Species-rich Stands Research Articles

PREDICTING WOODY-PLANT SPECIES RICHNESS IN TROPICAL DRY FORESTS: A CASE STUDY FROM SOUTH FLORIDA, USA

Tropical dry forests are one of the world's most endangered forest types. Currently there are no comparative data on extent or levels of species richness for remaining forest fragments. This research identifies landscape metrics and spectral indices that can be applied at the stand and patch level to predict woody-plant species richness in tropical dry forests. This study was undertaken in 18 stands of tropical dry forest with nine sites in the Florida Keys and nine sites within an urban–agricultural matrix in mainland Florida, USA. Woody-plant species richness was quantified at the stand level (belt transects totaling 500 m2) and patch level (presence/absence data for 65 native tropical plants ≤2.5 cm dbh) for all study sites. Landsat Enhanced Thematic Mapper Plus (ETM+) satellite images (pixel resolution 30 × 30 m) were used to assess the utility of landscape metrics (forest patch area, nearest neighbor distance, shape index, boundary complexity) and spectral indices (normalized-difference vegetation index [NDVI] for nine pixels and 500 pixels directly over transects, and all pixels in the forest patch area) for predicting stand- and patch-level species richness. The 18 stands of tropical dry forest sampled in this study included 4248 woody plants, representing 71 species. Islands in the Florida Keys had higher levels of woody-plant species richness than mainland sites. There was a significant positive relationship between mean NDVI for the nine pixels over each stand and stand species richness and a significant negative relationship between species richness and standard deviation of NDVI for nine pixels over each stand. The density of evergreen plants explained 66% of the variability in mean NDVI. At the patch level, forest patch area and mean NDVI at the stand, 500-pixel, and patch level were all positively associated with patch species richness. However, combining forest patch area with NDVI significantly improved the prediction of patch species richness. Results from this study support the species–energy theory at the level of a forest stand and patch and suggest that a first-order approximation of woody-plant species richness in stands and patches of tropical dry forest is possible in biodiversity hot spots.

Resource use efficiency as a function of species richness and stand composition in upper montane conifer forests of the Sierra Nevada

Abstract Questions: 1. Does resource use efficiency increase with increased species richness in conifer forests? 2. Do patterns found in resource use support niche differentiation/complementarity between species, or is any increase indicative of a selection effect? Location: All data were collected from upper montane (2200–2600 m a.s.l) conifer forests of the Desolation Wilderness in the central California Sierra Nevada, USA. Methods: We established 281 plots of varying levels of conifer richness throughout the wilderness area. Within each plot we used hemispherical photos to measure canopy closure and LAI, total soil carbon and nitrogen from the A-horizon, and stand basal area. We used linear regression and ANOVA to analyse the relationship between stand species richness and resource availability. Results: We found no correlation of either soil nitrogen or carbon with stand biomass. Nor did soil nitrogen and carbon levels change with species richness. Canopy closure increased with species richness but al...

Patterns of Bryophyte Richness in a Complex Boreal Landscape: Identifying Key Habitats at McClelland Lake Wetland

The McClelland Lake Wetland Complex is a large (3,481 ha), boreal, wetland complex dominated by peatlands located in northeastern Alberta, Canada. We intensively sampled the bryophyte flora in 44 sites chosen to capture all landscape features of the wetland. We furthermore partitioned these 44 sites into 67, structurally defined stands. One hundred and fourteen species of bryophytes (91 mosses and 23 hepatics) were found. Mean stand species richness is 16.6, with a range of 2–41 species. Thirty-nine species were recorded only 1–2 times in the 67 stands and these are defined as locally rare species. Additionally, 18 species were recorded that are currently on the Alberta Rare Species Tracking List (ANHIC), although commonness of some within the complex suggests regional under-collection. A strong relationship was found between species richness and locally rare species occurrence at both the site and stand levels. Neither species richness nor locally rare species occurrence is related to landscape position within the wetland complex nor to internal wetland chemical gradients. Both species richness and local species rarity are influenced by stand type and structure. Shrubby, wooded, or forested stands contain 70% of the locally rare species occurrences, and swamps and wooded fens are species rich habitats. Stands with high numbers of locally rare species also tend to be stands that have high species richness; however, not all stands with high species richness have high numbers of locally rare bryophytes. Indicators and assessment protocols based on rare species and richness are developed to define Key Habitats for this wetland complex. Criteria for Key Habitats are stands with both high species richness and high numbers of locally rare species—‘Category 6’ stands, and these are identified as significant features in developing management protocols for bryophyte species and wetland function. Six ‘Category 6’ stands capture 58% of the locally rare species and 90% of the total wetland species richness. All six Key Habitats are wooded or forested.

Brown Root Rot Disease in American Samoa's Tropical Rain Forests

Phellinus noxius (Corner) Cunningham causes root and lower stem rot of woody plants throughout the South Pacific region. Its hosts include rubber, mahogany, cacao, and many timber, fruit, and landscape trees. Though endemic to the Tropics, no reports were found describing brown root rot disease in native forests, exclusively. Incidence, distribution, and host range of P. noxius were measured in primary and secondary rain forests on Tutuila Island, American Samoa. Phellinus noxius was recorded in 19 of 20 strip transects and 1.2-ha established plots and in all vegetation types, infecting 37 tree species in 30 genera and 22 families. Species most affected were Myristica fatua, Dysoxylum samoense, and Hibiscus tiliaceusN25, 16, and 10%, respectively. Of 62 infection centers, 33 contained the same tree species and 13 were dominated by a single species. The fewest infections were recorded at primary montane and ridge top sites. Regenerating secondary valley sites had the highest incidence of disease and greatest number of infection centers. Infection centers at these disturbed sites also contained more trees on average than centers at primary sites. Disease incidence was influenced more by human disturbance than by vegetation type, topography, stem diameter, stem density, or soil type. The disturbed sites also appeared to lack the species richness of mature sites. This agrees with other host/pathogen associations, such as Douglas-fir/P. weirii and hardwood/P. noxius plantations, where disease incidence and spread was higher in species-poor than in species-rich stands.

The Effects of Invasion by Acacia saligna on the Guild Structure and Regeneration Capabilities of South African Fynbos Shrublands

1. The impact of dense stands of the alien invasive species Acacia saligna (Labill) Wendl. on the guild structure of indigenous fynbos vegetation was investigated at three sites on the Cape Peninsula, South Africa. Two Acacia stands of either recent (1-2 fire cycles) or longer (>2 fire cycles) origin were compared with neighbouring uninvaded vegetation. 2. At one site fynbos recruitment was monitored following complete removal of vegetation in the three different stands in order to assess the restoration potential of invaded vegetation. 3. Fynbos species richness, cover and frequency all declined through each invasion stage in the standing vegetation. Guild structure also changed: species with vertebrate-dispersed seeds were relatively more frequent in long-invaded stands and at two of the three sites long-invaded stands had relatively more tall shrubs and fewer shrubs with leptophyllous (ericoid) leaves compared to fynbos. Serotinous shrubs were virtually absent in long-invaded stands. 4. Richness per plot of species recruited by seedlings was highest in fynbos and declined both with stage of invasion and time after clearing. However, the total stand species richness was nearly as high in recently invaded as in uninvaded fynbos. 5. Ephemeral forbs constituted the majority of seedlings in all stands, but after two years they remained the most important growth form in terms of density and cover only in the long-invaded stand. 6. At 18 months after clearing, indigenous canopy cover was about 50% in all stands, but only in uninvaded fynbos did this continue to increase over the second summer. After two years, resprouters formed about half the canopy cover in fynbos and recently invaded stands, but were insignificant in the long-invaded stand. 7. After clearing, many species recruiting in the long-invaded stand were not present in the standing vegetation, indicating that persistent seed banks exist. 8. As representatives of all the major fynbos growth forms were recruited into the long-invaded stand after clearing, albeit at a low density, such stands could revert to vegetation resembling fynbos in structure. However, in order to speed up the restoration process and to improve the probability of a fully functioning ecosystem being established, guilds which have been eliminated, such as serotinous Proteaceae, should be reintroduced.

Species Richness, Species Rarity and Conservation Evaluation of Rich-Fen Vegetation in Lowland England and Wales

(1) The botanical resource of rich-fen sites in England and Wales is analysed, based on a survey between 1972-85 of most known sites. The 464 plant species recorded in the survey are segregated into those (153) for which fens are a major habitat (principal fen species), those (203) that are as well or better represented in other habitats as in fens (affiliated species) and those (108) essentially atypical of fens (accidental species). (2) The occurrence of principal fen species of low frequency (occurring in < 5% of samples) (i.e. rare species) is analysed from 2900 quadrats from herbaceous and wooded fen vegetation. Many rare species occur mainly in just a few distinctive herbaceous vegetation types of low crop mass. Most do not occur at all in fen carr. (3) Variation in species richness (number of species 100 m-2) in 2100 samples of herbaceous fen vegetation is analysed. Very species-rich stands are infrequent and referable to just a few vegetation types. These are the ones that also contain most rare species. (4) Individual fen plant species (principal and affiliated species) occupy a discrete range of vegetation species-richness (the 'associated-richness') in herbaceous fen vegetation samples. Those species which show only small variation in the associated-richness values (interquartile range <50% median associated-richness value) are 'richness indicator species' and their occurrence can be used to predict the species-richness of herbaceous fen vegetation. (5) Regressions of total number of species and number of common species against number of rare species within vegetation samples both show a strong (P < 0 0001) positive relationship. The proportion of rare species within the vegetation also increases with increasing species richness. (6) The present infrequency of species-rich vegetation (and its associated rare species) in undrained fens is probably mainly due to increase in vegetation crop mass at many sites, caused by the abandonment of traditional management regimes perhaps exacerbated by increased net productivity caused by fertilizer run-off from the catchments. (7) A few rare species are most characteristic of comparatively species-poor vegetation of fairly high crop-mass. The reasons for their current rarity are not known. (8) The data on species-richness and rarity provide a basis for conservation priorities in rich-fens. Four possible indices, based on richness and rarity, for the evaluation of fen sites for conservation are proposed and fifteen sites are evaluated using these.

Species richness in the Phanerozoic: Compensating for sampling bias

Sampling biases are the greatest impediment to resolving the history of species richness of fossilizable marine invertebrates in the Phanerozoic. Actual patterns of species richness have remained uncertain because no method is available to compensate for variations in sampling intensity. Data are not obtainable which would permit application of techniques that allow direct compensation for sampling intensity, such as rarefaction, but actual patterns can be estimated with a sampling model designed to account for sampling bias. One can estimate the total species richness of a geologic period if one knows the relative sampling intensity devoted to that period, the original species-abundance distribution of all species that existed during the interval, and the number of species that existed during the Cenozoic. The model presented here is based on the assumption that the species-abundance distributions of fossilizable marine invertebrates were lognormal and that sampling was proportional to sediment area, volume, or paleontologist interest units. The model produces consistent results with different estimates of total Cenozoic species richness and sampling intensity and strongly suggests low diversity during the Paleozoic and Mesozoic, followed by a dramatic early Cenozoic increase in standing species richness. These results are consistent with Valentine9s (1970) Empirical model of species richness.

Species richness in the Phanerozoic: an investigation of sampling effects

Given estimates of the variation in total standing species richness through the periods of the Phanerozoic, mean species duration, and the relative intensity of the sampling of the fauna from each of the periods, the expected number of described species can be predicted for each period of the Phanerozoic using an analytic sampling model. This model is based on the assumption that the relative abundances of species in any geologic period can be approximated by the canonical (lognormal) species-abundance distribution.Three commonly cited models of standing species richness (Valentine, 1973; Gould et al., 1977; Bambach, 1977) each suggest different patterns of species richness in the Phanerozoic. By assuming that sampling of the fossil record is proportionate to sediment volume, it can be shown with the sampling model that the Empirical, Equilibrium, and Species-Richness Models each predict that the number of described species will be strongly correlated with sediment volume. Equally high correlations are predicted if it is assumed that sampling is proportionate to sediment area or to paleontological interest. The correlations predicted for each of the three models are remarkably similar. The impact of sampling effects is so strong that the variations in species richness postulated by these three models are almost completely obscured. Preservational biases will probably only further obscure the relationship between the number of described species and total species richness. Therefore, it seems likely that analysis of trends in the total number of described species will be of little use in determining trends in worldwide species richness in the Phanerozoic.Comparison of the actual patterns of variation in the number of described species and the expected numbers of described species predicted by the sampling model reveals that more species are known from the Cenozoic than would be predicted from the abundance of Cenozoic sediments or from the amount of paleontological interest in the Cenozoic. This might have resulted from the Cenozoic sediments remaining relatively free of diagenetic effects which might have destroyed the fossils entombed in the sediments.