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.     

Spatial pattern of seedlings 1 year after fire in a Mediterranean pine forest

Summary The spatial distribution of seedlings of the dominant perennial plant species (Pinus halepensis, Cistus salviifolius, Rhus coriaria) and may annual species was studied after a wild fire in an eastern Mediterranean pine forest. The spatial distribution of all seedlings is affected by the location of the old burned pine trees. Seedling density of Pinus and Cistus is higher at a distance from the burned pine canopy and lower near the burned pine trunk. It is also higher beneath small burned pine trees than under big ones. Rhus seedling density is higher under big burned pine trees and also near the burned trunks. Seedlings of Pinus, Cistus and Rhus growing under the burned canopy of big pine trees tend to be taller than seedlings under small ones or outside the burned canopy. Most annual species germinate and establish themselves outside the burned canopies, and only a few annual species are found beneath them. It is suggested that variation in the heat of the fire, in the amount of ash between burned pine trees of different sizes, and in the distance from the burned canopy are responsible for the observed pattern of seedling distribution. The possible ecological significance of the spatial pattern of seedlings distribution and their differential growth rate are discussed.     

A Markov approach for describing post-fire succession of vegetation

Vegetation dynamics in the coastal area of the Seto Inland Sea region in Japan, where wild fires occur frequently, were described using a stationary Markov model. In this region, vegetation types ofMiscanthus-Pleioblastus grassland,Lespedeza-Mallotus scrub,Pinus-Rhododendron forest andCrassocephalum-Erechtites community have been identified, and these show cyclic succession under the influence of fires. The model uses parameters determining fire frequency and rate of successional change to analyze the effect of variation in these parameters on the areal ratio of each vegetation type at equilibrium and on the time taken for one vegetation type to succeed another (elapsed successional time). The effect of fire frequency differs between hypothetical habitats with high and low productivity. A policy for vegetation management in areas of high and low productivity is proposed. The advantages and limitations of applying Markov models to studies of vegetation succession are also discussed.     

Root System Asymmetry of Mediterranean Pines

Three groups of Mediterranean pines were examined to describe the development of root symmetry on sites characterized by shallow soils and low water availability. Sampling included: (1) 3-year-old planted seedlings of Pinus halepensis Mill. taken from Sithonia Halkidiki, northern Greece, (2) 5-year-old natural regenerated seedlings of Pinus brutia Ten. taken from Kedrinos Lofos, Thessaloniki and (3) 65-year-old trees of Pinus brutia taken from Kedrinos Lofos, Thessaloniki. Root system symmetry was examined by measuring the number, the diameter, the cross-sectional area (CSA), the root area index (RAI) and the length of the lateral roots of each root system, and by analyzing their distribution around the stem. Above-ground plant symmetry was also estimated. The findings of the study indicated that there was an asymmetric root system in all three groups that is characterized by the concentration of the main laterals along the contour lines instead of uphill or downhill; however, the asymmetry was much higher in the young plants. This asymmetry was not correlated with the above-ground plant growth form, which was found to be symmetric. The asymmetric development of root can be attributed to the shallow soil and the high mechanical resistance of the underground bedrock that stopped the taproot growth, restricted the root penetration in the deeper layers and obliged the roots to elongate towards the surface soil layers, where there is more available water.     

Differential field response of two Mediterranean tree species to inputs of sewage sludge at the seedling stage

Land degradation and desertification is a common feature in Mediterranean landscapes due to extensive and intensive land use and natural or man induced disturbances. The ecosystem may need external inputs to recover its composition and function as soils are often impoverished and vegetal key stone species lost. We evaluated the effects of the application of fresh and air-dried biosolids in the establishment and morphological and physiological performance of seedlings of Pinus halepensis and Quercus ilex under dry Mediterranean field conditions. Seedling survival was not affected by biosolid treatments in any of the studied species both two and ten years after planting. During the first two years, growth was enhanced by the two biosolid treatments in relation to control, although the change in the biomass allocation pattern differed between species. Rooting depth was significantly enhanced by liquid biosolid in Q. ilex and marginally reduced in P. halepensis as well as the exploration of soil. As a consequence, root-to-shoot ratio reduced significantly with dry and liquid sludge due to promoted aboveground growth while maintaining and even reducing belowground fractions. An improvement of the nutritional status, of fertilized seedlings especially of phosphorus, is the explanation for the better field performance. Vector analysis revealed an important phosphorus limitation for both species that was overcome with the application of liquid (both species) and air-dried biosolid (pine). The higher growth of pine seedlings attained in the liquid biosolid treatment was coupled with a significant decrease in foliar δ¹³C, suggesting lower water use efficiency. The significant increase in foliar δ¹⁵N in the biosolid treatments in both species suggested that a large proportion of the total nitrogen uptake came from the applied biosolids. Instead, with regard to the low biosolid application rate used in the study, treatments had an overall positive effect as a restoration tool by improving nutritional status and promoting growth of planted seedlings.     

Fungal succession on pine needles in Germany

The mycofloral succession on the needles ofPinus sylvestris was investigated in Tübingen, southwest Germany. Dead needles attached to the branches (D-type), those caught on branches (C-type) and three types of fallen needles, i.e., freshly fallen (L-type), slightly discolored (OL-type) and almost black needles (F-type) were examined for their fungal flora. Common primary saprophytes were rich on the dead needles on the tree, and on the L-type needles. They were replaced by successive species that contained the well-known species preferring pine needles as their substratum, such asVerticicladium trifidum orSympodiella acicola. Their ecological niches in pine leaf litter and their distribution patterns from a biogeographical viewpoint were discussed.     

Seedling performance in sewage sludge-amended degraded Mediterranean woodlands

Biosolids have been widely used for land reclamation, but information on their use in restoration, i.e., on less degraded areas, is scarce. Biosolids may be used to restore forest ecosystems by fostering tree establishment in degraded shrublands. Detailed knowledge on the effects of biosolid application is needed to optimize such practice. We evaluated the effect of different rates (0, 7.5 and 14.5 kg dry weight per plant) and types of biosolid application on the performance of Pinus halepensis and Quercus ilex seedlings, and operational costs. Biosolids increased seedling mortality in both species, particularly when seedlings were planted in direct contact with them. Mortality mostly occurred during the first year, and was probably favored by soil shrinking and salinity. Foliar and needle nitrogen concentration increased with biosolid rate in the short term, but biosolids affected negatively (P. halepensis), or had no effect (Q. ilex) on phosphorus and potassium concentration. Biosolids had a positive effect on P. halepensis growth, and a negative effect on Q. ilex growth at the highest rate when seedlings were in contact with biosolids. Cost of this type of biosolid application approximately doubled plantation cost, but were similar or cheaper that landfill disposal of biosolids. The lowest application rate showed the best balance between seedling response and costs for P. halepensis, whereas biosolid use cannot be recommended for Q. ilex.     

Fungal succession in the early decomposition process of pine cones on the floor ofPinus densiflora forests

The fungal succession on pine cones on the floor ofPinus densiflora forest was investigated in the early decomposition process (within ca. 30% decrease in dry weight). The fungal flora was examined by both washing and surface-sterilization methods on artificially placed cones and naturally fallen cones. The decomposition rates of artificially placed cones were 0.081–0.082 yr^–1. On withered cones still attached to the tree,Pestalotiopsis spp. were dominant. These fungi also occurred with higher frequencies after cones had lain on the floor and on cones in the L and FH horizons.Xylaria sp. andPhomopsis sp., which seem to colonize the interior of the tissue, occurred with higher frequencies on the cones on the tree, but their occurrence frequencies decreased after cones had lain on the forest floor. Conversely,Mortierella spp. andTrichoderma spp. newly occurred or their occurrence frequencies increased on lying cones. Of these,Trichoderma koningii increased rapidly and showed high occurrence frequencies.Thysanophora penicillioides, which prefers coniferous substrates, showed higher occurrence frequencies in the early stages of lying on the forest floor. On cones lying on the floor, the fungal flora did not significantly change during the investigation period.     

Fungal successions on pine needles fallen at different seasons: The succession of surface colonizers

Field experiments were carried out to investigate influences of seasonal change on the fungal succession occurring on the surface of decaying pine needles at a moder site in Japan. At different seasons, the needles fallen for a short period were collected and marked, then placed on the surface of the O horizon. The needles were removed at intervals and their fungal communities were examined by using a washing technique. Unlike the successions of interior colonizers studied at the same time, those of surface colonizers observed on the fallen needles at four different times are roughly similar to each other.Thysanophora penicillioides was the major first colonizer on the sample needles from the O horizon, andTrichoderma species followed it. In an experiment started in late autumn, three dematiaceous fungi,Chloridium viride var.chlamydosporis, Sporidesmium omahutaense, andChalara sp., commonly occurred and contributed to the darkening of colonized needles. Seasonal variation in climate may have a stronger effect on internal colonizers than external colonizers of needles. Contributions from Sugadaira Montane Research Center, No. 165.     

Spatial and temporal distribution of the zoobenthos community in a woodland pond (Switzerland)

Spatial and temporal changes of zoobenthos composition and density were assessed in a woodland pond, near Geneva (Switzerland), by monthly sampling (during 15 months), on the three main substrates: a submerged macrophyte (Chara sp.), an emergent macrophyte (Typha latifolia stems) and allochthonous detritus (oak leaves).Many taxa showed preferences for one or two of the substrates, as expressed by differences in densities, but few taxa presented an exclusivity for one substrate. Zoobenthos densities (per m² of pond bottom) were largely dominated on all substrates and seasons by Chironomidae and Oligochaeta. Other dense macroinvertebrates included Ostracoda (on Chara and Typha stems), Gastropoda (on Typha stems), Ephemeroptera (all substrates), and Ceratopogonidae (on Typha stems).The magnitude of temporal differences in densities was expressed by the ratio of maximal to minimal monthly densities and reached values between 2.8 to 11.8. On all substrates the highest monthly densities were observed in summer or beginning of autumn. The temporal changes in densities were strongly influenced by the life cycles of the invertebrates: presence of numerous young individuals in summer (for example Cypridopsis vidua, Cloeon dipterum, Caenis horaria, Ferrissia wautieri), and emergence (for example Chironomidae in April). Fluctuations in densities, especially on Chara and leaves, were also attributed to modification of substrate condition (surface availability, stage in the decomposition or senescence process). Temporal fluctuations of densities were compared with other lentic water bodies: highest densities showed a common trend, occurring between end of spring and beginning of autumn.     

Post-fire regeneration in a Mediterranean pine forest with historically low fire frequency

Species of Mediterranean vegetation are known to regenerate directly after fire. The phenomenon of autosuccession (direct regeneration) has been found to be often combined with an increase of species richness during the first years after fire due to the high abundance of short-lived herbaceous plants facilitated by plentiful nutrients and light. The high degree of vegetation resilience, which is expressed in terms of autosuccession, has been explained by the selective pressure of fire in historic times. According to existing palaeoecological data, however, the Pinus halepensis forests in the Ricote Mountains (Province of Murcia, SE Spain) did not experience substantial fire impact before the presence of man nor are they especially fire-prone today. Therefore, we studied post-fire regeneration to find out if direct succession is present or if species from pre-fire vegetation are absent during the post-fire regeneration stages. Patterns of succession were deduced from observations made in sample plots on sites of a known regeneration age as well as in adjacent unburnt areas. The results of the vegetation analyses, including a Detrended Correspondence Analysis, indicate that Pinus halepensis forest regeneration after fire resembles autosuccession. As regards the presence of woody species, there is a high percentage similarity on north (83%) and south (70%) facing slopes during the first year after fire vs. reference areas which is due, for example, to direct regeneration of the resprouting Quercus coccifera or seeders like Pinus halepensis or Fumana laevipes. However, if herbaceous species are included in the comparison, the similarity on north-facing sites decreases (to 53%) with the presence of additional species, mainly ruderals like Anagallis arvensis or Reseda phyteuma, and even woody species on the burnt plots. This effect indicates “enhanced autosuccession”, which was not found on south-facing sites where overall species richness was very high irrespective of the impact of fire. Locally we found limited regeneration of some species, for example Pinus halepensis at high altitudes (1000 m), even 22 years after fire. As we assume that historical fires did not play an important role in the area and direct succession is present nevertheless, our results support the theory that autosuccession is not a process restricted to fire-prone areas. Fire has been only one of several selective forces since human settlement that probably led to a set of species pre-adapted against recurrent disturbance.     

Changes in nutrient use efficiency, status and retranslocation in young post-fire regeneration Pinus halepensis in response to sudden N and P input, irrigation and removal of competing vegetation

The capacity of Mediterranean species to adapt to variable nutrient supply levels in a global change context can be a key factor to predict their future capacity to compete and survive in this new scenario. We aimed to investigate the capacity of a typical Mediterranean tree species, Pinus halepensis, to respond to sudden changes in N and P supply in different environmental conditions. We conducted a fertilisation, irrigation and removal of competing vegetation experiment in a calcareous post-fire shrubland with an homogeneous young (5 years old) population of P. halepensis in order to investigate the retranslocation and nutrient status for the principal nutrients (N, P, Mg, K, S, Ca and Fe), and the nutrient use efficiency (NUE) of the most important nutrients linked to photosynthetic capacity (N, P, Mg and K). P fertilisation increased P concentration in needles, P, N, Mg and K retranslocations, and NUE calculated as biomass production per unit of nutrient lost in the litterfall. The P fertilisation was able to increase the aboveground biomasses and P concentration 3 years after P fertiliser application. Those responses to P fertilisation were enhanced by the removal of competing vegetation. The N needle and litterfall concentration decreased after P fertilisation and this effect was greater when the P fertilisation was accompanied by removal of competing vegetation. The increase of P availability decreased the P-NUE and increased the N-NUE when these variables were calculated as aboveground biomass production per unit of P present in the biomass. Both P-NUE and N-NUE increased when calculated as total aboveground production per unit of nutrient loss. The results show that it is necessary to calculate NUE on a different basis to have a wider understanding of nutrient use. The irrigation did not change the needle nutrient concentrations and the litterfall production, but it significantly changed the nutrient litterfall concentrations and total aboveground contents (especially P and K). These results show a high capacity of P. halepensis to quickly respond to a limiting nutrient such as P in the critical phases of post-fire regeneration. The increase in P availability had a positive effect on growth and P concentrations and contents in aboveground biomass, thus increasing the capacity of growth in future periods and avoiding immediate runoff losses and leachate. This capacity also strongly depends on neighbour competition.     

Climate-related variability in carbon and oxygen stable isotopes among populations of Aleppo pine grown in common-garden tests

The Aleppo pine (Pinus halepensis Mill.) is found in the Mediterranean under a broad range of moisture and thermal conditions. Differences in severity and duration of water stress among native habitats may act as selective forces shaping the populations’ genetic make-up in terms of contrasting drought strategies. We hypothesised that these strategies should translate into intraspecific variation in carbon isotope composition (δ¹³C, surrogate of intrinsic water-use efficiency, WUE_i) of wood holocellulose, and such variation might be linked to changes in oxygen isotope composition (δ¹⁸O, proxy of stomatal conductance) and to some climatic features at origin. Thus, we evaluated δ¹³C, δ¹⁸O, growth and survival for 25 Aleppo pine populations covering its geographic range and grown in two common-garden tests. We found intraspecific variability for δ¹³C and growth, with high-WUE_i populations (which showed ¹⁸O-enriched holocellulose) having low growth. These results suggest stomatal regulation as common control for δ¹³C and productivity. We also detected sizeable relationships between δ¹³C and climate factors related to the magnitude and timing of drought such as the ratio of summer to annual rainfall. The main climate variable associated with δ¹⁸O was minimum temperature, but only in the coldest trial, suggesting differences in growth rhythms among sources. Overall, slow growing populations from highly-seasonal dry areas of the western Mediterranean exhibited a conservative water-use, as opposed to fast growing sources from the northernmost distribution range. The particular behaviour of the Mediterranean Aleppo pine as compared with other conifers demonstrates different selective roles of climate variables in determining intraspecific fitness.     

Structural patterns and biodiversity in burned and managed Aleppo pine stands

Increasing anthropic pressure is making forest fires more frequent in the Mediterranean Basin and therefore affecting the response of native flora and fauna. Two large fires occurred in summer, 1994, in the Southeastern Iberian Peninsula. Aleppo pine, the main tree species, regenerated naturally after the fire. In this study we are interested in strategies for maximizing Aleppo pine tree recovery and conservation of its ecosystem. We performed thinning and pruning in the pine tree stands 5 and 10 years after the fire and took measurements on structural patterns and plant diversity using several indices. In addition, we measured macro-lichen and faunal diversity indirectly. Results show significant differences between treated-burned plots and untreated-unburned plots. The plots thinned 10 years after the fire and the unburned plots (mature stands) showed a regular, non-aggregated distribution and a low diameter differentiation. Also, these plots showed similar plant diversity values. The silvicultural treatments did not significantly affect the fauna and lichen index values. The high intensity of thinning and late pruning applied to young Aleppo pine stands improved the structural pattern and plant diversity.     

Community homogenization and the invasiveness of commensal species in Mediterranean afforested landscapes

The ecological consequences of homogenization remain relatively unexplored. One example of landscape-homogenizing is the establishment of plantations. We studied the effect of human-made forests by contrasting plant and small-mammal community composition between planted tree stands and adjacent natural habitat in two different Mediterranean habitats in Israel: (1) inland habitat where we focused on pine (Pinus halepensis) and carob (Ceratonia siliqua) stands, and (2) coastal sand dune habitat where we focused on planted acacia (Acacia saligna) stands. We first wanted to verify whether planted trees modify plant species composition, and second, if and how the small-mammal community is affected by the different habitat conditions created in plantations with different canopy cover. We were especially interested in the abundance of the commensal house mouse (Mus musculus). All tree stands underwent biotic homogenization indicated by abundance of house mice coupled with lower diversity of indigenous vegetation and small-mammal abundances and diversities. Habitat structural diversity was positively related with small-mammals diversity and was lower in artificial tree stands in both habitats. Our results suggest that using the abundance of commensal generalist species such as the house mouse relative to other more specialist small-mammals is a good approach to determine ecosystem integrity. Pre-commercial thinning treatment is a potential management tool to maintain a proportion of native tree species within the canopy of planted tree stands. However, until sufficient data is available for making generalizations, the exact level of thinning necessary to reverse the homogenization processes in man-made plantations and keeping indigenous small-mammal communities diverse and less prone to invasion must be determined empirically.     

Optimization of in vitro bud induction and plantlet formation from mature embryos of Aleppo pine (Pinus halepensis Mill.)

Summary Studies were undertaken to optimize tissue culture conditions for micropropagation of Aleppo pine (Pinus halepensis Mill.) from mature embryos and various explants of the embryo. Over 90% of the embryo explants gave rise to adventitious buds within 4 wk. Intact embryos were the most suitable explants for shoot bud induction. Both isolated cotyledons and hypocotyls produced adventitious buds, but these developed slowly and failed to elongate. N⁶-Benzyladenine (BA) alone at 5.0μM was the most effective cytokinin when added to gelled to gelled von Arnold and Eriksson’s (AE) medium containing 3% sucrose. Adventitious bud development was achieved on hormone-free AE medium, and shoot elongation was optimum on three quarter-strength Bornman’s MCM medium, with 0.1% conifer-derived activated charcoal. Shoots were multiplied on three-quarter strength MCM medium, containing 5μM BA. To induce adventitious roots on the elongated shoots, pulse treatment with 1 mM IBA for 6 h, followed by the transfer of the shoots to sterile peat:vermiculite (1:1) mixture, was beneficial. After acclimatization for 3 to 4 wk under mist, almost all the rooted shoots could be transplanted successfully to the greenhouse, where the plants exhibited normal growth habit. Histologic studies on the ontogeny of adventitious shoot formation from mature embryo explants revealed temporal structural changes in different parts of the explant. Induction of mitotic divisions on the shoot-forming medium resulted in the formation of meristemoids in the epidermal and subepidermal layers of the explant, located initially at both the tips of the cotyledons and the axils of adjacent cotyledons. Shoot buds arising in the axils of adjacent cotyledons were due to new cell division and not to any preexisting meristem.     

Modelling the distribution of diameter growth along the stem in Scots pine

This paper presents an empirical model for the distribution of diameter growth along the stem in Scots pine (Pinus sylvestris L.) and for the consequent stem form over time. First, the distribution of annual mass growth in the stem is determined as a function of the total annual growth in stem mass, current stem mass and the distribution of the latter along the stem. Second, the distribution of diameter growth is obtained by converting the fraction of annual growth in the stem mass at a given height in the stem into the thickness of the annual ring at the same height. Application of the model to Scots pine data sets including both young and mature trees not used in parameter estimation showed that the model was capable of reconstructing the distribution of diameter growth from the stem butt to the apex and from the pith to the stem surface at any height in the stem in both young and mature trees. The resulting empirical model was also linked to a physiological, process-based model in order to study its performance in a simulated stand. Simulations representing trees grown in unthinned and thinned Scots pine stands with trees of different status (from dominant to suppressed) showed that the response in tree growth to thinning in terms of the distribution of diameter growth along the stem was quite realistic relative to measured data.     

Germination response to fire-related factors of seeds from non-serotinous and serotinous cones

Pinus halepensis, a Mediterranean pine tree, is a partially serotinous species: individual trees of this species carry both non-serotinous and serotinous cones. Serotinous cones open mainly after fire, whereas non-serotinous cones open in absence of fire. In this study we addressed the question, whether or not this cone response is linked with the germination response of seeds to fires. Two main factors associated with fire are heating of seeds and soil pH. A combination of high heat and high pH simulates a scenario with fire, whereas low heat and low pH simulates a scenario without fire. We assessed the separate and combined effects of heat and pH on the germination rate and the percentage of germination of seeds from non-serotinous cones and two age classes of serotinous cones of P. halepensis. Heat had no effect on the percentage of germination of seeds from any of the cone types, but did positively affect the germination rates of seeds from both age-classes of serotinous cones. High pH negatively affected the germination rate of seeds from all cone types as well as the percentage of germination of seeds from non-serotinous cones. The combinations of heat and pH had different effects on the three cone types: percentage of germination and rate of germination of seeds from non-serotinous cones was higher in the combination high heat-high pH than in the combination low heat-low pH. In the combination high heat-high pH, seeds from serotinous cones germinated better than seeds from non-serotinous cones. The different germination responses of seeds from non-serotinous and serotinous cones could not be attributed to differences in cone age. Our results indicate that the cone response is linked to the germination response of the seeds in P. halepensis, with seeds from serotinous cones being more tolerant to fire related factors. This revised version was published online in June 2006 with corrections to the Cover Date.     

Conifer seedling distribution and survival in an alpine-treeline ecotone

The importance of seedling establishment to the position ofalpine-treeline is recognized, yet little is known about factorsaffecting the survival of seedlings of treeline conifers during their initialyears of growth and establishment. This establishment period may have thegreatest mortality of all life stages until death of mature trees by disease orfire. Spatial and temporal patterns in the distribution and survival ofseedlings of Picea engelmannii and Abieslasiocarpa were evaluated over four years in analpine-treeline ecotone of the Snowy Range, Wyoming, USA. Seedlings andsaplings of both species occurred most frequently near islands of adult trees.For P. englemannii, this appeared partly due to decreasedsurvivorship of young seedlings (< 5 cm height) with greaterdistance away from tree islands. Survival of emergents of P.engelmannii was 28% greater on the north compared to southsides of tree islands, 48% lower on south-facing slopes comparedto other aspects, and 70% greater with overhead cover such as treebranches. Survival of emergents was greater in microsites with grass cover(90% survival) compared to without ground cover (44% survival),but lowest in microsites surrounded, but not covered, by grass (19%).From 1994–1999, natural seedling emergence and survival washighest in 1995 (80% survival of 221 P.engelmannii,and 100% of seven A. lasiocarpa, in a sample areaof432 m²), when the smallest mean difference in dailymaximum and minimum temperatures occurred, and lowest in 1994 (30% ofseven P. engelmannii), when above-averagetemperatures were accompanied by low rainfall and clear skies. The growthseasons of 1994 and 1995 had among the lowest and highest precipitation of theprevious 30-year period, respectively. In an artificial seedingexperiment, less than 20% of seedlings of both species survived theirfirst complete year of growth. In the autumn of the second year, almost25% additional mortality was observed in the remaining experimentalseedlings when they were exposed to clear, cold skies without the normalprotection of snowcover. Both spatial and temporal patterns of seedlingsurvivalsuggest that exposure to high sunlight may exacerbate low-temperatureandwater stress in young conifer seedlings, inhibiting their establishment in thisalpine treeline.     

湖北省马尾松精准适宜性空间分布

马尾松作为南方主要的造林树种,研究其适宜性精准空间分布对其退化评价、造林选地等具有生产指导价值。本研究采用多元线性回归克里金模型利用R语言对湖北省降雨量、气温等15个气象因子进行30×30m的空间插值,插值结果作为气象因子空间变量,插值的交叉检验结果≥90%。利用30m的DEM提取坡度、坡向、高程3个地形因子空间变量。首先利用年均温、最冷月最低温、年降水量、高程、土壤类型等限制性因子进行空间叠加排除不适宜的空间单元,然后在可能适宜的空间单元内,再基于18个空间变量和294个样方数据,利用最大熵模型(MAXENT)计算每个格网的适宜性指数,最后按照适宜指数进行适宜性分类。区别于以往大尺度区域研究,其结果是落实到地块尺度的精准计算。结果表明:ROC模型的评价效果达到较好水平(ROC=0.826),高程、土壤、降雨相对标准差、最湿季降雨量、坡度、年均温为湖北省马尾松的适宜性主要影响因子,马尾松中、强适宜区主要分布在湖北省东北部及中北部地区,主要分布在高程低于1200m、坡度在40°以下、年均温13-18℃的区域,中等及以上适生区面积共计4.65万km~2,占湖北省总面积的25.01%。