Plant Community Development Research Articles

Палинологическая зональность живетско-франского стратиграфического интервала в Тимано-Североуральском регионе

The zonal scheme of the Givetian-Frasnian boundary interval in the Timan-Northern Urals region was detailed according to the higher plants spores. Palynological zones were correlated with faunal, including conodont — orthostratigraphic group in the Devonian. The correlation of the identified critical boundaries in the development of plant communities with the divisions’ borders of the International Stratigraphic Scale — series and stages, were established and options for the level of the border of the Middle and Upper Devonian in the regional stratigraphic scheme of the new generation were considered.

Synthesis on the effectiveness of soil translocation for plant community restoration

Abstract Many degraded ecosystems need active restoration to conserve biodiversity and re‐establish ecosystem function, both highlighted targets of the UN Decade on Ecosystem Restoration and the proposed EU Nature restoration law. Soil translocation, where both plant propagules and their associated soil biota are co‐introduced, has increasingly been proposed as a powerful restoration technique for terrestrial ecosystems. However, a synthesis of the effectiveness of this method across ecosystems is lacking. To address how soil translocation affects restoration success, we performed a meta‐analysis synthesizing data from 46 field experiments and their respective reference ecosystems in 17 countries across four continents. In each experiment, vegetation composition was recorded in response to soil translocation treatments and the resultant vegetational changes (diversity and composition) were quantified. We found that soil translocation leads to plant community development further away from the control and more towards the reference plant communities compared with treatments where only plant propagules were introduced. However, the variability of effect sizes among experiments was large, suggesting strong dependence of restoration success on restoration context. We found that restoration success was more likely on loamy soils and when translocation treatments were implemented over larger spatial areas (>180 m2). Furthermore, we found that restoration success either consistently increased or decreased over time depending on the experiment. Not only is this congruent with positive feedbacks between plant and soil communities driving plant community development, but it also suggests that the composition of the translocated plant and soil communities, and initial starting conditions, are critical for long‐term restoration success. Synthesis and applications. Our analysis highlights soil translocation can be a successful restoration method across a broad range of ecosystems. However, its implementation needs to depend on a thorough evaluation of local conditions and the potential added value. Further refinement of soil translocation techniques is needed to increase success rates.

REFORESTATION PROCESS AFTER A GROUND FIRE AND CLEAR CUTTING IN LIANA-VARIED-SHRUB BROAD-LEAVED-DARK-CONIFEROUS-KOREAN-PINE FORESTS OF SOUTHERN SIKHOTE-ALIN

A comparative analysis of the formation and natural course of development of plant communities was carried out in two plots: (1) passed through by a stable ground fire and (2) subjected to experimental clear cutting with preserving young generation of tree species in liana-varied-shrub broad-leaved-dark-coniferous-Korean-pine forests of the mid-mountain belt of the Southern Sikhote-Alin. The features of natural recovery, course of growth, development and dynamics of the number of woody plants in the first 35 years of the reforestation process are considered. Taxation characteristic of the forest stands before their destruction by the fire and cutting, as well as at the first stages of the formation of young tree stands, are given. The dynamics of the species composition and phytomass of the aboveground parts of plants of the shrub and low-shrub-herb layers is considered.

Twenty Years of Urban Reforestation: Overstory Development Structures Understory Plant Communities in Lexington, KY, USA

Urban forests provide critical ecosystem services in an increasingly urbanized global landscape. The reforestation of undeveloped parcels and serially mowed grasslands can increase urban forest cover, but plant community development in planted urban forests is poorly understood. We conducted a study to elucidate the roles of time since tree planting, invasive species abundance, and other abiotic and biotic site-level factors in structuring understory plant communities within a 20-year chronosequence of planted urban forests in Lexington, KY, USA. We assessed the percent of groundcover of all understory species in fixed-radius plots on the site. Understory herbaceous plant communities demonstrated shifts from graminoid dominance to forb dominance over time, and plant communities in successively younger sites were increasingly dissimilar from that of the 20-year-old site. Invasive plant species were abundant, representing 21% of total groundcover across all surveyed plots, and became increasingly prevalent over time. Understory plant diversity was negatively associated with invasive species abundance. Overall, site factors, including time since planting, forest canopy closure, density of tree and shrub reproduction, and soil pH, accounted for much of the variability among understory communities. Understory plant communities across the chronosequence of planted sites demonstrated apparent structural shifts with overstory canopy development, but the increasing prevalence of invasive species and their negative impacts to plant diversity warrant future management to ensure the continuation of the desired successional trajectories.

Early ecosystem establishment using forest floor and peat cover soils in oil sands reclamation

ABSTRACT Early trends of plant community development provide the basis of ecosystem function and reclamation success of oil sand extraction sites. However, few studies have explicitly investigated species-level interactions with different cover soil types, placement depths, and time since reclamation during early plant community development in boreal forests. We investigated effectiveness of forest floor mineral mix (FMM) and peat mineral mix (PMM) cover soils and placement depths (10 and 20 cm) at four research sites 4 to 13 years after reclamation. Outcomes of this study indicate FMM had a more positive influence on woody plant densities, vegetation cover, and species richness than PMM. Species assemblage, composition, dominance, and types (successional stages, habitat types, competitive-stress tolerant-ruderal strategies) also showed FMM cover soil performed better than PMM. Greater vegetation cover and richness on deeper (20 cm) cover soil placements were evident. However, this effect of cover soil depth would likely decrease with time. Dominant and subdominant species on FMM were native and early to late successional, thus trajectory community development on FMM followed typical early succession of boreal forests (from ruderal and annual to perennial communities), while PMM was dominated by non-native and annual forbs which could slow succession and ecosystem recovery.

Aphananthe Planch. (Cannabaceae) flower preserved in the Mexican amber

Cannabaceae (Urticalean Rosids clade) is a small family with ten genera and a wide distribution in tropical and temperate regions worldwide. A complete understanding of the history of the lineage is fundamental to the integration of its fossil record, which needs to be better documented in low latitudes of North America. This work recognizes a new species, Aphananthe manchesteri Hernández-Damián, Rubalcava-Knoth et Cevallos- Ferriz sp. nov. (Cannabaceae), from the Miocene amber deposits of Simojovel de Allende, Chiapas, Mexico, based on a flower analyzed with reflected light and CT-scanning. Flowers of Cannabaceae are generally staminate or pistillate and small; staminate flowers have five sepals and opposite five stamens, and a pubescent pistillode, such as the fossil. However, the presence of three unguiculate and two ovate sepals with a puberulent surface are characteristics that allow its recognition as Aphananthe, the fossil is morphologically similar to Aphananthe monoica, an extant species that grows along the Pacific coast of Mexico. The presence of Aphananthe manchesteri sp. nov. in southern Mexico during the middle-early Miocene, ~23–15 Ma ago, supports the history of the lineage in lowlatitude North America, representing an expansion of the Boreotropical Flora. It adds to the taxonomical diversity of angiosperms preserved in Mexican amber, comparable with amber deposits from the Dominican Republic, where another anemophilous extinct species member of the Urticalean Rosids clade has been reported. This coincidence further supports the development of similar plant communities between these fossiliferous localities.

Mathematical modeling of plant community composition for urban greenery plans

Urban green space is critical for humans and other organisms living in cities. Researchers have noticed that urban green space planning has been focusing more on ornamental and public management purposes but less on its ecological purpose, which has a negative impact on eco-sustainability. We hypothesized that an urban greenery management plan with high eco-sustainability can be achieved by calculating the composition of a plant community through mathematical modeling. To test our hypothesis, we created a nonlinear programming function that generated a plant community composition aiming for high plant fitness, high biodiversity, and low managing cost. Green fields in a Beijing city park, comprising different combinations of plant species were used to optimize our model. Although the outputs of the optimized model do not match completely with the composition of testing fields, they illustrate possible patterns for plant community development. By applying this model, urban green space can be finely designed to become both ecologically and economically sustainable.

Interactions between soil water and plant community during vegetation succession in the restored grasslands on the Loess Plateau of China

AbstractPlant–soil water relations are important for understanding the development of plant communities, especially in arid and semiarid areas. However, the interactions between vegetation characteristics and soil water dynamics in the restored grasslands along succession chronosequence were limitedly understood. In this study, we measured the functional traits of dominant species, plant community characteristics and soil water dynamics in grasslands restored for 5, 15, and 30 years (RG5, RG15 and RG30, respectively), and investigated the linkage between plant traits and soil water at the community/plot scale. The results showed that soil water content was high at RG5, while soil water storage increment at RG5 was low. With soil water content highest at RG5 (16.25%), decreased at RG15 (14.81%), and then recovered in some degree at RG30 (15.2%), dominant plant species changed from pioneer species Artemisia capillaries to perennial legume Lespedesa davurica with high specific leaf area, and finally to perennial forb Stipa bungeana with low specific leaf area and low shoot/root ratio. Plant community characteristics including aboveground biomass, vegetation coverage, species diversity all increased with restoration and reached the highest value at RG15 or RG30. Aboveground biomass of perennial grass, as well as species richness showed a significantly positive relationship with soil water recharge and soil water storage increment at deeper layers (10–120 cm and 40–120 cm). Species diversity had positive correlations with soil water content in 0–10 cm layer, a negative correlation with soil water storage increment in 0–10 cm layer and no correlation in 10–20 cm layer. Our findings suggested that changes in soil water content might enhance perennial grass species in semiarid grasslands, and time lag also existed in the plant–soil water interactions.

Species‐specific soil legacy effects on ecosystem multifunctionality via regulating plant overyielding

AbstractSoil legacy effects and biodiversity play important roles in driving plant community dynamics and functioning. However, experimental evidence of the effects of soil legacy on ecosystem multifunctionality (maintaining multiple functions simultaneously) is lacking. We first conducted a mesocosm experiment in which three common species (grass, legume, and forb) were planted in monocultures and mixed cultures to produce soil legacies. Subsequently, soils were sampled to test the soil legacy effects on ecosystem multifunctionality in a greenhouse experiment. Our findings showed that plant‐mediated soil legacy effects were species‐specific and strongly influenced the productivity of subsequent plants or combinations. Specifically, plant‐specific soil legacies had considerable impacts on the magnitude and direction of diversity‐dependent overyielding effects. Such effects can compensate for non‐legume soil legacy effects and maintain overall productivity. Functional diversity and ecosystem multifunctionality were largely affected by soil legacy effects and were significantly positively correlated with functional group richness. Based on our results, plant‐specific soil legacy is an important factor limiting the development of plant community and ecosystem multifunctionality in the early stage of community construction. The rational use of the synergistic effects of plant‐specific soil legacy and functional group richness may be a key to ensure the successful establishment of vegetation and grassland management.

Mechanisms underlying the succession of plant rhizosphere microbial community structure and function in an alpine open-pit coal mining disturbance zone

Elucidating the responses and potential functions of soil microbial communities during succession is important for understanding biogeochemical processes and the sustainable development of plant communities after environmental disturbances. However, studies of such dynamics during post-mining ecological restoration in alpine areas remain poorly understood. Microbial diversity, nitrogen, and phosphorus cycle functional gene potential in the Heishan mining area of Northwest China was studied, including primitive succession, secondary succession, and artificial succession disturbed by mining. The results revealed that: (1) The dominant bacteria in both categories (non-remediated and ecologically restored) of mining area rhizosphere soil were Proteobacteria, adopting the r strategy, whereas in naturally occurring soil outside the mining area, the dominant bacteria were actinomycetes and Acidobacteria, adopting the k strategy. Notably, mining perturbation significantly reduced the relative abundance of archaea. (2) After restoration, more bacterial network node connections were observed in mining areas than were originally present, whereas the archaeal network showed the opposite trend. (3) The networks of microbial genes related to nitrogen and phosphorus cycle potential differed significantly, depending on the succession type. Namely, prior to restoration, there were more phosphorus related functional gene network connections; these were also more strongly correlated, and the network was more aggregated. (4) Soil factors such as pH and NO3–N affected both the mining area remediation soil and the soil outside the mining area, but did not affect the soil of the original vegetation in the mining area. The changes in the structure and function of plant rhizosphere microorganisms after mining disturbance can provide a theoretical basis for the natural restoration of mining areas.

Late‐season drought exerts more negative effects on plant diversity and cover than early‐season drought through changing soil moisture in a semi‐arid grassland

AbstractQuestionsDrought timing during the growing season can profoundly influence plant diversity and cover, with subsequent impacts on ecosystem functions and services in terrestrial environments. However, the different responses of plant communities to drought in different periods of the growing season remain uncertain.LocationThe research was conducted in a semi‐arid grassland at the Duolun Restoration Ecology Research and Demonstration Station, in Inner Mongolia, China.MethodsThe responses of plant species richness and cover to early‐ and late‐season drought with a four‐year field experiment were examined in a semi‐arid grassland in northern China. Soil moisture at different depths was measured to explore the underlying mechanisms of the drought effects on plant richness and cover.ResultsOver the four years, late‐ rather than early‐season drought suppressed plant richness. Decreased species richness (−1.65 species) under late‐season drought was mainly due to suppressed perennial forb richness (−1.88 species). Late‐season drought also exerted greater negative effects on plant cover than early‐season drought. Effects of late‐season drought on plant cover depended on annual precipitation. Reduced plant cover (−7.5%) under early‐season drought stemmed from declines in shrubs and semi‐shrubs, particularly Artemisia frigida cover (−4.9%), which is sensitive to water deficits because of its shallow root depth (14.01 cm). Declined plant cover (−39.0%) under late‐season drought was mainly caused by suppressed perennial forb (−21.5%) and shrub and semi‐shrubs cover (−17.4%). The combined effects of early‐ and late‐season drought on plant cover were greater than the treatment alone, likely due to aggravating water deficits under growing‐season drought.ConclusionsOur results suggest late‐season drought is more critical for shifting plant communities. than early‐season drought. Our findings highlight the regulatory role of drought timing on plant community composition and development in arid and semi‐arid regions.

Zonal features of bioecological properties and honey productivity of species of the family Onagraceae Juss

Representatives of the cypress family (Onagraceae) are among the most valuable melliferous plants of the herbaceous flora of temperate latitudes in Russia. These honeybees are inferior to linden and white acacia among woody plants. It is known that maximum honey yields from the narrow-leaved willow (Epilobium angustifolium L.) are obtained in fresh heaths (3-5 years). The paper considers the dynamics of nectar production in different geographical zones depending on the bioecological characteristics of the honeybee. The ecological conditions on the unforested lands of the Middle Taiga in the Northwest region (Leningrad region) differ significantly from those of the rangelands. Distinct from particularly young havens, which form during certain periods of plant community development. Therefore, the willow herb on forest edges and glades is not as abundant (20 pcs./m2). The number of flowers per plant is lower (62 pcs.) than that of plants on fire sites (92 pcs.). The honey productivity is 140 kg/ha on fallow land and 50 kg / ha at the forest edges. In the taiga zone of western Siberia after deforestation and fires, narrow-leafed willow (Epilobium angustifolium) produces abundant nectar for the first 5-7 years. Control hive readings reach 18-24 kg per day, honey production reaches 350 kg/ha. Analysis of the main pollinators and honey collectors on Cypress flowers showed that in the southern regions of Western Siberia, beekeepers do not feel the presence of competing honeybees. A census of melliferous species in the Vasyugany region revealed the presence of marsh bunting (Epilobium palustre L.), from which bees collect pollen (21.31 g, 2.09 % of total pollen) in July in a beige-purple color. In the south, the honey productivity of the strong bearer cypress (Epilobium angustifolium L.) reaches 800 kg/ha, while in the north it does not produce nectar. On the territory of the Republic of Mari El, the productivity of honey in the burned areas of pine and linden spruce forests, where powerful thickets of willow herb develop, reaches 492 kg/ha.

Late Pennsylvanian vegetation changes in the Donets Basin: syndynamic aspect

The purpose of the article. The article is devoted to the study of one from forms of syndynamics in Late Pennsylvanian time, namely phytocoenogenesis. The study of the phytocoenogenesis of ancient plant communities, i.e., the formation of new types of palaeophytocoenoses, is based on the research of vegetation diversity that is reflected in the ecological-floristic classification of the Late Pennsylvanian phytocoenoses of the Donets Basin by the Brown-Blanquet method. Material and research methods. The phytocoenogenetic researches consisted of the analysis of the changes of the species and syntaxonomic composition of vegetation cover throughout the Late Pennsylvanian. The peculiarities and main factors of phytocoenogenesis have been identified on the palaeosyntaxa in rank of the orders of the following vegetation types: wetland forests and woodlands of coastal lowlands, wetland forests and woodlands of deltaic plains, seasonally dry woodlands of river valleys and lagoon coasts. The palaeophytocoenotic data are based on the plant fossil assemblages from lacustrine, lacustrine-swamp, lacustrine-deltaic, floodplain-lacustrine, floodplain and lacustrine-lagoon deposits in more than 17 localities and 11 boreholes located within the Bakhmutska and Kalmius-Toretska troughs. Research results. Based on the analysis of the phytocoenogenetic processes (progressive and regressive development of plant communities) and the manifestations of phytocoenogenesis (formation of new communities and loss of old communities) in the development of the Late Pennsylvanian vegetation, three models of the formation of new communities and one model of the loss of communities from vegetation cover have been proposed. Each of the models reveals the relationship between the phytocoenogenetic processes and environmental changes. The evolution-progression model reflects the progressive development of palaeophytocoenoses that is expressed by the appearance of evolutionary new coenopopulations in the conditions of the expansion of landscape types (expanding biotopes). The migration-progression model conforms to the progressive development of palaeophytocoenoses as a result of the migration of plants from decreasing landscape types to expanding ones (expanding biotopes). The substitution-regression model is consistent with the regressive development of palaeophytocoenoses along with structure simplification and dominant substitution of plant communities due to the contraction of certain landscape types (decreasing biotopes). The elision-regression model of the loss of communities reflects the regressive development of palaeophytocoenoses that is expressed by the decrease in the number of coenopopulations and the number of individuals in remaining coenopopulations in the conditions of the contraction of some landscape types (decreasing biotopes). The scientific novelty. For the first time, the Late Pennsylvanian vegetation dynamics (syndynamic) have been studied. The proposed three models of the formation of new communities and one model of the loss of communities reveal the main directions in evolution of palaeophytocoenoses and give the first ideas about phytocoenogenesis in late Palaeozoic times.

Effects of drawdown on growth and reproduction of submerged macrophyte Vallisneria spinulosa

Water regime plays a determinant role in plant community development and patterns of plant zonation in wetlands. The waters located in the middle reach of the Yangtze River (China) have experienced a large decrease in wetland area from human activities for a long time, especially after the hydrological drought events in recent years. This outdoor study was conducted to clarify the morphological responses and reproductive strategy of Vallisneria spinulosa to water depth gradients (0.6 m, 1.0 m, 1.5 m) and to drawdown (down to 0.3 m). In static water, water depth of 1.0 m was the best condition for V. spinulosa to grow, manifested as high biomass of vegetative parts, tubers and sexual structures. However, V. spinulosa growing in water depth of 1.5 m was able to adapt to the decline in water depth in autumn, expressed as increased ramet number, stolon weight and belowground biomass. The low water depth of 0.6 m produced small plants with slight vegetative biomass and drawdown produced more tuber biomass. The drawdown caused a decline in vegetative ratio of V. spinulosa. Moreover, it caused an increase in clonal ratio at water levels of 1.5 m and 0.6 m, and a decline in sexual ratio at water levels of 1.5 m and 1.0 m. The results show that under the condition of relatively large fluctuations in water level, V. spinulosa will reduce the allocation of sexual biomass and increase the allocation of clonal biomass in order to cope with environmental changes so that it can proliferate better. Thus, water level changes have a great influence on the growth and reproduction of V. spinulosa.

Active space garnering by leaves of a rosette plant

Near-ground growth offers low-statured plants many benefits but also exposes them to the risk of being overtopped and losing access to sunlight. Plant community development is often portrayed as a process of serial dominance by successively taller species, but here we describe a mechanism by which a low-growing rosette species alters community spatial structure. Elephantopus elatus (Asteraceae), an herbaceous savanna plant with low-growing leaves that emerge radially from a central bud, pushes neighboring plants away and thereby avoids being overtopped. Active pushing is possible because the leaves have stout petioles that are basally anchored rather than attached to flexible twigs or stems. This growth-mediated leaf pushing introduces a novel example of active plant interactions that is likely important for other rosette plants.

Plant community development trends on mixed grass prairie well sites 5 years after reclamation

Over the last 90 years, dry mixed grass prairie across North America has been severely impacted by agriculture, urbanization, and oil and gas operations, presenting significant challenges for land reclamation and range management. This study examined how seed mix and natural recovery revegetation treatments influenced plant community development trends on reclaimed well sites in Alberta, Canada. Three seed mixes, dominant wheatgrass (four species with 95% wheatgrass), non-dominant wheatgrass (five species with 80% non-wheatgrass), and diverse (22 grass and forb species), and natural recovery (unseeded) revegetation treatments were compared to undisturbed mixed grass prairie. Five years after reclamation natural recovery led to a plant community with lesser graminoid and greater forb cover, greater species richness and diversity, and greater bare ground relative to seed mix treatments. Seeded treatments resulted in communities dominated by native wheatgrass species. Multivariate tests revealed community composition of undisturbed prairie and the natural recovery treatment differed from seeded treatments. Indicator species analysis showed the natural recovery treatment was dominated by secondary successional perennial species, while the diverse treatment was dominated by native and non-native early to late successional perennial species. This implies that vegetation recovered more rapidly after disturbance with natural recovery than with a diverse seed mix. Non-native species cover showed a declining trend, and five years after reclamation it was <5% across treatments. Natural recovery revegetation was more effective than seeded treatments; however, a diverse seed mix could be used for mixed grass prairie reclamation.

Establishing new grasslands on crop fields: short-term development of plant and arthropod communities.

Establishment of semi-natural grasslands offers a valuable approach to the conservation of threatened grassland biodiversity. We established new grassland strips on former crop fields adjacent to old semi-natural grasslands and monitored the development of plant, carabid, spider, and wild bee communities over 3 years. The studied plant and arthropods communities were significantly different between newly established grassland strips and old grassland. Our results suggest that restoring plant and arthropod communities takes longer than 3 years to become similar to old semi-natural grasslands.

Nitrogen cycling and urban afforestation success inNew York City

Afforestation projects are a growing focus of urban restoration efforts to rehabilitate degraded landscapes and develop new forests. Urban forests provide myriad valuable ecosystem services essential for urban sustainability and resilience. These essential services are supported by natural soil microbial processes that transform organic matter to critical nutrients for plant community establishment and development. Nitrogen (N) is the most limiting nutrient in forest ecosystems, yet little information is known about N cycling in urban afforestation efforts. This study examined microbially mediated processes of carbon (C) and N cycling in 10 experimental afforested sites established across New York City parklands under the MillionTreesNYC initiative. Long-term research plots were established between 2009 and 2011 at each site with low and high diversity (two vs. six tree species) treatments. In 2018, 1-m soil cores were collected from plots at each site and analyzed for microbial biomass and respiration, potential net N mineralization, and nitrification, denitrification potential, soil inorganic N, and total soil N. Field observations revealed markedly different trajectories between sites that exhibited a closed canopy and leaf litter layer derived from trees that were planted and those that did not fit this description. These two metrics served to group sites into two categories (high vs. low) of afforestation success. We hypothesized that: (1) afforestation success would be correlated with rates of C and N cycling, (2) high diversity restoration techniques would affect these processes, and (3) inherent soil properties interact with plants and environmental conditions to affect the development of these processes over time. We found that high success sites had significantly higher rates of C and N cycling processes, but low and high diversity treatments showed no differences. Low success sites were more likely to have disturbed soil profiles with human-derived debris. Afforestation success appears to be driven by interactions between initial site conditions that facilitate plant community establishment and development that in turn enable N accumulation and cycling, creating positive feedbacks for success.

Biocrusts Influence Vascular Plant Community Development, Promoting Native Plant Dominance

The soil and its biota can shape the development of colonizing vascular plant communities. Because they occupy soil surfaces where most seeds disperse to, biological soil crusts (biocrusts) are uniquely positioned to influence vascular plant communities established by direct seeding, e.g., for restoration. We created mesocosms of soil overtopped by intact biocrust transplants from the field, varying in key community attributes: total cover, species richness, and proportional cover of mosses relative to lichens. We seeded the same diverse mixture of vascular plants into all mesocosms, including desired native species and problematic exotic invasive species. We tracked plant community development for two full growing seasons, both under ambient outdoor conditions and with supplemental irrigation to remove the influence of water limitation. Under ambient conditions, we found that total biocrust cover suppressed exotic plant emergence and biocrust richness slightly promoted native emergence (r = −0.23 to −0.39) but had weaker and less consistent effects on cover of either native or exotic plants (r ≤ |0.25|). Early emergence events were generally strong drivers of vascular plant recruitment (r = 0.17–0.78) and continued to influence community composition after 2 years, suggesting a priority effect. Biocrust cover also promoted final plant biomass under ambient conditions (r = 0.17–0.33) but did not influence the total cumulative number of native species (r ≤ |0.07|) nor the fecundity of exotics (r ≤ |0.08|). Biocrusts’ influence on total vascular plant biomass was minor. When water was added, biocrust effects sometimes switched from positive or negative to neutral, or vice-versa, indicating that our detection probability of biocrust effects on plants changes with moisture availability. Our results demonstrate that the condition of pre-existing biocrust communities can influence—but not strongly dictate—the outcome of multi-species restoration seedings, mostly positively or neutrally under normal conditions, but switching to potentially negatively under irrigated conditions. Our study also suggests that locations with more intact and richer biocrust communities might be slightly more conducive to successful seeding outcomes, while also providing additional contributions to ecosystem functions. As such, biocrusts, alongside vascular plants, have a role in restoring damaged or degraded ecosystems.

Changes in the direction of the diversity–productivity relationship over 15 years of stand development in a planted temperate forest

Abstract Experiments manipulating diversity in both forests and grasslands have often observed a positive diversity–productivity relationship (DPR) which tends to strengthen during plant community development. This pattern is generally attributed to an increase in niche complementarity or facilitation. Most analyses do not examine species dominance and density, which also change over time. Moreover, how neighbourhood‐scale interactions among tree species affect the DPR is not well‐understood. We analysed growth and mortality data from the Simplex experiment, a part of the BIOTREE tree diversity experiment. Simplex consists of 36 plots each planted with four common and commercially important tree species to create a gradient of tree species evenness at two tree densities (6667 and 3556 trees ha−1). We test whether: (a) the effect of evenness on total above‐ground biomass productivity increase with stand development (year), (b) the effect of evenness on productivity is stronger in dense plots; and (c) intraspecific competition from neighbours negatively affect the growth of dominant species more strongly compared to co‐dominant species, and whether this negative effect is stronger in denser plots. The direction of DPR was initially negative because the fast‐growing long‐lived pioneer Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) dominated. However, with time, shade‐tolerant Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) increased in abundance (by biomass), and the relationship between evenness and biomass increment changed from negative to positive in high‐density plots. Neighbourhood analyses revealed that for Douglas fir and Norway spruce, conspecifics reduced individual growth rates across density levels and years. Synthesis. We observed a shift in the diversity–productivity relationship over 15 years in our experiment. Over time, increasing intraspecific competition limited the increment of the abundant Douglas fir in uneven plots, and a persistent increase in the abundance (by biomass) of shade‐tolerant Norway spruce and European beech in even plots led to a higher community biomass increment, which led to a positive DPR. Emergence of a positive DPR in temperate forest plantations requires significant time and is importantly promoted by diversity at the neighbourhood scale (intimate mixtures) as well as higher density planting.