Survival Of Planted Seedlings Research Articles

The phenotypic and genetic effects of drought-induced stress on wood specific conductivity and anatomical properties in white spruce seedlings, and relationships with growth and wood density.

Drought frequency and intensity are projected to increase with climate change, thus amplifying stress on forest trees. Resilience to drought implicates physiological traits such as xylem conductivity and wood anatomical traits, which are related to growth and wood density. Integrating drought-stress response traits at the juvenile stage into breeding criteria could help promote the survival of planted seedlings under current and future climate and thus, improve plantation success. We assessed in greenhouse the influence of drought-induced stress on 600 two-year-old white spruce (Picea glauca) seedlings from 25 clonal lines after two consecutive growing seasons. Three levels of drought-induced stress were applied: control, moderate and severe. Seedlings were also planted at a 45° angle to clearly separate compression from normal wood. We looked at the phenotypic and genetic effects of drought stress on xylem specific hydraulic conductivity, lumen diameter, tracheid diameter and length, and the number of pits per tracheid in the normal wood. We detected no significant effects of drought stress except for tracheid length, which decreased with increasing drought stress. We found low to high estimates of trait heritability, which generally decreased with increasing drought stress. Genetic correlations were higher than phenotypic correlations for all treatments. Specific conductivity was genetically highly correlated positively with lumen diameter and tracheid length under all treatments. Tracheid length and diameter were always negatively correlated genetically, indicating a trade-off in resource allocation. Moderate to high genetic correlations sometimes in opposite direction were observed between physico-anatomical and productivity traits, also indicating trade-offs. A large variation was observed among clones for all physico-anatomical traits, but clonal ranks were generally stable between control and drought-induced treatments. Our results indicate the possibility of early screening of genetic material for desirable wood anatomical attributes under normal growing conditions, thus allowing to improve the drought resilience of young trees.

Assessment of Farmer’s Tree Preferences and Their Seasonal Frost Management Practices in Frost-Affected Highlands of Eastern Ethiopia

Deforestation, land degradation, and low survival of planted seedlings are serious problems in highland Ethiopia. To address these problems, different land management practices such as afforestation and conservation program have been implemented; however, the success to date limited due to environmental stress and insufficient post-planting care. Therefore, the objective of this study was to investigate farmer’s tree needs and their traditional knowledge of seasonal frost management practices in selected frost-affected highlands of Eastern, Ethiopia. A total of 111 households were randomly selected for interviews on farmer’s tree species preference, frost management practices, and the causes of seedling mortality in the study area. Furthermore, key informant interviews and focus group discussions were used to collect the data. Descriptive statistics were used to analyze the data. The results confirm that season frost (55.6%) followed by free grazing (22.2%), inappropriate species site match (11.1%), and inappropriate planting time (5.6%) were major causes of seedling mortality in the study area. Organic mulch, plant cover, smoking, watering, and manuring were seasonal frost management practices applied by farmer’s to enhance seedlings’ survival in the study areas. However, this indigenous knowledge should be encouraged by the government through improved research, and extension services, to enhance seedlings’ survival in the study areas as well as to introduce it in different frost-prone highlands of Ethiopia. Moreover, species such as Eucalyptus globulus’ Labill, Cupressus lusitanica Mill., Juniperus procera Hochst. ex Endl., Hagenia abyssinica a (Bruce) J.F.Gmel, and Podocarpus falcatus (Thunb.) Mirb. (syn. P. gracilior Pilg.), were suggested as frost-tolerant species in the study area. Therefore, it is recommended that planting these tree species through research and campaign is essential to reduce land degradation in the frost-affected highlands area of the country, particularly in the study area.

Growth performance of planted mangrove seedlings on an intertidal area of the Bali Sea

Mangrove ecosystems have various services, one of them being a barrier to strong waves and seawater currents. Growing mangroves in the physical environment with sandy soil, high differences between high and low tides, big waves, and strong seawater currents such as in the Bali Sea under a highway interchange is not easy. To cope with this kind of less-understood environmental condition, the experiment planting was done by applying three kinds of planting techniques: mangrove incubator (guludan), strip line planting, and cluster planting using the mangrove (Rhizophora mucronata) seedlings having sufficient tolerance to high salinity and sandy soils. Two months after planting, the tree planting techniques showed a high percentage of survival of planted seedlings (PSS=100%) and well healthy growing performance of seedlings (no infected by pest and disease), the average increments of seedling stem diameter ranged from 0.73 to 1.15 mm, height ranged from 8.70 to 10.98 cm, and the number of leaves ranged from 1.08 to 1.45 pieces in a month. Furthermore, the best planting technique was the mangrove incubator (guludan) in terms of stem diameter growth, while the strip line and cluster techniques were the best in terms of seedling height growth.

Two studies of the potential of drought preconditioning to enhance deep root production in seedlings of western larch (Larix occidentalis)

Climate change is increasing the frequency and intensity of drought in the western USA. Evidence suggests that drought preconditioning of plants may improve the survival of planted seedlings under dry conditions through enhanced water uptake by roots, but the mechanisms underlying enhanced survival under drought remain unknown. We tested whether the vertical distribution of roots in root plug cross-sections varied with drought preconditioning and seed source. We subjected western larch (Larix occidentalis Nutt.) seedlings from eight different provenances to Low (50-65% gravimetric water content), Moderate (65-75%), and High (≥75%) watering regimes in a nursery. We then investigated dry root mass across four root-plug sections, including the taproot and three lateral root cross-sections (top 1/3rd, middle 1/3rd, and bottom 1/3rd of root plugs). We also tested for carry-over effect of drought preconditioning on the mass of egressed roots observed among cross-sections of potting soil in a 30-day potted study. Root plug mass varied significantly (P< 0.001) with watering regime, root plug cross-section, and an interaction between watering regime and cross-section. Overall, seedlings that received less water produced lateral root plug cross-sections of greater mass, which coincided with taproots of less mass. In contrast to findings from the root plug study, the distribution of egressed root mass among cross-sections of potting soil did not vary with drought preconditioning. This is the first study to assess seedling root growth in response to drought preconditioning in western larch with a focus on the distribution of root mass in root plugs and egressed root mass among soil cross-sections. We expect this work to facilitate future efforts to improve drought hardiness of western larch seedlings. Future improvement of western larch seedlings will require investigation into whether altered root plug mass distribution translates to improved seedling performance in outplanting trials.

Use of direct seeding and seedling planting to restore Korean pine (Pinus koraiensis Sieb. Et Zucc.) in secondary forests of Northeast China

The poor natural regeneration of Korean pine represents a substantial hurdle limiting the restoration of secondary forests to mixed broad-leaved Korean pine forests (MBKPFs). Active restoration based on direct seeding or planting seedlings is accordingly considered to be a prerequisite for promoting Korean pine recruitment in secondary forests. To evaluate the most effective practices for restoring Korean pine in secondary forests, we studied the effects of microsites associated with gaps of different sizes and within-gap locations on direct seeding (rodent access/exclusion and soil/litter cover) and seedling planting (1-, 2-, and 3-year-old seedlings). We found that an average of 82.4% of sown seeds were eaten by rodents, with only 9.9% germinating and surviving after two growing seasons. Among the germinated seedlings, 37.6% were subsequently excised by rodents, whereas 6% died due to other natural causes. Furthermore, compared with the control sites (forest understorey), we detected no significant differences among the different microsites with respect to an effective reduction in rodent damage or promotion of seed germination, whereas rodent exclusion was more effective in protecting seeds from predation than the effect of microsite. With regards to planted seedlings, we found that the proportion of survival and relative root collar diameter growth were highest in the center (64.1%) and edge (60.0%) sites of large gaps, and that the survival of planted seedlings (43.7%) was considerably higher than that of seedlings derived from directly sown seeds (9.9%). Collectively, our findings indicate that, owing to seed predation and seedling excision by rodents, direct seeding with either mesh or soil cover would not represent an effective strategy for promoting Korean pine recruitment in secondary forests. Accordingly, for the purposes of restoring secondary forests to MBKPFs, we recommend planting 3-year-old Korean pine seedlings in large gaps within secondary forests.

Effects of different site preparation methods on the root development of planted Quercus petraea and Pinus nigra

Mechanical site preparation (MSP) is often performed prior to planting to improve the growth and survival of planted seedlings. In this study, we compared root development of 5-years-old Quercus petraea and Pinus nigra seedlings planted in plots that had been prepared with different methods, i.e. deep scarification, deep scarification combined with mounding-subsoiling, herbicide and a control without preparation. Seventy-two trees were excavated (36 per species) and their root system was measured by recording points in a three-dimensional space along their roots. The variation of the number of roots with depth and distance to root collar was assessed and analysed, as well as the root projection area. Our results showed that root development was better in the plots with mechanical preparation, for both Q. petraea and P. nigra, when compared to the control. Combining mounding to subsoiling made the roots extending deeper, especially for Q. petraea. A strong relationship was found between root projection area and root collar diameter, indicating the primary effect of lateral root spread on tree growth. The herbicide treatment induced the highest root growth, which raised questions about the potential negative effects of changes in soil properties caused by MSP methods.

Effects of spot mounding and inverting on growth of conifers, exposed mineral soil and natural birch regeneration

In Nordic forests, consistent evidence about better seedling survival rate and increased growth due to site preparation have been obtained in numerous studies. Proper site preparation method can reduce costs of the whole regeneration chain through its effects on survival of planted seedlings, abundance of natural regeneration and competition in early stand development. This study compared the natural regeneration of birches (silver birch ( Roth) and downy birch ( Ehrh.)), amount of exposed mineral soil, and growth of planted seedlings between spot mounding and inverting site preparation methods. Present study was conducted in eight forest stands established in 2012 or 2015. Even though difference was not statistically significant, inverting exposed less mineral soil than spot mounding and thus reduced the natural regeneration of birch seedlings by 6135 seedlings ha compared to spot mounding. However, the variation between regeneration areas was remarkable. There was no difference in seedling mortality or growth between the site preparation methods. In order to achieve high growth of conifers, moderate amount of exposed mineral soil and thus less naturally regenerated birch, inverting should be favored over spot mounding.Betula pendulaB. pubescens–1

Incidence and impact of Sahyadrassus malabaricus (Moore) on planted seedlings of Dipterocarpus bourdillonii Brandis

During post evaluation on the restoration of Diptercarpus bourdillonii, a critically endangered tree of the Southern Western Ghats, Kerala; incidence of Sahyadrassus malabaricus (Moore) (Lepidoptera: Hepialidae) was found out first time as host plant for the insect-pest. The pest had severe impact on survival of planted seedlings and estimated 60-70% loss after 2-3 years of planting. The pest incidence recorded thus becomes the major factor affecting the restoration success of the species in situ compared least occurrence ex situ extent plantation potential of the species.

Stand Volume Production in the Subsequent Stand during Three Decades Remains Unaffected by Slash and Stump Harvest in Nordic Forests

The renewable energy policies of the European Union rely on forest biomass in achieving climate mitigation targets. In Sweden, where secondary residues from the forest industries are fully utilized, primary residues following harvest such as stumps and slash offer a potential as an additional biomass source. Stump and slash harvest may, however, have adverse effects on site productivity due to increased nutrient loss from the site which could negatively impact the stand volume production of the subsequent stand. Stand volume production is also affected by seedling survival, seedling input from natural regeneration and management of the regenerated stand. In this study, we evaluate the effects of stump and slash harvest on stand volume production of the subsequent stand based on data from eight experimental sites across Sweden planted with Scots pine (Pinus sylvestris L.) or Norway spruce (Picea abies (L.) Karst.) over period of 31–34 years after clearcut with (1) traditional stem-only harvest; (2) stem and stump harvest; (3) stem and slash harvest; and (4) stem, stump and slash harvest. With the goal to explain treatment differences in stand volume production, treatment effects on site productivity estimated through initial height growth (10–19 years after planting), seedling survival, and input of seedlings through natural regeneration were also analyzed. We found that stand volume production was higher following stump harvest as compared to slash harvest, but stand volume production for the more intense harvest treatments (2)–(4) did not differ from stem-only harvest (1). Initial height growth (i.e., site productivity) did not differ between treatments, but followed the trend in stand volume production with (2) > (4) > (3) > (1). Survival of planted seedlings was not affected by the treatments, whereas natural regeneration after 5 years was significantly increased after both treatments including slash harvest (3) and (4) in comparison to stem-only harvest. However, since most of that natural regeneration was removed in subsequent pre-commercial thinnings, this initial increase did not affect stand volume production. The absence of a significant interaction between treatment and species planted for all independent variables tested suggests that there were no species related response differences. Since the experimental design did not allow for site-level analyses, we cannot exclude the possibility that site-specific harvest treatment effects might have masked general effects across all sites. Thus, slash and stump harvest effects at the site level need to be further studied. These results suggest, at least over a 3-decade perspective, that logging residues like stumps and slash can provide an additional renewable energy source to help achieving climate change mitigation goals in the Nordic countries without depleting the future forest biomass resource.

Structural and functional responses of xylem in <em>Rhizophora mucronata</em> Lam. seedlings under drought and hypersaline conditions

Water translocation in mangrove seedlings is often affected by water stress conditions such as drought, hyper-salinities and their frequent variations. This study was therefore aimed at studying the wood anatomical responses of xylem tissue and hydraulic conductivity of Rhizophora mucronata Lam., a common species in mangrove planting, under different levels of drought [25%, ~50% and ~100% of water holding capacity (WHC)] and soil salinity [high salinity (35 psu), moderate salinity (15 psu) and freshwater (0 psu)]. As wood anatomical responses, significantly higher vessel density, vessel grouping (P<0.001) along with narrow vessel elements (P<0.001) were observed in plants grown in the 25% and 50% WHCs and high salinity treatments. All these anatomical responses are more directed towards avoidance of vessel cavitation which is commonly found under water deficit conditions. The results showed that R. mucronata plants failed to maintain efficient transportation of water when the field capacity was 50% of WHC or lower and the level of salinity was 35 psu or greater, as evident by the reduction of water conductive areas, vessel areas and hydraulic conductivity (P<0.05). Overall, water use efficiency of R. mucronata seedlings under the imposed water stress conditions has remarkably reduced and it further indicated that such imposed stress conditions directly affect the survival of planted seedlings as depicted by the significantly low survival in 25% and 50% of WHCs and high salinity. Therefore, in-depth study on lagoon hydrology including inundation levels, water depth, salinity and the selection of correct tidal positioning is highly recommended as prerequisites in mangrove planting. Keywords. Hydraulic architecture, hydraulic conductivity, mangroves, restoration, water stress.

Assessing the Role of Quality Thresholds on Early Performance of Tree Seedlings Planted on Degraded Highlands

The present study highlights the effect of seedling quality on the resultant early performance of our planted tree seedlings. Four priority species tree seedlings: Cordia africana, Casuarina equisetifolia, Cupressus lusitania and Grevillia robusta were raised in the nursery using recommended substrate mixes of ratio (3% top soil: 2% manure: 1% sand). Seedlings were then sorted in to sturdiness quotient classes: quotient class one (I) comprising height to collar diameter ratio less than 6 and quotient class two (II) height to collar diameter ratio greater than 6 to compare early growth and survival among species and evaluate the significance of correlations between quotient categories and tree growth parameters on the degraded highlands of Yerer, Ethiopia. Two factor RCBD with three replications was used as an experimental design to handle eight factor combinations that resulted from four species types and two quotient classes. ANOVA indicated significant difference among tree species tested in the study area in terms of survival and early growth performances at P=0.05. Casuarina equisetifolia though its height and diameter performance in varying quotient categories was not statistically different it was found a priority species to establish plantation in the study area. The correlations between quotient categories and growth parameters were found statistically non-significant at P=0.05. Cupressus lusitanica and Grevellia robusta followed in the priority list to best adapt the site though the observed differences were not attributed to the anticipated variation in sturdiness quotient. Thus, the study results revealed that sturdiness quotient plays lower predictive role in early growth performances and survival of planted seedlings and it was found out to be a less rigorous quality parameter.

Afforestation of cutaway peatlands: effect of wood ash on biomass formation and carbon balance

Abstract Alternatives to the restoration of cutaway peatlands include afforestation, energy forests, agricultural production, wetland restoration (restoration of peataccumulating function), reed canary grass (energy mower) or wild berries (blueberry, cranberry) cultivation, protected area for birds, and artificial lakes. Investigations made in several countries suggest that one of the most promising ways of regenerating cutaway peatlands is afforestation. The re-vegetation of Estonian cutaway peat production fields is mainly the result of natural processes, which are generally very slow: vegetation covers only 10–20% of a peat field. Carbon dioxide is not bound anymore in cutaway peatlands where vegetation layer has been destroyed and therefore photosynthetical processes no more occur. Using biofuel ashes (wood ash, etc.) for the afforestation of cutaway peatlands helps to balance the content of nutrients in peat substrate, which improves the survival of planted seedlings and significantly increases bioproduction. Drained and mined peatlands have become a significant source of CO2 but stimulated woody biomass production can be helpful to balance CO2 emission from cutaway peatlands. Because of the limited resources of fossil fuels and negative impacts on the environment in recent decades alternative sources of energy have been actively looked for. In Scandinavia a lot of attention has been paid to finding possibilities for using biofuels. The situation in Estonia is that only very few types of ashes (for example certified oil shale fly ash with product name Enefix) have been founded to be suitable for utilization and have been used for recycling in agriculture.

The effect of oil shale ash and mixtures of wood ash and oil shale ash on the above- and belowground biomass formation of Silver birch and Scots pine seedlings on a cutaway peatland

Use of biofuel ashes for the afforestation of cutaway peatlands helps to balance the content of nutrients in peat substrate, which improves the survival of planted seedlings and increases significantly bio-production. The purpose of this study was to investigate the effect of fertilization with alkaline ashes on the above- and belowground biomass formation of four-year-old Silver birch (Betula pendula Roth) and five-year-old Scots pine (Pinus sylvestris L.) stands on a cutaway peatland. Five treatments were established: three mixtures with different proportions of wood ash (10–15tha−1) and oil shale ash (10–15tha−1), pure oil shale ash (10tha−1) and control (unfertilized plot). Three years after fertilization with ashes the content of phosphorus was up to 150 times and that of potassium 23 times higher in the peat substrate treated with ashes than on the control plot. The growth and biomass formation varied among treatments and depends strongly on the content of P and K in the growth substrate. The best results were observed on plots of Silver birch treated with mixed ashes; there the seedlings annual height increment was 2–3 times (first year), 5–7 times (second year) and 8–9 times (third year) greater than on the control plot. The effect of mixed ashes on the annual height increment of Scots pine was weaker: the annual height increment was 1.4 times (first year), 3 times (second year) and 5 times (third year) greater than on the control plot. The effect of pure oil shale ash on the growth and biomass formation of trees was the smallest. The greatest root collar diameter increment of birch and pine was observed on the third vegetation period. Roots formed the largest part of the total Silver birch biomass, followed by stem, branches and leaves. At the end of the third year after treatment the largest part of the biomass of Scots pine was allocated to the needles, followed by roots, stem and branches. The biomass and biomass production were the greatest on the plots treated with mixed ashes, especially on the WA15+OSA10 and WA15+OSA10 treatments. The total bio-productivity of birch was until 4 times intense than in the case of pine. The average current annual biomass production of Silver birch and Scots pine stands were respectively 0.17–0.21t ha−1 and 0.3–0.56t ha−1 (mixed ashes), 0.04t ha−1 and 0.16t ha−1 (OSA10) and 0.02t ha−1 (control).

Enrichment planting to improve habitat quality and conservation value of tropical rainforest fragments

Many areas of tropical rainforest have been fragmented and the habitat quality of fragments is often poor. For example, on Borneo, many forest fragments are highly degraded by repeated logging of Dipterocarpaceae trees prior to fragmentation, and we examined the viability of enrichment planting as a potential management tool to enhance the conservation value of these forest fragments. We planted seedlings of three dipterocarp species with contrasting light demands and tolerances (Parashorea malaanonan (light demander), Dryobalanops lanceolata (intermediate), Hopea nervosa (shade tolerant)) in eight forest fragment sites (3–3529 ha), and compared seedling performance with four sites in continuous forest. Eighteen months after planting, survival rates of seedlings were equally high in fragment sites (mean survival = 63 %), and in continuous forest sites (mean survival = 68 %). By contrast, seedling growth and herbivory rates were considerably higher in fragments (by 60 % for growth and 45 % for herbivory) associated with higher light environments in degraded forest fragments compared with continuous forest sites. Among the three study species, H. nervosa seedlings had the highest survival rates overall, and P. malaanonan seedlings generally grew fastest and suffered highest herbivory rates. There were no interactions between species performance and the effects of fragment site area, forest structure or soil characteristics of sites suggesting that the three species responded similarly to fragmentation effects. High survival of planted seedlings implies that enrichment planting would be a successful forest management strategy to improve forest quality, and hence conservation value, of fragments.

Re‐vegetation with native species does not control the invasive Ruellia simplex in a floodplain forest in Florida, USA

AbstractQuestionPlanting or seeding native species after control of invasive species can limit re‐invasion and hasten establishment of native species. Ruellia simplex (Mexican petunia) invades floodplain forests in Florida, and is controlled with glyphosate herbicide. Will herbicide application used to control this weed allow establishment of native vegetation and limit R. simplex?LocationFloodplain forest altered by stormwater run‐off, Lake Jesup Conservation Area, Sanford, FL, US.MethodsWe evaluated re‐vegetation following herbicide application to control R. simplex. For re‐vegetation, we planted or seeded native species (Andropogon glomeratus, Juncus effusus, Panicum longifolium, Solidago fistulosa) and measured stem density, percentage cover, above‐ground biomass and species richness for 1 yr. We compared the results to those from control plots (i.e. no herbicide, no re‐vegetation) and plots where R. simplex was sprayed with herbicide but not planted or seeded with native species.ResultsUnassisted re‐colonization (i.e. plots where R. simplex was sprayed but not planted or seeded with native species) did not result in native plant restoration. Re‐vegetation treatments (i.e. plots where R. simplex was sprayed and planted or seeded with native species) did not restore native vegetation; nor did re‐vegetation treatments reduce R. simplex stem density, percentage cover or biomass compared to control plots. However, total species richness, including native and exotic species richness, increased in plots planted with a native plug mix compared to control plots (i.e. no herbicide, no re‐vegetation). Native species failed to germinate in all seeding treatments. Plugs had adequate survival (2–57% depending on species) but did not prevent re‐invasion of R. simplex. Re‐invasion of R. simplex occurred in plots despite application of glyphosate herbicide and re‐vegetation treatments.ConclusionsRe‐vegetation by seeding or planting did not establish native vegetation in the first year, instead, R. simplex reinvaded. Abiotic and biotic site conditions, e.g. invasive species propagule pressure and altered soil nutrients, may have limited seed germination and survival of planted seedlings. More research is necessary to determine if a reduction in invasive species propagules through repeated herbicide application coupled with planting native species results in native plant restoration in the longer term.

Post-fire ponderosa pine regeneration with and without planting in Arizona and New Mexico

Forest fires are increasing in size and severity globally, yet the roles of natural and artificial regeneration in promoting forest recovery are poorly understood. Post-fire regeneration of ponderosa pine (Pinus ponderosa, Lawson and C. Lawson) in the southwestern U.S. is slow, episodic, and difficult to predict. Planting of ponderosa pine after wildfire may accelerate reforestation, but little is known about survival of plantings and the amount of post-fire natural regeneration. We compared ponderosa pine regeneration between paired planted and unplanted plots at eight sites in Arizona and New Mexico that recently (2002–2005) burned severely. Two sites had no natural regeneration and no survival of planted seedlings. Seedling presence increased with number of years since burning across all plots, was positively associated with forb and litter cover on planted plots, and was positively associated with litter cover on unplanted plots. Survival of planted seedlings, measured five to eight years after planting, averaged 25% (SE=8) and varied from 0% to 70% across sites resulting in seedling densities of 0–521 trees ha−1. Based on a projected 44% survival of seedlings to mature trees and target density of mature trees determined by historical range of variability and ecological restoration principles, four of eight sites have a seedling density in planted plots (125–240ha−1) that will produce a density of mature trees (55–106ha−1) close to desired levels, whereas seedlings are currently deficient at three planted sites, and in surplus at one site, which had abundant natural regeneration. Natural regeneration in unplanted plots during the first decade after burning produced seedling densities inconsistent with desired numbers of mature trees. Natural regeneration in unplanted plots produced less than 33 seedlings ha−1 at seven of eight sites, but produced 1433 seedlings ha−1 at one high-elevation site that supported a more mesic vegetation community before burning than the other sites. Our results show that current practices for planting ponderosa pine after severe fires in Arizona and New Mexico produce desired numbers of seedlings in approximately half of all projects, whereas natural regeneration rarely does within the first decade after burning.

Unique competitive effects of lianas and trees in a tropical forest understory.

Lianas are an important component of tropical forests, contributing up to 25% of the woody stems and 35% of woody species diversity. Lianas invest less in structural support but more in leaves compared to trees of similar biomass. These physiological and morphological differences suggest that lianas may interact with neighboring plants in ways that are different from similarly sized trees. However, the vast majority of past liana competition studies have failed to identify the unique competitive effects of lianas by controlling for the amount of biomass removed. We assessed liana competition in the forest understory over the course of 3 years by removing liana biomass and an equal amount of tree biomass in 40 plots at 10 sites in a secondary tropical moist forest in central Panama. We found that growth of understory trees and lianas, as well as planted seedlings, was limited due to competitive effects from both lianas and trees, though the competitive impacts varied by species, season, and size of neighbors. The removal of trees resulted in greater survival of planted seedlings compared to the removal of lianas, apparently related to a greater release from competition for light. In contrast, lianas had a species-specific negative effect on drought-tolerant Dipteryx oleifera seedlings during the dry season, potentially due to competition for water. We conclude that, at local scales, lianas and trees have unique and differential effects on understory dynamics, with lianas potentially competing more strongly during the dry season, and trees competing more strongly for light.

Twelve-year responses of planted and naturally regenerating conifers to variable-retention harvest in the Pacific Northwest, USA

We studied patterns of conifer regeneration over 12 years as part of a regional-scale experiment in variable-retention harvest in the Pacific Northwest, the DEMO Study. We compared survival and height growth of planted conifers and density and seral composition of natural regeneration among treatments with differing retention levels (15% versus 40%) and patterns (dispersed versus aggregated) replicated across a range of latitudes and forest zones. We also assessed plot-scale relationships of natural regeneration with overstory density and basal area, competing vegetation, and slash accumulations. Early (1- to 2-year) survival of planted seedlings was greater in dispersed treatments (Pinus monticola Douglas ex D. Don, Abies spp.) or unaffected by retention level or pattern (Pseudotsuga menziesii (Mirb.) Franco). Later (5- to 12-year) survival did not differ (all species), but growth was distinctly reduced in dispersed treatments and (or) at higher levels of retention. Density of natural regeneration was 1.5–2.5 times greater in dispersed treatments than in the cleared areas of aggregated treatments. Low-level dispersed retention promoted Pseudotsuga, the early-seral dominant, presumably by enhancing seed rain within a relatively high-light environment. Dispersed retention favored late-seral conifers. The ability to manipulate retention pattern and level to influence regeneration density and composition provides managers with flexibility in developing structurally complex and compositionally diverse forests.

Mortality of girdled trees and survival of seedlings in canopy gaps after logging in a terra firme forest in Brazilian Amazon

Post harvest silvicultural practices in managed forests are seldom applied in the Amazon region. To tackle this problem an experiment was established in 700 ha of terra firme dense forest of the Brazilian Amazon aiming to test the main silvicultural treatments applied elsewhere in the tropics in order to select the most promising ones and recommend their application as part of forest management practices in the region. The experimental area is located in the Rio Capim Forest Management Unit, municipality of Paragominas (2o25’-4o09’S, 46o25’-48o54’W), State of Para, Brazil, where some post-harvest silviculture activities are performed such as tree girdling, planting in gaps and assistance of natural regeneration in gaps, which were discussed in the present paper. Large sized trees had higher mortality rates corroborating with some studies carried out in Amazonia and elsewhere. In general survival of planted seedlings was considerable high (over 75%). Prospects of success of this approach as post harvest silviculture are very promising. Survival of seedlings from natural regeneration of commercial species, mainly light-demanding, was high in the gaps created by logging, suggesting that natural regeneration can establish stands of commercial value.

Allelopathic potential of the neotropical dry-forest tree Acacia pennatula Benth.: inhibition of seedling establishment exceeds facilitation under tree canopies

Secondary succession after land abandonment in tropical dry forests has been suggested to be favoured by the facilitation effects for seedling establishment exerted by pioneer trees isolated in these savannah-like landscapes. However, it has also been noticed that these pioneer species may sometimes have an encroaching effect and arrest succession for several decades. We investigated in this study whether allelopathy can play a role in limiting seedling establishment of co-occurring tree species under the canopy of Acacia pennatula by means of lab bioassays and field experiments in north-west Nicaragua. Leaf extracts of A. pennatula did not affect seed germination but reduced the general growth and especially the development of the root compartment in seedlings, shifting their biomass allocation model to a reduced root/shoot ratio. Survival of planted seedlings under the canopy of A. pennatula was about 20–30% lower than outside, and this reduction was particularly pronounced as the dry season progressed, despite the milder conditions (e.g. higher soil moisture) being experienced in the inner positions under the canopy. Altogether, our results suggest that, rather than facilitating, A. pennatula may inhibit the establishment of seedlings under its canopy probably by means of an allelopathic interference in the development of the root system with critical negative consequences for young seedlings in terms of overcoming the dry season. This article warns about overemphasizing the nucleation effect that remnant and isolated trees may have to facilitate secondary succession in these highly disturbed savannah-like tropical dry forests.