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

Plate 13. Fungus Collybia sp., on site in Nidzica Forest District - photo by Jerzy Wawrzoniak

In 2002, the monitoring of the threat to forests posed by pathogenic fungi was carried out on 576 observation plots within the network of 148 fist-level POPs in all natural-forest regions. The total forest area subject to the monitoring was 8,145 ha; the largest area (1,657 ha) was in the Wielkopolska-Pomorze natural-forest region and the smallest one (0,603 ha) - in the Sudeten natural-forest region.

The selected plots were highly representative both on the scale of the Regional Directorate of State Forests and the natural-forest region. The areas represented the main forest-site types occurring in Poland (a total of 15 typological units). The prevailing forest-site types on an overall number of 413 plots were: fresh coniferous forest (Bśw), fresh mixed coniferous forest, fresh mixed coniferous forest (BMśw), fresh broadleaved forest (Lśw) and fresh mixed broadleaved forest (LMśw). The lowland forest-site type was represented by 464 plots, the upland - by 32 plots, and the mountain forest-site type - by 80 plots.

The age of forests subject to phytopathological monitoring ranged from 41 to 138 years. The average age approximated to 77 years and was by 5 years higher than that in the 2001.

The total number of 2395 stumps included 1266 pines (53%), 383 spruces (16%) and 199 oaks (8%). The number of stumps of coniferous species amounted to 1769 (74%), and of broadleaved species - to 625 (26%).

The assessment of the threat to forest stands posed by fungi was based on the analysis of the number of shoots fallen onto the ground (Wg) and the intensity of shoot infection (Wp) by fungi causing dieback of pine shoots. A synthetic threat index WZD for the stands with potential shoot dieback was calculated by multiplying Wg by Wp. The values of the Wg index directly indicated the presence of pathogenic fungi and infection of shoots. The Wp is a less reliable index because it can be influenced by possible causes other than pathogens, inter alia acute winds, foraging of insect pests, tending treatments, etc.

In 2002, the threat to pine stands posed by fungi causing damage to assimilatory organs was low (Tab. 10). The WZD index was slightly higher than that observed in 2001 and lower than in the years 2000 and 1999. In 2002, the Wp value (1.099) was slightly lower that that in the previous years (it ranged from 1.104 in 2001 to 1.228 in 1999). The higher Wg values (1.452) in 2002 when compared to the values in 2001 (1.371) were the result of damage to some of the plots caused by hurricane winds.

In 2002, the values of the WZD index were highly variable among the natural-forest regions. They ranged between 1.00 in the Sudeten and Carpathian natural-forest regions to 2.15 in the Małopolska natural-forest region. This was mainly due to forest damage caused above-mentioned hurricane winds and a small number of surveyed plots with pine stands at the foothills and in the mountain areas. The variability of the Wp index was not so high (it ranged from 1.00 to 1.91) - see Tab. 10.

In 2002, the number of stumps (Pn/ha) found on POPs under the phytopathological monitoring ranged from 175 stumps per hectare (Mazury-Podlasie natural-forest region) to 371 stumps per hectare (Małopolska natural-forest region) with the average for the country being 272 stumps per hectare, which was slightly higher than the average in 2001 (268 stumps/ha) - see Tab. 11. The index of colonisation of stumps by fungi (WG) varied among the natural-forest regions, from 22.39% (Sudeten natural-forest region) to 48.41% (Baltic natural-forest region) with the average for the country being 32.87%. This value was much lower than that in the previous year (44.11%) and approximated the 2000 average (36.90%). It can indicate that the colonisation of stumps by fungi was maintained at the level considered as natural for the survey performed. 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 were similar to those noted in previous years - see Tab. 11.

In 2002, the pathogen incidence expressed in the number of stumps colonised by root rot fungus or honey fungus (P/ha) slightly declined when compared with the results from 2000 and 2001 (24.8 and 23.7, respectively), and the country mean was 23.7 stumps per hectare - see Tab. 12, Ryc. 22. The value of the index of stump colonisation by pathogens (WP) in 2002 was also lower (6.98%) than the values in previous years (8.85% in 2001 and 8.50% in 2000). Taking into consideration the species structure of stands and stumps surveyed in 2002 and before, the decreased occurrence of root pathogens in 2002 appears to reflect the changes in the site and age structure of the stands surveyed. In 2002, the share of plots located on fertile sites (mixed and other broadleaved forest-site types) equalled 47.9% while in 2001 - 54.9%. The average age was 77 and 72 years, respectively. This indicates that more coniferous stands occupying fertile sites unsuitable for this species were inventoried in 2001 and that they were younger and more vulnerable to infection by root pathogens than the stands inventoried in 2002. Stumps of coniferous species especially pine, spruce and, to a lesser extent, fir were most vulnerable to colonisation by root pathogens. This observation verifies the hypothesis that the lack of matching the composition of species and the structure of stands to the capabilities of the site can be the primary predisposing factor in the process of root diseases in the managed stands of Poland.

The incidence of pathogens noticeably varied among the natural-forest regions. The greatest number of stumps colonised by agents causing root disease were recorded in the Carpathian and Sudeten natural-forest regions (P/ha> 30 stumps/ha, WP 14.29% and 10.45%, respectively) - see Tab. 12. The spatial distribution of pathogens was considerably lower in the Mazury-Podlasie, Wielkopolska-Pomorze, Małopolska and Baltic natural-forest regions, where the P/ha index did not exceed 15 stumps per hectare, and the share of stumps colonised by pathogens (WP index) ranged from 3.68% (Małopolska natural-forest region) to 6.75% (Baltic natural-forest region).

Saprophytic fungi on POPs were less frequent in 2002 than in 2001. The 2002 country mean values of indexes S/ha and WS were 71.8% stumps/ha and 26.44%, while the 2001 values were 94.4 stumps/ha and 35.26%. The 2002 values were similar to those found in 2000 - see Tab. 12.

The interregional variation in the colonisation of stumps by saprophytic fungi was high. The greatest abundance of fungi was found on stumps in the Małopolska natural-forest region (S/ha index=106.5 stumps/ha), while the lowest ones - in the Sudeten ad Silesian natural-forest regions (less than 50 stumps/ha). The WS index values in most natural-forest regions oscillated between 20 and 30%; in the Sudeten natural-forest region those values were 12.94% and in the Baltic natural-forest region - 42.06%.

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) - see Table 12. The country average values for the WD index (3.79) in 2002 were similar to those in previous years (3.98 in 2001 and 3.34 in 2000). However, the value for the EP index (10.39%) in 2002 was significantly lower than the values in 2001 (15.83%) and in 2000 (13.46%). Taking into consideration the aforementioned causes (higher age of stands surveyed in 2002 and their superior adjustment to site conditions), the "improvement" of the index values seems to be natural and expected. Accordingly, it can be suggested that there was no dynamic changes to the threat posed by root pathogens in the managed stands over the country.

The differences in the WD and EP values among the natural-forest regions were highly variable. The greatest threat occurred in the Sudeten (WD=1.24 and EP=13.46%) and Carpathian (WD=1.82 and EP=23.78%) natural-forest regions. In other natural-forest regions, the WD values were higher and ranged from 2.5 to 7.81, and the EP values were lower and ranged from 5.38 to 13.08%. The lowest threat posed by root pathogens was found in the stands of north-western, eastern and central Poland in the Wielkopolska-Pomorze, Baltic and Małopolska natural-forest regions.