The well-documented decline of the Pinus palustris ecosystem has resulted from several anthropogenic influences, such as forest clearing (e.g. pine plantation forestry, agriculture) and urban development, both of which are closely related to increases in human populations. Other impacts have arisen from alterations in disturbance regimes responsible for maintaining the structure and function of these ecosystems. Restoration and management of degraded pine savanna ecosystems is critical. Identification of ecological processes that determine the structure and function of the intact system are important because successful restoration efforts should be based on sound scientific understanding. In this paper, we introduce this special issue on the ecology, conservation, and restoration of the Pinus palustris ecosystem. Some global climate change scenarios have suggested that future changes may occur that alter frequency and severity of disturbances such as fires and hurricanes. Such changes may have large effects on pine stands, and ultimately entire Pinus palustris savanna ecosystems, thus presenting further challenges to their sustainable management.

Question: What are the mechanisms by which fire reduces competition for both a short-lived and a long-lived species in old-growth ground-cover plant communities of wet pine savannas (originally Pinus palustris, replaced by P. elliottii)?

Location: Outer coastal plain of southeastern Mississippi, USA.

Methods: I reviewed previous competition experiments and proposed a new hypothesis to explain the relationship between fire, competition, and species co-existence in wet longleaf pine savannas. The first study is about growth and seedling emergence responses of a short-lived carnivorous plant, Drosera capillaris, to reduction in below-ground competition and above- plus below-ground competition. The second study deals with growth and survival responses of a long-lived perennial carnivorous plant, Sarracenia alata, to neighbour removal and prey-exclusion to determine if a reduction in nutrient supply increased the intensity of competition in this nutrient-poor system.

Results: Fire increased seedling emergence of the short-lived species by reducing above-ground competition through the destruction of above-ground parts of plants and the combustion of associated litter. Prey exclusion did not increase competitive effects of neighbours on the long-lived species. However, because the experiment was conducted in a year without fire, shade reduced nutrient demand, which may have obviated competition for soil nutrients between Sarracenia alata and its neighbours.

Conclusion: Repeated fires likely interact with interspecific differences in nutrient uptake to simultaneously reduce both above-ground competition and competition for nutrients in old-growth ground cover communities in pine savannas. Restoration practitioners should consider the possibility that the composition of the plant community is just as important as fire in ensuring that frequent fires maintain species diversity.

Nomenclature: Clewell (1985) and Schnell (1976).

Question: How diverse are Louisiana pine savanna plant communities and how is diversity affected by time since burn and removal of a competitively dominant species?

Location: Lake Ramsay, southeastern Louisiana, USA.

Methods: Species-area curves were constructed from nine nested quadrats in open savanna differing in time since burn (6, 18 and 30 months). Species frequency was determined for 100 1-m² quadrats. The dominant grass, Andropogon virginicus, was removed with herbicide from moist and dry sites to test for possible effects of competition.

Results: Slopes of log-log species-area relationships were steep (0.195 to 0.379). Time since burn did not affect the richness of herbaceous plants, only woody species. More than half of all species recorded (43/79, 54 %) were infrequent (in < 10 % of quadrats). After two years, there were no differences in species richness and composition for plots with and without A. virginicus.

Conclusions: The high species diversity is typical of other savannas across the coastal plain. The large number of infrequent species indicates that the core-satellite pattern of species occurrence found in temperate grasslands does not apply to southern pine savannas. The absence of effects due to removal of a dominant may be due to insufficient observation time, or low competition. Most species have traits, such as diminutive life forms, that suggest they are weak competitors for light in the presence of robust matrix grasses and in the absence of fire. Many species in Pinus palustris savannas are likely either fugitive or peripheral species.

Nomenclature: Integrated Taxonomic Information System ( http://www.itis.usda.gov/).

Question: What are the effects of fire season and intensity on resprouting of different root-crown bearing shrub species in second-growth Pinus palustris (longleaf pine) savannas?

Location: northern Florida and eastern Louisiana, USA.

Methods: In Florida, quadrats were burned biennially either during the dormant season or the growing season. In Louisiana, we applied intensity treatments to quadrats by manipulating ground-cover fuels, just prior to biennial growing season fires. Maximum fire temperatures were measured, and stem densities were censused before and after fires in both regions.

Results: After dormant season fires in Florida, stem densities were seven times greater than initial levels for Hypericum spp. In contrast, growing season fires reduced densities of H. brachyphyllum by 65%, but did not change densities of H. microsepalum. Only resprouting of H. microsepalum decreased with increased fire intensity. In Louisiana, fire intensity influenced Ilex vomitoria, but not Quercus spp. Following fires, stem densities of I. vomitoria were five times greater in fuel removal than fuel addition areas.

Conclusions: Past use of dormant season fires likely contributed to increased abundances of some species of root-crown bearing shrubs observed today in old-growth savannas. Reintroduction of growing season fires will be effective in maintaining or decreasing stem densities, depending on species and fuel type. Genet mortality and stem density reductions appear most likely in areas at localized scales where tree falls and needle coverage create hotspots in Pinus palustris savannas.

Nomenclature: Godfrey (1988).

Question: Does the overstorey of pine savannas influence plant species biodiversity in the ground cover?

Location: Camp Whispering Pines (30°41′ N; 90°29′ W), eastern Louisiana (USA).

Methods: We used ecologically sensitive restoration logging to remove patches of Pinus palustris (longleaf pine) in a second-growth loess plain Pinus palustris savanna managed using frequent lightning season fires. Five years later, we measured numbers of vascular plant species and transmitted light in replicated 100-m² plots. Treatments involved three different overstorey conditions: no overstorey for 5 years, no overstorey for several decades, and overstorey pines present for decades.

Results: Both recent and long-term openings contained, on average, about 100 vascular plant species per 100 m², 20% more than in similar-sized areas beneath overstorey trees. Responses varied with life form; more herbaceous species occurred in recent and older overstorey openings than beneath overstorey trees. Total numbers of all species and of less abundant forb species were positively and linearly related to light transmitted to ground level. Those species responding to openings in the overstorey and positively associated with increased transmitted light levels were monocarpic and short-lived perennial forb and grass species with a seed bank in the soil. In addition, community structure, as reflected in species composition and abundances, appeared to vary with canopy condition.

Conclusions: Restoration involving ecologically sensitive removal of patches of overstorey pines in frequently burned pine savannas should benefit the ground cover and increase plant species biodiversity as a result of increased abundance of seed bank species.

Abbreviations: CWP = Camp Whispering Pines; MRPP = Multi-response permutation procedures.

Question: How do studies of the distribution of genetic diversity of species with different life forms contribute to the development of conservation strategies?

Location: Old-growth forests of the southeastern United States.

Methods: Reviews of the plant allozyme literature are used to identify differences in genetic diversity and structure among species with different life forms, distributions and breeding systems. The general results are illustrated by case studies of four plant species characteristic of two widespread old-growth forest communities of the southeastern United States: the Pinus palustris - Aristida stricta (Longleaf pine - wiregrass) savanna of the Coastal Plain and the Quercus - Carya - Pinus (Oak-hickory-pine) forest of the Piedmont. Genetic variation patterns of single-gene and quantitative traits are also reviewed.

Results: Dominant forest trees, represented by Pinus palustris (longleaf pine) and Quercus rubra (Northern red oak), maintain most of their genetic diversity within their populations whereas a higher proportion of the genetic diversity of herbaceous understorey species such as Sarracenia leucophylla and Trillium reliquum is distributed among their populations. The herbaceous species also tend to have more population-to-population variation in genetic diversity. Higher genetic differentiation among populations is seen for quantitative traits than for allozyme traits, indicating that interpopulation variation in quantitative traits is influenced by natural selection.

Conclusion: Developing effective conservation strategies for one or a few species may not prove adequate for species with other combinations of traits. Given suitable empirical studies, it should be possible to design efficient conservation programs that maintain natural levels of genetic diversity within species of conservation interest.

Question: Can the geographic patterning of endemic plant species inform reserve selection in a region of high endemism?

Location: The southeastern Coastal Plain of North America, focusing primarily on the imperiled Pinus palustris (longleaf pine) ecosystem.

Methods: We documented the high level of plant endemism in the region, and characterized the endemic taxa into distributional subregions.

Results: A total of 1630 plant taxa are endemic to the Coastal Plain, a large proportion of which are endemic to phytogeographical subregions within the Coastal Plain, with particularly large numbers of narrow endemics occurring in the East Gulf Coastal Plain and Florida Peninsula.

Conclusions: This pattern of local endemism presents challenges in conserving the full biota of the region: a reserve system focusing on few and large conservation areas has theoretical benefits for long-term management and viability, but will fail to capture many local endemics. We propose that the dispersed distribution of endemic species will require a mixture of large core reserves and smaller satellite reserves.

Nomenclature: Kartesz (1999) with minor exceptions and modifications and updates from the taxonomic literature.

Question: Do case studies from silvicultural and restoration studies and applied conservation management in second-growth Pinus palustris stands provide unique insights for conservation models?

Methods: A review of management paradigms that conserve the high biological diversity and rare species, drawn from characteristics in both second-growth and old-growth stands, is presented for fire-maintained Pinus palustris (longleaf pine) forests.

Results: A common assumption that old-growth stands provide the primary information for the development of conservation management strategies de-emphasizes lessons learned from second-growth and restoration studies. Primary conservation management goals for the Pinus palustris ecosystem include the perpetual regeneration of the fire-maintained forest and conservation of the characteristically high biological diversity and rare species. Several attributes, such as a sustained population of Picoides borealis (red-cockaded woodpecker), Aristida stricta (wiregrass)-dominated ground cover, and undisturbed upland-wetland ecotones, can predict a diverse and ecologically functional ecosystem. Such indicators are linked to critical structural and functional features of the system and reflect previous land management histories that suggest sustainable approaches.

Conclusions: A traditional definition of ‘old-growth’ relying on overstorey may be limited in describing important features of healthy, diverse Pinus palustris ecosystems. Some characteristics are significantly more important for maintenance of diversity than age of the trees and these features may be present in old- or second-growth forests. We advocate that the management history, structural characteristics and landscape context of stands that harbour desirable conservation attributes (red-cockaded woodpeckers, wiregrass, gopher tortoises and undisturbed upland-wetland ecotones) can be used as indicators to identify important conservation and forest management principles.

Abbreviation: NWR = St. Marks National Wildlife Refuge; RCW = Red cockaded woodpecker; SNA = Stoddard-Neel approach.

Global warming can potentially influence ecological communities through altered disturbance regimes in addition to increased temperatures. We investigate the response of pine savannas in the southeastern United States to global warming using a simple Lotka-Volterra competition model together with predicted changes to fire and hurricane disturbance regimes with global climate change. In the southeastern United States, decreased frequency of both fires and hurricanes with global warming will shift pine savannas toward a forested state. A CO₂ fertilization effect that increases the growth rate of tree populations will also push southeastern landscapes from open savannas towards closed forests. Transient dynamics associated with climate driven changes in vegetation will last on the order of decades to a century. In our model, the sensitivity of savannas to relative changes in the frequency of fire versus hurricanes is linearly dependent on the growth rate and mortality of trees in fire and hurricane disturbances.

Question: The decline of the Pinus palustris ecosystems has resulted from anthropogenic influences, such as conversion to pine plantation forestry, agriculture and land development, all of which are closely related to increases in human populations. Other effects, however, have arisen from alterations in disturbance regimes that maintain the structure and function of these ecosystems. How have alterations of the disturbance regime altered the physiognomy of ‘old-growth’ stands, and what are the implications for ecosystem conservation and restoration?

Methods: In contrast to models that emphasize close interactions among the vertically complex strata, we develop a conceptual phenomenological model for the physiognomic structure of Pinus palustris stands. We relate two natural disturbances (tropical storms and fire) that affect different stages of the life cycle to different aspects of the physiognomic structure. We then compare overstorey stand structure and ground cover composition of two old-growth longleaf stands near the extremes of different composite disturbance regimes: the Wade Tract (frequent hurricanes and fire) and the Boyd Tract (infrequent hurricanes and long-term fire exclusion).

Results: We predict that tropical storms and fires have different effects on stand physiognomy. Tropical storms are periodic, and sometimes intense, whereas fires are more frequent and less intense. Hurricanes directly influence the overstorey via wind-caused damage and mortality, and indirectly influence the herb layer by altering the spatial distribution of shading and litter accumulation. Fire exerts direct effects on juvenile stages and indirect effects on the herb layer via fine fuel consumption and selective mortality of potential competitors of P. palustris juveniles. These differences in effects of disturbances can result in widely different physiognomies for P. palustris stands. Finally, some global climate change scenarios have suggested that changes may occur in tropical storm and fire regimes, altering frequency and severity. Such changes may greatly affect pine stands, and ultimately entire pine savanna ecosystems.

Conclusions: Our phenomenological model of disturbance regimes in Pinus palustris old-growth produces very different physiognomies for different disturbances regimes that reflect natural process and human management actions. This model can be used to derive restoration strategies for pine savannas that are linked to reinstitution of important ecological processes rather than specific physiognomic states.

Nomenclature: Anon. (2006).

Questions: Are calorimeters and pyrometers accurate and reliable for describing fire parameters in large-scale ecological projects, and can data from them predict data derived from thermocouples? Do mechanical pre-treatments in Florida scrub areas alter fire properties?

Location: Lake Wales Ridge, Florida, USA.

Methods: We deployed thermocouples attached to digital dataloggers, copper and lacquer paint pyrometers and aluminium can calorimeters filled with water in four areas of undisturbed Florida scrub and sandhill vegetation and in adjoining areas pre-treated with logging, subcanopy felling or mowing. Individual dataloggers were positioned in areas spanning a range of vegetation structure; three calorimeters and three pyrometers were placed with each thermocouple. We also deployed individual calorimeter-pyrometer pairs. Sites were burned, after which we compared methods for characterizing fire, particularly the ability of pyrometers and calorimeters to predict values derived from thermocouples.

Results: Pyrometers best predicted peak 1-minute mean temperatures and were least successful at estimating maximums. Calorimeters were associated with the number of minutes maximum temperatures exceeded 60 °C, but were damaged at high residence times and inconsistent at low temperatures. Both pyrometers and calorimeters detected site and treatment differences in fire intensities. These analyses and logistic considerations give pyrometers an edge over calorimeters in situations where dataloggers are impractical. Mechanical pre-treatments to fire altered fire parameters. Mowing reduced fire temperatures but had different effects on areas burned; this was related to the length of time elapsed between mowing and burning. Subcanopy felling increased both fire coverage and temperatures.

Conclusion: Pyrometers outperformed calorimeters as a cheap method for describing relative temperature regimes that are a function of both temperature and residence time. Pyrometers were able to demonstrate how mechanical treatments applied prior to prescribed burning altered fire parameters. Pyrometers are a useful tool for investigating biological responses to fire at multiple scales and in heterogeneous vegetation.

Abbreviations: AREA60 = the integrated area under the instantaneous temperature curve defined by a threshold of 60 °C; AREA150 = the integrated area under the instantaneous temperature curve defined by a threshold of 150 °C; CALOR = mean percent water loss from calorimeters adjusted for evaporation; MAX = peak instantaneous temperature (°C); MAX60 = number of minutes where the instantaneous temperature > 60 °C; MAX150 = number of minutes where the one minute mean temperature > 150 °C; MEAN = peak one minute mean temperature (°C); MEAN60 = number of minutes where the one minute mean temperature > 60 °C; MEAN150 = number of minutes where the one minute mean temperature > 150 °C; PYRO = median pyrometer reading.

Nomenclature: Wunderlin & Hansen (2003).

Question: How does grazing intensity affect plant density, cover and species richness in an Patagonian arid ecosystem?

Location: Monte steppe ecoregion, SW Argentina.

Methods: I analysed the effect of grazing on plant density, cover and species richness using a stocking rate gradient within the same habitat. Six paddocks were used with stocking rates ranging between 0.002 - 0.038 livestock/ha. Plant density, species richness, plant cover and percentage of grazed branches were determined by sampling plots within each paddock. The percentage of grazed branches was used as an independent measurement of grazing intensity.

Results: Higher stocking rates were related to lower plant density, species richness and plant cover. The paddock with the lowest grazing intensity had 86% more plants per unit area, 63% more plant cover and 48% higher species richness. The percentage of grazed branches and the quantity of dung increased with stocking rate.

Conclusions: Introduced livestock seriously affect native vegetation in the Patagonian Monte. The damage observed in this xerophytic plant community suggests that plant adaptations to aridity do not provide an advantage to tolerate or avoid grazing by vertebrate herbivores in this region. Plant degradation in this arid environment is comparable to the degradation found in more humid ecosystems.

Nomenclature: Correa (1969–1998).

Abbreviations: MAP = Mean annual precipitation.

Question: Is seedling recruitment of a fleshy-fruited tree in degraded Afromontane savanna dependent on shelter from pioneer shrubs, and is shelter availability related to shrub traits? Location: Degraded montane savanna in northern Ethiopia (13°36′ N, 39°21′ E).

Method: Nurse plants of Olea europaea ssp. cuspidata seedlings were recorded using T-square plotless sampling and clustered according to shrub traits, using Ward's method after Principal Components Analysis. Facilitation was further examined through experimental planting and Kaplan-Meier survival analysis.

Results: Both in grazed and protected areas, Olea recruits were found exclusively under shrubs, primarily under Euclea racemosa although Acacia etbaica was more abundant. Olea recruitment is distributed randomly at landscape scale, but depends on shelter at patch scale. Shelter ability is related to shrub shape and species identity. Dense multi-stemmed shrubs with a wide base and crown on a mulch-rich mound are key recruitment foci. Euclea shrubs have these favoured traits and probably act as preferential perching sites for avian seed dispersers. Soil and organic matter accumulation under Euclea shrubs may also create favourable conditions for Olea germination and survival. Experimentally planted seedlings had a better chance for survival under Euclea.

Conclusions: Olea regeneration is probably subject to both passive (disperser-mediated) and active facilitation. Small changes of shrub traits can alter the suitability of a patch for Olea recruitment. Protection of shrubs can increase facilitation for seedlings, while pruning may reduce competition for saplings and thus enhance forest succession. Planting of raised Olea seedlings under Euclea shrubs in years with a good rainy season may further assist forest restoration.

Abbreviation: TSB = Byth robust T-square estimator.

Nomenclature: Hedberg & Edwards (1989); Hedberg et al. (2003); Klopper et al. (2005).

Questions: Does the litter layer of Pteridium aquilinum (bracken) act as a barrier to certain species in the seed bank? Does bracken control/restoration treatment affect seed transfer through the litter layer?

Location: Five experiments at three sites across the UK covering two major vegetation types; acid-grassland and heath-land.

Methods: At each experiment a range of bracken control and vegetation restoration treatments were applied for about ten years. The seed bank was sampled in both the bracken litter and the soil. The cover (%) of each species in the vegetation and the bracken litter abundance (cover and depth) was also estimated.

Results: The bracken litter layer acts as an inert barrier as it contained a large proportion of seeds available in the litter-soil profile (38% - 67% of the total). Bracken litter depth and cover also influenced significantly the seed bank composition in both the bracken litter and the soil. These effects were site-specific, and species-specific. The application of treatments changed significantly the balance between seed inputs and outputs in the bracken litter layer for some species. This was either a positive or negative response relative to the untreated control plots.

Conclusion: For heathland and acid-grassland restoration, the bracken litter layer may be an important seed source, but it must be disturbed particularly before seed addition.

Abbreviation: RDA = Redundancy Analysis.

Nomenclature: Stace (1997).

Question: How to improve reforestation success of Quercus pyrenaica.

Location: 1800 m a.s.l., southern Spain.

Methods: One-year-old Quercus pyrenaica seedlings were planted using two treatments: (1) bare soil, using a 30-cm diameter augur bit (conventional technique) and (2) under the canopy of a pioneer shrub, Salvia lavandulifolia, using a 12-cm diameter augur bit. Survival and growth were monitored for six years. Our hypothesis is that the use of shrubs as nurse plants is an alternative technique of reforestation with higher success than traditional techniques, in which pre-existing vegetation is usually considered a source of competition. The rationale for the study was that for environments with a dry season, pre-existing vegetation buffers summer drought stress, ameliorates the water status of seedlings and thus usually increases seedling recruitment.

Results: Quercus survival was 6.3 × higher when planted under individuals of the pioneer shrub as compared to open areas. Quercus seedlings under shrubs also had shoots 1.8 × longer, while the number of shoots per plant did not differ among treatments. The first summer was the period with the highest mortality (49.1% of seedlings). Summer drought was the main cause of mortality.

Conclusions: The use of shrubs as nurse plants for Q. pyrenaica reforestation is a viable technique to increase establishment success. The technique could be similarly useful in other environments with a dry period and for other Quercus species. In addition, this technique offers the advantage of following natural succession, thus minimizing the impact in the community.

Question: Does understorey richness, cover and biomass change during succession in abandoned Castor canadensis impoundments of riparian Nothofagus forests?

Location: Magellanic Nothofagus forests at Tierra del Fuego National Park (54°50′32.4″ S, 68°32′11.5″ W), Argentina.

Methods: Five meadows of different time since abandonment (1, 5, 6, 9 and 20 years ago) and two controls (pure N. pumilio and mixed N. pumilio - N. betuloides forests) were sampled. Understorey variables (species richness, cover and biomass) in beaver meadows were measured at eight plots, as well as sapling and seedlings age and height. In control treatments, ten plots on each forest type characterized forest structure.

Results: Beavers alter vegetation dynamics, modifying biomass and composition of the original forest communities. Richness, cover and biomass were significantly modified when compared to the original understorey. Ferns are the most affected group, while grasses became more abundant. Many species established in the impacted sectors, which did not grow in primary forests. Trees did not regenerate in impacted areas for long periods, and many understorey original species are missing. Nothofagus forests are not adapted to support a long-term beaver impact.

Conclusions: Beavers modify the original ecosystem from closed forest to a grass- and sedge-dominated meadow, due to the lack of adaptive regeneration strategies in the Nothofagus forests. The maintenance of the present level of the beaver population is not sustainable over time, due to utilized and impacted tree biomass which could not be replaced by the natural dynamics of the forest ecosystem.

Abbreviations: FA = Forest stand; GIS = Geographical information system; LF = Nothofagus pumilio forest; LGF = N. pumilio/N. betuloides mixed forest.

Nomenclature: Correa (1969–1998); Moore (1983).