, and that soil scarification without the timely occurrence of a mast year of desired tree species is not effective in the type of forest studied.

Gap Shape Classification using Landscape Indices and Multivariate Statistics

This study proposed a novel methodology to classify the shape of gaps using landscape indices and multivariate statistics. Patch-level indices were used to collect the qualified shape and spatial configuration characteristics for canopy gaps in the Lienhuachih Experimental Forest in Taiwan in 1998 and 2002. Non-hierarchical cluster analysis was used to assess the optimal number of gap clusters and canonical discriminant analysis was used to generate the discriminant functions for canopy gap classification. The gaps for the two periods were optimally classified into three categories. In general, gap type 1 had a more complex shape, gap type 2 was more elongated and gap type 3 had the largest gaps that were more regular in shape. The results were evaluated using Wilks’ lambda as satisfactory (p < 0.001). The agreement rate of confusion matrices exceeded 96%. Differences in gap characteristics between the classified gap types that were determined using a one-way ANOVA showed a statistical significance in all patch indices (p = 0.00), except for the Euclidean nearest neighbor distance (ENN) in 2002. Taken together, these results demonstrated the feasibility and applicability of the proposed methodology to classify the shape of a gap.

EVALUATION OF FOREST CANOPY AND UNDERSTORY GAP FRACTION DERIVED FROM TERRESTRIAL LASER SCANNING

The quantification of forest carbon sequestration is helpful to understand the carbon storage on the Earth. The estimation of forest carbon sequestration can be achieved by the use of leaf area index (LAI), which is derived from forest gap fraction. The hemispherical image-based technique is the most popular non-destructive means for obtaining such information. However, only the gap fraction of the top canopy is derived due to the limitation of imaging technique. The gap fraction information of understory is thus neglected. In this study, we evaluate the use of a terrestrial laser scanner (TLS) to obtain the forest canopy and understory gap fraction. The forest TLS data were manually classified as the top canopy and understory layers to facilitate the estimation of top canopy and understory gap fraction, respectively.

EVALUATION OF FOREST CANOPY AND UNDERSTORY GAP FRACTION DERIVED FROM TERRESTRIAL LASER SCANNING

Abstract. The quantification of forest carbon sequestration is helpful to understand the carbon storage on the Earth. The estimation of forest carbon sequestration can be achieved by the use of leaf area index (LAI), which is derived from forest gap fraction. The hemispherical image-based technique is the most popular non-destructive means for obtaining such information. However, only the gap fraction of the top canopy is derived due to the limitation of imaging technique. The gap fraction information of understory is thus neglected. In this study, we evaluate the use of a terrestrial laser scanner (TLS) to obtain the forest canopy and understory gap fraction. The forest TLS data were manually classified as the top canopy and understory layers to facilitate the estimation of top canopy and understory gap fraction, respectively.

The gas exchange performance of the European blackberry (Rubus fruticosus agg.) and ecological traits for interpreting colonization in forest canopy gaps

Blackberry is a considerable weed in both antropogenous habitats and semi-natural vegetation, and this results in robust colonization in open sites. Our research investigated the carbon gain and water exchange performance of this species under ecologically contrasted forest gap conditions in temperate deciduous forests. We used a Kruskal–Wallis test to assess this species ecophysiological behaviour in response to the functional relevance of light environment, seasons and forest gap character. Our research also confirmed significant relationships between abundance, gap characteristics and light response measures. Light environment plays an essential role in the development of assimilation and water use efficiency. Seasonal variation affects transpiration, and forest type influences stomatal conductance. The amount of precipitation and canopy gap size is linked to the relative abundance of the species. These characteristics integrate with a nitrogen biomass trade-off across forest types. Measures of stomatal conductance and assimilation turned out to be the most significant functional variables including a gas exchange indicator for species abundance. Extended functional leaf phenology can promote successful colonization under adequate abiotic conditions. Our results conclude that environmental-related canopy gap size can be recommended for ecologically contrasted forest types, thus modulating the biomass production of the blackberry.

Canopy gaps do not help establish pioneer species in a South Florida dry forest

Abstract:Canopy gaps create a temporary spatial heterogeneity, often allowing pioneer species to establish and grow in mature forests. In this study, we asked whether the above model holds for tropical dry forests in the Florida Keys. Six hundred and forty-eight canopy gaps in an extensive Key Largo forest were identified with a LiDAR digital canopy model. The structure and composition of juvenile trees were examined in 45 selected gaps in three stands of known age, and weighted averaging calibration and regression were applied to the data to determine the successional age optimum for each tree species, and the inferred age for each gap based on its sapling composition. Less than 1% of the forest area was recorded as canopy gaps in the LiDAR model. The inferred stand ages were about 70 y greater in canopy gaps in young forest than in the surrounding, unimpacted forest. This suggested that gap formation advanced succession rather than reversing or resetting it. The apparent lack of recruitment by early-successional species may be due to the small size of canopy gaps in this forest, and the minimal contrast between gap and understorey environments; light and water conditions in the small gaps may favour late-successional rather than pioneer species. Establishment of pioneer species may not take place without intense, large-scale disturbances such as fires and hurricanes that remove the entire canopy and consume or erode soils.

The effect of treefall gaps on the understorey structure and composition of the tropical dry forest of Nizanda, Oaxaca, Mexico: implications for forest regeneration

Abstract:The role of canopy gaps in tropical dry forest (TDF) dynamics remains unclear. Here, 75 canopy gaps, mostly formed by the fall of Bursera spp. and Pachycereus pecten-aboriginum individuals, are described, and their potential consequences for forest regeneration are analysed in a Mexican TDF. In 50 randomly selected gaps, understorey vegetation was sampled with a paired design (inside and outside gaps) and by distinguishing two plant height categories. In total, 1940 plants were recorded (63% in gaps and 37% in non-gap plots). Community attributes (density, community cover, taxonomic richness and Shannon diversity) were significantly higher for both height categories in gap plots. Conversely, neither an NMDS ordination nor a multinomial classification of 187 species by habitat affinities revealed floristic segregation between gaps and non-gaps; almost all species were classified as habitat generalists, with only a few opportunistic forbs (but no single tree species) being classified as gap specialists. The most important effects of gap formation are significant increases in plant abundance and species richness, but not a different species composition. Against earlier views that gap-phase dynamics is inconsequential for TDF dynamics, these results suggest a more active, albeit modest, role of treefall gaps in TDF, through promoting an abundant establishment.

Das aktuelle Vegetationshöhenmodell der Schweiz: spezifische Anwendungen im Waldbereich

Current model of canopy heights in Switzerland: specific applications in forestry A national vegetation height model was calculated for Switzerland for the first time last year using digital aerial images. The ADS80 stereo aerial images, which were routinely gathered by the Swiss Federal Office of Topography (swisstopo), contain information about the height of vegetation in forests. We used the stereo aerial images to first calculate a digital surface model (DSM) with a very high spatial resolution (1 × 1 m). The DSM was then normalized to obtain the actual vegetation heights using a digital terrain model (DTM) based on laser data with the buildings masked out, and to produce a vegetation height model (VHM). Such a model could be calculated in the framework of the Swiss National Forest Inventory (NFI) with consistent methods and a very high level of detail. For covering the whole of Switzerland, we used summer aerial images from the years 2007 to 2012. The VHM reached almost nationwide coverage (98% of the country's surface area). Some areas, such as steep mountainsides or very bright glaciers, were problematic for calculating the model, and appear in it as gaps. Vegetation height information collected with this method is most useful for analyzing entire forest stands, but the data do not have a high enough spatial resolution for single-tree-based analyses. The VHM can be applied in a wide variety of ways. Here, we describe three of these: 1) generating forest masks, 2) extracting forest canopy gaps, and 3) detecting changes in the stocking of a forested area.

Tree Species Establishment in Urban Forest in Relation to Vegetation Composition, Tree Canopy Gap Area and Soil Factors

The study of density and growth of pine, birch and oak seedlings and saplings in canopy gaps in the urban boreal forest in Riga, Latvia, indicates that natural regeneration can increase diversity in small gaps caused by tree mortality, and can ensure conversion from even-aged pine forest. Abundant regeneration in small gaps showed that light (gap area) was only one of the factors affecting tree regeneration in the gaps. The depth of the O layer and pH were suggested to be important factors for the establishment and growth of pine and birch. For oak, the main factors for establishment and growth were favorable moisture, higher pH and N concentration. Knowledge of ecological factors affecting the establishment of seedlings and growth of saplings of the most common trees species in the urban boreal forest is needed to predict successional trajectories and to aid management.

Long‐term fragmentation effects on the distribution and dynamics of canopy gaps in a tropical montane forest

Fragmentation alters forest canopy structure through various mechanisms, which in turn drive subsequent changes to biogeochemical processes and biological diversity. Using repeated airborne LiDAR (Light Detection and Ranging) mappings, we investigated the size distribution and dynamics of forest canopy gaps across a topical montane forest landscape in Hawaii naturally fragmented by lava &gt;100 yr ago. The combined effects of long‐term isolation were evaluated using edge‐proximity patterns in the distribution of gaps identified in year 1 (“existing gaps”). In addition, using the data from year 2, we investigated patterns in the loss of canopy (“new gaps”) and regrowth of canopy (“filled gaps”). The size distributions of the three gap types were modelled using the power‐law exponent, λ. We found that fragmentation has resulted in some large changes in gap dynamics, with both the total area of gaps and the relative proportion of large existing gaps increased with distance to fragment edge. In models of power‐law distribution scaling, λ estimates decreased to asymptotic values within 20 m of fragment edges for existing gaps. The size distributions of new and filled gaps were surprisingly similar. However, the total area of filled gaps was less than that of new gaps, and this difference was greatest near fragment edges. From these results, we conclude that fragmentation may be capable of continuously altering gap‐phase dynamics of a forest for more than a century.

Describing forest canopy gaps efficiently, accurately, and objectively: New prospects through the use of terrestrial laser scanning

Canopy gaps are an important ecological component in forested landscapes. One limitation to investigating gaps is the lack of efficient, accurate, and objective methods to characterize gap size and shape. This study aimed at investigating various methodologies to overcome this limitation. Six man-made canopy gaps were measured in a coniferous and a deciduous Stand (total of twelve) using a terrestrial laser scanner. Using the point clouds from these measurements, gap sizes were manually derived as a baseline to assess the accuracy of using fully automatic delineations of edge-lines for gap size calculations. Furthermore, we compared these results to those obtained from simulated conventional gap measurements that are based on assumptions regarding the gap shape (ellipse) or on a varying number of distance measurements (between gap center and Stand edge). Using the manual gap delineations as a reference, automatic delineations yielded slightly smaller gap sizes with a relative root mean square error between 3.4% and 5.3%, depending on gaps size. All simulated conventional approaches (with various numbers of measurements and shape assumptions) yielded larger errors. However, the gain in accuracy by increasing the sample size declined rapidly when more than 16 measurements were taken to describe the gap shape. To further the discussion about gap shape, we developed an approach to calculate the fractal dimension of the canopy gap edge-line from laser point clouds. Finally, we discuss other approaches to deepen our understanding of gap related processes in forests by means of a more detailed description of the three-dimensional gap shape.

Gap formation and susceptible Abies trees to windthrow in the forests of Odaesan National Park

Extremely strong winds and heavy rainfall caused canopy gaps in a mixed Abies holophylla broadleaf forest and a Quercus mongolica-dominated forest in Odaesan National Park, Korea in October 2006. The impact of the combination of strong winds and torrential rain on the development of forest gaps and canopy structures were investigated. The mean size of newly created gaps were 205 m2 in the mixed forest and 86 m2 in the Quercus forest, and were created by 2.8 and 1.4 gap-maker trees, respectively. Among the 73 trees lost in the mixed forest, 59% succumbed because of direct wind damage while 41% were struck by neighboring trees that fell into them. Most of these trees downed by wind were uprooted (74%), while the trees downed by neighboring tree falls snapped (78%). 21 trees in the Quercus forest died from direct wind dam¬age, and 57% of them were uprooted. Although the relative density of Abies nephrolepis and A. holophylla represented only 0.2% and 6.4%, respectively, of all species in the intact mixed forest, they accounted for 27% and 15%, respectively, of all trees affected by wind on that site. In fact, 85% of the total A. nephrolepis and 91% of the total A. holophylla in the mixed forest fell directly due to strong wind. By contrast, only one Abies species, A. nephrolepis, was found in the Quercus-dominated forest, and it accounted for 7.3% of the species composition. These findings suggest that A. nephrolepis and A. holophylla are particularly susceptible to high winds because of their great heights and shallow root systems.

Mapping the occurrence of Chromolaena odorata (L.) in subtropical forest gaps using environmental and remote sensing data

Globally, subtropical forests are rich in biodiversity. However, the native biodiversity in these forests is threatened by the presence of invasive species such as Chromolaena odorata (L.) King and Robinson, which thrives in forest canopy gaps. Our study explored the utility of WorldView-2 data, an 8-band high resolution (2 m) imagery for mapping the probability of C. odorata occurrence (presence/absence) in canopy gaps of a subtropical forest patch, the Dukuduku forest, South Africa. An integrated modelling approach involving the WorldView-2 vegetation indices and ancillary environmental data was also assessed. The results showed a higher performance of the environmental data only model (deviance or D 2 = 0.52, p < 0.05, n = 77) when compared to modelling with WorldView-2 vegetation indices such as the enhanced vegetation index, simple ratio indices and red edge normalized difference vegetation index (D 2 = 0.30, p < 0.05, n = 77). The integrated model explained the highest presence/absence variance of C. odorata (D 2 = 0.71, i.e. 71 %). This model was used to derive a probability map indicating the occurrence of invasive species in forest gaps. A 2 × 2 error matrix table and the receiver operating characteristic curve derived from an independent validation dataset (n = 38) were used to assess the model accuracy. Approximately 87 % of canopy gaps containing C. odorata were correctly predicted at probability threshold of 0.3. The derived probability map of C. odorata occurrence could assist management in prioritizing target areas for eradication of the species.

Gap pattern of the largest primeval beech forest of Europe revealed by remote sensing

Little is known about the gap pattern of primeval beech forests, since large‐scale studies with continuous coverage are lacking. Analyses of forest structural patterns have benefitted from advances in remote sensing, especially with the launch of satellites providing data of submetric ground resolution. These developments can strongly advance our knowledge of natural forest dynamics and disturbance regimes. The Uholka‐Shyrokyi Luh forest in the Ukrainian Carpathians, the largest remnant of primeval European beech (Fagus sylvatica L.) covering 102.8 km2, is an outstanding object to analyze the frequency distribution of gap sizes and to infer processes of forest dynamics. A stereo pair of very high‐resolution WorldView‐2 satellite images was used to characterize the forest's gap pattern. Canopy gaps were first digitized stereoscopically based on the image pair. In a second step, spectral properties in the red and yellow frequency bands were used to distinguish the stereoscopically mapped gap areas from non‐gap areas, which enabled gap mapping over the entire study area. To validate the spectral gap mapping 338 randomly distributed samples were assigned manually to gap and non‐gap areas based on the ortho‐images. We found excellent agreement except for an overestimation of gaps close to clouds due to diffuse image areas. The frequency distribution of gap size revealed the forest to be structured by a small‐scale mosaic of gaps mainly &lt;200 m2 (98% of the gaps). Only a few large, stand‐replacing events were detected, most probably caused by a wind storm in March 2007 and a heavy wet snow fall in October 2009. The small canopy gaps reflect fine‐scale processes shaping forest structure, i.e., the death of single trees or groups of a few trees and is in line with the findings of the terrestrial forest inventory. We conclude that remote sensing approaches based on very high‐resolution satellite images are highly useful to characterize even small‐scale forest disturbance regimes and to study long‐term gap dynamics. Stereo satellite images provide two viewing angles of the study area, thus allowing for a highly accurate mapping of canopy gaps in forests with a complex topography.