Successional Forest Stands Research Articles

Could different structural features affect flammability traits in Mediterranean forest ecosystems?

Key messageMediterranean forest stands manifest diverse flammability traits according to their potential ecological successional stage and promoting a gradient from flammable to less flammable ecosystem.From a general consideration of vegetation as ‘fuel’, it has been well proven that plant traits have the potential to promote the forest stand gradient from flammable to less flammable. While the ever-growing literature helps to assess the relationship between plants and their flammability at species level, at the landscape scale this relationship should be evaluated along with a variety of forest features such as structural and stand parameters and from the perspective of successional forest stages. To this end, we clustered several forest stands in Southern Europe (Apulia region, Italy), characterized by oaks, conifers, and arboreal shrub species, according to their flammability traits. We hypothesized that flammability traits change along different horizontal and vertical structural features of forest stands, shifting from high to low-flammability propensity. The results confirmed that forest stands with greater height and diameter classes are associated with traits with a low-flammability propensity. It is worth highlighting the importance of shrub coverage in differentiating the clusters denoting their strong influence in increasing fuel load (litter and fuel bed traits). Finally, our findings lead us to assume that high-flammability propensity traits are associated with typical pioneer successional stages, supporting the notion that later successional forest stands are less flammable and, therefore, that flammability decreases along with succession.

Multiple drivers of aboveground biomass in a human-modified landscape of the Caatinga dry forest

Aboveground biomass is an important predictor of net primary productivity and provision of ecosystem services such as carbon storage and food supply. However, biomass can be a complex and multi-driven ecosystem feature, particularly in tropical forests experiencing human disturbances. Here we examine the potential effects of forest successional stage, species richness, plant assemblage functional composition, rainfall, grazing and soil fertility as drivers of biomass in a human-modified landscape of the Caatinga dry forest. We recorded 8911 stems (DSH ≥ 3) across 35 0.-ha plots and calculated the aboveground biomass adopting allometric model developed specifically for Caatinga dry forest. Caatinga flora was dominated by species bearing moderate to heavy wood, with aboveground biomass concentrated into a few dominating species and narrow stems. Biomass averaged 28.48 ± 23.32 Mg ha−1 with a high cross-stand variation as it resulted from a complex interaction of age of forest stand, rainfall and species richness; i.e. old-growth forest stands supported twice as much biomass (38.81 ± 25.08 Mg ha−1) than successional stands (14.68 ± 10.52 Mg ha−1). Drivers of plot-level biomass also affected biomass at species level as well as the abundance of the species which contributed most for forest biomass. Our results confirm that slash-and-burn agriculture supports the emergence of biomass mosaics associated to the presence of old-growth and successional forest stands of varying age. In this context, Caattinga supports reduced forest biomass, which responds to both natural and human–driven forces and their complex interactions. Moreover, biomass persistence in human-modified landscapes requires not only long fallow periods, but also the protection of species-rich forest assemblages.

Gap dynamics of late successional sugar maple–yellow birch forests at their northern range limit

AbstractQuestionsWe investigated whether the gap disturbance rate (percentage area disturbed by canopy gaps per year) differed at the northern range limit of sugar maple (Acer saccharum)–yellow birch (Betula alleghaniensis) forests compared to broad‐leaf temperate deciduous forests located more to the south. As an ancillary question, we assessed the relationship between species composition and gap disturbance rate at the stand scale.LocationLate successional sugar maple–yellow birch forests at their northern range limit in western Quebec, Canada.MethodsTo reconstruct past gap disturbances, we identified growth releases using the boundary line method applied to tree‐ring chronologies obtained from 0.25‐ha plots sampled within 11 late successional forest stands. We reconstructed past canopy gaps using release events, calculated historical gap disturbance rates and used redundancy analysis to evaluate the relationship between gap disturbance rate and species composition at the stand scale.ResultsThe mean gap disturbance rate across the 11 late successional stands was 0.96 ± 0.51%·yr−1. Mean gap size was 39 ± 44 m2and almost 85% of the gaps were <50 m2. Stands with smaller gaps and lower gap disturbance rates had high importance values for balsam fir (Abies balsamea) and/or yellow birch.ConclusionsThe gap disturbance rate at the northern limit of sugar maple–yellow birch forest was similar to that reported in broad‐leaf temperate deciduous forests located ca. 575–1300 km to the south. However, gaps were more numerous and smaller, which could be related to latitudinal differences in allometric traits of the dominant tree species and climate.

Changes in composition and diversity of fungal communities along Quercus mongolica forests developments in Northeast China

A better understanding of fungal community composition and diversity and their dynamic patterns driving forces under different successional forest will contribute to the maintenance and preservation of natural ecosystems. The aim of this study was to compare soil fungal communities and soil microbial activities among three successional temperature Quercus mongolica forest stands (20, 30 and 40 years old) in Northeast China to investigate the maintenance mechanism of fungal diversity and provide the basic theory basis for the functions of fungus in nutrient cycle. Based on the sequences of rRNA with Illumina Miseq, 508 different fungal phylotypes were identified and grouped into Ascomycota, Basidiomycota, Chytridiomycota, Glomeromycota and Zygomycota. Russula was the dominant genus in these three successional stages of Q. mongolica forests. Fungal communities differed across these three stands and the fungal diversity and richness was significantly lower in the 30 years stand than in the 20 years and 40 years stands. Meanwhile, a total of 93 ectomycorrhizal fungus (EMF) phylotypes were observed and the EMF diversity was similar across the three successional stands. The activity of soil urease increased with forest development ages and cellulase activity first decreased and then increased from 20 years stand to 40 years stand. Both nitrogen mineralization and nitrification were the lowest in September in the 30 years stand and reached the maximum value in August. Both soil net N mineralization and N nitrification were the lowest in 40 years forest stage in October. The Redundance analysis showed that fungal community was strongly affected by stand ages and environmental factors and the nine plots in the three successional forest stands were significantly clustered across successional forest stands. The dominant Lachnum in Ascomycota positively, while the dominant Russula in Basidiomycota negatively, correlated with total P, available P, Soil organic carbon (SOC), NO3−-N, soil moisture or pH. Our results could provide insights into relationships between taxonomic fungal diversity and soil chemical properties along different stages of forest. The findings also imply the functions of soil fungi in sustaining soil biogeochemical cycling were driven by the secondary succession in temperate ecosystems.

Size‐dependent growth of two old‐growth associated macrolichen species

Relationships between thallus size and growth variables were analysed for the foliose Lobaria pulmonaria and the pendulous Usnea longissima with the aim of elucidating their morphogenesis and the factors determining thallus area (A) versus biomass (dry weight (DW) gain. Size and growth data originated from a factorial transplantation experiment that included three boreal climate zones (Atlantic, suboceanic and continental), each with three successional forest stands (clear-cut, young and old). When A was replaced by the estimated photobiont layer area in an area-DW scatterplot including all thalli (n = 1080), the two separate species clusters merged into one, suggesting similar allocation patterns between photobionts and mycobionts across growth forms. During transplantation, stand-specific water availability boosted area gain in foliose transplants, consistent with a positive role of water in fungal expansion. In pendulous lichens, A gain greatly exceeded DW gain, particularly in small transplants. The A gain in U. longissima increased with increasing DW:A ratio, consistent with a reallocation of carbon, presumably mobilized from the dense central chord. Pendulous lichens with cylindrical photobiont layers harvest light from all sides. Rapid and flexible three-dimensional A gain allows the colonization of spaces between canopy branches to utilize temporary windows of light in a growing canopy. Foliose lichens with a two-dimensional photobiont layer have more coupled A and DW gains.

Changes in pools of depsidones and melanins, and their function, during growth and acclimation under contrasting natural light in the lichen Lobaria pulmonaria

This study analysed relationships between secondary chemistry, lichen growth rates and external habitat factors for two groups of UV-B-absorbing secondary compounds in the lichen Lobaria pulmonaria in order to test some hypotheses on their formation and function. Medullary depsidones and cortical melanins were quantified in thalli transplanted to three successional forest stands (shaded young forest, open old forest, sun-exposed clear-cut area) and subjected to different watering regimes (spraying with water, water + nitrogen, no spraying). Growth rates were already known. The total concentration of all seven depsidones was constant across the entire range of growth rates and sun exposures, showing that these depsidones serve functions other than photoprotection. Thalli from the well-lit transplantation sites had the highest synthesis of melanins. Within each forest type there was a trade-off between growth and melanin synthesis. Melanins and photosynthetic acclimation enhanced survival on a subsequent exposure to high light intensity, despite excessive temperatures resulting from higher absorption of solar energy in melanic thalli relative to pale thalli. In conclusion, the highly responsive melanic pigments play a photoprotective role in light acclimation, whereas the constant amount of depsidones across a wide spectrum of growth ranges and irradiances is consistent with herbivore defence functions.

Influence of stand age and physical environment on the herb composition of second‐growth forest, Strouds Run, Ohio, USA

AbstractAim Historical land use in eastern North America and much of Europe has created a mosaic of successional forest stands of widely varying age. An estimate of the rate of successional community development would allow the conservation value of individual stands to be assessed. We estimate the rate of herb community development in secondary forests in our region, and the extent to which physical gradients determine herb distributions.Location Second‐growth forest in the Appalachian Oak section of the Central Hardwoods Region, southeastern Ohio, USA.Methods Thirty‐five plots were surveyed in old (82–193 years) and young (35–40 years since pasture) deciduous forest stands and pine plantations. In each plot, herb species cover and environmental factors were measured.Results Herb community composition was clearly distinguishable between oak‐dominated upland sites and mixed mesophytic stands in moist ravines. In both community types, young stands were compositionally distinct from old stands. Species lacking obvious seed dispersal mechanisms were disproportionately uncommon in young stands, implying dispersal limitation in the process of recolonization. Among old stands, distributions of many species showed significant regressions on the environmental variables, whereas few showed significance in young stands. Species with weak dispersal tended to be more frequently linked to environmental gradients in old stands than in young stands.Main conclusions Early arriving forest species appear to assort rapidly along physical gradients, defining communities early in the successional trajectory. The re‐assembly of the full forest community continues over a longer period as individual species assort on environmental gradients at rates determined by their dispersal abilities. Thus, long‐established stands show more spatial variation than successional stands, and offer greater opportunities for conservation of the forest community.

Carbon dynamics in successional and afforested spruce stands in Thuringia and the Alps

AbstractChanges in the carbon stocks of stem biomass, organic layers and the upper 50 cm of the mineral soil during succession and afforestation of spruce (Picea abies) on former grassland were examined along six chronosequences in Thuringia and the Alps. Three chronosequences were established on calcareous and three on acidic bedrocks. Stand elevation and mean annual precipitation of the chronosequences were different. Maximum stand age was 93 years on acid and 112 years on calcareous bedrocks. Stem biomass increased with stand age and reached values of 250–400 t C ha−1 in the oldest successional stands. On acidic bedrocks, the organic layers accumulated linearly during forest succession at a rate of 0.34 t C ha−1 yr−1. On calcareous bedrocks, a maximum carbon stock in the humus layers was reached at an age of 60 years.Total carbon stocks in stem biomass, organic layers and the mineral soil increased during forest development from 75 t C ha−1 in the meadows to 350 t C ha−1 in the oldest successional forest stands (2.75 t C ha−1 yr−1). Carbon sequestration occurred in stem biomass and in the organic layers (0.34 t C ha−1 yr−1on acid bedrock), while mineral soil carbon stocks declined.Mineral soil carbon stocks were larger in areas with higher precipitation. During forest succession, mineral soil carbon stocks of the upper 50 cm decreased until they reached approximately 80% of the meadow level and increased slightly thereafter. Carbon dynamics in soil layers were examined by a process model. Results showed that sustained input of meadow fine roots is the factor, which most likely reduces carbon losses in the upper 10 cm. Carbon losses in 10–20 cm depth were lower on acidic than on calcareous bedrocks. In this depth, continuous dissolved organic carbon inputs and low soil respiration rates could promote carbon sequestration following initial carbon loss.At least 80 years are necessary to regain former stock levels in the mineral soil. Despite the comparatively larger amount of carbon stored in the regrowing vegetation, afforestation projects under the Kyoto protocol should also aim at the preservation or increase of carbon in the mineral soil regarding its greater stability of compared with stocks in biomass and humus layers. If grassland afforestation is planned, suitable management options and a sufficient rotation length should be chosen to achieve these objectives. Maintenance of grass cover reduces the initial loss.

Growth response of three native timber species to soils with different arbuscular mycorrhizal inoculum potentials in South Cameroon: Indigenous inoculum and effect of addition of grass inoculum

After tropical forest disturbance, mycorrhizal inoculum could be insufficient. Increasing mycorrhizal density through inoculum addition is then crucial for successful regeneration of deforested lands. Greenhouse bioassays were set up to determine the effectiveness of native arbuscular mycorrhizal fungi in soils from different disturbance stages on the growth of three important timber species, Terminalia superba, Distemonanthus benthamianus, and Entandrophragma utile. Soils were collected from late and early successional forest stands, fields of food crops, fallow of Chromolaena odorata, skid trails, bare soil landings, and landings with the pioneer tree Musanga cecropioides. These soils were used to grow seedlings without or with addition of an inoculum collected under the grass Paspalum conjugatum. The extent to which seedlings responded to indigenous inoculum and inoculum addition varied with tree species and with mycorrhizal inoculum potential. After inoculum addition, Terminalia strongly increased root colonization with a small increase in shoot dry weight and Distemonanthus hardly increased root colonization but showed a strong increase in shoot dry weight. Entandrophragma increased both root colonization and shoot dry weight. Plant biomass was lower in soils with low inoculum potential such as late successional stands, skid trails, and both kinds of landings; the mycorrhizal inoculation effect was then large. Plant biomass was high in agricultural fields and fallow; mycorrhizal inoculation effect was sometimes even negative. These data indicate that low inoculum might limit plant re-establishment after disturbance and that mycorrhizal inoculation has a potential for improving seedling establishment on deforested land.

Annual Tree‐Litter Production by Successional Forest Stands, Juneau, Alaska

Litter production in four stands (pioneer Alnus—Salix to old—growth Tsunga heterophylla/Picea sitchensis) for 3 years averaged 2,850 kg/ha. Production varied among stands and years, but no real differences were apparent. Nonwoody litter was about 64% of total litter and, although less variable, there were no consistent differences for stands nor years.