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Tree seedling richness, but not neighborhood composition, influences insect herbivory in a temperate deciduous forest community

View Article: PubMed Central - PubMed

ABSTRACT

Insect herbivores can serve as important regulators of plant dynamics, but their impacts in temperate forest understories have received minimal attention at local scales. Here, we test several related hypotheses about the influence of plant neighborhood composition on insect leaf damage in southwestern Pennsylvania, USA. Using data on seedlings and adult trees sampled at 36 sites over an approximately 900 ha area, we tested for the effects of total plant density, rarefied species richness (i.e., resource concentration and dietary‐mixing hypotheses), conspecific density (i.e., Janzen–Connell hypothesis), and heterospecific density (i.e., herd‐immunity hypothesis), on the proportion of leaf tissue removed from 290 seedlings of 20 species. We also tested for the effects of generic‐ and familial‐level neighborhoods. Our results showed that the proportion of leaf tissue removed ranged from zero to just under 50% across individuals, but was generally quite low (<2%). Using linear mixed models, we found a significant negative relationship between insect damage and rarefied species richness, but no relationship with neighborhood density or composition. In addition, leaf damage had no significant effect on subsequent seedling growth or survival, likely due to the low levels of damage experienced by most individuals. Our results provide some support for the resource concentration hypothesis, but suggest a limited role for insect herbivores in driving local‐scale seedling dynamics in temperate forest understories.

No MeSH data available.


Related in: MedlinePlus

The location (black star) and boundary of Powdermill Nature Reserve (PNR) in Rector, Pennsylvania, showing the sampling design of the 2008 adult tree survey. A total of 647 120 × 120 m grid cells were used to cover the entire area, within which all trees ≥8 cm DBH were sampled within nine adjacent circular plots, each with a radius of 10 m. Within 45 randomly selected 120 × 120 m grid cells, four 10 × 1 m belt transects were established in 2012 to sample seedlings ≥7 cm tall. From these 45 plots, 36 contained seedlings ≥20 cm where photographs were taken to quantify herbivore damage (red outline).
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ece32336-fig-0001: The location (black star) and boundary of Powdermill Nature Reserve (PNR) in Rector, Pennsylvania, showing the sampling design of the 2008 adult tree survey. A total of 647 120 × 120 m grid cells were used to cover the entire area, within which all trees ≥8 cm DBH were sampled within nine adjacent circular plots, each with a radius of 10 m. Within 45 randomly selected 120 × 120 m grid cells, four 10 × 1 m belt transects were established in 2012 to sample seedlings ≥7 cm tall. From these 45 plots, 36 contained seedlings ≥20 cm where photographs were taken to quantify herbivore damage (red outline).

Mentions: In 2008, a large‐scale vegetation survey was conducted at PNR to document the distribution and abundance of trees and shrubs across the entire reserve. A total of 647 quadrats were sampled on a grid and permanently marked using steel rebar (Fig. 1; Murphy et al. 2015). At these locations, nine adjacent circular plots of 10 m radius were sampled. All adult trees ≥8 cm diameter at breast height (DBH) were identified and measured, which we used to calculate adult neighborhood metrics. In 2013, we randomly selected a subset of 45 of the larger quadrats to sample the understory seedling layer in more detail. Only quadrats that were within mature forest (as estimated using historical aerial photographs from 1939) were used in our random sample (see Murphy et al. 2015 for details). Within these quadrats, four 10 × 1 m belt transects were established to sample woody seedlings (Fig. 1). Each belt transect was divided into 10 individual 1 × 1 m subquadrats, and all seedlings ≥7 cm tall were tagged, identified, and measured for height. Sampling occurred from June to August 2013 and from July to August 2014. Data from the 2013 seedling census were used to calculate seedling neighborhood metrics as described below in more details.


Tree seedling richness, but not neighborhood composition, influences insect herbivory in a temperate deciduous forest community
The location (black star) and boundary of Powdermill Nature Reserve (PNR) in Rector, Pennsylvania, showing the sampling design of the 2008 adult tree survey. A total of 647 120 × 120 m grid cells were used to cover the entire area, within which all trees ≥8 cm DBH were sampled within nine adjacent circular plots, each with a radius of 10 m. Within 45 randomly selected 120 × 120 m grid cells, four 10 × 1 m belt transects were established in 2012 to sample seedlings ≥7 cm tall. From these 45 plots, 36 contained seedlings ≥20 cm where photographs were taken to quantify herbivore damage (red outline).
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5016651&req=5

ece32336-fig-0001: The location (black star) and boundary of Powdermill Nature Reserve (PNR) in Rector, Pennsylvania, showing the sampling design of the 2008 adult tree survey. A total of 647 120 × 120 m grid cells were used to cover the entire area, within which all trees ≥8 cm DBH were sampled within nine adjacent circular plots, each with a radius of 10 m. Within 45 randomly selected 120 × 120 m grid cells, four 10 × 1 m belt transects were established in 2012 to sample seedlings ≥7 cm tall. From these 45 plots, 36 contained seedlings ≥20 cm where photographs were taken to quantify herbivore damage (red outline).
Mentions: In 2008, a large‐scale vegetation survey was conducted at PNR to document the distribution and abundance of trees and shrubs across the entire reserve. A total of 647 quadrats were sampled on a grid and permanently marked using steel rebar (Fig. 1; Murphy et al. 2015). At these locations, nine adjacent circular plots of 10 m radius were sampled. All adult trees ≥8 cm diameter at breast height (DBH) were identified and measured, which we used to calculate adult neighborhood metrics. In 2013, we randomly selected a subset of 45 of the larger quadrats to sample the understory seedling layer in more detail. Only quadrats that were within mature forest (as estimated using historical aerial photographs from 1939) were used in our random sample (see Murphy et al. 2015 for details). Within these quadrats, four 10 × 1 m belt transects were established to sample woody seedlings (Fig. 1). Each belt transect was divided into 10 individual 1 × 1 m subquadrats, and all seedlings ≥7 cm tall were tagged, identified, and measured for height. Sampling occurred from June to August 2013 and from July to August 2014. Data from the 2013 seedling census were used to calculate seedling neighborhood metrics as described below in more details.

View Article: PubMed Central - PubMed

ABSTRACT

Insect herbivores can serve as important regulators of plant dynamics, but their impacts in temperate forest understories have received minimal attention at local scales. Here, we test several related hypotheses about the influence of plant neighborhood composition on insect leaf damage in southwestern Pennsylvania, USA. Using data on seedlings and adult trees sampled at 36 sites over an approximately 900 ha area, we tested for the effects of total plant density, rarefied species richness (i.e., resource concentration and dietary‐mixing hypotheses), conspecific density (i.e., Janzen–Connell hypothesis), and heterospecific density (i.e., herd‐immunity hypothesis), on the proportion of leaf tissue removed from 290 seedlings of 20 species. We also tested for the effects of generic‐ and familial‐level neighborhoods. Our results showed that the proportion of leaf tissue removed ranged from zero to just under 50% across individuals, but was generally quite low (<2%). Using linear mixed models, we found a significant negative relationship between insect damage and rarefied species richness, but no relationship with neighborhood density or composition. In addition, leaf damage had no significant effect on subsequent seedling growth or survival, likely due to the low levels of damage experienced by most individuals. Our results provide some support for the resource concentration hypothesis, but suggest a limited role for insect herbivores in driving local‐scale seedling dynamics in temperate forest understories.

No MeSH data available.


Related in: MedlinePlus