Aboveground carbon biomass of plantation-grown American chestnut (Castanea dentata) in absence of blight

Forest management activities may help reduce global net CO₂ concentrations by capturing and storing atmospheric CO₂. Research related to carbon sequestration potential of plantations in North America has focused predominantly on conifers, with relatively little emphasis thus far on temperate deciduous forest tree species. American chestnut (Castanea dentata (Marsh.) Borkh.), a former dominant tree species in eastern North America until its demise associated with the introduced chestnut blight (Cryphonectria parasitica (Murr.) Barr.), is a temperate deciduous species that holds promise for future carbon sequestration programs with expected availability of blight-resistant backcross hybrids. We quantified aboveground biomass and bole carbon of American chestnut interplanted with black walnut (Juglans nirga L.) and northern red oak (Quercus rubra L.) across four blight-free experimental sites varying in site quality and/or age (8, 8, 12, and 19 years) isolated from the native American chestnut range in the Coulee Region of southwestern Wisconsin, USA. American chestnut exhibited more rapid growth and greater aboveground biomass and bole carbon than either of the other interplanted species. Aboveground biomass ranged from 46.9, 60.7, 55.0, and 179.9 Mg ha⁻¹ for the 8-, 8-, 12-, and 19-year-old sites, respectively, while bole carbon content ranged from 13.6, 18.6, 14.1, and 60.1 Mg ha⁻¹ for the 8-, 8-, 12-, and 19-year-old sites, respectively. Cross-referencing our data to studies conducted within this same physiographic region using other important forestry species (i.e., Populus tremuloides Michx., Pinus resinosa Ait., and Pinus strobus L.) showed that American chestnut compared favorably in growth and carbon uptake. Incorporating American chestnut into carbon sequestration plantations provides additional ecological and economic benefits associated with consistent production of quality nuts for wildlife, valuable timber, and contribution toward species restoration. Our data lend support to building evidence demonstrating rapid and sustained growth of American chestnut and the potential role of plantation-grown American chestnut in helping to mitigate climate change through carbon sequestration.     

Enrichment of big-leaf mahogany (Swietenia macrophylla King) in logging gaps in Bolivia: The effects of planting method and silvicultural treatments on long-term seedling survival and growth

To insure adequate regeneration and future timber yields of mahogany (Swietenia macrophylla King), many logged forests will have to be restocked through enrichment planting and managed using silvicultural techniques that maintain this species’ long-term survival and growth. This study compared the effects of planting method and two silvicultural treatments on the survival and growth of mahogany seedlings in logging gaps in Bolivia. We tested the hypotheses that survival and growth will be higher among transplanted seedlings than seedlings established from sown seeds and higher in silvicultural treatments that reduce competing vegetation and increase light. The first silvicultural treatment consisted of gaps logged 6 months prior to planting, gaps logged just prior to planting, and gaps treated with herbicide prior to planting. The second treatment, applied 12 months after planting, consisted of manual vegetation cleaning around mahogany seedlings in half of the gaps. The first hypothesis was supported in terms of initial seedling growth but not survival, which was similar between planting methods during the 12-92 months after planting. Transplanted seedlings grew significantly faster than those established from sown seeds during the first year, but this growth advantage disappeared by the second year. Although transplants were 84 cm taller than seed-sown seedlings by the end of the study, this height gain was probably not worth the cost of growing and transplanting seedlings. The second hypothesis was supported in terms of both survival and growth. A significantly greater proportion of seedlings survived in herbicide (62%) compared to 6-month-old (46%) and recent gaps (18%) and in cleaned (51%) versus control gaps (39%). Seedlings initially grew faster in herbicide and recent gaps than in 6-month-old gaps. These differences among silvicultural treatments were largely explained by canopy cover, which, throughout the study, was at least 14% lower in herbicide gaps and 9% lower in cleaned gaps relative to their respective alternatives. By 64 months growth diminished to near zero and no longer differed among gap treatments, despite lower canopy cover in herbicide gaps. By 92 months, saplings in herbicide gaps were only 145 and 77 cm taller than those in recent and 6-month-old gaps, respectively. To maximize survival and growth of mahogany seedlings in logging gaps while minimizing costs, silvicultural strategies should focus on direct seed sowing and appropriately timed interventions (i.e. manual cleaning) to control competing vegetation.     

Direct seeding of Quercus robur L. for reforestation: The influence of mechanical site preparation and sowing date on early growth of seedlings

Compared with conventional planting, direct seeding of Quercus spp. is a method that can reduce the costs of reforestation considerably. However, interference from natural vegetation and predation on acorns contribute to regeneration failures. Mechanical site preparation has the potential to reduce both these problems. To study the influence of sowing date and of different mechanical site preparation treatments on early seedling growth, an experiment was carried out in storm-felled areas, formerly Norway spruce forests, in southern Sweden from May 2006 to September 2008. Five treatments were applied and acorns were planted in May and July 2006. The treatments were: disc trenching, patch scarification, topsoil removal, mounding and an undisturbed control. A delay of less than two months in seeding resulted in the equivalent of one year's growth reduction with respect to oak seedling's height and biomass. This could be explained by delayed emergence of seedlings, and by the dry conditions during summer seeding. The seedlings only exhibited a weak positive biomass growth response following disc trenching, patch scarification and top soil removal. In the latter case this might be explained by increased soil compaction and extensive removal of the humus layer. Site preparation by mounding resulted in good vegetation control, an increased biomass growth response and deeper seedling roots. In this treatment, we found high relative light levels near seedlings, reduced soil moisture and dry bulk density of the soil and higher soil temperatures. One or more of these environmental factors could have influenced the growth response. Whether this increased early growth rate persists throughout young stand development is, however, uncertain.     

Nutrient store and export rates of Eucalyptus urograndis plantations in eastern Amazonia (Jari)

Nutrient loss due to export of wood and bark of 4.5-year-old Eucalyptus urograndis was studied in the Jari project, eastern Amazonia, Brazil. Results are based on estimates of biomass, above-ground nutrient store, and nutrient stores in the soil. Thirteen stands varying in site conditions and the number of previous rotations (up to three), were studied. Average nutrient losses due to export of wood and bark, as a percentage of the element store in the above-ground tree biomass, were: N, 65%, P, 54%; Ca, 76%; K, 57%; Mg, 61%. A comparison of export losses with the present soil stores of Ca, K and Mg cations shows that export is equal to or surpasses the remaining soil store to a depth of 100 cm. As a result of the last narvest, about 200–250 kg Ca and about 100 kg K ha⁻¹ were removed. In spite of uncertainties about other unknown inputs and outputs, one has to conclude that the next rotation may be endangered by acute deficiency of mineral nutrients, especially of Ca.     

Field performance of <Emphasis Type="Italic">Pinus halepensis</Emphasis> planted in Mediterranean arid conditions: relative influence of seedling morphology and mineral nutrition

In Mediterranean arid regions, relatively small planting stock has traditionally been used in an attempt to reduce drought susceptibility, though few studies have examined influences of initial seedling morphology and nutrition on long-term plantation establishment. We fertilized Pinus halepensis Mill. seedlings in the nursery with controlled release fertilizer (CRF) varying in formulations and rates; 9-13-18 and 17-10-10 (N-P-K) formulations at 3, 5 and 7 g l⁻¹ substrate plus an unfertilized control and we evaluated growth and survival 7 years after planting in arid conditions in Almería province, southeast Spain. Interactions between initial height and fertilizer treatments occurred during the first 3 years; initial size advantages of specific fertilizer treatments (7 g l⁻¹ of 9-13-18 and 17-10-10 at 3 g l⁻¹) persisted after 7 years. The largest and most nutrient-rich seedlings from 9-13-18 at 7 g l⁻¹ (41.0 cm tall, 4.4 mg of P per g of root tissue at time of planting) exhibited the highest survival after 7 years (79%), while survival declined to 42% for non-fertilized plants (12.9 cm tall and 0.6 mg of P per g of root tissue). Initial seedling morphological parameters were most consistently correlated with field performance. Root P concentration was the nutrient variable most closely related to survival. Our data emphasizes importance of longer-term experiments to accurately assess influences of nursery treatments on field responses, particularly in arid areas. We suggest that larger seedlings with greater nutrient reserves than are currently being used should be incorporated into Mediterranean plantations.     

Distribution and nest site selection of red-shouldered hawks (Buteo lineatus) in forests of northeastern Wisconsin (USA)

Red-shouldered hawks (Buteo lineatus) are threatened in Wisconsin and when nest sites are found during the cruising or marking stage of timber harvesting, the harvest is altered to accommodate the hawks. If nest site locations are known before initiation of timber harvest, foresters can employ a proactive approach to manage red-shouldered hawks while maintaining timber production. We searched for red-shouldered hawks nest sites on Marinette County Forest (MCF) which encompasses 94,000 ha in northeastern Wisconsin and is the second largest county forest in the state. We used a comparative modeling approach to evaluate distribution and habitat relationships of red-shouldered hawk nest sites in relation to a suite of environmental variables in MCF. Models were used to develop forest management recommendations for red-shouldered hawks in Wisconsin. During the spring of 2006 and 2007, we broadcasted conspecific calls to survey 1121 calling stations along forest roads and trails. We located 20 and 25 active nesting territories in 2006 and 2007, respectively (11 of which were active in both years). To understand nest site selection, we measured 22 habitat variables within 0.04-ha plots at active nest sites (n = 34) and at stratified random sites (n = 61). Logistic regression with information-theoretic model selection identified a model including greater tree species richness and closeness to forested wetland as the best-approximating model. Variable selection with Discriminant Function Analysis (DFA) indicated that nest selection was best explained by greater number of tree species, closer distance to forested wetlands, greater volume of downed woody debris, fewer small sawlogs, and increased proximity to streams. Univariate comparisons identified four of the five aforementioned variables in the DFA model as significant. Red-shouldered hawks are likely more common in Wisconsin than their state status suggests. Forest management for red-shouldered hawk nest sites should focus on increasing tree species richness, increasing down woody debris volume, and protecting forested wetlands. These recommendations may assist property managers to locate and plan for continued persistence of this species on MCF.     

Germination and seedling growth of Quercus (section Erythrobalanus) across openings in a mixed-deciduous forest of southern New England, USA

In this study three species of the genus Quercus section Erythrobalanus (Quercus coccinea, Quercus rubra, Quercus velutina) were investigated. All occur together as canopy trees in forests of southern New England. Acorns of each Quercus species were planted in plots located in five zones that represent a range of forest gap/canopy conditions that can occur within a southern New England forest. These five zones were demarcated adjacent to and across large openings of two physiographic sites—valley and ridgetop. Experiments were designed to monitor germination and initial growth of seedlings for the first three growing seasons. During the start of the first growing season germination was monitored. At the end of the first growing season measurements of height and number of flushes were taken and destructive samples of seedlings made for dry mass of root, stem and leaves. At the end of the third growing season height was recorded for surviving seedlings. Comparisons were made of germination and growth of seedlings located in the different gap/canopy conditions.

Results demonstrated clear differences in patterns of germination and early growth among species and among gap/canopy conditions of the sites. All species showed an increased lag in germination with reduced amounts of light. Highest growth and flushing rate were in the center conditions of the openings for all species during the first growing season. Quercus rubra had the greatest height growth the first growing season but a lower number of flushes than Q. velutina and Q. coccinea. In comparison with the other species, Q. rubra had the greatest total dry mass in most gap/canopy conditions after the first growing season. However, Q. velutina had the greatest total dry mass in the center of the ridgetop opening. In almost all gap/canopy conditions Q. velutina had greater proportions of dry mass allocated to roots compared with the other species.

After 3 years, greatest height growth in any of the gap/canopy conditions was recorded for all three species in the center of the valley site. Under this condition Q. rubra had significantly greater growth than Q. velutina and Q. coccinea. Quercus rubra also had significantly greater height growth and survival beneath the canopy conditions of the valley site than the other species. On the ridgetop site regeneration failed to establish beneath canopy conditions that provided low amounts of light. Quercus velutina showed greatest height growth after three years in the center and edge conditions of the ridgetop opening compared with the other species. Environmental influences that determine species germination and growth performance are suggested.     

Effects of silvicultural treatments and seasonal patterns on foliar nutrients in young post-fire Pinus halepensis forest stands

Tree growth and health status appear to be related to foliar nutrient contents. Foliar nutrient concentration might be the result of a complex interaction between soil nutrients and effective availability caused by climate, water and other site and treatment effects. This study examines foliar macronutrient (N, P, K, Ca, Mg) and organic C concentrations in Aleppo pine (Pinus halepensis) needles (between 5 and 18 months old), as well as time course variability (nine dates, from July 1999 to November 2001). Variability was assessed depending on quality site (two sites, Yeste and Calasparra; SE Spain) and seven silvicultural treatments including thinning, scrubbing, pruning and particular combinations of them. Foliar macronutrient concentrations for Aleppo pine in South-eastern Spain were slightly lower (N, P, K,) or higher (Mg, Ca) than the considered as adequate ranges for Aleppo pine and Pinus genera. However, our results agree well with other normal ranges reported for Aleppo pine in Spain and for other North American Pinus species such as P. elliottii, P. taeda and P. palustris. Site, treatment and date (season) affected significantly the foliar macronutrient and C concentration, although the most important was the date, likely due to the two growth periods per year that Aleppo pine has in Mediterranean sites. Silvicultural treatments affected foliar nutrient concentration, so that the concentrations of N, P and K were higher when treatments included thinning than those that did not. The contrary was true for Mg and Ca. However, treatments did not affect the time course of the concentration, i.e., seasonality was not broken due to treatments. Moreover, the effect of the treatments was markedly high along the first year after they were applied but the differences were attenuate 2 years later. Site affected the time course of N, K, Mg and C in a different way: while for N, K and C, at the end of study period, they were higher in Calasparra than in Yeste, for Mg the contrary was true. Nutrient ratios had a different behaviour regarding to single nutrient: although date was significant, we did not appreciate seasonality. In addition, some nutrient ratios were not affected by treatments (N/P, N/K, Ca/Mg,) or by site (N/Ca, K/Ca). Average foliar N concentration and Ca/Mg ratio explained significantly the mean diameter and height growth, so that higher is the foliar N concentration and lower is Ca/Mg, higher is the growth.     

Restoring rainforest species by direct seeding: Tree seedling establishment and growth performance on degraded land in the wet tropics of Australia

The establishment and growth performance of directly seeded rainforest tree species on degraded sites was investigated in the wet tropical region of north east Queensland, Australia. Trials were established at three degraded sites previously covered by rainforest, using two different sowing times (the beginning and end of the wet season), and a range of species having different seed sizes and successional status. The results two years after sowing showed that the effects of sowing time on tree seedling establishment were small despite pronounced differences in cumulative rainfall received by the seedlings. Results suggested that at some sites more serious weed competition might be avoided by sowing later in the season. Although some small seeded early successional species could grow quickly, the establishment of these was found to be significantly negatively affected by the growth of weeds, and in most cases, large seeded species showed more consistent establishment. On the other hand the growth rates of larger seeded species were often rather slow, limiting their contribution to early site capture. Results indicate that direct seeding can be a viable establishment method, but the identity of species to be used, the circumstances under which they should be directly sown and the most appropriate timing of sowing will vary with situations. Species characteristics, including seed size, growth rate potential and light requirement will be important to consider in relation to the probable conditions that will develop for seedlings following germination (particularly in relation to plant competition) with or without post-sowing site management, such as removal of weeds.     

Hollows in jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) trees: I. Hollow sizes, tree attributes and ages

One hundred and fifty-four jarrah (Eucalyptus marginata) and 85 marri (Corymbia calophylla) trees were measured and assessed, and the numbers and sizes of hollows in these trees were determined by destructive sampling; 665 hollows were located and measured. The relationship between tree diameter and tree age was determined from counts of annual growth rings on 162 of these trees. Large trees and trees with moderately senescent crowns individually bear the most hollows. Although the number of hollows found in individual trees increased with tree diameter, the distribution of tree diameters in the forest is skewed and the large number of small trees with diameters between 40 and 80 cm contribute approximately 50% of all hollows in the jarrah forest. The distributions of entry size, and of hollow depth, are highly skewed, with small hollows occurring more frequently than large hollows. Although jarrah trees bear more hollows than marri trees and the distribution of entry sizes is similar for both tree species, the hollows in jarrah are significantly smaller than the hollows in marri. Most hollows are cylindrical in shape, vertically oriented and occur in dead wood in the tree crown. Relatively few hollows (14%) occur in the tree bole or at crown break. Counts of hollows made from ground level are inaccurate as estimates of the actual number of hollows in trees.     

Effects of structural complexity enhancement on eastern red-backed salamander (Plethodon cinereus) populations in northern hardwood forests

Managing for stand structural complexity in northern hardwood forests has been proposed as a method for promoting microhabitat characteristics important to eastern red-backed salamanders (Plethodon cinereus). We evaluated the effects of alternate, structure-based silvicultural systems on red-backed salamander populations at two research sites in northwestern Vermont. Treatments included two uneven-aged approaches (single-tree selection and group-selection) and one unconventional approach, termed “structural complexity enhancement” (SCE), that promotes development of late-successional structure, including elevated levels of coarse woody debris (CWD). Treatments were applied to 2 ha units and were replicated two to four times depending on treatment. We surveyed red-backed salamanders with a natural cover search method of transects nested within vegetation plots 1 year after logging. Abundance estimates corrected for detection probability were calculated from survey data with a binomial mixture model. Abundance estimates differed between study areas and were influenced by forest structural characteristics. Model selection was conducted using Akaike Information Criteria, corrected for over-dispersed data and small sample size (QAIC_c). We found no difference in abundance as a response to treatment as a whole, suggesting that all of the uneven-aged silvicultural systems evaluated can maintain salamander populations after harvest. However, abundance was tied to specific structural habitat attributes associated with study plots within treatments. The most parsimonious model of habitat covariates included site, relative density of overstory trees, and density of more-decayed and less-decayed downed CWD. Abundance responded positively to the density of downed, well-decayed CWD and negatively to the density of poorly decayed CWD and to overstory relative density. CWD volume was not a strong predictor of salamander abundance. We conclude that structural complexity enhancement and the two uneven-aged approaches maintained important microhabitat characteristics for red-backed salamander populations in the short term. Over the long-term, given decay processes as a determinant of biological availability, forestry practices such as SCE that enhance CWD availability and recruitment may result in associated population responses.     

The impact of roe deer (Capreolus capreolus), seedbed, light and seed fall on natural beech (Fagus sylvatica) regeneration

The aim of the present study was to quantify the effects of roe deer browsing relative to the effects of soil preparation, shelterwood density (light) and seed fall. Ultimately, the goal was better silvicultural guidelines to support the use of natural beech regeneration in the close-to-nature forestry context. In spring 1995, an experiment on natural regeneration with three experimental stands (0.28–0.6 ha) was installed in a beech (Fagus sylvatica) dominated broadleaved forest inhabited by a dense roe deer (Capreolus capreolus) population (24 deer km⁻²). The autumn of 1995 offered a large beech mast (stand average 307–1168 beechnuts m⁻²).Treatments installed included fencing to exclude deer, soil preparation, shelterwood thinning, and the relevant control treatments. Roe deer and soil preparation had dramatic effects on regeneration from the moment the seedlings sprouted in the spring 1996. The regeneration sprouted only sparsely in the unprepared seedbed producing only 5 seedlings m⁻² (average across fence treatments) after 2 months, which was reduced to 1 sapling m⁻² 8 years later. Deer had no significant effect on the regeneration density of the unprepared seedbed. In contrast, the cultivated seedbeds produced initially (after 2 months) up to 191 seedlings m⁻² protected by fence, whereas the densities in the unfenced treatments peaked by 22 seedlings m⁻². By the end of the study, these densities were reduced to 22 saplings m⁻² in the permanently fenced mineral soil seedbed and to 2 saplings m⁻² in the unfenced mineral soil seedbed. Regeneration height outside the permanent fence was generally only half the height of the regeneration inside. Additionally, we found significantly positive effects of increasing light and seed fall on regeneration density and of light on regeneration growth.We conclude that the roe deer only reduced the regeneration density of the dense regenerations established in the cultivated seedbeds. However, the regeneration density of the unprepared seedbed was not sufficient to support a future high quality stand. We found no treatment that within the timeframe of this study could support successful regeneration establishment outside the permanent fences. Whether this will change in the future with more time given for the regeneration to establish is yet to be revealed.     

Tree-root influence on soil physical conditions, seedling establishment and natural thinning of Acacia seyal var. seyal on clays of Central Sudan

Acacia seyal is an important component of the agrosilvopastoral systems of the Sahelian zone of Africa. The relationships between lateral spreading of the tree roots and the establishment of the understorey vegetation are, however, little understood. The effect of the tree roots on soil bulk density, soil moisture content and understorey vegetation was studied in the Central Clay Plains of the Sudan. Three study sites were included: a forest, a-two-year-old logged-over area and a-one-year-old abandoned farm, and these sites were distributed over three different geographical locations. Roots of trees, tree seedlings and annual herbs were concentrated in the top 70 cm of soil, possibly due to compacted soil and the confinement of rain water in this layer. Soil bulk density at the 60 to90 cm layer was high in forest, low in logged-over and intermediate in farm. Soil moisture content varied in the reverse order. The low soil moisture content and the high soil bulk density reduced seedling survival. Abundant Acacia seyal seeds germinated and grew during the rainy season. During the first dry season, however, 86% of seedlings of forest died, whereas only 11% of logged-over and 14% of farm died; canopy shading did not seem to affect seedling survival. Tree seedlings and agricultural crops are not able to compete with the A. seyal trees for soil resources but appear to benefit from the ameliorated soil texture, structure and fertility following tree felling. This revised version was published online in June 2006 with corrections to the Cover Date.     

Climate and groundwater effects on the establishment, growth and death of Prosopis caldenia trees in the Pampas (Argentina)

Semiarid woodlands dominated by Prosopis caldenia thrive at the dry edge of the Argentinean Pampas. Deforestation and increased precipitation have driven sustained water table level rise in the region that are likely to affect the dynamics of remnant woody vegetation patches. Here we analyze the effect of climate and groundwater level on the establishment, growth and death of P. caldenia located on lowland (current water table <0.5 m deep) and upland (current water table 8 m deep) positions within rolling sandy landscape. Standard dendrochronological techniques were applied on 98 cross sections and cores of P. caldenia trees. Results allowed us to estimated that trees in the lowland established a few years earlier than in the upland (1929 vs. 1936) and died between 1991 and 2002, while trees in higher positions are still alive. As a result of a faster growth in the lowland, maximum mean basal area increment took place earlier (1950s vs. 1990s) and achieved a higher mean value than in the upland (41.63 vs. 37.41 mm²). While mean annual chronologies were not associated across stands, an opposite highly significant association was found for the mean growth trends suggesting long-term effects of water table depths on growth. We found a different association between mean annual growth and climate, with lowland trees showing a negative response to precipitation before and during the growing season, and upland trees displaying a positive response to summer rainfall inputs. Temperature at the end of the growing season had a positive effect in the lowland whereas temperature during the growing season had a positive effect in the upland. These results show how groundwater can induce diverging sensitivity of forest growth and survival to climate variability, enhancing growth at optimum depths (2-8 m in our study) but depressing it or even killing trees when it approaches the surface (<2 m in our study). Groundwater dynamic should be considered in forest management and conservation strategies in semiarid woodlands in Central Argentina.     

Numerical response of birds to an irruption of elm spanworm (Ennomos subsignarius [Hbn.]; Geometridae: Lepidoptera) in old-growth forest of the Appalachian Plateau, USA

Populations of forest birds were studied during two years of an outbreak of the elm spanworm Ennomus subsignarius (Hbn.) in a silviculturally unmanaged, old-growth conifer–northern hardwood forest on the Appalachian Plateau, PA. Canopy defoliation of hardwoods (mostly American beech Fagus grandifolia and red maple Acer rubrum) increased by at least 50% during the local peak of the outbreak (1993); territorial densities of birds were the highest (15% greater) during the regional peak of the outbreak (1994). Compared to a nearby but uninfested forest of similar age and composition, total bird abundance was as much as 22–33% higher at sites with extensive spanworm defoliation. In addition to canopy gleaners, several other foraging guilds exhibited one or more significant numerical responses to outbreak location or intensity, including bark foraging, understory gleaning, ground foraging, and pursuing species. Like other irruptions of forest Lepidoptera, populations of arboreal canopy-gleaning Parulinae (the warblers D. magnolia, D. fusca) were especially prone to fluctuate during this geometrid irruption.     

Effects of submergence in water on seed germination and vigor of the Copaifera lucens （Fabaceae） seedlings

We analyzed the tolerance of Copaifera lucens seeds to sub- mersion in water to assess the use of this species for direct seeding in riparian forest restoration programs. Seeds were submerged in water for 2, 4, 8, 16 and 32 days or not submerged （control = 0 days of submer- gence）. For the control and at the end of each period of submersion, germination and seedling vigor tests were carried out. For germination tests, seeds were sown in plastic pots containing sand and kept in labora- tory conditions. The percentage of seed germination, the germination rate and the average germination time were analyzed. For seedlings, total biomass, leaf area, leaf mass per area and leaf area ratio were analyzed. Submersion time drastically affected the dissolved oxygen content and seed germination. Between 4 and 8 days of submersion there was a de- crease from 83.8% to 15.6% in the germination percentage. No seed germination occurred after 16 days of submersion. Although there was a significant decrease in the percentage of seed germination between 4 and 8 days of submersion, seedling vigor was not affected. Seeds of this species were partially tolerant to submersion in water, suggesting that C. lucens is a promising species for direct seeding in riparian forest restora- tion projects.     

Sand pine (Pinus clausa) seedling distribution and biomechanics in relation to microsite conditions and proximity to potential nurse plants

We investigated the distribution of sand pine (Pinus clausa) seedlings in relation to the locations of hardwoods and palmettos that had resprouted in five recently clear-cut and one burned stand in sand pine scrub vegetation in Ocala National Forest (Florida, USA). We also studied how the shade and mechanical support provided by the taller resprouts affect the allometry and biomechanics of sand pine seedling stems. Although soil surface temperatures were higher and soil moisture contents (0–5 cm) were lower in open than in covered microsites, sand pine seedling densities did not vary in relation to proximity to resprouted hardwoods and palmettos. There was no apparent nurse plant effect on sand pine seedling distributions, but seedlings that grew up under the resprouts had larger whole stem flexibilities, greater height:diameter ratios, and less tapered stems. In response to the mechanical support and shade of neighboring plants, sand pine seedlings grow taller per unit investment in stem tissue, thereby shortening the period during which they presumably suffer from above-ground competition. This biomechanical plasticity increases the rates at which sand pine seedlings can overtop their resprouted competitors.     

Influence of slope position, stand type and rhododendron (Rhododendron ponticum) on litter decomposition rates of Oriental beech (Fagus orientalis Lipsky.) and spruce [Picea orientalis (L.) Link]

Oriental beech (Fagus orientalis Lipsky.) and Oriental spruce [Picea orientalis (L.) Link] are the two most common tree species in northeast Turkey. Their distribution, stand type and understorey species are known to be influenced by topographical landforms. However, little information is available as to how these changes affect litter decomposition rates of these two species. Here, we investigated the effects of slope positions (top 1,800 m, middle 1,500 m and bottom 1,200 m), stand type (pure and mixed stands) and purple-flowered rhododendron (Rhododendron ponticum) on litter decomposition rates of Oriental beech and spruce for 4 years using the litterbag technique in the field. Among these three factors, stand type had the strongest influence on litter decomposition (P < 0.001, F = 58.8), followed by rhododendron (P < 0.001, F = 46.8) and slope position (P < 0.05, F = 11.6). Litter decomposition was highest under mixed beech/spruce forest, followed by pure beech and spruce forest. Beech and spruce litter decomposed much faster in mixed bags (beech–spruce) than they did separately under each stand type. Purple-flowered rhododendron significantly reduced litter decomposition of Oriental beech and spruce. Beech and spruce litter decomposed much slower at top slope position than at either bottom or middle position. Differential litter decomposition of Oriental beech and spruce was mainly due to adverse conditions in spruce forest and the presence of rhododendron on the ground which was associated with lower soil pH. Higher elevations (top slope position) slowed down litter decomposition by changing environmental conditions, most probably by decreasing temperature as also other factors are different (pH, precipitation) and no detailed investigations were made to differentiate these factors. The adverse conditions for litter decomposition in spruce forest can be effectively counteracted by admixture of beech to spruce monoculture and by using the clear-cutting method for controlling rhododendron.     

Long-term effects of establishment practices on plant communities across successive rotations in a loblolly pine (Pinus taeda) plantation

Implementation of repeated, high-intensity short rotations in forest plantations raises concerns about the effects of such practices on herbaceous layer biodiversity and overall sustainability. To investigate these concerns, we conducted a comparative study of second and third rotation plant communities in a loblolly pine plantation in the Piedmont of North Carolina. The second rotation stand was established in 1960 using conventional practices and was harvested in 1981, leaving two plots in each of three blocks as “historical” plots representing the second rotation. The third rotation was planted in 1982, and a 2 × 2 factorial experiment was established within an area that had been complete-tree harvested, using two site preparation (drum-chop versus shear, pile, and disk) and two cultural (vegetation control versus no vegetation control) treatments in each of three blocks. Presence/absence data for vascular plant taxa were collected in the second rotation historical plots at year 22 and also in the third rotation treatment plots at year 18 and analyzed using non-metric multidimensional scaling (NMDS) ordination, indicator species analysis, analysis of species richness, and computation of species turnover. Results indicated overall similarities in the herbaceous layer from year 22 in the second rotation to year 18 in the third rotation, while revealing some key differences in species composition, including persistence of disturbance-responsive species associated with the vegetation control treatment in the third rotation plots. The addition of these species largely accounted for an increase in species richness from the second to the third rotation. Species composition in low intensity third rotation plots (chop, no vegetation control) most closely resembled that of the second rotation plots of similar age. In addition, differences in species composition due to soil and topographic differences within the study persisted through both rotations, while compositional effects of treatments implemented at the beginning of the third rotation diminished with time. We conclude that more intensive silvicultural practices, such as site preparation and vegetation control, reduce initial competition from woody species and thus permit the persistence of early successional species, increasing overall diversity. From the larger perspective of the entire study, the second and third rotation stands converged to similar species composition after approximately two decades post-planting despite early treatment-related differences in the third rotation. It remains to be seen whether additional harvests, rotations, and intensive practices will continue to support a functioning understory plant community in these short rotation plantation forests.     

Site preparation,fertilization, and 10-year yields of hybrid poplar on a clearcut forest site in eastern Maine,USA

Cuttings of two similar hybrid poplar clones were planted on a drum-chopped, chip-harvested clearcut in eastern Maine. The site had never been previously cleared for agriculture. The coarse loamy glacial till soils were acid (pH < 5.0) and moist—moderately well—to somewhat poorly drained. Control, lime (L), L nitrogen (N), L phosphorus (P), LNP, and LNP potassium (K) treatments were established. Competing woody vegetation was mowed once per year for the first three years on half the area. Each mowed treatment produced significantly greater hybrid poplar biomass than the corresponding unmowed treatment. After 10 years, the mowed+LNPK treatment attained the greatest total biomass, 45 Mgha^-1, while the unmowed control attained the least, 2 Mgha^-1. On mowed plots, L produced 4 times the biomass of control: 32 vs 8 Mgha^-1. Unmowed plots with L and N produced about as much hybrid poplar biomass as the mowed control (8 Mgha^-1). Mowing and L each improved survival as well as growth.Deceased