Forest Closure Research Articles

The Effect of Elevation on the Population Structure, Spatial Patterning and Intraspecific Interactions of Picea schrenkiana in the Eastern Tianshan Mountains: A Test of the Stress Gradient Hypothesis

Changes in age structure, spatial distribution and intraspecific interactions across environmental gradients often reflect adaptations of plant populations to their environment. Our study explored the growth status of the Picea schrenkiana population on the north slope of the eastern Tianshan Mountains and tested the stress gradient hypothesis (SGH) against changes in the age structure and spatial pattern of P. schrenkiana populations along the environmental gradient. We sampled the forests at eight elevational locations, comprising a total of 24 plots of 30 × 30 m area from 1800 to 2500 m a.s.l. in the Jiangbulake region. By scanning the 3D structure of the forests and sampling tree rings in each plot, we precisely determined the spatial location and diameter of the breast height (DBH) of each P. schrenkiana individual. By fitting the DBH-age power model and g(r) function of the point pattern, we examined the age structure, spatial patterning and intraspecific interactions of local P. schrenkiana populations within each plot and their correlation with habitat parameters. The results indicate that (1) juveniles dominate the overall population density, age structure and spatial patterning of the P. schrenkiana population. Trees of low–middle elevations represent younger forests with faster growth and better regeneration, while trees at high elevations form older forests with slower growth and poorer regeneration. (2) The aggregated population patterns and positive intraspecific interactions occur mostly at medium elevations (2000 and 2100 m a.s.l.). (3) Population density, aggregation intensity and intraspecific interaction strength are strongly and positively correlated (p < 0.01). Our results did not fit the SGH but support a hump-shaped hypothesis that proposes that facilitation is stronger under medium stress along the elevational gradient. This study validates the spatial point pattern testing of the SGH of different types. We recommend the implementation of more intensive forest closure measures, together with a reduction in the harvesting intensity of trees to ensure the sustainable regeneration of P. schrenkiana forests in the eastern Tianshan Mountains.

Impact of Forest Canopy Closure on Snow Processes in the Changbai Mountains, Northeast China

Forest canopy closure affects snow processes by changing the redistribution of snowfall, snow interception, accumulation, sublimation, and melt. However, how the forest closure impacts snow processes at different periods has not been well explored. We conducted 3-year measurements of snow density and depth and carried out snow process calculations (i.e., interception, sublimation, and snowmelt) from 2018 to 2021 in four mixed forests with different canopy closures and an open site in the Changbai Mountains, northeast China. We found that the snow density of the five study sites varied greatly (0.14–0.45 g/cm3). The snow depth (SD) at four mixed forests sites was smaller than that of the nearby open site. The SD decreased as the forest canopy closure increased. Additionally, the forest interception effect increased with the canopy closure and decreased as the snowfall intensity increased. The total interception efficiency of the four mixed forests in normal snow years changed from 34% to 73% and increased with forest canopy closure. The averaged sublimation rate (Ss) and snowmelt rate (Sr) of the four mixed forests varied during different periods of snow process. The Ss was 0.1–0.4 mm/day during the accumulation period and 0.2–1.0 mm/day during the ablation period, and the Sr was 1.5–10.5 mm/day during the ablation period. There was a good correlation between Ss, or Sr, and canopy closure, but interannual variation was observed in the correlation. The mean values of the effect of the four mixed forests on understory SWE (snow water equivalent) over the 3 years ranged from −45% to −65%. Moreover, the impact effect was correlated with the forest canopy closure and enhanced with the canopy closure. This study provided more scientific information for studies of snow cover response to forest management.

Liana species decline in Congo basin contrasts with global patterns.

Lianas, woody climbing plants, are increasing in many tropical forests, with cascading effects such as decreased forest productivity, carbon sequestration, and resilience. Possible causes are increasing forest fragmentation, CO2 fertilization, and drought. Determining the primary changing species and their underlying vital rates help explain the liana trends. We monitored over 17,000 liana stems for 13 yr in 20 ha of old‐growth forest in the Congo Basin, and here we report changes and vital rates for the community and for the 87 most abundant species. The total liana abundance declined from 15,007 lianas in 1994 to 11,090 in 2001 to 9,978 in 2007. Over half (52%) of the evaluated species have significantly declining populations, showing that the community response is not the result of changes in a few dominant species only. Species density change (i.e., the change in number of individuals per hectare) decreased with mortality rate, tended to increase with recruitment rate, but was independent of growth rate. Species change was independent of functional characteristics important for plant responses to fragmentation, CO2, and drought, such as lifetime light requirements, climbing and dispersal mechanism, and leaf size. These results indicate that in Congo lianas do not show the reputed global liana increase, but rather a decline, and that elements of the reputed drivers underlying global liana change do not apply to this DR Congo forest. We suggest warfare in the Congo Basin to have decimated the elephant population, leading to less disturbance, forest closure, and declining liana numbers. Our results imply that, in this tropical forest, local causes (i.e., disturbance) override more global causes of liana change resulting in liana decline, which sharply contrasts with the liana increase observed elsewhere.

Forest closure and encroachment at the grassland interface: a century‐scale analysis using oblique repeat photography

AbstractWe used repeat oblique photography to quantify and determine the drivers of vegetation change, particularly forest closure and encroachment, in the Rocky Mountains of southern Alberta, Canada, from the beginning of the twentieth century to the present. We classified the landscape into seven distinct vegetation types (closed‐canopy conifer forest, broadleaf deciduous forest, mixedwood forest, open‐canopy woodlands, shrublands, grasslands and meadows, non‐vegetated) and assessed vegetation change between the two time periods. We found that closed‐canopy coniferous forest, broadleaf deciduous forest, and mixedwood forest increased on an area basis by 35%, 45%, and 80%, respectively, over this time period; concomitantly, grasslands and open‐canopy woodlands declined by 25% and 39%, respectively. Overall, 28% of the landscape was in a more advanced successional state in 2008 as compared to the early twentieth century. The Montane and Subalpine Natural Subregions (NSR) experienced the most change (42% and 26%, respectively, in a more advanced successional state). The loss of open‐canopy woodlands was observed across the entire landscape, while grassland and meadow losses were most acute in the Subalpine and Alpine NSRs. The probability of vegetation change to a more advanced successional condition was greater at higher elevations and in areas receiving lower amounts of solar insolation. The changes observed are consistent with what we would expect to see due to lengthening of fire return intervals. Understanding the magnitude of change in vegetation types and the drivers of this change is important for the development of effective contemporary ecosystem management and restoration practices.

Лісівничо-екологічний аналіз насаджень Populus alba та Populus nigra на ріках лівобережного лісостепу України

<p>Here the sylvicultural and ecological analysis of typological structure of plantings silver and black poplar are presented for the riverine habitats of the Psel, Sula and Vorskla (the middle reaches of Seversky Donets river). Our analysis was based on forestry management electronic databases of Ukrainian National Forest Project Enterprise.</p><p>More than 38 forest types on the area of 4.9 thousand hectares were examined. The biological features of silver and black poplar were described briefly. The silver and black poplar reproduction pattern of the Left-bank Forest-steppe of Ukraine was also examined. There was carried out the area allocation of tree species according the following points: forest type and origin, forest site quality, closure degree and age groups. By the tree stratum origin silver and black poplar are mostly artificially propagated, what is equivalent to 77.3 and 88.3 percent.</p><p>The silver and black poplar area around the rivers’ watershed of the Left-bank Forest-steppe of Ukraine occupies 2813 and 2173 ha consequently.</p><p>Among forest types on research subject there are some forest types which dominate: fresh quercetum fluvialis (25.0 %), wet quercetum fluvialis (17.4 %), wet quercetum-birchbark-maple fluvialis (16.3 %), wet lime tree-oak-pine tree sudubrava (11.4 %), fresh lime tree, oak, pine tree sudubrava (5.2 %), the rest of tree types represents less than 4.0 % of the total land area, covered with sylva. The silver and black poplar plantings’ distribution according to the site quality of forest on the rivers’ columbine of the Left-bank Forest-steppe of Ukraine can be described in the following way: II and IV classes of the site quality of forest prevail, and the medium stocked tree stratum fluctuates from 52.9 to 87.8 per cent according to the normality.</p>

黔北火电厂周边森林土壤重金属污染现状研究

为探索山区火电厂周边森林土壤重金属污染现状，调查了贵州省黔北火电厂周边7个森林样地物种群落结构概况，在7个森林样点的中心部分、林地边缘及林外耕地进行了土壤样品采集，分析研究了土壤样品中铅、镉、汞、砷、铜与铬6中重金属的污染水平。结果表明林地土壤重金属Pb基本源于土壤形成的基岩，受外界污染较小。林地植被对大气沉降引起的Pb污染具有较好屏蔽效果，但对Hg、Cd两种元素的屏蔽效果相对较弱，主要受林分与密闭度的影响。基于贵州省土壤背景值及单因子指数与综合污染指数法评价结果，研究区土壤主要存在Hg、Cd、Pb的污染，而As、Cu及Cr则不存在污染现象。 To study the heavy metals pollution status of soils from forest land surrounding coal-fired plant in mountainous area, species community structures of 7 forest lands surrounding Qianbei Coal-fired Plant were investigate. Soil samples were collected at central parts and edge parts of these forest lands, and soils in cropland out of these forest lands were sampled as well. Pollution levels of Pb, Cd, Hg, As, Cu and Cr were analyzed. The results suggested that Pb in soils of forest land was mainly associated with rock weathering; forest trees are good shields against the Pb pollution caused by atmospheric deposition. For Hg and Cd pollution, its protection primary depended on its forest closure and components. According to the single factor and Nemerow comprehensive index method, study region was polluted with Hg, Cd and Pb, and no pollution of As, Cu and Cr in these areas was observed.

Forest‐cutting rapidly improves the demographic status of Paeonia officinalis, a species threatened by forest closure

AbstractIn the Mediterranean region, the spread and densification of woodlands and shrublands subsequent to rural depopulation is a critical issue for the conservation of open‐habitat plant species. Our objective was to assess the effectiveness of forest management to reduce the negative impact of forest closure on the persistence of a protected herbaceous perennial species Paeonia officinalis. Using demographic surveys from 2003 to 2008 in a woodland, open and managed habitat clear‐cutted for the aim of our study, we assessed the effect of forest opening on plant performance and population dynamics. In addition, we performed a shading experiment on reproductive plants to mimic canopy closure and study its impact on plant growth and fecundity. Based on quadrat surveys and matrix models, we showed that forest cutting induced a rapid increase in plant performance and population asymptotic growth rate. Indeed, within 2 years, plant size, flower, seed and ovule numbers as well as the plant stage distribution, asymptotic growth rates and elasticity patterns shifted from values similar to those in the woodland habitat to values similar to those in the open habitat. Similarly, artificially shaded reproductive plants regressed within 2 years towards the vegetative stage. For perennial plants which have a stage in their life‐cycle which allows for individual survival under unfavourable conditions such as the vegetative stage for P. officinalis, such demographic plasticity may be fundamental for their long‐term persistence in temporally heterogeneous environments. Our study highlights the need to mix an experimental approach with a mid‐term demographic survey in order to design efficient conservation management strategies for declining populations of rare species.

Shifts of forest species along an elevational gradient in Southeast France: climate change or stand maturation?

AbstractAimRecent vegetation changes in mountain areas are often explained by climate warming. However, effects of land‐use changes, such as recolonization of abandoned pastures by forest, are difficult to separate from those of climate change. Even within forest belts, changes in stand structure due to forest management and stand maturation could confound the climate signal. Here, we evaluate the direction and rate of plant species elevation shifts in mountain forests, considering the role of stand dynamics.LocationForests in the plains and mountains of Southeast France.MethodsWe compared floristic data from the French National Forest Inventory collected in the 1980s and 1990s. They provided a large‐scale (30 985 plots) and representative sample of vegetation between 0 and 2500 m a.s.l. Species response curves along the elevation and exposure gradients were fitted with a logistic regression model. In order to assess the effect of changes in successional stages of the forest stands, we compared plant species shifts in the whole set of stands with those solely in closed stands.ResultsA total of 62 species shifted downward, whereas 113 shifted upward, resulting in a significant upward mean shift of 17.9 m. Upward shifting species were preferentially woody and heliophilous, suggesting a role for forest closure and maturation in the observed changes. Excluding all open forest stages from analyses, the upward trend became weaker (−3.0 m) and was not significant. Forests of the study area have undergone closure and maturation, more strongly at lower altitudes than at higher ones, producing an apparent shift of species.ConclusionsIn the mountain relief of Southeast France, changes in the successional stages of stands appear as the main cause of the apparent upslope movement of forest species. Since a similar trend of forest maturation exists in large areas throughout Europe, forest dynamics should be better taken into account among the causes of vegetation changes before inferring any climate change effect.

The interplay of pollination, costs of reproduction and plant size in maternal fertility limitation in perennial Paeonia officinalis

Although several factors can limit female fertility in perennial plants, rarely have they been jointly studied in a single species over several years. In this study we experimentally manipulate seed production and simultaneously analyse the potential contribution of pollen limitation, costs of reproduction and plant size to variation in seed output over a 3-year period in the perennial herb Paeonia officinalis, in southern France. Since this rare species is threatened by forest closure in many sites we also examine the causes of female fertility variation in relation to habitat closure (open habitat vs. woodland). P. officinalis has a partial self-incompatibility system and only very low ability for autonomous self pollination in the absence of pollinators. However, supplementary pollination of individual plants in three consecutive years did not significantly increase seed production above natural levels. Forest closure was associated with a decline in ovule and seed production, which again was not due to pollen limitation since supplementary pollination had no significant effect on seed set in the woodland habitat. Comparison of the maternal fertility of plants which were previously excluded from reproduction with those which were hand pollinated to maximise seed set in two previous years produced no evidence that seed production in year three is limited by costs associated with prior reproduction. Likewise, flowering probability was not related to prior seed production but was however positively related to plant size. The absence of any influence of pollen limitation or prior reproduction on seed production suggests that sub-maximal seed production in long-lived perennial herbs may be part of a size-dependent strategy that maximises life-time seed production and fitness without compromising survival.

The impact of forest spread on a marginal population of a protected peony (Paeonia officinalis L.): the importance of conserving the habitat mosaic

In the Mediterranean region of Europe, land-use changes have allowed for rapid colonisation of open habitats by woody species. As a result, it is critical to gather information on how protected species in open habitats respond to forest spread in such areas. Our objective is to quantify whether spatial heterogeneity of the vegetation associated with recent forest closure influences demographic structure and maternal fertility in a population of the protected Paeonia officinalis L. In closed woodland, adult plants of P. officinalis are almost exclusively vegetative, in open habitats seedlings are rare and on the woodland edge there is a relative over-representation of flowering plants and seedlings. Forest closure dramatically reduces flowering frequency, but has no significant effect on maternal fertility of flowering plants. The spatial aggregation of seedlings close to the maternal plants suggests that dispersal is spatially restricted. Together, these results suggest that the viability of the population requires a transitional habitat between open garrigues or grassland with spaced trees and woodland. A management programme incorporating tree and shrub thinning and cutting of parcels in rotation to maximise the length of the forest edge could maintain a habitat mosaic that favours the persistence of this species in the study site.

Simulating changes in forest recreation demand and associated economic impacts due to fire and fuels management activities

Abstract The objective of this study is to simulate the linkages from fire and fuels management activities to changes in forest recreation demand, and ultimately to regional economic impacts. Using available survey data collected in New Mexico (United States) during the summer of 2001, a pooled travel cost and contingent behavior model of forest recreation demand is developed. An endogenously stratified truncated Poisson model is used to estimate consumer surplus and predict changes in recreation visits under different fire and fuels management scenarios. Using the econometric results on the predicted changes in recreation demand, regional Input–Output models, at both the state (New Mexico) and local (southwestern New Mexico) level, are constructed to simulate the varying regional economic impacts of three different fire and fuels management scenarios. For comparison, we also simulate the regional economic impacts, at both the state and local level, of forest closure scenarios during a significant part of the summer recreation season in New Mexico.

Stem Growth and Epicormic Branch Formation in Understorey Beech Trees (Fagus sylvatica L.)

A study of the formation of epicormic branches on suppressed beech trees revealed developmental sequences that had not hitherto been studied in depth. By combining architectural analysis and anatomy, it was possible to trace the history of the plant and thus fully understand the ontogenesis of the individuals studied. The main sequences observed were: (1) the formation of moribund trees that were gradually covered in epicormic branches from the base of the stem to the crown following gradual forest closure; (2) the formation of this new crown of epicormic branches was combined with a very sharp reduction in stem cambial activity (partial rings, if any) and modifications to the ligneous sections; and (3) resumed girth increment following the establishment of epicormic branches. After describing in detail the methods and individual variation, we highlight the spatial and temporal patterns of the phenomena observed. Lastly, we put forward functional hypotheses with a view to setting these results against a background of forest tree ontogenesis in general.

Relationship of Mn-carbonates in varved lake-sediments to catchment vegetation in Big Watab Lake, MN, USA

Mn-carbonates are documented in the late-glacial varved sediments from Big Watab Lake, Minnesota, USA. The Mn-carbonate is authigenic and forms rims around contemporaneous epilimnetic calcite. Although such carbonates are found in minor amounts throughout the entire late-glacial sequence, significant quantities of Mn-carbonate are associated mainly with laminated intervals.Because of the suspected difference in isotopic fractionation between different carbonate minerals, the stable-isotopic compositions of bulk carbonate samples are used as a proxy for relative amounts of the Mn-carbonate in the sediment. High δ18O and low δ13C values are associated with abundant Mn-carbonates. Low δ18O and high δ13C values are associated with only minor concentrations of Mn-carbonates.The oxygen-18 record is correlated with fluctuations in the vegetation assemblage based on pollen spectra using a multiple regression model with backward elimination. The proposed link between the sedimentary archive and local vegetation is the mediation of advective mixing in the lake by forest composition. In this model, periods of forest closure resulted in a well-stratified water column that was anoxic at the sediment/water interface, permitting the formation of authigenic Mn-carbonates. Openings of Artemisia in the forest allowed wind shear to mix oxygen to depth, causing bioturbation of the laminations and preventing the formation of Mn-carbonate.

Palaeoecology of postglacial treeline shifts in the northern Cascade Mountains, Canada

Postglacial changes in vegetation and chironomid communities at a subalpine lake in the Engelmann Spruce–Subalpine Fir zone in the northern Cascade Mountains, British Columbia, indicate patterns of treeline and climate fluctuation during the Holocene. In late-glacial sediments of Cabin Lake, pollen assemblages representative of alpine vegetation and cold-stenothermous chironomids indicate cold conditions prior to the Holocene. In the early Holocene (10,090 to 7000 14C yr BP) co-occurrence of spruce–fir parkland and a warm-adapted chironomid community indicates a warm and probably dry climate. In the mid-Holocene, inferred forest closure suggests that precipitation increased, and a mixture of warm- and cold-adapted chironomids indicates temperatures warmer than present, but cooler than in the early Holocene. This period between 7000 and 3200 14C yr BP represents a transitional climate in which temperature gradually declined, culminating in cool neoglacial conditions. This transitional interval may correspond with the `mesothermic period' proposed for lowland sites in southern British Columbia. Palaeobotanical evidence suggests that moist subalpine forest began to establish around 4800 14C yr BP with minimum temperatures and maximum precipitation between 2435 and ca. 1700 14C yr BP, corresponding with neoglacial advances throughout the northern Cordillera. A cool late Holocene (3200 14C yr BP to present) is also supported by a further decline in warm-adapted chironomids. Comparisons with other study sites in the Pacific Northwest reveal that regional climatic changes were a major factor in driving biotic changes in this area.

Plant Recolonization and Vegetation Succession on the Krakatau Islands, Indonesia

The development of the vegetation and floras of the Krakatau Islands in the Sunda Straits, Indonesia, since their "sterilization" in 1883 is described. Key features of the post—1883 environment, such as pedogenesis, geomorphology (coastal change), human influence, and recent volcanic activity are detailed, and their possible influence on spatial and temporal patterns in both vegetation and flora is discussed. Field work conducted in 1979, 1983, and 1984 has enabled an assessment of the present state of vegetation development, aided by plot—based sampling and analysis of the arboreal component, employing numerical classification (by TWINSPAN) and ordination (by DCA). The coastal communities were established early and have remained little changed, although the distribution of the various components has changed according to the influence of a dynamic coastal geomorphology. Fifty years after forest closure, the forest of the interiors remain species—poor and composed of typical early—seral species. Rakata was dominated inland by Neonauclea calycina and Ficus pubinervis up to ≈550 m altitude, above which a mossy forest of Ficus spp. and Schefflera polybotrya scrub was recorded. The main inland forest types on Rakata Kecil and Sertung were of young, evenaged stands of Timonius compressicaulis (extensive) and older stands of Dysoxylum gaudichaudianum (often with a T. compressicaulis understory). The principal axes of variation within the data were found to be between extremes of the Rakata forest types, with Sertung and R. Kecil stands remaining undifferentiated until lower levels of the analyses. These patterns were ascribed to a mix of environmental variation (coastal and altitudinal factors), chance variations in colonization, and to volcanic action following the emergence of Anak Krakatau in 1927. Disturbance by volcanism (e.g., in 1930, 1934—1936, 1939, 1952—1953, 1961) has resulted in the deflection of vegetation succession on R. Kecil and Sertung into a different pathway from that followed on Rakata, which has remained unaffected by the activity. On Anak Krakatau, volcanic action has prevented successful colonization away from accreting coastal deposits, and has several times eliminated the entire flora. In addition, the major source of propagules for Anak Krakatau is from within the group, and for these several reasons the new island is shown to be a poor analogue for the early recovery phases of the other islands. Complete floral lists are given for each recorded survey for each island in the group, including data from surveys in 1979, 1982, and 1983. These data have been revised from previous publications on the basis of recent herbarium work and literature searches. The data are analyzed according to several different models: cumulative species totals, species totals for particular combinations of surveys, and totals calculated on the assumption of minimum turnover. The early beach spermatophyte assemblages of Rakata have undergone relatively few losses in comparison to the assemblages of the interior, while within the latter there has been a relatively high proportion of losses among the pioneering pteridophytes. The possession of major habitat types has been identified as critical in determining the shape of the overall colonization curve, through the passive sampling of different source pools. The diversity of the floras of the group as a whole and of Rakata and Anak Krakatau has continued to increase. The curves of species present on Sertung and R. Kecil have levelled and fallen respectively, as a result of the volcanic activity of Anak Krakatau. It is shown that the number of animal—transported species on the Krakatau group has continued to increase over the last 50 yr, and that this accounts for the majority of the increase in the size of the spermatophyte flora. The animal—transported species and the early sea—dispersed species appear to be species—stable groups. Later sea—dispersed species included ephemerals and species of temporary habitats, and have experienced a relatively high proportion of losses. Few beach species that have established on all of the three main islands have subsequently become extinct from the group. The number of pteridophytes on the islands has increased over the last 50 yr, mainly through the addition of forest species. A large proportion of plant species has been found only on Rakata, which samples an upland source pool not represented on the other islands. It is argued that the assumptions of "classical" island biogeography are inappropriate to these data and that the pattern in floral recolonization can best be understood as a successional process involving broad habitat and dispersal mechanism determinants. The implication of these findings is that community dynamics are highly significant in determining rates of immigration, colonization (i.e., successful immigration), and extinction, and that the probabilities of each vary among different groups of species and through time.

A mid-Holocene record of vegetative change in central Alberta

Sediments from three lakes in central Alberta, Smallboy Lake (53°35′N, 114°8′W), E.I. Pond (53°38′N, 112°51′W), and Hastings Lake (53°25′N, 112°53′W), have been analyzed for their pollen content, charcoal remains, and (in two lakes) pyrite spherule concentration. The earliest record (radiometrically dated at 7400 years BP) indicates the existence of mixed-wood parkland vegetation. By 5000 years BP the regional vegetation had a considerably more open structure than now and was subject to frequent fires, presumably a response to the warm, dry Hypsithermal climate of this time. The termination of the Hypsithermal Interval (4000 years bp) is recorded in all three lakes by a marked increase in precipitation. The onset of a cooler, moister climatic regime stimulated forest closure and reduced regional fire activity, although the local vegetation of each of the three study sites responded in a unique way to the changing climate. By 3000 years BP the vegetation resembled the modern vegetation. Little change is recorded in the sediments from 3000 years BP to the present.