Classification of vegetational diversity in managed boreal forests in eastern Finland

Diversity of vegetation in managed forests is studied. A classification based on forest stand structure, the abundances of vegetation species and variations in these abundances is developed and diversity indices are calculated for the classes to describe the diversity of the vegetation within the classes. The classes were formed using detrended correspondence analysis (DCA), global nonmetric multidimensional scaling (GNMDS) and TWINSPAN classification. Discriminant analysis was used to determine the environmental variables differentiating between the classes, and Duncan's multiple range test was used to examine the ability of the diversity measures to distinguish the classes. Beta diversity was estimated with Økland's method based on DCA ordination of the sample plots. The results point to fertility and the successional stage of the stand as the main factors affecting species diversity, in addition to which soil type, the number of tree species, crown cover, basal area and certain variables describing the management of the stand were relevant to the classification. The most distinct diversity indices were the reciprocal of Simpson, Pielou's J' and species richness, while the highest alpha diversity was found in young stands with a low crown cover on herb-rich or mesic forest sites. Beta diversity was quite high, its highest values of all for the whole data being recorded along the fertility gradient.     

Implications of floristic and environmental variation for carbon cycle dynamics in boreal forest ecosystems of central Canada

Abstract. Species composition, detritus, and soil data from 97 boreal forest stands along a transect in central Canada were analysed using Correspondence Analysis to determine the dominant environmental/site variables that differentiate these forest stands. Picea mariana stands were densely clustered together on the understorey DCA plot, suggesting a consistent understorey species composition (feather mosses and Ericaceae), whereas Populus tremuloides stands had the most diverse understorey species composition (ca. 30 species, mostly shrubs and herbs). Pinus banksiana stands had several characteristic species of reindeer lichens (Cladina spp.), but saplings and Pinus seedlings were rare. Although climatic variables showed large variation along the transect, the CCA results indicated that site conditions are more important in determining species composition and differentiating the stand types. Forest floor characteristics (litter and humus layer, woody debris, and drainage) appear to be among the most important site variables. Stands of Picea had significantly higher average carbon (C) densities in the combined litter and humus layer (43530 kg‐C.ha^‐1) than either Populus (25 500 kg‐C.ha^‐1) or Pinus (19 400 kg‐C.ha^‐1). The thick surface organic layer in lowland Picea stands plays an important role in regulating soil temperature and moisture, and organic‐matter decomposition, which in turn affect the ecosystem C‐dynamics. During forest succession after a stand‐replacing disturbance (e.g. fires), tree biomass and surface organic layer thickness increase in all stand types as forests recover; however, woody biomass detritus first decreases and then increases after ca. 80 yr. Soil C densities show slight decrease with ages in Populus stands, but increase in other stand types. These results indicate the complex C‐transfer processes among different components (tree biomass, detritus, forest floor, and soil) of boreal ecosystems at various stages of succession.     

Compositional gradients in the forest vegetation of Finland

Abstract. Compositional gradients of forest vegetation in Finland were determined using detrended correspondence analysis, and ecologically interpreted with regression analysis. The data were collected in association with the 8th National Forest Inventory, and they comprised 1514 samples and 472 species, covering the whole forested land area of Finland. In the ordination space the first, very stable axis (DCA1) was much stronger than the following three, more unstable axes (DCA2 - 4). Site fertility (reflected by the forest site type series) and latitude had strongest covariation with the ordination space, followed by a number of variables primarily related to forest age or tree stand volume. Fertility variables were most closely parallel with DCA1, latitudinal ones with DCA1 and DCA2, and successional variables with DCA3. The results indicate that compositional overlap of sites classified into different Caj ander site types is considerable.     

Multiple successional pathways of boreal forest stands in central Canada

Predicting forest composition change through time is a key challenge in forest management. While multiple successional pathways are theorized for boreal forests, empirical evidence is lacking, largely because succession has been inferred from chronosequence and dendrochronological methods. We tested the hypotheses that stands of compositionally similar overstory may follow multiple successional pathways depending on time since last stand‐replacing fire (TSF), edaphic conditions, and presence of intermediate disturbances. We used repeated measurements from combining sequential aerial photography and ground surveys for 361 boreal stands in central Canada. Stands were measured in 8–15 yr intervals over a ~ 60 yr period, covering a wide range of initial stand conditions. Multinomial logistic regression was used to analyze stand type transitions. With increasing TSF, stands dominated by shade‐intolerant Pinus banksiana, Populus sp., and Betula papyrifera demonstrated multiple pathways to stands dominated by shade‐tolerant Picea sp., Abies balsamea, and Thuja occidentalis. Their pathways seemed largely explained by neighborhood effects. Succession of stands dominated by shade‐tolerant species, with an exception of stands dominated by Picea sp., was not related to TSF, but rather dependent on edaphic conditions and presence of intermediate disturbances. Varying edaphic conditions caused divergent pathways with resource limited sites being dominated by nutrient‐poor tolerant species, and richer sites permitting invasion of early successional species and promoting species mixtures during succession. Intermediate disturbances promoted deciduous persistence and species diversity in A. balsamea and mixed‐conifer stands, but no evidence was detected to support “disturbance accelerated succession”. Our results demonstrate that in the prolonged absence of stand‐replacing disturbance boreal forest stands undergo multiple succession pathways. These pathways are regulated by neighborhood effects, resource availability, and presence of intermediate disturbance, but the relative importance of these regulators depends on initial stand type. The observed divergence of successional pathways supports the resource‐ratio hypothesis of plant succession.     

Underplanting degraded exotic Pinus with indigenous conifers assists forest restoration

We propose that nonharvest plantations could provide important opportunities for restoration of indigenous forest cover and related ecosystem services. We assessed the relative performance of three Podocarpaceae (podocarps) species planted into a degraded Ponderosa Pine (Pinus ponderosa) plantation, central North Island, New Zealand. We hypothesised that the degraded pine plantation overstorey could provide suitable conditions for the development of a podocarp‐dominated forest structure within ca. 50 years of underplanting and that podocarp growth would differ depending on the species suitability to the site. Rimu (Dacrydium cupressinum) significantly outperformed both Totara (Podocarpus totara) and Kahikatea (Dacrycarpus dacrydioides) in height and diameter growth. Rimu was now the structurally dominant tree where it occurred rather than pine. Per annum scaled carbon storage within Rimu stands was significantly greater than the Totara, Kahikatea or Pine stands. All podocarp species had attained a greater stand density compared to the pine overstorey. Possible reasons for the differing podocarp growth performance include different light requirements, response to soil nutrients, elevational distributions and frost susceptibility. There were significant differences in understorey species richness among the different stands of podocarp species. Underplanting accelerated successional development by incorporating late‐successional indigenous canopy dominants within the forest succession and overcame limitations imposed on forest succession at the site from its isolation from indigenous forest tree seed sources.     

Understorey vegetation change in a Picea mariana chronosequence

Eighteen black spruce (Picea mariana) stands, representing postfire ages of 26 to 120 yr, were surveyed for understorey vegetation and site/microsite characteristics at two spatial scales. This enabled comparison of within- versus among-stand compositional variation.Detrended correspondence analysis (DCA) ordination among the 18 stands revealed a complex age/moisture gradient. DCA ordination among 1 800 quadrats within the stands indicated a similar gradient with much compositional overlap. Quadrats were grouped, using two-way indicator species analysis (TWINSPAN), into 9 classes each representing a phase in understorey vegetation composition. These phases shifted in abundance from young to old stands with a high degree of concordance among replicates in the same age class. Understorey succession is strongly linked to the stages in tree growth, mortality and thinning coupled with the accumulation of site moisture.Abbreviations DCA Detrended Corrospondence Analysis     

Succession in the southern part of the Canadian boreal forest

Forest succession following fire in a forest mosaic of northwestern Quebec has been studied in order to: (1) describe the successional pathways using communities of different ages and (2) evaluate convergence of successional pathways and possible effect of fire suppression on the establishment of steady-state communities. As a first step, ordination and classification techniques were used in order to remove changes in forest composition which are related to abiotic conditions. Then, ordinations based on tree diameter distributions were used to study shifts in species composition in relation to time since the last fire.Even under similar abiotic conditions, successional pathways are numerous. However, regardless of forest composition after fire, most stands show convergence toward dominance of Thuja occidentalis and Picea mariana on xeric sites and dominance of Abies balsamea and Thuja occidentalis on more mesic sites. Stable communities of >300 yr occur on xeric sites while on mesic sites directional succession still occurs after 224 yr. Nearly all species involved in succession are present in the first 50 yr following fire. Only Abies balsamea and Thuja occidentalis increase significantly in frequency during succession. Following initial establishment, successional processes can generally be explained by species longevity and shade tolerance. Early successional species may be abundant in the canopy for more than 200 yr while the rapid decrease of Picea glauca, a late successional species could be related to spruce budworm outbreaks. Considering the short fire rotation observed (about 150 yr), a steady-state forest is unlikely to occur under natural conditions, though it may be possible if fire is controlled.     

Variation in terricolous bryophyte and macrolichen vegetation along primary gradients in Canadian boreal forests

Abstract. Compositional variation among 172 boreal forests stands, based upon the understorey terricolous bryophyte and macrolichen vegetation, is compared with that based upon vascular vegetation. Detrended correspondence analysis (DCA) of the two datasets yielded stand ordinations each indicating a single dominant upland-bottomland gradient. This was most clear among 138 stands in the cryptogam dataset. Canonical correspondence analysis (CCA) of the 138 stand subset yielded a pronounced first axis gradient from dry, nutrient poor pine dominated forest sites to moist, nutrient rich bottomland sites dominated by balsam poplar woodland. Individual species response curves, by the method of log-linear least squares regression, yielded three different respective patterns among the most abundant tree, understorey vascular and cryptogamic plant species. Whereas curves for the tree species were ‘Gaussian’ in shape and displaced at somewhat regular intervals along the gradient, the abundant understorey vascular plant species curves clustered in the mesic, mixed wood region two thirds of the way along. Curves for the abundant cryptogams were mostly linear in shape and absent from the mixed wood zone, showing concentrations at one end of the gradient or the other. Two interpretations of the understorey pattern are considered. One proposes competitive exclusion of cryptogams from the mesic mixed wood region by the vascular understorey plants. Another proposes that the cryptogams are adapted to the sharply contrasting ecosystems encountered at one end of the gradient or another but that none can effectively cope with the intermediate, mixed wood ecosystems. Evidence from the response curves favours this second interpretation.     

Succession in sub‐boreal forests of West‐Central British Columbia

Abstract. Structural and compositional changes were analysed over the course of 400+ yr of post‐fire succession in the sub‐boreal forests of west‐central British Columbia. Using a chronosequence of 57 stands ranging from 11 to 438 yr in age, we examined changes in forest structure and composition with complementary PCA and DCA ordination techniques. To determine stand ages and timing of tree recruitment, approximately 1800 trees were aged. Most early successional forests were dominated by Pinus contorta, which established rapidly following fire. Abies lasiocarpa and Picea glauca × engel‐mannii were also able to establish quickly, but continued to establish throughout the sere. Few Pinus contorta survived beyond 200 yr, resulting in major changes in forest structure. In some stands P. contorta never established, which led to considerable variation among stands less than 200 yr old. The oldest forests converged on dominance by Abies lasiocarpa. Vascular plant diversity decreased during succession whereas canopy structure became more complex as gap dynamics developed. Although these sub‐boreal forests contain few tree species, successional changes were pronounced, with structure changing more than composition across the chronosequence.     

Restoration of natural vegetation in degraded Imperata cylindrica grassland: understorey development in forest plantations

Abstract. Reclamation of former, degraded forest lands occupied by Imperata cylindrica is one of the crucial environmental and forestry issues in the humid tropics, notably Southeast Asia. We suggest that it is possible to gradually restore the original natural forest cover with the help of a sacrifice fallow crop of fast-growing exotic tree species. Recently, a set of suitable fast-growing plantation tree species has been identified and stand establishment methods developed for this purpose. We assessed the regeneration of natural vegetation in stands of different plantation tree species and evaluated the ecological impact of species composition in the plantation understorey. PCA ordination, regression analysis and analysis of covariance were applied at different stages of the study. We found a marked vegetational resemblance between stands dominated by Acacia mangium: they had the highest number of indigenous trees in their understorey, whereas stands of other plantation trees supported more diverse grass and herb vegetation. A high proportion of evergreen woody vegetation reduces the risk of fire and grass competition and enhances secondary succession towards natural forest.     

Causes of arrested succession in coastal dune forest

Dispersal or recruitment limitation may arrest succession after disturbance. In north-eastern South Africa the Acacia karroo successional pathway is used to facilitate coastal forest recovery after strip-mining. However, although A. karroo establishes naturally, it forms monospecific stands, arresting forest succession for decades. This casts doubt on the efficacy of this restoration pathway. We investigated the causes of arrested succession. The seed and seedling banks of A. karroo stands and of forest at Cape Vidal, and three A. karroo stands (7–27 years old) on rehabilitated strip-mined dunes at nearby Richards Bay were examined. The establishment and growth of seedlings at Cape Vidal were also considered. The seed bank was larger and more diverse in forest, but the seedling bank was larger in Acacia stands. At Richards Bay, the size of the seed bank increased and the seedling bank decreased with Acacia stand age. Excluding mammalian herbivores in Acacia stands at Cape Vidal resulted in greater species richness and survival of naturally established seedlings, as well as two experimentally planted species. Neither seed dispersal nor seedling establishment limited recruitment of tree species in Acacia stands. Herbivory arrested forest succession by causing the differential mortality of seedlings. In contrast, at Richards Bay where there were few mammalian herbivores, the advanced regeneration in A. karroo stands converged on the diversity of nearby forests 29 years after restoration. Controlling herbivore access and seeding Acacia stands with forest species are site-specific options for preventing arrested succession when using the A. karroo successional pathway.     

Predicting the composition of Canadian southern boreal forest in different fire cycles

Abstract. Post-fire succession was reconstructed for a sector located in the southern part of the Québec boreal forest. Forest composition for different periods since fire was evaluated using a stand initiation map together with ecological maps representing both site conditions and stand types. Nine fires covering at least 100 ha and representing a chronosequence of more than 230 yr were used. Although a relatively clear successional pattern from deciduous to coniferous composition relating to time-since-fire was observed, Pinus banksiana stands showed an erratic distribution not related to succession but possibly to the pre-fire stand composition. A comparison with forest cover maps produced after a recent spruce budworm outbreak, showed that succession toward coniferous dominance appeared to be interrupted by spruce budworm (Choristoneura fumiferana) outbreaks which, by killing Abies balsamea, lead to a mixed deciduous forest composition. A simple empirical model based on a negative exponential distribution of age classes was developed to evaluate how changes in the fire cycle would affect the composition of the forest mosaic. The transition between deciduous dominance and coniferous dominance occurs in a fire cycle > 200 yr. Although pure deciduous stands tend to disappear during long fire cycles, the proportion of mixed stands remains relatively constant. Prediction of the forest composition for longer fire cycles is complicated by the interaction between post-fire composition and stand vulnerability to spruce budworm outbreaks.     

Correlation between stand structure and ground vegetation: an analytical approach

The effect of stand structure on the diversity of the forest's ground vegetation was examined based on data on permanent sample plots collected in the northern parts of North-Carelia, eastern Finland. Different ordination methods (DCA, GNMDS, LNMDS, and HMDS) were used together with the TWINSPAN classification method. The aim was to construct a basis for classifying forests with respect to the biodiversity of the forest vegetation. Fertility and stand age showed the strongest correlation with the variation in ground vegetation. Other important factors were basal area, tree species composition, and crown cover. These variables were important in the division of the sample plots into different classes. According to the diversity indices, species diversity was at its highest in young stands on fertile forest sites. As a result, twenty-one different classes were formed based on the relative abundance of understorey species. The variables with the highest correlation were used to describe the stand structure in these classes.     

子午岭地区植被恢复演替过程与环境因子的分类与排序

在野外实地调查基础上,采用双向指示种分析法(TWINSPAN)和除趋势对应分析(DCA)对子午岭地区植物群落进行了数量分类和排序。结果显示:(1)TWINSPAN将50个样方划分为14个群系;DCA排序结果与TWINSPAN分类结果相互印证。(2)第一排序轴上显示出植被由草地、灌丛到森林的恢复演替系列,在此演替过程中土壤中的速效磷逐渐减少,全氮和有机质逐渐增加;第二排序轴反映环境因子的梯度不明显,但植被的演替过程会受到海拔、坡度的影响。研究表明,随着植被恢复演替的进展群落结构在变化,乔木层的重要值增加,所在群落中的全氮、速效磷、有机质等亦呈现规律性变化。     

Riverscape-level patterns of riparian plant diversity along a successional gradient, Willamette river, Oregon

Riparian forest communities dominated by Populus balsamifera ssp. trichocarpa L. (Torr. and Gray ex Hook.) Brayshaw are important contributors to biodiversity in terrestrial and aquatic ecosystems of the Western United States. Species composition along a successional gradient from stand initiation to late-succession of P. balsamifera-dominated riparian forests was investigated along 145 km of the Willamette River, Oregon. There were 151 total species encountered across 28 stands and a mean species richness of 33.3 species per stand. Young stands were dominated by P. balsamifera and Salix tree spp. and opportunistic herbaceous species. Understory trees, shrubs, and herbaceous species as well as late-successional tree species established 12–15 years after stand initiation. Fraxinus latifolia Benth. was the dominant late-successional tree species. Vertical structural diversity, P. balsamifera mean diameter at breast height, large tree biomass, and stand age were strongly correlated with understory species presence and abundance based on non-metric multidimensional scaling (NMS) ordination. There were no young stands on mid and high terraces and this was reflected in geomorphic position being strongly correlated with the stand age gradient. Abundance of Phalaris arundinacea L. an invasive grass species, was also significantly correlated with plant species composition and abundance. This study indicates that Willamette River riparian forests are diverse and therefore important to the biodiversity of the Willamette River valley and that their presence as a mosaic of communities of different successional stages may be threatened by human interventions, including influences exerted by introduced plant species.     

Long‐term successional forest dynamics: species and community responses to climatic variability

Question: Are trees sensitive to climatic variability, and do tree species differ in their responses to climatic variability? Does sensitivity of forest communities to climatic variability depend on stand composition? Location: Mixed young forest at Walker Branch Watershed near Oak Ridge, East Tennessee, USA. Methods: Using a long‐term dataset (1967–2006), we analyzed temporal forest dynamics at the tree and species level, and community dynamics for forest stands that differed in initial species composition (i.e., chestnut oak, oak–hickory, pine, and yellow poplar stands). Using summer drought and growing season temperature as defined climate drivers, we evaluated relationships between forest dynamics and climate across levels of organization. Results: Over the four‐decade study period, forest communities underwent successional change and substantially increased in biomass. Variation in summer drought and growing season temperature contributed to temporal biomass dynamics for some tree species, but not for others. Stand‐level responses to climatic variability were related to the responses of component species, except in pine stands. Pinus echinata, the dominant species in pine stands, decreased over time due to periodic outbreaks of pine bark beetle (Dendroctonus frontalis). These outbreaks at Walker Branch could not be directly related to climatic conditions. Conclusions: The results indicate that sensitivity of developing forests to climatic variability is stand type‐dependent, and hence is a function of species composition. However, in the long term, direct effects of climatic variability on forest dynamics may be small relative to autogenic successional processes or climate‐related insect outbreaks. Empirical studies testing for interactions between forest succession and climatic variability are needed.     

海南岛热带山地雨林天然次生林的功能群划分

热带林极高的物种丰富度使许多生态分析非常困难,把功能相似的物种划分为不同功能群,将为热带林的生态研究提供新的途径。以物种的7个功能特性因子(生长型、分布的海拔高度、分布的林型、木材密度、喜光性、演替地位和寿命)和9个林分结构因子(相对生物量、相对胸高断面积、相对树高、相对密度、相对频度、相对冠幅、相对更新数、相对死亡数和相对萌生数)为基础,应用数量化分析的方法,对海南岛典型的热带山地雨林天然次生林群落进行了功能群的划分。结果表明:(1)应用CCA分析林分结构因子时,可将山地雨林天然次生林的物种划分为6类功能群,它们的相对生物量、相对密度、相对频度、相对更新数、相对萌生数和相对死亡数等,随胸径和高度的增加而呈现有规律的变化;(2)应用CCA分析物种功能特性因子时,可将山地雨林天然次生林的物种划分为5类功能群,它们的功能特性都随演替过程而呈现有规律的变化;(3)在综合考虑两个不同角度CCA分析的基础上,最后将热带山地雨林天然次生林的物种共划分为11类功能群,它们能充分体现物种随胸径和高度结构的变化特点及其在演替过程中所处的阶段;(4)演替初期的灌木类功能群与各不同演替时期的乔木功能群共同分布于的中下层,但其大多处于死亡状态;(5)演替初期与演替中后期的乔木功能群则共同组成的主层林,但其死亡数量也较高。可见,海南岛热带山地雨林天然次生林目前正处不同功能群的激烈竞争阶段。     

Changes in diversity along a successional gradient in a Costa Rican upper montane Quercus forest

Changes in terrestrial vascular plant diversity along a successional gradient were studied in a Costa Rican upper montane Quercus forest. In 1991 and 1992 species presence and cover were recorded in 12 successional 0.1 ha forest plots. A total of 176 species in 122 genera and 75 families were found. Asteraceae was the most speciose family. With the help of TWINSPAN three successional phases were classified: (i) Early Secondary Forest (ESF, 145 spp.), (ii) Late Secondary Forest (LSF, 130 spp.) and (iii) Primary Forest (PF, 96 spp.). Detrended Correspondence Analysis (DCA) species ordination using DECORANA illustrates that different ecological species groups can be distinguished along the time sequence. Alpha diversity (Shannon-Wiener index, among others) in ESF and LSF was significantly greater than in PF. This is probably explained by downslope migration of numerous sub(alpine) species to cleared and recently abandoned montane sites. Beta diversity applying Sørensen's similarity coefficients declined during succession. Using linear regression, the minimum time required for floristic recovery following disturbance and abandonment was calculated at 65.9 years. A comparison with other studies shows that secondary forests in upper montane Costa Rica can be as diverse as in neotropical lowlands.     

Long‐term forest structure and regeneration after wildfire in Russian Karelia

We examined forest structure and regeneration in a 350‐ha forest dominated by Pinus sylvestris 31 yr after a wildfire in the Vienansalo wilderness, Russian Karelia. In most parts of the area, the 1969 fire was not stand replacing but had left larger trees alive so that the area generally remained forest covered. In some localities, however, all trees apparently died and distinct gaps were formed, suggesting that the fire severity varied considerably, contributing to increased variation in stand structure. Living and dead wood volumes were similar, 112 and 96 m³.ha^‐1, respectively. The tree species proportions of dead vs living wood indicated that prior to fire disturbance Picea was more common in the area. Regeneration was abundant (saplings, ca. 14 000 ind.ha^‐1, height 20 ‐200 cm) and tree seedling recruitment had occurred over a long period of time. Regeneration density was highest on the mesic Vaccinium‐Myrtillus forest site type, decreasing towards nutrient‐poor site types. The most common regeneration microsites were level ground (56% of saplings), immediate surroundings of decayed wood (23%) and depressions (11%). The high proportion of saplings on level ground suggests that after the fire regeneration conditions have been favourable across the whole forest floor. Nevertheless, the areas in the vicinity of decayed wood have been particularly important microsites for seedling establishment. The results provide an example of the effects of wildfire on forest structure in a natural Pinus sylvestris dominated forest, demonstrating the non stand replacing character of fire, high variability in stand structure and the abundance of post‐fire regeneration.     

Differences in forest composition in two boreal forest ecoregions of Quebec

Abstract. In order to describe and compare the post‐fire succession patterns of the two ecological regions (mixed‐wood and coniferous ecoregions) of northwestern Quebec, 260 forest stands were sampled with the point‐centred plot method. The mixed‐wood ecological region belongs to the Abies balsamea‐Betula papyrifera bioclimatic domain whereas the coniferous ecological region belongs to the Picea mariana‐moss bioclimatic domain. In each plot, tree composition was described, surficial deposits and drainage were recorded, and fire history was reconstructed using standard dendro‐ecological methods. Ordination techniques (Correspondence Analysis and Canonical Correspondence Analysis) were used to describe the successional patterns of forest vegetation and to correlate them with the explanatory variables. The results showed the importance of surficial deposits, the time since fire and the ecoregion in explaining the variation of stand composition. Abies balsamea tends to increase in importance with an increase in time since fire, and this trend is more pronounced in the mixed‐wood region. Even when controlling both for surficial deposits and time since fire, differences in successional trends were observed between the two ecoregions. As all the species are present in both ecoregions and as they are all observed further north, our results suggest that both the landscape configuration and fire regime parameters such as fire size and fire intensity are important factors involved in these differences.