Late-successional Tree Research Articles

Object-based, multi-sensor habitat mapping of successional age classes for effective management of a 70-year secondary forest succession

Multi-temporal change detection over decades including the pre-satellite era is challenging due to the different image types available over time, and this explains the scarcity of long-term studies of vegetation succession which can play a pivotal role in the restoration of biodiversity in regenerating forests. This study describes a semi-automated, object-based habitat classification method for change detection of tropical forest succession since 1945. The study uses a set of black and white aerial photographs and high-resolution satellite images which differ in quality and resolution, to investigate forest successional patterns and their implications for informed ecosystem and land rehabilitation management. For optimized habitat boundary delineation from black and white aerial photographs and panchromatic satellite images, three levels of hierarchical image object primitives were created. The minimum object sizes of 50 m2, 500 m2, and 1000 m2 maximized inter-object and minimized intra-object variability according to the scale of habitat patches and imagery used. Object-Based Image Analysis (OBIA) provided additional Grey-Level Co-occurrence Matrix (GLCM) textural features of segmented objects which helped to incorporate knowledge-based rule-sets into the final habitat classification which was done manually. Results show accuracies for grassland greater than 94%, monoculture plantations were distinguished from natural forest with 95% accuracy, and isolated mature stands of natural forest achieved 75% accuracy. Consideration of multi-date images increased the accuracy of distinguishing between mixed plantations and natural forest as well as between shrubland and young secondary forest. The resulting maps of vegetation structure at five time periods from 1945 to present gave new insights into the ecological processes of secondary forest succession. These include the surprising rapid rate of natural forest regeneration, at an annual rate of 7.7% from 1945 to 2014, and an even faster rate of 11% during a period when hill fires were controlled. The last areas to succeed to forest are those which are still, or at some time have been under exotic mono-cultural plantations. This suggests that long term protection from hill fire would be a better option for assisting natural succession in the landscape than plantations, which are both costly, and act as barriers to natural succession. Overall, with more than 92% mapping accuracy, the method can be adapted for other multi-temporal, multi-sensor studies as it enables inclusion of spatial theories by dividing the satellite image into time-consistent geographic entities according to the scale of target objects and image resolution. The accurate maps of forest cover patches at different successional stages can also help in site specific management of the recovering forest, such as introduction of shrub seedlings to bridge bottlenecks in seed dispersal according to shrub density and dispersal distances for forest birds. Late successional tree species can also be introduced in areas where only early successional species are present after 50 years of succession.

The ecology of Central European tree species: Trait spectra, functional trade-offs, and ecological classification of adult trees

Plant functional traits offer insights into the plant-environment relationship and may help to understand how plants influence ecosystem functions. Applying trait-based models on climate and land-use change to forests is often hindered by poor data quality, as many data are estimates and traits are often parameterized for juvenile and not adult trees. For advancing theory building and improving the quality of trait data with relevance for adult trees, we compiled a unique trait database for the complete tree flora of Central Europe (42 species from 11 families), covering 38 morphological and physiological traits mostly parameterized with sun and shade crown and root data from adult trees. Despite only small variation in climate, several traits vary largely in this tree species sample, likely reflecting regional edaphic variation, while the influence of phylogenetic diversity is low and restricted to the angiosperm-gymnosperm divergence. The well-established shade tolerance-drought tolerance and wood density-drought sensitivity trade-offs are not supported by our data set, possibly due to the explicit consideration of adult trees and the absence of extended climatic gradients. For the 11 major tree species with high information density, a principal components analysis (PCA) identified three key functional traits, (i) minimum light demand of the adult trees’ shade leaves, (ii) stand leaf area index (LAI), and (iii) maximum tree height, which allows distinguishing five tree functional groups, among them a mid-successional tree group. Only a small minority of traits changes significantly along the early-to-late successional axis, contradicting a main paradigm in forest succession research. The functional contrast between early- and late-successional trees is smaller in the sun canopy of adults than in seedlings or saplings, suggesting that trait data from juveniles cannot simply be extrapolated to adults. Focusing on adult trees and on traits with a more direct link to the underlying processes may significantly improve tree functional classification and trait-based models in forest ecology and biogeochemistry.

Comparison of woody species composition between rocky outcrops and nearby matrix vegetation on degraded karst hillslopes of Southwest China

Habitats with different features such as soil depth and soil/rock conditions can provide favorable environments for species with different requirements, while anthropogenic disturbances normally exert additional effects on species composition. However, specific studies have rarely been conducted in the degraded karst regions of Southwest China despite the high heterogeneity of karst habitats and past human disturbances. In this study, woody species richness and composition on rocky outcrops on a typical karst hillslope were investigated and compared with those of nearby matrices on shallow and rocky soil. Our results showed that matrix vegetation was more diverse in genera and species than vegetation on rocky outcrops. This might relate to the contrasting substrate features and different disturbance histories of these two habitats. Unlike the significant effect of slope on species richness of the matrix vegetation, rocky outcrops exhibited no significant differences between upper and lower slope positions, largely because their microhabitats were similar in different slope positions. Although the study area has been reforested naturally for about 30 years, woody species of the matrix vegetation were still dominated by pioneer shrub species. Rocky outcrops were dominated by late-successional tree species, which was primarily related to their isolated features and resistance to certain disturbances. Most of these late-successional species were not habitat endemics, indicating the possibility for their encroachment into surrounding the matrix. From this aspect, further studies will be necessary to identify and address the limiting factors for the encroachment of these late-successional species into the surrounding environment.

Evaluating restoration success of a 40-year-old urban forest in reference to mature natural forest

We assessed whether forest restoration was successful in Expo ’70 Commemorative Park in Osaka Prefecture, Japan, which was planted in the 1970s with native late-successional tree species. Detailed survey and analysis of species composition, stand vertical stratification, and forest dynamics, including comparison with a reference, natural late-successional forest, were conducted. The restoration plots had grown to larger basal area compared with the reference plots, however, this was a consequence of very high densities of the overstory trees due to low self-thinning rate. Stand vertical structure of the restoration plots was biased toward overstory layers, causing high mortality of understory trees and shrubs. Because there are no mature forests near the restoration site that could act as a seed source, abundance and diversity of understory trees are likely to continue decreasing in the restoration plots, resulting in single-layered forest structure similar to those of monocultures and even-aged forests. Many seedlings of exotic species emerged in the restoration plots and this could lead to a plagiosere where exotic species dominate the vegetation inhibiting regeneration and growth of native species. Ordination analysis using different measures, basal area and abundance, showed apparently contradicting results, suggesting that multiple criteria are needed to evaluate forest restoration success. Our results indicate restoration of mature, late-successional forest cannot be achieved by simultaneous planting of native species. To sustain urban forests into the future, we must conduct long-term monitoring and management referencing natural forest structure and dynamics.

The last hornbeam forests in SW Europe: new evidence on the demise of Carpinus betulus in NW Iberia

Carpinus betulus L. is a mesic, usually considered late-successional tree widely distributed in Europe, but almost absent from Iberia, where it is generally assumed that disappeared during the coldest stages of the Wurm. High-resolution pollen analyses were carried out in 14C dated sediments from a drowned estuary (ria) and a small mountain lake. Carpinus pollen identification was confirmed by comparative light and scanning electron microscopy. Hornbeam dynamics are interpreted using palaeoclimatic reconstructions based on independent proxies (diatoms, chironomids and dinocysts). Our results support that hornbeam declined between ca. 60,000 and ca. 9,000 cal yr bp, when multiproxy evidence suggests a major regional relative sea-level rise. Moreover, chironomid-inferred July temperatures show an increase of more than 6 °C between 15,600 and 10,500 cal yr bp, while freshwater aquatics and diatoms indicate a general tendency towards increasing precipitation and a more oceanic climate. Carpinus survived during the Wurm in a variety of habitats in coastal valleys in NW Iberia which had adequate climatic and edaphic conditions. Such habitats might be comparable to the oak-ash, ravine, and hardwood floodplain forests currently existing in other regions of Europe. Large areas of these coastal ecosystems disappeared at the onset of the Holocene, when the sea-level rose. Later hornbeam was apparently unable to compete and expand further inland. Therefore, the sea-level rise combined with the climatically-induced Holocene tree succession and the increasing human impact during the Mid and Late Holocene led to hornbeam progressively becoming a marginal tree in the area.

Natural regeneration of tree species in pastures on peasant land in Chiapas, Mexico

Abstract In recent decades, large forested areas in southern Mexico have been degraded and even eliminated, often due to conversion of these areas to pastures for cattle grazing. Silvopastoral systems combine livestock raising with tree use, favor conservation of biological diversity, and provide a variety of services to the environment and to farmers. In this study, we evaluated tree regeneration in cattle pastures in the Tulija River Valley of Chiapas, Mexico. We argue that density of seedlings/saplings in the pastures studied is associated with the density of adult trees, with the type of dominant grass (induced or introduced), and with the practice of weeding around seedlings and saplings. We sampled trees in pastures according to categories of size, as well as herbaceous vegetation in 35 cattle pastures, and interviewed farmers with respect to their practices of weeding around seedlings and saplings. We evaluated specieś capacity for regeneration, and classified species as having adequate or limited natural regeneration capacity (ANR and LNR, respectively). Furthermore, we constructed a generalized least squares model to identify whether density of adult trees, type of grass cover (induced vs. introduced), and farmerś practice of weeding affect the density of seedlings and saplings of tree species. Finally, we identified dispersal agents of each tree species recorded and then compared the relative abundance of seedlings/saplings with adult trees for each dispersal agent, using chi-square goodness-of-fit test. In the 35 cattle pastures, we found 17 species (28%) with ANR capacity, 90% of which belonged to secondary vegetation, and 44 species (72%) with LNR capacity; most of these belonged to late successional tree species. Density of seedlings/saplings was positively associated with density of adult trees and the practice of manual weeding. The greatest abundance of seedlings/saplings corresponded to species dispersed by cattle, followed by those dispersed by wind. For adult trees, the most common type of dispersal was by wind, followed by cattle. These results suggest that native tree species are principally dispersed by cattle and wind, and cattle have a positive effect on the regeneration capacity of the most abundant tree species in the pastures studied. We conclude that Chol Mayan silvopastoral management practices in the study communities in Chiapas, Mexico allow for and promote regeneration of native tree species, most of which belong to secondary vegetation, although some belong to late successional species. These simple management practices allow for harvesting some trees in the pasture while also maintaining the regeneration process.

Variations in photoprotective potential along gradients of leaf development and plant succession in subtropical forests under contrasting irradiances

The successful development of photosynthetic organs is the basis of plant growth and community development. To reveal photo-acclimation to high irradiance in tree species during the course of leaf development and plant succession of subtropical forests, photosynthetic efficiency and photoprotective compounds were analyzed in young and mature leaves of three mid-successional tree species (Castanopsis fissa, Castanopsis chinensis and Schima superba) and three late-successional tree species (Machilus chinensis, Cryptocarya chinensis and Cryptocarya concinna), grown in 100% full sunlight (FL) or 30% of FL (low light, LL). Young leaves of the two species groups exhibited lower chlorophyll (Chl) content, Rubisco content, net photosynthetic rate (Pn), carboxylation efficiency (CE), effective photochemical yield (ΦPSII), photorespiratory electron flow (JO), but higher dark respiration (Rd), and ratios of carotenoids/chlorophylls (Car/Chl), anthocyanins/chlorophylls (Anth/Chl), flavonoids/chlorophylls (Flav/Chl), phenols/chlorophylls (Phen/Chl) and total antioxidant capacity/chlorophylls (TAC/Chl) than those of mature leaves, regardless of growth irradiance. Young leaves of both species groups demonstrated a higher flexibility of Anth/Chl, Flav/Chl, Phen/Chl and TAC/Chl in response to different light conditions than mature leaves. Flav/Chl in young leaves of late-successional group was remarkably higher than that of mid-successional group under the same light conditions. There was a negative correlation between antioxidant-dependent photoprotective potential and photosynthetic efficiency in young and mature leaves of the six tree species grown under either FL or LL. Our results explain partial mechanisms that lie behind the replacement of communities in subtropical forests: highly integrated photoprotective potential allows young leaves of shade-tolerant late-successional species to develop smoothly into mature organs under high irradiance.

Sixteen years changes in tree density and aboveground biomass of a logged and burned dipterocarp forest in East Kalimantan, Indonesia

Toma T, Warsudi, Osone Y, Sutedjo, Sato T, Sukartiningsih. 2017. Sixteen years changes in tree density and aboveground biomass of a logged and burned dipterocarp forest in East Kalimantan, Indonesia. Biodiversitas 18: 1159-1167. Changes in tree density and aboveground biomass (AGB) of a logged and burned lowland dipterocarp forest were monitored in Bukit Soeharto Research and Education Forest (BSREF) of Mulawarman University, East Kalimantan, Indonesia. A 9-ha plot was established in 1997 to investigate the effect of second felling and the subsequent recovery. Experimental felling was conducted in October 1997, and the plot was burned by uncontrolled fires between February and April 1998. Stem diameter of living trees (diameter at breast height ≥ 10 cm) in the plot was recorded annually. Allometric functions and the annual tree inventory were used to estimate changes in AGB. Tree density in the 9-ha plot was 429 trees ha−1 before the experimental felling.This decreased to 76 trees ha−1 in 2000 because of the felling and fires. Tree density increased to 515 trees ha−1 until 2008 and then decreased to 408 trees ha−1 in 2014. AGB of the 9-ha plot was 279 Mg ha−1 in 1997,which decreased to 96 Mg ha−1 in 2000 and then increased to 139 Mg ha−1 in 2014. After 16 years of the 1998 fires, in 2014, BSREF consists of a mosaic of forest stands that are dominated by either large late successional tree species or small pioneer trees. The former stands consisted of numerous late successional tree species that survived the felling and fires. The latter stands were dominated by a few pioneer species. In 2016, 16 years after the fire, these pioneer dominating stands are now undergoing a transitional stage from pioneer to late successional trees that grow longer and larger than the pioneer trees. Logged and burned forest stands may recover their AGB comparable to that of the original forest (≥400 Mg ha−1), if these stands are saved from further logging and fires in the longterm.

Combined effects of seed and soil quality drive seedling performance of a late‐successional canopy tree in a tropical forest

AbstractHabitat loss and fragmentation affect the structure and functioning of forested ecosystems worldwide, yet we lack an understanding of how species respond to environmental changes. Here, we examined reproductive success and seedling performance of Poulsenia armata (Moraceae) in continuous and fragmented forests of Los Tuxtlas, southern Mexico. We further investigated how maternal habitat and soil conditions manifested in the seedling stage. We determined seed quality and seedling performance by combining isotopic analyses in seed quality with field observations of P. armata fruit production and a common‐‐garden experiment. Soil conditions in forest fragments negatively impacted P. armata reproductive success. Trees of P. armata in forest fragments were smaller in size and produced fewer fruits and smaller seeds with lower quality compared with trees from the continuous forest. The combined effects of maternal habitat and soil conditions determined seedling survival and growth of this tropical tree. Notably, seedlings had restricted plasticity for biomass allocation to roots, limiting the capacity of fragmented populations to compensate for the initial low N content in seeds. Trees in forest fragments at Los Tuxtlas produced offspring competitively inferior and potentially less resilient than counterparts in continuous forest, jeopardizing future persistence of this late‐successional tree species.

Carbon stocks and dynamics at different successional stages in an Afromontane tropical forest

Abstract. As a result of different types of disturbance, forests are a mixture of stands at different stages of ecological succession. Successional stage is likely to influence forest productivity and carbon storage, linking the degree of forest disturbance to the global carbon cycle and climate. Although tropical montane forests are an important part of tropical forest ecosystems (ca. 8 %, elevation > 1000 m a.s.l.), there are still significant knowledge gaps regarding the carbon dynamics and stocks of these forests, and how these differ between early (ES) and late successional (LS) stages. This study examines the carbon (C) stock, relative growth rate (RGR) and net primary production (NPP) of ES and LS forest stands in an Afromontane tropical rainforest using data from inventories of quantitatively important ecosystem compartments in fifteen 0.5 ha plots in Nyungwe National Park in Rwanda. The total C stock was 35 % larger in LS compared to ES plots due to significantly larger above-ground biomass (AGB; 185 and 76 Mg C ha−1 in LS and ES plots), while the soil and root C stock (down to 45 cm depth in the mineral soil) did not significantly differ between the two successional stages (178 and 204 Mg C ha−1 in LS and ES plots). The main reasons for the difference in AGB were that ES trees had significantly lower stature and wood density compared to LS trees. However, ES and LS stands had similar total NPP (canopy, wood and roots of all plots ∼ 9.4 Mg C ha−1) due to counterbalancing effects of differences in AGB (higher in LS stands) and RGR (higher in ES stands). The AGB in the LS plots was considerably higher than the average value reported for old-growth tropical montane forest of south-east Asia and Central and South America at similar elevations and temperatures, and of the same magnitude as in tropical lowland forest of these regions. The results of this study highlight the importance of accounting for disturbance regimes and differences in wood density and allometry of tree species dominating at different successional stages in an attempt to quantify the C stock and sink strength of tropical montane forests and how they may differ among continents.

Regeneration Responses to Management for Old-Growth Characteristics in Northern Hardwood-Conifer Forests

Successful tree regeneration is essential for sustainable forest management, yet it can be limited by the interaction of harvesting effects and multiple ecological drivers. In northern hardwood forests, for example, there is uncertainty whether low-intensity selection harvesting techniques will result in adequate and desirable regeneration. Our research is part of a long-term study that tests the hypothesis that a silvicultural approach called “structural complexity enhancement” (SCE) can accelerate the development of late-successional forest structure and functions. Our objective is to understand the regeneration dynamics following three uneven-aged forestry treatments with high levels of retention: single-tree selection, group selection, and SCE. Regeneration density and diversity can be limited by differing treatment effects on or interactions among light availability, competitive environment, substrate, and herbivory. To explore these relationships, manipulations and controls were replicated across 2 ha treatment units at two Vermont sites. Forest inventory data were collected pre-harvest and periodically over 13 years post-harvest. We used mixed effects models with repeated measures to evaluate the effect of treatment on seedling and sapling density and diversity (Shannon–Weiner H’). The treatments were all successful in recruiting a sapling class with significantly greater sapling densities compared to the controls. However, undesirable and prolific beech (Fagus americana) sprouting dominates some patches in the understory of all the treatments, creating a high degree of spatial variability in the competitive environment for regeneration. Multivariate analyses suggest that while treatment had a dominant effect, other factors were influential in driving regeneration responses. These results indicate variants of uneven-aged systems that retain or enhance elements of stand structural complexity—including old-growth characteristics—can generally foster abundant regeneration of important late successional tree species depending on site conditions, but they may require beech control where beech sprouting inhibits desired regeneration.

Impact of Cardamom Cultivation on the Composition and Dynamics of Soil Seed Banks in a Conservation Forest in Sri Lanka: Implications for Conservation

Cultivation of cash crops, such as cardamom (Elettaria cardamomum) in the forest understorey is a common practice in many tropical forests. Over time, cultivation may change forest structure and species composition, leading to gradual degradation of biodiversity and ecosystem services. Effective conservation of these forests requires an enhanced understanding of the demographic processes such as soil seed bank that may greatly influence future forest composition. We examined how the soil seed bank structure and composition responds to cardamom cultivation in a high conservation value Sri Lankan montane rain forest. Soil samples from natural forest with abandoned cardamom plantations (CP) and adjacent natural forest (NF) patches without cardamom were collected in dry and wet seasons. Soil samples were spread out in trays in a shade house and germination was recorded weekly for 19 weeks. The density of seeds in the soil seed bank was much higher in CP than NF. While grasses and forbs contributed the highest number and percentage of seeds in soils of both forest types, their densities in the soil seed bank were 9 and 2 times greater in the CP than the NF, respectively. Seeds of the non-native herbs Ageratina riparia and E. cardamomum were 4 and 20 times greater in the soil of CP, respectively. Seeds of light demanding tree species such as Macaranga indica were restricted to soils of CPs. Overstorey tree community of each forest type was poorly represented in their respective soil seed banks. The high density of seeds of pioneer trees and non-native herbs in the soil of CPs, combined with higher light transmission to the ground floor may exacerbate competition for resources with the seedlings of late successional trees of high conservation value. To overcome this barrier and enhance conservation value of the forest, restoration strategies may need to focus on transplanting seedlings of these species into forest with abandoned cardamom plantations.

Late-Holocene fire history as revealed by size, age and composition of the soil charcoal pool in neighbouring beech and spruce forest landscapes in SE Norway

European beech and Norway spruce are late successional tree species that have become rapidly dominant in northern Europe in late-Holocene. The northern distribution limit for natural beech forests is in SE Norway, where beech forests and boreal spruce forests meet. Here we have estimated the size, composition and age of the macroscopic charcoal pool to infer past fire history and the establishment of neighbouring Norwegian beech- and spruce forests. To encompass landscape level scales of variations in the charcoal pool, we have analysed the charcoal record in 100 soil cores that were collected using a restricted random procedure. The sizes of the soil charcoal pools ranged from 2 to 1214 g m−2, and they were significantly more spatially variable in the beech forest landscape than in the spruce forest landscape. We show that today’s beech forests took over the dominance from Norway spruce in the landscape about 300 years ago, and that fire disturbances on the landscape level preceded the establishment of beech in the former spruce forest landscape. Interestingly, large-scale fire disturbances have not occurred ever since beech gained dominance. Conversely, we show that today’s spruce forests took over the dominance from Scots pine in the landscape, and that also the establishment of spruce was preceded by fire disturbances on the landscape level.

Differences between root traits of early- and late-successional trees influence below-ground competition and seedling establishment

Abstract:The competitive influence of the root system of the exotic grassUrochloa brizanthaand the widespread forbLeonotis nepetifoliaon the emergence, survival and early growth of the seedlings of eight tropical heliophilous herbaceous species, six early-successional woody species and five late-successional woody species from Brazil, grown in 3500-cm3pots and in greenhouse without light restriction were assessed. The density of fine-root systems produced by the forb and the grass in pots were 6.8 cm cm−3soil and 48.1 cm cm−3soil, respectively. Seedlings survival of the heliophilous herbaceous, early- and late-successional woody species were 86%, 70% and 100% in presence of the forb root system and 12%, 14% and 100% in competition with grass root system, respectively. The competitive pressure applied by the grass root system on seedling growth of the heliophilous herbaceous, early- and late-successional woody species were 2.4, 1.9 and 1.4 times greater than the forb root system. Total root length of the heliophilous herbaceous, early- and late-successional woody species grown without competitors were 13, 33 and 5 times greater than in competition with forb, and were 66, 54 and 6 times greater than in competition with grass root system, respectively. The averages of fine-root diameter of plants grown without competitors were 209 μm for the heliophilous herbaceous, 281 μm for early-successional trees and 382 μm for late-successional trees. The root system of the forb did not avoid seedling establishment of most plant species, but the grass root system hampered more the establishment of heliophilous herbaceous and early-successional woody species than the seedling establishment of late-successional woody species. The different density of root systems produced in soil by the forb and the grass, and the distinct root traits (e.g. root diameter and root tissue density) of the early- and late-successional plant species can explain the differences in the establishment of seedlings of plant species belonging to different groups of tropical succession when exposed to below-ground competition.

Restoration of Spanish pine plantations: A main challenge for the 21st century

Most of the Iberian Peninsula has a Mediterranean climate, which strongly determines the objectives, strategies and techniques of forest restoration. This communication addresses a main forest restoration challenge for Mediterranean-climate woodlands in Spain: the transformation of old monospecific pine plantations to more diverse, resistant and resilient forest systems. I also present how afforestation methods and some ideas on plant quality have evolved in the last 80 years. Productivity of Mediterranean forests is low, which discourages private owners to invest in woodland management. Therefore, woodland management strongly relies on public funds. Large-scale afforestation in the 20th century has created huge areas of monospecific pine plantations, which have been under thinned and are very simple structurally with almost no understory. The stands are very prone to fires, diseases and drought dieback. However, old pine plantations can facilitate the establishment of late successional trees and shrubs when properly thinned. Therefore, pine plantations are an opportunity for restoring several types of oak-dominated forests at a large scale and resources should invested to preserve and gradually transform these plantations into mixed forests. Funds should be invested in thinning progressively rather than to plant new areas. In many plantations close to oak forests remnants, thinning is the only management required. However, many pine plantations are far from seed sources and enrichment plantations together with thinning are needed. Extensive enrichment plantations are expensive. Therefore, an option is to develop a network of small islets strategically placed inside pine plantations and properly managed as seed foci to foster pine plantation colonization. This option is cheaper than conventional extensive low-density enrichment plantations but research is needed to assess its effectiveness for pine plantation transformation.

Pigment patterns and photoprotection of anthocyanins in the young leaves of four dominant subtropical forest tree species in two successional stages under contrasting light conditions.

Light-driven subtropical forest succession is a dynamic process in which mesophytic climax communities replace heliophytic ones. Juvenile leaves (particularly mesophytic ones) are sensitive to high irradiances. To determine the photoprotection strategy that juvenile leaves use during subtropical forest succession, anthocyanin accumulation patterns were investigated in the young leaves of two mid-successional dominant trees (i.e., Schima superba and Castanopsis fissa) and two late-successional dominant trees (i.e., Cryptocarya concinna and Acmena acuminatissima) grown in 100% (FL) and 25% (LL) of full sunlight. All four tree species produced anthocyanins in their juvenile leaves when <50% of chlorophylls and carotenoids had developed. Higher anthocyanin concentrations accumulated in the young leaves grown in FL than in those grown in LL and in late-successional than in mid-successional trees. The juvenile leaves of late-successional trees were subjected to higher light-induced photoinhibition than those of mid-successional trees, despite of the fact that the leaves of late-successional trees showed greater non-photochemical quenching than those of mid-successional trees. Under LL conditions, photosystem II excitation pressure (1 - qP) was significantly higher in the juvenile leaves of late-successional trees than those of mid-successional trees. Under either FL or LL conditions, anthocyanin concentrations in juvenile leaves were negatively related to the light compensation point in mature leaves across species. However, anthocyanin concentrations were positively related to the antioxidant capacity of juvenile leaves. These results indicate that anthocyanin accumulation in the juvenile leaves of subtropical dominant trees during forest community succession is a flexible photoprotective response to ambient irradiances according to leaf sensitivity to light.

Sprucification in protected forests: myth or veracity? – Clues from 60 yrs survey data

AbstractQuestionsThe purpose of this study was to examine how compositional characteristics of forest reserves in production landscapes change over time and to explore the local site conditions that drive these processes. Our hypothesis was according to the general paradigm that suppression of natural disturbance regimes and lack of active management causes protected forest areas (PFAs) to develop into forests of high density dominated by late successional tree species.LocationBoreal and hemiboreal forests of Sweden.MethodsWe used long‐term (60 yrs) data from the Swedish National Forest Inventory (NFI), representing all the PFAs in Sweden, to study changes in tree species composition in relation to site factors and the initial state of the forest.ResultsDuring the period of our study the average density expressed by the growing stock (GS) increased from 70 to 140 m3·ha−1. This increase concerned both early and late successional tree species and there was no evidence for a faster increase of the late successional species Norway spruce (Picea abies) and the species composition was stable over time. A net volume increment (NVINCR) in spruce was mostly related to sites where spruce already was present, sites with high productivity and forest of high age. The probability of an increase in Scots pine (Pinus sylvestris) was negatively linked to productivity and stand age, while the NVINCR was higher on more productive sites. The NVINCR of deciduous trees was unrelated to site productivity and age but positively affected by the initial GS, increasing slope and soil depth.ConclusionsOur results suggest that the relative composition of species is stable over time and balanced by site productivity, which is in accordance with the resource‐ratio hypothesis. An important cause of this stability could be the low number of tree species in northern Europe, which limits the number of potential successional pathways.

Light availability drives tree seedling success in a subtropical coastal dune forest in South Africa

In subtropical coastal dune forests of South Africa, the microenvironment of tree seedlings is largely influenced by a pervasive understorey woody herb, Isoglossa woodii. We examined whether the additional shading by I. woodii explains the competitive response of tree seedlings from these forests. Seedlings of four common mid- to late-successional tree species (Diospyros natalensis, Euclea racemosa, Sideroxylon inerme and Apodytes dimidiata) were grown at three densities of I. woodii in a common garden experiment under greenhouse conditions. The seedlings were grown at 1.6% and 13.5% of full sunlight and supplied with 1% and 10% nitrogen in half-strength Hoagland's nutrient solution. Total biomass and biomass allocation parameters were used to measure the competitive response of the seedlings. Seedlings attained maximum biomass at high light and high nutrient levels and showed species- and light-specific responses to biomass of I. woodii neighbours. Seedlings' allocation to roots increased with increasing light levels but decreased at higher nutrient levels. The leaf mass fraction (LMF) response to light and nutrient levels was opposite to that shown by root allocation. Specific leaf area (SLA) and leaf area ratio (LAR) decreased with increasing light conditions but were not responsive to manipulation of nutrients. The presence of I. woodii neighbours reduced LMF whilst the responses of SLA to neighbours depended on the light level and species. Leaf trait responses to manipulation of light conditions, I. woodii neighbour density and soil nutrient concentration are complex but overall demonstrate an overwhelming role of light in influencing seedling establishment in coastal dune forests. The competitive response of these seedlings to low irradiance reiterates the notion of phenotypic clustering at the seedling stage amongst shade tolerant tree species, which promotes seedling persistence and gradual transition into the tree layer. Our results highlight the role of additional understorey shading by the herb stratum in influencing tree recruitment dynamics and ultimately tree community structure in many of Africa's tropical lowland forests.

Recovery of plant community functional traits following severe soil perturbation in plantations: a case-study

ABSTRACTWe present a case study in which we assessed the effects of a severe soil perturbation on the plant community and soil variables in young hybrid poplar (Populus sp.) plantations of southern Québec (Canada). Our overall goal was to test if soil perturbation and planting fast-growing species could promote the reestablishment of a relatively diverse plant community. A chronosequence that included three plantations (4, 8, and 12-year old) established after soil scarification, paired with three natural stands representative of the local temperate mixedwood forest comprising both pioneer and late-successional tree species, was implemented. Vegetation surveys and soil collection were performed in 2012 and species traits were provided by the Traits Of Plants In Canada and TRY databases. Principal response curve analyses showed species and functional trait divergence between treated and natural stands at ages 4 and 8, but that those divergences were less at age 12. Species and trait convergences were slower in the scarification furrows than in the scarification berms (mounds between furrows). However, severe site preparation did not appear to affect soil variables on the study sites. Our results suggest that even following severe site preparation, gradual recovery of species and trait composition similar to that of natural stands appears possible in the long term, mainly through fast canopy development by hybrid poplar. However, organic material export and soil erosion risks associated with this type of site preparation need to be evaluated.EDITED BY Sheila Ward

Reforestation with resprouter species to increase diversity and resilience in Mediterranean pine forests

Under Mediterranean conditions, drought and fire are prevalent disturbances that play a fundamental role in the distribution, organization and evolution of ecosystems. Reforestation programs were carried out in degraded areas by planting pines. Presently, the spontaneous regeneration of other species is scarce and species diversity is poor. Introducing woody resprouter species under pine forests would increase species diversity and ecosystem resilience to cope with different types of disturbances, such as wildfires. In this study, we investigated the survival, growth and functional responses of six Mediterranean trees and shrub resprouter species planted under pine forests. Experiments were done in a dry Mesomediterranean climate. Seedlings from a wide array of early to late successional trees and shrub species were outplanted in different pine densities, low, medium and high, which corresponded to 22%, 48% and 62% of the maximum sunlight received, respectively. The time course of survival and growth (height and basal diameter) were analyzed for 3years after outplanting. Survival was higher than 78%, although differences between species and pine densities were found. Seedling growth also reflected different interactions among introduced seedlings and density of pines. Water use efficiency of species based on isotopic determinations (δ13C and δ18O) differed between densities and species according to functional groups. These results have relevant implications for the management and restoration of fire-prone Mediterranean pine forests.