Abstract
Background: Understorey plants are key to maintaining forest structure and functioning. They protect the soil, improve its structure and fertility, reduce water run-off and sustain the below-ground biota, amongst other ecological services. However, little is known about the environmental conditions that regulate the occurrence of these plants. This study focuses on determining how canopy cover influences the occurrence of understorey species and identifying the most important soil properties that affect these species. The study area was a pine-oak forest in the Sierra Madre Occidental, an important source of ecological services for northwestern Mexico. Methods: To assess the conditions influencing the presence of herbaceous and shrub species, 25 soil variables were examined in relation to the species occurring in forest gaps and under the canopy. Sampling was conducted in five plots, each of 100 × 100 m. In each plot, 4 subplots, each of 20 × 20 m, were each subdivided in a grid of 2 × 2 m units, in which the presence-absence of herbaceous and shrub species was recorded (2000 units in total). Soil samples were extracted for analysis from the central point in each subplot. Data were analyzed using a Binomial Logistic Model (BLM) and Random Forest (RF) classification. Results: Understorey species were more strongly affected by soil variables than by their location in gaps or below canopy. The concentrations of Ca, P, K, Fe, Na, C, Zn, Mn, nitrates, organic matter, sand, silt, and percentage water saturation were statistically significantly associated with the presence of some plant species, whilst no significant differences were found in regard to preference for gaps or canopy, although several species were more frequent in open areas. Conclusions: Given the importance of the understorey cover in forest system functioning, we propose that understorey should be considered in integrated management and conservation practices for the temperate forests of northern Mexico.
Highlights
The composition and distribution of vegetation are influenced by many factors, including abiotic environmental factors and physiographic factors [1,2,3,4]
Analysis of the occurrence of herbaceous and shrub species in the five sampling plots revealed that the species presence is influenced by 22 soil variables, but not by position under the canopy or in the gaps, as indicated by the Kruskal-Wallis test, including Bonferroni correction (Table 2)
The results highlight the usefulness of soil variables for local scale modelling, in order to determine which edaphic elements influence the presence of understorey species
Summary
The composition and distribution of vegetation are influenced by many factors, including abiotic environmental factors (e.g., humidity, temperature, rainfall, wind and soil) and physiographic factors (e.g., slope, exposure, altitude and latitude) [1,2,3,4] These factors control growth, plant spatial patterns and diversity and have local and regional effects on plant communities [5,6,7,8]. Understorey plants are important for maintaining the structure and function of forests and contribute to ecosystem dynamics They protect and conserve the soil, improve its structure and fertility, enhance nutrient cycling, reduce water run-off and sustain the belowground biota, among other ecological services [14,15,16,17,18]. Understorey plants are key to maintaining forest structure and functioning They protect the soil, improve its structure and fertility, reduce water run-off and sustain the belowground biota, amongst other ecological services. Conclusions: Given the importance of the understorey cover in forest system functioning, we propose that understorey should be considered in integrated management and conservation practices for the temperate forests of northern Mexico
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