12. The level of threat to forests posed by pathogenic fungi

Paweł Lech

Photo 5. Hypholoma fasciculare Fr. - RadziwiłówForest District - by Jerzy Wawrzoniak

In 2003, the monitoring of the threat to forests posed by pathogenic fungi was carried out on 552 observation plots within the network of 148 fist-level POPs in all natural-forest regions.

The assessment of the threat to forest stands posed by fungi causing shoot dieback was carried out on 285 POPs. The number of shoots fallen to the ground (Wg = 1.456) in 2003 was almost identical to that of the previous year. The share of pine trees with damaged assimilatory apparatus approached 9.32% at a country scale, which was considered low in forest management.

The index of colonisation of stumps by fungi (WG) varied among the natural-forest regions, from 31.8% in the Mazury-Podlasie natural-forest region to 72.9% in the Baltic natural-forest region with the average for the country being 41.9%. In 2003, these figures were higher than in the previous year and similar to those from 2001 and 1999.

No high variation in the mean values was found between the stump age index and stump decomposition index among the natural-forest regions and their mean values for the country (2.43 and 2.22) were similar to those observed in previous years.

Among the main forest tree species, the highest percentage of stumps colonised by pathogenic fungi (root rot and Armillaria sp.) was noted for spruce (32.79%) and was twice as high as the average for all monitored species (16.84%). Values approximating the average were characteristic for fir (17,65%), oak (20.25%) and beech (16.02%), while for pine, birch and admixture species those values were markedly lower - Table 18.

Armillaria sp. most frequently colonised stumps of felled oaks (18.18% of colonised stumps of that species), firs (17.65%), beeches (14.36%) and spruces (14.14%), while the least colonised species was pine (1.39%).

Most commonly colonised by the root rot were stumps of spruce and pine (18,65% and 9,99%, respectively). This figure for stumps of other species did not exceed 5% (root rot was not found on fir).

Saprophytic fungi were found on all main and admixture forest species. The variation in the percentage of colonised stumps was less distinct than in the case of pathogens and ranged between 17.42% (spruce) and 45.86% (beech) with the average for all species 25.06% - Table 18.

In 2003, pathogen occurrence on stumps expressed as the number of stumps colonised by root rot or Armillaria sp. per 1 hectare (P/ha) was found to be twice as great as in the years 2002, 2001 and 2000 and equalled 49.0 stumps per hectare. The value for the WP index (16.84%) in 2003 was considerably higher than that in the years 2000-2002.

At the same time the number of stumps with pathogenic fungi, meaning de facto the number o infested and removed trees, provided information about potential threat to stands that could result from secondary infection via root systems of trees.

In 2003, the values of saprophyte dominance index S/ha and WS index were similar to those in 2002. The 2003 country average values of indices S/ha and WS% were 72.9 stumps/ha and 25.06%.

The threat posed to forest stands by root diseases (root decay caused by honey fungus and root rot) was expressed as the index of saprophyte dominance WD) and the index of pathogen occurrence on stumps (EP) - Table 19. The country average values for those indices (1.49 and 28.99%) in 2003 were distinctly higher than previous years' values (3.98 in 2001 and 3.34 in 2000), which might indicate elevated threat posed by root pathogens to Polish forests.

The assessment of damage to 5388 trees and shrubs of 30 species was carried out within the framework of pathological monitoring. The most frequently represented were pine (51% of trees), followed by oak and spruce (13% and 11% of trees, respectively). Among the monitored main forest species, the most frequent damages were found on spruce (on 41.09% of this species). The percentage share of damaged fir, oak and beech species oscillated around 20%, while for pine, birch and admixture species it was lower - less than 13% - Table 20.

Damages to assimilatory apparatus (including shoots, buds and leader dieback, and discolouration of foliage) were the most abundant type of damage found on pine, as well as on spruce, oak and admixture species. The dieback of shoots and buds itself was found to be the most common type of damage on pine, spruce and oak. Decay of wood was the most abundant among other types of damage to beech while open wounds - to birch

The threat to Scots pine caused by the dieback of shoots was low and its level was typical for a period between epiphytoses.