Arthropods and pathogens damage leaves in natural ecosystems and may reduce photosynthesis at some distance away from directly injured tissue. We quantified the indirect effects of naturally occurring biotic damage on leaf-level photosystem II operating efficiency (ΦPSII) of 11 understory hardwood tree species using chlorophyll fluorescence and thermal imaging. Maps of fluorescence parameters and leaf temperature were stacked for each leaf and analyzed using a multivariate method adapted from the field of quantitative remote sensing. Two tree species, Quercus velutina and Cercis canadensis, grew in plots exposed to ambient and elevated atmospheric CO2 and were infected with Phyllosticta fungus, providing a limited opportunity to examine the potential interaction of this element of global change and biotic damage on photosynthesis. Areas surrounding damage had depressed ΦPSII and increased down-regulation of PSII, and there was no evidence of compensation in the remaining tissue. The depression of ΦPSII caused by fungal infections and galls extended >2.5 times further from the visible damage and was ∼40% more depressed than chewing damage. Areas of depressed ΦPSII around fungal infections on oaks growing in elevated CO2 were more than 5 times larger than those grown in ambient conditions, suggesting that this element of global change may influence the indirect effects of biotic damage on photosynthesis. For a single Q. velutina sapling, the area of reduced ΦPSII was equal to the total area directly damaged by insects and fungi. Thus, estimates based only on the direct effect of biotic agents may greatly underestimate their actual impact on photosynthesis.

https://www.life.illinois.edu/delucia/PUBLICATIONS/Aldea%20et%20al%20Oecologia%202006.pdf

Comparison of photosynthetic damage from arthropod herbivory and pathogen infection in understory hardwood saplings

During the past decade, Swiss needle cast (SNC) damage has intensified in many Douglas-fir plantations in the Coast Range of Oregon, particularly along the immediate north coast In plantations with severe symptoms, growth losses and reduced tree vigor are evident, but the magnitude of growth losses associated with varying intensities of damage is not known A growth impact study was conducted in 1997 to quantify retrospectively the relationship between growth losses and visual symptoms in 10to 30-yr-old Douglas-fir plantations in coastal northwestern Oregon, a population totaling 75,700 ha A random sample of 70 Douglas-fir plantations was selected from the population and evaluated for Swiss needle cast severity One 002 ha plot was destructively sampled in each plantation to reconstruct past height and basal area growth trends and to characterize foliage loss and distribution The SNC “effect” was assessed by comparing growth of plantations with varying degrees of Swiss needle cast to growth of those that retained maximal amounts of foliage, after correcting for initial stand density, Douglas-fir growing stock, age, and site index Of numerous possible SNC indices, mean needle retention (yr) explained the largest amount of variation in both basal area and top height growth Prior to 1990, top height growth was similar across all plantations after correcting for site quality and plantation age; but, by 1992, top height growth losses appeared and were proportional to apparent foliage losses In 1996, top height growth was reduced by up to 25% relative to plantations with little or no SNC Basal area growth reductions began to appear around 1990, and in 1996 basal area growth of the most heavily damaged plantations was 35% less than the growth that would be expected in absence of SNC damage The inferred volume growth loss for 1996 averaged 23% for the 75,700 ha target population, but this loss averaged as high as 52% for the most severely impacted plantations West J Appl For 17(2):86–95

http://sncc.forestry.oregonstate.edu/sites/default/files/Maguire%2C%20Kanaskie%2C%20Voelker%2C%20Johnson%2C%20Johnson%20WJAF%202002.pdf

Growth of young Douglas-fir plantations across a gradient in Swiss needle cast severity.

Swiss needle cast of Douglas-fir (Pseudotsuga menziesii) is caused by the ascomycete Phaeocryptopus gaeumannii. Symptoms are foliage chlorosis and premature needle abscission due to occlusion of stomata by the ascocarps of the pathogen, resulting in impaired needle gas exchange. Growth losses of 20%-50% due to Swiss needle cast have been reported for approximately 150 000 ha of Douglas-fir plantations in western Oregon since 1996. In the western Coast Range of Oregon and in New Zealand, winter temperature is strongly correlated with pathogen abundance. Models for predicting disease severity based on winter temperature account for 77% and 78% of the variation in 1- and 2-year-old needles, respectively, for western Oregon sites and approximately 80% for New Zealand. A trend of temperatures increasing by 0.2–0.4 °C during the winter months and spring precipitation increasing by 0.7–1.5 cm/decade since 1970 suggests that regional climate trends are influencing the current distribution and severity of...

Predicting effects of climate change on Swiss needle cast disease severity in Pacific Northwest forests

Kimberley, M. O., Hood, I. A., and Knowles, R. L. 2011. Impact of Swiss needle-cast on growth of Douglas-fir. Phytopathology 101:583-593. Phaeocryptopus gaeumannii, the cause of Swiss needle-cast, is widely distributed in plantations of Douglas-fir in many parts of the world. Nevertheless, information remains limited on its precise effect on stand growth, particularly in relation to regional climate, and on its consequent economic cost. In New Zealand, the spread of P. gaeumannii over a period of ≈30 years following its discovery in 1959 was closely monitored, and the timing of its arrival in different forests is known. This information was coupled with data from permanent sample plots in order to quantify the associated historical growth increment loss. Analyses revealed a steady decline in growth rate over the period from the first appearance of P. gaeumannii to a point when it stabilized at a lower increment level 14 to 20 years later. The cumulative mean reduction was 25% for mean top height, 27% for basal area, and 32% for stem volume. Volume growth rate decline was greater in the North Island (35%) than the South Island (23%) of New Zealand. These reductions in volume growth are estimated to equate to a loss in net present value of $NZ2,620 ha –1 and $NZ1,470 ha –1 for the North and South Islands, respectively, using a discount rate of 6%. Mortality did not increase as a result of infection by P. gaeumannii. The disease had less effect on cooler sites, especially those with low spring minimum temperatures (P < 0.001). Negligible growth decline occurred on sites with daily minimum October temperatures averaging <3.2°C.

/pdf/impact-of-swiss-needle-cast-on-growth-of-douglas-fir-dxecg9u96e.pdf

Impact of Swiss needle-cast on growth of Douglas-fir.

https://sncc.forestry.oregonstate.edu/sites/default/files/watt%20et%20al%20snc%20new%20zealand.pdf

Predicting the severity of Swiss needle cast on Douglas-fir under current and future climate in New Zealand

The needle-infecting fungus Phaeocryptopus gaeumannii (Rohde) Petrak spread to stands of Douglas fir [Psendotsuga menziesii (Mirb.) Franco] in most parts of New Zealand following its first detection in the central North Island in 1959. At Hanmer Forest in the South Island, the percentage of infected needles rose more rapidly in a provenance from northern inland California than in one from Kaingaroa Forest in the North Island. Increase in infection was accompanied by a significant decrease in the proportion of needles retained on shoots of certain age classes, the reduction in the Californian seedlot being greater than in that from Kaingaroa. More older foliage was retained in the Kaingaroa provenance at Hanmer Forest, when infection averaged under 30 %, than at two other locations where mean infection exceeded 90 %. It is suggested that heavily infected production stands of Douglas fir suffer some premature casting of older needles, even when crowns appear healthy.

Changes in needle retention associated with the spread and establishment of Phaeocryptopus gaeumannii in planted Douglas fir

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Changes in needle retention associated with the spread and establishment of Phaeocryptopus gaeumannii in planted Douglas fir