The influence of American beech thickets on biodiversity in the northern hardwood forest

Transcription

1 The influence of American beech thickets on biodiversity in the northern hardwood forest Theme 4: Stacy A. McNulty Adirondack Ecological Center SUNY-ESF 6312 State Route 28N Newcomb, NY John D. Castello, SUNY-ESF Stephen A. Teale, SUNY-ESF Completed: September 2011 Thickets of American beech can significantly reduce local floral diversity. Forest craneflies, amphibians, and small mammal diversity were not impacted by beech thickets. Funding support for this project was provided by the Northeastern States Research Cooperative (NSRC), a partnership of Northern Forest states (New Hampshire, Vermont, Maine, and New York), in coordination with the USDA Forest Service.

2 Project Summary Beech bark disease (BBD) has dramatically altered hardwood forest structure and composition across northeastern North America. Extensive overstory mortality has resulted in prolific root suckering in some stands leading to the development of understory thickets of clonal small-stemmed beech. Beech thickets may impact local forest biodiversity, but this has not been adequately evaluated. We hypothesized significant differences in diversity of groundcover flora, small mammals, amphibians, and craneflies between plots with and without beech thickets. Paired plots were established in unevenaged northern hardwood forest stands with no recent management history at two sites in the Adirondack Mountains of New York State. Groundcover plants, terrestrial craneflies, amphibians and small mammals were sampled on twenty paired plots. Discriminant analysis showed a significant difference between thicket and non-thicket (control) areas; important variables in plot type separation were beech sapling abundance, leaf litter depth, and coarse woody debris volume. Groundcover plant cover, richness, and diversity was significantly lower in thicket plots compared to non-thicket plots, while thicket density explained 17%-38% in groundcover plant species diversity. No significant differences were found between the diversity of cranefly, amphibian and small mammal communities of each plot type. This study shows beech thickets to be important in determining local biodiversity.

3 Background and Justification Biodiversity is important to many ecological functions, including nutrient cycling and primary productivity. Loss of foundation species (e.g. trees in forests) can have cascading effects on forest biota. By killing mature trees, invasive pathogens and insect pests can alter forest structure and composition. The beech bark disease (BBD) complex affects populations of mature American beech (Fagus grandifolia) trees across eastern North America Involves the felted beech scale (Cryptococcus fagisuga) and at least one fungal pathogen (Neonectria sp.). Bark lesions, crown dieback, and reduced radial growth culminate in death of host trees. Clonal sprouts arise from roots of dead mature trees.

4 Background and Justification In forests experiencing heavy BBD-induced mortality extensive thickets of root sprouts can dominate lower forest strata. It remains unclear whether or not beech thickets impact local floral and faunal diversity. Alterations to light quality and quantity due to thicket presence may negatively impact the diversity of groundcover plants. The diversity of insects feeding on woody debris and soil organic matter (e,g, craneflies) may also be negatively impacted as leaf litter inputs are primarily low nutrient beech leaves, in thickets. Beech thickets may provide forest amphibians with a stable moisture environment and, therefore, act provide an environment favoring a greater diversity than adjacent non-thicket regions. Some small mammal species preferentially occupy densely vegetated areas which provides cover from predators. Beech thickets may favor greater small mammal species diversity.

5 Methods In 2009 twenty paired plots (forty total) were established in areas with and without beech thickets. Plot type determination was made by sapling counts along a 16 x 2 m assessment transect Mature canopy and developing saplings were sampled using 11.5 m and 8 m fixed area radial plots, respectively. Groundcover plants were sampled by estimated percent cover of all species occupying five 1m 2 quadrats (Fig 1). Faunal sampling was conducted in 2010 Craneflies were sampled using pyramidal emergence traps covering a 1 m 2 area, traps were checked weekly (Fig 1). Forest amphibians were sampled using 20 min timed searches of cover objects and leaf litter (Fig 1).

6 Methods Small mammals were sampled using a 5 x 5 point trapping grid. We alternated between small Sherman and Tomahawk traps were place at each point (Fig 1). Trapping occurred for three consecutive nights at each plot. Shannon-Weiner and inverse Simpson s diversity indices and species richness were calculated for each plot. Canonical discriminant analysis was used to examine the similarity of plot types Paired t-tests and Mann-Whitney U- tests were used to compare the diversity of functional groups between plot types Figure 1. Diagram of sampling design.

7 Results/Project outcomes Canonical discriminant analysis indicated thicket and non-thickets were significantly different due to beech sapling density, leaf litter depth, and coarse woody debris volume. Observed 43 groundcover plant species. Plant diversity was 19%, 21%, and 32% lower in beech thickets than non-thickets for Shannon-Wiener index, inverse Simpson s index, and species richness, respectively (Table 2). Table 1. Mean diversity metric value and t-test results for comparisons between plot types. Diversity was significantly lower in thicket plots for all metrics

8 Results/Project outcomes Beech thicket density explained 31%, 17%, and 38% of the variation in Shannon-Wiener index, inverse Simpson s index, and species richness values. Indicating the number of beech saplings in an area has a strong influence on groundcover plant diversity. Observed 22 cranefly, 11 amphibian, and 7 small mammal species. No significant differences were observed between plot types for any faunal group, regardless of diversity metric (Tables 2 and 3). Table 2. Mean value for each diversity metric for each faunal group. No significant differences were observed between plot types.

9 Results/Project outcomes Among the small mammal species observed, more mice (Peromyscus spp.) were caught than any other species (Table 3). Table 3. Catch per unit effort (CPUE) values for each species by plot types

10 Results/Project outcomes Results will be used in a variety of educational and outreach formats: College courses on forest ecology and management Groups visiting the SUNY ESF Adirondack Interpretive Center located at the HWF study site Professional foresters and other managers PreK-12 students Public

11 Implications and applications in the Northern Forest region Forested regions of the Northern Forest having experienced heavy BBD mortality and subsequent root sprout proliferation may see a decrease in local floral diversity. Forest managers may want to consider site preparation techniques, such as mechanical removal of understory beech, to ameliorate the impacts of thickets.

12 Future directions Future work on American beech and biodiversity continues on Huntington Wildlife Forest. This includes changes in forest structure and function, impacts of management on biodiversity and forest health, invasive species, etc.

13 List of products Peer-reviewed publications Cale, J.A., McNulty, S.A., Teale, S.A., and Castello, J.D. The impact of beech thickets on biodiversity. Biological Invasions. In review. Other publications Cale, J.A., McNulty, S.A., Teale, S.A., and Castello, J.D Beech thickets impact northern hardwood forest biodiversity. Journal of Forestry. 108(8):423. Presentations Cale, J.A., McNulty, S.A., Teale, S.A., and Castello, J.D Beech thickets impact northern hardwood forest biodiversity. Oral and poster presentations at the Northeastern Natural History Conference, Albany, NY. Cale, J.A., McNulty, S.A., Teale, S.A., and Castello, J.D Beech thickets impact northern hardwood forest biodiversity. Poster presented at the Society of American Foresters national meeting, Albuquerque, NM. (3 rd Place winner, student poster session)