Early Successional Tree Species Research Articles

Removal of native bamboo promotes natural regeneration in degraded temperate rainforests in North‐Patagonia, Chile

Forest degradation often permits the proliferation of dense understories that inhibit the development of natural regeneration over long periods. In South American temperate rainforests, native Chusquea bamboo species become unusually competitive after logging and invade forest understories, creating dense and continuous thickets under remnant canopy tree species. In this study, we aim to evaluate how natural regeneration of native species develops after removal of the Chusquea bamboo understory and to define which microsite conditions can facilitate species' early development. To achieve this, we removed the Chusquea understory in 45 experimental units, systematically established in a 4 ha experiment located in degraded temperate forests on Chiloé Island, North‐Patagonia, Chile. We evaluated microsite conditions and monitored the natural regeneration response during 5 years. After 5 years, greater than 81% of the remnant canopy tree species were regenerating, mostly from seed, and there was a 55.5% increase in total natural regeneration (p < 0.05; increase >1 individuals/m2 yr−1), with species like Amomyrtus spp. increasing abundance by greater than 121%. Total natural regeneration presented positive significant correlations (p < 0.01) with the depth of the water table (rs: 0.40), soil carbon (rs: 0.44), nitrogen (rs. 0.41), and organic matter (rs: 0.44). We conclude that removing the Chusquea understory assists the natural recovery of degraded temperate rainforests by facilitating additional recruitment of early, mid, and late successional tree species. In this process, early and mid‐successional tree species are more specific in their microsite preferences than successionally late ones.

Disentangling the roles of bracken fronds and litter on natural seedling recruitment in fire-disturbed tropical montane habitats

Tropical montane forests are diverse ecosystems often affected by uncontrolled human-induced fires causing tree mortality and creating large deforested areas. After fires, Pteridium spp. ferns (bracken) often dominate, and forest regeneration in these areas is slow. In this study, we evaluated the effects of bracken fronds and litter, as well as the micro-environmental conditions created by the fern, on the density and species diversity of naturally recruiting seedlings. At eight sites, 120 experimental plots were established among forest and bracken-dominated areas with the following treatments: (a) fronds and litter intact (F+L+); (b) fronds intact and litter removed (F+L-); (c) fronds removed and litter intact (F-L+); and (d) fronds and litter removed (F-L-). After one year, all seedlings were registered, identified and classified according to their life-form (tree, shrub, herb, vine), dispersal vector (wind- or animal-dispersed) and successional status (early-, mid-, and late-successional). For all treatments we assessed 12 micro-environmental variables. We identified 3649 naturally-recruiting seedlings corresponding to 278 species from 70 families. We found positive effects of bracken fronds particularly on tree seedling recruitment: treatments with fronds had greater densities of both animal- and wind-dispersed tree seedlings, 1.8 and 1.4 fold higher, respectively, compared to treatments without fronds. Similarly, the density of early-, mid- and late-successional tree species was 1.3, 1.7 and 1.9 times higher in treatments with than without fronds. Furthermore, species diversity of early-, mid- and late-successional tree species was higher in the treatments with fronds. The environmental conditions generated by bracken presence, such as photosynthetically active radiation, soil temperature, live bracken biomass and litter depth, had positive effects on seedling density of all, animal-dispersed and early-successional tree species, and negative effects on seedling recruitment of other life-forms, notably from early successional stages. To promote forest regeneration in bracken-dominated areas, active restoration measures such as direct seed addition and transplants of nursery-raised seedlings of mid- and late-successional species should be considered. Since bracken can hinder the establishment of some life forms and species but favor others, it is recommended to include a trait-based approach to understand species responses to environmental factors and select species that are optimally adapted to bracken-dominated habitat conditions to promote forest regeneration.

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.

Fungal Community Succession of Populus grandidentata (Bigtooth Aspen) during Wood Decomposition

Fungal communities are primary decomposers of detritus, including coarse woody debris (CWD). We investigated the succession of fungal decomposer communities in CWD through different stages of decay in the wide-ranging and early successional tree species Populus grandidentata (bigtooth aspen). We compared shifts in fungal communities over time with concurrent changes in substrate chemistry and in bacterial community composition, the latter deriving from an earlier study of the same system. We found that fungal communities were highly dynamic during the stages of CWD decay, rapidly colonizing standing dead trees and gradually changing in composition until the late stages of decomposed wood were integrated into soil organic matter. Fungal communities were most similar to neighboring stages of decay, with fungal diversity, abundance, and enzyme activity positively related to percent nitrogen, irrespective of decay class. In contrast to other studies, we found that species diversity remained unchanged across decay classes. Differences in enzyme profiles across CWD decay stages mirrored changes in carbon recalcitrance, as B-D-xylosidase, peroxidase, and Leucyl aminopeptidase activity increased as decomposition progressed. Finally, fungal and bacterial gene abundances were stable and increased, respectively, with the extent of CWD decay, suggesting that fungal-driven decomposition was associated with shifting community composition and associated enzyme functions rather than fungal quantities.

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.

Disturbance has variable effects on the structural complexity of a temperate forest landscape

The temporal dynamics of forest canopy structure are influenced by disturbances that alter vegetation quantity and distribution. While canopy structural indicators such as leaf area index (LAI), canopy cover, and canopy height have been widely studied in the context of disturbance, the post-disturbance temporal dynamics of structural complexity, which summarizes the heterogeneity of vegetation arrangement, are poorly understood. With the goal of advancing conceptual and empirical understanding of the temporal dynamics of structural complexity following disturbance, we synthesized results from three large-scale disturbance manipulation experiments at the University of Michigan Biological Station (UMBS): the 4-year Forest Resilience Threshold Experiment (FoRTE) manipulating levels of disturbance severity; the decade-long Forest Accelerated Succession Experiment (FASET), in which all early successional tree species were stem-girdled within 39 ha in the same landscape; and forest chronosequences established following clear-cut harvesting. We found that the temporal dynamics of canopy structure following disturbance were dependent upon three factors: (1) the source and severity of disturbance; (2) the spatial and temporal scales of analysis; and (3) the measure of structure assessed. Unlike vegetation area index and canopy cover, which initially decreased in response to disturbance, structural complexity measures such as canopy and top rugosity did not consistently respond to moderate levels of disturbance severity. Over multi-decadal timescales, structural complexity increased to a maximum, regardless of whether fire occurred at the time of stand establishment, but intervening low-to-moderate severity disturbance in regrown century-old forests altered trajectories of canopy rugosity. We conclude that structural complexity indicators display a more nuanced temporal and directional response to disturbance than conventional leaf area and cover indexes. Predicting what disturbance conditions modify trajectories of structural complexity remains critical to disturbance characterization and the inference of ecosystem functioning.

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.

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.

Responses of fine root exudation, respiration and morphology in three early successional tree species to increased air humidity and different soil nitrogen sources.

Global climate change scenarios predict an increase in air temperature, precipitation and air humidity for northern latitudes. Elevated air humidity may significantly reduce the water flux through forest canopies and affect interactions between water and nutrient uptake. However, we have limited understanding of how altered transpiration would affect root respiration and carbon (C) exudation as fine root morphology acclimates to different water flux. We investigated the effects of elevated air relative humidity (eRH) and different inorganic nitrogen sources (NO3- and NH4+) on above and belowground traits in hybrid aspen (Populus × wettsteinii Hämet-Ahti), silver birch (Betula pendula Roth.) and Scots pine (Pinus sylvestris L.) grown under controlled climate chamber conditions. The eRH significantly decreased the transpiration flux in all species, decreased root mass-specific exudation in pine, and increased root respiration in aspen. eRH also affected fine root morphology, with specific root area increasing for birch but decreasing in pine. The species comparison revealed that pine had the highest C exudation, whereas birch had the highest root respiration rate. Both humidity and nitrogen treatments affected the share of absorptive and pioneer roots within fine roots; however, the response was species-specific. The proportion of absorptive roots was highest in birch and aspen, the share of pioneer roots was greatest in aspen and the share of transport roots was greatest in pine. Fine roots with lower root tissue density were associated with pioneer root tips and had a higher C exudation rate. Our findings underline the importance of considering species-specific differences in relation to air humidity and soil nitrogen availability that interactively affect the C input-output balance. We highlight the role of changes in the fine root functional distribution as an important acclimation mechanism of trees in response to environmental change.

Large trees in restored tropical rainforest

Restoration interventions aim to accelerate forest recovery by skipping the early stages of succession where short-lived early-successional tree species dominate. Large trees (≥30 cm of Diameter at Breast Height [DBH]) provide ecosystem functions, such as carbon storage and acting as stepping stones for the movement of animals through the landscape. Here, we evaluated two mixtures of planted and, unplanted areas to figure out which restoration treatment was more successful in skipping the early stages of succession. For this, we measured forest structure of large trees in restoration settings after 10 years in Los Tuxtlas, Veracruz, Mexico. In 2006, cattle grazing was excluded from 24 plots (30 × 30 m). Eight of those plots were planted with 12 wind-dispersed species, eight plots were planted with 12 animal-dispersed species (a total of 2,304 planted trees), and eight plots were left to undergo natural succession without plantings. Planted and naturally recruited trees have been assessed periodically since 2007. A total of 835 planted and naturally recruited trees of 45 species reached large size. Including all trees (planted and recruited), the richness and abundance of late-successional trees was higher in plantings than under natural succession while richness of large recruits of late-successional species was as higher in plantings as in natural succession. Also, including all trees, plantings of animal-dispersed species have higher richness and abundance of trees dispersed by bats and both bats and birds; while species and trees dispersed by birds were present equally at all treatments. Richness and abundance of bat-dispersed recruits were similar in plantings and natural succession while plantings of wind-dispersed species had higher bird-dispersed recruits. Composition heterogeneity, driven by natural recruitment, was largest for early-successional trees in natural succession. After 10 years, the first stages of succession (20–30 years) were skipped in plantings: plantings have higher abundance of large seeded late-successional species. For an overall increase in composition heterogeneity in permanent agricultural landscapes, we suggest establishing areas to undergo natural succession along with plantings that include a higher percentage of late-successional species with large seeds.

Landsat near-infrared (NIR) band and ELM-FATES sensitivity to forest disturbances and regrowth in the Central Amazon

Abstract. Forest disturbance and regrowth are key processes in forest dynamics, but detailed information on these processes is difficult to obtain in remote forests such as the Amazon. We used chronosequences of Landsat satellite imagery (Landsat 5 Thematic Mapper and Landsat 7 Enhanced Thematic Mapper Plus) to determine the sensitivity of surface reflectance from all spectral bands to windthrow, clear-cut, and clear-cut and burned (cut + burn) and their successional pathways of forest regrowth in the Central Amazon. We also assessed whether the forest demography model Functionally Assembled Terrestrial Ecosystem Simulator (FATES) implemented in the Energy Exascale Earth System Model (E3SM) Land Model (ELM), ELM-FATES, accurately represents the changes for windthrow and clear-cut. The results show that all spectral bands from the Landsat satellites were sensitive to the disturbances but after 3 to 6 years only the near-infrared (NIR) band had significant changes associated with the successional pathways of forest regrowth for all the disturbances considered. In general, the NIR values decreased immediately after disturbance, increased to maximum values with the establishment of pioneers and early successional tree species, and then decreased slowly and almost linearly to pre-disturbance conditions with the dynamics of forest succession. Statistical methods predict that NIR values will return to pre-disturbance values in about 39, 36, and 56 years for windthrow, clear-cut, and cut + burn disturbances, respectively. The NIR band captured the observed, and different, successional pathways of forest regrowth after windthrow, clear-cut, and cut + burn. Consistent with inferences from the NIR observations, ELM-FATES predicted higher peaks of biomass and stem density after clear-cuts than after windthrows. ELM-FATES also predicted recovery of forest structure and canopy coverage back to pre-disturbance conditions in 38 years after windthrows and 41 years after clear-cut. The similarity of ELM-FATES predictions of regrowth patterns after windthrow and clear-cut to those of the NIR results suggests the NIR band can be used to benchmark forest regrowth in ecosystem models. Our results show the potential of Landsat imagery data for mapping forest regrowth from different types of disturbances, benchmarking, and the improvement of forest regrowth models.

Successional loss of two key food tree species best explains decline in group size of Panamanian howler monkeys (Alouatta palliata)

AbstractNegative impacts of discrete, short‐term disturbances to wildlife populations are well‐documented. The consequences of more gradual environmental change are less apparent and harder to study because they play out over longer periods and are often indirect in their action. Yet, they can drive the decline of wildlife populations even in seemingly pristine and currently well‐protected habitats. One such environmental change is a successional shift in a community's species composition as it regenerates from disturbance caused by past human land use. Early and middle successional tree species often provide key foods to folivores and frugivores, but the abundance of these resources drops as the forest matures, with adverse repercussions for these consumers. Our 44‐year record (1974–2018) of howler monkey (Alouatta palliata) group sizes and demographic composition from Barro Colorado Island, Panama, a protected reserve, documents an example of this phenomenon. After 70 years of relative stability, the mean size of howler monkey groups exhibited a marked decline, beginning in 2003. This downward trajectory in group size has continued through the most recent census in 2018. The composition of howler groups also changed significantly during the study period, with the patterns of decline differing among age/sex classes. There is no evidence that these changes were caused by increased rates of emigration, group fission, predation, parasitism, or disease. Rather, they are best explained by an island‐wide, succession‐driven decline in the densities of two species of free‐standing fig trees, Ficus yoponensis and F. insipida, which together were providing ~36% of BCI howlers’ annual diet.Abstract in Spanish is available with online material.

Historical range of variability for restoration and management in Wisconsin

In Wisconsin, as in other states, management goals sometimes include restoration of historical forest conditions, which may prepare forests to be more compatible with future climates, disturbances such as drought and fire, and forest health threats. We quantified historical (1830–1866) composition and structure to develop historical reference conditions for restoration and documented changes based on current (2005–2009) forest surveys in Wisconsin. We provided structural metrics, functional group composition, and forest types for 186 ecological land types, and we also summarized trends in composition and structure. Wisconsin forests historically were comprised of 46% oak or pine savanna or woodland, 6% pine forest, and 48% forests primarily consisting of late-successional eastern broadleaf forest species and early-successional northern mixed forest species; densities of these forest types ranged from 60 to 460 trees/ha. In the Eastern Broadleaf Forest ecological division, increased composition of the early-successional and mid-successional eastern broadleaf forest groups (from 10 to 40%) and (planted) pine group (8–23%) occurred along with decreased fire-tolerant oak composition (from 65 to 23%). Density increased in current forests compared to historical forests by a factor of 2.2; despite increased density, basal area increased only slightly due to the presence of larger diameter trees in historical tree surveys. In the Northern Mixed Forest ecological division, increased composition of the mid-successional eastern broadleaf forest group (from 12 to 24%) and late-successional northern mixed forest group (from 10 to 17%) occurred due to decreased composition of the fire-tolerant pine group (from 17 to 9%) and late-successional eastern broadleaf forest group (from 30 to 20%). Density remained similar in current forests compared to historical forests but current basal area was 50% of historical basal area. The transition from open fire-tolerant oak and pine forests, with rarity of early-successional tree species, to closed forests composed of a variety of early- and mid-successional tree species parallels results from other research. Replacement of open oak or pine forest ecosystems by dense forests has moved Wisconsin outside of the historical range of variability, likely reducing plant and wildlife species associated with open oak and pine ecosystems.

Effects of host species, environmental filtering and forest age on community assembly of ectomycorrhizal fungi in fragmented forests

Abstract Understanding the assembly of biological communities in space and time is a major goal in community ecology. While most studies have focused on community assembly patterns in macro-organisms, there are comparatively few studies on micro-organisms. Here, we investigated how communities of ectomycorrhizal (EcM) fungi assemble in fragmented forests. We used a space-for-time substitution as an alternative for long-term studies to investigate variation in EcM fungal communities in three host species collected from 41 forest patches of different ages. Metabarcoding of root samples revealed that community composition was affected by a combination of host plant, soil variables, and forest age. While there were no clear effects of forest age on EcM fungal communities in early-successional tree species alder and hawthorn, forest age did affect the EcM fungal communities in hazel, which is typically associated with ancient forest. EcM fungal communities in early-successional species were affected mostly by soil conditions.

Growth Variations of Tree Saplings in Relation to Species Diversity and Functional Traits in a Tree Diversity Pot Experiment

Despite the accumulating evidence of the beneficial effects of diverse mixed species forests on ecosystem functioning and services, foresters in subtropical forest cultivation in China still prefer easily managed monocultures, which is also due to the complexity of mixed forests and the unknown underlying mechanisms related to relationships between biodiversity and forest growth. In a designed pot experiment, we selected two early-successional tree species (Pinus massoniana Lamb., Liquidambar formosana Hance.) and two late-successional tree species (Schima superba Champ., Elaeocarpus decipiens Hemsl.) and planted four saplings in one pot with regard to tree species diversity (monoculture, two species and four species mixtures), each combination replicated four times. In this three-year duration experiment, the effect of tree species diversity, tree identity, and functional traits on sapling growth (tree height, ground diameter, crown projection area), were analyzed. The results showed that the increments of ground diameter and crown projection area increased with tree species richness, whereas the mean tree height increment showed the opposite effect. This growth variation was species specific and related to functional traits (early or late succession), as the increments of the early successional tree species (P. massoniana Lamb. and L. formosana Hance.) had a positive correlation with tree species richness, while the late successional tree species (E. decipiens Hemsl. and S. superba Champ.) showed negative effects. In addition, our study provided evidence for the allometric differences between mixtures and monocultures, which have an important reference value on mixed-species forests.

Vegetative and reproductive tree phenology of ecological groups in a tropical dry forest in central Veracruz, Mexico

Background Tree phenology has been related to abiotic and biotic factors that trigger and regulate phenological patterns.&#x0D; Question We investigated whether tree species classified into ecological groups of species of successional status (late-, early-successional tree species) and seed dispersal mode (anemochory, autochory, zoochory) would display different phenological patterns.&#x0D; Study site and dates A tropical dry forest in eastern Mexico; November 2007 to September 2010.&#x0D; Methods We monthly recorded leaf fall, leafing, flowering, and fruiting in 165 trees belonging to 16 species tagged along a trail inside a forest fragment (21 ha). Monthly precipitation and temperatures data were obtained from the nearest meteorological station. Phenological periodicity was analyzed using circular statistics.&#x0D; Results Leaf fall occurred during the dry season and leafing at the beginning of the rainy season. Flowering at community level was not significantly cyclic because of differences within groups: late-successional and zoochorous species displayed a flowering peak during the rainy season, whereas the early-successional, anemochorous and autochorous species do during the dry season. Fruiting occurred over an extended period but showed a cyclic pattern: Late successional and zoochorous species fruited at the beginning of the dry season, whereas early-successional and autochorous species tend to displayed a peak of fruiting at mid-dry season and the anemochorous at the end of the dry season.&#x0D; Conclusions. Vegetative phenological patterns were similar at the levels studied and were clearly related to climatic variables. However, the phenological patterns of reproduction differed within tree ecological groups and were not consistently correlated with precipitation or temperature.

The effects of agricultural history on forest ecological integrity as determined by a rapid forest assessment method

Forests are an important terrestrial biome, comprising large areas of the earth’s surface and providing important ecosystem services. Conservation efforts frequently focus on minimizing perceived threats to forests that could impact these services, but often without a clear understanding of the site specific factors that affect local forest composition, structure and threat magnitude. In this study, we examined the factors affecting forest ‘ecological integrity’ in a 334ha forest that includes mature forest remnants and areas recovering from agricultural activity. We developed a rapid upland forest assessment (RUFA) method to facilitate our examination of forest integrity since forest quality can vary at fine spatial scales (e.g., 100m) and time consuming assessment methods may not be feasible for many local conservation organizations. In general, we found that land use history and especially soil conditions associated with history were the primary factors affecting forest ‘ecological integrity’ (i.e. composition, structure and threat presence). In forests that developed after agricultural abandonment, soil pH significantly increased, while soil carbon and nitrogen content declined. This was associated with increased presence of invasive, early successional tree, shrub and herb species and a general lack of some structural components, such as the presence of light gaps, within the forest. Our results are discussed in light of conservation efforts that seek to enhance overall forest quality and how rapid assessment methods, such as the one presented here, can be used to further conservation objectives in forest systems.

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.

Mixed afforestation of young subtropical trees promotes nitrogen acquisition and retention

SummaryAfforestation is globally increasing to produce timber and pulp wood, but also to enhance ecosystem services such as carbon sequestration, nutrient retention or groundwater recharge. In China, large areas have been and will be afforested in order to compensate for the negative impacts of former clear‐cuttings and to make use of the ecosystem services associated with afforestation. In order to further optimize these services with regard to balanced nutrient (particularly nitrogen) cycles, it is important to know whether the use of mixtures of native tree species in afforestation projects promotes the acquisition and retention of nitrogen compared with the currently established large‐scale monocultures.To test the effect of species richness on system N retention and tree sapling N uptake, we conducted a15N tracer experiment in a young tree plantation. To this end, saplings of four abundant early successional tree species were planted in monocultures, in two‐ and four‐species mixtures and as single trees.Nitrogen retention increased with higher species richness due to enhanced N pools in sapling biomass. These species richness effects strengthened over time.Species‐specific differences in15N recoveries over time revealed below‐ground niche differentiation with regard to N uptake, which is likely to result in complementary resource use among coexisting species.Synthesis and applications. This study provides evidence that mixed afforestation promotes N retention from the sapling stage. To further improve ecosystem services associated with afforestation, we strongly suggest the use of mixtures of native tree species instead of monocultures. Mixtures of four species may reduce system N losses and thus may lessen groundwater contamination due to N leaching. We encourage further investigations to find optimal species combinations that promote a wide range of ecosystem services related to more closed nutrient cycles and minimized soil erosion. In our study, the plantations' capability to retain N could be optimized by means of both increasing tree species richness and by choosing the optimal species combinations.

Foliar respiration and its temperature sensitivity in trees and lianas: in situ measurements in the upper canopy of a tropical forest

Leaf dark respiration (R) and its temperature sensitivity are essential for efforts to model carbon fluxes in tropical forests under current and future temperature regimes, but insufficient data exist to generalize patterns of R in species-rich tropical forests. Here, we tested the hypothesis that R and its temperature sensitivity (expressed as Q10, the proportional increase in R with a 10 °C rise in temperature) vary in relation to leaf functional traits, and among plant functional types (PFTs). We conducted in situ measurements of R of 461 leaves of 26 species of tree and liana in the upper canopy of a tropical forest in Panama. A construction crane allowed repeated non-destructive access to measure leaves kept in the dark since the previous night and equilibrated to the ambient temperature of 23-31 °C in the morning. R at 25 °C (R25) varied among species (mean 1.11 μmol m(-2) s(-1); range 0.72-1.79 μmol m(-2) s(-1)) but did not differ significantly among PFTs. R25 correlated positively with photosynthetic capacity, leaf mass per unit area, concentrations of nitrogen and phosphorus, and negatively with leaf lifespan. Q10 estimated for each species was on average higher than the 2.0 often assumed in coupled climate-vegetation models (mean 2.19; range 1.24-3.66). Early-successional tree species had higher Q10 values than other functional types, but interspecific variation in Q10 values was not correlated with other leaf traits. Similarity in respiration characteristics across PFTs, and relatively strong correlations of R with other leaf functional traits offer potential for trait-based vegetation modeling in species-rich tropical forests.