Disturbance is a major factor in determining the spatial structure and temporal dynamics of ecological systems. Many studies have been conducted concerning the plant assemblages around Dipodmys spectabilis mounds compared to the off mound area. These studies have shown that annual plant cover is higher on the kangaroo rat mound compared to off the mound. However, no studies have addressed the effects of these rodents disturbance on the soil seed bank. Soil seed banks are an important component of the plant community particularly in arid environments. Annual plants have been known to create viable seeds that remain dormant in the soil for many years making their seed bank a persistent one. A persistent seed bank allows for future recruitment of plants given favorable conditions that could have a dramatic impact on the overall species diversity of the community. We studied the seed bank of eight forb taxa to ask the following questions: 1) Are there more seeds in the seed bank around kangaroo rat mounds compared to other microhabitats? 2) Does the seed composition differ among the different microhabitats? 3) If the seed composition does differ, do specific physical components of microhabitats predict seed populations?
Selecting of kangaroo rat mounds
25 active kangaroo rat mounds were located on the grassland and 10 mounds were randomly selected for this experiment. Once mounds were selected they were semi-permanently marked with their given number and soil samples were taken.
Collecting of soil samples
Ten active mounds were randomly selected. Sub-samples were taken from each mound and grouped into four categories: the base of the mound (base), one meter from base samples (surrounding), six meters from base samples at the edge of black grama grass clumps (edge) and six meters from base samples in the inter-space between black grama grass clumps (inter-space) (Figure 1). Mound locations will be referred to as base, surrounding, edge, and inter-space for the remainder of the manuscript. Base and surrounding samples were considered on the mound where edge and inter-space samples were considered off the mound. Samples were collected using a soil auger with a 10cm diameter and a 2cm depth. Also, we recorded percent cover of undisturbed bare soil, vegetation, litter, gravel and animal disturbance within a 900cm2 area at each sample location to understand the potential effects of these physical variables on seed accumulation. Undisturbed bare soil percent cover was calculated by subtracting the sum of the percent cover for the other variables from the total.
Processing of samples
Soil samples were dried in an oven for 48 h at 50 C. Then, samples were sifted using the finest possible sieve to capture small seeds and a larger sieve to exclude large particles. To further separate seeds from the soil remaining after sifting, samples were floated in a 1:2:5 salt solution (sodium bicarbonate: sodium hexa-meta-phospate: magnesium sulfate) and then dried. Sub-samples were taken and all seeds were tested for viability and counted. Eight target taxa were identified based on their high occurrences at an adjacent study site. Four of the taxa (Cryptantha crassisepala, Descurainia pinnata, Phacelia integrifolia, and Plantago patagonica) are spring annuals, three (Astragalus missouriensis, Lesquerella fendleri, and Oenothera spp.) are perennial forbs that flower in the spring, and one (Sphaeralacea spp.) is a perennial forb that flowers in the fall. Since we could not distinguish species for the seeds of Sphaeralacea and Oenothera at our site, we analyzed these seeds at the genus level. Identifications were made using a reference collection compiled by Sevilleta biologists along with seeds that we had collected. Viability was tested using the pressure method.
Data currently not available to the public.
Data were visually assessed for any errors.
Additional Information on the Data Collection Period
Data were collected the last week in August 2001.
Additional Study Area Information
Study Area Name: Five Points Grass Core Site
Study Area Location: Five Points is the general area which emcompasses the Black Grama Grassland (known as Five Points Grassland) and Creosote Core (Five Points Larrea) study sites and the transition between Chihuahuan Desert Scrub and Desert Grassland habitats. Both core sites are subject to intensive research activities, including measurements of NPP, phenology, pollinator diversity, and ground dwelling arthropod and rodent populations. There are drought rain-out shelters in both the Grassland and Creosote sites, as well as another set in the mixed ecotone with co-located ET Towers. The grassland Small Mammal Exclosure Study is located here, as well as many plots related to patch mapping and biotic transitions.Elevation: 1616 m
Vegetation: Desert Grassland habitat is ecotonal in nature and the Black Grama Core site is no exception, bordering Chihuahuan Desert Scrub at its southern boundary and Plains-Mesa Grassland at its northern, more mesic boundary. There is also a significant presence of shrubs, dominantly broom snakeweed (Gutierrezia sarothrae), along with less abundant fourwing saltbush (Atriplex canescens), Mormon tea (Ephedra torreyana), winterfat (Krascheninnikovia lanata), tree cholla (Opuntia imbricata), club cholla (O. clavata), desert pricklypear (O. phaeacantha), soapweed yucca (Yucca glauca), and what are presumed to be encroaching, yet sparsely distributed, creosotebush (Larrea tridentata). Characteristically, the dominant grass was black grama (Bouteloua eriopoda). Spike, sand, and mesa dropseed grasses (Sporobolus contractus, S. cryptandrus, S. flexuosus) and sand muhly (Muhlenbergia arenicola) could be considered co-dominant throughout, along with blue grama (B. gracilis) in a more mesic, shallow swale on the site. Notable forb species included trailing four o’clock (Allionia incarnata), horn loco milkvetch (Astragalus missouriensis), sawtooth spurge (Chamaesyce serrula), plains hiddenflower (Cryptantha crassisepala), blunt tansymustard (Descarania obtusa), wooly plaintain (Plantago patagonica), globemallow (Sphaeralcea wrightii), and mouse ear (Tidestromia lanuginosa).North Coordinate:34.3381South Coordinate:34.3381East Coordinate:106.717West Coordinate:106.717