The limited role of canopy gaps in the successional dynamics of a mature mixed Quercus forest remnant

Question: Are canopy gap dynamics responsible for driving the structural and compositional changes that have occurred over a 26‐year period in a mature Quercus forest remnant? Location: Dobbs Natural Area, an unlogged 3.6‐ha forest preserve in west‐central Indiana, USA. Methods: We analyzed mapped permanent plot data for a site that illustrates a trend common in Quercus‐dominated forests in eastern North America, where recruitment of new stems is dominated by mesophytic, shade‐tolerant species such as Acer saccharum, rather than Quercus. We developed a GIS database from stand census measurements taken in 1974 and 2000, employing it to conduct tree‐by‐tree comparisons that allow direct determination of ingrowth, mortality and survivorship, and to relate the spatial patterns of subcanopy dynamics to canopy gap occurrence. Results: The re‐census shows modest changes in canopy composition, but much greater turnover in the subcanopy. Nearly half of all individuals originally present died; much of this mortality resulted from a major decline in subcanopy Ulmus americana. While overall density remained fairly constant, the subcanopy experienced substantial ingrowth of shade‐tolerant Acer saccharum, Fagus grandifolia, and Tilia americana. Canopy gaps, although forming at rates in the upper range of regional averages, did not significantly benefit subcanopy populations of Quercus spp. or most other taxa with limited shade tolerance. Conclusions: Canopy gaps play a minor role in driving the recent demographic trends of this stand. The spatial and temporal scales of light availability in gaps do not support regeneration of most shade‐intolerant species. Compositional change parallels a historical shift in light regimes.     

Spatial patterns and associations in a Quercus‐Betula forest in northern China

Question: Are species‐specific regeneration strategies and competition the dominant processes facilitating species coexistence in a Quercus liaotungensis dominated temperate deciduous forest? Location: Dongling Mountains, North China, 1300 m a.s.l. Methods: Ripley's K‐function was used to characterize the spatial patterns and spatial associations of two dominant tree species, Quercus liaotungensis and Betula dahurica, and a common subcanopy species, Acer mono, at different growth stages (adult, sapling, seedling). Results: Seedlings, saplings and adults of all three species exhibited clumped distributions at most spatial scales. Quercus seedlings and saplings were positively associated with conspecific adult trees and spatially independent of dead trees suggesting that seed dispersal and vegetative regeneration influenced the spatial patterning of Quercus trees. Betula seedlings and saplings were positively associated with both live and dead trees of conspecific adults at small scales (<5 m) but negatively associated with live and dead trees of other species indicating sprouting as an important mechanism of reproduction. Saplings of Acer had a strong spatial dependence on the distribution of conspecific adult trees indicating its limited seed dispersal range. Negative associations between adult trees of Betula and Quercus demonstrated interspecific competition at local scales (<5 m). Conclusions: Different regeneration strategies among the three species play an important role in regulating their spatial distribution patterns, while competition between individuals of Betula and Quercus at the adult stage also contributes to spatial patterning of these communities. The recruitment limitations of Betula and Quercus may affect the persistence of these species and the long‐term dynamics of the forest.     

Structural heterogeneity and tree spatial patterns in an old-growth deciduous lowland forest in Cantabria, northern Spain

Old-growth deciduous forests in western Europe, for the most part, consist of small tracts that often may be atypical due to human disturbance, poor soil productivity or inaccessibility. In addition, very little information on tree age distributions, structural heterogeneity and tree spatial patterns appears to be available for west-European forests. Characterization of the structural features of tree populations in these old-growth stands can provide the basis to design conservation plans and also inform on how present forests might look in the absence of human interference. Four old-growth stands in a deciduous forest in the Cantabrian lowlands, northern Spain, were surveyed to determine forest structure and spatial patterns. Live and dead trees were identified, measured and mapped, and live trees were cored for age estimation. Structural heterogeneity was analyzed by means of the spatial autocorrelation of tree diameter, height and age, and the uni- and bivariate spatial patterns of trees were analyzed. The dominant species, Fagus sylvatica and Quercus robur, showed reverse-J shaped size distributions but discontinuous age distributions, with maximum ages of 255–270 yr. Tree ages suggested that the forest was largely modified by past changes in forest-use, especially by temporal variation in grazing intensity. Spatial autocorrelation revealed that former parkland stands were heterogeneous with respect to tree height only, while high forest stands were composed of patches of even-aged and even-sized trees. Young trees were clumped at varying distances and establishment occurred preferentially in canopy gaps, except for Ilex aquifolium that mainly occurred beneath mature Quercus trees. Surviving trees became less intensely clumped in the dominant species, and more strongly clumped in understorey ones, which may have been due to the effects of intraspecific competition and of canopy trees on tree survival, respectively. The spatial associations between species varied within the forest, probably as a consequence of specific establishment preferences and competitive interactions.     

Canopy disturbance patterns and regeneration of Quercus species in two Ohio old-growth forests

This study was conducted to determine the abundance of Quercus species, the spatial pattern of Quercus regeneration, the current canopy disturbance pattern, and their interrelationship in two old-growth deciduous forests in Ohio (Goll Woods and Sears-Carmean Woods). Acer saccharum and Fagus grandifolia had the greatest density and basal area in both forests, yet the largest trees (by basal area) present at each site were Quercus spp. Quercus spp. appeared to be decreasing in abundance in both sites. Though Quercus seedlings were common, few Quercus saplings or subcanopy trees were present. The current disturbance regimes were dominated by small canopy gaps created by death of 1–2 trees; canopy gaps 100 m² in size were rare and only 2.5–2.8% of the forest area was covered by recognizable canopy gaps. No significant differences in the density of Quercus seedlings or saplings were found between gaps and non-gap areas at either site. Though no significant barrier to seedling establishment appeared to exist, the present disturbance regimes are not well suited for the growth of Quercus into the subcanopy size class or the recruitment of Quercus into the canopy. The most frequent gapmakers in Goll Woods were Tilia americana and Acer saccharum, and those in Sears-Carmean Woods were A. saccharum and F. grandifolia. The species most frequent as gap fillers were A. saccharum (in both sites) and F. grandifolia (in Goll Woods). These results suggest that A. saccharum will continue to increase in abundance, and Quercus decrease in abundance, in these two old-growth stands.     

天山云杉天然林不同林层的空间格局和空间关联性

天山云杉(Picea Schrenkiana)林是天山林区的重要针叶林。研究调查了分别代表天山云杉增长型种群和成熟型种群的两块标准地,应用Ripley's K系数法研究了天山云杉更新层、低林层、中林层和高林层的空间格局和不同林层的空间关联性,并应用Moran's I系数法研究了不同林层的林木高度的空间自相关性。结果表明:所有林层的天山云杉活立木都是显著聚集的,只是发生聚集格局的强度和聚集尺度不同。更新层天山云杉具有最大的聚集强度,从更新层到低林层,聚集强度急速降低。两块标准地中天山桦(Betula tianschanica Rupr.)、天山柳(Salix tianschanica Rgl.)和天山云杉活立木的空间关联性的表现不同。研究结果表明:增长型种群中天山桦、天山柳在所有尺度上都抑制天山云杉的生长;而成熟型种群中天山桦、天山柳在1-10 m尺度内对天山云杉种群的生长没有影响,10-40 m表现出正相关,40 m以上没有表现出明显的关联性;同时天山桦、天山柳基本上在所有尺度都抑制天山云杉的更新。在更新层和低林层间表现出正相关;而更新层和枯死木之间的空间关联性为正相关。     

Composition and structure of a chronosequence of young, mixed-species forests in southeastern Ohio, USA

Clearcutting, a commonly used silvicultural practice in southeastern Ohio, often results in a forest stand with a different species composition than the parent stand. The time frames during which shifts in species composition occur on different sites are unclear. While some studies have documented species composition at specific points in time, none have attempted to examine differences throughout the first decades of stand development. This study focused on the early successional dynamics of young, mixed-species forests of southeastern Ohio. Species compositions were examined across a chronosequence of sixteen stands that developed following clearcutting. Stand ages ranged from six to 26 years. The sample was limited to dry-mesic hardwood forests on southerly aspects and on soils derived from residuum or colluvium. Across the chronosequence, stand density ranged from 17 636 stems ha^-1 at age 6 to 2759 stems ha^-1 at age 26, and basal area ranged from 8.2 m² ha^-1 to 22.1 m² ha^-1. Clumps comprised a substantial portion of the total stand density and basal area. At age 6–8 years after clearcutting, clumped stems accounted for 35.1% of the density and 48.2% of the basal area. At age 26 years, these proportions were 25.7% and 29.4%, respectively. Clumped stems were significantly larger (p<0.05) than non-clumped stems at each age group except 26 years. Total Quercus spp. density was greatest at age 6–8 years (3386 stems ha^-1), and least at age 26 years (581 stems ha^-1). When considered as a proportion of the total stand, however, the proportion was relatively stable, averaging 21.3%. However, importance value (IV=[relative density + relative basal area]/2) of Quercus in the upper canopy (dominant and codominant crown classes) was twice as much (72%) at age 26 years compared to age 6–8 years (35%). Quercus prinus L. was the major species across the chronosequence. For all age groups except 18–20 years. Q. prinus IV was the highest of any individual species in the upper canopy, and it ranged from 27 in the youngest stands (6–8 years) to 69 in the oldest stand (26 years). Within the intermediate crown class, the IV of Q. prinus equaled or exceeded those of all other species, except for the 18–20 year age group where it was second to A. rubrum. Quercus alba L. and Quercus velutina Lam. were minor components at age 26 years, although they dominated a comparison sample of six mature stands of the same ecosystem type. Liriodendron tulipifera L. was abundant 6–8 years after clearcutting, but nearly absent at age 26 years. Acer rubrum L. was the major species in both the intermediate and overtopped crown classes throughout the chronosequence. As gaps in the canopy occur. A. rubrum may become a more common species within the dominant-codominant crown class.     

Variations in resistance to canopy disturbances and their interactions with the spatial structure of major species in a cool‐temperate forest

Question: How does typhoon‐related disturbance (more specifically, disturbance in the understorey due to tree‐fall and branch‐fall) affect different species mortality rates in a vertically well‐structured forest community? Location: Cool‐temperate, old‐growth forest in the Daisen Forest Reserve, Japan. Methods: We investigated the canopy dynamics and mortality rate trends of trees ≥5 cm diameter at breast height in a 4‐ha study plot, and analysed the effects of tree diameter and spatial structure on the mortality risks for major tree species in the understorey. Results: Significant differences were found in the mortality rates and proportions of injured dead stems between census periods, which were more pronounced in the understorey than in the canopy. Acer micranthum, which showed increased mortality during typhoon disturbance periods, had a clumped distribution. In contrast, Acer japonicum and Viburnum furcatum, which showed similar mortality rates between census periods, had a loosely clumped spatial distribution and a negative association with canopy trees, respectively. In the understorey stems of Acanthopanax sciadophylloides and Fagus crenata, whose spatial distribution patterns depended on canopy gaps, significant increases in mortality rates were observed only during severe typhoon‐related disturbance periods. Conclusions: The sensitivity of trees to typhoon‐related canopy disturbance is more pronounced in the lower layers of vertically structured forest communities. Differences in mortality patterns generated through the combined effects of spatial variation in disturbance regime and species‐specific spatial distribution patterns (spatial aggregation, association with canopy trees, and canopy gap dependency) contribute to the co‐existence of understorey species in forest communities that are subject to typhoon‐related disturbance.     

长白山阔叶红松林中红松与紫椴的空间分布格局及其关联性

以长白山阔叶红松林25hm2样地调查数据为基础,采用点格局分析方法O-ring统计,分析了红松与紫椴两个优势树种在主林层、次林层和林下层的空间分布格局,以及各林层之间的种内和种间关联性.结果表明:在小尺度上,红松和紫椴总体上呈聚集性分布,但不同林层的分布格局各异.物种在较低的林层呈明显的聚集分布,而在较高的林层则呈随机或规则分布,聚集度随林层的增高而降低.主林层与次林层红松在<11m的尺度内呈明显的正相关.主林层与次林层、林下层紫椴之间呈负相关.红松和紫椴在整体上表现为正相关,但不同林层间的关联性各异.主林层红松与3个林层紫椴之间没有明显的关联性;次林层红松与次林层紫椴在>4m的尺度上呈负相关,而与林下层紫椴没有明显的关联性;主林层紫椴与次林层红松在0~100m尺度内都表现为显著正相关.     

The cupule-carpel theory. A defence

Background: Spatial patterns within forests reflect their formative processes. In Kamchatka, the dominant stone birch (Betula ermanii) forest exists in a primeval state. Betula species can reproduce via clonally produced ramets, leading to a clustered distribution of stems, or from seed on open ground, although subsequent mortality may obscure initial establishment patterns.

Methods: Spatial patterns of all trees and regenerating stems in a fully mapped 0.25 ha plot were analysed using the g(r) function and the pattern of trees modelled using a Matérn cluster process. Mark correlation analysis was used to detect patterns in stem sizes.

Results: Clustering of trees at scales up to 3 m occurred, with model parameters indicating a density of 180 clusters ha^?1, each containing on average three stems >1 cm diameter at breast height (DBH) within a 1.6 m radius. Stem size compensation was detected, with nearby trees smaller than expected by chance. Regenerating stems were strongly clustered at scales below 3.5 m and from 5–8 m, and were aggregated around small trees (<10 cm DBH) but not large trees (≥10 cm DBH), or in gaps.

Conclusions: These patterns are consistent with clonal reproduction followed by competition as the processes determining spatial structure in old-growth stone birch forests.     

Spatial patterns of trees in natural forests of East-Central Europe

The analysis of spatial patterns is one of the ways to estimate the role of competition among trees in forest dynamics. Three hypotheses concerning distribution patterns in old-growth stands were tested: (1) fine-scale spatial patterns of trees are regular; (2) patterns do not differ significantly from a random distribution, and (3) spatial patterns at larger scales are clumped because of site heterogeneity. Old-growth forest stands in Poland and the Czech Republic were analysed with a modified Ripley K function, using distribution maps of tree stems. Fine-scale spatial patterns (with distances among trees not exceeding 15 m) were usually intermediate between random and regular. Trends towards a regular distribution occurred more often among dead than among live individuals. No significant relationships between tree species were found at smaller scales; however, at larger scales (distances from 15–25 m) negative associations between some species were found. This reflects site heterogeneity rather than any direct influence of one tree species upon another.     

Gap-scale disturbance processes in secondary hardwood stands on the Cumberland Plateau,Tennessee, USA

Disturbance regimes in many temperate, old growth forests are characterized by gap-scale events. However, prior to a complex stage of development, canopy gaps may still serve as mechanisms for canopy tree replacement and stand structural changes associated with older forests. We investigated 40 canopy gaps in secondary hardwood stands on the Cumberland Plateau in Tennessee to analyze gap-scale disturbance processes in developing forests. Gap origin, age, land fraction, size, shape, orientation, and gap maker characteristics were documented to investigate gap formation mechanisms and physical gap attributes. We also quantified density and diversity within gaps, gap closure, and gap-phase replacement to examine the influence of localized disturbances on forest development. The majority of canopy gaps were single-treefall events caused by uprooted or snapped stems. The fraction of the forest in canopy gaps was within the range reported from old growth remnants throughout the region. However, gap size was smaller in the developing stands, indicating that secondary forests contain a higher density of smaller gaps. The majority of canopy gaps were projected to close by lateral crown expansion rather than height growth of subcanopy individuals. However, canopy gaps still provided a means for understory trees to recruit to larger size classes. This process may allow overtopped trees to reach intermediate positions, and eventually the canopy, after future disturbance events. Over half of the trees located in true gaps with intermediate crown classifications were Acer saccharum, A. rubrum, or Liriodendron tulipifera. Because the gaps were relatively small and close by lateral branch growth of perimeter trees, the most shade-tolerant A. saccharum has the greatest probability of becoming dominant in the canopy under the current disturbance regime. Half of the gap maker trees removed from the canopy were Quercus; however, Acer species are the most probable replacement trees. These data indicate that canopy gaps are important drivers of forest change prior to a complex stage of development. Even in relatively young forests, gaps provide the mechanisms for stands to develop a complex structure, and may be used to explain patterns of shifting species composition in secondary forests of eastern North America.     

Dendrochronological analysis of the canopy history of two Ohio old-growth forests

This study examined the temporal patterns of establishment, suppression, and release of major tree species in two old-growth Ohio forest remnants as a means to determine the past disturbance history of these forests. Increment cores were taken from a total of 154 trees from two well-drained, upland plots and two poorly-drained, bottomland plots in each of the two forested areas. Acer saccharum and Fagus grandifolia exhibited multiple episodes of suppression and release prior to becoming canopy trees, and could tolerate suppressions as long as 84 years. In contrast, Quercus macrocarpa, Q. muehlenbergii, Prunus serotina, and Acer saccharinum rerely exhibited any tolerance to suppression and appeared to have entered the canopy after single disturbances had opened large areas of canopy. There was clear synchrony in the temporal pattern of establishment and final release from suppression among trees from bottomland plots scattered throughout the stands, indicating that relatively large disturbances were important in these poorly-drained areas. In contrast, there was little synchrony among trees from well-drained upland plots, except in a single instance where selective cutting of Quercus trees opened the canopy. Thus, the canopy of upland site was likely subjected only to small disturbances resulting from the death of one or a few trees. At the whole of forest level, there was evidence of episodic recruitment of canopy trees in both forests. Establishment of Fraxinus spp. and Quercus spp. were particularly episodic, and few Fraxinus or Quercus trees alive today established during the last century. These data suggest that large disturbances have affected canopy dynamics of both upland and bottomland areas prior to 1900 and in bottomland forests through this century. In contrast, disturbances in upland areas during this century have been restricted to small, treefall-generated canopy gaps.     

Is climate an important driver of post‐European vegetation change in the Eastern United States?

Many ecological phenomena combine to direct vegetation trends over time, with climate and disturbance playing prominent roles. To help decipher their relative importance during Euro‐American times, we employed a unique approach whereby tree species/genera were partitioned into temperature, shade tolerance, and pyrogenicity classes and applied to comparative tree‐census data. Our megadata analysis of 190 datasets determined the relative impacts of climate vs. altered disturbance regimes for various biomes across the eastern United States. As the Euro‐American period (ca. 1500 to today) spans two major climatic periods, from Little Ice Age to the Anthropocene, vegetation changes consistent with warming were expected. In most cases, however, European disturbance overrode regional climate, but in a manner that varied across the Tension Zone Line. To the north, intensive and expansive early European disturbance resulted in the ubiquitous loss of conifers and large increases of Acer, Populus, and Quercus in northern hardwoods, whereas to the south, these disturbances perpetuated the dominance of Quercus in central hardwoods. Acer increases and associated mesophication in Quercus‐Pinus systems were delayed until mid 20th century fire suppression. This led to significant warm to cool shifts in temperature class where cool‐adapted Acer saccharum increased and temperature neutral changes where warm‐adapted Acer rubrum increased. In both cases, these shifts were attributed to fire suppression rather than climate change. Because mesophication is ongoing, eastern US forests formed during the catastrophic disturbance era followed by fire suppression will remain in climate disequilibrium into the foreseeable future. Overall, the results of our study suggest that altered disturbance regimes rather than climate had the greatest influence on vegetation composition and dynamics in the eastern United States over multiple centuries. Land‐use change often trumped or negated the impacts of warming climate, and needs greater recognition in climate change discussions, scenarios, and model interpretations.     

Comparative phylogeography of red maple (Acer rubrum L.) and silver maple (Acer saccharinum L.): impacts of habitat specialization,hybridization and glacial history

Aim We analysed variation in chloroplast DNA (cpDNA) in red maple (Acer rubrum L.) and silver maple (Acer saccharinum L.) across a large part of their geographic ranges. Acer rubrum is one of the most common and morphologically variable deciduous trees of eastern North America, while its sister species A. saccharinum has a more restricted habitat distribution and displays markedly less morphological variation. Our objective was to infer the impact of biogeographic history on cpDNA diversity and phylogeographic structure in both species. Location Deciduous forests of eastern North America. Methods We sequenced 1289 to 1645 bp of non‐coding cpDNA from A. rubrum (n = 258) and A. saccharinum (n = 83). Maximum parsimony networks and spatial analysis of molecular variance (SAMOVA) were used to analyse phylogeographic structure. Rarefaction analyses were used to compare genetic diversity. Results A total of 40 cpDNA haplotypes were recovered from A. rubrum (38 haplotypes) and A. saccharinum (7 haplotypes). Five of the seven A. saccharinum haplotypes were shared with nearby samples of A. rubrum. SAMOVA recovered four phylogeographic groups for A. rubrum in: (1) south‐eastern USA, (2) the Gulf and south‐eastern Coastal Plain, (3) the lower Mississippi River Valley, and (4) the central and northern regions of eastern North America. Acer saccharinum had significantly lower haplotype diversity than A. rubrum, and novel haplotypes in post‐glaciated northern limits of its range were shared with A. rubrum. Main conclusions This is the first study of A. rubrum to report a distinct phylogeographic group centred on the lower Mississippi River, and the first to examine data comparatively with A. saccharinum. We hypothesized that A. rubrum would display stronger phylogeographic structure and greater haplotype diversity than A. saccharinum because of its greater geographic range, and ecological and morphological variation. This hypothesis was supported by the cpDNA analysis. The sharing of cpDNA and chloroplast simple sequence repeat (cpSSR) haplotypes in areas of geographic overlap provides evidence of introgression, which led to an increase in haplotype diversity in both species, and to novel phylogeographic structure in A. rubrum. We recommend that introgression be considered, along with other potential causes, as an explanation for the phylogeographic structure of cpDNA in plants.     

Bottomland hardwood productivity: case study in a rapidly subsiding,Louisiana, USA,watershed

The Verret basin was formerly an overflow area between the Mississippi and Atchafalaya rivers and contains about 41,000ha of forested wetlands. Water levels are rising at the rate of over 1 cm/year in this area, and the forests are subjected to longer and deeper flooding. Tree growth, litterfall, and species composition were monitored across a flooding gradient during January 1985–December 1986. The driest area was only 20 cm higher in elevation than the wettest area, but the structure of the forest changes greatly over this range. The drier area was dominated by sweetgum (Liquidambar styraciflua L.), oaks (Quercus spp.), and sugarberry (Celtis laevigata Willd.), while green ash (Fraxinus pennsylvanica Marsh.), red maple (Acer rubrum L.), and baldcypress (Taxodium distichum (L.) Rich.) were dominant in the wetter area. Green ash and bitter pecan (Carya aquatica (Michaux. f.) Nutt.) were found in all plots, but these two species are under severe stress in the more flooded area as evidenced by dead and dying trees. Stem wood production increased from 1985 to 1986 in the driest (392 to 473 g/m²/yr) and wettest (199 to 399 g/m²/yr) plots, but remained relatively unchanged in the transitional area (386 to 380g/m²/yr). Leaf litter production decreased across the gradient from dry to flooded plots during both years. Over 40% of the litterfall in the drier plot was from flood-tolerant shrub species. In the flooded plots, red maple and baldcypress were major contributors to total litterfall. Increased flooding of dry bottomland forests in the future could lead to decreased litterfall and increased tree death over the entire watershed.     

Multi-Scale Assessment of Male Northern Yellow Bat Roost Selection

Knowledge of roost selection by northern yellow bats (Lasiurus intermedius) is limited to a small number of known roost locations. Yet knowledge of basic life history is fundamental to understanding past response to anthropogenic change and to predict how species will respond to future environmental change. Therefore, we examined male northern yellow bat roost selection on 2 Georgia, USA, barrier islands with different disturbance histories. Sapelo Island has a history of extensive disturbance and is dominated by pine (Pinus spp.) forests; Little Saint Simons Island has a limited disturbance history with maritime oak (Quercus spp.) forest as the dominant cover type. From March–July 2012 and 2013, we radio-tracked 35 adult male northern yellow bats to diurnal roosts and modeled roost characteristics at the plot and landscape scales. We located 387 roosts, of which 95% were in Spanish moss (Tillandsia usneoides) hanging in hardwood trees. On both islands, bats selected roost trees with larger diameters than surrounding trees and selected roost locations with greater open flight space (i.e., low midstory clutter) underneath. Roosts were located farther from open areas on Sapelo and closer to fresh water on Little Saint Simons compared to random locations. Lower availability of hardwood forest on Sapelo may have resulted in small-scale roost site selection (i.e., plot level) despite potential increased costs of commuting to water and open areas for foraging. In contrast, greater availability of hardwood forest on Little Saint Simons likely allowed selection of roosts closer to fresh water, which provides foraging and drinking opportunities. Our results indicate that mature hardwood trees in areas with low midstory clutter are important in male northern yellow bat roost selection, but landscape-level features have varying influences on roost selection, likely as a result of differences in disturbance history. Therefore, management will differ depending on the landscape context. Further research is needed to examine roost selection by females, which may have different habitat requirements. © 2020 The Wildlife Society.     

Codominance of <Emphasis Type="Italic">Acer saccharum</Emphasis> and <Emphasis Type="Italic">Fagus grandifolia</Emphasis>: the role of <Emphasis Type="Italic">Fagus</Emphasis> root sprouts along a slope gradient in an old-growth forest

We studied how the unusual capacity of mature Fagus grandifolia to form clumps of clonal stems from root sprouts can contribute to its frequent codominance with Acer saccharum in southern Quebec, Canada. In an old-growth forest, the degree of dominance by the two species shifted along topographic gradients spanning a few hundreds of meters, with Fagus more frequent on lower slopes and Acer on upper slopes. The frequency distribution of Fagus stem diameter had an inverse J distribution at all slope positions, which is indicative of continuous recruitment. Acer stem diameter also had an inverse J pattern, except at lower slope positions where size structure was discontinuous. For stems <2 m tall, Fagus regenerated mainly by sprouts at the upper and mid-slopes, while regeneration from seed was more pronounced on the lower slope. This change of regeneration mode affected the spatial pattern of Fagus stems. Understory trees of Fagus were positively correlated with conspecific canopy trees on upper and mid-slopes, but not on lower slopes where Fagus regenerated mainly by seedlings. Understory trees of Acer were positively correlated with conspecific canopy trees only on the mid-slope. There were many Fagus seedlings around Acer canopy trees at the lower slope, suggesting the potential replacement of Acer canopy trees by Fagus. This study suggests that the regeneration traits of the two species changed with slope position and that Fagus patches originating from root sprouts can contribute to the maintenance of Acer–Fagus codominance at the scale of local landscapes.     

Characterization of microsatellite markers in sycamore (Acer pseudoplatanus L.)

Sycamore (Acer pseudoplatanus L.) is a tetraploid European hardwood tree species. The reproduction system of the insect‐pollinated trees and patterns of genetic variation are largely unknown. We isolated and characterized eight polymorphic microsatellite markers for Acer pseudoplatanus L. The high degree of polymorphism observed at these markers makes them useful to observe genetic variation patterns at various spatial scales and to analyse gene flow and the mating system. Primers developed for the amplification of microsatellites in A. pseudoplatanus were tested for 21 different species of genus Acer. Amplification products of the expected size were obtained in most cases.     

Tree seedling establishment under insect herbivory: edge effects and inter- annual variation

As the density and species composition of insects may change in relation to distance from the forest edge, the role of herbivory in tree establishment may also change across edges. To determine the importance of insect herbivory in tree establishment, insect densities were experimentally altered at different distances from the forest edge. Plots were established at three distances from the edge, with plots located in forest, edge, and field habitats. In half of each plot, insect densities were reduced by insecticide application. Seeds of two tree species, Acer rubrum and Fraxinus americana, were planted into each plot in 1995. The experiment was repeated in 1996 with the addition of Quercus palustris and Quercus rubra.Distance from the forest edge was the most important factor in determining seedling emergence and mortality. Overall seedling performance increased from field to edge to woods, although responses varied among species. In 1995, a drought year, insect removal increased emergence and decreased mortality of tree seedlings. In 1996, a year with normal precipitation, insect removal had much less effect on A. rubrum and F. americana. For the two Quercus species, mortality was reduced by insect removal. The tree species differed in their susceptibility to insect herbivory, with Acer rubrum the most susceptible and Fraxinus americana the least. Herbivory by insects was shown to have the potential to affect both the composition and spatial pattern of tree invasions. Herbivore importance differed greatly between the two years of the study, making the interaction between insects and tree seedlings variable both in space and time.     

后河自然保护区珍稀植物群落主要树种6年动态变化

用每木定位监测方法分析了后河自然保护区常绿落叶阔叶混交林1 hm2固定样地主要乔木树种6年的（2001～2007年）动态变化。样地主要分布有14种普通树种和5种珍稀树种。对这19个树种胸径≥5 cm的林木动态进行分析。2001年,样地有998株主要树种,到2007年,其中100株死亡,样地中新增81株更新幼树。19个主要树种基盖度从19.56 m2/hm2增加到20.14 m2/hm2,群落的径级结构没有明显变化,中等径级个体死亡率最高,且死亡植株在小尺度上聚集分布,较大尺度上随机分布,更新幼树几乎在所有尺度聚集分布,活树和死树在所有尺度空间正关联,活树和更新幼树在大部分尺度负关联。稀有濒危植物能长期稳定地在群落中存在,表明干扰、种内和种间竞争共同影响着群落的发展,群落处于动态平衡状态。