Late-successional Tree Species Research Articles

Xylem adjustment and growth response of early- and late-successional tree species to rapid warming

Climate changes have dramatically affected forest succession. However, how trees at different successional stages respond to climate warming is unclear in the subtropics. Here, we compared the radial growth (RW) and xylem features of the early-successional stage Castanea mollissima and late-successional stage Quercus fabri in subtropical forests and assessed their response to climate changes. All parameters, including RW, number of vessels (VN), vessel density (VD), mean (MVA) and total (TVA) vessel area, percentage of conductive area within xylem (RCTA), theoretical (Kh) and xylem-specific (Ks) hydraulic conductivity, except for MVA of C. mollissima were significantly higher than those of Q. fabri. During the drought period, a notable adverse correlation between two cluster parameters of Q. fabri, associated with hydraulic safety and efficiency, suggested a pronounced hydraulic trade-off in Q. fabri under drought conditions. Castanea mollissima was more sensitive to climate and more prone to hydraulic failure than Q. fabri. Temperatures and moisture conditions positively and negatively affected the hydraulic efficiency-related parameters of C. mollissima. Moisture conditions in the previous summer and winter were significantly negatively and positively related to the radial growth of both species. The impact of generalized warming was not evident due to variations in hydraulic strategies and species characteristics, trade-offs between non-growing and growing season climates, and specific competition. If climate warming continues, C. mollissima growth will probably significantly decline due to the increasing risk of hydraulic failure. Warming may accelerate species replacement and forest succession in the study area by changing their lifespans and competitive relationships.

Young temperate tree species show different fine root acclimation capacity to growing season water availability

Background and aimsChanges in water availability during the growing season are becoming more frequent due to climate change. Our study aimed to compare the fine-root acclimation capacity (plasticity) of six temperate tree species aged six years and exposed to high or low growing season soil water availability over five years.MethodsRoot samples were collected from the five upper strata of mineral soil to a total soil depth of 30 cm in monoculture plots of Acer saccharum Marsh., Betula papyrifera Marsh., Larix laricina K. Koch, Pinus strobus L., Picea glauca (Moench) Voss and Quercus rubra L. established at the International Diversity Experiment Network with Trees (IDENT) field experiment in Sault Ste. Marie, Ontario, Canada. Four replicates of each monoculture were subjected to high or low water availability treatments.ResultsAbsorptive fine root density increased by 67% for Larix laricina, and 90% for Picea glauca, under the high-water availability treatment at 0–5 cm soil depth. The two late successional, slower growing tree species, Acer saccharum and Picea glauca, showed higher plasticity in absorptive fine root biomass in the upper 5 cm of soil (PIv = 0.36 & 0.54 respectively), and lower plasticity in fine root depth over the entire 30 cm soil profile compared to the early successional, faster growing tree species Betula papyrifera and Larix laricina.ConclusionTemperate tree species show contrasting acclimation responses in absorptive fine root biomass and rooting depth to differences in water availability. Some of these responses vary with tree species successional status and seem to benefit both early and late successional tree species.

Sap flow responses in pioneer and late-successional tree species in secondary tropical montane forests of Eastern Himalaya, India.

The interactive role of life-history traits and environmental forcing on plant-water relations is crucial for understanding species response to climate change but remains poorly understood in secondary tropical montane forests (TMFs). Comparing contrasting life-history traits (pioneer vs late-successional species) in a biodiverse Eastern Himalayan secondary TMF, we investigated sap flow responses in co-occurring pioneer species, Symplocos racemosa (n=5) and Eurya acuminata (n=5), and late-successional species, Castanopsis hystrix (n=3), using modified Granier's Thermal Dissipation probes. The fast-growing pioneers S. racemosa and E. acuminata) had 2.1- and 1.6-times higher sap flux density than the late-successional C. hystrix, respectively, and exhibited characteristics of long-lived pioneer species. Significant radial and azimuthal variability in sap flow (V) between species was observed and attributed to life history traits and the canopy's access to sunlight. Nocturnal V (1800-0500hr) was 13.8 % of daily V and is attributed to stem recharge for evening V (1800-2300hr) and to endogenous stomatal controls for pre-dawn V (0000-0500hr). Both the shallow-rooted pioneer species exhibited midday depression in V attributed to photosensitivity and diel moisture stress response. In contrast, deep-rooted C. hystrix transpired unaffected across the dry season likely accessing groundwater. Thus, the secondary broadleaved TMFs, with the dominance of shallow-rooted pioneers, are more prone to the negative impacts of drier and warmer winters than primary forests, which are dominated by deep-rooted species. The study provides an empirical understanding of life-history traits and microclimate modulating plant-water use in widely distributed secondary TMFs in Eastern Himalaya and highlights their vulnerability against warmer winters and reduced snowfall due to climate change.

High-Quality Genome of the Tree Pathogen Phytophthora plurivora—A Novel Resource for Epidemiological Research

Phytophthora plurivora can affect a range of ecologically and silviculturally important tree species, including European beech ( Fagus sylvatica), a common late successional tree species native to Europe. Here, we report on the high-quality genome of P. plurivora strain TJ71 (CBS 124093). We sequenced it using Oxford Nanopore MinION and PacBio Sequel II long-read sequencing with 80× coverage, chromatin conformation capture (Hi-C) sequencing with 400× coverage, and DNBSEQ 150-bp paired-end short reads sequencing with 200× coverage. This complex sequencing approach allowed for assembly of the genome at the chromosome level. Specifically, the P. plurivora genome resulted in 18 scaffolds of 47 Mbp total size with 95% completeness of the eukaryotic gene set as implemented in BUSCO. This is a considerable improvement relative to the previous NCBI reference genome of P. plurivora (NMPK00000000.1) with ∼41 Mbp organized in 1,898 scaffolds with 93.8% eukaryotic BUSCO completeness. This high-quality genome provides a valuable resource for further evolutionary, epidemiological, and population genomic studies. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Post-storm management determines early tree species composition and browsing intensity in regenerating beech forest

Natural disturbances such as fire, insect pests, and windstorms are affecting forests with increasing intensity. Fallen and damaged trees are commonly removed by salvage logging, which can affect tree regeneration and browsing pressure. Yet, the interaction of logging intensity and browsing and their cumulative effects on natural tree regeneration remain poorly understood. We applied three treatments of differing logging intensity to temperate beech (Fagus sylvatica) forest affected by windstorm, using adjacent undamaged forest as reference. We monitored tree regeneration for the first four years following disturbance, and browsing on experimentally planted one-year-old Quercus robur saplings for one year on a total of 20 plots. Natural tree regeneration was present on all plots, regardless of treatment. Species richness and cover of natural regeneration did not differ between disturbance treatments, tree species composition shifted towards early successional species with increasing management intensity, i.e., decreasing amount of deadwood remaining on-site. Community composition of regenerating trees on plots with intensive logging was significantly dissimilar to undamaged forest. Browsing intensity by roe deer decreased with decreasing logging intensity. Browsing by voles and mice showed the opposite effect direction. We show that salvage logging intensity influences species composition of natural regeneration, and that dead wood retention modulates browsing. Salvage logging of moderate intensity promotes the regeneration of early- and late-successional tree species similarly, thereby reducing the need for afforestation.

Are nurse plants useful for facilitating the reintroduction of mid- and late successional tree species in tropical montane cloud forests?

Background: In Mexico, where 50 % of the original Tropical montane cloud forest (TMCF) has been lost due to human activities, the restoration of these forests is essential.
 Questions and/or hypotheses: (1) L. styraciflua favors the survival and growth of Q. germana and M. schiedeana species (2) Are there competitive effects between nurses and beneficiary species? and (3) Is the magnitude of these positive/negative interspecific interactions affected by the canopy cover of nurses?
 Studied species: Liquidambar styraciflua L. (pioneer tree), Magnolia schiedeana Schltdl. (mid-successional tree) and Quercus germana Schltdl. & Cham. (late-successional tree).
 Study site and dates: A fallow in Xilitla, state of San Luis Potosí, Mexico, between 2016 and 2018.
 Methods: Seedling of mid- and late-successional species were transplanted 0.3 m and 2 m away from the stems of pioneer tree (protected and unprotected saplings, respectively). Performance of the species were compared after two years and the effects of canopy cover of pioneer trees.
 Results: Pioneer trees facilitated the establishment probabilities of the mid-and late-successional ones. Increasing canopy cover of pioneer trees enhanced the establishment probabilities of both beneficiary species.
 Conclusions: Joint transplanting of pioneer trees with mid- and late-successional tree seedlings in their close vicinity is a strategy to favor the recovery of the ecosystem.

Differences in leaf photoprotection strategies of tree species at different successional stages in subtropical forests under seasonal climate change and their relationship to construction cost strategies

Differences in response patterns to spatio-temporal changes in environmental stressors mediated by seasonal climatic differences reflect the underlying adaptation strategies of plants, and can provide key information on how tree species respond to seasonal climatic changes at different successional stages. However, in forests dominated by subtropical broadleaf evergreen species, the relationship between leaf photoprotection strategies and their construction cost strategies in different seasons remains unclear. It limits the assessment of the impact of seasonal climate change on community growth and exploration of potential drivers of community succession. In this study, we measured photoprotective substances, chlorophyll fluorescence, photosynthetic pigments and leaf construction cost (CC) in leaves of three mid-successional and three late-successional tree species in a subtropical broadleaf evergreen forest in different seasons. Our data showed that the young leaves of mid-successional trees had higher photoprotection ability in summer compared to winter, and were therefore better adapted to high temperature and high light conditions in summer, but not to low temperature and high light conditions in winter. The young leaves of late-successional trees had strong and flexible photoprotection in both summer and winter, which ensured normal growth of the young leaves under high temperature and high light in summer, and under low temperature and high light in winter. In addition, the photoprotection of the leaves was positively correlated with CC, suggesting that an increase in photoprotective capacity of plants was accompanied by an increase in its investment in CC. This was a response of the plants to environmental stress and the sacrifices it needed to make to maintain its survival. The differential growth patterns of late-successional species, which could grow normally in summer and winter, and mid-successional species, which were adapted to grow in summer but not in winter, may be key clues to the gradual replacement of mid-successional species by late-successional species.

Downregulation of PSI regulates photosynthesis in early successional tree species. Evidence from a field survey across European forests

Photosynthesis rates and electron transport are key physiological traits that distinguish the successional status of plants (early successional – ES, and late successional – LS) in a community. ES plants can respond quickly to sudden changes in sunlight radiation exposure and display a greater photosynthetic plasticity, with respect to the LS ones, thanks to their ability to regulate the photosynthesis. Photosynthesis regulation is connected to the efficiency of the two photosystems (PSI and PSII). PSI plays an important role in the photosynthetic machinery functioning to respond against sudden changes of metabolism in response to heterogeneous environmental conditions. It can be downregulated under high pressure of reductants, to maintain the balance between the reductant pressure and the metabolic demand. The efficiency of PSII and of PSI can be estimated, respectively, by the maximum quantum yield of photosystem II (FV/FM) and the contribution of the thermal phase in the chlorophyll fluorescence emission (expressed by the parameter ΔVIP, that quantify the I-P phase in the fluorescence emission transient). Both parameters are evaluated in dark-adapted samples and can be measured by prompt fluorescence technique. Here, we analyzed a large dataset from a European-wide survey on mature forests, considering four representative forest tree species growing at six sampling sites distributed along a latitudinal gradient. Two early successional (Pinus sylvestris and Betula pendula) and two late successional (Picea abies and Fagus sylvatica) species were considered. The correlations between FV/FM and I-P phase were mostly positive for different plant species at each sampling site for FV/FM values < 0.82 (assumed as optimal threshold for this parameter), but not for FV/FM values > 0.82. In this last case, the correlations were mostly negative for early successional species, and not significant for late successional species. Foliar nitrogen concentration plays a relevant role for the PSI regulation in early successional species: trees with high nitrogen content have higher I-P phase values and negative correlations between FV/FM and I-P phase for FV/FM > 0.82. An opposite pattern was found in tree species with low foliar nitrogen level. We conclude that the late successional tree species show a substantial regulation and stability of the photosynthetic machinery and photosystem stoichiometry, whereas early successional species have more dynamic behavior of PSI. Early successional species can modulate the photosynthetic efficiency and are able both to up-regulate and down-regulate the PSI concentration and activity in relation to quantum yield capacity and leaf nitrogen content.

Temporal change in abundance of potential nesting cavities for wood ducks (Aix sponsa) in Northern Minnesota, United States

Wood duck females often nest in tree cavities located in large-diameter deciduous trees. Temporal changes in forest age and composition during recent decades may have influenced the abundance of stems with suitable nesting cavities in the forested portion of Northern MN, United States. Thus, we ascertained whether temporal changes in the abundance of such stems occurred in this area during six Forest Inventory and Analysis (FIA) evaluation cycles (i.e., 1977 to 2015–2019). We used FIA data and independently estimated proportions of stems with suitable cavities in different tree-species, health-status, and diameter classes to estimate change in the abundance of such stems at three spatial scales. These spatial scales increased in areal extent from a study area to three ecological subsections to the Laurentian Mixed Forest ecological province. We used a Bayesian analytical approach to accommodate changes in FIA protocols among cycles. Both the abundance of stems with suitable cavities and an attribute associated with cavity occurrence changed during the analysis period, but findings were not entirely consistent among spatial scales. The estimated abundance of both suitable stems overall and those of late-successional tree species generally increased at all scales during the analysis period. Since 1990, increases in the abundance of health-impacted stems that were suitable for nesting occurred at all spatial scales. Our estimated densities of suitable stems during the 2005–2009 (1.20 [85% CrI: 1.04–1.39] suitable stems / ha) and 2015–2019 cycles (1.41 [85% CrI: 1.21–1.63] suitable stems / ha) were substantially greater than the &amp;lt;0.25 and 0.25–0.49 suitable stems / ha another study predicted would occur in Northern Minnesota during 2008 and 2018, respectively. Our results can inform forest management decisions and research directions for follow-up studies of nesting wood ducks.

Restoration of tropical montane cloud forest in bracken dominated pastures: The role of nurse shrubs

Bracken (Pteridum arachnoideum) is an invasive fern species that slows or inhibits forest regeneration over vast areas worldwide, affecting biodiversity, ecosystem functions and productivity. To overcome arrested succession, effective restoration interventions are necessary. We examined the effects of planting pioneer shrubs on establishment success in mid- to late-successional tree species transplants, and their combined effects on bracken dominance in abandoned pastures of former cloud forest in Mexico. We hypothesised that the rapid development of nurse shrubs will reduce bracken growth and facilitate mid- to late-successional tree species establishment. We analysed the effects of planting cuttings of the shrubs Tithonia diversifolia and Sambucus nigra on bracken and on the seedling performance of Juglans pyriformis, Quercus insignis, Meliosma alba and Tapirira mexicana, in three sites under four treatments: (1) trees without shrubs, (2) trees with T. diversifolia, (3) trees with S. nigra, and (4) trees with both T. diversifolia and S. nigra. Increased transplant performance was expected under mixed shrub species, compared to single shrub species plantings, due to complementarity in the use of resources (niche separation). After two years, plantings with shrubs and trees reduced bracken cover by >60% and bracken live rhizome biomass by >50%. Shrubs effects were species-specific, reflecting a complex combination of facilitation and competition mechanisms. In comparison to the trees without shrubs, survival of M. alba and Q. insignis significantly increased with T. diversifolia, T. mexicana survival decreased with S. nigra and J. piriformis survival decreased with T. diversifolia and the mixture. The results support the use of cuttings of T. diversifolia or S. nigra separately, rather than in combination, and the inclusion of mid- to late-successional trees, to assist recovery of degraded cloud forest areas where succession has been stalled by bracken. An integrated management approach that considers synergistic factors causing plant mortality in bracken sites needs to be addressed.

Invertebrate herbivory rather than competition with tussocks will increasingly delay highland forest regeneration in degraded areas under active restoration

Determining barriers to tree regeneration along elevational gradients is important to predict shifts in regeneration patterns under climate change scenarios. The stress-gradient hypothesis predicts that facilitation predominates at high elevations and competition at low elevations. Invertebrate herbivory may also play an important, yet hardly recognized role, in low elevation and degraded areas. Our objective was to understand the relative changes in facilitation, competition and invertebrate herbivory along an elevational gradient degraded by long-term livestock rearing and repeated wildfires. Our study area was a seasonally dry ecosystem in central Argentina subjected to forest restoration activities. We planted 3000 saplings of the dominant early and late successional tree species in a full factorial design that included elevation (3 levels: low, 1300; intermediate, 1800; and high, 2300 m a.s.l.), microsite treatment, where we manipulated facilitation and competition (4 levels: tussock grasses mowed to the ground, tussock grasses mowed to 15 cm above the ground, unmowed tussock grasses with an average height of 70 cm, and tussock grasses mowed to the ground near rock outcrops) and 5 blocks per elevation. We monitored sapling survival, change in height, and damage by invertebrate herbivores during one year. For both species, sapling survival significantly increased with elevation, while sapling change in height decreased. Survival and change in height for microsite treatments suggest weak competition for the early successional species and facilitation for the late successional species. Notably, we did not find the elevation and microsite treatment interaction predicted by the stress-gradient hypothesis. The main invertebrate herbivores were leaf-cutting ants, which damaged 42, 33 and 0%, and 25, 27 and 0% of the saplings according to species, for the low, intermediate and high elevations, respectively. Damage did not differ significantly between microsite treatments for either species. Survival for saplings with evidence of damage by leaf-cutting ants was 2.5 and 3.4 times lower as compared saplings with no evidences, according to species. Our findings imply that under a climate warming scenario, future facilitation and competition effects will be similar to current effects, whereas leaf-cutting ants rather than competition may increasingly limit tree regeneration.

Tree stand assessment before and after windthrow based on open-access biodiversity data and aerial photography

The ground-based surveys of areas affected by storms might be difficult or even impossible because of the limited ability to move within the damaged area. Therefore, this work was aimed to estimate storm damage based on aerial photography and open biodiversity data available via the Internet. The study was carried out in the old-growth hemiboreal forests of the Kologrivsky Forest State Nature Reserve (Kostroma Region, Russia), which was affected by a catastrophic windthrow caused by a storm on 15.05.2021. The sampling area was 100 000 m2. We used our previous ground-survey studies and open-access biodiversity data available through the Global Biodiversity Information Facility for describing the forest stands composition before the catastrophic event. The aerial photography data were used for estimating tree stands damages after the windthrow. For remote data collecting, we used an unmanned aerial vehicle – quadrocopter DJI Phantom 4. Agisoft Metashape software was used for aerial photographs processing. The obtained photogrammetric digital elevation model (DEM) and orthophoto-mosaic were processed with QGIS software. Damaged areas were detected automatically based on the DEM. Individual fallen trees were visually detected using the orthophoto-mosaic. We found before the windthrow the study area was covered by old-growth stands developed naturally over a long time. The stand structure was multi-layered and uneven-aged. The ontogenetic spectra of late-successional tree species Picea abies (hereinafter – spruce) and Tilia cordata (hereinafter – linden) were normal. The old-growth stands were heterogeneous before the windthrow: the canopy closed multi-layered and uneven-aged stands, decaying spruce stands and areas where spruce completely fell out and the tree stand was absent. In addition, old-growth linden stands were present. According to the obtained results, the stand structure was critically changed caused by the windthrow. The DEM-processing results showed the windthrow strongly damaged 33.1% stands in the study area. Using the orthophoto-mosaic, we visually detected 759 fallen trees. Among them, 82.9% were associated with strongly-damaged areas. According to the DEM classification, the rest of the visually detected fallen trees were in non-damaged areas and canopy gaps established before the windthrow. The analysis showed that these were less damaged areas with survived stands or groups of trees after the storm. Thus, our results showed that it is necessary to use both the DEM and the orthophoto-mosaic for more accurate estimates. Our exploratory analysis of different tree stand damages found that apparently, spruce stands were more affected by the storm than linden stands. It is explained by the different wind resistance of spruce and linden and differences in regrowth density and species composition in these stands.

Timing and drivers of local to regional scale land-cover changes in the hemiboreal forest zone during the Holocene: A pollen-based study from South Estonia

Current land use and climate change pose a threat to the continued provision of ecosystem services expected from terrestrial land cover. Studies on past land-cover responses to such changes provide valuable information for future decisions. The hemiboreal zone, situated between temperate and boreal biomes, is a natural sensitivity hotspot for land cover change: it contains a continuous distribution limit of several temperate (Quercus robur, Tilia cordata, Fraxinus excelsior, Ulmus glabra, etc.) and some boreal (e.g. Picea abies) tree species. High resolution pollen data from three lakes in South Estonia, a hemiboreal zone in Northern Europe, was used to reconstruct the climate-driven dynamics of vegetation composition, anthropogenic deforestation, species-specific responses to climate cycles, and plant related environmental variables during the Holocene at a local and regional scale. The Landscape Reconstruction Algorithm (LRA) was used to reconstruct the vegetation composition, the Ellenberg Indicator Values for environmental reconstructions, and the Wavelet analysis for detecting cyclic patterns. The major land cover and environmental changes are in good accordance with the climate-based formal tripartite subdivision of the Holocene: a quick succession of tundra, boreal, and nemoral biomes during the Early Holocene, a dominance of temperate, broad-leaved forests during the Middle Holocene, and an expansion of mixed boreal forests and anthropogenic deforestation during the Late Holocene. Several episodes of compositional turnover ranging from a century (e.g., the transition from wet to dry tundra) to several millennia (e.g., the replacement of the temperate deciduous forests with boreal mixed forests) were identified. Our results show that local community changes have a shorter duration than the regional ones. The introduction of slash-and-burn agriculture caused abrupt forest composition changes at a local scale, promoting early successional tree species, even prior to the establishment of a permanently open cultural landscape. The only late successional tree species favoured by slash-and-burn cultivation was Picea abies. However, the application of more permanent cultivation strategies reduced its representation considerably. The determined cyclic changes in the proportions of tree taxa show, that most late successional trees exhibit high frequency (ca 200–400 year) cyclicity, probably reflecting the stand scale regeneration processes. The observed 1600 ± 200 and 1200 ± 200 year cycle changes in the occurrences of Quercus robur, Ulmus glabra and U. laevis, and Picea abies have a possible connection with a 1500 ± 500 year Bond cycle. Most of the tested tree taxa also had a statistically significant correlation with the ca 2200–2500 year Bray solar forcing cycle.

Effects of logging on landscape-level tree diversity across an elevational gradient in Bornean tropical forests

Logging has caused a substantial loss of biodiversity and associated ecosystem services. Therefore, it is important to examine how logging affects biodiversity on a landscape scale to plan responsible management of a tropical forest. Although a number of plot-based studies have shown the effect of logging on local tree species richness (alpha diversity), the effect on species turnover along environmental gradients (beta diversity) remains largely unknown. In this study, we evaluated how logging disturbance affects alpha and beta diversity along an elevational gradient on the eastern slope of Mount Trus Madi in Borneo. We further investigated how pioneer and late-successional tree species differed in the habitat range to clarify the mechanism underlying the beta diversity pattern. We selected 90 plots, each with a radius of 20 m, with a range of disturbance intensity (five classes from highly degraded forests to pristine forests) in lower (285–600 m asl) and higher elevation areas (600–1105 m asl). The remaining above-ground biomass, which is an indicator of past disturbance intensity, strongly varied across the plots (5.4–570.6 and 3.1–771.6Mgha−1 in lower and higher elevation areas, respectively). Diameter at breast height (DBH) and species name were recorded for all trees with a DBH larger than 10 cm. We calculated the species number per 20 individual trees for each plot to represent alpha diversity. Beta diversity along the elevational gradient was calculated as the slope of the relationship between standardized compositional dissimilarity (beta deviation) and the elevational difference. Alpha diversity decreased in higher (17.3–12.3 species per 20 trees) and lower areas (16.8–11.3 species per 20 trees) with increasing logging intensity. Beta diversity along the elevational gradient also decreased to almost zero in highly disturbed areas. Pioneer tree species had a wider elevational range than late-successional species. These results suggest that the shift in dominant tree species after logging (from late-successional to pioneer species) was the main driver of the decline in beta diversity along the elevational gradient. We conclude that preserving and restoring beta diversity are important to sustain tropical production forests.

Accelerating tropical cloud forest recovery: Performance of nine late-successional tree species

Tree planting is a common strategy for forest restoration. The use of mid- and late-successional species is less common, but could accelerate succession, enhance diversity and secure their presence. In this study, we determined the survival and growth of 559 saplings from nine native mid- and late-successional species after three years of growth under a range of habitat conditions to evaluate their potential utility in restoration plantings. Since mid- and late-successional tree species have shade-tolerant attributes and the light environment is a determinant factor for their growth and survival, we expected sapling performance to vary among species depending on the percentage of canopy cover and on factors associated with this variable. For this, we identified habitat conditions that influenced sapling performance in a degraded tropical cloud forest: the conditions ranged from closed-canopy secondary forest to open pastures dominated by exotic grasses. Overall, the studied species presented a high performance: sapling survival (40 to 90%) and relative growth rates in height (0.14 to 0.50 cm cm−1 year−1) and in diameter (0.04 to 0.50 mm mm−1 year−1) were within or above the ranges previously reported for cloud forest species. The final sizes and growth rates in height and diameter were mostly explained by the canopy and grass cover (71.5% of the variation). Integrated Response Index (IRI) values showed wide variation among species (from 6.44 to 41.41 with inclusion of height, and from 2.13 to 44.77 with inclusion of diameter). In general, there was a negative correlation between canopy cover and final sapling size and growth rates in height and diameter, but there were important variations among species. Based on their IRI values, species such as Ulmus mexicana and Oreomunnea mexicana are suggested for restoration plantings. Given their low performance, however, Fraxinu uhdei and Juglans pyriformis are recommended for use only in advanced forest successional stages or in conjunction with other restoration techniques to increase their survival. Our results show that these threatened mid- and late-successional native species can be successfully matched to microsite conditions and established in degraded areas as a strategy by which to secure their presence and accelerate forest recovery.

Interpretation of the difference in shade tolerance of two subtropical forest tree species of different successional stages at the transcriptome and physiological levels.

Differences in plant shade tolerance constitute a major mechanism driving the succession of forest communities in subtropical forests. However, the indirect effects of differences in light requirements on the growth of mid- and late-successional tree species are unclear, and this potential growth effect has not been explained at the transcriptome level. Here, a typical mid-successional dominant tree species, Schima superba Gardn. et Champ, and a typical late-successional dominant tree species, Cryptocarya concinna Hance were used as materials and planted under 100% full light (FL) and 30% FL (low light, LL) to explore the responses of tree species in different successional stages of subtropical forests to different light environments. Transcriptome sequencing was used to analyze the expression changes in genes related to growth and photoprotection under different light environments. The young leaves of S. superba accumulated more malondialdehyde (MDA) and superoxide radicals (${\mathrm{O}}_2^{{{}^{\bullet}}^{-}}$) under LL. A lower hormone content (auxin, cytokinin, gibberellin) in the young leaves, a weaker photosynthetic capacity in the mature leaves and significant downregulation of related gene expression were also found under LL, which resulted in the total biomass of S. superba under LL being lower than that under FL. The young leaves of C. concinna had less MDA and ${\mathrm{O}}_2^{{{}^{\bullet}}^{-}}$, and a higher hormone contents under LL than those under FL. There was no significant difference in photosynthetic capacity between mature leaves in contrasting light environments. Although the biomass of C. concinna under LL was less than that under FL, the height of C. concinna under LL was higher than that under FL, indicating that C. concinna could grow well under the two light environments. Our results describing the acclimatization of light at the physiological, molecular and transcriptome levels are important for a complete understanding of successional mechanisms.

Edaphic factors determining the colonization of semiarid mine tailings by a ruderal shrub and two tree plant species: Implications for phytomanagement

Phytomanagement has been considered a feasible technique to decrease the environmental risks associated to mine tailings and its implementation relies on a suitable plant species selection. The goal of this study was to identify the edaphic factors, including microbiology, affecting the establishment of plant species with contrasting growth patterns during the phytomanagement of mine tailings. For this purpose, a comprehensive rhizosphere characterization was performed in an early ruderal colonizer, Zygophyllum fabago and two late successional tree species, Pinus halepensis and Tetraclinis articulata, growing at a mine tailings pile in southeast Spain. The neutral pH of the tailings determined low 0.01 M CaCl2 metal extractable concentrations (e.g. <10 μg kg−1 Pb and Cd). Thus, other soil properties different from metal concentrations resulted more determining to explain plant establishment. Results revealed that Z. fabago selectively colonized tailings patches characterized by high salinity (3.5 dS m−1) and high silt percentages (42%), showing a specific halotolerant rhizospheric microbial composition, such as the bacterial Sphingomonadales and Cytophagales orders and the fungal Pleosporales and Hyprocreales orders. The two tree species grew at moderate salinity areas of the tailings pile (1.7 dS m−1) with high sand percentages (85%), where Actinomycetales was the most abundant bacterial order (>10% abundance). The contrasting mycorrhizal behaviour of both tree species (ectomycorrhizal for P. halepensis and endomycorrhizal for T. articulata) could explain the differences found between their fungal rhizospheric composition. In terms of phytomanagement, the selective plant species colonization following specific soil patches at mine tailings would increase their biodiversity and resilience against environmental stressors.

The Economy of Canopy Space Occupation and Shade Production in Early- to Late-Successional Temperate Tree Species and Their Relation to Productivity

Light capture is linked to occupation of canopy space by tree crowns, which requires investment of carbon and nutrients. We hypothesize that (i) late-successional trees invest more in casting shade than in occupying space than early-successional trees, and (ii) shade production and crown volume expansion are generally greater in more productive species. For six Central European early-successional (Betula pendula, Pinus sylvestris), mid/late-successional (Quercus petraea, Carpinus betulus), and late-successional tree species (Tilia cordata, Fagus sylvatica), we measured through full-tree harvests (1) crown volume, (2) the costs of canopy space exploration (carbon (C) and nutrients invested to fill crown volume), of space occupation (annual foliage production per volume), and of shade production (foliage needed to reduce light transmittance), and (3) related the costs to aboveground productivity (ANPP). The C and nutrient costs of canopy volume exploration and occupation were independent of the species’ seral stage, but increased with ANPP. In contrast, the cost of shade production decreased from early-to late-successional species, suggesting that the economy of shade production is more decisive for the competitive superiority of late-successional species than the economy of canopy space exploration and occupation.

Different photoprotection strategies for mid- and late-successional dominant tree species in a high-light environment in summer

Light adaptability is a major driver of succession and evolution in natural forest plant communities. However, the relationship between plants and light is contradictory; light provides energy for plant growth, but excessive light negatively affects plant growth. To reveal the pattern of plant adaptation to diurnal variation in light, photoprotection strategies were analyzed in young and mature leaves of six dominant species at two successional stages. Mature leaves of both mid- and late-successional dominant species exhibited a higher net photosynthetic rate (Pn) than young leaves. In particular, the mature leaves of the mid-successional tree species had higher high-light tolerance because of a higher Pn, water use efficiency (WUE) and electron transfer rate (ETR). In contrast, the mature leaves of the late-successional tree species had a higher restoration ability after high-light stress because of higher thermal energy dissipation and faster stomatal regulation. Young leaves of both the mid- and late-successional dominant species exhibited a higher photoprotection capability than mature leaves. The young leaves of the mid-successional tree species had higher high-light tolerance because of their highest WUE and anthocyanin/chlorophyll (Anth/Chl) and higher flavonoid/chlorophyll (Flav/Chl), total phenolics/chlorophyll (Phen/Chl) and total antioxidant capacity/chlorophyll (TAC/Chl) ratios. The young leaves of the late-successional tree species had a stronger restoration ability due to highest Flav/Chl, Phen/Chl, and TAC/Chl ratios and a higher moisture content and non-photochemical quenching coefficient (qN, NPQ). This study shows that in a high-light environment, when leaves are at the same developmental stage, mid-successional tree species better tolerate high-light, while late-successional tree species have a greater restoration ability after high-light stress.

Leaf and Crown Optical Properties of Five Early-, Mid- and Late-Successional Temperate Tree Species and Their Relation to Sapling Light Demand

The optical properties of leaves and canopies determine the availability of radiation for photosynthesis and the penetration of light through tree canopies. How leaf absorptance, reflectance and transmittance and radiation transmission through tree canopies change with forest succession is not well understood. We measured the leaf optical properties in the photosynthetically active radiation (PAR) range of five Central European early-, mid- and late-successional temperate broadleaf tree species and studied the minimum light demand of the lowermost shade leaves and of the species’ offspring. Leaf absorptance in the 350–720 nm range varied between c. 70% and 77% in the crown of all five species with only a minor variation from the sun to the shade crown and between species. However, specific absorptance (absorptance normalized by mass per leaf area) increased about threefold from sun to shade leaves with decreasing leaf mass area (LMA) in the late-successional species (Carpinus betulus L., Tilia cordata Mill., Fagus sylvatica L.), while it was generally lower in the early- to mid-successional species (Betula pendula Roth, Quercus petraea (Matt.)Liebl.), where it changed only a little from sun to shade crown. Due to a significant increase in leaf area index, canopy PAR transmittance to the forest floor decreased from early- to late-successional species from ~15% to 1%–3% of incident PAR, linked to a decrease in the minimum light demand of the lowermost shade leaves (from ~20 to 1%–2%) and of the species’ saplings (from ~20 to 3%–4%). The median light intensity on the forest floor under a closed canopy was in all species lower than the saplings’ minimum light demand. We conclude that the optical properties of the sun leaves are very similar among early-, mid- and late-successional tree species, while the shade leaves of these groups differ not only morphologically, but also in terms of the resource investment needed to achieve high PAR absorptance.