Shrub Strata Research Articles

Community structure and floristic composition of Quercus fusiformis and Carya illinoinensis forests of the Northeastern Coastal Plain, Coahuila, Mexico

In order to describe community structure and richness in oak and walnut forests occurring along the San Rodrigo, San Diego, Escondido and Arroyo de las Vacas rivers on the Northeastern Coastal Plain (NE Coahuila, Mexico), we established 30 1 000-m2 circular plots, where we measured diameter at breast height (DBH) and tree heights. Tree regeneration and herb and shrub stratum were assessed in 5 2-m2 quadrats per site. A total of 48 species distributed in 29 families were recorded. Families with the largest richness were Poaceae, Asteraceae, and Malvaceae. For the oak forest, tree stratum density and basal area values were 386 stems/ha and 24.36 m2/ha, respectively, whereas for the walnut forest the corresponding values were 302 stems/ha and 21.26 m2/ha. The species with the highest relative importance values were Quercus fusiformis (59.48%) and Carya illinoinensis (57.58%). Total tree richness was 14 species, the most common ones being Celtis reticulata and Diospyros texana, followed closely by C. illinoinensis and Q. fusiformis. Anthropogenic impact appears to result in a poor regeneration reflected as a low sapling density, as well as in the reduction and fragmentation of these communities; in turn, this process has led to intrusions of species typical of the xerophytic Tamaulipan Thorn Scrub. Further studies are needed on the regeneration of the dominant species of these forests in order to describe their dynamics and to promote their preservation.

Deer density effects on vegetation in aspen forest understories over site productivity and stand age gradients

Studies examining the interacting effects of ungulate herbivore pressure and site productivity on vegetation are mostly on grassland–grazing systems and have shown conflicting patterns. Here we examine the effects of deer density (>30 years differences in density between two landowners), site productivity (site index, SI) and stand age on subcanopy vegetation characteristics in 60 closed canopy, clear-cut origin Populus tremuloides dominated stands, Michigan, USA. Stand age effects were included because age varied among stands and can affect subcanopy vegetation patterns. Compared with fewer deer, stands with more deer had greater total forest floor vegetation mass, and its major components bracken fern (Pteridium aquilinum), sedge (mostly Carex pensylvanica) and trees/shrubs <0.25m tall, but lower forb mass and lower forest floor vegetation species richness and diversity. Deer density and SI had strong interacting effects on total forest floor mass, forb mass, and species richness. Forb mass increased with SI, but only in stands with fewer deer, whilst total vegetation mass was greater in stands with more deer at lower SI and declined with SI more sharply than for stands with fewer deer. Species richness increased with SI but more so at lower than higher deer density. Deer density and age had interacting effects on mass of trees/shrubs <0.25m tall and sedge. Compared with fewer deer, stands with more deer had greater sedge and tree/shrub mass, and sedge mass decreased and tree/shrub mass increased more sharply with age. In lower deer stands there was a dense subcanopy tree and shrub strata within and beyond the reach of deer 0.9–10m tall whereas in higher deer stands this vegetation layer was nearly absent. We conclude that higher deer browse pressure in early successional Populus stands (1) strongly limits the recruitment of woody stems to larger (>0.9m tall) size classes, which could affect long-term successional trajectories, and (2) diminishes forb density and species richness, especially at higher site productivity, but increases total forest floor vegetation mass (mostly bracken fern and sedge), especially at lower site productivity. Given associations of bracken fern and sedge with poorer and/or more open sites and assuming high palatability of forbs, this pattern may result from the combination of selective herbivory and higher light availability caused by limited recruitment of trees and shrubs to taller strata.

Predicting understory maximum shrubs cover using altitude and overstory basal area in different Mediterranean forests

In some areas of the Mediterranean basin where the understory stratum represents a critical fire hazard, managing the canopy cover to control the understory shrubby vegetation is an ecological alternative to the current mechanical management techniques. In this study, we determine the relationship between the overstory basal area and the cover of the understory shrubby vegetation for different dominant canopy species (Pinaceae and Fagaceae species) along a wide altitudinal gradient in the province of Catalonia (Spain). Analyses were conducted using data from the Spanish National Forest Inventory. At the regional scale, when all stands are analysed together, a strong negative relationship between mean shrub cover and site elevation was found. Among the Pinaceae species, we found fairly good relationships between stand basal area and the maximum development of the shrub stratum for species located at intermediate elevations (Pinus nigra, Pinus sylvestris). However, at the extremes of the elevation-climatic gradient (Pinus halepensis and Pinus uncinata stands), stand basal area explained very little of the shrub cover variation probably because microsite and topographic factors override its effect. Among the Fagaceae species, a negative relationship between basal area and the maximum development of the shrub stratum was found in Quercus humilis and Fagus sylvatica dominated stands but not in Quercus ilex. This can be due to the particular canopy structure and management history of Q. ilex stands. In conclusion, our study revealed a marked effect of the tree layer composition and the environment on the relationship between the development of the understory and overstory tree structure. More fine-grained studies are needed to provide forest managers with more detailed information about the relationship between these two forest strata.

Seasonal variation in prey abundance influences habitat use by greater horseshoe bats (Rhinolophus ferrumequinum) in a temperate deciduous forest

The hypothesis that patterns of habitat selection of greater horseshoe bats ( Rhinolophus ferrumequinum (Schreber, 1774)) vary across seasons in a temperate deciduous forest was investigated. Variables associated with potentially important ecological factors for greater horseshoe bats (physical structure of shrub stratum, crown canopy, insect availability, lunar phase, and weather) were collected for different seasons, and 75 sampling sites were established in the Luotong Mountain Nature Reserve in northeast China. Insect abundance was highest in late summer and lowest in late autumn. Poisson generalized linear models showed that the activity of greater horseshoe bats was positively related to the height and density of shrub stratum in late summer, whereas the activity of greater horseshoe bats was associated with insect abundance in early and late autumn. During periods of intermediate prey abundance (early summer), the height and density of shrub stratum, as well as insect abundance, influenced the activity of greater horseshoe bats. Shrub stratum may provide shelter against predation for foraging greater horseshoe bats. These results support our prediction that there was a trade-off between importance of food and cover among seasons for foraging bats. These findings are useful for the conservation and management of greater horseshoe bats.

Structure and composition of subalpine summit habitats on Mt. Gede-Pangrango complex, Cibodas Biosphere Reserve, West Java, Indonesia

SADILI, A., KARTAWINATA, K., KARTONEGORO, A., SOEDJITO, H. & SUMADIJAYA, A. 2009. Structure and composition of subalpine summit habitats on Mt. Gede-Pangrango complex, Cibodas Biosphere Reserve, West Java, Indonesia. Reinwardtia 12 (5): 391–404. We undertook a phytosociological analysis of the subalpine herbaceous and shrubby vegetation at the Mandalawangi and Suryakencana meadows and the scrub at the Crater Side at the tops of Mt. Gede and Mt. Pangrango in the Cibodas Biosphere Reserve. We recorded 30 species of 18 families of saplings, shrubs, seedlings and herbs in 78 quadrats with a total area of 7,800 m2. Anaphalis javanica, a woody tall herb and long-lived pioneer was the dominant species in the sapling and shrub stratum, while Isachne pangerangensis, Tripogon exiguus and Carex verticillata were prevalent in the seedling and herb stratum at Mandalawangi and Suryakencana. Stunted shrub is Vaccinium varingaeifolium, dominant in the Crater Side scrub. Based on the importance values, the Mandalawangi meadow may be designated as the Anaphalis javanica-Isachne pangerangensis community type, the Suryakencana meadow as Anaphalis javanica-Tripogon exiguus community type and the Crater Side scrub as Vaccinium varingiaefolium-Seliguea feei community type. The similarity indices between Mandalawangi and Suryakencana community types were very high (>75 %) while those between the Crater Side and Mandalawangi and the Crater Side and Suryakencana were very low (<10 %). Poor soil conditions and fire seem responsible for the perpetual existence of A. javanica.

Relating landscape structure, environment and management to biodiversity indicators estimated from forest inventory data in Catalonia (NE Spain)

There is an increasing need to develop efficient methods for characterising and monitoring forest biodiversity. A landscape scale approach and assessment can provide complementary and valuable information in this respect, by considering patterns and processes that operate at broad scales and influence different aspects of forest biodiversity. Here we analysed the relationships between six forest biodiversity indicators (related to the tree and shrub layers and estimated from a large set of field plots in the Third Spanish National Forest Inventory) and landscape structure, environmental and management variables at a 10 x 10 km scale in the region of Catalonia (NE Spain) through the variation partitioning method. The tree layer indicators were those most predictable from the set of explanatory variables considered, and up to a 77.2 % of total variation was explained for tree species richness. Landscape variables were much more relevant to explain biodiversity patterns than environmental and spatial factors, and landscape composition outperformed the predictive capacity of configuration metrics. Management had a weak but positive effect on the tree layer indicators, while the amount of early successional forest was negatively associated to the tree layer indicators but positively to those of the shrub stratum. Our results highlight the need to (1) concentrate field sampling efforts in those indicators that are less predictable from the landscape scale, such as those related to rare species with a high conservation value, and to (2) incorporate landscape structure variables for forest biodiversity assessments in the Mediterranean, where a landscape management approach may be particularly suited to allow the adaptation of forest biodiversity to the ongoing landscape dynamics related to broad-scale processes such as rural land abandonment or climate change.

Human&amp;#8211;Nature Relationship in Mediterranean Streams: Integrating Different Types of Knowledge to Improve Water Management

Gonzalez, C., A. Clemente, K. A. Nielsen, C. Branquinho, and R. Ferreira dos Santos. 2009. Human–nature relationship in Mediterranean streams: integrating different types of knowledge to improve water management. Ecology and Society 14(2): 35. https://doi.org/10.5751/ES-03069-140235

Observations on flocking behavior of Worthen's Sparrows (Spizella wortheni) and occurrence in mixed-species flocks

Worthen's Sparrow (Spizella wortheni) is one of the most endangered species in Mexico. Its survival depends on appropriate conservation strategies and reliable information about the species. Our study on winter groups of Worthen's Sparrow flocking with other grassland bird species provides preliminary ecological and behavioral information on this species, and its relation to other migratory and resident bird species in La Perforadora Valley, Coahuila, Mexico. We observed flocking associations of Worthen's Sparrow with 16 other species. Ochiai's Association Coefficient indicated Worthen's Sparrow often associated with Vesper Sparrow (Pooecetes gramineus) (0.60), Black-throated Sparrow (Amphispiza bilineata) (0.33), Horned Lark (Eremophila alpestris) (0.27), and Western Bluebird (Sialia mexicana) (0.22). Worthen's Sparrow occurred more frequently in mixed than in monospecific flocks in winter. It foraged more frequently on the ground but also searched in shrub stems, branches, and foliage from perches, and at times hawked for flying insects from perches. Most perches were in the shrub stratum, but fences also were used. Worthen's Sparrow in mixed-species flocks spent more time in foraging activities than those in monospecific flocks.

Development issues in extending plant-based IBIs to forested wetlands in the Midwestern United States

Most plant-based indices of biotic integrity (IBIs) developed for wetlands have focused on emergent wetlands. A Vegetation Index of Biotic Integrity (VIBI-Forest) was developed for forested wetlands in the four large ecoregions of the Ohio. Assessing the effect of human disturbance on the ecological condition of wetland forests is complicated by several factors. First, forest canopies can remain largely intact even after significant degradation of the herb and shrub stratum. Second, increases in total diversity may not be good. In forested wetlands, a major artifact of disturbance is the addition of non-wetland or wetland native or adventive plant species adapted to full sun conditions to their floras. Initial versions of the VIBI-Forest metrics were very sensitive to disturbance-induced increases in diversity. Correcting this problem required modifying or replacing metrics so that only forest dependent species were included in metric calculations. The final VIBI-Forest included metrics which evaluated each forest stratum including the ground layer (% bryophyte), herb layer (shade or seed-less vascular plant species), shrub layer (subcanopy importance value (IV), relative density of young trees), canopy (canopy IV), and composite metrics for all vertical strata (Floristic Quality Assessment Index score, % hydrophytes, % sensitive, % tolerant). Assessing wetland forest condition is further complicated by the fact that some successional communities after canopy death or destruction (shrub swamp, marsh, wet meadow) may have intrinsic value as wetland community types. The solution is not to attempt to derive a one-size-fits-all assessment method but to derive separate protocols for other successional phases that are of value or interest.

Regional faunal decline - reptile occurrence in fragmented rural landscapes of south-eastern Australia

Many species of reptiles are sedentary and depend on ground-layer habitats, suggesting that they may be particularly vulnerable to landscape changes that result in isolation or degradation of native vegetation. We investigated patterns of reptile distribution and abundance in remnant woodland across the Victorian Riverina, south-eastern Australia, a bioregion highly modified (&gt;90%) by clearing for agriculture. Reptiles were intensively surveyed by pitfall trapping and censuses at 60 sites, stratified to sample small (&lt;30 ha) and large (&gt;30 ha) remnants, and linear strips of roadside and streamside vegetation, across the regional environmental gradient. The recorded assemblage of 21 species was characterised by low abundance and patchy distribution of species. Reptiles were not recorded by either survey technique at 22% of sites and at a further 10% only a single individual was detected. More than half (53%) of all records were of two widespread, generalist skink species. Multivariate models showed that the distribution of reptiles is influenced by factors operating at several levels. The environmental gradient exerts a strong influence, with increasing species richness and numbers of individuals from east (moister, higher elevation) to west (drier, lower elevation). Differences existed between types of remnants, with roadside vegetation standing out as important; this probably reflects greater structural heterogeneity of ground and shrub strata than in remnants subject to grazing by stock. Although comparative historical data are lacking, we argue that there has been a region-wide decline in the status of reptiles in the Victorian Riverina involving: (1) overall population decline commensurate with loss of &gt;90% of native vegetation; (2) disproportionate decline of grassy dry woodlands and their fauna (cf. floodplains); and (3) changes to populations and assemblages in surviving remnants due to effects of land-use on reptile habitats. Many species now occur as disjunct populations, vulnerable to changing land-use. The status of reptiles in rural Australia warrants greater attention than has been given to date. Effective conservation of this component of the biota requires better understanding of the population dynamics, habitat use and dispersal capacity of species; and a commitment to landscape restoration coupled with effective ecological monitoring.

Influence of environment, history and vegetative interactions on stand dynamics in a Connecticut forest1

Goslee, S. C. (Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708), W. A. Niering (Department of Botany, Connecticut College, New London, CT 06320), D. L. Urban and N. L. Christensen (Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708). Influence of environment, history and vegetative interactions on stand dynamics in a Connecticut forest. J. Torrey Bot. Soc. 132: 471–482. 2005.—We examined the changing influence of environmental factors and land use history on the composition of the canopy tree, shrub, herb and tree seedling strata of a Connecticut forest over 45 years. The many herb and shrub species initially found in post-agricultural areas of this site declined or disappeared as the forest canopy closed. Tsuga canadensis ([L.] Carriere) increased in importance in the forest canopy until the introduction of the hemlock woolly adelgid (Adelges tsugae Annand). Shade-intolerant understory species are now increasing in abundance as the death of large T. canadensis opens gaps in the canopy. Mantel path analysis, a multivariate technique that allows examination of indirect and direct relationships among variables, was used to quantify the complex network of relationships among environment, land use history and plant community composition. Overall environmental variability was uncorrelated with vegetation, except within the shrub stratum. Slope and drainage were the most important individual environmental factors measured. Land use history was strongly correlated with all four strata, and the strength of this relationship decreased over time. The composition of the tree seedling stratum was highly variable through time; other strata showed more self-similarity between sample dates. Land use history appears to impact the vegetation so strongly as to conceal any effects of environmental variation on this site.

The phytosociology of the Vermaaks, Marnewicks and Buffelsklip valleys of the Kammanassie Nature Reserve, Western Cape

Long-term conservation ecosystems require a broader understanding of the ecological processes involved. Because ecosystems react differently to different management practices, it is important that a description and classification of the vegetation of an area are completed. A vegetation survey of the valley areas of the Kammanassie Nature Reserve was undertaken as part of a larger research project to assess the environmental impacts of large-scale groundwater abstraction from Table Mountain Group aquifers on ecosystems in the reserve. From a TWFNSPAN classification, refined by Braun-Blanquet procedures, 21 plant communities, which can be grouped into 13 major groups, were identified. A classification and description of these communities, as well as a vegetation map of the different areas are presented. Associated gradients in habitat w ere identified by using an ordination algorithm (DECORANA). The diagnostic species as well as the prominent and less conspicuous species of the tree, shrub, forb and grass strata are outlined. The study also resulted in a total number of 481 species being identified and the discovery of a new Erica species. These vegetation surveys and descriptions provide baseline information for management purposes and that allows monitoring as well as similar surveys to be conducted in future.

Estimating aboveground biomass of broadleaved woody plants in the understory of Florida Keys pine forests

Species-specific allometric equations that provide estimates of biomass from measured plant attributes are currently unavailable for shrubs common to South Florida pine rocklands, where fire plays an important part in shaping the structure and function of ecosystems. We developed equations to estimate total aboveground biomass and fine fuel of 10 common hardwood species in the shrub layer of pine forests of the lower Florida Keys. Many equations that related biomass categories to crown area and height were significant ( p < 0.05), but the form and variables comprising the best model varied among species. We applied the best-fit regression models to structural information from the shrub stratum in 18 plots on Big Pine Key, the most extensive pine forest in the Keys. Estimates based on species-specific equations indicated clearly that total aboveground shrub biomass and shrub fine fuel increased with time since last fire, but the relationships were non-linear. The relative proportion of biomass constituted by the major species also varied with stand age. Estimates based on mixed-species regressions differed slightly from estimates based on species-specific models, but the former could provide useful approximations in similar forests where species-specific regressions are not yet available.

Tree growth and competition in a Betula platyphylla-Larix cajanderi post-fire forest in central Kamchatka.

Fire is the dominant disturbance in central Kamchatka boreal forests, yet patterns and mechanisms of stand recovery have not been investigated. Measurements were made of 1433 stems > or =1.3 m height and annual radial increments of 225 randomly selected trees in a 0.4-ha plot of a 53-year-old fire-origin mixed-species stand to examine the spatio-temporal variation in establishment, growth, size inequality and the mode of competition among individual trees. Growth variations were related to tree size, age and local interference with neighbours. Betula platyphylla formed the main canopy following a fire in 1947, with Larix cajanderi and Pinus pumila progressively reinvading the lower tree and shrub stratum. Most B. platyphylla originated from sprouts in small patches (polycormons) during the first 15 post-fire years. Betula platyphylla had normal distributions of diameter and age classes, but negatively skewed height distribution, as expected from shade-intolerant, pioneer species. Larix cajanderi had fewer tall and many short individuals. The smaller and younger B. platyphylla grew disproportionately more in diameter than larger trees from 1950 to 1975, and hence stem size inequalities decreased. The reverse trend was observed from 1995 to 2000: larger trees grew more, indicating an increasing asymmetry of competition for light. Betula platyphylla had steady diameter growth in the first 25 post-fire years, after which the growth declined in smaller trees. Neighbourhood analysis showed that the decline resulted from increased competition from taller neighbours. The observed growth patterns suggest that mode of interactions altered during stand development from early stages of weak competition for soil resources released by fire to later stages of asymmetric competition for light. Asymmetric crown competition started later than reported in other studies, which can be attributed to the lower stem density leaving much space for individual growth, greater relative importance of below-ground competition in this site of nutrient-poor volcanic soil, and the vegetative origin of B. platyphylla. Larix cajanderi growing under B. platyphylla had steady diameter growth during the first 20 years, after which growth declined. It is suggested that early succession fits the tolerance model of succession, while inhibition dominates in later stages.

Temporal patterns of vascular plant diversity in southeastern New Hampshire forests

A chronosequence of 22 sites in Durham, NH, was used to study upland successional patterns of species diversity over a span of 14–209 years of forest development and to test the hypothesis that diversity is maximized at mid-succession. Nested quadrat sampling was used to estimate the relative importance values of vascular plant species in the tree, shrub, and herb strata. The successional status of each site was estimated using two dendrochronological indices: oldest tree index and abandonment index. Four indices of species diversity were calculated for each site and stratum: species richness, the Shannon index, Hurlbert’s probability of interspecific association, and Pielou’s evenness. Within the quadrats of all 22 sites, total richness was 168 species of vascular plants. Richness decreased linearly over the 200-year chronosequence in all strata for both successional indices, from a maximum of 74 species at 14 years to a low of 13 species at 209 years. Evenness showed no evidence of a successional pattern, so the combined indices of diversity (Shannon and Hurlbert) displayed only weak trends. Multiple regression showed that successional age was always a significant predictor of species richness in every stratum (except the shrub stratum when using the abandonment index), and that stem density (i.e., the “sample size effect”) was not significant in the tree stratum when using the oldest tree index. Age indices held comparable or lower P-values than stem density in most strata. It is likely that richness increased from a low value immediately following farm abandonment to a peak around the age of the youngest sites sampled (over a span of 15–30 years), the rate of increase being governed by the availability of dispersing seeds. The observed decline in richness over the rest of succession was probably caused in part by a decrease in available light. The rate of decline was apparently determined by the rate of competitive elimination of shade-intolerant species.

Regeneração de um trecho de floresta de restinga na Reserva Ecológica Estadual de Jacarepiá, Saquarema, Estado do Rio de Janeiro: II - Estrato arbustivo

RESUMO O estrato arbustivo representa o estágio mais adiantado da regeneração da floresta de restinga da Reserva Ecológica Estadual de Jacarepiá, impactada em 25% da área total em 1986. As espécies Trema micrantha e Aegiphila sellowiana são as pioneiras mais abundantes. O método de parcelas, embora moroso, foi eficiente, pois permite o acompanhamento da regeneração. As trepadeiras, no momento não estão relacionadas à reversão da regeneração. Espécies arbóreas que ocorrem na floresta não perturbada parecem ser favorecidas com perturbação; outras são desfavorecidas e outras são capazes de rebrotar. De 110 táxons encontrados, somente 21 são comuns a outros estudos realizados no Brasil em áreas perturbadas de restinga e mata atlântica.

Cutover effects of the vegetation and soil in a natural forest

The disturbance produced on vegetation and soil after selective and total cutover of two sites were evaluated. The working area is located in Bovril, Entre Ríos, Argentina. It belongs to the Espinal Province, Ñandubay District, which has humid temperate climate and clay, compact and waterlogged soil. The woody structure was evaluated by the linear and fringe transecting methods. Each site was analyzed to study the floristic composition and the Sorensen similarity index (Is) was applied. Forage and weeds productivity was determined. The soil variables: total nitrogen, phosphorous, total organic carbon and others were estimated. The DCA design was continued. Dates was compared through ANOVA and Tukey test with SAS statistic siystem. The mean crown coverage for trees was 56,65 % and 38 % in the monte and the renoval. The tree density was 1,814 individuals ha–1 and 1,120 individuals ha–1 for both areas. The mean tree height was 4,10 and 2,9 m in each case. The shrub stratum presented few species and the herbaceous carpet was composed of Poaceae, Ciperaceae and Compositeae and a great diversity of others families of less importance. The annual forage volume was 3,505 and 3,271 kg M.S. ha–1 in both sites. The M.O., total nitrogen, assimilated phosphorous and nitrate reached higher values in forest vegetation soil than in soil lacking forest vegetation. The total removal of natural vegetation in the second gorwth forest produced a substantial alteration in its herbaceous, shrub-like and tree structure and the soil nutritive level.

Bird use of three types of field margins in relation to intensive agriculture in Québec, Canada

Habitat structure and bird use of field margins were studied in intensive farmlands of southern Québec, Canada. The main objectives were: (1) to assess the value of field margins for conserving avian diversity in agricultural landscapes, (2) to document their potential as breeding habitats for bird species particularly those considered as nuisance for crops, and (3) to describe habitat variables that best explained bird use of field margins. Three types of field margins were distinguished: (a) natural hedgerows ( n=27) with well developed tree and shrub strata, (b) planted windbreaks ( n=17) mostly composed of coniferous trees and generally devoid of a well structured shrub stratum, and (c) herbaceous field margins ( n=17) with isolated shrubs. A total of 42 bird species were recorded. Bird use of hedgerows and windbreaks was similar, herbaceous field margins having fewer bird species and individuals than the other two types of field margin. Field margins did not contribute significantly as breeding habitats of bird species that may damage crops, but offered shelter to a broad range of species potentially useful for biological pest control. Bird use of field margins was mostly related to hedges’ structural complexity and dimension. Conserving natural hedgerows, minimising mechanical and chemical control of the vegetation in field margins, and planting a mix of deciduous and coniferous species in windbreaks represent efficient conservation strategies both from a wildlife and an agronomic point of view.

Plant species of traditional Mayan homegardens of Mexico as analogs for multistrata agroforests

The shortened fallow period in traditional slash and burn agriculture of the Maya of Quintana Roo, Mexico, has reduced soil fertility, crop yields, biodiversity, and mature forest vegetation. Studies have shown that agroforests that mimic local ecosystem processes can be used to provide for the farmers' well-being while protecting and preserving forest resources and biodiversity. The objective of this investigation was to identify, describe, and evaluate Mayan crop plants that could be used as analog species in agroforest design. We used participant observation, interviews with farmers, and field measurements to collect information on the social, agricultural, and ecological aspects of the plants. We identified five horizontal and one vertical strata in mature homegardens: the herbaceous stratum, the low shrub stratum, the tall shrub stratum, the fruit tree stratum, the timber tree stratum, and the viny stratum. We categorized 77 forbes, shrubs, and vines identified for their temporal and spatial placement in an agroforest. The plants evaluated can be placed in one of the four developmental stages of an agroforest: the herbaceous stage, and the shrub stage, the fruit tree stage, and the timber tree stage. By using the identified plants and the analog hypothesis, we can design an agroecological system that provides for the farmers' needs, and efficiently utilizes the resources on-site for the production of food, timber, medicinal plants, and nontimber products in a manner that protects the natural resource base of the region.

DOES VERTICAL PARTITIONING OF NEST SITES DECREASE NEST PREDATION?

Abstract Partitioning of nest heights among co-occurring species in response to nest predation has been proposed as a process that helps to structure avian species assemblages. In the experiment reported here, we used artificial nests baited with Japanese Quail (Coturnix japonica) eggs to test (1) whether both rate and final level of nest predation differed among nests placed at ground, shrub, and tree strata; and (2) whether vertical partitioning of nest sites among the three strata decreased nest predation. Although rates of nest predation increased from ground, to partitioned, to shrub, to tree strata, the only significant pairwise differences were between predation on ground nests versus all other treatments. The proportion of nests depredated at the conclusion of the experiment was lowest for the ground treatment, intermediate for the partitioned treatment, and highest for the shrub and tree treatments. Predation was significantly higher in 1988 than in 1989, and significant variation in predation oc...