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Multiple environmental changes drive forest floor vegetation in a temperate mountain forest

View Article: PubMed Central - PubMed

ABSTRACT

Human‐induced changes of the environment and their possible impacts on temperate forest understory plant communities have been examined in many studies. However, the relative contribution of individual environmental factors to these changes in the herb layer is still unclear. In this study, we used vegetation survey data covering a time period of 21 years and collected from 143 permanent plots in the Northern Limestone Alps, Austria. Data on soil chemistry (49 plots), light condition (51 plots), soil temperature and moisture (four and six plots), disturbance (all plots), climate (one station in a clearing area), and airborne sulfur (S) and nitrogen (N) deposition (two forest stands) were available for analyses. We used these data together with plot mean Ellenberg indicator values in a path analysis to attribute their relative contributions to observed vegetation changes. Our analysis reveals a strong directional shift of the forest understory plant community. We found strong evidence for a recovery of the ground‐layer vegetation from acidification as response to decreased S deposition. We did not observe a community response to atmospheric N deposition, but we found a response to altered climatic conditions (thermophilization and drying). The path analysis revealed that changes in the light regime, which were related to small‐scale disturbances, had most influence on herb layer community shifts. Thermophilization and drying were identified as drivers of understory community changes independent of disturbance events.

No MeSH data available.


Related in: MedlinePlus

Conceptual model that was used for the path analysis. Boxes represent the different variables and arrows the hypothesized relationships among them: We assumed disturbance as the only factor controlling tree layer cover and also controlling shrub cover and directly affecting the herb layer via soil perturbations. The tree layer has a key role by influencing the microclimate and soil conditions, limiting the light availability for the understory and thus the development of the herb and the shrub layer. Ungulate browsing may differ between open and dense forests and impacts the shrub and the herb layer. Although some relationships may have reciprocal influence, we used only one‐directional pathways to avoid a too complex model
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ece32801-fig-0001: Conceptual model that was used for the path analysis. Boxes represent the different variables and arrows the hypothesized relationships among them: We assumed disturbance as the only factor controlling tree layer cover and also controlling shrub cover and directly affecting the herb layer via soil perturbations. The tree layer has a key role by influencing the microclimate and soil conditions, limiting the light availability for the understory and thus the development of the herb and the shrub layer. Ungulate browsing may differ between open and dense forests and impacts the shrub and the herb layer. Although some relationships may have reciprocal influence, we used only one‐directional pathways to avoid a too complex model

Mentions: Specifically, we asked the following questions, which are based on the theoretical model in Figure 1: (1) What are the changes in environmental (e.g. climate, airborne nitrogen deposition) and biotic (e.g. browsing, changes in tree layer composition) drivers during the last two decades that potentially affected forest floor vegetation? (2) Which drivers did influence changes in the forest floor species composition and structure? Given changes in climate and deposition, we hypothesized that (i) disturbance had most impact on the species composition of the herb layer because it controls light regime in the forest understory, (ii) climate change favoured thermophilic and drought‐tolerant species, (iii) basophilic plant species increased and acidophilic decreased, and (iv) eutrophic plant species became more frequent. As to species diversity we hypothesized that (v) increasing disturbance increased species numbers in plots and that disturbance led to higher compositional differences among plots. We did not expect climate change effects on species diversity as immigration of thermophilic species should offset potential losses of cold‐tolerant species, nor did we expect that N deposition or soil recovery from acidification to have a significant effect because the study area is not strongly N limited and has a high buffer capacity for acid deposition.


Multiple environmental changes drive forest floor vegetation in a temperate mountain forest
Conceptual model that was used for the path analysis. Boxes represent the different variables and arrows the hypothesized relationships among them: We assumed disturbance as the only factor controlling tree layer cover and also controlling shrub cover and directly affecting the herb layer via soil perturbations. The tree layer has a key role by influencing the microclimate and soil conditions, limiting the light availability for the understory and thus the development of the herb and the shrub layer. Ungulate browsing may differ between open and dense forests and impacts the shrub and the herb layer. Although some relationships may have reciprocal influence, we used only one‐directional pathways to avoid a too complex model
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383490&req=5

ece32801-fig-0001: Conceptual model that was used for the path analysis. Boxes represent the different variables and arrows the hypothesized relationships among them: We assumed disturbance as the only factor controlling tree layer cover and also controlling shrub cover and directly affecting the herb layer via soil perturbations. The tree layer has a key role by influencing the microclimate and soil conditions, limiting the light availability for the understory and thus the development of the herb and the shrub layer. Ungulate browsing may differ between open and dense forests and impacts the shrub and the herb layer. Although some relationships may have reciprocal influence, we used only one‐directional pathways to avoid a too complex model
Mentions: Specifically, we asked the following questions, which are based on the theoretical model in Figure 1: (1) What are the changes in environmental (e.g. climate, airborne nitrogen deposition) and biotic (e.g. browsing, changes in tree layer composition) drivers during the last two decades that potentially affected forest floor vegetation? (2) Which drivers did influence changes in the forest floor species composition and structure? Given changes in climate and deposition, we hypothesized that (i) disturbance had most impact on the species composition of the herb layer because it controls light regime in the forest understory, (ii) climate change favoured thermophilic and drought‐tolerant species, (iii) basophilic plant species increased and acidophilic decreased, and (iv) eutrophic plant species became more frequent. As to species diversity we hypothesized that (v) increasing disturbance increased species numbers in plots and that disturbance led to higher compositional differences among plots. We did not expect climate change effects on species diversity as immigration of thermophilic species should offset potential losses of cold‐tolerant species, nor did we expect that N deposition or soil recovery from acidification to have a significant effect because the study area is not strongly N limited and has a high buffer capacity for acid deposition.

View Article: PubMed Central - PubMed

ABSTRACT

Human‐induced changes of the environment and their possible impacts on temperate forest understory plant communities have been examined in many studies. However, the relative contribution of individual environmental factors to these changes in the herb layer is still unclear. In this study, we used vegetation survey data covering a time period of 21 years and collected from 143 permanent plots in the Northern Limestone Alps, Austria. Data on soil chemistry (49 plots), light condition (51 plots), soil temperature and moisture (four and six plots), disturbance (all plots), climate (one station in a clearing area), and airborne sulfur (S) and nitrogen (N) deposition (two forest stands) were available for analyses. We used these data together with plot mean Ellenberg indicator values in a path analysis to attribute their relative contributions to observed vegetation changes. Our analysis reveals a strong directional shift of the forest understory plant community. We found strong evidence for a recovery of the ground‐layer vegetation from acidification as response to decreased S deposition. We did not observe a community response to atmospheric N deposition, but we found a response to altered climatic conditions (thermophilization and drying). The path analysis revealed that changes in the light regime, which were related to small‐scale disturbances, had most influence on herb layer community shifts. Thermophilization and drying were identified as drivers of understory community changes independent of disturbance events.

No MeSH data available.


Related in: MedlinePlus