Community and population dynamics of serpentine grassland annuals in relation to gopher disturbance

Summary This study examines the effects of soil disturbance by gophers on patterns of species abundance in an annual grassland community on serpentine soil. We assessed production, dispersal and storage of seed, germination, survivorship and growth of the most abundant species in undisturbed vegetation and on gopher mounds. Fewer seeds of the dominant species were dispersed onto gopher mounds due to the limited movement of seeds from within the closed vegetation. Species with taller flowering stalks were more likely to colonise gopher mounds. The timing of gopher disturbance in relation to the timing of seed fall determined which species could colonise mounds. Lower numbers of seeds falling onto gopher mounds resulted in lower seedling densities of several species compared with undisturbed areas. Survivorship of the commonest species differed between undisturbed areas and gopher mounds formed at different times of year. This resulted in characteristic spectra of species abundance on the different microhabitats, giving rise to distinct spatial patterning in the community. Plants growing on gopher mounds were generally larger and produced more seed than plants in undisturbed vegetation. We suggest that continued gopher disturbance is a factor allowing several species, including perennial grasses, to persist in this community.     

Impact of pocket gopher disturbance on plant species diversity in a shortgrass prairie community

Summary We examined the impact of pocket gopher disturbances on the dynamics of a shortgrass prairie community. Through their burrowing activity, pocket gophers (Thomomys bottae) cast up mounds of soil which both kill existing vegetation and create sites for colonization by competitively-inferior plant species. Three major patterns emerge from these disturbances: First, we show that 10 of the most common herbaceous perennial dicots benefit from pocket gopher disturbance; that is, a greater proportion of seedlings are found in the open space created by pocket gopher disturbance than would be expected based on the availability of disturbed habitat. Additionally, these seedlings exhibited higher growth rates than adjacent seedlings of the same species growing in undisturbed habitat. Second, we tested two predictions of the Intermediate Disturbance Hypothesis and found that species diversity was greatest for plots characterized by disturbances of intermediate age. However, we did not detect significant differences in diversity between plots characterized by intermediate and high levels of disturbance, indicating that many species are adapted to or at least tolerant of high levels of disturbance. Third, we noted that the abundance of grasses decreased with increasing disturbance, while the abundance of dicots increased with increasing disturbance.     

Original Articles: Differential Influence of Plant Species on Soil Nitrogen Transformations Within Moist Meadow Alpine Tundra

Plant species can influence nitrogen (N) cycling indirectly through the feedbacks of litter quality and quantity on soil N transformation rates. The goal of this research was to focus on small-scale (within-community) variation in soil N cycling associated with two community dominants of the moist meadow alpine tundra. Within this community, the small-scale patchiness of the two most abundant species (Acomastylis rossii and Deschampsia caespitosa) provides natural variation in species cover within a relatively similar microclimate, thus enabling estimation of the effects of plant species on soil N transformation rates. Monthly rates of soil N transformations were dependent on small-scale variation in both soil microclimate and species cover. The relative importance of species cover compared with soil microclimate increased for months 2 and 3 of the 3-month growing season. Growing-season net N mineralization rates were over ten times greater and nitrification rates were four times greater in Deschampsia patches than in Acomastylis patches. Variability in litter quality [carbon:nitrogen (C:N) and phenolic:N], litter quantity (aboveground and fine-root production), and soil quality (C:N) was associated with three principal components. Variability between the species in litter quality and fine-root production explained 31% of the variation in net N mineralization rates and 36% of net nitrification rates. Site variability across the landscape in aboveground production and soil C:N explained 33% of the variation in net N mineralization rates and 21% of net nitrification rates. Within the moist meadow community, the high spatial variability in soil N transformation rates was associated with differences in the dominant species' litter quality and fine-root production. Deschampsia-dominated patches consistently had greater soil N transformation rates than did Acomastylis-dominated patches across the landscape, despite site variability in soil moisture, soil C:N, and aboveground production. Plant species appear to be an important control of soil N transformation in the alpine tundra, and consequently may influence plant community structure and ecosystem function.     

Plant Colonizers Shape Early N-dynamics in Gopher-mounds

Disturbances by fossorial mammals are extremely common in many ecosystems, including the California annual grassland. We compared the impact of juveniles of four common plant colonizers (Aegilops triuncialis, Cerastium glomeratum, Aphanes occidentalis and Lupinus bicolor) on the pools and fluxes of N in mounds created by pocket gophers (Thomomys bottae Mewa). The mechanisms and magnitude of biotic N retention differed among plant species. In mounds colonized by Cerastium, Aphanes and Lupinus, the microbial N pool was significantly larger than the plant N pool, as is typical in California grasslands in the early spring, whereas in mounds colonized by Aegilops, there was a more equal distribution of biotic N between plant and microbial pools. A 1-day ¹⁵N pulse field experiment demonstrated that plant species significantly differed in their effects on the distribution of isotopic N, with the N-fixing Lupinus leaving most (82%) ¹⁵N as inorganic N in soil, whereas more ¹⁵N was immobilized in plants or otherwise removed from the available soil pool in mounds colonized by other species. The impacts of early colonizers on N dynamics suggest that the identity of plant species that initially colonize gopher mounds may have important consequences on the dynamics of the overall grassland community.     

The effects of windthrow on plant species richness in a Central European beech forest

The effects of soil disturbance caused by the uprooting of a single or a few canopy trees on species richness and composition of vascular plant species and bryophytes were examined in a temperate beech forest (Fagus sylvatica) in northern Germany. We recorded the vegetation in 57 pairs of disturbed and adjacent undisturbed plots and established a chronosequence of mound ages to study the effect of time since microsite formation on plant species richness and composition. We found significant differences in plant species richness and composition between disturbed and adjacent undisturbed plots. Species richness of both vascular plants and bryophytes was higher in the disturbed than in the undisturbed plots, but these differences were more pronounced for bryophytes. We suggest that three main factors are responsible for this differential response. The availability of microsites on the forest floor that are suitable for the recruitment of bryophytes is lower than for vascular plants. Establishment of bryophytes in disturbed microsites is favoured by a greater abundance of propagules in the close vicinity and in the soil of the disturbed microsites, as well as by a greater variety of regeneration strategies in bryophytes than in vascular plants. Time since mound formation was a major factor determining plant species richness and composition. A significant decrease in the mean number of species was found from young mounds to intermediate and old mounds. However, differences were observed between vascular plants and bryophytes in the course of changes through time in species richness and composition. A large number of exclusive and infrequent vascular plant species was observed on young mounds, among them several disturbance specialists. We suggest that the establishment of many vascular plant species was infrequent and short-lived due to unfavourable light conditions and a low abundance of propagules. By contrast, the development of a litter layer was the main reason for the decreased mean number of bryophytes on old mounds. Our study supports the view that groups of species differing in important life history traits exhibit different responses to soil disturbance.     

Contrasting effects of ectomycorrhizal and arbuscular mycorrhizal tropical tree species on soil nitrogen cycling: the potential mechanisms and corresponding adaptive strategies

While it is increasingly recognized that ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) tree species vary in their effects on soil nitrogen (N) cycling, little is known about the mechanisms causing and how ECM and AM trees adapt to this variation. Using monoculture plots of six ECM and eight AM tropical trees planted in a common garden, we examined whether the contrasting effects of ECM and AM trees on soil N cycling could be explained by their differences in plant traits. Furthermore, rhizosphere effects on soil N transformations and soil exploration by fine roots were also measured to assess whether ECM and AM trees differed in N acquisition capacities. Results showed that soil NH₄⁺‐N concentration, net N mineralization and net nitrification rates were markedly lower, but soil C:N ratio was significantly higher beneath ECM trees than beneath AM trees. This more closed N cycling caused by ECM trees was attributed to their resource‐conservative traits, especially the poorer leaf litter decomposability compared with AM trees. To adapt to their induced lower soil N availability, ECM trees were found to have greater rhizosphere effects on NO₃^‐‐N concentration, net N mineralization and net nitrification rates to mine N, and higher soil exploration in terms of root length density to scavenge N from soils, indicating that these two strategies work in synergy to meet N demand of ECM trees. These findings suggest that ECM and AM trees have contrasting effects on soil N cycling owing to their differences in leaf litter decomposability and correspondingly possess different N acquisition capacities.     

Gopher mounds decrease nutrient cycling rates and increase adjacent vegetation in volcanic primary succession

Fossorial mammals may affect nutrient dynamics and vegetation in recently initiated primary successional ecosystems differently than in more developed systems because of strong C and N limitation to primary productivity and microbial communities. We investigated northern pocket gopher (Thomomys talpoides) effects on soil nutrient dynamics, soil physical properties, and plant communities on surfaces created by Mount St. Helens’ 1980 eruption. For comparison to later successional systems, we summarized published studies on gopher effects on soil C and N and plant communities. In 2010, 18 years after gopher colonization, we found that gophers were active in ~2.5 % of the study area and formed ~328 mounds ha^?1. Mounds exhibited decreased species density compared to undisturbed areas, while plant abundance on mound margins increased 77 %. Plant burial increased total soil carbon (TC) by 13 % and nitrogen (TN) by 11 %, compared to undisturbed soils. Mound crusts decreased water infiltration, likely explaining the lack of detectable increases in rates of NO₃–N, NH₄–N or PO₄–P leaching out of the rooting zone or in CO₂ flux rates. We concluded that plant burial and reduced infiltration on gopher mounds may accelerate soil carbon accumulation, facilitate vegetation development at mound edges through resource concentration and competitive release, and increase small-scale heterogeneity of soils and communities across substantial sections of the primary successional landscape. Our review indicated that increases in TC, TN and plant density at mound margins contrasted with later successional systems, likely due to differences in physical effects and microbial resources between primary successional and older systems.     

Effects of the northern pocket gopher (Thomomys talpoides) on alpine soil characteristics, Niwot Ridge, CO

Effects of the northern pocket gopher (Thomomys talpoides) on surface soilcharacteristics were examined at the alpinesite of Niwot Ridge, CO. We measured erosionof soil from gopher mounds and compared thecharacteristics of gopher mound (disturbed) andundisturbed soils in two major plant communitytypes. Our measurements of erosion indicatelong-term susceptibility of gopher-disturbedsoils to redistribution by water and/or wind inthis ecosystem. Ecosystem heterogeneityintroduced by the gopher is reflected insignificantly lower SOM in gopher mounds thanin surrounding undisturbed soils, acharacteristic which appears to be causallyassociated with other effects of gopherdisturbance including changes in soil textureand significantly lower clays, total C, totalN, total P, and labile P. In contrast toplant-available P, NO₃ ^– was higherand steadily increased for the short term in both gopher mound soils and those beneath the mounds. These pools of NO₃ ^– thendecreased to pre-disturbance levels by thefollowing spring. Collectively our resultsindicate that, through the physicalmanipulation of soil and subsequent effects onsoil resources, the northern pocket gopherfunctions as an agent of increased ecosystemheterogeneity and soil mass and nutrientredistribution at Niwot Ridge.     

Temporal vegetation dynamics and recolonization mechanisms on different-sized soil disturbances in tallgrass prairie

Assessing the various mechanisms by which plants revegetate disturbances is important for understanding the effects of disturbances on plant population dynamics, plant community structure, community assembly processes, and ecosystem function. We initiated a 2-yr experiment examining temporal vegetation dynamics and mechanisms of recolonization on different-sized soil disturbances created to simulate pocket gopher mounds in North American tallgrass prairie. Treatments were designed to assess potential contributions of the seed rain, soil seed bank, clonal propagation from the edges of a soil mound, and regrowth of buried plants. Small mounds were more rapidly recolonized than large mounds. Vegetative regrowth strategies were the dominant recolonization mechanisms, while the seed rain was considerably less important in maintaining the diversity of forbs and annuals than previously believed. All recolonization mechanisms influenced plant succession, but stem densities and plant mass on soil mounds remained significantly lower than undisturbed controls after two growing seasons. Because natural pocket gopher mounds are indistinguishable from undisturbed areas after two seasons, these results suggest that multiple modes of recruitment concurrently, albeit differentially, contribute to the recolonization of soil disturbances and influence tallgrass prairie plant community structure and successional dynamics.     

Factors Regulating Nitrogen Retention During the Early Stages of Recovery from Fire in Coastal Chaparral Ecosystems

Fire is a fundamental reorganizing force in chaparral and other Mediterranean-type ecosystems. Postfire nutrient redistribution and cycling are frequently invoked as drivers of ecosystem recovery. The extent to which N is transported from slopes to streams following fire is a function of the balance between the rate at which soil microbes retain and metabolize N into forms that readily dissolve or leach, and how rapidly recovering plants sequester this mobilized N. To better understand how fire impacts this balance, we sampled soil and plant N dynamics in 17 plots distributed across two burned, chaparral-dominated watersheds in Santa Barbara County, California. We measured a variety of ecosystem properties in both burned and unburned plots on a periodic basis for 2 years, including soil water content, pH, soil and plant carbon and nitrogen, extractable inorganic nitrogen, dissolved organic nitrogen, and microbial biomass. In burned plots, nitrification was significantly enhanced relative to rates measured in unburned plots. Ephemeral herbs established quickly following the first postfire rain events. Aboveground plant biomass assimilated N commensurate with soil net mineralization, implying tight N cycling during the early stages of recovery. Microbial biomass N, on the other hand, remained low throughout the study. These findings highlight the importance of herbaceous species in conserving ecosystem nutrients as shrubs gradually recover.     

Nitrogen cycling in a northern hardwood forest: Do species matter?

To investigate the influence of individual tree species on nitrogen (N) cycling in forests, we measured key characteristics of the N cycle in small single-species plots of five dominant tree species in the Catskill Mountains of New York State. The species studied were sugar maple (Acer saccharum), American beech (Fagus grandifolia), yellow birch (Betula alleghaniensis), eastern hemlock (Tsuga canadensis), and red oak (Quercus rubra). The five species varied markedly in N cycling characteristics. For example, hemlock plots consistently showed characteristics associated with "slow" N cycling, including low foliar and litter N, high soil C:N, low extractable N pools, low rates of potential net N mineralization and nitrification and low NO ₃ ^– amounts trapped in ion-exchange resin bags buried in the mineral soil. Sugar maple plots had the lowest soil C:N, and the highest levels of soil characteristics associated with NO ₃ ^– production and loss (nitrification, extractable NO ₃ ^– , and resin bag NO ₃ ^– ). In contrast, red oak plots had near-average net mineralization rates and soil C:N ratios, but very low values of the variables associated with NO ₃ ^– production and loss. Correlations between soil N transformations and litter concentrations of N, lignin, lignin:N ratio, or phenolic constituents were generally weak. The inverse correlation between net nitrification rate and soil C:N that has been reported in the literature was present in this data set only if red oak plots were excluded from the analysis. This study indicates that tree species can exert a strong control on N cycling in forest ecosystems that appears to be mediated through the quality of soil organic matter, but that standard measures of litter quality cannot explain the mechanism of control.     

Soil-mixing effects on inorganic nitrogen production and consumption in forest and shrubland soils

Soils that are physically disturbed are often reported to show net nitrification and NO₃⁻ loss. To investigate the response of soil N cycling rates to soil mixing, we assayed gross rates of mineralization, nitrification, NH₄⁺ consumption, and NO₃⁻ consumption in a suite of soils from eleven woody plant communities in Oregon, New Mexico, and Utah. Results suggest that the common response of net NO₃⁻ flux from disturbed soils is not a straightforward response of increased gross nitrification, but instead may be due to the balance of several factors. While mineralization and NH₄⁺ assimilation were higher in mixed than intact cores, NO₃⁻ consumption declined. Mean net nitrification was 0.12 mg N kg⁻¹ d⁻¹ in disturbed cores, which was significantly higher than in intact cores (−0.19 mg N kg⁻¹ d⁻¹). However, higher net nitrification rates in disturbed soils were due to the suppression of NO₃⁻ consumption, rather than an increase in nitrification. Our results suggest that at least in the short term, disturbance may significantly increase NO₃⁻ flux at the ecosystem level, and that N cycling rates measured in core studies employing mixed soils may not be representative of rates in undisturbed soils.     

Influence of the phenolic compound bearing species Ledum palustre on soil N cycling in a boreal hardwood forest

The effects of the understory shrub Ledum palustre on soil N cycling were studied in a hardwood forest of Interior Alaska. This species releases high concentrations of phenolic compounds from green leaves and decomposing litter by rainfall. Organic and mineral soils sampled underneath L. palustre and at nearby non-Ledum sites were amended with L. palustre litter leachates and incubated at controlled conditions. We aimed to know (i) whether L. palustre presence and litter leachate addition changed net N cycling rates in organic and mineral soils, and (ii) what N cycling processes, including gross N mineralization, N immobilization and gross N nitrification, were affected in association with L. palustre. Our results indicate that N transformation rates in the surface organic horizon were not affected by L. palustre presence or leachate addition. However, mineral soils underneath L. palustre as well as soils amended with leachates had significantly higher C/N ratios and microbial respiration rates, and lower net N mineralization and N-to-C mineralization compared to no Ledum and no leachates soils. No nitrification was detected. Plant presence and leachate addition also tended to increase both gross N mineralization and immobilization. These results suggest that soluble C compounds present in L. palustre increased N immobilization in mineral soils when soil biota used them as a C source. Increases in gross N mineralization may have been caused by an enhanced microbial biomass due to C addition. Since both plant presence and leachate addition decreased soil C/N ratio and had similar effects on N transformation rates, our results suggest that litter leachates could be partially responsible for plant presence effects. The lower N availability under L. palustre canopy could exert negative interactions on the establishment and growth of other plant species.     

Effects of understory removal, N fertilization, and litter layer removal on soil N cycling in a 13-year-old white spruce plantation infested with Canada bluejoint grass

Canada bluejoint grass [Calamagrostis canadensis (Michx.) Beauv., referred to as bluejoint below] is a competitive understory species widely distributed in the boreal region in North America and builds up a thick litter layer that alters the soil surface microclimate in heavily infested sites. This study examined the effects of understory removal, N fertilization, and litter layer removal on litter decomposition, soil microbial biomass N (MBN), and net N mineralization and nitrification rates in LFH (the sum of organic horizons of litter, partially decomposed litter and humus on the soil surface) and mineral soil (0–10 cm) in a 13-year-old white spruce [Picea glauca (Moench.) Voss] plantation infested with bluejoint in Alberta, Canada. Removal of the understory vegetation and the litter layer together significantly increased soil temperature at 10 cm below the mineral soil surface by 1.7 and 1.3°C in summer 2003 and 2004, respectively, resulting in increased net N mineralization (by 1.09 and 0.14 mg N kg⁻¹ day⁻¹ in LFH and mineral soil, respectively, in 2004) and net nitrification rates (by 0.10 and 0.20 mg N kg⁻¹ day⁻¹ in LFH and mineral soil, respectively, in 2004). When the understory vegetation was intact, nitrification might have been limited by NH₄ ⁺ availability due to competition for N from bluejoint and other understory species. Litter layer removal increased litter decomposition rate (percentage mass loss per month) from 2.6 to 3.0% after 15 months of incubation. Nitrogen fertilization did not show consistent effects on soil MBN, but increased net N mineralization and nitrification rates as well as available N concentrations in the soil. Clearly, understory removal combined with N fertilization was most effective in increasing rates of litter decomposition, net N mineralization and nitrification, and soil N availability. The management of understory vegetation dominated by bluejoint in the boreal region should consider the strong effects of understory competition and the accumulated litter layer on soil N cycling and the implications for forest management.     

Influence of pocket gopher mounds on a Texas coastal prairie

Summary Effects of pocket gopher (Geomys attwateri) mound-building activity on plant community composition and soil nutrient concentrations were investigated in south Texas on both burned and unburned coastal prairie sites. Pocket gophers deposited large amounts of soil which were lower in nutrient content than randomly-collected samples. Above-ground plant biomass was greater around mounds than in random samples mainly because of increased dicots around mounds on the burned area when compared with random samples on the same area. Pocket gophers may have concentrated their activities (and therefore, mounds) in areas with higher dicot biomass on the burned area since they prefer perennial dicots as food, or the presence of mounds may have ameliorated the apparent negative effect of fire on dicots.     

Temporal patterns in seedling establishment on pocket gopher disturbances

Disturbances often facilitate seedling establishment, and can change the species composition of a community by increasing recruitment of disturbance-adapted species. To understand the effects of pocket gopher disturbances on alpine seedling dynamics, we examined the gopher disturbances effects on seedling emergence and survival on gopher disturbances 0 to 5 years old. In contrast to results from most other ecosystems, these recently created gopher mounds had lower seedling emergence and survival rates than undisturbed areas. A lack of correlation between species abundances on gopher mounds and undisturbed sites in one of the two communities studied suggested that a suite of disturbance-adapted species recruited onto the mounds. To explain low seedling emergence on recent gopher mounds, we quantified gopher mound seed banks and studied recruitment in a site with mounds that ranged from 0 to >20 years old. Seed numbers in first-year gopher mound soils were extremely low relative to undisturbed soils, and this pattern was mirrored in seedling establishment patterns over the long term. Gopher disturbance depressed seedling emergence density for the first 5 years. Subsequently, emergence density increased until at least 20 years following the disturbance. Emergence on disturbances more than 20 years old was higher than on undisturbed sites. Therefore, gopher disturbances probably facilitate seedling establishment in alpine dry and moist meadow; however, this process takes place over decades.     

Invasion by <Emphasis Type="Italic">Aegilops triuncialis</Emphasis> (Barb Goatgrass) Slows Carbon and Nutrient Cycling in a Serpentine Grassland

Invasive plant species alter plant community composition and ecosystem function. In the United States, California native grasslands have been displaced almost completely by invasive annual grasses, with serpentine grasslands being one of the few remaining refugia for California grasslands. This study examined how the invasive annual grass, Aegilops triuncialis, has altered decomposition processes in a serpentine annual grassland. Our objectives were to (1) assess howA. triuncialis alters primary productivity and litter tissue chemistry, (2) determine whether A. triuncialis litter is more recalcitrant to decomposition than native litter, and (3) evaluate whether differences in the soil microbial community in A. triuncialis-invaded and native-dominated areas result in different decomposition rates of invasive and/or native plant litter. In invaded plant patches, A. triuncialis was approximately 50% of the total plant cover, in contrast to native plant patches in which A. triuncialis was not detected and native plants comprised over 90% of the total plant cover. End-of-season aboveground biomass was 2-fold higher in A. triuncialis dominated plots compared to native plots; however, there was no significant difference in belowground biomass. Both above- and below-ground plant litter from A. triuncialis plots had significantly higher lignin:N and C:N ratios and lower total N, P, and K than litter from native plant plots. Aboveground litter from native plots decomposed more rapidly than litter from A. triuncialis plots, although there was no difference in decomposition of belowground tissues. Soil microbial community composition associated with different soil patch types had no effect on decomposition rates. These data suggest that plant invasion impacts decomposition and nutrient cycling through changes in plant community tissue chemistry and biomass production.     

Spatial and temporal variability in California annual grassland: results from a long-term study

Abstract. We present data from the first 11 years of a longterm study of the dynamics of an annual grassland on serpentine soil in Jasper Ridge Biological Preserve, Northern California. Annual rainfall amounts and distributions varied greatly over the period 1982-1993, as did the amount and distribution of gopher disturbance. Temporal variation in gopher disturbance showed no relationship with rainfall, but spatial variation in disturbance frequency was related to soil depth. The disturbance regime experienced by the grassland is complex, both spatially and temporally, and most of the area is disturbed at least once every 3-5 years. Plant species abundances showed a variety of responses to climate variation and disturbance. Abundances of individual species in any given year could not be linked directly to rainfall amount due to hysteresis effects and other interactions. The grassland composition changed markedly over the study. Exclusion of gophers suggested that changing abundances of several species were linked to gopher disturbance. In particular, perennial species' abundances increased greatly in the years following exclosure, but then subsequently declined. Data on plant densities on gopher mounds disturbed at different times of year and in different years indicate that the local species composition remains distinct for a number of years following disturbance. Disturbance history is hence a major factor controlling local community variation. Changing species importances, a complex disturbance regime and the importance of disturbance history make prediction and modelling of this system difficult. It is suggested that the same is probably true for many plant communities, and that long-term studies must be an essential part of ecological research programs. This study illustrates the practical problems inherent in maintaining long-term field experiments and in analyzing complex time series data which suffer from inadvertent deviations from the original experimental design.     

Genetically based trait in a dominant tree affects ecosystem processes

Fundamental links between genes and ecosystem processes have remained elusive, although they have the potential to place ecosystem sciences within a genetic and evolutionary framework. Utilizing common gardens with cottonwood trees of known genotype, we found that the concentration of condensed tannins is genetically based and is the best predictor of ecosystem‐level processes. Condensed tannin inputs from foliage explained 55–65% of the variation in soil net nitrogen (N) mineralization under both field and laboratory conditions. Alternative associations with litter lignin, soil moisture or soil temperature were relatively poor predictors of litter decomposition and net N mineralization. In contrast to the paradigm that the effects of genes are too diffuse to be important at the ecosystem‐level, here we show that plant genes had strong, immediate effects on ecosystem function via a tight coupling of plant polyphenols to rates of nitrogen cycling.     

Simulation models of the interactions between herbivore foraging strategies, social behavior, and plant community dynamics

Herbivory often operates through a feedback in which herbivores affect the success and location of plants, which in turn affects the foraging behavior of animals. Factors other than food, such as social behavior, may influence the interactions between herbivores and the plants they consume. We used a simulation model to compare the effects of foraging and social behavior on plant distribution and foraging efficiency by gophers (Thomomys bottae) in a system characteristic of California grasslands. In this system, annual forbs are the preferred food items, and their abundance increases in areas disturbed by gopher burrowing. In addition, gopher social interactions generate buffer zones between adjacent burrows. During the first year of the simulations, before gophers affected the plant community, feeding efficiency declined with increased gopher density. However, after 40 yr, annual plant abundance increased with increasing gopher density, yielding higher maximum gopher density and per capita foraging efficiency. Conversely, increased width of the buffer zones lowered maximum gopher density and annual plant abundance resulting in lower feeding efficiency. In addition, the compact burrow structure of gophers employing an area-restricted search strategy allowed a higher density of gophers to coexist, resulting in higher annual plant abundance and higher per capita food-capture rates.