Forest management, coarse woody debris and saproxylic organisms: Fennoscandian boreal forests as an example

The purpose of this chapter is to describe a conceptual framework for understanding how trees grow and how they and other perennial plants defend themselves. The concept of compartmentalization has developed over many years, a synthesis of ideas from a number of investigators. It is derived from detailed studies of the gross morphology and cellular anatomy of the wood and bark of roots and stems in healthy angiosperms and gymnosperms. It is based on research in tree physiology and the chemistry of wood and bark. It is founded on observations of trees injured in the field by wind, snow, ice, fire, animals, and insects, as well as during pruning, coppicing, sugaring, and other forest and orchard management practices. It is based on experimental studies of natural and artificial wounds with and without controlled inoculations with selected pathogenic and saprophytic microorganisms. These microbes have included wood-decaying Basidiomycetes and Ascomycetes, wood-staining Ascomycetes and Fungi Imperfecti, canker fungi, and a myriad of woodinhabiting bacteria. The end result of all these studies is an integrating concept that involves defenses laid down by trees prior to injury and defenses laid down by trees after injury.

https://www.fs.fed.us/nrs/pubs/jrnl/1984/ne_1984_shigo_001.pdf

Compartmentalization: A Conceptual Framework for Understanding How Trees Grow and Defend Themselves

summary
The wood (xylem) in a living tree is protected from microbial attack by the secondary plant surface (periderm and rhytidome), which provides an effective barrier preventing the entry of most potential pathogens, and by constitutive and induced defence mechanisms in the bark (cortex and phloem). Although a few pathogens are able To penetrate these outer tissues directly, most xylem pathogens gain entry through wounds that expose this tissue and render it more vulnerable to attack. In functional sapwood, microbial colonization might be restricted by active defence mechanisms, or by passive microenvironmental restriction consequent upon the high water content and low availability of O2 in healthy conductive xylem. These factors are not mutually exclusive: indeed, they may operate in concert in many host-pathogen interactions. Sapwood lesions made by wood-decaying fungi are characteristically bounded by multiccllular walls OT barrier zones (compartmentalization wall 4 barriers and reaction zones (column boundary layers)), which may function both as inhibitory or degradation-resistant barriers to further pathogen spread, and as seals to maintain xylem function and prevent the drying and aeration that could predispose to further infection. A range of putative antimicrobial defence mechanisms contributing to the effectiveness of such barriers has been identified in sapwood tissues. This includes cell wall alterations, constitutive and induced antimicrobial compounds, necrotic responses of living cells and the deposition of gummy materials, often resinous or polyphenolic, at the host-pathogen interface. Nutritional, environmental and anatomical features of living wood might also contribute to pathogen restriction. Although there might be differences in detail, the defences operating in gymnospenns and angiosperms are generally similar. Defence responses against a variety of pathogen categories also have much in common. Dynamic studies are crucial in elucidating the roles of the various components of the host-pathogen interaction in the wood of living trees. A model for the protection and defence of xylem tissues in woody angiosperms is suggested, based largely upon results from dynamic studies of host-pathogen interactions in the wood of sycamore (Acer pseudoplatanus L.).

Antimicrobial defences in the wood of living trees

A systematic study was made of the endophytes of Azadirachta indica A. Juss (the neem tree) growing in several of its natural habitats in India. A total of 233 isolates of endophytic fungi representing 18 fungal taxa were obtained from segments of bark, stem, and leaves of this tree. Hyphomycetes (62.2%) were the most prevalent followed by the Coelomycetes (27.4%) and Mycelia Sterilia (7.7%). As mathematically determined, the maximum species richness and frequency of colonization of endophytes appeared in leaf segments rather than stem and bark tissues from each location. Endophytic colonization frequency was also greater in leaves (45.5%) than bark (31.5%). The leaf samples from all locations were nearly constant in their endophytic composition, whereas bark samples showed maximum diversity at different locations. Inter-site comparisons for endophytic diversity, however, were not significantly different with Loc1 and Loc2 having a maximum of 66.67% Jc. The smallest similarity was between Loc2 and Loc3 of 54.17% Jc. The dominant endophytic fungi isolated were Phomopsis oblonga, Cladosporium cladosporioides, Pestalotiopsis sp., Trichoderma sp, and Aspergillus sp. Genera such as Periconia, Stenella, and Drechslera are reported here for the first time as endophytes from this host plant. This report illustrates the value of sampling different tissues of a given plant in several locations to obtain the greatest species diversity of endophytes. The rich and sizeable collection of endophytic fungi from this specific plant may represent a unique source of one or more of the interesting and useful bioactive compounds normally associated with A. indica such as the azadirachtins and related tetranortriterpenoids.

The endophytic mycoflora of bark, leaf, and stem tissues of Azadirachta indica A. Juss (neem) from Varanasi (India).

Isolations of microorganisms were made from the sapwood of Norway spruce (Picea abies) (L.) Karst. infested by the spruce bark beetle Ips typographus L. The most important group of fungi isolated, the species of Ophiostomataceae, is treated. Ten species were isolated, of which Ophiostoma polonicum Siem. appears to be the most active invader of the sapwood. Three new species are described, Ophiostoma ainoae sp. nov., O. flexuosum sp. nov. and O. cucullatum sp. nov. and three new combinations are proposed, O. davidsonii (Olchow. & Reid.) comb. nov., O. europhioides (Wright & Cain) comb. nov. and O. sagmatospora (Wright & Cain) comb. nov.

Species of Ophiostomataceae isolated from Picea abies infested by the bark beetle Ips typographic

Ascomycetes, Fungi imperfecti, and Bacteria invading experimentally created wounds on stems of 55–60 years old Picea abies were studied after 1,2, and 4 years. The effect of wounding season, number of years since wounding, tree diameter class, height above ground, size and depth of the wounds is discussed. A general discussion is given of all isolated microorganisms, the Hymenomycetes included. Mutual influence of microorganisms is discussed.

Microorganisms which invade Picea abies in seasonal stem wounds. II. Ascomycetes, Fungi imperfecti, and Bacteria. General discussion, Hymenomycetes included.

Various pine species and provenances attacked by Scleroderris lagerbergii are reviewed with respect to their resistance. Pinus aristata is a new host. Introduced pine species may often become attacked if the ecological conditions in the new localities are different from those occurring under natural circumstances. Usually local provenances are more resistant than southern ones, but less resistant than more northern ones.

Scleroderris lagerbergii: Resistance and differences in attack between pine species and provenances

Field studies of damage and mortality were carried out through 16 years in six young plantations, mostly of Pinus contorta, but also P. sylvestris and P. sibirica. Differences between pine species, P. contorta provenances, sites, and soil treatments are reported and discussed, as are influences of environment, climatic conditions, snow cover, and nutrient deficiency. Gremmeniella abietina was by far the most important cause of mortality; there were great differences between the sites as to development and seriousness. Other important causes of mortality and damage were Phacidium infestans, elk (Alces alces L.), voles, and snow pressure.

Gremmeniella abietina, Phacidium infestans, and other causes of damage in alpine, young pine plantations in Norway

Melampsoridium betulinum from Betula verrucosa was found able in infection experiments to infect Alnus barbata, A. cordata, A. glutinosa, A. incana, A. orientalis, A. rhombifola, and A. viridis. Melampsoridium collections on Alnus spp. in Norway, Finland, Scotland, and Ireland were identified with M. betulinum. Alnus species seem to be poorer hosts for M. betulinum than the Betula species. M. alni is conspecific with M. betulinum.

Melampsoridium on Alnus in Europe. M. alni conspecific with M. betulinum

Cultivars of Paeonia differed widely in their resistance to Cronartium flaccidum in Norway; ‘Globe of Light’ and ‘Noemie Demay’ were found to be immune. The practical importance for silviculture and horticulture is discussed.

Resistance of Paeonia cultivars to Cronartium flaccidum in Norway

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