Abstract
Understory plant communities play critical ecological roles in forest ecosystems. Both above- and below-ground ecosystem properties and processes influence these communities but relatively little is known about such effects at fine (i.e., one to several meters within-stand) scales, particularly for forests in which the canopy is dominated by a single species. An improved understanding of these effects is critical for understanding how understory biodiversity is regulated in such forests and for anticipating impacts of changing disturbance regimes. Our primary objective was to examine the patterns of fine-scale variation in understory plant communities and their relationships to above- and below-ground resource and environmental heterogeneity within mature lodgepole pine forests. We assessed composition and diversity of understory vegetation in relation to heterogeneity of both the above-ground (canopy tree density, canopy and tall shrub basal area and cover, downed wood biomass, litter cover) and below-ground (soil nutrient availability, decomposition, forest floor thickness, pH, and phospholipid fatty acids (PLFAs) and multiple carbon-source substrate-induced respiration (MSIR) of the forest floor microbial community) environment. There was notable variation in fine-scale plant community composition; cluster and indicator species analyses of the 24 most commonly occurring understory species distinguished four assemblages, one for which a pioneer forb species had the highest cover levels, and three others that were characterized by different bryophyte species having the highest cover. Constrained ordination (distance-based redundancy analysis) showed that two above-ground (mean tree diameter, litter cover) and eight below-ground (forest floor pH, plant available boron, microbial community composition and function as indicated by MSIR and PLFAs) properties were associated with variation in understory plant community composition. These results provide novel insights into the important ecological associations between understory plant community composition and heterogeneity in ecosystem properties and processes within forests dominated by a single canopy species.
Highlights
Understory vegetation is an integral component of the ecological functioning and biodiversity of forests [1]
Understory plant communities play critical ecological roles in forest ecosystems. Both above- and below-ground ecosystem properties and processes influence these communities but relatively little is known about such effects at fine scales, for forests in which the canopy is dominated by a single species
Constrained ordination showed that two above-ground and eight below-ground properties were associated with variation in understory plant community composition
Summary
Understory vegetation is an integral component of the ecological functioning and biodiversity of forests [1]. The understory plant community plays important roles in influencing both community and ecosystem properties above- and below-ground [2, 3]. The composition and biodiversity of these ecologically important understory plant communities is affected by both above- and below-ground factors, with complex interactions among them [8]. Below-ground microbial communities actively contribute to ecosystem functions that include litter decomposition [16], plant productivity [17], and plant nutrition through mycorrhizal relationships [18]. Explicit relationships between understory plant communities and below-ground resources remain underappreciated and understudied in most plant community ecological studies [20]
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