Species–area relationships in the Hantam-Tanqua-Roggeveld,Succulent Karoo,South Africa

The Hantam-Tanqua-Roggeveld subregion is part of the Succulent Karoo hotspot of biodiversity which stretches along the southwestern side of South Africa and Namibia. Forty Whittaker plots were surveyed in the spring of 2005, in eight vegetation associations, to gather diversity data for the Hantam, Tanqua Karoo and Roggeveld areas. Seven plot sizes were used to construct species–area curves using three different models namely: the untransformed linear function, the power function and the exponential function. In general, the power and exponential functions produced a more significant fit to the data than the untransformed linear function. Linear regressions using environmental parameters indicated that altitude, mean annual precipitation and mean annual temperature were significant predictors of species richness at the 1, 10, 100 and 1000 m² scales. To illustrate the variation in species–area curves and species richness across the landscape, a transect through the study area is discussed. The transect stretches eastwards from the Tanqua Karoo across the escarpment into the Roggeveld and crosses five different vegetation associations. Differences between associations were found in species richness in the 1000 m² plots. Each association also produced species–area curves with their own characteristics. Slope values for the samples within an association did not differ significantly, although the intercept value often did. Comparisons between associations along the transect revealed significant differences in the slope value between the associations, except for the Dicerothamnus rhinocerotis Mountain Renosterveld which did not differ significantly from the associations bordering it on either side.     

Life-form species–area relationships in a temperate eucalypt woodland community

Viewing species–area curves in the context of the different life forms that generate them might be instructive for understanding why high species density develops in some plant communities. In order to evaluate the patterns of species density in an Australian temperate eucalypt woodland community, we used species–area curves and document rate of species accumulation by life forms in six nested plots ranging in size from 1 m² to 0.1 ha at 13 woodland sites. Mean total species density was 82 ± 3.8 species at 0.1 ha scales (range 49–104 species), making them amongst the most diverse woodlands in Australia at these spatial scales. Species–area relationships for total species were best described by power function models (log–log linear) with slopes (z) ranging from 0.12 to 0.35 (mean = 0.17 ± 0.02). When species were analysed by life form, species–area relationships were similarly well-described by the power function for all life forms, although their slopes differed significantly; annuals had the lowest slope and woody species the highest. Annuals and perennial herb species density were equal at the smallest spatial scales (mean 11.7 and 11.5 species/m², respectively) and hence, both life forms help generate high small scale species density. Small-scale total species density, but not individual life form, was a significant predictor of larger-scale total species density (r ² = 0.36, P = 0.03). Our findings suggest that high species density may be a general property of temperate eucalypt woodlands with herbaceous understoreys and that the mechanisms that underpin these patterns require further study.     

Species–area curves indicate the importance of habitats’ contributions to regional biodiversity

We examined species–area curves, species composition and similarity (Jaccard's coefficients), and species richness in 17 vegetation types to develop a composite index of a vegetation type's contribution to regional species richness. We collected data from 1 to 1000 m² scales in 147 nested plots in Rocky Mountain National Park, Colorado, USA to compare three species–area curve models’ abilities to estimate the number of species observed in each vegetation type. The log(species)–log(area) curve had the largest adjusted coefficients of determination (r² values) in 12 of the 17 types, followed by the species–log(area) curve with five of the highest values. When the slopes of the curves were corrected for species overlap among plots with Jaccard's coefficients, the species–log(area) curves estimated values closest to those observed. We combined information from species–area curves and measures of heterogeneity with information on the area covered by each vegetation type and found that the types making the greatest contributions to regional biodiversity covered the smallest areas. This approach may provide an accurate and relatively rapid way to rank hotspots of plant diversity within regions of interest.     

A nested-intensity design for surveying plant diversity

Managers of natural landscapes need cost-efficient, accurate, and precise systems to inventory plant diversity. We investigated a nested-intensity sampling design to assess local and landscape-scale heterogeneity of plant species richness in aspen stands in southern Colorado, USA. The nested-intensity design used three vegetation sampling techniques: the Modified-Whittaker, a 1000-m² multiple-scale plot (n = 8); a 100-m² multiple-scale Intensive plot (n = 15); and a 100-m² single-scale Extensive plot (n = 28). The large Modified-Whittaker plot (1000 m²) recorded greater species richness per plot than the other two sampling techniques (P < 0.001), estimated cover of a greater number of species in 1-m² subplots (P < 0.018), and captured 32 species missed by the smaller, more numerous 100-m² plots of the other designs. The Intensive plots extended the environmental gradient sampled, capturing 17 species missed by the other techniques, and improved species–area calculations. The greater number of Extensive plots further expanded the gradient sampled, and captured 18 additional species. The multi-scale Modified-Whittaker and Intensive designs allowed quantification of the slopes of species–area curves in the single-scale Extensive plots. Multiple linear regressions were able to predict the slope of species–area curves (adj R ² = 0.64, P < 0.001) at each Extensive plot, allowing comparison of species richness at each sample location. Comparison of species–accumulation curves generated with each technique suggested that small, single-scale plot techniques might be very misleading because they underestimate species richness by missing locally rare species at every site. A combination of large and small multi-scale and single-scale plots greatly improves our understanding of native and exotic plant diversity patterns.     

Use of species richness estimators improves evaluation of understory plant response to logging: a study of redwood forests

The recovery of native understory plant communities after timber harvest has received a great amount of attention worldwide. However, most of these studies have ignored the potentially significant effects that differences in habitat across forest development may have on the species–area relationship, even though sampling efficacy among forest developmental stages may differ markedly as a result of equal sampling within stages. We examined vascular plant community structure in coastal redwood forests of northern California (USA) in forest patches in each of four forest stages that develop with forest age: Initiation, Closure, Mature, and Old-growth. We also used a set of traditional and novel approaches to assess sampling efficacy and guide our sampling design. We initially sampled 75 circular plots (0.04 ha) in stands within each forest stage across a 1,347 km² area. The species–area relationship suggested we had adequately sampled all stages after the first season of data collection, but non-parametric richness estimators (Incidence-based Coverage Estimator or ICE) and Michaelis–Menten means (MMMeans) rarefaction curves, indicated inadequate sampling of the older stages. Thus, we added four more samples within the Old-growth forest stage, establishing a more equitable sample of all stages. Our full data set demonstrated significant differences between plant communities in previously harvested forests (‘managed’ = Initiation, Closure, and Mature) and ‘unmanaged’ forests (Old-growth). Though several understory species were present in all stages, a suite of Old-growth indicator and restricted species suggest that recovery of some species may take long periods in managed forests. Interestingly, a separate suite of common understory species were lacking in Old-growth, and species richness in this stage was lower than in the mature managed forests. We discuss how this departure from the prediction of peak richness in Old-growth may relate to fire suppression in Old-growth forests. Lastly, analysis of our initial, smaller sampling of plots suggested that Old-growth plots were the least species rich. However, additional sampling of the Old-growth stage demonstrated that Old-growth plots were as rich as Closure plots. This has important implications for all studies concerned with measuring recovery after forest disturbances; stage-dependent habitat-mediated differences that affect sampling efficacy may not be captured by traditional sampling methods.     

The relationship between psyllid leaf galls and redbay (Persea borbonia) fitness traits in sun and shade

Spatial autocorrelation in vegetation has been discussed extensively, but little is yet known about how standard plant sampling methods perform when confronted with varying levels of patchiness. Simulated species maps with a range of total abundance and spatial autocorrelation (patchiness) were sampled using four methods: strip transect, randomly located quadrats, the non-nested multiscale modified Whittaker plot and the nested multiscale North Carolina Vegetation Survey (NCVS) plot. Cover and frequency estimates varied widely within and between methods, especially in the presence of high patchiness and for species with moderate abundances. Transect sampling showed the highest variability, returning estimates of 19–94% cover for a species with an actual cover of 50%. Transect and random methods were likely to miss rare species entirely unless large numbers of quadrats were sampled. NCVS plots produced the most accurate cover estimates because they sampled the largest area. Total species richness calculated using semilog species-area curves was overestimated by transect and random sampling. Both multiscale methods, the modified Whittaker and the NCVS plots, overestimated species richness when patchiness was low, and underestimated it when patchiness was high. There was no clear distinction between the nested NCVS or the non-nested modified Whittaker plot for any of the measures assessed. For all sampling methods, cover and especially frequency estimates were highly variable, and depended on both the level of autocorrelation and the sampling method used. The spatial structure of the vegetation must be considered when choosing field sampling protocols or comparing results between studies that used different methods.     

Predicting yellow toadflax infestations in the Flat Tops Wilderness of Colorado

Understanding species–environment relationships is important to predict the spread of non-native species. Yellow toadflax (Linaria vulgaris Mill.) is an invasive perennial recently found in the Flat Tops Wilderness of the White River National Forest on the western slope of the Colorado Rocky Mountains. We hypothesized yellow toadflax occurrence could be predicted from easily measured site characteristics. We used logistic regression with stepwise selection to generate a model to predict yellow toadflax occurrence on a particular plot based on that site’s physical characteristics. The experimental design was a paired-plot study in two locations using circular 1,018-m² plots. Sixty-eight plots that did not contain yellow toadflax and 65 plots that contained yellow toadflax were sampled at the Ripple Creek site in 1999. In 2000, 54 non-toadflax plots and 55 toadflax-containing plots were sampled in the Marvine Creek site. Site characteristics sampled included: vegetation type; under-canopy light level; slope; aspect; soil properties; presence of disturbance, trails, and/or water; and total species richness. A model that correctly classified >90% of the 242 plots sampled included two vegetation type parameters, the presence of trails, and total species richness. Yellow toadflax is most often found in areas that were open-canopy sites, along trails, and with higher species diversity plots (>23 species). This approach can be used for other species in other areas to rapidly identify areas vulnerable to invasion.     

Plot shape effects on plant species diversity measurements

Abstract. Question: Do rectangular sample plots record more plant species than square plots as suggested by both empirical and theoretical studies? Location: Grasslands, shrublands and forests in the Mediterranean‐climate region of California, USA. Methods: We compared three 0.1‐ha sampling designs that differed in the shape and dispersion of 1‐m² and 100‐m² nested subplots. We duplicated an earlier study that compared the Whittaker sample design, which had square clustered subplots, with the modified Whittaker design, which had dispersed rectangular subplots. To sort out effects of dispersion from shape we used a third design that overlaid square subplots on the modified Whittaker design. Also, using data from published studies we extracted species richness values for 400‐m² subplots that were either square or 1:4 rectangles partially overlaid on each other from desert scrub in high and low rainfall years, chaparral, sage scrub, oak savanna and coniferous forests with and without fire. Results: We found that earlier empirical reports of more than 30% greater richness with rectangles were due to the confusion of shape effects with spatial effects, coupled with the use of cumulative number of species as the metric for comparison. Average species richness was not significantly different between square and 1:4 rectangular sample plots at either 1‐ or 100‐m². Pairwise comparisons showed no significant difference between square and rectangular samples in all but one vegetation type, and that one exhibited significantly greater richness with squares. Our three intensive study sites appear to exhibit some level of self‐similarity at the scale of 400 m², but, contrary to theoretical expectations, we could not detect plot shape effects on species richness at this scale. Conclusions: At the 0.1‐ha scale or lower there is no evidence that plot shape has predictable effects on number of species recorded from sample plots. We hypothesize that for the mediterranean‐climate vegetation types studied here, the primary reason that 1:4 rectangles do not sample greater species richness than squares is because species turnover varies along complex environmental gradients that are both parallel and perpendicular to the long axis of rectangular plots. Reports in the literature of much greater species richness recorded for highly elongated rectangular strips than for squares of the same area are not likely to be fair comparisons because of the dramatically different periphery/area ratio, which includes a much greater proportion of species that are using both above and below‐ground niche space outside the sample area.     

A Modified-Whittaker nested vegetation sampling method

A standardized sampling technique for measuring plant diversity is needed to assist in resource inventories and for monitoring long-term trends in vascular plant species richness. The widely used Whittaker plot (Shmida 1984) collects species richness data at multiple spatial scales, using 1 m², 10 m², and 100 m² subplots within a 20 m × 50 m (1000 m²) plot, but it has three distinct design flaws involving the shape and placement of subplots. We modified and tested a comparable sampling design (Modified-Whittaker plot) that minimizes the problems encountered in the original Whittaker design, while maintaining many of its attractive attributes. We overlaid the two sampling methods in forest and prairie vegetation types in Larimer County, Colorado, USA (n=13 sites) and Wind Cave National Park, South Dakota, USA (n=19 sites) and showed that the modified design often returned significantly higher (p<0.05) species richness values in the 1 m², 10 m², and 100 m² subplots. For all plots, except seven ecotone plots, there was a significant difference (p<0.001) between the Whittaker plot and the Modified-Whittaker plot when estimating the total number of species in the 1000 m² plots based on linear regressions of the subplot data: the Whittaker plot method, on average, underestimated plant species richness by 34%. Species-area relationships, using the Modified-Whittaker design, conformed better to published semilog relationships, explaining, on average, 92% of the variation. Using the original Whittaker design, the semilog species-area relationships were not as strong, explaining only 83% of the variation, on average. The Modified-Whittaker plot design may allow for better estimates of mean species cover, analysis of plant diversity patterns at multiple spatial scales, and trend analysis from monitoring a series of strategically-placed, long-term plots.     

Facilitations between the Introduced Nitrogen-fixing Tree, Robinia pseudoacacia, and Nonnative Plant Species in the Glacial Outwash Upland Ecosystem of Cape Cod, MA

Robinia pseudoacacia, a nitrogen-fixing, clonal tree species native to the central Appalachian and Ozark Mountains, is considered to be one of the top 100 worldwide woody plant invaders. We initiated this project to determine the impact of black locust (Robinia pseudoacacia) on an upland coastal ecosystem and to estimate the spread of this species within Cape Cod National Seashore (CCNS). We censused 20 × 20 m plots for vegetation cover and environmental characteristics in the center of twenty randomly-selected Robinia pseudoacacia stands. Additionally, paired plots were surveyed under native overstory stands, comprised largely of pitch pine (Pinus rigida) and mixed pitch pine–oak (Quercus velutina and Quercus alba) communities. These native stands were located 20 m from the edge of the sampled locust stand and had similar land use histories. To determine the historical distribution of black locust in CCNS, we digitized and georeferenced historical and current aerial photographs of randomly-selected stands. Ordination analyses revealed striking community-level differences between locust and pine–oak stands in their immediate vicinity. Understory nonnative species richness and abundance values were significantly higher under Robinia stands than under the paired native stands. Additionally, animal-dispersed plant species tended to occur in closer stands, suggesting their spread between locust stands. Robinia stand area significantly decreased from the 1970’s to 2002, prompting us to recommend no management action of black locust and a monitoring program and possible removal of associated animal-dispersed species. The introduction of a novel functional type (nitrogen-fixing tree) into this xeric, nutrient-poor, upland forested ecosystem resulted in ‘islands of invasion’ within this resistant system.     

Breeding ecology of an Old World high-altitude warbler, Phylloscopus affinis

Reproduction of Tickell’s Leaf Warblers Phylloscopus affinis was studied in an alpine valley (29°27′N, 91°40′E, 3,980–5,600 m) in the Lhasa mountains, Tibet, at the upper elevational limit of the species’ breeding range. This species is a summer breeder, and is the only breeding Phylloscopus species in the valley. It nested in all types of shrubby vegetation across the altitudinal range of the valley. Most nests were placed close to the ground (<1 m) in low thorn bushes. Egg-laying dates fell between late May and early July, most within the first 3 weeks after the commencement of breeding. Mean clutch size was 4.0 (3–5) and mean brood size at fledging 3.4 (2–5). Incubation was by the females and lasted 13–14 days, and both parents cared for the young for 14–17 days. Nestlings ready to leave the nest were 13% heavier than the adults. Overall, 76% of nesting attempts produced at least one fledged young. Some aspects of the breeding biology of this high-altitude warbler were compared with those of lower-altitude Phylloscopus species.     

Optimizing conservation of forest diversity: a country-wide approach in Mexico

A recent vegetation study [Palacio-Prieto et al. (2000) Bol Inst Geogr UNAM 43:183–203] showed that Mexico’s forest area has declined to 33.3%, from originally 52.0% of the country’s land area. In order to assess strategies for tree diversity conservation, we compiled a list of 846 tree species native to Mexico, and determined for each the presence or absence in 234 geographical squares of 1° latitude by 1° longitude (approximately 106 × 106 km). On the average, any two squares shared only 6% of their species composition. Using a standard optimization method from engineering and economics [Dantzig (1963) Linear programming and extensions. Princeton University Press, Princeton, NJ, USA, 625 p], we determined the minimally necessary land area in Mexico to conserve the 846 tree species, while securing that each species is found in an area of (approximately) 1,100 km² of currently existing forest vegetation. Furthermore, we took into account 15 existing protected areas with a size of at least 1,100 km² each. With these constraints, the total minimum area needed to conserve all 846 tree species is 45,136 km² of currently existing forest vegetation, or 2.3% of Mexico’s surface. While this analysis can be refined with subsequent field work, the proposed reserve network indicates that efficient land use planning on a national scale may be able to conserve tree species diversity in a relatively small portion of Mexico, even after severe deforestation has taken place.     

Diversity and productivity of plant communities across the Inland Northwest,USA

No definitive explanation for the form of the relationship between species diversity and ecosystem productivity exists nor is there agreement on the mechanisms linking diversity and productivity across scales. Here, we examine changes in the form of the diversity–productivity relationship within and across the plant communities at three observational scales: plots, alliances, and physiognomic vegetation types (PVTs). Vascular plant richness data are from 4,760 20 m² vegetation field plots. Productivity estimates in grams carbon per square meter are from annual net primary productivity (ANPP) models. Analyses with generalized linear models confirm scale dependence in the species diversity–productivity relationship. At the plot focus, the observed diversity–productivity relationship was weak. When plot data were aggregated to a focus of vegetation alliances, a hump-shaped relationship was observed. Species turnover among plots cannot explain the observed hump-shaped relationship at the alliance focus because we used mean plot richness across plots as our index of species richness for alliances and PVTs. The sorting of alliances along the productivity gradient appears to follow regional patterns of moisture availability, with alliances that occupy dry environments occurring within the increasing phase of the hump-shaped pattern, alliances that occupy mesic to hydric environments occurring near the top or in the decreasing phase of the curve, and alliances that occupy the wettest environments having the fewest species and the highest ANPP. This pattern is consistent with the intermediate productivity theory but appears to be inconsistent with the predictions of water–energy theory.     

Plant composition in the Maya Biosphere Reserve: natural and anthropogenic influences

We studied the floristic composition and stand structure of lowland forests of the Maya Biosphere Reserve (MBR) of El Petén, Guatemala. Sampling was performed over a gradient of human influence, including a newly established returnee community (migrant), the cooperative Unión Maya Itzá, as well as an adjacent protected area within the core area of the MBR. Five 1-ha plots, each divided into 100 contiguous 10 × 10 m² subplots, were used to record presence of all tree and vine species. The study area is a low-diversity rainforest with a canopy layer dominated by species of Fabaceae, a shrub layer dominated by Rubiaceae, and vines dominated by Bignoniaceae. Vines were conspicuous both in number and in diversity. Variation in both tree life-form composition and canopy abundance pattern apparently reflect variation in intensity of forestry among the plots. The similarities between the plots in the cooperative (a logging plot and a settlement plot) with regard to species area curves, and mean number of tree and understory species per subplot, may indicate effects of disturbance (in general) on vegetation structure. Detrended correspondence analysis (DCA) was used to investigate gradients in species composition among the five plots (125 subplots) and to generate hypotheses about vegetation–environment relationships. The study area appears as a mosaic of site-specific forest types or associations determined by a particular species or groups of co-dominant species. The main environmental characteristics of the area determining species composition and structure are related to the drainage of soils and human disturbance.     

Low vegetation recovery after short-term cattle exclusion on Robinson Crusoe Island

Livestock browsing and grazing are considered serious threats to the conservation of the Juan Fernández Islands’ flora, Chile. Nowadays the elimination of grazing by cattle is very difficult. In order to prevent the␣entrance of cattle into the native forests, an 8.3 km-long fence was established on the main island (Robinson Crusoe). The response of the vegetation was evaluated during 27 months of exclusion. The changes in abundances and composition of species were monitored in 12 permanent plots, each of 25 m², located in ungrazed and grazed areas. We expected an increase in plant height and total ground cover in the ungrazed area, and also a directional compositional change towards forest species. We found five different patterns of variation or non-variation for the 22 species observed: (i) one species (Acaena argentea) diminished in abundance in the ungrazed area; (ii) another one (Conium maculatum) increased in the ungrazed area; (iii) one species (Vulpia bromoides) increased in the grazing area; and some species displayed no net variation, but they showed (iv) a nearly constant occurrence, or (v) they appeared and disappeared sporadically. Contrary to our hypothesis, the vegetation showed no net differences in cover on both sides of the fence. As expected, plant height increased in the ungrazed area. In this area, we detected no noteworthy changes in floristic composition towards forest species. On the contrary, four new pastureland species appeared outside of the exclusion area during the last year of evaluation. Other ungrazed sectors of the island showed qualitative differences from grazed sectors, such as major height and density of plants, and lower intensity of browsing, grazing, and trampling, attributable to a reduction of herbivorous pressure. The modest responses reported in this study could be related to the short lapse of time since the exclusion, soil compaction, overgrowth by a single species (A. argentea), great seasonal variations in different species’ abundances, the reduction in the number of cattle grazing the area previous to the fence’s installation, and persistent herbivory by rabbits (Oryctolagus cuniculus L.). We conclude that the effect of grazing by cattle is␣less than expected, and that there are other factors that delay the recovery of the Juan Fernández pasturelands.     

Protected areas of Borneo fail to protect forest landscapes with high habitat connectivity

Throughout the world, previously extensive areas of natural habitats have been degraded and fragmented, and improving habitat connectivity may help the long-term persistence of species, and their ability to adapt to climate changes. We focused on Borneo, where many remaining areas of tropical forest are highly fragmented, and we assessed the extent to which Protected Areas (PAs) protect highly-connected forest sites. We analysed remotely-sensed land cover data (0.86 km² grid cell resolution) using ‘Zonation’ reserve design software, and we ranked grid cells (rank 0–1) according to forest extent and connectivity. PAs currently cover 9% of Borneo, but <20% of highly-connected cells (i.e. cells with Zonation ranks ≥0.9) lie within PAs. Approximately 65% of highly-connected cells were located above 400 m elevation, although >60% of Borneo’s total land area lies below 200 m and only 15% of highly-connected cells occurred in these low elevation areas. These findings were relatively insensitive to assumptions about species’ dispersal ability (within the range 1–20 km; representing relatively mobile animal species). The percentage of highly-connected grid cells within PAs could rise from <20 to >50% under proposed new PAs (including the ‘Heart of Borneo’ project), although many other highly-connected sites will remain unprotected. On-going land-use changes mean that existing PAs in lowland areas are likely to become increasingly isolated within inhospitable agricultural landscapes, and improving connectivity through reforestation and rehabilitation of degraded forest may be required to maintain the conservation value of these PAs in future.     

Hurricane disturbance in a temperate deciduous forest: patch dynamics, tree mortality, and coarse woody detritus

Patch dynamics, tree injury and mortality, and coarse woody detritus were quantified to examine the ecological impacts of Hurricane Fran on an oak-hickory-pine forest near Chapel Hill, NC. Data from long-term vegetation plots (1990–1997) and aerial photographs (1998) indicated that this 1996 storm caused patchy disturbance of intermediate severity (10–50% tree mortality; Woods, J Ecol 92:464–476, 2004). The area in large disturbance patches (>0.1 ha) increased from <1% to approximately 4% of the forested landscape. Of the forty-two 0.1-ha plots that were studied, 23 were damaged by the storm and lost 1–66% of their original live basal area. Although the remaining 19 plots gained basal area (1–15% increase), across all 42 stands basal area decreased by 17% because of storm impacts. Overall mortality of trees >10 cm dbh was 18%. The basal area of standing dead trees after the storm was 0.9 m²/ha, which was not substantially different from the original value of 0.7 m²/ha. In contrast, the volume and mass of fallen dead trees after the storm (129 m³/ha; 55 Mg/ha) were 6.1 and 7.9 times greater than the original levels (21 m³/ha; 7 Mg/ha), respectively. Uprooting was the most frequent type of damage, and it increased with tree size. However, two other forms of injury, severe canopy breakage and toppling by other trees, decreased with increasing tree size. Two dominant oak species of intermediate shade-tolerance suffered the largest losses in basal area (30–41% lost). Before the storm they comprised almost half of the total basal area in a forest of 13% shade-tolerant, 69% intermediate, and 18% shade-intolerant trees. Recovery is expected to differ with respect to vegetation (e.g., species composition and diversity) and ecosystem properties (e.g., biomass, detritus mass, and carbon balance). Vegetation may not revert to its former composition; however, reversion of biomass, detritus mass, and carbon balance to pre-storm conditions is projected to occur within a few decades. For example, the net change in ecosystem carbon balance may initially be negative from losses to decomposition, but it is expected to be positive within a decade after the storm. Repeated intermediate-disturbance events of this nature would likely have cumulative effects, particularly on vegetation properties.     

Species response curves of oak species along climatic gradients in Turkey

The genus Quercus is one of the most important tree species in Turkey. However, little is known on the ecological preferences of Turkish oak species regarding climate. We analyzed species response curves using a HOF-model approach to describe the general pattern of oak distributions along climatic gradients and to identify the driving climatic factors for eight oak species in Turkey. While climate data were extracted from the free available worldclim dataset, occurrence data on oak species were assembled from the literature into a vegetation database (n = 1,104). From the analyzed species response curves, only fa ew (16%) showed unimodal responses, while most were linear (31%) or exhibited a threshold response (31%). The driving factors were seasonality of temperature and seasonality of precipitation, indicating that Turkish oak species can be characterized best by the preference of climatic stability. These findings have important implications for conservation and climate change research, which usually focuses on trends of the mean values of temperature or precipitation but less often on the seasonality. In this study, we further tested whether niche optima derived from raw mean values of occurrences could replace missing model optima due to non-responsiveness of HOF models of type I. However, we did not find this to be a satisfactory solution. Finally, we discuss the need for the construction of a national database based on phytosociological relevés for Turkey.     

Plant diversity in sacred forest fragments of Western Ghats: a comparative study of four life forms

The effect of fragmentation on different life forms within tropical forest plant communities is poorly understood. We studied the effect of degree of fragmentation and surrounding matrix on trees, lianas, shrubs and epiphytes in tropical forest fragments of Kodagu, Western Ghats, India. These fragments exist as sacred groves amidst a highly modified agricultural landscape, and have been preserved by the religious sentiments of local communities. Plants were sampled at two sites in continuous forests and 11 forest fragments. A total of 122 species of trees, 29 species of lianas, 60 species of shrubs and 66 species of epiphytes were recorded. Trees exhibited a significant species–area relationship (R ² = 0.74). Richness estimates after controlling for stem density (rarefaction) revealed that observed species–area relationship was not an artefact of passive sampling. Variation in species richness of the other three groups was explained by stem density and structural diversity. Linear distance from the reserve forest did not explain any variation in species richness. All life forms exhibited significant nested pattern. Trees were nested along the area gradient while nestedness in the other three groups showed evidence in support of habitat nestedness. The four life forms thus responded variably to degree of fragmentation. Our study revealed that 74% of the regional diversity for trees was contributed by diversity among plots, highlighting the importance of inter-patch habitat diversity in maintaining the total regional species pool. We conclude that trees alone cannot serve as good indicator for taking appropriate conservation measures to mitigate species loss resulting from habitat fragmentation.     

Response of ants and spiders to prescribed fire in oak woodlands of California

Conservation managers of oak woodlands have been reintroducing fire both as an ecological process per se and to assist in restoring native plant communities. To increase our understanding of the impacts of reintroduced fire on ground-dwelling invertebrates we examined the response of ants and spiders to a late season (autumn) prescribed fire conducted in a blue oak (Quercus douglasii) woodland ecosystem in northern California. Twelve 100 m × 100 m plots were established, six plots received a burn treatment and the remaining six plots were unburned controls. Ants and spiders were sampled using pitfall traps left open continuously and collected approximately every 32 days. Sampling was conducted over a year, consisting of four pre-burn and nine post-burn collections. Abundance was analyzed using a repeated measures ANOVA, which showed seed-harvester ants decreased significantly in the two months following the fire. Total spider abundance also showed a significant decrease in two months, although this did not occur immediately after the burn. One spider hunting guild, the ‘diurnal ambush’ group (Thomisidae) remained suppressed for up to nine months. Correspondence analysis measures of ant species abundance with environmental and vegetation variables (percent rock, bare ground, plant species richness and height of herbaceous vegetation) were higher than expected by chance, which assists in explaining some of the responses. Findings from this study revealed that the reintroduction of autumn burns has modest and short-term effect on the invertebrates sampled, suggesting that late season fires are compatible with other conservation goals for oak woodland ecosystems.