Can atmospheric input of nitrogen affect seed bank dynamics in habitats of conservation interest? The case of dune slacks

Questions: Does the increased atmospheric deposition of nitrogen, which can have major effects on the established vegetation of nutrient‐poor habitats, also impact germination from the soil seed bank? Location: Coastal dune slacks at Newborough Warren, Wales, UK. Methods: The effects of nitrogen addition (15 kg.ha^‐1.a^‐1) on seed germination from the soil seed bank were investigated using the seedling emergence method between September 2004 and February 2005. Results: More seedlings emerged from fertilised samples than unfertilised controls. Most species showed enhanced germination after fertilisation with nitrogen, with seedling numbers statistically significantly greater in nitrogen addition samples in a quarter of species abundant enough for analysis. Species that responded positively to fertilisation were species with low Ellenberg indicator values indicative of infertile sites. Conclusions: Most species showed increased germination after fertilisation with nitrogen, including early successional species normally growing in nutrient‐poor conditions. This suggests that the increased atmospheric deposition of nitrogen probably not only impacts on established vegetation, but also has the potential to alter seed bank dynamics.     

Atmospheric nitrogen deposition explains patterns of plant species loss

Atmospheric nitrogen (N) deposition across Europe increased substantially from the 1950s to the 1990s. Targeted surveys suggest a negative correlation between N deposition and species richness within quadrats in sensitive habitats. However, it remains unclear whether plant species losses at national recording scales are correlated with nitrogen deposition. We relate plant species losses before 1987 in Great Britain to reduced and oxidized N deposition, land use change and climate change. The mean Ellenberg fertility (N) indices of plant species lost in each 100 km² cell before 1987 was compared with those of species that were recorded between 1987 and 1999. In 45% of squares, indices of species lost were significantly lower than those for species present after 1986. For 17%, primarily upland, squares, the opposite effect was found. A generalized least squares regression model, with difference in the mean Ellenberg N index between samples as the dependent variable, showed that higher deposition of reduced N was significantly associated with selective loss of species with a lower index. Arable land use and change in arable land use also demonstrated this positive relationship. Rough grazing, change in rough grazing, change in pasture and change in annual precipitation showed negative effects. Difference in Ellenberg R index was highly correlated with difference in Ellenberg N and was negatively correlated with oxidized N deposition, suggesting that the lack of a significant effect of oxidized N deposition on Ellenberg N was because it had effects through both acidification and eutrophication, while the effect of reduced N deposition was primarily through eutrophication. Our results suggest that N deposition, along with land use and precipitation changes, has been a significant driver of local plant extinctions. With N deposition increasing in many parts of the world, local extinctions of plant species may be experienced in other regions.     

Changes over three decades in the floristic composition of nutrient-poor grasslands in the Swiss Alps

To investigate recent changes in the floristic composition and nature conservation value of nutrient-poor, semi-natural grasslands of the Swiss Alps, we resurveyed 151 phytosociological relevés in four regions, originally recorded between 1975 and 1985. In the original surveys, the mean number of plant species per plot (25–100 m²) ranged from 47.1 to 58.1 according to region. The flora included a total of 18 species that are protected in Switzerland and a high proportion of habitat specialists of nutrient-poor grasslands (NPG-species). In the second survey, conducted between 2002 and 2004, both mean species number per plot (−3.2 to +11.4) and species evenness (−0.05 to +0.07) were higher in most regions. However, the data revealed clear shifts in community composition, with a higher proportion of nutrient-demanding species (mean nutrient indicator value increased by +0.07 to +0.24 units) and a lower proportion per plot of NPG-species (−3.6 to −11.6%). These changes were greatest in pastures, and in meadows converted to sheep pastures, while the NPG-species were maintained in unfertilized meadows that were managed as ecological compensation areas. To prevent continuing decline in the conservation value of these grasslands, it is important to support low-intensity management, especially mowing, and to prevent further eutrophication.     

Clonal plants—What is their role in succession?

Fifteen successional seres from man-made habitats in central Europe were compared and the occurrence of clonal species assessed on the basis of cover data. The effects of soil moisture and nitrogen (expressed using Ellenberg indicator values) on the performance of clonal plants were also considered. Clonal species formed the dominant component of vegetation cover in the majority of the seres studied. In moist sites, their dominance was more pronounced and the peak in their relative cover occurred earlier in succession. The relative importance of species with guerilla type growth tended to increase with time in most seres and after 10 years these were mostly more important than those exhibiting phalanx type growth. The prevalence of guerilla species after 10 years was more obvious in moist seres. Clonal species were able to become dominant regardless of soil conditions, whereas the dominance of non-clonal species tended to be restricted to very wet and nutrient-poor sites. Clonal plant species appeared to maintain their dominance for a longer period than non-clonal plants.     

Inferring nitrogen deposition from plant community composition

Chronically elevated reactive nitrogen deposition has a severe impact on many ecosystems, and there is widespread interest in the possibility of using plant community composition to estimate the level of nitrogen deposition and consequent impacts. Existing approaches use a variety of simple measures including functional type ratios, Ellenberg numbers, and diversity indices. We propose an alternative approach in which species–environment models are constructed using national datasets designed to capture broad-scale deposition patterns. We construct models using partial least squares, weighted average, and maximum likelihood Gaussian logit regression for two British semi-natural habitats, and test how well they predict N deposition by cross-validation. We find that performance is good with R² values up to 0.7, and suggest that such models could be a useful addition to the bioindication toolbox.     

Plant functional trait response to environmental drivers across European temperate forest understorey communities

• Functional traits respond to environmental drivers, hence evaluating trait‐environment relationships across spatial environmental gradients can help to understand how multiple drivers influence plant communities. Global‐change drivers such as changes in atmospheric nitrogen deposition occur worldwide, but affect community trait distributions at the local scale, where resources (e.g. light availability) and conditions (e.g. soil pH) also influence plant communities.
• We investigate how multiple environmental drivers affect community trait responses related to resource acquisition (plant height, specific leaf area (SLA), woodiness, and mycorrhizal status) and regeneration (seed mass, lateral spread) of European temperate deciduous forest understoreys. We sampled understorey communities and derived trait responses across spatial gradients of global‐change drivers (temperature, precipitation, nitrogen deposition, and past land use), while integrating in‐situ plot measurements on resources and conditions (soil type, Olsen phosphorus (P), Ellenberg soil moisture, light, litter mass, and litter quality).
• Among the global‐change drivers, mean annual temperature strongly influenced traits related to resource acquisition. Higher temperatures were associated with taller understoreys producing leaves with lower SLA, and a higher proportional cover of woody and obligate mycorrhizal (OM) species. Communities in plots with higher Ellenberg soil moisture content had smaller seeds and lower proportional cover of woody and OM species. Finally, plots with thicker litter layers hosted taller understoreys with larger seeds and a higher proportional cover of OM species.
• Our findings suggest potential community shifts in temperate forest understoreys with global warming, and highlight the importance of local resources and conditions as well as global‐change drivers for community trait variation.

     

Changes in vegetation and soil characteristics in coastal sand dunes along a gradient of atmospheric nitrogen deposition

A field survey was conducted to detect signals of atmospheric nitrogen (N) in 11 dune systems along a nitrogen deposition gradient in the United Kingdom. In the mobile and semi-fixed dunes, above-ground biomass was positively related to N inputs. This increase was largely due to increased height and cover of Ammophila arenaria. In the long term, this increased biomass may lead to increased organic matter accumulation and consequently accelerated soil development. In the fixed dunes, above ground biomass also showed a positive relationship with N inputs as did soil C : N ratio while soil available N was negatively related to N inputs. Plant species richness was negatively related to N inputs. In the dune slacks, while soil and bulk vegetation parameters showed no relationship with N inputs, cover of Carex arenaria and Hypochaeris radicata increased. Site mean Ellenberg N numbers showed no relationship with N deposition either within habitats or across the whole dataset. Neither abundance-weighting nor inclusion of the Siebel numbers for bryophytes improved the relationship. The survey reveals that the relationships of soil and vegetation with atmospheric N deposition vary between sand dune habitats but, despite this variability, clear correlations with N inputs exist. While this survey cannot establish causality, on the basis of the relationships observed we suggest a critical load range of 10 - 20 kg N ha(-1) yr(-1) for coastal sand dunes in the UK.     

Interspecific competition in natural plant communities: mechanisms, trade-offs and plant-soil feedbacks

Interspecific competition in natural plant communities is highly dependent on nutrient availability. At high levels of nutrient availability, competition is mainly for light. As light is a unidirectional resource, high nutrient habitats are dominated by fast-growing perennials with a tall stature and a rather uniform vertical distribution of leaf area. Moreover, these species have high turnover rates of leaves and roots and a high morphological plasticity during the differentiation of leaves. There is less consensus, however, about the importance and intensity of interspecific competition in nutrient-poor environments. It is argued that selection in nutrient-poor habitats is not necessarily on a high competitive ability for nutrients and a high growth rate, but rather on traits which reduce nutrient losses (low tissue nutrient concentrations, slow tissue turnover rates, high nutrient resorption efficiency). Due to evolutionary trade-offs plants can not maximize both growth rate and nutrient retention. Thus, the low growth rate of species from nutrient-poor habitats should be considered as the consequence of nutrient retention rather than as a feature on which direct selection takes place. The contrasting traits of species from nutrient-poor and nutrient-rich habitats mutually exclude them from each others' habitats. Moreover, these traits have severe consequences for litter decomposability and thereby also for nutrient cycling. This leads both in nutrient-poor and nutrient-rich habitats to a positive feedback between plant species dominance and nutrient availability, thereby promoting ecosystem stability.     

Endozoochory by free-ranging, large herbivores: Ecological correlates and perspectives for restoration

Seed dispersal via ingestion and defecation by large herbivores provides a possible aid for ecological restoration of plant communities, by connecting source communities of target species with habitat restoration sites. It is also a possible threat due to invasion of weeds, grasses or exotic species. Insight into the factors determining internal seed dispersal could therefore improve the management of grazed ecosystems.

We recorded viable seed density in cattle, sheep and pony dung samples and monitored dung pat colonisation in the field. In addition, we counted the distribution of dung pats in plots spread over all habitat units in our study site.

The three herbivore species appeared to disperse large quantities of many species (61 in total) from a variety of plant families, monocots as well as dicots. The density of viable seeds in herbivore dung and the colonisation of dung pats were positively correlated with Ellenberg nitrogen indicator values and seed supply, but not with seed mass or shape.

The results imply that many seeds are dispersed from high productive to low productive parts of the grazed area. In free-ranging systems, we therefore recommend enclosure and separate management of plant communities on nutrient-poor soils with high conservation interest. For habitat restoration sites we recommend integrated grazing only with target plant communities on nutrient-poor soils and not with plant communities on nutrient-richer soils.     

Nitrogen deposition causes widespread loss of species richness in British habitats

We use national scale data to test the hypothesis that nitrogen (N) deposition is strongly negatively correlated with plant species richness in a wide range of ecosystem types. Vegetation plots from a national ecological surveillance programme were drawn from heathland, acid, calcareous and mesotrophic grassland habitats. Mean species number and mean plant traits were calculated for each plot and related to atmospheric N deposition. There was a significant reduction in species richness with N deposition in acid grassland and heathland even after fitting covarying factors. In acid grassland and heathland, evidence from trait changes suggested that acidification rather than increased fertility was responsible for species loss. In contrast, calcareous grassland showed evidence of eutrophication in response to increasing N deposition. Loss of species richness from chronic N deposition is apparent in infertile grasslands and heathland. Mechanisms associated with loss of species richness differ between habitats so mitigation of N deposition should be targeted to habitat type.     

Influence of light and nutrient conditions on seedling growth of native and invasive trees in the Seychelles

Several recent studies have shown that plant invasions can occur in resource-poor and relatively undisturbed habitats. It is, therefore, important to investigate whether and how life-history traits of species invasive in such habitats differ from those of species that are only invasive in disturbed and resource rich habitats. We compared the growth of seedlings of native and invasive tree species from nutrient-poor secondary forests in the tropical Seychelles. We hypothesised that the relative performance of the two groups would change predictably along resource gradients, with native species performing better at low levels of resource availability and invasive species performing better at higher levels. To test this hypothesis, we performed a common garden experiment using seedlings of six invasive and seven native tree species grown under three levels of light (65, 11 and 3.5% of ambient light) and two of nutrients (low and high). Due to large variation among species, differences in growth rates (RGR) were not significant among seedlings of the native and the invasive species. However, seedlings of the invasive species showed higher specific leaf areas (SLA) and higher leaf nutrient contents than seedlings of the native species. They also exhibited greater plasticity in biomass and nutrient allocation (i.e., greater plasticity in LAR, RSR and leaf nutrient contents) in response to varying resource availability. However, differences between the mean values of these parameters were generally small compared with variation within groups. We conclude that successful invaders on nutrient-poor soils in the Seychelles are either stress-tolerant, possessing growth traits similar to those of the native species, or fast-growing but adapted to nutrient-poor soils. In contrast, the more typical, fast-growing alien species with no particular adaptations to nutrient-poor soils seem to be restricted to relative nutrient-rich sites in the lowlands. The finding—that some introduced species thrive in resource-poor habitats—suggests that undisturbed habitats with low resource availability may be less resistant to plant invasions than was previously supposed.     

Avian population trends in the vulnerable montane forests of the Northern Appalachians,USA

Declines in bird populations are an important issue facing conservationists. Although studies have documented bird declines in a variety of lowland habitats, montane habitats are generally under represented in these investigations. Nevertheless, montane habitats are vulnerable because of their restricted geographic distribution as well as their exposure to environmental stressors such as atmospheric deposition and climate change. We surveyed birds at 768 points on 42 transects in montane spruce-fir forests the White Mountains of New Hampshire from 1993–2003. We detected 17,479 individuals of 73 species during this period, of which 10 were abundant enough for analyses. Of these 10 species, three exhibited significant population declines during the survey period: Yellow-bellied Flycatcher (Empidonax flaviventris), Bicknell’s Thrush (Catharus bicknelli) and Magnolia Warbler (Dendroica magnolia). Two of these species (Yellow-bellied Flycatcher and Bicknell’s Thrush) are considered ecological indicator species for montane spruce-fir forest. Declines in these species are an indication that recent concern on the part of conservationists about montane spruce-fir forest and the birds that inhabit them are justified. Our observation that these trends were not reflected in the National Breeding Bird Survey (BBS) analyses, and that one high priority species, the Bicknell’s Thrush, did not occur on BBS routes in New Hampshire during the survey period, argues for the importance of continued efforts to monitor these habitats.     

Nitrogen-use efficiency in six perennial grasses from contrasting habitats

1. We studied the nitrogen-use efficiency (NUE) in six perennial grasses adapted to a wide range of nutrient availability. The glasshouse experiment was carried out in pots containing nutrient solution, with two fertility treatments. Nitrogen-use efficiency was considered as the product of nitrogen productivity and mean residence time of the nitrogen in the plant (calculated using ¹⁵N pulse labelling).
2. The species investigated are characteristic of habitats ranging from very nutrient rich to extremely nutrient poor, in the following order: Lolium perenne, Arrhenatherum elatius, Festuca rubra, Anthoxanthum odoratum, Festuca ovina and Molinia caerulea .
3. Lolium perenne (adapted to nutrient-rich habitats) had higher nitrogen productivity ( A ) than M. caerulea (species adapted to nutrient-poor habitats) but lower than that of F. rubra (from habitats with an intermediate availability of nutrients).
4. In the low fertility treatment, species with the lowest nitrogen-use efficiency had the lowest N productivity and the highest mean nitrogen residence time (MRT); however, although species with the highest nitrogen use efficiency had the highest N productivity they did not have the lowest MRT. In all species the nitrogen-use efficiency decreased with increasing N supply. The two components of the NUE ( A and MRT) are inversely correlated along gradients of nutrient availability, but not at very high levels of nutrient availability.
5. The nitrogen-use efficiency of species at constant levels of nutrient supply tends to increase with increasing nutrient availability in their preferred habitat, according to the Clausman nutrient index, up to a certain nutrient availability and then decreases. The results support the contention that species from nutrient-poor sites are not necessarily adapted by a high nitrogen-use efficiency, but by low nutrient loss rates (high mean residence time of N in the plant).     

Climate warming and land‐use changes drive broad‐scale floristic changes in Southern Sweden

Land‐use changes, pollution and climate warming during the 20th century have caused changes in biodiversity across the world. However, in many cases, the environmental drivers are poorly understood. To identify and rank the drivers currently causing broad‐scale floristic changes in N Europe, we analysed data from two vascular plant surveys of 200 randomly selected 2.5 × 2.5 km grid‐squares in Scania, southernmost Sweden, conducted 1989–2006 and 2008–2015, respectively, and related the change in frequency (performance) of the species to a wide range of species‐specific plant traits. We chose traits representing all plausible drivers of recent floristic changes: climatic change (northern distribution limit, flowering time), land‐use change (light requirement, response to grazing/mowing, response to soil disturbance), drainage (water requirement), acidification (pH optimum), nitrogen deposition and eutrophication (N requirement, N fixation ability, carnivory, parasitism, mycorrhizal associations), pollinator decline (mode of reproduction) and changes in CO₂ levels (photosynthetic pathway). Our results suggest that climate warming and changes in land‐use were the main drivers of changes in the flora during the last decades. Climate warming appeared as the most influential driver, with northern distribution limit explaining 30%–60% of the variance in the GLMM models. However, the relative importance of the drivers differed among habitat types, with grassland species being affected the most by cessation of grazing/mowing and species of ruderal habitats by on‐going concentration of both agriculture and human population to the most productive soils. For wetland species, only pH optimum was significantly related to species performance, possibly an effect of the increasing humification of acidic water bodies. An observed relative decline of mycorrhizal species may possibly be explained by decreasing nitrogen deposition resulting in less competition for phosphorus. We found no effect of shortage or decline of pollinating lepidopterans and bees.     

Changes in species richness and composition in European acidic grasslands over the past 70 years: the contribution of cumulative atmospheric nitrogen deposition

Our study investigates the negative impact of nitrogen (N) deposition on species richness in acidic grasslands, based on a temporal comparison of vegetation data spanning a period of almost 70 years. We compiled a large data base of plots assigned to the Violion caninae grassland type, composed of managed, but unfertilized semi-natural grasslands on nutrient-poor, acidic soils. In total 1114 plots, mainly from Great Britain, the Netherlands and Germany, were compiled, dating back to 1939. Environmental site information included geographical and soil (mean Ellenberg values) variables as well as estimates of cumulative N and sulphur (S) deposition since 1939. Statistical analyses were carried out separately for the data subsets from the three regions. In all regions, the vegetation differentiation was mainly related to soil acidity and nutrient availability, as well as to the year of sampling and the cumulative amounts of N and S deposition. Plot-species richness of vascular plants and bryophytes (analysed for Great Britain only) decreased with time and analyses suggest these are affected by various factors, notably soil pH, but also latitude and cumulative N deposition. The latter explained more of the variation in species number than the year of sampling and cumulative S deposition, which supports the interpretation that the decline in species richness is mainly caused by increasing N availability and less by altered management and soil acidification. For Great Britain and Germany, cumulative N deposition showed a strong negative relationship with several biodiversity measures, especially the proportion of dicots, whereas it was positively related to the proportion of grass species. In general, our results give temporal evidence for the negative effect of N deposition on species richness in semi-natural vegetation.     

Motor vehicles as vectors of plant species from road verges in a suburban environment

The objective of this study was to assess the potential contribution of car-borne flora to species dispersal in a suburban area in Flanders (Belgium). Therefore, motor vehicle-borne flora was evaluated monthly for a random sample of 20 cars between October 1988 and September 1989. At the end of the experiment 33 car-borne plant species, with a total of 690 seedlings were identified from mud, attached to these vehicles. There was considerable temporal variation in the mud mass attached to the vehicles and therefore also the size and composition of the vehicle-borne flora varied during the year. Because mud retention on cars is a crucial factor in seed dispersal, the number of emerging seedlings is negatively correlated with precipitation in the week preceding the sampling. The flora dispersed by vehicles consists mostly of species with small, light seeds and a persistent seed bank. Usually, they are pioneer species of nitrogen-rich habitats. The nature of the vehicle dispersed flora was compared with the local flora of road verges and differed significantly from this in, e.g., seed length, seed weight, ecological groups, Ellenberg indicator values for nitrogen supply, potential dispersal strategies and rarity. A larger resemblance with the flora of the zone immediately adjacent to the carriageway was found. We only found a low similarity to other motor vehicle-borne floras.     

Spontaneous Establishment of Woody Plants in Central European Derelict Sites and their Potential for Reclamation

The performance of woody plants was analyzed in 15 successional seres starting at bare ground in central European manmade habitats. The total cover of woody species after 10 years of succession was significantly related neither to initial soil moisture nor to nitrogen (expressed using Ellenberg indicator values). But the comparison of seres indicates that establishment of woody plants was easier under moderate environmental conditions and retarded in extreme habitats (dry, nutrient-poor, or acid). The arrival of the first woody plants was delayed in dry sites. No significant differences were found between primary and secondary seres, either with respect to the total cover of woody plants reached after 10 years of succession or considering the time of their arrival. In total, 24 woody species (10 shrubs and 14 trees) appeared in the series investigated. Their successional performance (in terms of the number of seres in which the species occurred and maximum cover reached in any sere) was not related to species traits (life strategy, type of mycorrhizae, mode of dispersal, diaspore weight), except for the regeneration strategy, species with seasonal regeneration by seeds were capable of creating higher cover. Betula pendula (European birch) was the most successful species in spontaneous succession, especially on moist sites. Practical suggestions for the management of particular habitats (sites disturbed by mining, sites reclaimed after acid rain deforestation, urban sites, abandoned fields) are provided regarding the establishment of woody plants.     

Fear of the dark: decline in plant diversity and invasion of alien species due to increased tree canopy density and eutrophication in lowland woodlands

The abandonment of traditional forest management and the conversion of lowland woodlands from coppices to high forests may lead to a reduction in plant diversity. We studied long-term changes in semi-natural lowland woodland vegetation in the Czech Republic (Central Europe) by resampling 29 vegetation plots (relevés) first sampled in the 1950s. The results indicated a shift to shady plant communities (i.e. loss of heliophilous species and expansion of shade-tolerant species), caused by an increase in the tree and shrub layer canopy due to the expansion of deciduous tree species. At the same time, species richness (alpha diversity) had declined significantly, though we noted no signs of homogenisation in the vegetation cover. Species typical of nutrient-rich habitats and alien and/or invasive species had expanded. We confirmed the shift in vegetation composition, which was probably caused by changes in lowland woodland forest management (decline in coppicing), eutrophication (deposition of atmospheric nitrogen, agricultural runoff) and disturbance effects of game, especially wild boar (Sus scrofa).     

Possible shift in macaque trophic level following a century of biodiversity loss in Singapore

Biodiversity loss in tropical forests is a major problem in conservation biology, and nowhere is this more dire than in Southeast Asia. Deforestation and the associated loss of species may trigger shifts in habitat and feeding preferences of persisting species. In this study, I compared the habitat use and diet of long-tailed macaque (Macaca fascicularis) populations in Singapore from two time periods: museum specimens originally collected between 1893 and 1944, and living macaques sampled in 2009. I collected hair and used stable carbon and nitrogen isotope analysis to identify temporal changes in dietary source and trophic position, respectively. δ¹³C ratios were virtually identical, suggesting that macaques foraged in similar habitats during both time periods. However, δ¹⁵N ratios decreased considerably over time, suggesting that macaques today feed at a lower trophic level than previously. This decline in trophic level may be because of the disappearance or decline of other species that compete with macaques for fruit. This study highlights the effect of biodiversity loss on persisting species in degraded habitats of Southeast Asia, and improves our understanding of how species will adapt to further human-driven changes in tropical forest habitats.     

Retrospective assessment of the dynamics of nitrogen availability in pine forests of the near-Moscow region based on the data of phytoindication

Earlier published data on the long-term geobotanic monitoring in permanent pilot plots have been used to analyze changes in trophic conditions and estimate nitrogen nutrition availability to pine forests of the Serebryanyi Bor Forestry located in the Moscow oblast. The assessments of habitats based on the ecological scales of soil richness with nitrogen, which were developed by D.N. Tsyganov and G. Ellenberg, and analysis of the dynamics of stenobiont species have revealed the properties of changes in the species composition and conditions of nitrogen availability to forests for the period from 1957–1961 to 2003. The results indicate increased nitrogen availability to forests in the studied period for all permanent plots, but reflect different intensities of the trend of eutrophication in different monitoring stages. A more intense growth in soil richness with nitrogen in all permanent plots was in the period since 1957–1961 to 1989–1990. In the next years, the level of nitrogen availability to phytocenoses almost did not change. The improvement in the trophic conditions was accompanied by the growth in total species richness and increase in the number of stenobionts with high requirements to nitrogen nutrition. The results from analyzing the dynamics of stenobionts confirm the division of the period under consideration into two stages. From 1957–1961 to 1989–1990, changes in the species composition of plant communities in the pine forests under consideration were similar but differed in intensity. From 1989–1990 to 2003 (against the background of total deceleration of the eutrophication trend), the similarity of species dynamics in the communities was disturbed. The impact of air pollution by NOx on nitrogen nutrition availability to forests was examined with consideration for the fact that the studied area is within the capital agglomeration. The dynamics of the intensity of air nitrogen deposition is in good agreement with the revealed changes in the species composition of phytocenoses and nitrogen soil richness. It gives reasons to suppose that the trend of forest eutrophication in the 1960s–1980s was strengthened by the impact of increased levels of atmospheric nitrogen deposition.