Survival Of Conifer Seedlings Research Articles

Effects of nurse shrubs and biochar on planted conifer seedling survival and growth in a high-severity burn patch in New Mexico, USA

The synergistic effects of widespread high-severity wildfire and anthropogenic climate change are driving large-scale vegetation conversion. In the southwestern United States, areas that were once dominated by conifer forests are now shrub- or grasslands after high-severity wildfire, an ecosystem conversion that could be permanent without human intervention. Yet, the reforestation of these landscapes is rarely successful, with a mean planted seedling survival of just 25 %. Given these low rates, we carried out a planting experiment to quantify the impacts of biochar as a soil amendment and shrubs as nurse plants on planted conifer seedling survival and growth following high-severity wildfire. We planted 1200 seedlings of three species (Pinus ponderosa, P. strobiformis, and Pseudotsuga menziesii) in a 2-ha area within the footprint of the Las Conchas fire in New Mexico, USA. We used four treatments: under shrubs, or in the open and with or without biochar in a full-factorial design. We found that planting tree seedlings underneath shrubs increased tree seedling survival by 46 % after 3 years, with some marginal evidence that shrubs inhibited seedling diameter growth (mean R2 = 0.08). The addition of biochar increased seedling survival by 11 % but had no effect on seedling growth. Our study suggests that planted seedling survival in post-wildfire areas can be increased by planting under shrubs in soil amended with biochar. The widespread adoption of these methods may improve the success rates of post-wildfire reforestation efforts in semi-arid areas, regaining some of the ecosystem services lost to high-severity wildfire.

Conifer Seedling Survival in Response to High Surface Temperature Events of Varying Intensity and Duration

Forests face accelerating threats due to increases in the severity and frequency of drought and heat stress associated with climate change. In particular, changing patterns of forest regeneration after disturbance will be important in predicting future forest distribution across the western United States, where patterns of recurring fire and regrowth are important in establishing landscape dynamics. To predict shifting landscape patterns, it will be important to identify environmental boundaries for forest regeneration using environmental variables with clear consequences for seedling survival. Here, we explore soil surface temperature as an environmental variable with direct consequences for seedling survival and forest regeneration potential. We conducted a literature search to identify five previous laboratory experiments, spanning a period of 1924 to 1986, that exposed conifer seedlings to elevated soil surface temperatures for varying durations. We then synthesized the data from these studies to explore the survival of western U.S. conifer species in response to differing surface temperature levels. We found mortality thresholds consistent with previously reported measurements in field and lab studies, but found that as surface temperatures reach these lethal thresholds the duration of exposure matters greatly to survival outcomes. This work leverages an intuitive climate metric with clear consequences for seedling survival as an indicator of forest regeneration potential.

Differences in morphological and physiological plasticity in two species of first-year conifer seedlings exposed to drought result in distinct survivorship patterns.

First-year tree seedlings represent a critical demographic life stage, functioning as a bottleneck to forest regeneration. Knowledge of how mortality is related to whole-seedling carbon and water relations is deficient and is required to understand how forest compositions will be altered in future climatic conditions. We performed a greenhouse drought experiment using first-year seedlings of two common pine species found in the Intermountain West, USA. Gas exchange, biomass gain, allometry and xylem water potentials were compared between well-watered and droughted seedlings from emergence until drought-induced mortality. In both species, morphological adjustments to confer drought tolerance, such as increased leaf mass per unit area, were not observed in seedlings exposed to drought, and droughted seedlings maintained photosynthesis and whole-seedling carbon gain well into the experiment. Yet, there were important differences between species in terms of carbon budgets, physiological responses and mortality patterns. In Pinus ponderosa P. & C. Lawson, physiological acclimation to drought was much greater, evident through stronger stomatal regulation and increased water-use efficiency. Photosynthesis and carbon budgets in P. ponderosa were greater than in Pinus contorta Dougl. ex. Loud., and survival was 100% until critical hydraulic thresholds in leaf water content and seedling water potentials were crossed. In P. contorta, physiological adjustments to drought were less, and mortality occurred much sooner and well before injurious hydraulic thresholds were approached. First-year conifer seedlings appear canalized for a suite of functional traits that prioritize short-term carbon gain over long-term drought tolerance, suggesting that conifer seedling survival is linked with carbon limitations, even during drought, with survival in species having narrower carbon survival margins being more hampered by carbon limitations.

Regeneration processes on coarse woody debris in mixed forests: do tree germinants and seedlings have species‐specific responses when grown on coarse woody debris?

Summary Tree regeneration on coarse woody debris (CWD) is considered to be one the most ecologically valuable aspects of CWD in forest systems. However, most studies have focused solely on uncovering the differences in establishment and growth on CWD (regarded as a homogeneous substrate) in comparison with the forest floor. Our study concentrates on the underlying mechanisms of germinant and seedling colonization patterns and demographic responses relative to various properties of CWD. We analysed the effects of CWD properties (decay class, form, species and diameter) on: (i) germinant and seedling annual counts; (ii) annual germinant and seedling survival; and (iii) seedling growth and height. Our study comprised three species (beech, fir and spruce) over 7‐year span in two old‐growth stands in the Western Carpathians, and employed generalized linear models and mixed models to test for differences between species. CWD properties affected regeneration at the germination stage. There were some demographic differences between species relative to CWD properties. Decay class had the most pronounced effect on beech, not only on its establishment but also survival and growth. Beech and spruce established and survived in higher densities on beech CWD, while their height growth was enhanced on conifer‐derived CWD, particularly on spruce CWD. Stumps enhanced establishment of all species and survival of conifer seedlings. Synthesis. Our study shows that CWD properties do influence seedling establishment, growth, height distribution and survival. Moreover, there may be trade‐offs between seedling growth and survival among tree species growing on different species of CWD. This highlights the need to include CWD heterogeneity as a factor that can affect the role of CWD in regeneration in forest ecosystems.

Seasonal Variation in Understory Light Near a Gap Edge and Its Association with Conifer Seedling Survival in a Southern New England Forest

Forest edge-generated gradients in understory light are known to influence the survival of tree seedlings in North American deciduous forests, but the seasonality of that influence has not been investigated for the forests of southern New England. We examined the winter versus summer difference in photosynthetically active radiation (PAR) transmitted through a southern New England forest canopy in the vicinity of a large experimental canopy gap and investigated if this difference influenced the survival of Pinus strobus L. (White Pine) and Tsuga canadensis (L.) Carr. (Eastern Hemlock) seedlings along a gap—forest gradient using Kaplan-Meier survival curves and Cox proportional hazards models. The mean and the spatial distribution of winter understory PAR transmittance (%T) across the gap—forest gradient were significantly different from those of summer %T. Distance from gap edge into the forest and variability in %T during the winter months were associated with the survival of White Pine seedlings, but not with that of Eastern Hemlock seedlings, which had a constant survival probability throughout the gap—forest gradient. Summer %T was not associated with the survival of seedlings of either species. Experimentally, we found that digital fisheye canopy photos did not accurately capture the range in understory light level along a gap—forest gradient. Thus they are a poor proxy for direct PAR transmittance measurements and should be used with caution in southern New England forests, which are highly fragmented and contain many edges. Forest management actions for the conservation of White Pine should take into account winter understory light regimes rather than summer regimes.

Evaluating SeaDust Wildlife Controllant™ as a Repellent to Reduce Deer Browse on Douglas-fir Seedlings

Herbivory by black-tailed deer affects growth form and survival of conifer seedlings in western Oregon and Washington, especially Douglas-fir. Several deterrents have been employed to reduce damage to forest resources yet most are ineffective or cost prohibitive. Use of chemical repellents is socially appealing because they offer a potential non-lethal alternative to reduce plant damage (i.e., browse). Commercial deer repellents may employ one or more mechanisms in their formulation, which affect taste, odor, visual, and/or tactile cues when consumed by deer. I evaluated the commercial SeaDust Wildlife Controllant ™ as a tool to repel black-tailed deer from Douglas-fir seedlings during spring bud burst in western Oregon (mid-May through early July), because its ingredients have the potential to employ multiple avoidance mechanisms targeted on tactile, taste, and odor cues. Evidence indicated that deer browse was affected by an interaction of treatment and site; therefore, sites were evaluated separately. Treated seedlings were browsed less by deer than untreated seedlings on 2 of 3 tree farms where percent browse ranged from 0.08%-0.17% in treated plots and 0.15%-0.37% in control plots. Browse was similar at the third tree farm (0.15%). However, number of seedlings browsed in the third tree farm was greater than one site and less than the other, suggesting that statistical significance may not represent biological significance in this study. Future research is needed to incorporate acceptable loss to browsing and cost:benefit analyses.

Availability of ectomycorrhizal fungi to black spruce above the present treeline in Eastern Labrador.

Ectomycorrhizal fungi (ECMF) are an important biotic factor in the survival of conifer seedlings under stressful conditions and therefore have the potential to facilitate conifer establishment into alpine and tundra habitats. In order to assess patterns of ectomycorrhizal availability and community structure above treeline, we conducted soil bioassays in which Picea mariana (black spruce) seedlings were grown in field-collected soils under controlled conditions. Soils were collected from distinct alpine habitats, each dominated by a different ectomycorrhizal host shrub: Betula glandulosa, Arctostaphylos alpina or Salix herbacaea. Within each habitat, half of the soils collected contained roots of ectomycorrhizal shrubs (host+) and the other half were free of host plants (host−). Forest and glacial moraine soils were also included for comparison. Fungi forming ectomycorrhizae during the bioassays were identified by DNA sequencing. Our results indicate that ECMF capable of colonizing black spruce are widespread above the current tree line in Eastern Labrador and that the level of available inoculum has a significant influence on the growth of seedlings under controlled conditions. Many of the host− soils possessed appreciable levels of ectomycorrhizal inoculum, likely in the form of spore banks. Inoculum levels in these soils may be influenced by spore production from neighboring soils where ectomycorrhizal shrubs are present. Under predicted temperature increases, ectomycorrhizal inoculum in soils with host shrubs as well as in nearby soils without host shrubs have the potential to facilitate conifer establishment above the present tree line.

Response of Gaultheria shallon and Epilobium angustifolium to large additions of nitrogen and phosphorus fertilizer

A study was established in coastal British Columbia to determine if repeated nitrogen (N) and phosphorus (P) fertilization negatively influences the reestablishment of salal (Gaultheria shallon Pursh) on cleared and burned cedar–hemlock (Thuja plicata Donn ex D. Don – Tsuga heterophylla (Raf.) Sarg.) forests. Fertilizers were applied for 3 years, and the biomass of ground vegetation and conifer seedling survival and growth were measured. Salal biomass decreased with high levels of N application (1000 kg N/ha), but not when 400 kg P/ha was added with 1000 kg N/ha. The addition of 500 kg N/ha, with or without P, stimulated salal growth. The biomass of fireweed (Epilobium angusti folium L.) increased with the addition of N + P but not with N alone. In the high N and N + P treatments, conifer seedling survival and heights were reduced. These results confirm earlier reports that salal responds negatively to high N applications and that this negative response can be alleviated with simultaneous additions of P. The response of fireweed to N + P, but not to N alone, suggests that the abundance of this species is more indicative of P than N availability.

Responses of planted conifers and natural hardwood regeneration to harvesting, scalping, and weeding on a boreal mixedwood site

Recent emphasis on ecosystem-based forest management has increased interest in promoting species mixtures to enhance stand-level diversity. However, there is little information on silvicultural approaches to regenerate mixtures of conifers and hardwoods in northern Ontario. This study tested fifth-year effects of harvest intensity (uncut, 50% partial cut with and without removal of residuals after 3 years, and clearcut), site preparation level (none and scalped), and chemical weeding frequency (none, single, and multiple) on survival and growth of planted white spruce ( Picea glauca [Moench] Voss) and jack pine ( Pinus banksiana Lamb.), height and density of hardwood regeneration, and cover of competing shrubs. The study is located in a hardwood-dominated mixedwood stand on a fertile, mesic, upland site in northeastern Ontario. Although throughfall precipitation, wind speed, and temperature were moderated by residual cover, only light level varied sufficiently among treatments to account for differences in regeneration success. Damage to regeneration by mammals, weather, or equipment was minor, but up to 17% of residual basal area was lost to windthrow in partial cuts. Scalping had no effect on the development of conifer seedlings, hardwood regeneration, or shrubs. Survival of conifer seedlings was enhanced by harvesting but not by weeding, and spruce survival exceeded pine survival at all harvest levels. Seedling height and diameter growth increased with harvest intensity and weeding frequency, and the beneficial effects of weeding increased with harvest intensity. Height and density of hardwood regeneration increased with harvest intensity and decreased with weeding frequency. Single weeding reduced but did not eliminate hardwoods. Harvesting slightly increased shrub cover and weeding sharply decreased it. Dense suckering of trembling aspen ( Populus tremuloides Michx.) followed removal of residuals 3 years after the initial 50% partial cut. Thus, final removal cuts on mixedwood sites should be delayed until conifer seedlings are well established. Underplanting cannot be recommended for uncut mixedwood stands in Ontario because of unacceptably high seedling mortality. Compared to clearcutting, partial cutting without removal of residuals reduced fifth-year hardwood density on unweeded plots. However, hardwoods on that treatment overtopped spruce seedlings by 90 cm and pine seedlings by 64 cm. Partial cutting with reduced weeding produced acceptable stocking of conifer and hardwood regeneration, but did not promote seedling growth. Weeding was required to maintain spruce as a viable understory component, to ensure pine codominance with hardwoods, and to reduce shrub cover below 50%. Separating species into alternating patches or corridors may be more productive than promoting integrated mixtures, since it allows silvicultural treatments to be adapted to the needs of each species. Long-term monitoring of crop trees and associated vegetation following mixedwood management options on a range of boreal sites is required to advance the knowledge base and produce reliable operational guidelines.

Underplanted conifer seedling survival and growth in thinned Douglas-fir stands

In a multilevel study to determine limits to underplanted conifer seedling growth, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), western redcedar (Thuja plicata Donn ex D. Don), and western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings were planted beneath second-growth Douglas-fir stands that had been thinned to basal areas ranging from 16 to 31 m2/ha. Understory vegetation was treated with a broadcast herbicide application prior to thinning, a directed release herbicide application 2 years later, or no treatment beyond harvest disturbance. Residual overstory density was negatively correlated with percent survival for all four species. Broadcast herbicide application improved survival of grand fir and western hemlock. Western redcedar, grand fir, and western hemlock stem volumes were inversely related to overstory tree density, and this effect increased over time. There was a strong indication that this was also the case for Douglas-fir. Reduction of competing understory vegetation resulted in larger fourth-year stem volumes in grand fir and western hemlock.

Underplanted conifer seedling survival and growth in thinned Douglas-fir stands

In a multilevel study to determine limits to underplanted conifer seedling growth, Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco), grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), western redcedar (Thuja plicata Donn ex D. Don), and western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings were planted beneath second-growth Douglas-fir stands that had been thinned to basal areas ranging from 16 to 31 m 2 /ha. Understory vegetation was treated with a broadcast herbicide application prior to thinning, a directed release herbicide application 2 years later, or no treatment beyond harvest disturbance. Residual overstory density was negatively correlated with percent survival for all four species. Broadcast herbicide application improved survival of grand fir and western hemlock. Western redcedar, grand fir, and western hemlock stem volumes were inversely related to overstory tree density, and this effect increased over time. There was a strong indication that this was also the case for Douglas-fir. Reduction of competing understory vegetation resulted in larger fourth-year stem volumes in grand fir and western hemlock. Resume : Des semis de douglas de Menzies (Pseudotsuga menziesii (Mirb.) Franco), de sapin grandissime (Abies gran- dis (Dougl. ex D. Don) Lindl.), de thuya geant (Thuja plicata Donn ex D. Don) et de pruche de l'Ouest (Tsuga hetero- phylla (Raf.) Sarg.) ont ete plantes dans des peuplements de seconde venue de douglas de Menzies qui avaient ete

Mycorrhization, physiognomy, and first-year survivability of conifer seedlings following natural fire in Grand Teton National Park

Ectomycorrhiza formation, survivability, and physiognomic characteristics were assessed for conifer seedlings encountered 1 and 2 years postfire in the Huck burn site near Grand Teton National Park. Pinus contorta Dougl. ex Loud. germinated and was abundant throughout the first growing season. Abies lasiocarpa (Hook.) Nutt. germinated during May and June but was rarely encountered by September. First-year survivorship of P. contorta seedlings was about 50% for east-facing burn and edge and west-facing burn treatments. Mortality was higher in the west-facing edge treatment at about 64%. Pinus contorta seedlings collected in July and August had allocated approximately 75% more biomass to epicotyl production than to hypocotyl production, whereas by September seedlings had allocated 30-50% of their biomass to hypocotyls, regardless of site or treatment. Few or no ectomycorrhizae were formed until September. By September 100% of surviving seedlings were ectomycorrhizal. The number of ectomycorrhizae was positively correlated with the number of primary needles and the root/shoot ratio. These results highlight the importance of mycorrhizae to conifer seedling survival during the initial growing season and point to alteration of carbon allocation as a primary mechanism affecting seedling survival.

Effect of bryophytes on survival of conifer seedlings in subalpine forests of central Japan

AbstractBryophytes form the major seedbed for coniferous trees in the subalpine forests of central Japan. Field experiments were conducted on the floor of a closed stand dominated by Tsuga on Mt Fuji to examine the seedling survival of Abies veitchii and Tsuga diversifolia in seven substrate types in relation to the morphological characteristics of the seeds and seedlings. Neither Abies nor Tsuga seedlings could survive on dwarf‐bamboo litter beyond 2 years after the seed rain. Abies seedlings survived not only in all types of bryophyte communities but also in larch litter. In contrast, the survival of Tsuga seedlings was restricted to communities of smaller‐statured bryophytes found on logs. The seeds and 1st year seedlings of A. veitchii were larger than those of T. diversifolia. Abies seedlings produced hypocotyls taller than any bryophyte community and radicles which were long enough to penetrate into the moist humus layer, whereas Tsuga seedling radicles presumably penetrate into humus only in bryophyte communities forming a thin mat on logs. The effect of bryophytes on survival of tree seedlings therefore depends on the relationships between the morphology of seeds and seedlings and the structure of bryophyte communities.

Small Rodent Populations and Conifer Seedling Damage on a Reclaimed Area in West Central Alberta

Small rodent populations and conifer seedling survival were monitored on a reclaimed area in west central Alberta from September 1979 to September 1985. Although several species of cricetid rodents and shrews were captured during the live-trapping program, only meadow voles (Microtus pennsylvanicus) and deer mice (Peromyscus maniculatus) occurred in sufficient number to monitor annual changes in abundance. Meadow voles increased rapidly on the reclaimed area from 1979–1981, remained at high numbers until 1984, then declined sharply in 1985. Deer mice increased to moderate numbers from 1979–1981 and declined gradually until 1983. By 1984–1985, very few deer mice were present.Two species of conifer seedlings, lodgepole pine (Pinus contorta) and white spruce (Picea glauca) were planted on the reclaimed area in 1979 and 1980. Numbers of seedlings killed or damaged by small rodents, primarily by girdling, increased sharply in 1981 and remained at high levels through to 1984. Significant correlations between the percentage of the annual mortality of seedlings attributed to small rodents or the percentage of live seedlings damaged by small rodents, and the abundance of meadow voles the previous winter, indicate that the amount of mortality and damage to seedlings in this reclamation area is in part determined by the overwintering abundance of meadow voles. This is in direct agreement with conclusions from similar studies in other areas of North America and Europe.

Tree Seedlings on Logs in Picea‐Tsuga Forests of Oregon and Washington

Logs are the major seedbed for trees in coastal Picea sitchensis–Tsuga heterophylla forests. Field experiments were conducted at Cascade Head, Oregon, and Hoh River, Washington, to examine pathogens, predation, competition, and standing water as causes for this close seedling–log association. More seedlings survived on log blocks than on soil blocks, regardless of whether the blocks were raised or placed flush with the soil surface. Standing water was therefore an unlikely cause of the seedling–log association. Comparisons of plots protected from and exposed to predation revealed that predation was minor and of equal intensity on soils and logs. Sterilizing soils did not consistently increase seedling survival above controls. Clearing ground–layer vegetation from soil plots significantly increased the survival of conifer seedlings compared with that on uncleared soils. The seed penetration rates through moss mats indicated that <1% of the seedlings germinated within moss mats. Competition with herbs and mosses on the forest floor therefore appears to be responsible for the disproportionate number of tree seedlings found on logs. Recently fallen logs represent sites where competition is low enough for tree seedling recruitment within many Picea–Tsuga forests.

Growth Inhibition of Mycorrhizal Fungi by Gibberellin

tions by parasitic fungi. Since the survival of conifer seedlings often may be associated with the presence of mycorrhizal fungi on their roots (2), the loss of seedlings in the study by Kraus and Johansen could reflect gibberellin inhibition of the fungal symbiont. Levisohn (4) reported that pure cultures of Boletus granulatus, B. scaber and Rhizopogon luteolus had slightly decreased colony diameters when growing on agar media containing 100 ppm gibberellin. The present study was undertaken to observe the effect of gibberellin on liquid cultures of fungi which are known to form mycorrhizal associations with the roots of conifers (Hacskaylo, E., 1959, personal communication). The fungi were the basidiomycetes Amanita caesaria, A. rubescens, A. muscaria, Boletus luteus and B. bicolor and a representative of the Fungi Imperfecti, Cenococcum graniforme. The fungi were grown 14 days on Hoagland's medium (glucose, 20 g; KH2PO4, 1 g; MgSO,i7H20, 0.5 g; ammonium tartrate, 0.5 g; ZnSO4, 2.5 mg; 1 per cent ferric citrate chelate, 0.5 ml; thiamine HCl, 50 /jg; H20, 1 liter; pH adjusted to 4.5) in triplicate bottle-bead cultures (5) containing various levels of gibberellin (potassium gibberellate, Chas. Pfizer & Co.), TABLE I. The