Diversifying native pinewoods using artificial regeneration

Little is known about broadleaf establishment within the nativepinewoods of Scotland, yet such information is critical to currentrestoration initiatives. A 2-year field trial was set up toassess the growth and performance of seedlings of four broadleavedspecies within different developmental stages of Pinus sylvestris(Scots pine) woodland in the Scottish Highlands. The developmentalstages included stem initiation (establishment stage), stemexclusion (thicket/pole stage) and canopy break up (old-growthcanopy), providing sites of varying shade and resource availability.It was predicted that differences in establishment between siteswould occur due to species-specific differences in ‘tolerance’of shade, low-nutrient availability and poor soil drainage.Analysis of trial results showed high survival but growth rates(relative stem height and basal diameter growth) declined rapidlyin year two. In year two, Ilex aquifolium achieved the highestmean growth rates in the stem exclusion stands (average 15 percent light) where there was a lower percentage of Phytomyzailicis (holly leaf miner) infection and frost damage. Sorbusaucuparia exhibited generalist behaviour with similar growthand performance across all stand treatments. Betula pubescensmaintained similar growth rates across stand types but was moresusceptible to insect damage in deeper shade. Overall, Alnusglutinosa grew more successfully than the other species andachieved highest mean growth rates in canopy break up (average44 per cent light) and stand initiation (average 71 per centlight) stages. Broadleaf establishment within pinewood standsis challenging on account of acidic nutrient-poor soil regimes,and in places, poor drainage, aggressive understorey competitionand canopies that restrict light availability and insect herbivory.Forest restoration techniques, including matching species tosite, accelerating establishment and using framework species(individuals of high field performance that are able to restoresite productivity and nutrient cycles), are discussed.     

Infection by Armillaria mellea and some Factors Affecting Host Resistance and the Severity of Disease

Infection by A. mellea in Britain occurs by means of rhizomorphs;the transfer of mycelium at root contacts is probably not importantas a means of spread. Following the initial phase of rhizomorphpenetration, established infection in the cambium is precededby ectotrophic spread of mycelium in the bark scales. Field investigation confirmed reports in the literature thatin susceptible conifers the greatest number of deaths generallyoccurs approximately 6–8 years after planting. However,attacks can also occur in much older crops and the reasons forthis are discussed. Inoculation experiments showed that suppressed trees and thoseexperiencing conditions of reduced light intensity are moresusceptible to infection than dominant trees and trees in fulllight. Species susceptibility in a variety of soils was studiedby inoculation of trees 20–30 cm tall. Of the coniferstested Pseudotsuga menziesii and Abies grandis were more resistantthan Picea abies, P. sitchensis, Larix kaempferi and Pinus sylvestris.Quercus robur and Fagus sylvatica were more resistant than allthe conifers except A. grandis. Soil type influenced diseasedevelopment and the proportion of trees infected was higherin an acidic sand soil than in an alkaline clay soil.     

Nursery Sterilization and Inoculation Regimes for Alder Production

Nursery experiments using common alder (Alnus glutinosa) toexamine the interaction of soil sterilization and inoculationwith Frankia are described. Seedling growth was stimulated whensoil was sterilized with methyl bromide or dazomet at currentrecommended rates, but nodulation was reduced. Inoculation withcultured Frankia or a crushed nodule suspension significantlyimproved nodulation, especially if the inoculant was appliedbefore seed germination. However, seedling growth was significantlylarger using cultured Frankia than the crushed nodule inoculant.If the latter is used to inoculate alder seedlings, a reductionin the recommended rate of dazomet application to c. 285 kgha^–1 is likely to encourage nodulation, though seedlinggrowth will be reduced slightly.     

THIRTY YEARS' DEVELOPMENT OF AFFORESTATION TECHNIQUES ON DIFFICULT GROUND TYPES IN SOUTH-WEST SCOTLAND

The development of ploughing, draining, planting, and the useof turfs and of phosphate is considered in detail for each oftwo main types. For Molinia lands, the 1952 technique securesadequate drainage and a very considerable turnover of turf,and here the spruces Picea abies Karst. and P. sitcbensis Carr.remain the first choice. For Calluna lands, the developmentof methods and the choice of species is more difficult. Thespruces refuse to grow pure and unnursed on the poorer Callunatypes and the use of Scots pine (Pinus sylvestris L.), P. contortaDoug., the Mountain pine (P. uncinata Ramond), Japanese larch(Larix leptolepis Gord.), and Douglas fir (Pseudotsuga taxifoliaBrit.) is discussed. The main requirements for successful afforestationof these ground types are summarized.     

An analysis of crown condition of Picea, Fagus and Abies in relation to environment in Switzerland

The health of Swiss forests is now being monitored at some 160permanent sites at 8 km intervals on a square grid. Data onthe conditions of the tree crowns in 1993 and on the soil, climate,and topography have been analysed to determine the extent towhich crown condition depends on these factors. Transparencywas the only widespread symptom of ill health or lack of vigour,and it was common in only three species, Picea abies (L.) Karst.,Abies alba Mill., and Fagus sylvatica L. Relations between transparencyand the environmental variables recorded were weak, and forFagus too weak to be of consequence. The strongest relationsare with the soil water holding capacity for Picea, and withwater holding capacity and carbonate content for Abies. It seemsthat the loss of leaves is the trees' natural physiologicalresponse to lack of water in the soil: drought is a sufficientexplanation for the observed crown condition. The results andinterpretation accord with those elsewhere in Europe in 1993.     

Variations in the Growth of Different Seeds of Acer pseudoplatanus and Betula verrucosa Grown on Different Soils

Seed of Acer pseudoplatanus was obtained from six widely scatteredlocations in Europe, and seedlings from these seed-sources weregrown on 25 different soils, covering a wide range of soil properties.Seedlings from four seed-sources of Betula verrucosa were alsogrown. There was a very wide variation in growth on the differentsoils, and between the two species; but relatively little variationbetween seed-lots within a species, and no significant interactionbetween seed-lot and soil, over the 2-year period of the experiment.It is concluded, therefore, that any one of the seed-lots usedin this experiment could have been used to assess the responseof seedlings of that species to changes in soil type, and thatvariation in growth due to genetic differences within thesespecies is likely to be small in comparison to the variationdue to soil conditions.     

Establishing forest tree species on peatland in a reflooded area of the Huleh Valley, Israel

The study evaluates the establishment performance of four treespecies (Ficus carica, Fraxinus syriaca, Salix acmophylla, Platanusorientalis) 3 years after planting in the peatland in the HulehValley. To develop good tree establishment and avoid uprooting,two types of soils were tested as alternatives for the rhizosphere.For each tree 6 m³ of soil (2 x 2 x 1.5 m) were replaced withriver bed alluvium or terra-rossa, in which the tree was planted.Control trees were planted directly in the peat. Changing therhizosphere soil type to river bed alluvium significantly improvedthe establishment and performance of Salix acmophylla and Fraxinussyriaca (survival, height, diameter and canopy shade area).Ficus carica was not affected by changing the soil in the rhizosphere,while Platanus orientalis was affected mainly in canopy shadearea. Terra-rossa improved establishment only of Salix acmophylla;it did not affect the other species.     

Species-specific drought effects on flower and fruit production in a Mediterranean holm oak forest

A holm oak forest was exposed to an experimental drought (reductionof 15 per cent soil moisture as predicted for this area forthe next decades by General Circulation Models and ecophysiologicalmodels) during 7 years to elucidate the reproductive responsesof the dominant species Quercus ilex L., Arbutus unedo L. andPhillyrea latifolia L. Soil moisture was partially reduced byplastic strips intercepting rainfall and by ditch exclusionof water runoff. During the period studied, meteorological conditionsand soil moisture were continuously monitored, together withflower and fruit production in the three dominant species. InQ. ilex and A. unedo, flower and specially fruit productionwere strongly correlated with annual rainfall, but not in P.latifolia. The experimental drought reduced flower and fruitproduction in Q. ilex by 30 per cent and 45 per cent, respectively.Reductions in flower and fruit production were not significantin A. unedo and were not observed in P. latifolia. A decreasein production of reproductive structures and the different responseof the species studied to a decrease in water availability couldinduce important changes in the competitive ability of the differentspecies and in the long term in the community species compositionand future distribution of these Mediterranean species.     

The effect of roots and litter of Calamagrostis canadensis on root sucker regeneration of Populus tremuloides

Marsh reed grass (Calamagrostis canadensis (Michx.) Beauv.)is a common, highly competitive grass native to the boreal mixedwoodforest. This grass increases in abundance after clear-cut loggingbut little is known about its effects on trembling aspen (Populustremuloides Michx.) sucker regeneration. The effects of Calamagrostissod and its litter on aspen regeneration were studied in twoseparate greenhouse studies. Calamagrostis sod did not affectthe initiation of suckers, but resulted in 30 per cent fewersuckers emerging above the soil that were smaller and had 40per cent less leaf area. Calamagrostis litter had little effecton the initiation and number of emerged suckers; however, itdelayed emergence by 10 days. The physical barrier by rootsand litter of Calamagrostis reduced or delayed the expansionof suckers and therefore prolonged their dependence on rootreserves. By the time the suckers reached the surface, theyhad to compete for light with Calamagrostis shoots that hademerged a week earlier. This, coupled with low soil temperaturesassociated with Calamagrostis in other experiments, will significantlyreduce the number and growth of suckers. Any reduction and delayin sucker emergence will decrease aspen regeneration and productivitysince the growing season in the boreal forest region is short.     

Effects of climate and management history on the distribution and growth of sycamore (Acer pseudoplatanus L.) in a southern British woodland in comparison to native competitors

Sycamore (Acer pseudoplatanus L.) is an invasive, non-nativespecies in Great Britain and its management in conservationareas is controversial. Climate change adds further uncertaintyto decision making. We investigated the role of management historyin determining present-day abundance and the effects of climaticvariability on growth, photosynthesis and phenology at WythamWoods, a UK Environmental Change Network (ECN) monitoring site.Relatively few sycamore trees were found in undisturbed ancient,semi-natural woodland and recent plantations, despite beingcommon in other areas of the site. Sycamore grew more slowlythan ash (Fraxinus excelsior L.), its principal competitor,but at a similar rate to pedunculate oak (Quercus robur L.)in the period 1993–2005. There were fewer sycamore thanash seedlings, regardless of which species dominated the canopy.Growth of sycamore was slower in dry periods than wet ones andlower photosynthetic rates were measured in canopy leaves underdry compared with wet soil conditions. This study thereforesuggests that sycamore does not present a serious threat toundisturbed ancient woodland on the site and that it may eventuallydecline in areas of the site where it competes with ash, inthe absence of disturbance. It may also decline under climatechange if summer droughts become more frequent.     

Initial recovery of compacted soil—planting and technical treatments decrease CO<Subscript>2</Subscript> concentrations in soil and promote root growth

Key message

The combination of technical treatments and planting of alder trees in a compacted forest soil improves the circulation of air and water through the pore system. This leads to decreases in CO ₂ concentrations and increases in root growth in the soil. Both are indicative of an initial recovery of soil structure.

Context

The compaction of forest soils, caused by forest machinery, has as a principal consequence: the destruction of soil structure and thus the reduction of the soil aeration status. Thus, the gas exchange between soil and atmosphere is reduced and the depth propagation of roots is limited, resulting in the shortage of water and nutrient supplies for trees.

Aims

This research aimed at detecting the first stages of recovery of soil structure in a compacted forest soil, which was treated with a combination of techniques (i.e., planting tree species, mulching, addition of lime), which could presumably accelerate the regeneration of soil structure.

Methods

The variation of CO₂ concentrations and the dynamics of root growth were repeatedly measured. Linear mixed models were developed in order to test the effects of the treatments and the planting of trees on soil aeration, as well as to identify the influence of the different environmental effects on CO₂ concentration in soil.

Results

The planting of root-active trees showed significant effects on decreases in CO₂ concentrations. However, during the short-term observation, some negative effects occurred especially for the mulched sites. Nevertheless, all applied technical treatments promoted an improved soil aeration and a higher root growth compared to untreated sites which points to an initial enhanced recovery of soil structure. Pronounced seasonal and interannual variations of soil respiration were highly influenced by soil temperature and soil water content variations.

Conclusion

An initial regeneration of soil structure is indicated by distinct changes of the soil aeration status. This regeneration is partially enhanced by the applied treatments. The quantitative potential of the regeneration techniques needs a longer observation period for mid- and long-term soil recoveries.

     

Thermal and Aeration Properties of Mor Layers in Finland

Thermal conductivity (K _T), air permeability (K _a) and relative diffusivity of oxygen (ratio of oxygen diffusion coefficient in the soil to the oxygen diffusion coefficient in free air, D/D ₀) were measured from undisturbed mor samples taken from low-fertility (CT) Scots pine (Pinus sylvestris L.) sites and medium-fertility (MT) Norway spruce (Picea abies (L.) Karst.) sites. K _T     

Shading Reduces both Visible and Invisible Frost Damage to Norway Spruce Seedlings in the Field

Two-year-old cuttings of Norway spruce were subjected to nightfrosts in spring on an exposed site in southern Sweden. Shadingwas used to assess the influence of sunlight on the extent ofdamage resulting from night frost. Chlorophyll fluorescencewas measured in needles in flushing shoots, and in shoots atthe stage of bud burst. The F_v:F_m ratio was significantly lowerfor plants exposed to light, compared with shaded plants onthe days following the night frost (minimum temperature –6°C).The effect was similar both in 1-year-old and current year needles.The low F_v:F_m ratios indicate damage to photosystem H, causedby an interaction between sub freezing temperatures and highlight intensity. Shading also increased the survival of flushingshoots. It is suggested that regeneration of Norway spruce onsites exposed to frost should be carried out in partial shade,for example under a shelterwood.     

GROWTH STIMULATION OF FOREST TREE SEEDLINGS BY THE ACTIVITY OF FREE-LIVING MYCORRHIZAL MYCELIA

Observations by the late Dr. M. C. Rayner on a field experimentand the results of subsequent pot-culture experiments demonstratethat the soil activity of mycorrhizal fungi can improve thedevelopment of forest tree seedlings (Picea, Pinus, Betula)before actual mycorrhizal infection takes place. Further experimentsshow that ectotrophic mycelia are capable of stimulating endotrophictree species (Fraxinus excelsior, Cbam?cyparis lawsoniana, Robiniapseudacacia), i.e. that these ectotrophic mycorrhiza-formersbring about growth stimulation of the plant although no infectionis formed at a later stage. It is suggested provisionally thatat least some ectotrophic mycelia, Boletus scaber and Rbizopogonluteolus, may influence seedling growth by attacking soil organicmatter and liberating ‘nutrients’ from which thehigher plant benefits.     

Sheet Mulching as an Aid to Broadleaved Tree Establishment: I. The Effectiveness of Various Synthetic Sheets Compared

In two experiments growth of ash (Fraxinus excelsior L. ) andhornbeam (Carpinus betulus L. ) transplants was greatly increasedby various synthetic sheet mulches. Killing the weeds with herbicidesbefore laying the mulches increased tree growth a little. Clearpolythene gave the highest soil temperatures and reduced ashsurvival. However, soil temperature appeared to have littleeffect on tree growth, tree growing well despite the low soiltemperatures induced by aluminium foil. The ability of the mulchto remain intact and resist weed invasion was more importantthan soil temperature. Opaque mulches were found to be preferableto translucent ones, since weeds grew beneath the latter anddislodged them. Tree growth was better with impermeable thanpermeable translucent mulches: it is suggested that this differencewas related to the mulches ability to retain moisture transpiredby the weeds beneath them. Practical recommendations for sheetmulching are made.     

A Phytotoxic Effect of Captan on the Growth of Conifer Seedlings

Captan was found to have an inhibitory effect on the seedlinggrowth of Picea sitchensis, Pinus sylvestris, and Tsuga heterophylla.A single application of captan reduced the rate of shoot growthfor at least two weeks, with a further decrease after a secondtreatment. Seedlings grown in sand appeared to be more adverselyaffected than those grown in soil. Weights of root, shoot, andleaves were all reduced in treated plants grown in sand. Nophytotoxic effects were detected when captan was applied totomato, barley, or cress seedlings grown in either sand or soil. It is suggested that the use of captan should be avoided duringgrowth analysis experiments on conifer seedlings, or, if fungalproblems make its use desirable, experimentation should be delayedfor at least three weeks after treatment.     

Cherry Leaf Roll Virus in Juglans regia in the United Kingdom

Cherry leaf roll virus (CLRV) was detected in foliage, pollenor seeds of 43 of 113 mature/overmature Juglans regia L.; twohad foliar yellow-brown ring patterns whereas seven other infectedtrees had leaf necroses. Male catkins of a few infected treeswere malformed and blackened. Infection was rare (3/43) in the widely scattered J. regia ofnorthern England and Scotland, but commoner (40/70) in southernEngland. When J. regia seed was grown in methylbromide treated soil,six per cent (18/300) of the seedlings were symptomlessly infected.Four out of ten groups of imported seedlings were infected toa similar extent, CLRV being present in a total of 40 out of1146 trees aged five years or less. When 3 years old, CLRV infectedJ. regia were shorter and thinner than healthy seedlings. CLRV from walnut was serologically distinguishable from Betula,Prunus, Cornus and Sambucus isolates. One English walnut isolate(Ox) was distinguishable from two Italian walnut isolates. Anisolate (Sr) of CLRV obtained in Finland from Sambucus racemosaL. was antigenically distinct from S. ebulus and S. nigra isolates.     

Controlling Rhododendron spp. in the Turkish Black Sea Region

Rhododendrons (Rhododendron ponticum L. and Rhododendron luteumSweet) dominate the understories of the mesic forests of theBlack Sea Region (BSR) of Turkey. They dramatically reduce forestgrowth and regeneration and local plant diversity. This paperreports the results of a large rhododendron control experimentestablished on two different sites in the western and easternBSR of Turkey 5 years after treatments (YAT). The paper alsopresents the second-year results of a second experiment in whichthe foliar herbicides of the previous experiment were testedon rhododendron at much lower rates on a western BSR site. FiveYAT, grubbing and foliar spraying were still the best rhododendroncontrol methods in the first experiment. Cut-stump sprayingprovided an intermediate level of woody control. Hand-cuttingwas ineffective on R. ponticum and did not significantly differfrom the control treatment in rhododendron basal area 5 YAT.The performance ratings of foliar triclopyr ester and imazapyrfor woody control in both experiments were rate dependent. Athigh rates ranging between 2.6 and 5.8 kg ae ha^–1, foliarimazapyr controlled both rhododendron species significantlybetter than foliar triclopyr ester in the first experiment,suggesting enhanced imazapyr translocation to the roots. Someoff-target damage was observed in the beech overstory for imazapyrat high rates. The performance ratings of these foliar herbicideswere significantly reversed in the second experiment 2 YAT,where much lower rates were used (0.3–2.0 kg ae ha^–1)than in the first experiment. Insufficient imazapyr accumulationin rhododendron roots might account for the poor impact of thisherbicide. No beech damage was apparent from any of the herbicidesin the second experiment. The low-rate foliar triclopyr esteris recommended for effective and cost-efficient rhododendroncontrol.     

CONIFEROUS LITTER AMENDMENTS AND THE GROWTH OF SITKA SPRUCE

The growth of semi-checked Sitka spruce (Picea sitcbensis Carr.)on heathland has been stimulated to different degrees by theannual application of litter of Scots pine (Pinus sylvestrisL.), Corsican pine (P. nigra var. calabrica Schneid), Lodgepolepine (P. contorta Dougl.), Japanese larch (Larix leptolepisGord.), and Sitka spruce, at rates corresponding to normal plantationconditions, following an initial heavier rate. Foliar analysissuggests that the response is at least partially attributableto the influence of the litters on the nitrogen nutrition ofthe spruce and differences between litters appear to be largelydetermined by their total nitrogen contents. In this respect,Japanese larch, with an annual needle fall generally greaterthan that of the pines and a higher nitrogen content, offersthe best promise as a nurse species for spruce.