Frost tolerance of various Pinus pure species and hybrids

Pinus species are widely planted by the South African forestry industry and are utilised for pulp, paper and saw timber products. Historically, Pinus patula Schiede ex Schltdl. et Cham. was the most widely planted commercial species in the summer rainfall area, but has come under severe threat due to the fungus Fusarium circinatum. Fusarium circinatum causes mortality in nurseries and in-field after establishment. Other Pinus species, such as P. tecunumanii F.Schwerdtf. ex Eguiluz et J.P.Perry and P. oocarpa Schiede ex Schltdl., have been crossed with P. patula to increase tolerance to F. circinatum and these hybrids have largely overcome the post-planting mortality problem. However, these hybrid-partner species are more prone to frost damage. This study reviewed laboratory screening techniques to assess the frost tolerance level of a range of Pinus pure species and hybrids. In vitro screening was done with the electrolyte leakage and whole-plant freezing techniques. Seedlings and rooted cuttings from a range of genotypes, supplied by Sappi, were tested in vitro at different target temperatures (?3, ?6, ?9 and ?12 °C) to determine their relative frost tolerance. These genotypes included a range of Pinus pure species, four interspecific hybrids (P. patula × P. tecunumanii low elevation [LE], P. patula × P. tecunumanii high elevation [HE], P. elliottii Engelm. × P. caribaea Morelet), and a three-way cross (P. patula × (P. patula × P. oocarpa)). Results from this study indicated that the electrolyte leakage technique was a reliable method to determine frost tolerance under laboratory conditions, with similar pure species rankings as experienced under field conditions. The interspecific hybrids of P. patula × P. tecunumanii LE and HE ranked intermediate between the parental species and the P. patula × P. tecunumanii HE hybrid was more frost tolerant than the P. patula × P. tecunumanii LE hybrid.     

Family variation in diameter growth and acoustic velocity in three 5‑year‑old South African‑grown Pinus elliottii×Pinus caribaea progeny trials established on three diverse sites

This paper discusses family differences in the stiffness of young Pinus elliottii×P. caribaea wood and how these differences relate to differences in growth rate and altitude. Trees for measurement were obtained from three 5?year?old progeny trials established at three diverse sites on the estate of Komatiland Forests (Pty) Ltd. The trials included the following controls: P. elliottii, P. patula, P. taeda, P. patula×P. tecunumanii and P. tecunumanii. Diameter at breast height and sound velocity (which has a direct relationship with wood stiffness) were measured on all healthy trees. Virtually all of the species and hybrids exhibited marked decreases in growth rate and velocity (stiffness) with increasing altitude; the effect on velocity was most likely partly due to the inverse relationship that normally exists between wood density and altitude in most pines. Differences in growth rate explained only a small proportion of the total variation in velocity. The average sound velocities of P. patula, P. patula×P. tecunumanii and P. tecunumanii surpassed the velocity values of most of the P. elliottii×P. caribaea crosses at all three sites. Results of Spearman rank correlations of average treatment velocity between sites suggested only some similarity in the ranking orders among sites. The inverse effect of altitude on wood stiffness suggests that trees grown at increased altitudes are likely to yield wood with higher proportions of wood not meeting the minimum stiffness requirement for structural lumber at final harvest. The wood of some P. elliottii×P. caribaea crosses would be particularly vulnerable. Considering the large variation found, presumably largely genetic, there can be little doubt that a good opportunity exists for the development of genotypes more suitable for planting at higher altitudes.     

Growth and dynamic modulus of elasticity of Pinus patula × Pinus tecunumanii hybrids in Mpumalanga,South Africa

Field establishment of South Africa’s most important commercial pine species, Pinus patula, is severely hampered by the pitch canker fungus, Fusarium circinatum. Importantly, hybrids between P. patula and other pine species tolerant to the pitch canker fungus, such as P. tecunumanii and P. oocarpa, have been identified as an alternative planting stock. In this study, variation in tree volume and dynamic modulus of elasticity (MOE_dym) of the P. patula × P. tecunumanii (low- and high-elevation [LE and HE] ecotypes) hybrid was compared with the P. elliottii × P. caribaea hybrid, and the pure species P. tecunumanii (LE) and P. patula. The MOE_dym was assessed using the Fakkop TreeSonic microsecond instrument across three sites. The results of the study showed that P. patula × P. tecunumanii LE performed significantly better than P. patula × P. tecunumanii HE for volume and MOE_dym, which in turn was significantly better than P. patula. The MOE_dym and tree growth decreased with an increase in elevation. There was significant taxon × site interaction for volume and MOE_dym. The results of these trials suggested that P. patula × P. tecunumanii LE is a suitable alternative to P. patula in the Sabie region of Mpumalanga in South Africa on frost-free sites, in terms of the traits that were assessed.     

Future outlook for Pinus patula in South Africa in the presence of the pitch canker fungus (Fusarium circinatum)

Approximately 50% of the area planted to softwood trees in South Africa has been established with Pinus patula, making it the most important pine species in the country. More effort has gone into developing this species for improved growth, tree form and wood properties than with any other species. This substantial investment has been threatened in the last 10 years by the pitch canker fungus, Fusarium circinatum. The fungus infects and contaminates nursery plants and, once transferred to the field, causes severe mortality of young trees in the first year after establishment. Although nurserymen have some control of the disease, it is recognised that the best long-term solution to mitigate damage because of F. circinatum infection is to identify tolerant species, clones and hybrids for deployment in plantations in the future. Research has shown that alternative species such as P. tecunumanii, P. maximinoi and P. elliottii are suitable for warm sites. Pine hybrids, particularly between P. patula and the high-elevation sources of P. tecunumanii, appear to be a suitable replacement on subtemperate and temperate sites. Although these alternative species and hybrids are more sensitive to subfreezing temperatures than P. patula, their planting range can be increased by including cold tolerance as a selection criterion. Future breeding efforts will most certainly focus on improving the tolerance of pure P. patula to F. circinatum, which can be achieved by identifying specific family crosses and tolerant clones. The commercial deployment of disease-tolerant control-pollinated P. patula and hybrid families will most likely be established as rooted cuttings, which requires more advanced propagation technology. In the long term, new seed orchards comprised of P. patula clones tolerant to F. circinatum could be used to produce seed for seedling production.     

The tolerance of Pinus patula × Pinus tecunumanii, and other pine hybrids, to Fusarium circinatum in greenhouse trials

The field survival of Pinus patula seedlings in South Africa is frequently below acceptable standards. From numerous studies it has been determined that this is largely due to the pitch canker fungus, Fusarium circinatum. Other commercial pines, such as P. elliottii and P. taeda, show good tolerance to this pathogen and better survival, but have inferior wood properties and do not grow as well as P. patula on many sites in the summer rainfall regions of South Africa. There is, thus, an urgent need to improve the tolerance of P. patula to F. circinatum. Operational experience indicates that when P. patula is hybridized with tolerant species, such as P. tecunumanii and P. oocarpa, survival is greatly improved on the warmer sites of South Africa. Field studies on young trees suggest that this is due to the improved tolerance of these hybrids to F. circinatum. In order to test the tolerance of a number of pine hybrids, the pure species representing the hybrid parents, as well as individual families of P. patula × P. tecunumanii, a series of greenhouse screening trials were conducted during 2008 and 2009. The results indicated that species range in tolerance and hybrids, between P. patula and these species, are intermediate in tolerance to F. circinatum. Within P. patula × P. tecunumanii, large family variation exists when pollen from the high elevation source of P. tecunumanii is used. The results of these studies illustrate the importance of developing pine hybrid breeding programs to overcome the susceptibility of our pure species to pathogens such as F. circinatum.     

Variation in pitch canker resistance among provenances of <Emphasis Type="Italic">Pinus patula</Emphasis> and <Emphasis Type="Italic">Pinus tecunumanii</Emphasis> from Mexico and Central America

Pinus patula and high-elevation (HE) sources of P. tecunumanii exhibit intermediate levels of resistance to pitch canker (Fusarium circinatum), compared to extremely resistant species such as P. oocarpa, and extremely susceptible species such as P. radiata. Seedlings from 20 P. patula provenances and 15 HE P. tecunumanii provenances were artificially inoculated with the pitch canker fungus at 21 and 12 weeks of age, respectively, and assessed for resistance 12–20 weeks later. There was important provenance variation in pitch canker resistance for both species. The 20-week LiveStem percentage ranged from 70.3% to 43.6% among the P. patula provenances and 59.6% to 11.7% among HE P. tecunumanii provenances. There was a geographic pattern to the provenance variation, and in both species, low altitude sources demonstrated more resistance than those from high elevation. Provenance variation in pitch canker resistance could be useful when making selection and breeding decisions with these species.     

Adaptation of tropical and subtropical pine plantation forestry to climate change: Realignment of Pinus patula and Pinus tecunumanii genotypes to 2020 planting site climates

Abstract

Pinus patula and Pinus tecunumanii, two pines native to Mexico and Central America, are important plantation species for the forestry sector in the tropics and subtropics. In recent decades, members of the International Tree Conservation & Domestication Program (CAMCORE), North Carolina State University, have established large, multisite provenance trials for these pine species. The data provide valuable information about species and provenance choice for plantation establishment in many regions with different climates. However, since climate is changing rapidly, it may become increasingly difficult to choose the right species and provenance to plant. The aim of this study is to test the suitability of seed material under changing climate of two P. patula varieties (P. patula var. patula and P. patula var. longipedunculata) and two P. tecunumanii ecotypes (highland and lowland). For each variety and ecotype, a site quality model was developed that statistically relates growth to environmental factors and couples the predictions to the average 2020 climate prediction of four general circulation models. Three developed models were significant and robust. Provenances of P. tecunumanii from lowland areas in Central America are expected to be most productive in 2020 because of their promising performance under rather hot and wet climates.     

The taxonomic status of closely related closed cone pines in Mexico and Central America

A taxonomic study on 14 cone and needle traits of 281 trees from 33 provenances of Pinus oocarpa, P. oocarpa var. ochoterenae, P. patula var. longipedunculata, P. patula var. patula and P. tecunumanii in Central America and Mexico was conducted to quantify the affinity between closely related species. A second objective was to determine the geographic range of P. tecunumanii in Mexico. Cluster analysis placed 52% of all provenances in taxa different from those assigned by field foresters. Trees from 15 provenances of what was locally known as Pinus oocarpa var. ochoterenae from Chiapas were statistically indistinguishable from high elevation Central American sources of P. tecuncumanii when assessed for cone and needle characteristics. However, trees from two provenances known locally as P. oocarpa var. ochoterenae from southwestern Oaxaca, Juquila and Tlacuache, were found to be distinct from P. tecunumanii and may be a variant of P. patula. Canonical discriminant analysis was used to determine the taxonomic affinity among newly formed clusters. The spatial (Mahalanobis) distance between P. tecunumanii and P. patula var. patula, P. patula var. longipedunculata, and P. oocarpa was 42.0, 44.4, and 109.4 respectively, and highly significant. The geographic range of Pinus tecunumanii in Mexico appears to be confined to the state of Chiapas.     

Sawn-timber and kraft pulp properties of Pinus elliottii × Pinus caribaea var. hondurensis and Pinus patula × Pinus tecunumanii hybrids and their parental species

A study was undertaken to evaluate the quality of the timber produced by Pinus elliottii × Pinus caribaea var. hondurensis (PECH) and the Pinus patula × Pinus tecunumanii low elevation (PPTL) and high elevation (PPTH) hybrids and their parent species for both kraft pulp and sawn-timber production. Trees were taken from unthinned tree improvement trials managed for pulpwood, ranging in age between 15 and 19 years. All sawn boards produced by study trees met the minimum wood density requirement for S5-grade structural timber (360 kg m^?3), but approximately 17% of the boards failed to meet the other requirements for the grade, largely due to knot-related defects. Results of dynamic modulus of elasticity assessments performed on all of the boards suggested that a large percentage of boards would not meet the specified average stiffness (7 800 MPa). This was confirmed by the results of static bending tests performed on a subsample of boards. All boards tested for all species and hybrids met the required fifth percentile bending strength value for grade S7 (15.8 MPa) according to SANS 6122 (2008) specifications. The kraft pulping results indicated that the samples taken from the upper part of the stem yielded slightly better results on average than the samples representing the whole tree with respect to uniformity in the kappa vs charge and temperature, and yield vs kappa traits, with slight improvement of pulp yield (52% vs 50%) and some strength properties compared with whole tree pulping. Samples from the upper part of the stem had a close delignification rate in the 60–80 kappa range. The delignification rate for PPTL in the 60–80 kappa range was slower and the yield was slightly lower than P. patula (53.17% vs 52.72%) despite a higher kappa number. The pulp strengths short-span compressive test, breaking length and tearing strength of PECH were similar to those of P. elliottii, which were in turn generally lower than those of P. patula. The pulp strengths of PPTL and PPTH were similar to those of P. patula, whereas P. caribaea strengths were intermediate between those of P. patula and P. elliottii. With the exception of a slightly lower pulp yield, PPTL emerged as the best all-round hybrid for both pulp and sawn-timber properties.     

Testing of selected South African <Emphasis Type="Italic">Pinus</Emphasis> hybrids and families for tolerance to the pitch canker pathogen, <Emphasis Type="Italic">Fusarium circinatum</Emphasis>

Plantations of Pinus spp. constitute approximately 50% of the South African forestry industry. The first aim of this study was to develop a reliable inoculation technique to screen Pinus spp., for tolerance to infection by F. circinatum, which threatens pine forestry in South Africa. Inoculation of branches was compared with stem inoculations and we considered the number of branches or trees required to obtain statistically significant results. Furthermore, variation in the susceptibility of some Pinus families, clones and hybrids was considered. Results showed that branch inoculations were closely correlated with those from stem inoculations, and that it is important to consider branch and stem diameters when assessing susceptibility of trees. Subsequent trials using branch inoculations showed significant differences in F. circinatum tolerance amongst a range of pine species and hybrids of potential interest to forestry in South Africa. Significant differences in susceptibility were also found among clones of two P. radiata families. The most tolerant trees were P. elliottii × caribaea and P. patula × oocarpa hybrids, while the most susceptible species were P. patula, P. greggii and hybrids of these two. This is the first trial considering the susceptibility of Pinus hybrids, Pinus clones and some P. patula provenances, and the results indicate excellent potential for breeding for tolerance to pitch canker in South Africa. Application The accurate selection of disease tolerant planting stock for the South African forestry industry is crucially important for the continued sustainability of this important industry. The work described here provides valuable information on an artificial inoculation technique that will assist the industry in screening trees for tolerance to the pitch canker fungus, F. circinatum. It also provides some indication of the relative susceptibility of a number of Pinus spp., hybrids and families currently being evaluated in the country.     

Susceptibility of provenances and families of Pinus maximinoi and Pinus tecunumanii to frost in South Africa

The future of South Africa’s most important pine species, Pinus patula, is threatened by the pitch canker fungus, Fusarium circinatum. Pinus maximinoi and P. tecunumanii represent two subtropical species that provide an alternative to planting P. patula on the warmer sites of South Africa. Extending the planting range of P. tecunumanii and P. maximinoi to include higher and colder altitude sites will reduce the area planted to P. patula and the risk of F. circinatum. During 2007 progeny trials of P. tecunumanii and P. maximinoi were planted on a sub-tropical and sub-temperate site. Shortly after the establishment of these trials, unusually cold weather conditions were experienced across South Africa (?3°C at the sub-temperate site) resulting in severe mortality. This provided the opportunity to assess the variation in survival as a measure of frost tolerance within these two species to determine whether it could be improved upon through selection. Results indicated that the variation in survival was under genetic control in P. tecunumanii (h _(0,1) ²  = 0.16, h _L ²  = 0.27) and P. maximinoi (h _(0,1) ²  = 0.11, h _L ²  = 0.23) at the sub-temperate site. Correlations in provenance ranking for survival across sites were high for both species. Moderate correlations in family survival for P. tecunumanii (r = 0.52) were found at the two sites. Improvements in cold tolerance can thus be made in both species extending their planting range to include greater areas planted to P. patula thereby limiting the risk of F. circinatum.     

Seedling growth and ectomycorrhizal colonization of Pinus patula and P. radiata inoculated with spores of Helvella lacunosa,Russula brevipes or Lycoperdon perlatum

Seedling growth and ectomycorrhizal colonization of Pinus radiata and P. patula seedlings growing in nursery containers with two application rates of spores of 3 different ectomycorrhizal fungi, Helvella lacunosa, Russula brevipes and Lycoperdon perlatum, was evaluated at 5 and 12 months. At 5 months of growth P. patula was less susceptible than P. radiata to colonization by fungi and percentage of ectomycorrhizal feeder roots was lower in all treatments. Growth response (either volume or top dry weight) to treatments was different among pines species. A significant seedling growth response was observed after 5 months in both pine species with the double rate of spores of either H. lacunosa or L. perlatum; this response was sustained in P. patula at 12 months with Helvella only. P. radiata seedlings inoculated with the double rate of spores of R. brevipes showed a significant growth response at 12 months.

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Resumen Se estudió en dos intervalos del crecimiento de Pinus patula y P. radiata, en envases de vivero, la inoculación con dos dosis de esporas de los hongos ectomicorrícicos Helvella lacunosa, Russula brevipes y Lycoperdon perlatum. P. patula se mostró, en la temprana edad (5 meses) menos susceptible a la colonización radicular por bongos; la proporción de sus raicillas micorrizadas es, en todos los tratamientos, mas baja que la del otro pino. La respuesta a la inoculación (volumen o peso seco) es diferente en las dos especies de pinos; a los 5 meses se observa en ambos un respuesta significativa a la doble dosis de esporas tanto de Helvella como de Lycoperdon. Esta respuesta es consistente a los 12 meses solo en P.patula inoculado con esporas de Helvella; en esta misma etapa, las plantulas de P.radiata inoculadas con la doble dosis de esporas de Russula mostraron una respuesta significativa en su crecimiento.

     

Development and commercialisation of the Pinus patula × P. tecunumanii hybrid in response to the threat of Fusarium circinatum

During the last 20 years a program to develop and commercialize the Pinus patula × Pinus tecunumanii hybrid, as a replacement for P. patula, has been successfully implemented. The first crosses were initiated during the early 1990s and lead to establishment of field trials across a wide variety of sites. This work gained further impetus when it became apparent that Fusarium circinatum, was causing poor post-planting survival of newly established stands of P. patula. P. tecunumanii, has been shown to be tolerant to this disease and thus a second, more comprehensive hybrid testing phase was implemented. Improvements in controlled pollination techniques and propagation methods, as well as access to genetically improved parent-stock and the use of molecular marker technology for fingerprinting was effectively utilized to greatly improve the process during this second phase. The use of artificial inoculation trials have demonstrated that the hybrid, in particular when using the low elevation (LE) provenances of P. tecunumanii, had substantially greater tolerance to F. circinatum than P. patula and survival figures from field trials support these results. Four-year volumes also indicate large growth improvements, although frost damage on certain sites presents a challenge for deployment on colder sites; and this is being tackled through breeding and accurate mapping of frost risk. Large-scale controlled pollinations and vegetative multiplication are now utilized commercially to produce the P. patula × P. tecunumanii (LE) hybrid as an alternative to P. patula.     

Selection of Pinus spp. in South Africa for tolerance to infection by the pitch canker fungus

The increasing threats from pests and diseases demand that the South African forest industry explores options to deploy alternative pine species in plantation development. This is especially true for species, such as Pinus patula Schiede and Deppe ex Schltdl. and Cham., which are highly susceptible to the pitch canker fungus Fusarium circinatum. Losses due to F. circinatum have been confined mostly to nurseries and at field establishment resulting in a significant cost to the industry. Although, the fungus has not as yet resulted in stem and branch infections on established P. patula in South Africa, it has caused pitch canker on other, more susceptible species such as P. radiata D. Don., and P. greggii Engelm. ex Parl. As alternatives to P. patula, on the warmer and cooler sites in South Africa, families of P. elliottii Engelm var. elliottii, P. tecunumanii (Schw.) Eguiluz and Perry, P. maximinoi H. E. Moore and P. pseudostrobus Lindl. were screened for tolerance to infection by F. circinatum in greenhouse studies. Seedlings were wounded and inoculated with spores of F. circinatum. Lesion development following inoculation was used to differentiate the levels of tolerance between families. The results showed that P. maximinoi, P. pseudostrobus, and the low elevation variety of P. tecunumanii are highly tolerant to infection with very little family variation. The narrow sense heritability estimates for these species were less than 0.06. In contrast, P. elliottii showed good tolerance with some family variation and a heritability of 0.22, while the high elevation source of P. tecunumanii showed a high degree of family variation and a heritability of 0.59. These results provide the industry with valuable information on pine species tolerant to F. circinatum that could be used as alternatives to P. patula in South Africa.     

Tree breeding model to assess financial performance of pine hybrids and pure species: deterministic and stochastic approaches for South Africa

Financial performance of the P. patula × P. tecunumanii, P. greggii × P. tecunumanii, P. taeda × P. tecunumanii hybrids and their parental species was studied for South Africa. A model was developed for use in determining the profitability of a tree-breeding program (TBP) with pine hybrids in commercial plantations. Growth measurement data were collected in four, 12-year-old genetic trials on Mondi and Sappi land holdings in South Africa. Growth models developed for P. patula and P. taeda in South Africa were used to infer models for the other taxa and to calculate the optimal financial rotation age at discount rates of 6 and 8%. Financial data on pine plantations were collected from different sources in South Africa. Optimal rotation lengths in this study were found to be between 12 and 16 years for pulpwood and 17 years for sawtimber. The model output shows the net present value (NPV), the internal rate of return, and the minimum area that a tree grower has to plant every year in order to justify the investment in a TBP. A stochastic approach with Monte Carlo simulation showed that the sensitivity of NPV to uncertainty in the wood price was greater than that for the planting, harvesting, and transport costs.     

Biology,incidence and host susceptibility of Pineus boerneri (Hemiptera: Adelgidae) in Colombian pine plantations

Adelgids (Hemiptera) in the genus Pineus have been reported as introduced insect pests causing serious losses to Pinus plantations worldwide. In 2008, Pineus boerneri was recorded for the first time in Colombia, with infestations noted on Pinus kesiya, P. tecunumanii, P. maximinoi and P. oocarpa. The lack of information on this insect in Colombia prompted investigations of its life cycle and infestation levels as well as host susceptibility of the main Pinus species planted in Colombia. In addition, the possibility of using a Ceraeochrysa species, an already established predator of adelgids in Colombia, for biological control was considered. Results showed that Pineus boerneri in Colombia has an anholocyclic life cycle comprised of four instars with a complete duration of between 49 and 97 d. Infestations were higher in the middle and upper part of trees. Pinus kesiya and P. maximinoi had the highest levels of susceptibility in field as well as in greenhouse trials. A survey of naturally infested trees showed P. tecunumanii to be moderately susceptible, whereas P. patula and P. oocarpa had low levels of susceptibility in a greenhouse trial but were not susceptible in the field. Investigations considering the impact of predation of Ceraeochrysa species showed a high predation rate of up to 140 P. boerneri consumed per day by a single Ceraeochrysa individual. Other predators of P. boerneri were recorded but were not sufficiently common to warrant detailed study.     

Differential responses of Central American and Mexican pine species and Pinus radiata to infection by the pitch canker fungus

Seedlings from a wide array of 23 species, varieties,and geographic races were screened for resistance topitch canker using artificial inoculation in agreenhouse. Seed to represent these taxa weregenerally collected in natural stands. In addition,seedlings from 79 families of P. radiata fromcommercial populations from Chile and New Zealand werescreened in a separate experiment. There was littlevariation in resistance among the commercial P.radiata families, with over 98% mortality. Similarresults were obtained with native P. radiatapopulations. All close relatives of P. radiata(sub-section Patula) were very susceptible. However,a number of closed-cone pine species (specifically,from sub-section Oocarpa) were generally veryresistant, with survival approaching 100%. Inaddition, in P. oocarpa, P. jaliscana, and P. tecunumanii from low elevation provenances anextremely high frequency of trees suffered no apparentdamage from the pathogen (92%, 85% and 80%,respectively).     

Loblolly and slash pine height and diameter are related to soil drainage in winter on poorly drained silt loams

Soil drainage characteristics in winter and the heights and diameters of 10-year-old loblolly and slash pines (Pinus taeda L. and P. elliottii Engelm. var. elliottii) were measured on three poorly-drained silt loam sites that had been bedded, furrowed, or disked before planting. Quadratic response functions were used to determine the relationship between depth to water table or volume of drained soil in winter and mean tree height or diameter. These quadratic response functions (species × height or diameter: drainage characteristics) showed that diameter and height were significantly related to soil drainage in winter on these silt loams soils. Slash pines grew better than loblolly pines under more poorly drained conditions while loblolly pines grew better under the better drained conditions. On unbedded silt loams, the soil drainage in winter needed to maximize tree height was 42 cm for loblolly and 49 cm for slash pine. Pines planted on beds did not generally grow better than those on flat-disked plots because where bedding would be most benefical the practice did not form enough additional drainage to significantly influence pine development.     

有无枯落物覆盖对加勒比松林地表径流及其K流失的影响

为了解有无枯落物对K随地表径流损失的影响,研究比较了有无枯落物加勒比松林地表径流中的K流失的特点,结果表明:有、无枯落物加勒比松林的年地表径流量分别为12.6、51.8 mm,主要发生在夏季,对应的地表径流系数分别为0.60%、2.48%,表明前者能有效削弱地表径流。2种林分的降水量和地表径流量的关系可用二项式方程表示。有、无枯落物加勒比松林各月的地表径流K浓度分别为3.2~36.3、1.8~6.0 mg.kg-1,通过地表径流输出的K量分别为701、982 g.hm-2。2008年5、6月为有枯落物加勒比松林的K流失高峰,6月为无枯落物加勒比松林的K流失高峰。地表径流的K浓度和径流量之间存在对数关系,K的流失量主要由径流量决定。     

The pine reproductive process in temperate and tropical regions

Our knowledge of the pine reproductive process is confined to the developmental stages and time relations in a particular species. Lacking in the literature is a comparative analysis from a broader perspective such as pines from temperate versus tropical regions. Also, important information that may have beneficial implications for pine breeding and management purposes may be missed by going with a single generalized reproductive cycle model which is usually derived from well-studied northern temperate species. Detailed developmental analysis of the reproductive process is necessary, particularly for tropical pines where information is limited. Most pines undergo a reproductive cycle that spans three calendar years with two dormant periods. In temperate pines, many of the stages that are initiated by fall generally come to a halt during the winter and development resumes in spring of the following year. In tropical pines, reproductive development appears to be generally a continuous process characterized by a gradual rate of development with indistinct first dormant period. The distinct first dormant period in north temperate pines serves to synchronize pollen release and seed-cone receptivity which results in higher pollination success and seed production. Tropical pines exhibit asynchrony in pollen release and thus has extended pollination period. Relatively less pollen are available which results in lower pollination success and seed set. Interestingly, since asynchrony may enhance cross-pollination, tropical pines might benefit from this through the capture of genetic diversity. The length of the second dormant period is generally the same in temperate and tropical pines which indicates strong genetic control.