Are long‐unburnt eucalypt forest patches important for the conservation of plant species diversity?

Question: Are long‐unburnt patches of eucalypt forest important for maintaining floristic diversity? Location: Eucalyptus forests of southeastern New South Wales, Australia. Methods: Data from 976 sites representing a range of fire history from three major vegetation formations – shrubby dry sclerophyll forest (SF), grassy dry SF and wet SF – were analysed. Generalized linear models were used to examine changes in species richness with increasing time since wildfire and analysis of similarities to examine changes in community composition. Chi‐squared tests were conducted to examine the distribution of individual species across four time since fire categories. Results: Plant species relationships to fire varied between the three formations. Shrubby dry SF supported lower plant species richness with increasing time since wildfire and this was associated with shifts in community composition. Grassy dry SF showed significant shifts in community composition and species richness in relation to time, with a peak in plant species richness 20–30 yr post fire (either prescribed fire or wildfire). Wet SF increased in species richness until 10–20 yr post wildfire then displayed a general declining trend. Species richness in each vegetation type was not related to the fire frequencies and fire intervals observed in this study. Conclusions: Long‐unburnt (30–50 yr post wildfire) forests appeared to play a minor role in the maintenance of plant species diversity in dry forest systems, although this was more significant in wet forests. Maintenance of a range of fire ages within each vegetation formation will assist in maintaining floristic diversity within regions.     

Wildfire–vegetation dynamics affect predictions of climate change impact on bird communities

Community‐level climate change indicators have been proposed to appraise the impact of global warming on community composition. However, non‐climate factors may also critically influence species distribution and biological community assembly. The aim of this paper was to study how fire–vegetation dynamics can modify our ability to predict the impact of climate change on bird communities, as described through a widely‐used climate change indicator: the community thermal index (CTI). Potential changes in bird species assemblage were predicted using the spatially‐explicit species assemblage modelling framework – SESAM – that applies successive filters to constrained predictions of richness and composition obtained by stacking species distribution models that hierarchically integrate climate change and wildfire–vegetation dynamics. We forecasted future values of CTI between current conditions and 2050, across a wide range of fire–vegetation and climate change scenarios. Fire–vegetation dynamics were simulated for Catalonia (Mediterranean basin) using a process‐based model that reproduces the spatial interaction between wildfire, vegetation dynamics and wildfire management under two IPCC climate scenarios. Net increases in CTI caused by the concomitant impact of climate warming and an increasingly severe wildfire regime were predicted. However, the overall increase in the CTI could be partially counterbalanced by forest expansion via land abandonment and efficient wildfire suppression policies. CTI is thus strongly dependent on complex interactions between climate change and fire–vegetation dynamics. The potential impacts on bird communities may be underestimated if an overestimation of richness is predicted but not constrained. Our findings highlight the need to explicitly incorporate these interactions when using indicators to interpret and forecast climate change impact in dynamic ecosystems. In fire‐prone systems, wildfire management and land‐use policies can potentially offset or heighten the effects of climate change on biological communities, offering an opportunity to address the impact of global climate change proactively.     

Effects of disturbances on scuttle flies (Diptera: Phoridae) in Pine Forests

I investigated the ecological consequences of disturbances (anthropogenic and natural) on the scuttle fly communities in four large Pine Forests in Poland. I used data on 17,547 male individuals representing 183 species. Communities found in pine plantations (established in clear-cut areas) and in differently treated post-windstorm (with windthrow logs being left or removed) were less diverse than those found in old-growth forest. The communities recorded in the same habitat types in different forest complexes (ca. 300 km apart) were found to display greater similarity than those recorded on adjacent plots in a given forest (ca. 1 km apart), but covering different habitats. The species-specific preference for habitats after disturbances (clear-cuts and post-windstorm areas) was highly correlated between the forests. The abundance of the species with saprophagous larvae was distinctly higher in the disturbed areas than in the old-growth stands. Also, the body length of the scuttle flies was significantly related to their preference for disturbed or undisturbed habitats: smaller species preferred clear-cuts and post-windstorm areas, whereas larger species were related to intact stands.     

Patterns of floristic richness in vegetation communities of California: regional scale analysis with multi-temporal NDVI

Aim Applying water‐energy dynamics and heterogeneity theory to explain species richness via remote sensing could allow for the regional characterization and monitoring of vegetation community assemblages and their environment. We assess the relationship of multi‐temporal normalized difference vegetation index (NDVI) to plant species richness in vegetation communities. Location California, USA. Methods Sub‐regions containing species inventories for chaparral, coastal sage scrub, foothill woodland, and yellow pine forest communities were intersected with a vegetation community map and an AVHRR NDVI time series for 1990, 1991, 1992, 1995 and 1996. Principal components analysis reduced the AVHRR data to three variables representing the sum and temporal trajectories of NDVI within each community. A fourth variable representing heterogeneity was tested using the standard deviation of the first component. Quadratic forms of these variables were also tested. Species richness was analysed by stepwise regression. Results Chaparral, coastal sage scrub, and yellow pine forest had the best relationships between species richness and NDVI. Richness of chaparral was related to NDVI heterogeneity and spring greenness (r² varied between 0.26 and 0.62 depending on year of NDVI data). Richness of coastal sage scrub was nonlinearly related to annual NDVI and heterogeneity (r² 0.63–0.81), with peak richness at intermediate values. Foothill woodland richness was related to heterogeneity in a monotonic curvilinear fashion (r² 0.28–0.35). Yellow pine forest richness was negatively related to spring greenness and positively related to heterogeneity (r² 0.40–0.46). Main Conclusions While NDVI's relationship to species richness varied, the selection of NDVI variables was generally consistent across years and indicated that spatial variability in NDVI may reflect important patterns in water‐energy use that affect plant species richness. The principal component axis that should correspond closely with annual mean NPP showed a less prominent role. We conclude that plant species richness for coarse vegetation associations can be characterized and monitored at a regional scale and over long periods of time using relatively coarse resolution NDVI data.     

Pollination of Aristolochia pallida Willd. (Aristolochiaceae) in the Mediterranean

A first study of the pollination biology of a Mediterranean Aristolochia species in its natural habitat is presented. In all, 183 flowers of Aristolochia pallida Willd. were investigated, which in total contained 73 arthropods, dominated by two groups of Diptera, black fungus gnats (Sciaridae representing 37%) and scuttle flies (Phoridae representing 19%), respectively. However, only Phoridae are regarded as potential pollinators, since pollen has been found exclusively on the body of these insects. All Phoridae belong to the genus Megaselia and are recognised as three morpho-species. The measurements of flower and insect dimensions suggest that size is an important constraint for successful pollination: (a) the insects must have a definitive size for being able to enter the flower and (b) must be able to get in touch with the pollen. Only very few insect groups found in A. pallida fulfil these size requirements. However, size alone is not a sufficient filter as too many fly species of the same size might be trapped but not function as pollinators. Instead, specific attraction is required as otherwise pollen is lost. Since all trapped Phoridae are males, a chemical attraction (pheromones) is proposed as an additional constraint. Since the flowers are protogynous, the record of Megaselia loaded with pollen found in a flower during its female stage proves that this insect must have had visited at least one different flower during its male stage before. Further on, this observation provides strong evidence that the flowers are cross-pollinated. All these factors indicate a highly specialised pollination of A. pallida by Megaselia species.     

Stand- and plot-level changes in a boreal forest understory community following wildfire

Background: Boreal forest understory plant communities are known to be resilient to fire – the species composition of stands after a fire is quite similar to the pre-fire composition. However, we know little about recovery of individual plants within particular locations in forest stands (i.e. plot-level changes) since we usually do not have pre-fire data for plots.

Aims: We wanted to determine whether species recruited into the same or different locations in a Pinus banksiana stand that experienced a severe wildfire.

Methods: We used pre-existing permanent plots to evaluate the cover of understory after an unplanned wildfire.

Results: Across the entire stand nine of 47 species showed a significant change in cover. The largest change in a plant functional group was in the mosses, with all species present before fire being eliminated. There was no change in species diversity or total cover. At the plot level, species composition showed a much greater change. An average of 47% of the species present in a plot before the fire were absent in the same plot after the fire, and the total species turnover in plots was 88% of the species present before the fire. The plots showed a similar shift in species composition.

Conclusions: These results confirm that boreal forest communities show a high degree of resilience to fire, but within a forest stand species will be found in different locations following fire, potentially exposing them to a different set of biotic and abiotic conditions in these new locations.     

Response of Sierra Nevada forests to projected climate–wildfire interactions

Climate influences forests directly and indirectly through disturbance. The interaction of climate change and increasing area burned has the potential to alter forest composition and community assembly. However, the overall forest response is likely to be influenced by species‐specific responses to environmental change and the scale of change in overstory species cover. In this study, we sought to quantify how projected changes in climate and large wildfire size would alter forest communities and carbon (C) dynamics, irrespective of competition from nontree species and potential changes in other fire regimes, across the Sierra Nevada, USA. We used a species‐specific, spatially explicit forest landscape model (LANDIS‐II) to evaluate forest response to climate–wildfire interactions under historical (baseline) climate and climate projections from three climate models (GFDL, CCSM3, and CNRM) forced by a medium–high emission scenario (A2) in combination with corresponding climate‐specific large wildfire projections. By late century, we found modest changes in the spatial distribution of dominant species by biomass relative to baseline, but extensive changes in recruitment distribution. Although forest recruitment declined across much of the Sierra, we found that projected climate and wildfire favored the recruitment of more drought‐tolerant species over less drought‐tolerant species relative to baseline, and this change was greatest at mid‐elevations. We also found that projected climate and wildfire decreased tree species richness across a large proportion of the study area and transitioned more area to a C source, which reduced landscape‐level C sequestration potential. Our study, although a conservative estimate, suggests that by late century, forest community distributions may not change as intact units as predicted by biome‐based modeling, but are likely to trend toward simplified community composition as communities gradually disaggregate and the least tolerant species are no longer able to establish. The potential exists for substantial community composition change and forest simplification beyond this century.     

Ecology of pollination in a tropical Venezuelan savanna

Pollination modes ecology of a total of 164 plant species was evaluated according to habitats and plant life forms in the Venezuelan Central Plain. Frequency distribution of nine pollination modes showed that, at the community level bee pollination (38.6%) was dominant. Butterfly (13.9%), fly (12.7%), and wasp (10.8%) pollination were the second most frequent. Moth (6.2%) and wind (10.4%) pollination occurred with similar frequency, and the least common were bird (3.1%), beetle (2.3%) and bat (1.9%) pollination. There was a significant interaction effect indicating that pollination mode was affected by the type of habitat. Bee pollination was the most common pollination mode in all habitats with butterfly, fly and wasp pollination being secondary for forest and forest-savanna transition; and butterfly, wasp, wind and fly pollination being secondary for savanna. Wind, butterfly and fly pollination were found in disturbed areas as secondary pollination modes. Pollination modes were significantly associated and affected by life forms. Bee pollination was dominant in all life forms with wasp, butterfly and fly pollination being the secondary for trees, shrubs, and lianas; and butterfly and wind pollination being the secondary for herbaceous species. The number of pollination modes (richness) among life forms ranged between four and nine for epiphytes and perennial herbs respectively. The highest values of diversity indexes among life forms were found in trees and shrubs. The richness and diversity indices of pollination modes were statistically higher for more structured habitats, forest and forest-savanna transition, than herbaceous habitats, savanna and disturbed areas, which is associated with the highest values of diversity indexes in trees and shrubs. Equitability was higher for forest and disturbed areas than forest-savanna transition and savanna. The results of comparative richness, equitability, diversity indices, and the frequency distribution of pollination modes of 19 samples from tropical and temperate communities indicated that richness of pollination modes may be different between tropical and temperate communities. The proportion of each pollination mode suggests four grouping: (1) rain forests and their strata, (2) grassland savanna, and associated disturbed areas, (3) temperate communities, and (4) the most heterogeneous group, contained mostly neotropical communities, including the four habitats of the Venezuelan Central Plain. The frequency of pollination modes, richness, diversity and equitability of communities, habitats, successional stages, and vegetation strata varies with respect to geography, vegetation structure, and plant species richness.     

Palm species richness,abundance and diversity in the Yucatan Peninsula,in a neotropical context

Species richness, abundance and diversity patterns in palm communities in the Yucatan Peninsula were compared at three sites with different forest types (semi‐deciduous, semi‐evergreen and evergreen), as well as different precipitation, geomorphology and soil depth. All individual palms, including seedlings, juveniles and adults, were identified and counted in forty‐five (0.25 ha) transects. A total of 46 000 individual palms belonging to 11 species from nine genera and two subfamilies were recorded. Palm richness, diversity and abundance were highest in the evergreen forest. Species from the subfamily Coryphoideae dominated the semi‐deciduous and semi‐evergreen forests while species from the subfamily Arecoideae dominated the evergreen forest. Seven species were found only in the evergreen forest. Chamaedorea seifrizii and Sabal yapa were found in all three forest types, while Thrinax radiata was found in the semi‐deciduous and semi‐ evergreen forests and Cocothrinax readii only in the semi‐evergreen forest. Compared to other neotropical palm communities, the richness and diversity in the Yucatan Peninsula are lower than in the western Amazon basin. Although palm richness and diversity on the Yucatan Peninsula were positively associated with precipitation, other variables, in particular soil depth and fertility as well as habitat heterogeneity (microtopography and canopy cover), need to be considered to better understand the observed patterns.     

Deconstructing the native–exotic richness relationship in plants

Aim Classic theory suggests that species‐rich communities should be more resistant to the establishment of exotic species than species‐poor communities. Although this theory predicts that exotic species should be less diverse in regions that contain more native species, macroecological analyses often find that the correlation between exotic and native species richness is positive rather than negative. To reconcile results with theory, we explore to what extent climatic conditions, landscape heterogeneity and anthropogenic disturbance may explain the positive relationship between native and exotic plant richness. Location Catalonia (western Mediterranean region). Methods We integrated floristic records and GIS‐based environmental measures to make spatially explicit 10‐km grid cells. We asked whether the observed positive relationship between native and exotic plant richness (R²= 0.11) resulted from the addition of several negative correlations corresponding to different environmental conditions identified with cluster analysis. Moreover, we directly quantified the importance of common causal effects with a structural equation modelling framework. Results We found no evidence that the relationship between native and exotic plant richness was negative when the comparison was made within environmentally homogeneous groups. Although there were common factors explaining both native and exotic richness, mainly associated with landscape heterogeneity and human pressure, these factors only explained 17.2% of the total correlation. Nevertheless, when the comparison was restricted to native plants associated with human‐disturbed (i.e. ruderal) ecosystems, the relationship was stronger (R²= 0.52) and the fraction explained by common factors increased substantially (58.3%). Main conclusions While our results confirm that the positive correlation between exotic and native plant richness is in part explained by common extrinsic factors, they also highlight the great importance of anthropic factors that – by reducing biotic resistance – facilitate the establishment and spread of both exotic and native plants that tolerate disturbed environments.