Competitive effects of herbaceous vegetation on tree seedling emergence,growth and survival: Does gap size matter?

Question: What is the effect of gap size on the seedling emergence, growth and survival of four common tree species in wooded pastures? Location: A pasture in the Jura mountains, Switzerland. Methods: Seeds were sown in a complete three‐way factorial design with eight blocks in May 2003. Each block consisted of a competition treatment (four gap sizes including zero) and a mowing treatment (mown and unmown). Emergence, survival and total biomass of tree seedlings of three species (Picea abies, Acer pseudoplatanus and Fagus sylvatica) were measured. A fourth species (Abies alba) failed to germinate. Results: Gaps had a positive influence on the early stages of tree development for all species. Larger gaps favoured growth and survival more than small gaps. Seedling growth was higher when vegetation around the openings was mown. Mowing the vegetation at gap size zero enhanced both growth and survival compared to unmown vegetation. Mown gaps larger than zero had increased seedling desiccation but decreased seedling predation. Species showed similar trends in their emergence and growth responses to gap size and mowing treatments but for Picea emergence rate was higher and survivorship was lower than for Acer and Fagus. Conclusions: Gap size does matter for tree seedling success but even in more favourable large gaps only a small percentage of seedlings emerged and survived. The effects of gaps on tree seedling establishment are complex as a result of interactions between biotic and abiotic changes caused by gaps.     

林窗对川西周公山柳杉人工林林下物种多样性的影响

采用典型样地法,以川西周公山柳杉人工林5种不同大小的林窗为研究对象,以林下非林窗为对照,研究了不同大小的林窗对柳杉人工林物种多样性的影响,同时分析了不同梯度林窗下林窗中心、林窗边缘、及林下群落的物种组成、物种多样性的变化情况。结果表明:(1)在所调查的18个样地231个样方中共记录到维管束植物141种,隶属于76科113属;随着林窗面积的增大,群落各层次的物种数呈现出先升高后降低的趋势,灌木层物种数在各林窗梯度上表现为林缘林下林窗中心,草本层物种数在各林窗梯度上表现为林缘林窗中心林下。(2)不同林窗优势种及其重要值不同,即在小林窗内,优势种为柳杉和野桐,其重要值之和高达0.292 3;在大林窗内,杉木及亮叶桦为群落优势物种,群落内出现大量其更新幼苗。(3)不同大小的林窗表现为灌木层物种丰富度指数(D)、Shannon-Wienner指数(H)、和Pielou均匀度指数(Jsw)值在400~450 m2面积的大林窗内达到一个均优水平,草本层物种的多样性在面积为100~150m2的小林窗内达到较高水平;不同梯度的林窗各层次群落D、H值整体表现为林缘林窗中心林下。研究认为:林窗的存在会改变群落物种组成,提高群落物种多样性水平,并且大林窗(400~450m2)更利于柳杉人工林林下树种更新及物种多样性的提高。     

Herbivore-induced expansion of generalist species as a driver of homogenization in post-disturbance plant communities

We used a controlled experiment to investigate how disturbance scale (canopy gap area) and herbivory influence post-disturbance plant community dynamics. Twenty canopy gaps were installed in a temperate hemlock-hardwood forest during the winter of 2002–2003: seven small gaps (50–150 m²), seven medium gaps (151–250 m²), and six large gaps (251–450 m²). Within each gap, we established 4–12 sample plots (depending on gap size); 1–3 of which were enclosed with wire mesh white-tailed deer (Odocoileus virginianus) exclosures in 2005. Gaps were revisited and intensively sampled in 2007. After five growing seasons, ground-layer plant communities in non-exclosed plots were more similar compositionally than exclosure plots. Non-exclosed plots in small and medium gaps were more similar to non-exclosed plots in large gaps than they were to exclosed plots in their respective gap size class. Shade-tolerant forbs and trees were less common outside exclosures, while generalist species associated with higher understory light levels and exotics were more prevalent outside exclosures. Our results suggest that even in forests with relatively low deer densities (6.5–9.3 deer km⁻²), white-tailed deer herbivory may influence the developmental trajectory of post-disturbance plant communities and be a mechanism for decreasing β-diversity along environmental gradients.     

Hyperspectral remote detection of niche partitioning among canopy trees driven by blowdown gap disturbances in the Central Amazon

Advanced recruitment and neutral processes play important roles in determining tree species composition in tropical forest canopy gaps, with few gaps experiencing clear secondary successional processes. However, most studies are limited to the relatively limited spatial scales provided by forest inventory plots, and investigations over the entire range of gap size are needed to better understand how ecological processes vary with tree mortality events. This study employed a landscape approach to test the hypothesis that tree species composition and forest structural attributes differ between large blowdown gaps and relatively undisturbed primary forest. Spectral mixture analysis on hyperspectral satellite imagery was employed to direct field sampling to widely distributed sites, and blowdown plots were compared with undisturbed primary forest plots. Tree species composition and forest structural attributes differed markedly between gap and non-gap sites, providing evidence of niche partitioning in response to disturbance across the region. Large gaps were dominated by classic Neotropical pioneer genera such as Cecropia and Vismia, and average tree size was significantly smaller. Mean wood density of trees recovering in large gaps (0.55 g cm⁻³) was significantly lower than in primary forest plots (0.71 g cm⁻³), a difference similar to that found when comparing less dynamic (i.e., tree recruitment, growth, and mortality) Central Amazon forests with more dynamic Western Amazon forests. Based on results, we hypothesize that the importance of neutral processes weaken, and niche processes strengthen, in determining community assembly along a gradient in gap size and tree mortality intensity. Over evolutionary time scales, pervasive dispersal among colonizers could result in the loss of tree diversity in the pioneer guild through competitive exclusion. Results also underscore the importance of considering disturbance processes across the landscape when addressing forest carbon balance.     

马尾松人工林林窗大小对四种凋落叶质量损失和养分释放的影响

马尾松人工林乔木层植物凋落物的分解对林地养分平衡和系统物质循环具有重要意义,并可能受不同大小林窗下微环境差异的影响。采用凋落物袋分解法,以马尾松(Pinus massoniana)人工林人为砍伐形成的7个不同大小林窗(G1:100 m~2、G2:225 m~2、G3:400 m~2、C4:625 m~2、G5:900 m~2、G6:1225m~2、G7:1600 m~2)为研究对象,林下(G0)为对照,研究林窗大小对红椿(Toona ciliata)、桢楠(Phoebe zhennan)、香樟(Cinnamomum camphora)和马尾松4种乡土树种凋落叶质量损失及养分释放的影响。结果显示:1)林窗大小(G0-G7)显著影响林窗中心放置的红椿和桢楠凋落叶N和P释放率、香樟凋落叶失重率和N、P、K释放率以及马尾松凋落叶P和K释放率。相对于林下,中小型林窗(G1-G4)的凋落叶失重率和N、P释放率明显较大,而大型林窗(G6-G7)的凋落叶K释放率明显较大。2)林窗内放置位置显著影响红椿、桢楠和马尾松凋落叶的K释放率及香樟凋落叶的P释放率。红椿和桢楠的凋落叶K释放率从林窗中心到边缘显著减少,而马尾松凋落叶K释放率及香樟P释放率从林窗中心到边缘显著增加。3)4种凋落叶类型中红椿凋落叶分解最快,其分解50%和95%所需时间分别为5.29和23.14个月。上述结果表明,林窗大小和林窗内位置对凋落物质量损失及其养分释放具有显著影响,但影响大小及趋势随物种初始基质质量的差异具有明显变化,研究结果为亚热带低山丘陵区马尾松人工低效林的科学经营及管理提高了一定的科学依据。     

Effects of Sward Height, Gap Size, and Slug Grazing on Emergence and Establishment of Trollius europaeus (Globeflower)

Abstract To determine the effects of sward height and gap size on the emergence and subsequent development of Trollius europaeus, seeds were introduced into artificially created gaps in mown and unmown wet meadow grassland in Ayr, Scotland. Emergence and establishment of nondormant seed (previously leached in running tap water and soaked in gibberellic acid) placed in a range of circular gaps (25 mm, 50 mm with and without root barrier, 100 and 200 mm diameter) were monitored over 305 days. Trollius demonstrated high field emergence (mean, 46% of viable seed sown) in this experiment. Emergence was not significantly affected by either sward height or gap size, although emergence was greater in mown swards. The critical factor determining subsequent survival of seedlings was slug predation rather than sward height or gap size. However, losses due to slug predation were significantly greater in unmown swards, resulting in more seedlings in mown swards. One hundred eleven days after sowing (September) seedling numbers had declined substantially in both unmown and mown swards, and by day 305 (April) seedlings were extinct in both sward types. The implications of the research for the restoration and management of T. europaeus are discussed.     

Forest development in canopy gaps in old-growth beech (Nothofagus) forests,New Zealand

Abstract. Tree size and age structures, treefall and canopy gap characteristics, and regeneration responses to treefalls were compared for three stands of old-growth beech (Nothofagus) forest dominated by N. fusca and N. menziesii on the South Island, New Zealand. Treefall gaps (up to 1000 m²) were most often caused by standing trees killed by drought and/or insect attack, or by trees snapped by wind. The causes of gap formation and the size and age distributions of treefall gaps varied between localities because of spatial and temporal differences in the histories of disturbance. At Fergies Bush where drought-related dieback had produced many large gaps with standing dead trees, gaps were generally young. Conversely, at Station Creek, small, old gaps formed by bolesnap dominated the disturbance regime. At Rough Creek, gaps of all ages and sizes were found along with an almost complete fern cover, and abundant shrubs and occasional subcanopy hardwood trees. Although overall patterns of regeneration were unrelated to differences in gap size, the relative abundance of N. fusca and N. menziesii varied between localities according to the seemingly minor differences in forest structure and disturbance history described above. Interpretations of regeneration response to gap parameters, therefore, need to account for differences in disturbance history between sites. Differences in the disturbance history between localities will also influence rates of gap closure, and because closure rates are used to estimate forest turnover times, meaningful comparisons of disturbance regimes for different forest types can only be made if this intersite variability is addressed.     

Gap dynamics in climaxFagus crenata forests

Gap characteristics and gap regeneration were studied in several climaxFagus crenata forests in Japan. 278 gaps were observed. Gaps covered 12% of the total land area of 20.05 ha. Gap density was 13.9 gaps per ha and, mean gap size was 92.0 m². Smaller gaps were much more frequent than larger ones. Gaps larger than 400 m² were rare. Most gaps were created by the death of single trees. Canopy trees died more often standing or with broken trunks than by uprooting, although uprooted trees were relatively abundant in the site with poor soil drainage and in the site on upper slope. Differences of gap regeneration behaviour were recognized among tree species.F. crenata regenerates in gaps from saplings recruited before gap creation and can replace not only its own gaps but also gaps of other species. Most species other thanF. crenata andMagnolia obovata could not regenerate in their own gaps. More successful regeneration ofF. crenata may occur in gaps smaller than 200 m², althought it regenerated in a wide range of gap size. However, increased relative density ofF. crenata in the canopy layer seems to prevent its successful regeneration. Gap regeneration of other species did not clearly depend on a species-specific gap size.     

Gap size effects on photoinhibition in understorey saplings in tropical rainforest

The sudden increase in irradiance after canopy disturbance in primary forest together with the accompanying increase in leaf temperatures is known to cause photoinhibition in shade acclimated foliage of understorey plants. We hypothesized that there is species specific variation among understorey saplings in the magnitude of photoinhibition in response to gap creation, which is related to their requirement for overstorey disturbance. Eleven more or less circular gaps were created varying in size from 60 up to 1459 m². Photoinhibition was assessed by determining predawn and midday F_v/F_m using chlorophyll fluorescence at two occasions during the first 3 weeks after creation of the gaps. The light environment was assessed using hemispherical photography. Five species that occurred in sufficient numbers in the understorey after gap creation were measured. They all showed an increase of photoinhibition with increasing gap size. Variation in exposure to direct sunlight within gaps contributed also to variation in photoinhibition. Dynamic photoinhibition, the overnight increase in F_v/F_m, was about 20% of total photoinhibition as measured at midday. The species responded quantitatively different. Oxandra asbeckii was most sensitive as evident from a decrease of predawn F_v/F_m from 0.79 in the understorey of undisturbed forest to 0.70 in the smallest and further to 0.41 in the largest gaps. Catostemma fragrans, the least sensitive species showed hardly any photoinhibition in the smallest gaps and less in the largest ones, whereas Lecythis concertiflora, Licania heteromorpha, and Chlorocardium rodiei had intermediate responses. Species rank order in sensitivity to photoinhibition was maintained across the whole range of gap sizes. The relationship between sensitivity to photoinhibition and species-specific gap size preference for regeneration is discussed.     

The effects of sheep grazing on seedling establishment and survival in grassland

This paper examines the effects of sheep and insect grazing on the generation of natural gaps in turf and the establishment of seedlings therein. The site is on an old field on limestone. There were five sheep grazing treatments: ungrazed, and grazed briefly in spring, briefly in autumn, in autumn or in summer and autumn. The first three of these treatments also contained plots in which insecticide was applied regularly during the growing season. Pins of increasing size (1.6 mm–12.8 mm diameter) were lowered at grid intersections in permanent quadrats to record gap type and the occurrence of seedlings on seven dates over 15 months.Heavily-grazed plots had more bare ground in spring and more herb seedlings established in them. Seedlings of annual species of Bromus were able to establish in gaps (bare ground and litter) of smaller size than was required by herb seedlings (which had much smaller seeds). The use of an insecticide increased seedling establishment in October in ungrazed and in spring-grazed paddocks but decreased it in autumn-grazed paddocks. This may indicate the greater importance of insect herbivory in making gaps in the matted sward of autumn-grazed plots.Seedlings which established in October 1986 and March 1987 were more likely to die than those establishing earlier in 1986. This may be because of winter-kill and especially vigorous spring vegetation growth respectively. Seedling mortality was not affected by gap size or grazing treatment (unless such effects operated before we detected the seedlings).     

Response of Japanese beech (Fagus japonica Maxim.) sprouts to canopy gaps

The response of Japanese beech (Fagus japonica Maxim.) sprouts to canopy gaps in natural beech forest in central Japan was studied using two contrasted gaps in which tree-ring chronologies of regenerating stems were analyzed. The gaps were created by uprooting of a single Quercus mongolica var. grosseserrata stem (diameter: 50 cm; gap size: 40 m²; 23 years old) and by concurrent uprootings of four F. japonica stools (gap size: 180 m²; 30 years old). Japanese beech sprouts emerged before and after the gap formation and dominated stem populations in both gaps. In gaps, growth of F. japonica sprouts was equal or lower than growth of stems of seed origin, but most sprouts (F. japonica, Acer mono var. marmoratum) appeared a few years before emergence of seedlings. The small gap created by single stem fall was dominated by some beech sprouts from stools adjacent to the gap. The multiple gap was not closed by beech sprouts from stools surrounding the gap, but some dominant beech stems were resprouts from the uprooted beech stools. The existence of a sprout bank under the canopy may play an important role in the closing process of gaps in natural Japanese beech forest.     

Environmental Effects of Canopy Gap Formation in High-Rainfall Mangrove Forests1

This study investigated the importance of gap formation in mangrove swamps on the island of Kosrae, Federated States of Micronesia, in order to understand better both natural processes of forest development and the effects of harvesting trees for firewood in these wetlands. Measurements were concentrated in seven plots located near four rivers: three in fringe zones and four in basin zones. Each plot was a cluster of five points and covered an area of ca 1.3 ha. From every point in each of the seven plots, the nearest canopy gap ≥10 m² was located; 25 of the 35 gaps were formed by harvesting. Porewater salinity was significantly higher under the canopy in fringe mangrove forests than in basin mangrove forests. Although gaps were small (mean gap size = 158 m²; median gap size = 92 m²), soil temperatures were significantly higher in gaps of both zones. Soil redox potential was significantly lower and porewater salinity significantly higher in the gaps than under the canopy in the basin zone only. Higher porewater salinity may be attributed to high evaporation rates from the soil and high transpiration rates from trees surrounding gaps. There were significantly more seedlings in gaps than under the canopy only in the fringe zones. Although gap formation alters the soil environment of Kosraean mangrove swamps, high freshwater input may buffer these effects in basin mangrove swamps by reducing porewater salinity. Current harvesting rates do not appear to be changing canopy species composition, but large gaps, especially in mangrove forests in more arid areas, may lead to major changes.     

The effects of gap disturbance on the seedling emergence,survival and growth of two different native species in Inner Mongolia

A field study was conducted to investigate the effects of gap disturbance on the seedling establishment process of two native species. Seeds of Agropyron cristatum and Stipa krylovii were reseeded to artificially created gaps in a degraded steppe in North China. There were seven treatments: shoot gaps and root gaps (10 cm, 20 cm and 40 cm in diameters), no gaps (control). Shoot gaps were formed by removing above ground vegetation and below ground biomass without restricting the re-growth of neighbor roots back into the gap. The root gaps were accomplished by using polyvinyl chloride pipes sunk in the soil of shoot gaps to exclude neighboring roots. Seedling emergence, survival and growth performance after 90 days of growing were recorded for both species. Gap significantly increased soil moisture, especially for root gaps. Emergence increased significantly for both species as gap size increased. Seedling emergence and survivorship of both species were greater in gaps than in controls. However, the gap size showed a significantly negative effect on Agropyron cristatum's survivorship. Growth performance of Agropyron cristatum and Stipa krylovii differ in their response to gap disturbance. Gap had positive effects on seedling growth (including seedling height, dry weight, and numbers of tillers and leaves) of Stipa krylovii, but had negative effects on seedling growth of Agropyron cristatum. The two species have significantly different responses to gap disturbance. All results suggest that Stipa krylovii is a gap-enhanced species, and Agropyron cristatum is not. Predation by insects may be one of the key reasons to explain the stand dominance in this grassland.     

Microclimatic differences between and within canopy gaps in a temperate rainforest

The microclimate in the understorey and in two canopy gaps of different size (249 m² and 12.6 m²) within a temperate rainforest in northern New Zealand were characterised using net all-wave radiation (Q ^*), vapour pressure deficit (VPD), vertical air temperature gradient (VTG), and maximum and minimum air temperatures. Hemispherical fisheye photographs were used to define the exposure to the sky at each microclimate recording site both within and between gaps, and in the understorey. Under condiions of clear skies during the summer, with the sun close to its maximum altitude, the large gap centre had a mean daytime (0700–1700 hours)Q ^* of 452 W/m². This value was similar to that estimated for an open field nearby, but three times greater thanQ ^* at the centre of the small gap, and six times greater than in the understorey. The east and west sides of both gaps had higher values ofQ ^* than the north and south sides. BothQ ^* and mean daily maximum temperature were strongly correlated with the amount of sky exposure. VPD and VTG were higher in gaps than in the understorey, with maximum values for both variables occurring at the centre of the large gap.     

Treefall gap characteristics and regeneration in the laurel forest of Tenerife

Abstract. We conducted a study in the laurel forest of Tenerife (Canary Islands, Spain) to describe the characteristics of natural gaps and to assess the role of treefall gaps in forest dynamics. Very little is left of the natural laurel forest with i.a. Laurus azorica, Ilex canariensis and Prunus lusitanica. We looked for treefall gaps in 80 randomly located 2500 m² plots. These plots represented ca. 1% of the remaining and protected laurel forest of Tenerife. We recorded the characteristics of the species causing the gaps, gap architecture and gap age in all observed gaps larger than 10 m². We inventoried the regeneration in each gap and in a neighbouring control plot with the same topography. Large gaps (>75 m²) were not common in the laurel forest. The absence of large gaps could be due to the physiognomy of the vegetation, the mild weather or the rarity of disturbances. Instead of forming gaps, many trees decompose in place and branches from neighbouring trees and suckers from the decomposed trees occupy the free space. Also, the high rate of asexual regeneration could contribute to the fast closing of the gap. The number of gaps created by Prunus lusitanica was higher than expected (based on canopy composition) while Ilex canariensis and Laurus azorica created fewer gaps. In this evergreen forest, differences between gap and non-gap conditions are not as distinct as in other forest types. Only 0.4% of the canopy is in the gap phase (0.6% including gaps smaller than 10m²). No differences were found in patterns of regeneration between gap and non-gap phases in the forest. Gaps do not explain the persistence of pioneer species in the laurel forest.     

Gap characteristics and gap regeneration in primary evergreen broad-leaved forests of western Japan

Gap characteristics and regeneration in gaps were studied in some primary evergreen broad-leaved forests of the warm temperate zone in western Japan. Total observed 161 gaps covered 15.7% of the total land area of 8.23 ha. Gap density was 19. 6 gaps ha⁻¹ and mean gap size was 80.3 m². Smaller gaps (<80 m²) were much more frequent than larger ones, and gaps larger than 400 m² were rare. Gaps created by the death or the injury of single trees were 79.5%. Canopy trees died most often with broken trunks and not so often by uprooting or leaving standing-dead. Different types of gap regeneration behaviour were recognized among the major canopy tree species, though gap regeneration of the common evergreen broad-leaved tree species did not clearly depend on a species-specific gap size.Distylium racemosum, which occurred in equal importance (about 25%) in the canopy layer of each study stand, regenerates in gaps from saplings recruited before gap creation and can replace not only its own gaps but also gaps of other species. Therefore, it can be considered a typical climax species in this forest type of western Japan.Persea thunbergii, which can reproduce vegetatively, showed a similar type of gap regeneration behaviour.Castanopsis cuspidata can replace itself with relatively higher frequency by means of vegetative reproduction (stump sprouting) after gap creation.Quercus acuta andQuercus salicina did not regenerate under the current gap-disturbance regime. Though the frequency of uprooting is low, soil disturbance by uprooting seems to be important for the perpetuation of the pioneer tree species,Fagara ailanthoides, which recruits from buried seeds in the soil     

Study on canopy disturbance regime and mechanism of tree species diversity maintenance in the lower subtropical evergreen broad-leaved forest,South China

ABSTRACT

The canopy disturbance, the gap environment, gap regeneration and maintenance of tree species diversity in the lower subtropical evergreen broad-leaved forest (LSEBF) of South China were studied in this paper. The most common manner of gap formation in the forest was by stem breakage. Most gaps were formed by two gap makers. The sizes of most expanded gaps (EG) and canopy gaps (CG) were in the range of 100 – 300 m² and 50 – 100 m², respectively. The ecological factors in gaps were analysed on the basis of contrasting measurement of the microclimatic regimes in gaps of different sizes and in non-gap stands. Tree species in the LSEBF were classified into 5 ecological species groups on the bases of their changes in order of importance values in gaps and in non-gap stands. Most of the species reached their peak of regeneration density around the gap sizes of 100 m² and 500 m². The curves of regeneration density vs. gap age for major species revealed two types. Regeneration densities of most species, and species diversity indices in gaps were greater than those in non-gap stands.     

Early establishment of planted Retama sphaerocarpa seedlings under different levels of light,water and weed competition

Large amounts of former cropland are being abandoned in developedregions. To formulate guidelines for land reclamation programmes, we exploredthe effects of artificial shading, irrigation, and removal of weed competitionon the performance of Retama sphaerocarpa (L.) Boiss.seedlings in a factorial experiment located in an abandoned cropland in CentralSpain. R. sphaerocarpa is of interest for revegetationbecause it is a drought tolerant leguminous shrub that is a major structuralcomponent of the native plant community. Seedling performance was evaluated inthree ways: seedling survivorship, growth, and photochemical efficiency. Wealsomeasured soil moisture and weed biomass production and found that bothincreasedunder artificial shading conditions. Soil moisture increased very slightlywhereweeds were removed. Thus, increased transpiration from weeds outweighed reducedevaporation from soils due to shading by weeds. Artificial shading was the mosteffective treatment for seedling survivorship, followed by removal ofcompetition by weeds. After summer, 34 % of the seedlings survived in the mostfavourable conditions (artificially shaded plots where weeds were removed),compared to ca. 1 % in full-light plots with no removal of weed competition. Apositive effect of irrigation was found for growth of seedling cover and heightin shaded plots. The analysis of photochemical efficiency pointed out therelevance of weed competition removal, and confirmed the usefulness of fastfluorescence transient techniques for the quantification of seedlingperformance. The data suggest that competition between seedlings and weeds wasprimarily for water rather than for light. We conclude that i) artificialshading improved seedling performance, but this is a little practical techniquebecause of its cost; ii) as weeds compete with, rather than facilitate, plantedseedlings, weed clipping around the seedlings is a feasible technique thatwouldimprove seedling survival; and iii) seedling performance could alsoconsiderablyimprove with a higher irrigation than was used in this experiment(75lm^–2 per growth period), provided that weedsare removed.     

Seed bank dynamics and tree‐fall gaps in a northwestern Mexican Quercus‐Pinus forest

Questions: How does the seed bank respond to different types of tree‐fall gaps and seasonal variations? How does the soil seed bank influence recovery of the standing vegetation in the mature forest and tree‐fall gaps? Location: 1800 — 2020 m a.s.l., Quercus‐Pinus forest, Baja California Sur, Mexico. Methods: Seed size, species composition and germination were estimated under different environmental conditions during dry and rainy seasons: a mature forest plot and gaps created by dead standing trees, snapped‐of f trees and uprooted trees. The soil seed bank was investigated using direct propagule emergence under laboratory conditions, from soil cores obtained during both seasons. Results: 21 species, 20 genera and 14 families constitute the seed bank of this forest community. Fabaceae, Asteraceae, Euphorbiaceae and Lamiaceae were the most frequently represented families in the seed bank. Floristic composition and species richness varied according to the different modes of tree death. Species composition of seed banks and standing vegetation had very low similarity coefficients and were statistically different. Seed bank sizes varied between 164 and 362 ind.m^‐2 in the mature forest plot for the dry and rainy seasons, respectively, while soil seed bank sizes for gaps ranged between 23–208 ind.m^‐2 forthe dry season and between 81–282 ind.m^‐2 for the rainy season. Conclusions: Seed bank sizes and germination response were always higher in the rainy season under all the environmental conditions analysed. Results suggest that timing responses to gap formation of the soil seed bank could be more delayed in this temperate forest than expected.     

The effects of gap size on some microclimate variables during late summer and autumn in a temperate broadleaved deciduous forest

The creation of gaps can strongly influence forest regeneration and habitat diversity within forest ecosystems. However, the precise characteristics of such effects depend, to a large extent, upon the way in which gaps modify microclimate and soil water content. Hence, the aim of this study was to understand the effects of gap creation and variations in gap size on forest microclimate and soil water content. The study site, in North West England, was a mixed temperate broadleaved deciduous forest dominated by mature sessile oak (Quercus petraea), beech (Fagus sylvatica) and ash (Fraxinus excelsior) with some representatives of sycamore (Acer pseudoplatanus). Solar radiation (I), air temperature (T _A), soil temperature (T _S), relative humidity (h), wind speed (v) and soil water content (Ψ) were measured at four natural treefall gaps created after a severe storm in 2006 and adjacent sub-canopy sites. I, T _A, T _S, and Ψ increased significantly with gap size; h was consistently lower in gaps than the sub-canopy but did not vary with gap size, while the variability of v could not be explained by the presence or size of gaps. There were systematic diurnal patterns in all microclimate variables in response to gaps, but no such patterns existed for Ψ. These results further our understanding of the abiotic and consequent biotic responses to gaps in broadleaved deciduous forests created by natural treefalls, and provide a useful basis for evaluating the implications of forest management practices.