Temperate forest ecosystems, including old-growth fragments, are subject to increasing pressures, both from biotic and abiotic factors. Frequent disturbance events, rising mean annual temperatures and longer-lasting droughts are causing changes in tree species composition, probably shifting the altitudinal distribution of herbaceous species as well. Our goal was to examine whether such shifts can be observed even in old-growth temperate forests, and if the changes in the species composition and spatial distribution of trees is reflected in the herbaceous layer. Our study was based on a survey of several old-growth forests from the 1970s that was repeated after 30 years. Using spatial point pattern methods and generalized linear mixed effect models, repeated measurements of mapped phytosociological relevés and detailed maps of tree positions from two survey periods allowed us to examine how the species composition of the herb layer and the spatial distribution of trees ≥ 10 cm DBH (diameter at breast height) changed over 30 years. On most of the studied sites, the total number of trees declined and the proportion of broadleaves increased between the two surveys. Analyses of tree spatial distribution showed a general shift from a regular spatial distribution in the 1970s to a clustered spatial distribution of trees in the 2000s. In the 2000s, herbaceous species showed an upwards shift in their distribution compared to the 1970s, even after accounting for the effect of changing tree spatial distributions in both survey periods. These effects could be an outcome of warmer and drier weather conditions during the past decades. Further investigation is needed to examine whether this trend is related to changes in climatic conditions.
In the past decades, forests in Central Europe have come under increasing pressure, for example from repeated outbreaks of insect pests (
Changes in the species composition and spatial distribution of trees are reflected in the cover and species composition of the herb layer (
Shifts in the distribution of herbaceous species along altitudinal or latitudinal gradients (
We used data from five natural forest sites in the Czech Republic belonging to the Hercynian and Bohemian-Moravian mountain region. Specifically, these included Boubín, Milešice, and Stožec in the Šumava mountains, Zofín in the Novohradské hory mountains and Zákova hora in the Ceskomoravská vrchovina highlands (
All the studied sites have been unmanaged for decades. Cambisols are the predominant soils at these sites, with fragments of hydromorphic soils in Boubín and Zofín. Boubín, Stožec, Milešice, and Zofín are mostly north-east to north-west oriented with slopes of 5-25°. Zákova hora is south-west oriented with slopes up to 15°. Except for Milešice, beech dominates the studied sites with occurrences of either spruce or fir. Milešice represents a mountain spruce forest with rare occurrences of fir in the main canopy layer and beech in the upper understorey. The sites are fenced, except for Stožec and Zákova hora. The mean annual precipitation is 740 mm and the mean annual temperature 6.1 °C in Zákova hora (
All standing and lying tree stems ≥ 10 cm DBH were repeatedly mapped and identified to species level (
A nonparametric Wilcoxon paired test for dependent samples was used to compare the number of coniferous and broadleaved trees in the 50 × 50 m plots between the initial and repeated surveys. The difference in the proportion of coniferous and broadleaved trees between surveys was assessed with Fisher’s exact test (
where
We applied two generalized linear mixed models with a binomial error distribution and logit link function (
where
In the second model, we added species-specific random slopes to
where
The performance of these two model types (random intercepts
In both models, we included 28 herbaceous species which were common to all sites:
The total number of trees ≥ 10 cm DBH per plot was significantly higher in the 1970s than the 2000s, based on the results of the Wilcoxon paired test for dependent samples (P = 0.00002). This was because the total number of coniferous trees per plot was significantly lower in the 2000s than 30 years before (Wilcoxon paired test: P < 0.0001). In contrast, the total number of broadleaved trees did not vary between the survey periods. As shown by the results of the Fisher’s exact test, the proportion of broadleaved and coniferous trees significantly differed in Zofín, Boubín and Zákova hora (
By comparing the random intercepts and random slopes models with a likelihood ratio test, the random slopes model showed better fit (df = 9, χ2 = 363.01, p < 0.001), demonstrating that species significantly varied in response to altitude, survey period and their interaction. Based on the results of this random slopes model, the probability of species presence was on average negatively related to altitude and positively related to the interaction between altitude and survey period (
It is clear that the number of trees on studied plots was lower at the beginning of the new millennium than in the 1970s (
In line with our findings, the proportion of European beech has rapidly increased over approximately the same time span in many Central European old-growth forests (
Thinning of the tree canopy layer indicated by clustered tree distribution (
A changing distribution of plant species along the altitudinal gradient has been associated with climate change at both regional and global scales (
We have shown that changes in the tree layer over the 30 year period indicate a shift towards a more complex forest structure and the gradual replacement of conifers by broadleaved tree species, especially beech. We also show that herbaceous species tended, on average, to occur at higher altitudes 30 years after the initial survey in the 1970s. This relationship was observed for almost 80 % of the studied herbaceous species, even when accounting for the spatial distribution of trees in both survey periods. This was mainly related to shade-tolerant species, which are usually independent of the distribution, size of canopy openings and of early-succession stages of forest communities following disturbance events.
This research was supported by the Czech Science Foundation, project 20-17282S and by the institutional subsidy of Ministry of Education, Youth and Sports of the Czech Republic.
Comparison of tree spatial patterns based on the pair correlation function g(r) in the 1970s (a) and the 2000s (b). Solid lines [
The effects of altitude, survey period (Period, P), spatial distribution of trees (Trees, T) and the interaction of altitude and survey period (Altitude × Period, A × P) on the probability of species presence based on the results of the random slopes model. Altitude was standardised within sites by subtracting the site-specific mean altitude and dividing by one site-specific standard deviation. The spatial distribution of trees is represented by relevé-specific values of the pair correlation function estimated at a distance of 0.5 m. Solid symbols denote statistically significant effects with
The interactive effects of altitude and survey period on the probability of species presence based on the results of the random slopes model. The predicted probabilities with 95% confidence intervals are displayed. Altitude (Altitudescaled) was standardised within sites by subtracting the site-specific mean altitude and dividing by one site-specific standard deviation.
Distribution of interactive effects of altitude and survey period on the probability of species presence based on the results of the random slopes model. Histogram bars are based on species-specific regression coefficients (random slopes) for 28 herbaceous species. Bars to the right of the solid zero line indicate species that occur at higher altitude in the 2000s compared to the 1970s. The average species-specific response (coefficient) to the interactive effect of altitude and survey period is indicated by the red dashed line.
Studied sites. (N): number of relevés.
Locality | Area(ha) | LatitudeN | LongitudeE | Altitude(m a.s.l.) | N | Firstsurvey | Repeatedsurvey |
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Boubín | 46.6 | 48°58′ 43″ | 13°48′ 43″ | 925-1107 | 23 | 1972 | 2006 |
Milešice | 8.9 | 48°59′ 05″ | 13°50′ 21″ | 1070-1125 | 2 | 1972 | 2011 |
Stožec | 16.2 | 48°52′ 50″ | 13°50′ 06″ | 750-900 | 16 | 1974 | 2013 |
Zákova hora | 17.5 | 49°39′ 20″ | 15°59′ 39″ | 752-800 | 22 | 1974 | 2011 |
Zofín | 74.2 | 48°39′ 58″ | 14°42′ 28″ | 730-837 | 42 | 1975 | 2008 |
Mean annual temperature and precipitation in decades during the period of survey. Mean values for whole Czech Republic (CZ) and for regions where surveyed forests are located (South Bohemia, Czech-Moravian highlands) are shown. Processed on the basis of data from the Czech Hydrometeorological Institute (https://www.chmi.cz/).
Parameter | Locality | Period | ||||
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1970-1979 | 1980-1989 | 1990-1999 | 2000-2009 | 2010-2019 | ||
Mean temperature(°C) | CZ | 7.36 | 7.33 | 7.97 | 8.39 | 8.71 |
South Bohemia | 6.84 | 6.91 | 7.39 | 7.88 | 8.26 | |
Highlands | 6.94 | 6.87 | 7.46 | 7.97 | 8.53 | |
Annualprecipitation(mm) | CZ | 655.8 | 668.9 | 659.6 | 703.9 | 657.5 |
South Bohemia | 655.8 | 653.6 | 644.4 | 743.2 | 672.3 | |
Highlands | 677.5 | 650.7 | 623.3 | 702.6 | 633.6 |
Number and volume of living trees and volume of deadwood in studied localities, average cover of herb layer and number of species of herb layer recorded in relevés in the survey periods. More detail information about number and volume of living trees is provided in Supplementary material (Tab. S1-S5).
Layer | DBHClass | Parameter | Boubín | Milešice | Stožec | Zofín | Zákova hora | |||||
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1972 | 2000 | 1972 | 2011 | 1974 | 2013 | 1975 | 2008 | 1974 | 2011 | |||
Living trees | ≥ 10 cm | No. all living trees ha-1 | 314.7 | 209.9 | 257.0 | 333.1 | 160.0 | 149.7 | 233.2 | 218.5 | 254.4 | 308.1 |
No. deciduous trees ha-1 | 121.0 | 107.6 | 85.9 | 72.1 | 96.7 | 80.1 | 146.5 | 156.8 | 222.9 | 286.9 | ||
No. coniferous trees ha-1 | 193.6 | 102.3 | 171.1 | 260.9 | 63.3 | 69.6 | 86.7 | 61.7 | 31.6 | 21.2 | ||
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10-39 cm | No. all living trees ha-1 | 236.0 | 107.6 | 205.3 | 214.7 | 58.1 | 72.5 | 145.6 | 152.1 | 200.6 | 208.6 | |
No. deciduous trees ha-1 | 96.8 | 60.3 | 72.7 | 30.5 | 26.0 | 29.5 | 110.5 | 117.6 | 186.4 | 202.4 | ||
No. coniferous trees ha-1 | 139.2 | 47.3 | 132.6 | 184.2 | 32.1 | 43.1 | 35.1 | 34.5 | 14.1 | 6.2 | ||
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40-79 cm | No. all living trees ha-1 | 72.0 | 89.4 | 50.0 | 111.3 | 92.7 | 56.0 | 77.2 | 53.3 | 50.3 | 89.9 | |
No. deciduous trees ha-1 | 24.0 | 45.9 | 13.2 | 41.1 | 65.9 | 35.6 | 32.7 | 33.0 | 34.1 | 78.2 | ||
No. coniferous trees ha-1 | 47.9 | 43.5 | 36.8 | 70.2 | 26.8 | 20.4 | 44.4 | 20.3 | 16.2 | 11.6 | ||
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≥ 80 cm | No. all living trees ha-1 | 6.6 | 12.8 | 1.7 | 7.1 | 9.3 | 21.2 | 10.4 | 13.1 | 3.6 | 9.6 | |
No. deciduous trees ha-1 | 0.2 | 1.4 | 0.0 | 0.6 | 4.8 | 15.1 | 3.3 | 6.2 | 2.3 | 6.2 | ||
No. coniferous trees ha-1 | 6.5 | 11.5 | 1.7 | 6.5 | 4.4 | 6.1 | 7.1 | 6.9 | 1.2 | 3.4 | ||
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Deadwood | - | No. of deadwood (pcs ha-1) | 111.6 | 153.9 | 40.5 | 126.9 | 14.7 | 86.0 | 32.2 | 122.4 | 42.0 | 68.2 |
Volume of deadwood (m3 ha-1) | 147.8 | 364.6 | 75.9 | 171.7 | 51.0 | 183.3 | 111.9 | 355.1 | 101.2 | 149.6 | ||
Herb layer | - | Average cover (%) | 66 | 53 | 70 | 10 | 77 | 65 | 76 | 51 | 66 | 28 |
No. of recorded species | 48 | 64 | 20 | 15 | 34 | 70 | 70 | 97 | 42 | 47 |
Changes in tree layer between surveyed periods. The total number of trees ≥ 10 cm DBH in 50 × 50 m plots recorded at all sites in two survey periods. The proportion of coniferous (con70, con00) and broadleaved (leaf70, leaf00) trees and the results of Fisher’s exact test comparing the proportion of coniferous and broadleaved between the first and repeated surveys are given.
Parameter | Boubín | Milešice | Stožec | Zákovahora | Zofín |
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No. of trees 1970 | 1237 | 229 | 637 | 1462 | 1758 |
No. of trees 2000 | 785 | 238 | 548 | 1458 | 1529 |
con70 (%) | 62 | 61 | 41 | 10 | 23 |
con00 (%) | 48 | 69 | 41 | 6 | 9 |
leaf70 (%) | 38 | 39 | 59 | 90 | 77 |
leaf00 (%) | 52 | 31 | 59 | 94 | 91 |
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Tab. S1 - Number and volume of living trees in DBH classes in locality Boubín.
Tab. S2 - Number and volume of living trees in DBH classes in locality Milešice.
Tab. S3 - Number and volume of living trees in DBH classes in locality Stožec.
Tab. S4 - Number and volume of living trees in DBH classes in locality Zofín.
Tab. S5 - Number and volume of living trees in DBH classes in locality Zákova hora.