Experiments E014, E054 and E122

Land Use and Succession

Experiment E014 - Successional Dynamics on a Resampled Chronosequence

Experiment E054 - Old-Field Chronosequence: Plant Productivity

Experiment E122 - Trophic Structure: Insect Species Diversity, Abundance and Body Size

Introduction

We are interested in the environmental constraints, organismal tradeoffs, and feedbacks that control the rate, pattern, and direction of succession (e.g., Huston and Smith 1987; Theme 2) because these give insights into the mechanisms controlling diversity, community assembly and ecosystem functioning (Theme 3). Moreover, successional patterns demonstrate the impacts and recovery from agricultural disturbance (Theme 1). The assembly of communities and the maintenance of diversity within them may relate to several potential mechanisms: (1) spatial heterogeneity in the physical environment (Tilman 1982, Tilman & Pacala 1993, Ritchie & Olff 1999, or); (2) temporal variability and non-equilibrium conditions (Levins 1979, Armstrong & McGehee 1980; Sommer 1984, 1985; Grover 1988, 1989; Huisman 1999); (3) multi-trophic level interactions and trophic complexity (Carpenter et al. 1985, Power 1990a,b, Oksanen et al. 1981, Fretwell 1977, Hairston & Hairston 1993); (4) neighborhood interactions and dispersal in spatial habitats (Skellam 1951, Levins & Culver 1971, Horn & MacArthur 1972, Levin 1976, 1992, Durrett & Levin 1994, Tilman 1993, 1994, 1997a); and (5) spatial interactions of competitively identical species (Hubbell & Foster 1986, Hubbell 1997). Theories based on these factors can also potentially explain successional dynamics. Recent work at Cedar Creek (Tilman 1997a, Ritchie & Olff 1999, or) and elsewhere (Brown & Nicoletto 1991, Levin 1992, Holling 1992, Hubbell 1997, Peterson et al. 1998) suggests that different mechanisms control community assembly at different spatial scales of observation (Theme 4). Our periodic re-sampling of an old-field chronosequence is allowing us to test these ideas.

Related Mechanistic Studies and Theory:

These results suggest that succession emerges from a complex interaction of plant colonization of abandoned fields, of local competition for N, and of herbivory that limits the abundance and impacts of N-fixers (see Section 2.B.D). Because it is well documented and data rich, this chronosequence has been used for short term “snapshots” of successional patterns of abundances of mycorrhizal fungal species (Johnson et al. 1991), microbial biomass and organic matter dynamics (Zak et al. 1990), litter mass (Inouye et al. 1987c), plant allocation to roots, leaves, stems, and reproduction (Gleeson & Tilman 1990; Craine et al. 1999a), plant tissue C and N, and arthropod diversity and abundances (Siemann et al. 1996, 1999a). These snapshots have been instrumental in showing that succession is driven more by colonization limitation than by the resource ratio hypothesis (Tilman 1985) that initially motivated this work. They continue to provide insights into mechanisms maintaining diversity and regulating C and N budgets following agricultural abandonment.

Future Research:

We will resample soils and vegetation of the full chronosequence, E014, in 2002, giving us five sampling dates over a 19 year period. In order to examine the temporal patterns of C and N accumulation, especially at greater soil depths, we will pull deeper cores (to 60 cm depth), which has not been done since our original sampling in 1983. We will continue sampling plant biomass (sorted to species), insect abundances, and small mammal abundances annually.

At Cedar Creek, we are uniquely poised to explore how patterns in insect and plant diversity are influenced by habitat fragmentation and disturbance across 4 orders of magnitude in spatial scale [plot (1 m), transect (80 m), field (100-500 m, and all of Cedar Creek (12 km)], and 2.5 orders of magnitude in temporal scale (1-240 months). Plant diversity patterns will be discerned from the cover plots sampled in each field. To explore this question for insects, we will undertake an extensive insect fauna survey of 8 major orders of insects in each field in 2002, using monthly sweep and pitfall trap samples within the area proscribed by the transects in each field in E014. This is possible because of the expertise of our on-site entomologist, John Haarstad. Using the annual grasshopper data, we will also explore patterns of grasshopper diversity and community patterns across different temporal scales. This survey will measure size-diversity relationships at 4 different spatial scales, following Siemann et al. (1996). These data should provide unique insights into the causes of variation in insect and plant diversity.

To further explore species’ effects on ecosystem function and succession, J. Knops and D. Wedin propose to examine the mechanism by which species impact ecosystem N cycling. This will use the 16 most abundant plant species of the chronosequence. They will perform a container experiment to determine if plant nutrient use (e.g. allocation patterns, photosynthetic N use efficiency, tissue longevity and stoichiometry) leads to positive feedbacks resulting in diverging productivity and N and C pools on initially identical soils. They will also determine species impacts on N input and losses and the consequence of such differential rates on primary productivity and ecosystem N and C pools. This will provide insights into the aspects of a species’ biology that determine the long-term consequences of successional replacements on ecosystem C and N dynamics. This also will test if short term studies of species impacts on N and C can predict long-term successional patterns.