Dendroecological analysis of a longleaf pine Pinus palustris forest in Mississippi

A climate model with time varying parameters was fit to longleaf pine (Pinus palustris) tree rings collected from the proposed Harrison Research Natural Area of the De Soto National Forest in southern Mississippi. The purpose of the analysis was to determine if any unexpected disturbances had influenced the growth of the trees. Current September temperature, August rainfall and February Palmer Drought Severity Index (PDSI) were found jointly to be the best variables in the model to predict growth. August rain had a constant significant effect on growth and February PDSI was not significant except between the years 1968–1983. It was concluded that the Harrison area has been in equilibrium for the past 50 years since no apparent outside influences have caused the trees to become less sensitive to climate. Thus, the forest is a good candidate for a Research Natural Area.Abbreviations (RNA) Research Natural Area     

Seed germination patterns of Salvia mellifera in fire-prone environments

Summary I examined the effects of pollen loads containing pollen from one, three and five donors on fruit production and fruit quality in Campsis radicans. Number of pollen donors had no significant effect on % fruit production, seed number, seed weight or seed germination. In singledonor pollinations the identity of the donor did have a strong effect on the above parameters. Furthermore, the best single donor sired fruits with more seeds and heavier seeds than any mixture containing this donor. This pattern indicates interference of pollens or preemption of some ovules by the inferior pollen. In Campsis, therefore, the number of pollen donors contributing to a pollen load is less important than the identity of these donors in determining fruit production and fruit quality. Seeds from fruits resulting from mixed pollination were slightly more variable than seeds from fruits resulting from single-donor pollinations.     

Fine root branch orders respond differentially to carbon source-sink manipulations in a longleaf pine forest

Fine roots are a key component of carbon (C) flow and nitrogen (N) cycling in forest ecosystems. However, the complexity and heterogeneity of the fine root branching system have hampered the assessment and prediction of C and N dynamics at ecosystem scales. We examined how root morphology, biomass, and chemistry differed with root branch orders (1–5 with root tips classified as first order roots) and how different root orders responded to increased C sink strength (via N fertilization) and reduced carbon source strength (via canopy scorching) in a longleaf pine (Pinus palustris L.) ecosystem. With increasing root order, the diameter and length of individual roots increased, whereas the specific root length decreased. Total root biomass on an areal basis was similar among the first four orders but increased for the fifth order roots. Consequently, total root length and total root surface area decreased systematically with increasing root order. Fine root N and lignin concentrations decreased, while total non-structural carbohydrate (TNC) and cellulose concentrations increased with increasing root order. N addition and canopy disturbance did not alter root morphology, but they did influence root chemistry. N fertilization increased fine root N concentration and content per unit area in all five orders, while canopy scorching decreased root N concentration. Moreover, TNC concentration and content in fifth order roots were also reduced by canopy scorching. Our results indicate that the small, fragile, and more easily overlooked first and second order roots may be disproportionately important in ecosystem scale C and N fluxes due to their large proportions of fine root biomass, high N concentrations, relatively short lifespans, and potentially high decomposition rates.Electronic Supplementary Material Supplementary material is available for this article at     

Nitrogen decreases and precipitation increases ectomycorrhizal extramatrical mycelia production in a longleaf pine forest

The rates and controls of ectomycorrhizal fungal production were assessed in a 22-year-old longleaf pine (Pinus palustris Mill.) plantation using a complete factorial design that included two foliar scorching (control and 95% plus needle scorch) and two nitrogen (N) fertilization (control and 5 g N m⁻² year⁻¹) treatments during an annual assessment. Ectomycorrhizal fungi production comprised of extramatrical mycelia, Hartig nets and mantles on fine root tips, and sporocarps was estimated to be 49 g m⁻² year⁻¹ in the control treatment plots. Extramatrical mycelia accounted for approximately 95% of the total mycorrhizal production estimate. Mycorrhizal production rates did not vary significantly among sample periods throughout the annual assessment (p = 0.1366). In addition, reduction in foliar leaf area via experimental scorching treatments did not influence mycorrhizal production (p = 0.9374), suggesting that stored carbon (C) may decouple the linkage between current photosynthate production and ectomycorrhizal fungi dynamics in this forest type. Nitrogen fertilization had a negative effect, whereas precipitation had a positive effect on mycorrhizal fungi production (p = 0.0292; r ² = 0.42). These results support the widely speculated but poorly documented supposition that mycorrhizal fungi are a large and dynamic component of C flow and nutrient cycling dynamics in forest ecosystems.     

Seed germination in temperate rain forest species of southern Chile: chilling and gap-dependency germination

Canopy gap and chilling requirements for seed germination were assessed in 61 and 44 species, respectively, in the temperate rain forest of southern Chile. Germination assays within canopy gap and understorey were carried out under natural conditions. Germination tests in cold stratified and non-stratified seeds were performed under laboratory conditions. Seeds were collected of common trees, shrubs, vines and perennial herbs of forests in southern Chile. Final percent germination was significantly enhanced under canopy gap conditions in 19 species, and significantly reduced in 11 species. Germination proved indifferent under gap vs. understorey conditions in half the species tested. Cold stratification affected germination in 11 species: significantly increasing final germination of four species, and significantly decreasing final percent germination of seven species. A Principal Components Analysis (PCA) was applied with the purpose of identifying groups of species with similar germination strategies. Four attributes were included in the PCA: final germination percentage in canopy gap, germination rate in the laboratory, and gap-and chilling-dependency indices (EGAP and STRAT, respectively). The first axis separated species mainly on EGAP variation while the second axis separated them mainly according to STRAT variation; the two axes together explaining 73% of the among-species variation. A small group of trees and vines germinating best in the understorey and neutral to chilling could clearly be distinguished from the remaining species analyzed. Multifactorial ANOVAs were used for evaluating the combined effect of successional status, seed mass, dispersal period, life form, phylogenetic categories, and dispersal syndrome on EGAP and STRAT variation. The EGAP value of secondary successional species proved significantly greater than that of primary successional species and species with endozoochorous seed dispersal were significantly less dependent on chilling (according to STRAT values) compared to species with mainly wind-dispersed seeds. The possible implications of these results for seedling establishment are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparative assessment of heat tolerance in weevils associated with a fire-prone ecosystem

1. Fire is an important cause of disturbance which directly shapes many ecosystems worldwide. While the effect of fire on the distribution and regeneration of plant species has been widely documented, little is known on how phytophagous insects are reacting to these disturbances.
2. This study explores the survival strategies of various weevil species, a highly diverse phytophagous beetle group in fire-prone ecosystems of the biodiversity hotspot of the Cape Floristic Region in South Africa. More specifically, we investigated how the lifestyle of species (location of larval development, phenology of adults, and flight ability) correlates with heat tolerance. We hypothesized that wingless species in particular will show better tolerance to heat as they have a limited ability to escape fire rapidly and usually remain hidden in the soil.
3. The thermal tolerance of a set of sixteen species with divergent lifestyles and geographic distribution was measured using a standard heat knockdown protocol at 48°C. Respirometry was then performed on the most resistant species using a ramping protocol in order to determine CT_max.
4. Our results show that the species tested exhibit high variation in thermal tolerance across taxonomic groups, clustering into three modalities: weak, intermediate, and high tolerance to heat stress. In addition, life history traits (diurnal vs. nocturnal adult activity and location of juvenile stages in plant tissues) likely better explain thermal tolerance at the species level than flight ability or the fire-proneness of ecosystems. Finally, results revealed that some non-flying weevil species are highly heat tolerant with CT_max values reaching up to 50.2 and 51.9°C in species among the Ocladiinae and Brachycerinae subfamilies, respectively.
5. Climate change is leading to an increase in the impact and frequency of fires. In this context, this study highlights the diversity of strategies developed by arthropods to escape extreme heat in fire prone ecosystems. Further work is necessary to examine the generality of these patterns across other fire prone ecosystems to better understand behavioural compensation and evolutionary responses, especially given the forecast increases in fire driven by drying and warming associated with climate change.

     

Seed dispersal, germination and seedling growth of six helophyte species in relation to water-level zonation

1. Seed dispersal, germination, and seedling growth characteristics of six helophyte species. Iris pseudacorus, Phalaris arundinacea, Phragmites australis, Typha angustifolia, T. latifolia and Scirpus lacustris, were investigated in relation to their water-level zonation. 2. The experiments demonstrated a large variation in these characteristics between the species. 3. Propagule floating capacities range from < 1 h (S. lacustris) to > 1000 h (I. pseudacorus). 4. Seed germination in a water-level gradient revealed two groups with respect to germination percentage - exposed soil species (I. pseudacorus, Phalaris arundinacea, Phragmites australis) and submerged soil species (T. angustifolia, T. latifolia). 5. There were two contrasting types of seedling growth response to submergence and exposure: one group of species formed longest leaves under exposed conditions (Phalaris arundinacea, Phragmites australis, I. pseudacorus), and the other under submerged conditions (S. lacustris, T. latifolia, T. angustifolia). 6. The results suggest that early life-history characteristics of the species relate to their locations in the riparian zonation: Phalaris arundinacea and Iris pseudacorus at the higher end, Phragmites australis intermediate, and Typha spp. and Scirpus lacustris at the lower end. Species occurring at lower locations show adaptations to (periodical) flooding of the soil (submersed germination and growth), while those from higher locations require prolonged exposed soil conditions to germinate and to survive the establishment stage.     

Seed germination and salinity tolerance in plant species growing on saline wastelands

Seven plant species including three chenopods:Suaeda fruticosa, Kochia indica, Atriplex crassifolia and four grasses:Sporobolus arabicus, Cynodon dactylon, Polypogon monspeliensis, Desmostachya bipinnata, varied greatly in their seed germination and growth responses to soil moisture or salinity. The germination percentage of each species was significantly lower at soil moisture level of 25 % of water holding capacity than at the levels ranging from 50 to 125 %. Increase in salinity resulted in gradual decrease in seed germination of each species. Growth responses of species to salinity varied widely from significant decrease with slight salinity to stimulation up to salinity levels of 20 dS m^-2. Higher K⁺Na⁺ratios in plant shoots of all species compared to that in the root medium indicated selective K⁺uptake. Higher tolerance in chenopod species seems to be attendant on their ability for internal ion regulation. We are thankful to Mr. Noor Ahmad for his assistance in experimental work.     

Seed screening of three pine species for glyphosate sensitivity for forest restoration

Austrian black pine (Pinus nigra J.F. Arnold), Scots pine (Pinus sylvestris L.), and maritime pine (Pinus pinaster Aiton) are commonly used in restoration practices in the Mediterranean base including Turkey. Direct seeding can secure desired level of tree establishment and survival on degraded sites wherever, favorable safe sites are scattered throughout the landscape. Glyphosate is a commonly used herbicide for weed control in forest, nursery and restoration sites worldwide, due to its broad-spectrum efficacy and considerably less toxicity on the environment compared to other chemicals. The present study screened the glyphosate phytotoxicity of three dominant pine species in Turkey during a seed germination trial, after seeds had been presoaked in 15 different dose-glyphosate solutions varying between 0 and 5%, v:v. Glyphosate applications damaged seed germination speed more than cumulative germination rate. As a systemic herbicide, glyphosate appeared highly phytotoxic to Austrian black pine. Scots pine showed an intermediate glyphosate phytotoxicity. Maritime pine was the least sensitive species, tolerating glyphosate at ≤1% doses. In conclusion, glyphosate may be used at low doses on restoration sites seeded with maritime pine while it is not recommended to be used on degraded sites seeded with Austrian black pine and Scots pine.     

The effects of fire regime on legume reproduction in longleaf pine savannas: is a season selective?

The biodiversity of fire-dependent ecosystems is increasingly threatened by habitat fragmentation and fire suppression. Reducing species loss requires that salient features of natural fire regimes be incorporated into managed regimes. Lightning-season burns have been emphasized as the critical component of disturbance regimes that maintain native biodiversity within endangered longleaf pine savannas, the most diverse plant community in North America. Over evolutionary time, lightning-season fire is thought to have exerted strong selection pressure on plant pollinator interaction, flower production, and seedling establishment. In this study, season of burn had no effect on pollination activity of native legumes. Contrary to the conventional paradigm, we found a wide range of reproductive responses among dominant legumes in response to the season of burn treatments, suggesting that a variable fire season, rather than a single season of burn, is appropriate to maintain a greater variety of native species. We propose that varying the components of fire regimes, rather than selecting a particular fire regime, is likely to be important to conserve biodiversity in this and other fire-dependent communities.     

乡土树种茶梨种子萌发特性及其对人工繁育的启示

本试验研究了中国南方优良的乡土树种茶梨(Anneslea fragrans)种子在假种皮有无、不同脱水水平、PEG渗透胁迫和不同温度、光照条件下的萌发特性.结果表明:假种皮的存在抑制了茶梨种子的正常萌发;新鲜种子含水量较高(65.6%),脱水对于种子萌发特征具有显著影响,随着在干燥剂硅胶中脱水时间的增加,种子萌发率和发芽势持续降低,在经过48 h的持续脱水后种子完全丧失萌发能力,表明茶梨种子属于顽拗性种子;种子萌发对PEG渗透胁迫较敏感,其萌发率和发芽势随着PEG胁迫浓度的增加而降低;茶梨种子萌发对光照并不敏感,其萌发的最适温度范围是20℃～25℃,高温会抑制种子萌发.基于种子萌发对不同生态因子的响应,提出了该物种人工繁育的合理建议.

Abstract：

This paper studied the seed germination characteristics of native species Anneslea fra-grans in Southern China under the conditions of aril removal, dehydration, PEG osmotic stress, and different light and temperature. Aril removal benefited the seed germination of A. fragrans. Fresh-harvested seeds had higher moisture content (65.6%), and dehydration gave significant impact on their germination. The germination rate decreased with increasing dehydration dura-tion, and the seed viability was completely lost after 48 h continuous dehydration. Soaking in 5% -30% PEG solution for 24 h decreased the seed germination rate significantly, indicating that A. fragrans seed germination was sensitive to osmotic stress. Light had little effects on the seed germination. The optimal temperature range for the seed germination was 20 ℃～25℃, while high temperature inhibited the seed germination. Based on the responses of the seed germination to the test factors, some suggestions were made on the artificial propagation of A. fragrans.     

Seed depredation negates the benefits of midstory hardwood removal on longleaf pine seedling establishment

Midstory hardwoods are traditionally removed to restore longleaf pine on fire‐excluded savannas. However, recent evidence demonstrating midstory hardwood facilitation on longleaf pine seedling survival has brought this practice into question on xeric sites. Also, midstory hardwoods could facilitate longleaf pine seedling establishment, as hardwood litter may conceal seeds from seed predators or improve micro‐environmental conditions for seedling establishment. However, little is known about these potential mechanisms. In this study, we tracked longleaf pine seed depredation and germination in artificially seeded plots (11 seeds/m²) in a factorial design fully crossing hardwood retention or removal with vertebrate seed predator access or exclusion in the Sandhills Ecoregion of North Carolina, U.S.A. Seed depredation averaged 78% across treatments and was greatest in unexcluded plots. Hardwood retention did not affect seed depredation. Longleaf pine averaged 3.6 germinants/4 m² across treatments, and was six times more abundant where vertebrates had been excluded. Hardwood removal had a strong positive effect on seedling germination, likely due to the removal of litter, but only when vertebrates were excluded. Our results indicated midstory hardwoods are not facilitating longleaf pine seedling establishment. Nevertheless, our results indicated that hardwood removal may not increase longleaf pine seedling establishment, as seed depredation diminished the effectiveness of hardwood removal under mast seed availability. Collectively, these results demonstrate the underlying complexity of the longleaf pine ecosystem, and suggest that planting may need to be part of the restoration strategy on sites where seed depredation limits longleaf pine natural regeneration.     

Seed colour and post-fire bird predation in a Mediterranean pine forest

In a Pinus halepensis Mill. forest, a field experiment was designed to evaluate post-fire seed predation as affected by combinations of seed colour and soil substrates: light grey and black seeds combined with light grey ash, dark grey ash and pale brown sand. A survey of bird species inhabiting the area was also carried out and polyphenolic content of seed coat was assessed in seed lots of different colour. Light grey seeds were observed to be less predated on light grey ash, suggesting eucrypsis as a protective strategy against bird predation. On the contrary, no clear pattern was observed for the predation of black seeds on different substrates. In the study area both bird species breaking the seed coat and eating the endosperm and bird species swallowing the whole seed were monitored. We have estimated that more seeds were swallowed than broken, in all colour categories. Light grey seeds, which were found to have a higher content of polyphenols, were predated more than black seeds when exposed on the same substrate. Thus, no evidence was produced that the amount of polyphenols in seed coat could protect seeds from predation.     

Role of heat tolerance and cone protection of seeds in the response of three pine species to wildfires

The post-fire regenerative ability of Pinus halepensis, Pinus nigra and Pinus sylvestris, three of the most important pine species present in the West Mediterranean basin, has been analyzed in the light of seed tolerance to different temperatures and times of exposure, and of seed position during the fire event (seeds inside cones versus free seeds). The combination of different fire intensities and degrees of seed protection allows us to draw different scenarios during the fire event: canopy scenarios (seeds inside cones), surface scenarios (seeds on the ground surface), and soil scenarios (seeds in the top soil layers). There were interspecific differences in the pattern of cone opening under the different heat treatments: cones of P. nigra and P. sylvestris showed similar percentages of opening, but considerably higher than those of P. halepensis. In the three species, seeds inside cones showed higher percentages of germination than those that were free, emphasizing the important role of cones in the protection of pine seeds from high temperatures. The percentage of germination decreased when both the temperature and the time of exposure increased, and there was also a significant species effect: P. halepensis showed higher germination rates than P. nigra, and both were higher than P. sylvestris. The overall scores of seed germination of these three pine species under the conditions tested suggests that their regeneration after fire should come either from the soil bank, or from the canopy bank, but rarely from the ground surface. As the existence of a permanent seed bank in Mediterranean pines is probably limited or nil, pine recruitment after fire appears to be mainly controlled by the existence of a canopy seed bank. The contribution of this canopy bank to the differences in postfire regeneration success of the three pine species is discussed in the light of their seeding phenology and the effects of fire severity on cone opening. The results obtained in this study contribute to explain the successful regeneration of P. halepensis, and the failure of P. nigra and P. sylvestris after fire.     

草木灰对四种松属种子发芽和幼苗生长的影响

火干扰不仅影响森林生态系统的结构与功能,而且影响群落更新与演替。为了研究草木灰对4种松属种子萌芽和幼苗生长的影响,在湖南省株洲市黄丰桥林场采集马尾松、云南松、湿地松和火炬松种子,以马尾松次生林火烧迹地的草木灰为基质,设置对照和3个草木灰处理,进行播种试验及生长观测。结果表明:(1)草木灰处理下4个物种的种子发芽率比对照试验低,并呈现随草木灰含量的增加而降低的趋势,低草木灰含量处理马尾松种子发芽率不及对照一半,中、高草木灰含量处理发芽率更低;云南松、湿地松和火炬松种子发芽率规律类似于马尾松,而高草木灰含量处理发芽率为0。(2)培养皿播种平均发芽时间比花盆播种长,无论草木灰处理还是培养条件(培养皿或花盆),马尾松和云南松种子平均发芽时间比湿地松和火炬松短。(3)4个物种种子播种14周后,对照试验中马尾松和云南松幼苗死亡率最低,而火炬松和湿地松幼苗死亡率相对增加。(4)播种14周后不同试验处理4个物种幼苗生长差异不明显。火炬松、湿地松、云南松和马尾松幼苗的单株平均干重分别达0.038、0.031、0.027、0.024 g。各物种叶干重按降序排列依次是火炬松(0.026 g)湿地松(0.019 g)云南松(0.017 g)马尾松(0.016 g),根和茎的干重比重相当,约占对应物种幼苗叶干重的三分之一。研究表明以草木灰为培养基质,马尾松和云南松种子的发芽率较高,平均发芽时间较短,更适合作为火烧迹地植被恢复先锋树种,为火干扰后选择人工促进天然更新树种提供参考。