Occurrence of Phytophthora species in riparian stands of black alder (Alnus glutinosa) in Slovakia

During the monitoring period of alder decline phenomenon in Slovakia, indicative symptoms of Phytophthora diseases were observed in riverside stands in Slovakia. The study aimed to test the presence and diversity of Phytophthora species in declining alder stands. The samples were collected from six stands situated by rivers/streams in the central and eastern parts of Slovakia. Phytophthora plurivora and P. cactorum were detected in soil, root and water samples. The most isolated species was P. plurivora. Both Phytophthora species have been recognized in the literature as the perpetrators of black alder dieback together with other species, such as P. alni or P. polonica. To our knowledge, this is the first report of P. plurivora and P. cactorum in riverside stands with the main share of black alder in Slovakia.     

Susceptibility of silver birch and black alder to several Phytophthora species isolated from soils in declining broadleaf forests in western Ukraine

In declining broadleaf forests in western Ukraine, several Phytophthora species including P. plurivora, P. bilorbang, P. polonica, P. gonapodyides and P. cactorum were recovered using soil baiting assays and identified using morphological and molecular methods. Pathogenicity tests of selected isolates were performed on black alder (Alnus glutinosa (L.) Gaerth.) and silver birch (Betula pendula Roth.) to assess susceptibility of these two tree species to the newly detected Phytophthora species. Phytophthora plurivora, P. bilorbang and P. polonica showed higher pathogenicity in both alder and birch compared to the other tested Phytophthora species.     

Pathogenicity of Phytophthora species to Pacific Northwest Conifers

Phytophthora root rot is described for the first time killing sugar pine (Pinus lambertiana) in a seed orchard and four species of true fir (Abies spp.) in a forest nursery. P. cactorum was recovered from true firs and P. megasperma was recovered from sugar pine. P. cryptogea was recovered from sugar pine and true fir but isolates from the two locations differed from each other in pathogenicity and colony appearance. Isolates recovered from these hosts and isolates of 6 Phytophthora species previously recovered from Douglas-fir (Pseudotsuga menziesii) were then tested for pathogenicity on seedlings of 9 Northwest conifers. P. megasperma Group 1, P. cryptogea, and P. cinnamomi were pathogenic to all tree species except western redcedar (Thujaplicata). Western hemlock (Tsuga heterophylla) and true firs were susceptible to most species tested; ponderosa (P. ponderosa) and sugar pines were damaged only by P. cryptogea and P. cinnamomi; western redcedar was resistant to all isolates.     

Red alder leaf decomposition and nutrient release in alder and conifer riparian patches in western Washington,USA

Current management practices encourage conversion of red alder (Alnus rubra) riparian forests to conifers in the Pacific Northwest U.S. Patches of young naturally regenerated conifers are commonly present in alder dominated riparian areas and an understanding of the soil processes in these patches will be helpful in guiding future riparian management. Study objectives were to: (1) determine decomposition rates of red alder leaves in riparian alder and conifer patches, (2) relate decomposition rates to environmental factors and litter chemistry, and (3) determine nutrient release from decomposing alder leaves in these patches. Study sites were riparian areas adjacent to Brown and Le Bar creeks in the Skokomish River basin, Olympic National Forest, Washington. Red alder leaves were placed in litterbags in red alder and conifer riparian patches along each stream in November 2000 and collected after 1 and 3 years. There was rapid mass loss of alder leaves in the first year in both patch types, but decomposition was significantly faster (p < 0.05) in alder patches (43.2% mass remaining, k = 0.855 year⁻¹) than in conifer patches (48.4% mass remaining, k = 0.734 year⁻¹). There was little mass loss after the first year and no significant difference in decomposition rates. After 3 years mass remaining was 44.2% (k = 0.283 year⁻¹) and 47.8% (k = 0.48 year⁻¹) in alder and conifer patches, respectively. Decomposition rate differences were attributed more to the effects of the different litters in each patch and the influence on soil microbial and faunal communities than differences in soil temperature and moisture. The forest floor was deeper in conifer patches (3.7 cm) than alder (1.8 cm) patches. This was ascribed to slower decomposition rates in conifer patches, greater litterfall in conifer patches, and/or removal of alder surface litter by flooding. Alder patches were lower in elevation (0.8 m above bankfull width) than conifer patches (2.2 m). Forest floor and soil C and N concentrations and pHs were not significantly different in alder and conifer patches. Nutrient release from decomposing alder leaves was not significantly different in conifer and alder patches, although there was a trend for C, N, P, K, and Ca to be lost faster from leaves in alder patches than conifer patches in the first year. Red alder litter input to riparian conifer patches will initially decompose rapidly and provide nutrients, particularly N and P to conifers, as well as enhancing soil C since long-term decomposition rates are slow.     

The impact of Phytophthora disease on riparian populations of common alder (Alnus glutinosa) in southern Britain

In 1994 a survey was established to obtain information on Phytophthora disease of common alder (Alnus glutinosa) on the riverbanks of southern England and east Wales. Within an area of 70 000 km² 63 observation plots were set up on stretches of river over 8 m wide. Average alder densities varied widely in different parts of the survey area; from 0.7 to 22.2 trees per 100 m of river. From the density figures and data on the total length of rivers over 8 m wide within the survey area, it was estimated that there were approximately 585 000 alder trees growing on the banks of such rivers. In 1994 3.9% of the trees showed crown symptoms of Phytophthora disease, and an additional 1.2% of trees were dead, although not all of these had been killed by Phytophthora. The disease occurred widely through the survey area with an indication that the highest percentage of affected trees was to be found in the south-east of England. Subsequent surveys showed that the combined percentage of symptomatic and dead trees rose to 6.0% in 1995 and to 7.9% in 1996. In the latter year, for an alder population of 585 000 trees, this would correspond to 32 800 symptomatic and 13 500 dead trees. The percentage of trees showing symptoms was seven times as high in trees growing within 1 m of the riverbank as in trees growing between 1 and 10 m of the bank. An examination of the relationships between disease incidence and various indices of water pollution revealed a positive association with total oxidized nitrogen. These results are discussed in relation to the biology and possible origin of the disease.     

Pathogenicity of Phytophthora species and Pythium undulatum isolated from Abies procera Christmas trees in Ireland

Phytophthora cryptogea, Phytophthora cinnamomi, Phytophthora cambivora, Phytophthora megasperma and Pythium undulatum were isolated from diseased Noble fir (Abies procera) seedlings and soil associated with dead Noble fir in Ireland. Seedlings of four Christmas tree species (A. procera, Picea sitchensis, Picea abies and Pinus contorta) were inoculated with these oomycetes to test their pathogenicity and the susceptibility of the various tree species. Phytophthora spp. and Pythium undulatum caused root rot on all tree species. Disease symptoms included reddish brown cambial discoloration, crown symptoms, brown foliage, dark brown roots, root rot and seedling mortality. These symptoms were similar to those observed on Noble fir in naturally infested plantations. Pythium undulatum appeared as the most virulent pathogen followed by P. cinnamomi, P. cambivora, P. megasperma and P. cryptogea. Noble fir showed to be most susceptible and lodgepole pine most tolerant while Sitka spruce and Norway spruce were intermediate.     

Phytophthora cambivora in Oregon and its pathogenicity to Chrysolepis chrysophylla

A new canker disease causing mortality of golden chinquapin trees [Chrysolepis chrysophylla (Dougl.) Hjelmqvist], in Oregon was recently observed. Most of the symptomatic or dead trees were located near roads. The cankers on the lower boles of trees are similar to those caused by species of Phytophthora on other trees in western North America. The cankers in the inner bark were reddish‐orange in colour and extended upward from necrotic roots. Phytophthora cambivora (Petri) Buisman was isolated from the cankers; identity was confirmed by morphological comparison with known isolates and internal transcribed spacer sequence analysis. Pathogenicity was confirmed by inoculation of chinquapin seedlings and mature trees. Seven of nine isolates from chinquapin were A2 mating type; 27 of 28 isolates from other hosts in Oregon and Washington were A1 mating type.     

First report of Phytophthora pseudosyringae recovered from aquatic ecosystems in Bulgaria

Two Phytophthora pseudosyringae isolates were recovered from aquatic ecosystems in Bulgaria during a two‐year investigation of Phytophthora distribution in water sources in the country. Isolate RVit2016/6d was derived from Boyana Lake at the Vitosha Mountain, whereas isolate RTr2016/32d was obtained from Erma River at the Ruy Mountain. Both isolates belong to P. pseudosyringae species according to their morphological and physiological characteristics, as well as to the DNA sequence analysis of the internal transcribed spacer (ITS) region. The pathogenicity of the isolates to wild cranberry plants (Vaccinium vitis‐idea) was studied by detached leaves experiments and in planta. Both P. pseudosyringae isolates were able to cause leaf necrosis and death of plants within 3 months. The ability of the pathogens to infect cranberry leaves at different temperatures was also investigated. The significance of P. pseudosyringae species and its potential threat for forest ecosystems is discussed. To our knowledge, this is the first report of P. pseudosyringae isolation in Bulgaria.     

Occurrence and diversity of Phytophthora species in declining broadleaf forests in western Ukraine

In western Ukraine, forest decline and dieback of several broadleaved tree species have become increasingly evident during recent years, and surveys in some areas have shown symptoms indicative of Phytophthora infections. In this study, we aimed to determine the occurrence and diversity of Phytophthora species associated with several broadleaved tree species (Alnus glutinosa, Betula pendula, Castanea sativa, Fagus sylvatica and Quercus robur) from forest stands where dieback has been observed. Rhizosphere soil samples were collected from 14 forest stands during 2017 and 2018 and tested for the presence of Phytophthora species using morphological and molecular methods. Seven Phytophthora species (P. bilorbang, P. cactorum, P. gallica, P. gonapodyides, P. lacustris, P. plurivora and P. polonica), and two other clade six taxa were detected from the various forest types, several of which are probable agents responsible for decline. Four of the Phytophthora species (P. bilorbang, P. gallica, P. plurivora and P. polonica) have previously never been reported from broadleaf forests in Ukraine.     

Pathogenicity of Phytophthora multivora to Eucalyptus gomphocephala and Eucalyptus marginata

Phytophthora multivora is associated with the rhizosphere of declining Eucalyptus gomphocephala, Eucalyptus marginata and Agonis flexuosa. Two pathogenicity experiments were conducted. The first experiment examined the pathogenicity of five P. multivora isolates and one Phytophthora cinnamomi isolate on the root systems of E. gomphocephala and one P. multivora isolate on the root system of E. marginata. In the second experiment, the pathogenicity of P. multivora to E. gomphocephala and E. marginata saplings was measured using under‐bark stem inoculation. In Experiment 1, the P. cinnamomi isolate was more aggressive than all P. multivora isolates causing significant loss of fine roots and plant death. Two P. multivora isolates and the P. cinnamomi isolate caused significant losses of E. gomphocephala fine roots 0–2 mm in diameter and significantly reduced the surface area of roots 0–1 mm in diameter. One P. multivora and the P. cinnamomi isolate significantly reduced the surface area of roots 1–2 mm in diameter. Two of the P. multivora isolates significantly reduced the number of E. gomphocephala root tips. In E. marginata, the length and surface area of roots 0–1 mm in diameter and number of root tips were significantly reduced by P. multivora infestation. Rhizosphere infestation with the P. multivora isolates and P. cinnamomi isolate on E. gomphocephala, and one P. multivora isolate on E. marginata, did not significantly influence the foliar nutrient concentrations. In Experiment 2, under‐bark inoculation with P. multivora caused significant lesion extension in E. gomphocephala and E. marginata saplings, compared to the control. We propose that P. multivora is inciting E. gomphocephala and E. marginata decline by causing fine root loss and subsequently interfering with nutrient cycling throughout the plant. The impact of fine root loss on the physiology of plants in sites infested with P. multivora requires further research.     

Structural and compositional controls on transpiration in 40- and 450-year-old riparian forests in western Oregon, USA

Large areas of forests in the Pacific Northwest are being transformed to younger forests, yet little is known about the impact this may have on hydrological cycles. Previous work suggests that old trees use less water per unit leaf area or sapwood area than young mature trees of the same species in similar environments. Do old forests, therefore, use less water than young mature forests in similar environments, or are there other structural or compositional components in the forests that compensate for tree-level differences? We investigated the impacts of tree age, species composition and sapwood basal area on stand-level transpiration in adjacent watersheds at the H.J. Andrews Forest in the western Cascades of Oregon, one containing a young, mature (about 40 years since disturbance) conifer forest and the other an old growth (about 450 years since disturbance) forest. Sap flow measurements were used to evaluate the degree to which differences in age and species composition affect water use. Stand sapwood basal area was evaluated based on a vegetation survey for species, basal area and sapwood basal area in the riparian area of two watersheds. A simple scaling exercise derived from estimated differences in water use as a result of differences in age, species composition and stand sapwood area was used to estimate transpiration from late June through October within the entire riparian area of these watersheds. Transpiration was higher in the young stand because of greater sap flux density (sap flow per unit sapwood area) by age class and species, and greater total stand sapwood area. During the measurement period, mean daily sap flux density was 2.30 times higher in young compared with old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. Sap flux density was 1.41 times higher in young red alder (Alnus rubra Bong.) compared with young P. menziesii trees, and was 1.45 times higher in old P. menziesii compared with old western hemlock (Tsuga heterophylla (Raf.) Sarg.) trees. Overall, sapwood basal area was 21% higher in the young stand than in the old stand. In the old forest, T. heterophylla is an important co-dominant, accounting for 58% of total sapwood basal area, whereas P. menziesii is the only dominant conifer in the young stand. Angiosperms accounted for 36% of total sapwood basal area in the young stand, but only 7% in the old stand. For all factors combined, we estimated 3.27 times more water use by vegetation in the riparian area of the young stand over the measurement period. Tree age had the greatest effect on stand differences in water use, followed by differences in sapwood basal area, and finally species composition. The large differences in transpiration provide further evidence that forest management alters site water balance via elevated transpiration in vigorous young stands.     

Phytophthora ×alni and Phytophthora lacustris associated with common alder decline in Central Portugal

Since the early 1990s, an emerging disease induced by the highly aggressive oomycete Phytophthora ×alni has caused widespread alder decline across Europe. In parallel, P. lacustris, a recently described species associated with riparian habitats, has been subject of increasing interest. A field survey conducted in 2014 showed high mortality rates in alder stands located in the riparian gallery along two rivers in Central Portugal. The pathogens isolated from necrotic alder stem base during this study were identified as P. ×alni and P. lacustris. This paper is the first to report the occurrence of P. lacustris in Portugal and presents the first finding of P. ×alni affecting mature trees in natural ecosystems located in Central Portugal.     

Response of old-growth conifers to reduction in stand density in western Oregon forests

The positive growth response of healthy young trees to density reduction is well known. In contrast, large old trees are usually thought to be intrinsically limited in their ability to respond to increased growing space; therefore, density reduction is seldom used in stands of old-growth trees. We tested the null hypothesis that old-growth trees are incapable of responding with increased growth following density reduction. The diameter growth response of 271 Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), ponderosa pine (Pinus ponderosa Dougl. ex Laws) and sugar pine (Pinus lambertiana Dougl.) trees ranging in age from 158 to 650 years was examined 20 to 50 years after density reduction. Density reduction involved either light thinning with removal of less vigorous trees, or shelterwood treatments in which overstory trees were not removed. Ratios of basal area growth after treatment to basal area growth before treatment, and several other measures of growth, all indicated that the old trees sometimes benefited and were not harmed by density reduction. Growth increased by 10% or more for 68% of the trees in treated stands, and nearly 30% of trees increased growth by over 50%. This growth response persisted for at least 20 years. During this 20-year period, only three trees in treated stands (1.5%) exhibited a rapid decrease in growth, whereas growth decreased in 64% of trees in untreated stands. The length of time before a growth response to density reduction occurred varied from 5 to 25 years, with the greatest growth response often occurring 20 to 25 years after treatment. These results have important implications both for the basic biology of aging in woody plants as well as for silvicultural practices in forests with old-growth trees.     

Relative susceptibility of oaks to seven species of Phytophthora isolated from oak forest soils

Isolates of Phytophthora cambivora, P. cinnamomi, P. citricola, P. europaea, P. quercetorum and two unidentified species were tested for their pathogenicity to eastern US oak species by root and stem inoculations. Experiments were conducted during two different periods and included 1‐, 2‐ and 20‐year‐old oaks grown under greenhouse and field conditions. Species of Phytophthora were pathogenic in varying degrees to the oak species tested. All species were pathogenic to fine and taproots of at least one oak species. The fine root damage caused by the species of Phytophthora ranged from 9 to 55% when compared to the controls. Roots were more susceptible during the fall inoculation period than the summer. With exception of Phytophthora sp1 and P. quercina‐like, all species of Phytophthora were pathogenic to oak stems with P. cinnamomi and P. citricola being the most aggressive. Quercus montana and Q. rubra were the most susceptible oak species to stem inoculation. Lesion sizes were considerably larger when 20‐year‐old trees were inoculated. Generally, no significant differences in lesion sizes were detected in greenhouse tests when the summer and fall inoculation periods were compared. However, on 2‐year‐old field‐grown seedlings, lesion sizes were considerably smaller or not significantly different from controls during the fall inoculation period, suggesting lower, late season temperatures may restrict lesion development.     

Foliar susceptibility of eastern oak species to Phytophthora infection

Seven different Phytophthora species were used to test the foliar susceptibility of the common eastern US oak species and understory plants to Phytophthora infection. The Phytophthora species employed were Phytophthora cambivora, Phytophthora cinnamomi, Phytophthora citricola, Phytophthora europaea, Phytophthora quercetorum, Phytophthora quercina‐like and Phytophthora sp1. Inoculation of detached‐leaves with agar plugs containing mycelia of Phytophthora provided an estimate of their relative susceptibility. Lesions were always greater when foliage was wounded and young. On deciduous plants, lesion sizes were considerably reduced with the increasing foliar age, although with evergreen plants lesion sizes remained similar regardless of foliar age when more aggressive isolates were tested. Infections seldom resulted when foliage was not wounded. With young and mature foliage, P. citricola usually produced the largest lesions. Young foliage of Quercus rubra was the most susceptible to infection followed by Castanea dentata for both wounded and non‐wounded inoculations. Mature foliage of Hamamelis virginiana, Kalmia latifolia and Quercus alba were the most susceptible to wound and non‐wound inoculations.     

Western Oregon forest landowner beliefs about the outcomes of mandatory riparian buffer regulations

Research about nonindustrial private forest (NIPF) landowners’ perspectives on voluntary conservation-based programs continues to proliferate. However, there is a gap in understanding NIPF landowner perspectives about the social and ecological outcomes of mandatory conservation-based regulations. We sent questionnaires to Oregon NIPF landowners to understand their beliefs about potential outcomes of proposed state regulations that strengthen mandatory riparian buffer habitat protection requirements. Factor analysis and multiple regression techniques revealed the most important variables that influence those beliefs. Overall, respondents believed that the socioeconomic outcomes were negative and the ecological outcomes were neutral or slightly positive. Respondents with more conservative political attitudes who owned larger properties were more likely to believe that the outcomes would be negative. As the importance of maintaining property for future generations and increasing timber productivity increased, respondents believed the potential outcomes would be increasingly negative. As the importance of improving water quality, increasing carbon storage, and improving recreational use on the property increased, respondents believed that the outcomes would be increasingly positive. We discuss management and policy implications, including communication strategies aimed at engaging with NIPF landowners to highlight the purpose and potential outcomes of forest and riparian management regulations.     

Phytophthora disease of alder (Alnus glutinosa) in France: investigations between 1995 and 1999

A severe decline of alder associated with an undescribed Phytophthora species was identified for the first time in England in 1993. No generalized decline of alder was reported in France before 1990. The first diebacks and mortalities of common alder were observed at the beginning of the 1990s, but the so‐called alder Phytophthora was not isolated in France until 1996. First, a synthesis about alder declines that were known in France before 1995 is presented. Then, a survey was established in north‐eastern France; 108 sites were visited and the alder Phytophthora was isolated from 57 of them. All the main rivers were found to be affected and damage levels are significant along some of them. The frequency of the alder Phytophthora and other fungi isolated from declining alders is discussed. Finally, information on other alder declines in France is presented region by region, and a map summarizes the known distribution of the disease. The alder Phytophthora is quite common and widespread in France, with western and north‐eastern France being especially affected; however, the number of diseased or dead trees varies greatly from one site to another. All records are from Alnus glutinosa; other Alnus species were seldom seen in the surveys.     

The responses of three riparian cottonwood species to water table decline

The influence of rate of water table decline was studied with three North American cottonwood (poplar) species: the prairie cottonwood, Populus deltoides; the narrowleaf cottonwood, P. angustifolia; and the balsam poplar, P. balsamifera. Shoot cuttings were rooted and transplanted into rhizopods, experimental devices that permit the controlled manipulation of water table depth. Three rates of water table decline were applied, 0, 4 and 10 cm day⁻¹, and growth and transpiration were studied.

Two clones of each species performed relatively similarly; the P. balsamifera clones grew fastest under all three treatments, followed by P. deltoides under 0 and 4 cm day⁻¹ conditions. Under the 10 cm day⁻¹ treatment, the P. deltoides grew as slowly as P. angustifolia. In all genotypes, shoot growth and apparent transpiration were progressively reduced with increasing rate of water table decline. Conversely, root growth was promoted by water table decline and root elongation was most rapid under the gradual 4 cm day⁻¹ treatment; root elongation was insufficient for the abrupt 10 cm day⁻¹ decline and some P. angustifolia and P. deltoides saplings died under that treatment.

The present study demonstrates that tolerance to water table decline varies across cottonwood genotypes and that P. balsamifera saplings were the most vigorous. This is relevant to the natural distribution in which P. balsamifera occurs in mountain regions where stream stages and riparian water table depths often change abruptly. The vigor of P. balsamifera is also consistent with the reproductive mechanism of ‘branch propagation', a process of clonal recruitment in which browsed or broken branch fragments root along stream edges, enabling dispersive propagation, particularly of P. balsamifera and P. trichocarpa.     

Response of vegetation, shade and stream temperature to debris torrents in two western Oregon watersheds

This study examines watershed patterns of riparian vegetation, shade, and stream temperature eight years after extreme storm events triggered numerous debris torrents throughout the Pacific Northwest. We examined twelve impacted streams in two western Oregon watersheds: the Calapooia River in the western Cascades and the Williams River in the Coast Range. Red alder (Alnus rubra) and willow (Salix spp.) were the dominant species on debris torrented areas in both watersheds. Post-disturbance vegetation recovery was significant in both watersheds, impacting shade and stream temperatures. However, red alder density, basal area, and height were significantly greater along streams in the Williams River watershed than along streams in the Calapooia River watershed. Willow density, basal area and height were similar between the watersheds. Stream shading levels mirrored red alder growth, with greater average shading in the Williams River watershed. The greater shade translated into lower summer maximum stream temperatures and maximum diurnal stream temperature fluctuations in the Williams River as compared to the Calapooia River watershed. Minimum stream temperatures were not different between the two watersheds. The rapid re-growth of red alder along the Williams River watershed ultimately lead to a rapid decline in maximum summer stream temperatures for that watershed compared to the Calapooia River watershed. The location where the disturbance occurred had an important role in determining the rate and pathway of stream recovery.