First-year Seedlings Research Articles

Influence des pentes fortes sur la dispersion et la structure génétique des populations de Quercus crispula

The seed dispersal patterns and genetic structure of plant populations in mountainous forests may differ from those on flat sites, because some seeds that fall from adults are likely to roll downhill, and thus cause the seed shadows from different mother trees to merge. In the study reported here we used six polymorphic microsatellite markers to track seed dispersal and examine the fine-scale spatial genetic structure of adults and first-year seedlings of Quercus crispula in 2500 m 2 plots on four slopes. In each of the four plots, leaves of adults, seedlings and endocarps of hypogeal cotyledons attached to the seedlings were genotyped to identify the seedlings' mother trees. The results showed that steeper slopes result in larger dispersion sa nd smaller genetic structure of seedlings. These findings are a crucial step towards an understanding of the effect of topography on tree regeneration.

Structural and physiological plasticity in response to light and nutrients in five temperate deciduous woody species of contrasting shade tolerance

Summary 1 Plants encounter a variety of light and nutrient availabilities during succession. However, there is an ongoing debate to which extent light-dependent structural and physiological plasticity is associated with species shade tolerance. 2 Seedlings of five species, Betula pubescens Ehrh., B. pendula Roth, Populus tremula L., Quercus robur L. and Acer platanoides L. (from most intolerant to most shade-tolerant), were grown at four different light and nutrient availabilities to test the hypotheses that intolerant species have higher physiological and tolerant species higher structural plasticity to light and also that there is an overall increase in plasticity with increasing nutrient availability. Two replicate experiments in different years were conducted. Plasticity was characterized by four estimates: (1) the range of variation of the components of relative growth rate (RGR), leaf area ratio (LAR) and net assimilation rate (NAR) (RGR = LAR·NAR) at common RGR; (2) average standardized slopes of physiological (RGR, NAR, i.e. physiological plasticity, ΠP) and structural (LAR, leaf dry mass per unit area, biomass allocation traits, i.e. structural plasticity, ΠS) traits vs. irradiance relationships; (3) standardized difference of plant traits measured at low to medium irradiance; (4) coefficient of variation across different irradiance treatments. 3 Plant growth was more strongly associated with NAR than with structural traits, but shade-intolerant species had a greater range of variation in both NAR and LAR at a common RGR. RGR, NAR and structural characteristics also responded more strongly to increases in irradiance in shade-intolerant species, but at low irradiance RGR and NAR were similar among all species. Owing to higher biomass fraction in leaves, the intolerant species produced less woody biomass. In nonfertilized plants, both ΠP and ΠS were negatively associated with shade tolerance. The plasticity was enhanced by nutrient addition, but the nutrient-dependent enhancement in plasticity was greater in more tolerant species. Therefore, differences in plasticity among species of varying tolerance were lower at higher nutrient availability. 4 Our study does not support the hypothesis of a trade-off between structural and physiological plasticity. Shade-tolerant species are generally less plastic than intolerant species, but increases in nutrient availability during succession reduce the differences in plasticity. Despite similar RGR in low light, first-year seedlings of shade-tolerant species produce more woody biomass, favouring survival and growth in subsequent years.

LIFE HISTORY TRADE-OFFS IN TROPICAL TREES AND LIANAS

It has been hypothesized that tropical trees partition forest light environments through a life history trade-off between juvenile growth and survival; however, the generality of this trade-off across life stages and functional groups has been questioned. We quantified trade-offs between growth and survival for trees and lianas on Barro Colorado Island (BCI), Panama using first-year seedlings of 22 liana and 31 tree species and saplings (10 mm < dbh < 39 mm) of 30 tree species. Lianas showed trade-offs similar to those of trees, with both groups exhibiting broadly overlapping ranges in survival and relative growth rates as seedlings. Life history strategies at the seedling stage were highly correlated with those at the sapling stage among tree species, with all species showing an increase in survival with size. Only one of 30 tree species demonstrated a statistically significant ontogenetic shift, having a relatively lower survival rate at the sapling stage than expected. Our results indicate that similar life history trade-offs apply across two functional groups (lianas and trees), and that life history strategies are largely conserved across seedling and sapling life-stages for most tropical tree species.

Interacting controls by light availability and nutrient supply on biomass allocation and growth of Betula pendula and B. pubescens seedlings

Interactions among environmental drivers commonly occur in natural environments, but their influence on plant performance is not fully understood. We tested for significant interactive effects of light and nutrient availabilities on foliage architecture, chemistry, biomass allocation and growth in shade intolerant temperate deciduous trees Betula pendula Roth. and B. pubescens Ehrh. First-year seedlings were grown at four irradiance and four N and P availability combinations, and the experiment was repeated in two consecutive years. In both species, increases in light availability resulted in larger net assimilation rate (NAR, total plant biomass production rate per unit leaf area), root mass fraction ( F R) and leaf mass per unit area ( M A), but reductions in leaf area ratio (LAR, foliage area per total plant dry mass), stem mass fraction ( F S) and leaf mass fraction ( F L). The strong decrease in LAR (LAR = F L/ M A) with light mainly resulted from increases in M A. The light-dependent increase in NAR was larger than the decline in LAR such that plant relative growth rate (RGR = NAR × LAR) scaled positively with light in both species. Nutrient availability mainly enhanced LAR, and moderately NAR, further improving RGR. The increase in LAR was primarily associated with increases in F L and decreases in F R. Significant interactions between light and nutrients were found for most of the studied variables, overall indicating that plant allocation and growth were more responsive to nutrients at higher light availability. Several significant species and year-to-year differences were observed among the allocation and growth characteristics that were driven by plant size, climate and seedling source. Greater RGR of B. pubescens that is a species colonizing habitats with lower nutrient availability was linked to its greater foliage nitrogen concentrations. Overall, the study highlights a significant light × nutrient interaction that can modify seedling performance along natural gap-understory gradients.

Simulated recruitment of riparian trees and shrubs under natural and regulated flow regimes on the Wisconsin River, USA

Models that link ecological responses to hydrologic changes are important for assessing the effects of flow regulation on aquatic and riparian ecosystems. Based on the Recruitment Box Model, a graphical model used to prescribe environmental flows for cottonwood (Populus spp.) recruitment, we designed a simulation model to represent the influence of river flow dynamics on seedling recruitment of riparian pioneer woody plants. The model simulates the influence of temporal patterns of river stage on dispersal, germination, initial recruitment and over-winter survival of first-year seedlings of riparian pioneer shrubs and trees. We used the model to simulate seedling recruitment patterns for five species (Acer saccharinum, Betula nigra, Populus deltoides, Salix nigra and Salix exigua) on the Wisconsin River (Wisconsin, USA) under three flow scenarios: historic (1935–2002), simulated natural (1915–1975) and simulated regulated flows (1915–1975). Simulation results agreed well with field-observed relative differences among years (1997–2000) in seedling densities for the five focal species. Simulated successful recruitment years were highly synchronous among species, but species differed in their sensitivity to flows at different times during the growing season, consistent with among-species differences in seed dispersal timing. Comparison of simulated natural and regulated flows for 1915–1975 showed that flow regulation decreased monthly flow variability, increased late summer to winter baseflow and reduced the magnitude of spring peaks. Simulated recruitment and over-winter survival of tree seedlings of all species was enhanced under the regulated flow scenario, likely due to increased summer baseflow and reductions in peak flood magnitude. Our analyses show the utility of extending the Recruitment Box Model to include multiple species of riparian shrubs and trees, and the effects of post-colonization flows on their recruitment success. However, some key functional relationships between flow patterns and woody seedling demography (e.g. shear stress thresholds for seedling mortality) have not been adequately quantified and merit further study. Copyright © 2006 John Wiley & Sons, Ltd.

Spatial concordance between seed rain and seedling establishment in bird‐dispersed trees: does scale matter?

Summary 1 We explored whether seedling recruitment was spatially predicted by seed rain (spatial concordance) at different scales (microsite, microhabitat and site) in the bird-dispersed trees Crataegus monogyna, Ilex aquifolium and Taxus baccata, in temperate secondary forests in north-west Spain. 2 We propose that both spatial concordance within each scale and consistency of concordance patterns across scales are dependent on differences between seed rain and post-dispersal processes in the partitioning of spatial variance at each scale. 3 We measured the density of dispersed seeds, the percentage of post-dispersal seed predation by rodents and the density of emerged first-year seedlings at sampling stations distributed throughout five microhabitats (under canopies of parental trees and in open gaps) and four localities over two seasons. 4 Seed rain density of all tree species varied most at the microhabitat scale, but microsite and site differences accounted for most of the spatial variance in post-dispersal seed predation and, especially, in seedling establishment. 5 All three species showed concordance between seed rain and seedling establishment at the microhabitat scale, because strong patchiness in avian-generated seed rain overrode the slight uncoupling effects exerted by the more homogeneous post-dispersal processes. Seed rain was also a good predictor of recruitment of Ilex and Crataegus at the microsite scale, but, for Taxus, the rather homogeneous dispersal across microsites contrasted with the heterogeneous post-dispersal losses. At the site scale, only Taxus showed a positive trend of concordance. 6 Concordance patterns were maintained from microsite to microhabitat in Crataegus and Ilex, and from microhabitat to site in Taxus. Low-variance allocation to the site scale at the seed rain stage precluded complete consistency in Crataegus and Ilex. 7 Positive responses of recruitment to seed dispersal depended on both species and scale, resulting in a complex template for dispersal-limitation effects on metapopulations and communities.

Season and substrate effects on the first-year establishment of current-year seedlings of major conifer species in an old-growth subalpine forest in central Japan

Seasonal and substrate effects on first-year seedling establishment of major conifer species ( Abies mariesii, Abies veitchii, Picea jezoensis var. hondoensis, and Tsuga diversifolia) were assessed in an old-growth subalpine forest in central Japan. Older seedlings (≥1 year) were more abundant on woody debris (WD), such as fallen logs, than on soil. It is known that this preferential seedling establishment on WD is determined by the first-year seedling establishment. The present results indicate that first-summer seedling survivorship clearly contributes to the creation of such seedling–substrate associations, because mortality during the first-summer was greater on soil than WD but that during the first-autumn/winter was not different. Although the standardized mortality rate of current-year seedlings on WD was not so different among the three seasons, that on soil significantly decreased in the winter; indicating that soil is not an unsuitable substrate for seedling survivorship during snow-covered winter. Thus, it can be concluded that biotic and abiotic factors enhancing seedling mortality on soil are most active during summer, and seedling–substrate associations seem to be determined mainly during the first-summer soon after seedling emergence. Furthermore, the first-year survivorship of P. jezoensis var. hondoensis, which has smaller-sized seeds/seedlings that are disadvantageous for early survival, decreased with progressing WD decay toward soil. This suggests that the properties of WD also affect current-year seedling survivorship, especially for species sensitive to substrate properties. In conclusion, initial survivorship affects seedling bank dynamics, and such early dynamics are greatly regulated by the highly heterogeneous substrate availability on forest floors.

Carbon limitation leads to suppression of first year oak seedlings beneath evergreen understory shrubs in Southern Appalachian hardwood forests

Inhibition of canopy tree recruitment beneath thickets of the evergreen shrubs Rhododendron maximum L. and Kalmia latifolia L. has long been observed in Southern Appalachian forests, yet the mechanisms of this process remain unresolved. We present a first-year account of suppression of oak seedlings in relation to Rhododendron and Kalmia basal area, light and resource availability, seedling performance and the rates of seedling damage i.e., herbivory. We found no evidence of first-year seedling suppression or significant resource deficiencies beneath thickets of K. latifolia in mature mixed hardwood stands. Suppression beneath R. maximum was apparent during the first growing season. We found that seedling biomass, light availability prior to canopy closure, and seedling tissue C:N ratios were negatively correlated with R. maximum basal area. Basal area of R. maximum was positively correlated with seedling mortality rates, soil Al, and early-growing season leaf herbivory rates. Seedling growth was positively correlated with light and tissue C:N, while negatively correlated with soil Al. Overall, our results support the inhibition model of shade-mediated carbon limitation beneath dense understory shrubs and indicate the potential importance of herbivory and aluminum toxicity as components of a suppression mechanism beneath R. maximum thickets. We present a causal model of first year inhibition beneath R. maximum in the context of our findings and the results of prior studies.

Seedling Evaluation of Atlantic Coastal and Piedmont Sources of Loblolly Pine and Their Hybrids for Height Growth

Abstract Seedlings of 60 loblolly pine (Pinus taeda L.) polycross families representing four populations, Atlantic Coastal (CxC), Piedmont (PxP), Coastal × Piedmont (CxP), and Piedmont × Coastal (PxC) were evaluated for first-year seedling height growth in an outdoor site in Raleigh, North Carolina. The CxP hybrids grew as well as the pure Coastal loblolly source, and the PxC hybrids were not significantly taller than the pure Piedmont population. The hybrid populations were intermediate between the parental populations and did not exhibit heterosis for height. However, the hybrids were 4–10% taller than the PxP population, which is the population currently used for forestation in the Piedmont region. There was an advantage for early seedling height growth in having the female parent from the Coastal plain, which appeared to be related to length of the growing season as measured by bud set time. There were strong family differences for seedling height within populations, indicating the potential for selecting the best families within the best populations. The implication is that the hybrid populations of CxP and PxC with improved growth may be better planting stock for the Piedmont than the pure Piedmont populations on some sites. Before implementing such a plan, cold-hardiness and long-term growth and adaptability should be evaluated. South. J. Appl. For. 28(2):83–90.

Effects of dispersal, shrubs, and density-dependent mortality on seed and seedling distributions in temperate forests

Processes limiting recruitment of trees may have large impacts on forest dynamics. In this paper, we determined the effects of dispersal, shrubs (Rhododendron maximum), and density-dependent mortality on seed and seedling distributions of Southern Appalachian trees. We quantified the spatial distribution of seed rain, seed bank densities, first-year seedlings, and older than first-year seedlings in five vegetation plots. We fit models to these data assuming effects of limited dispersal, R. maximum (an understory shrub), and (or) density-dependent mortality (as well as a null model with none of these effects) and used best-fitting models to indicate which processes affected a particular species. We found that all factors examined limit species distributions, and thus, affect seedling dynamics. Seedling densities are higher near parent trees long after dispersal occurs. This pattern is less frequently observed for animal-dispersed species than for wind-dispersed species, presumably due to secondary dispersal of seeds by animals. Seedling densities of five species are decreased beneath R. maximum. Shade tolerance does not explain which species are affected, suggesting that factors other than low light are responsible for increased seedling mortality under this shrub. Our results suggest that density-dependent mortality affects four species, decreasing seedling densities close to parent trees. Dispersal, density-dependent mortality, and R. maximum all act in ways that may promote or limit diversity, illustrating that multiple factors are likely to control species diversity.

Effects of exogenous gibberellin and auxin on shoot elongation and vegetative bud development in seedlings of Pinus sylvestris and Picea glauca.

The hormonal control of stem unit (foliar appendage and axillary structure, if present, plus subtending internode) number and length was investigated in shoots of Scots pine (Pinus sylvestris L.) and white spruce (Picea glauca (Moench) Voss). Seedlings were treated with six gibberellins (GA1, GA3, GA4, GA5, GA9 and GA20) and two auxins (indole-3-acetic acid (IAA) and naphthaleneacetic acid (NAA)) when either neoformed growth was occurring or the terminal vegetative bud was developing. Hormones were applied by drenching the shoot tip, injecting the stem or spraying the foliage. Combined results for all three application methods indicated that shoot elongation in first-year seedlings (i.e., neoformed growth) was promoted in both species by GA1, GA3, GA4 and, less obviously, by GA9. This promotion was attributable to an increase in length, rather than number, of stem units. However, the number of stem units formed during terminal bud development, as reflected in the number of needles (white spruce) or cataphylls (Scots pine) present on the shoot resulting from the terminal bud, was stimulated by GA1, GA3 and GA4 in both species and by GA9 in Scots pine. The GA-induced increase in the number of preformed stem units was associated with increased bud width in white spruce and increased bud length and resulting shoot length in Scots pine. In contrast, application of IAA or NAA either did not affect or inhibited both neoformed growth and terminal bud stem unit number, depending on the application method and concentration. We conclude that, in the Pinaceae, (1) GA stimulates the activity of both the subapical meristem during neoformed growth and the apical meristem during vegetative bud development, and (2) the early non-hydroxylation pathway, via GA9, is the major route of GA biosynthesis. The role of auxin in the control of stem unit number and length remains to be resolved.

Reproductive capacity of Pinus nigra ssp. salzmannii in relation to mother plant age

This paper analyses the possible reduction of fertility in Pinus nigra ssp. salzmanii as trees age in the managed forests of Cazorla mountain range (Southern Spain). Fertility was assessed by the combined values: frequency of empty seeds and viability of full seeds. Performance of one year seedlings was also evaluated. Plant material came from reproductive trees of up to 120 years old (the rotation period in the study area), and from older trees of over 1000 years old. The older tended to produce larger quantities of empty seeds than the younger ones, and their filled seeds tended to be lighter and slower to germinate. Nevertheless, the difference in these parameters shown by the trees studied was not so great so as to establish that ageing Salzmann pines are unable to regenerate managed forests. The growth of first year seedlings was positively correlated to seed weight and, therefore, negatively correlated to mother plant age. However, these factors could only account for a small amount of the variability in the size of first-year seedlings. Results suggest that reproductive function works normally in the very old (senescing) Salzmann pines, this being important in relation to the maintenance of biodiversity in the managed mountain forests of Southern Europe.

Leaf area accumulation helps juvenile evergreen trees tolerate shade in a temperate rainforest.

Most knowledge of the physiological correlates of interspecific variation in shade tolerance derives from studies of first-year seedlings in artificial environments. The present study relates growth, allocation, foliage turnover, biomass distribution and gas exchange traits to low-light survival of large seedlings (20-100cm tall) of eight temperate rainforest evergreens under field conditions. Taxa for which natural mortality was not observed in low light during the 14-month study are referred to here as "shade-tolerant" species, and those which did die in the shade are referred to as "light-demanding" species. In low light (2-5% canopy openness), shade-tolerant species had slightly lower light compensation points than light-demanders. Light-demanding species had more plastic aboveground allocation patterns, generally allocating proportionally less aboveground biomass to foliage production than shade-tolerant associates in high light (>10% canopy openness), but more in low light. Foliage turnover was generally much slower in shade-tolerant species (10-40% year-1) than in light-demanding species (30-190%). As these differences in leaf retention outweighed variation in allocation, shade-tolerant species displayed higher leaf areas at all light levels. Furthermore, all shade-tolerant species gained leaf area in low light during the study period, whereas light-demanding taxa showed leaf area declines. Higher leaf area ratios, plus differences in light compensation points, indicate that large seedlings of shade-tolerant evergreens enjoy net carbon gain advantages over light-demanding associates in low light. However, minimal growth rate differences in low light imply higher storage allocation in shade-tolerant species. This study provides a rather different picture from that which has emerged from recent reviews of first-year seedling data, illustrating the long-term consequences of foliage turnover differences for biomass distribution, and suggesting that shade tolerance in juvenile evergreen trees is associated with a suite of traits which enhance net carbon gain, but not growth, in low light. Accumulation of a large foliage area through long leaf retention times is probably a key mechanism enhancing low-light carbon gain in evergreens.

The regeneration of Quercus petraea (sessile oak) in southwest Ireland: a 25-year experimental study

The growth and survival of Quercus petraea saplings were monitored over a 25-year period, in an exclosure in a heavily-grazed oakwood on podzol soil in Killarney National Park. Seedlings were subjected to combinations of two levels of shading (under canopy and in an artificial clearing), two levels of competition (weeded and unweeded) and five fertiliser treatments (N, P, NP, Ca and control). Damage by Apodemus sylvaticus (long-tailed fieldmice) was confined to acorns and first-year seedlings, and was not a limiting factor. Invertebrate damage was unimportant. Seedling survival was greatly enhanced within the ungrazed exclosure, even under canopy. In the clearing, following a short-term breach of the fence in the second winter, Cervus nippon (sika deer) browsed 49% of oak seedlings in weeded plots but only 11% in unweeded plots, confirming that surrounding vegetation cover may exercise a protective effect. In later years, seedling survival was significantly higher in the weeded plots, presumably owing to reduced competition. Seedlings under canopy showed no significant response to fertilisation or weeding; the median proportion surviving per plot was zero within 8 years and all had died within 20 years. In the clearing, the median proportion surviving per plot was 0.33 after 8 years and 0.2 after 25 years. In a portion of the clearing with peaty soil and impeded drainage, seedlings showed reduced performance and significantly increased mortality. Microsphaera alphitoides (oak mildew) attacked seedlings mainly in the clearing; its impact appeared negligible. Fertilisation with P significantly enhanced performance in the clearing. No fertiliser treatment enhanced survival. Fertilisation with N alone led to sharply increased mortality in the clearing. I conclude that, in woodlands in western Ireland, successful oak regeneration is to be expected only in unshaded or lightly-shaded sites where grazing levels are low.

Substrate preferences of epiphytic bromeliads: an experimental approach

Based on the known vertical distributions of three epiphyte species we tested the hypothesis that observed interspecific differences are determined at a very early ontogenetic stage. We attached 1296 first-year seedlings of the three species Guzmania monostachya, Tillandsia fasciculata, and Vriesea sanguinolenta (Bromeliaceae) to substrates differing in orientation and relative position within the crown of the host tree, Annona glabra. Surprisingly, we found no evidence for differential mortality on different substrate types for any of the three species. Hence, differences in vertical distribution cannot be explained by interspecific differences in site-specific survival at this stage. This suggests that spatial distribution patterns are determined even earlier, probably resulting from species differences in seed dispersal or during germination.

Survival and growth of seedlings of 12 Chilean rainforest trees in two light environments: Gas exchange and biomass distribution correlates

Abstract Mortality, growth, gas exchange and biomass distribution were measured in the seedlings of 12 Chilean temperate rainforest angiosperm trees in two contrasting artificial light environments (150 and 12 μmoles m−2 s−1), in order to explore life history diversity in this forest type, and examine the physiological and/or morphological traits associated with interspecific variation in seedling performance. Gas exchange traits were measured only in the high‐light treatment (150 μmoles m−2 s−1), owing to the very small size of leaves in the low‐light treatment. Relative growth rates (RGR) in high light were strongly correlated with photosynthetic capacity (P&lt; 0.0001). Mortality rates in low light had a strong positive correlation with light compensation point (P = 0.007) and photosynthetic capacity (P = 0.004). Furthermore, high‐light RGR was strongly positively correlated with low‐light mortality (P = 0.001). Biomass distribution traits showed little relationship with mortality or growth within either light level, except for a marginally significant positive correlation (P = 0.04) between leaf area ratio and mortality in low light. In view of the large interspecific differences in final size, the weak relationships between biomass distribution parameters and plant performance could be partially attributable to ontogenetic drift in these traits. Among taxa with high mortality rates in low light, short‐lived species (e.g. Aristotelia chilensis) had lower light compensation points, had greater phenotypic plasticity and grew much faster in both light environments than did longer‐lived species (Nothofagus dombeyi, Weinmannia trichosperma, Eucryphia cordifolia). Results support the view that survival of first‐year seedlings in low light is not enhanced by morphological traits that maximize growth potential (e.g. high leaf area ratio), and that leaf‐level gas exchange traits have an important role as determinants of interspecific variation in seedling performance. However, the limited range of interspecific variation observed in light compensation points indicates that other traits apart from those that we measured (e.g. carbon storage) must also be involved in seedling shade tolerance differences. The weak relationship between longevity and shade tolerance level among our 12 species suggests that it may not be feasible to ordinate life histories of Chilean temperate rainforest trees on a single axis of trait variation.

Positive and negative interactions between environmental conditions affecting Cercocarpus ledifolius seedling survival

We evaluated the balance between positive and negative effects of environmental conditions on first-year seedling survival of the tree Cercocarpus ledifolius during two summers, 1996 and 1997. The experimental design was fully crossed with two levels of water, with and without supplementation, two levels of herbivory, with and without protection, and three major microhabitats, open interspaces, under the canopy of Artemisia tridentata shrubs, and under the canopy of mature C. ledifolius trees. Effects of drought and herbivory on seedling survival depended on the year. Water supplementation and herbivory protection during the dry summer of 1996 (27.7mm) generally increased seedling survival. Additionally, survival tended to be greatest beneath C. ledifolius canopies. More important ecologically were the significant interactions. In 1996, water supplementation increased survival more with than without herbivory protection. The three-way interaction, treatment-microhabitat combination, was most important; by far the greatest survival was in the water supplementation and herbivory protection in the tree microhabitat. During the wet summer of 1997 (158.5mm), neither water supplementation, herbivory protection, nor microhabitat were significant as main effects. The water-supplemented and herbivory-protected treatment again combined to yield highest survival, but this time in open interspaces rather than beneath trees. Our study shows how the importance of individual limiting factors and the relative favorableness of particular microhabitats appear to change across years depending on environmental conditions.

Fertilization of Container-Grown Baldcypress (Taxodium distichum (L.) Rich.)

Abstract Two fertilization experiments were conducted with first-year seedlings of baldcypress [Taxodium distichum (L.) Rich.] in containers (substrate = composted pine bark). First, seedlings were subjected to factorial combinations of dolomitic lime, soluble fertilizer (SF), and incorporated controlled-release fertilizer (CRF) (19.0N–2.6P–8.8K; 8- to 9-month release). Lime decreased growth. Incorporated CRF [4.8 kg/m3 (8 lbs/yd3)] yielded more growth than a single weekly application of SF (N = 0.5 g/liter). In the second experiment, most of the potential height growth and total plant dry weight were realized with 2.4 kg/m3 (4 lbs/yd3) and 4.8 kg/m3 (8 lbs/yd3), respectively, of incorporated CRF. At optimal growth, foliar N concentrations were 3.0%.

Population differences in stable carbon isotope ratio of Pinus contorta Dougl. ex Loud.: relationship to environment, climate of origin, and growth potential

Stable carbon isotope composition (δ13C) was used to examine genetic and environmental variation in water-use efficiency of 11 Pinus contorta Dougl. ex Loud. populations from western Canada. Sapwood cores from 20-year-old saplings established at three sites in British Columbia, and shoots of greenhouse-grown, first-year seedlings, were analyzed. δ13C values of whole sapwood and isolated cellulose were correlated at r = 0.990 (p &lt;&lt; 0.0001, n = 10). There were genetic differences in δ13C among populations. A population from the wet Pacific coast (P. contorta var. contorta) stood out from the others, which were all from the drier continental interior (P. contorta var. latifolia Engelm). This population had the highest indicated water-use efficiency. δ13C values of most populations increased from the wettest to the driest site with no significant change in ranking. Mean yield (stem volume) of the P. contorta var. latifolia populations was positively correlated with δ13C. Population differences at the seedling stage were not as pronounced, but δ13C values of seedling shoots and sapling wood cores were correlated. Among the 10 P. contorta var. latifolia sapling populations, δ13C decreased with an index of summer dryness and, less so, with increased elevation. It appears, therefore, that the most water-use efficient and most productive populations originate from relatively moderate, low-elevation sites with reduced likelihood of water stress.Key words: water-use efficiency, isotope discrimination, lodgepole pine, phenotypic plasticity, provenance trials.

Survival and growth of Pinus echinata and Quercus seedlings in response to simulated summer and winter prescribed burns

First-year seedlings of shortleaf pine (Pinus echinata Mill.), southern red oak (Quercus falcata Michx.), and white oak (Quercus alba L.) were subjected to simulated prescribed burns during August (growing season) or January (dormant season) on an Upper Coastal Plain site in southeastern Arkansas, U.S.A. Survival and growth of resprouting rootstocks were compared with control seedlings through one growing season after burning. Although 100% of the oaks and 99% of the pines were topkilled by the fires, survival of resprouting rootstocks exceeded 95% for all three species in the year following the winter burn. No pines resprouted following the summer burn, but rootstock survival of oaks averaged &gt;65%. Compared with controls, winter burns reduced (P &lt; 0.01) mean height and groundline diameter (GLD) of shortleaf pine sprouts through the next growing season. For southern red oak, season of burning did not negatively affect (P &gt; 0.05) the growth of sprouts during the year after burning. Although mean heights and GLDs of white oak sprouts versus controls were reduced (P [Formula: see text] 0.04) when means were averaged across burns, white oak sprouts on winter-burn plots were comparable in size with the control seedlings.