Open Canopy Conditions Research Articles

A meta-analysis of biodiversity responses to management of southeastern pine forests—opportunities for open pine conservation

Open canopy conditions in southeastern pine (Pinus spp.) forests were historically maintained by frequent fire and other disturbances, without which midstory hardwoods create closed canopy conditions limiting value of pine stands for many endemic, disturbance-adapted species. Intensively managed pine forests, which comprise 19% of forests in the southeastern U.S., can emulate historical open pine conditions, providing appropriate vegetation structure and composition for many endemic species. However, exact mechanisms for producing and maintaining open pine conditions and subsequent effects on biodiversity have not been examined across regions and stand ages. To better inform managers about options for providing open pine conditions in intensively managed pine stands, we used meta-analyses to examine biodiversity and open pine focal species responses to 5 stand establishment intensities and 4 mid-rotation practices (prescribed fire, selective herbicide, fire and herbicide combination, and thinning). We calculated 1742 biodiversity and 169 open pine focal species effect sizes from 42 publications of manipulative studies at 14 unique study sites in managed loblolly pine (P. taeda L.) forests in the Atlantic and Gulf Coastal Plains of the southeastern U.S. We quantified diversity and abundance responses by taxa and management practices for vegetation, birds, amphibians, reptiles, small mammals, and invertebrates. Diversity and abundance responses generally decreased as stand establishment intensity increased, but those reductions appeared to be short-term (<3years). Birds and open pine focal species responded positively to chemical stand establishment relative to a mechanically-prepared control. Thinning elicited positive diversity and abundance responses from reptiles and small mammals. Effects of prescribed fire, selective herbicide, and their combination on biodiversity responses varied by taxa (e.g., following fire, vegetative and avian diversity increased but amphibian and invertebrate diversity decreased). Further research is warranted on under-represented taxa (e.g., herpetofauna and invertebrates) in literature and long-term effects of forest management on biodiversity. Understanding how silvicultural management practices produce and maintain open pine forest conditions and influence biodiversity responses is necessary to inform opportunities for open-pine wildlife communities in working forested landscapes.

Assessing patterns of oak regeneration and C storage in relation to restoration-focused management, historical land use, and potential trade-offs

Restoration of composition, structure, and function in oak dominated ecosystems is the focus of management in temperate forests around the world. Land managers focused on oak ecosystem restoration are challenged by the legacy effects of complex land-use histories, urbanization, climate change, and potential stakeholder response to management. Trade-offs may exist between managing forests for climate mitigation (e.g., maximizing C storage or sequestration) and promoting shade-intolerant species historically associated with frequent or high-severity disturbances. This study assessed the potentially conflicting goals of sustained live biomass accrual and increased oak regeneration in the East Woods Natural Area at The Morton Arboretum in Lisle, IL, USA. We evaluated how biomass trends and oak regeneration were related to management regimes, land-use history, current stand structure and composition, and topoedaphic factors. Our results indicated no significant trade-off between sustained live biomass accrual and oak regeneration. Live biomass was increasing across the landscape (biomass increment averaged 18,186kgha−1yr−1) and was not strongly related to differences in management or land-use history. Oak regeneration was rare, especially beyond the seedling stage (∼226 seedlings and 9 saplings ha−1) and was also not strongly related to recent management. Our results indicate that even 20+ years of annual prescribed burning combined with understory thinning has failed to produce the open canopy conditions and high light availability that are necessary for successful oak recruitment. The absence of any trade-offs between biomass accrual and oak regeneration may, therefore, be largely related to the ineffectiveness of current management for promoting oak regeneration. More intensive management utilizing canopy manipulations could produce greater trade-offs, but is likely necessary to establish and release oak regeneration.

Composition, Structure, and Trajectories of Great Lakes Coastal Pine Forests in Relation to Historical Baselines and Disturbance History

Pine forests have historically been an important component of Great Lakes coastal ecosystems that provide wildlife habitat and other ecosystem functions. The area covered by coastal forests and the dominance of pines within remaining forests have been greatly reduced over the past ∼200 y by logging, development, and other anthropogenic activities. This study assessed stand history and composition of remnant coastal pine forests and compared contemporary stands to historical baselines to support restoration efforts in these ecosystems. Sampling was conducted in 23 stands at eight sites along the shores of Lakes Michigan and Superior in Michigan, U.S.A. and was focused on stand composition, age structure, and disturbance history. Current data were compared with data from presettlement Public Land Survey records in coastal pine forests across the region. Composition in contemporary forests differed greatly from presettlement conditions in southern sites and was significantly, but not as strongly, different in the northern part of the region as well. Pine dominance in remnant stands was lowest with moderate levels of pine-logging-era canopy removal. Comparisons of overstory and understory dominance suggested a continued trend away from pine dominance toward mesophytic species in all stands. Restoration of disturbance regimes (particularly surface fires) and open canopy conditions may be necessary to maintain a pine component in these ecosystems.

Using population dynamics modelling to evaluate potential success of restoration: a case study of a Hawaiian vine in a changing climate

SUMMARYDemographic comparisons between wild and restored populations of at-risk plant species can reveal key management strategies for effective conservation, but few such studies exist. This paper evaluates the potential restoration success ofAlyxia stellata, a Hawaiian vine. Stage-structured matrix projection models that compared long-term and transient dynamics of wild versus restoredA. stellatapopulations, and restored populations under different levels of canopy cover, were built from demographic data collected over a four year period. Stochastic models of wild populations projected stable or slightly declining long-term growth rates depending on frequency of dry years. Projected long-term population growth rates of restored populations were significantly higher in closed than open canopy conditions, but indicated population decline under both conditions. Life table response experiments illustrated that lower survival rates, especially of small adults and juveniles, contributed to diminished population growth rates in restored populations. Transient analyses for restored populations projected short-term decline occurring even faster than predicted by asymptotic dynamics. Restored populations will not be viable over the long term under conditions commonly found in restoration projects and interventions will likely be necessary. This study illustrates how the combination of long-term population modelling and transient analyses can be effective in providing relevant information for plant demographers and restoration practitioners to promote self-sustaining native populations, including under future climates.

The association of two invasive shrubs, common buckthorn (Rhamnus cathartica) and Tartarian honeysuckle (Lonicera tatarica), with oak communities in the midwestern United States

Oak forests throughout North America are declining due to changes in disturbance regimes that have led to increased competition from other tree and shrub species. We evaluated associations between oak regeneration, the occurrence of two common invasive shrubs (common buckthorn ( Rhamnus cathartica L.) and Tartarian honeysuckle ( Lonicera tatarica L.)), and forest edges in oak forests in a portion of the midwestern United States where bur ( Quercus macrocarpa Michx.), red ( Quercus rubra L.), and white oak ( Quercus alba L.) were historically dominant. We found poor recruitment of oaks in comparison to other, more shade-tolerant tree species. Results further revealed a strong stand-scale association between bur oak, open canopy conditions, high soil nutrient levels, and the presence of common buckthorn and Tartarian honeysuckle; these same site characteristics were disassociated with red and white oak. Within red and white oak stands, however, the presence of the invasive shrubs was more pronounced near forest edges. While oak recruitment is hampered throughout stands, our research suggests that predominant constraints may vary based on soil and light gradients found along forest edges.

Transpiration of forest trees and stands at different altitude: consistencies rather than contrasts?

Compared to lowland trees and forests, evidence on water relations at mountainous and sub-alpine sites with their climatic and topographic peculiarities is scarce. On such limited grounds, the outcome of three pilot studies is reviewed, intended to launch working hypotheses for initiating integrative research across the altitudinal gradient of the European Alps. Highlighted are tree transpiration and structural differentiation as well as stand water balance of mono-specific and/or mixed forests with Picea abies, Pinus cembra, Larix decidua and Fagus sylvatica at sub-alpine (timberline ecotone), mountainous and colline elevation. Given the preliminary evidence, tree-allometric structures of relevancy for water transport appeared to be independent of elevation and forest type, although timberline trees under open-canopy conditions did not buffer transpiration by internal water storage and had enhanced foliage/sapwood area ratios. Transpiration appeared to depend on site conditions rather than site-dependent adaptation. Canopy transpiration approached 20% of the high seasonal precipitation at the mountainous site, with about 60% being ascribed to run-off, whereas the water budget of the colline site was balanced during summer. The water balance of the subalpine site resembled, at lower precipitation, that of the mountainous site. The derived hypotheses focus on mixed-stand transpiration under altitude-specific topography and moisture regimes, hydraulic adaptation and water demand versus uptake capacity, as this latter ratio is crucial at high altitude in view of expected warming. The clarification of consistencies relative to contrasts indicated by the pilot studies will be challenging across altitudes in view of tree species, forest types and topography.

A rapid assessment approach on soil seed banks of Atlantic forest sites with different disturbance history in Rio de Janeiro, Brazil

This study represents a rapid assessment approach on the composition of soil seed banks in the Atlantic rainforest in Brazil and therefore marks a tool for the fast estimation of one important aspect of the regeneration ability of forest sites with different disturbance histories. The project was carried out in a private reserve in the state of Rio de Janeiro, where research plots were established in three different forest sites: in continuous forest where selective logging took place, in forest regrowth after complete cutdown about 60 years ago and in a forest fragment. Additionally data from another forest remnant in this region were added to compare especially the results concerning the influence of fragmentation processes on soil seed bank structure. With remarkably less sampling effort compared to germination experiments the sieving method is resulting in a fast gain of information on this particular topic which still is comparable to already published results. Every investigation site in our study differs considerably in soil seed bank composition concerning their disturbance history. Furthermore coherences between canopy structure and the density of small-sized seeds in the soil, as well as edge effects within the forest fragments were observed. We recognised a higher amount of small seeds under more open canopy conditions in general and discovered trends of higher species richness near the forest boundary in the forest fragments. This rapid assessment approach might be an easy to handle tool and a practical alternative to more extensive germination experiments for upcoming investigations on the regeneration capability in highly fragmented and disturbed landscapes like the Atlantic rainforest.

Line thinning promotes stand growth and understory diversity in Japanese cedar (Cryptomeria japonica D. Don) plantations

We studied the effects of line thinning on stand structure, microclimate and understory species diversity of two Cryptomeria japonica D. Don plantations in south-central Japan. In each of two study sites we compared stand structure between the thinned stand and an adjacent unthinned stand and found that line thinning increased the growth rate of residual trees such that stand basal area may recover within 10 years after thinning. In the thinned stand, more open canopy conditions resulted in higher maximum temperatures on the forest floor during the early growing season than in the unthinned stand. The thinned stand had greater understory plant species richness and biomass than the unthinned stand. This study suggested that line thinning could potentially enhance biodiversity while simultaneously increasing tree-growth rates in overstocked Cryptomeria japonica plantations.

Plant community response to burning and herbicide site preparation in eastern Louisiana, USA

High yield commercial forests are an important source of fiber for global forest product needs and the southeastern United States is a key region for global wood supply needs with intensively managed pine stands ( Pinus spp.) an important component of forested landscapes in this region. Concern has arisen over possible effects of stand establishment practices on vegetation communities within commercial forests, particularly relative to use of herbicides and burning. Therefore, we examined response of plant communities to site preparation within intensively managed pine stands in eastern Louisiana, USA that were either prescribe burned (PF; n = 5) or treated with a combination of herbicides (imazapyr and triclopyr) and prescribe burned (PFH; n = 5) during 2002. We used 5 m line intercepts ( n = 10 per stand) to quantify species richness, diversity, and relative abundance of plant species for 3 years post-treatment (2003–2005) with a repeated measures analysis of variance. We documented 80 genera or species of plants and neither species richness nor diversity differed between treatments. Site preparation with PFH appeared to promote development of an herbaceous plant community and reduced relative abundance of woody plants, whereas PF-treated sites were dominated by woody vegetation. Our results demonstrate that different plant communities result from PF and PFH site preparation and may place stands on different successional trajectories. We suggest PFH site preparation may increase availability of early successional vegetation associations on managed forest landscapes and may extend the time stands stay in this successional stage. However, increased crop tree growth from site preparation may shorten open canopy conditions.

Standard and Real-Time Accuracy and Reliability of a Mapping-Grade GPS in a Coniferous Western Oregon Forest

Abstract Accuracy requirements for forested resource measurements can vary greatly depending on analysis and management objectives. Technologies that present efficiencies for reliable measurement collection may help organizations better meet data requirements. We tested the accuracy and reliability of a mapping-grade GPS in a variety of forested conditions in western Oregon. Our objectives were to measure the performance of a GPS operating in a standard configuration and also with real-time US Coast Guard Beacon signals. We also examined the influence of postfield differential corrections and the number of GPS points collected on measurement accuracy and reliability. We found measurement accuracies between 1 and 4 m from true position depending on the amount of canopy closure and the type of GPS configuration. Our results indicated that both standard-mode GPS and US Coast Guard Beacon signals can produce very accurate measurements in open-canopy conditions but are less reliable in young-forest conditions. Postprocessing of field measurements generally yielded improved measurements in young-forest settings but led to slightly reduced accuracies for US Coast Guard Beacon data collected in open-canopy settings. Our results also indicated that collecting a greater number of points does not necessarily lead to improved measurement accuracies. West. J. Appl. For. 21(4):222–227.

Growth of Douglas-fir, lodgepole pine, and ponderosa pine seedlings underplanted in a partially-cut, dry Douglas-fir stand in south-central British Columbia

The effects of partial cutting on seedling growth of three conifer species were studied at a very dry, hot interior Douglas-fir site near Kamloops, British Columbia. Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.), and ponderosa pine (Pinus ponderosa Dougl. ex. P. &amp; C. Laws.) seedlings were planted in mechanically prepared 50 cm × 50 cm patches under different canopy conditions created by harvesting 60% of the original stand volume. The prepared areas were selected to represent canopy closures from open to closed, slopes from 0 to 60%, and all aspects. After six years, survival of Douglas-fir, lodgepole pine and ponderosa pine was 78%, 76% and 70%, respectively. Light level had a strong influence on survival and condition. Growth of all species increased linearly with light, and was greatest for lodgepole pine, followed by ponderosa pine and Douglas-fir. Multiple regression analysis showed that six-year seedling size was most significantly affected by total light, and only occasionally by aspect, slope, or crown closure. The best models explained 53%, 47% and 42% of the variation in diameter of lodgepole pine, ponderosa pine, and Douglas-fir, respectively. Natural abundance 13C was positively correlated with light and soil moisture availability, reflecting higher photosynthetic capacity of all species in the wetter, open canopy conditions. Patterns in isotopic discrimination also indicated greater water use efficiency of Douglas-fir and ponderosa pine than lodgepole pine under low light conditions. Underplanting stands thinned to a basal area of less than 15m2 per ha offers a solution to regeneration difficulties on hot, dry Interior Douglas-fir sites. Key words: partial cutting, Douglas-fir, lodgepole pine, ponderosa pine, light, soil moisture, 13C, growth, survival, Opax Mountain Silvicultural Systems Project

Foraging Area Size and Habitat Use by Red Bats (Lasiurus borealis) in an Intensively Managed Pine Landscape in Mississippi

Forest managers are increasingly expected to incorporate biodiversity objectives within forest landscapes devoted to timber production. However, reliable data on which to base management recommendations for bats within these systems are extremely limited. Although the red bat (Lasiurus borealis) is a widespread common species in temperate forests of North America, little is known of its ecology within intensively managed pine (Pinus spp.) forests of the southeastern United States. Therefore, we investigated size of foraging areas and habitat use by red bats during summer 2000 and 2001 in an intensively managed pine landscape in east-central Mississippi, USA. We captured bats using four-tier mist nets placed over water and attached radiotransmitters to red bats. Radiotagged red bats (n = 16) used habitat types randomly at the study area and foraging area scale. Mean size of foraging areas and mean maximum distance traveled between diurnal roosts and foraging locations were not different (P < 0.05) among adult male, adult female, juvenile male or juvenile females (n = 18). Most foraging areas contained a reliable source of water and all but one diurnal roost was located within foraging areas. Location of diurnal roosts may dictate location of foraging areas. Open canopy conditions in intensively managed pine stands (young, open canopy stands, thinned stands and riparian hardwood stands) likely provide appropriate foraging habitat for red bats. Landscape context may influence size of foraging areas and commuting distances of red bats. Provision of appropriate aged forest stands for diurnal roosts may be the best management action for red bats within intensively managed pine landscapes.

Stand dynamics of an insular population of an invasive tree, Acer platanoides

Acer platanoides L. (Norway maple) is an invasive exotic tree species in the eastern and central United States that poses a serious threat to native forests. In order to improve our understanding of how this species invades native forests, we conducted a retrospective analysis of the stand dynamics of an established population of A. platanoides in a natural area on a temperate forested island in Lake Huron, Michigan, USA. Tree ring analysis was used to reconstruct the canopy recruitment of contemporary A. platanoides overstory trees, and a simple gap capture method was used to investigate gap capture rates for A. platanoides and native species. Given the extreme shade-tolerance of A. platanoides, surprisingly few of the contemporary A. platanoides overstory trees in the forest showed evidence of past suppression suggesting that most established under relatively open canopy conditions and/or in canopy gaps. Height growth comparisons with native species suggest that A. platanoides should be able to capture canopy gaps at least a decade before most common tree species on the island. A. platanoides displayed rapid juvenile growth rates that declined significantly ( P < 0.001) with age once trees reached the overstory. These results suggest that A. platanoides ability to form pure stands and dominate native forests is closely linked to its ability to successfully out compete and competitively exclude native shade-tolerant species. While our results suggest that initial establishment of A. platanoides may follow disturbance, once established, populations appear to be self-sustaining. Consequently, monitoring and control efforts in edge and recently disturbed environments may help prevent the spread of this species into intact forest communities; however, chance long distance dispersals into the forest matrix may be more problematic since rare individuals may go unnoticed until they have established a new population.

Wildfire Regime in the Boreal Forest and the Idea of Suppression and Fuel Buildup

The explanation often given for the large wildfires that have burned each year in North America in the last two decades is that fire suppression after the 1950s produced a buildup of fuel and changed the landscape-age mosaic (e.g., Gayton 1998; Smalley et al. 2000), creating conditions for catastrophic fires. This idea of “unnatural fuel buildup” ( Brown 1983) was originally developed for Pinus ponderosa ecosystems in the interior West of the United States, where a historical regime of frequent surface fires had maintained open-canopy conditions. With the arrival of European settlers, the frequency of surface fires decreased, changing both the accumulation and arrangement of fine fuel. Growth of an intermediateheight layer of vegetation and the increased bulk density of canopy fuel allowed surface fires to burn into the crown, thus creating a crown-fire regime (Fuli et al. 1997; Shinneman & Baker 1997). Unfortunately, this fuel-buildup idea has been uncritically and inappropriately applied to closed-canopy ecosystems that have always had crown-fire regimes. Keeley and Fotheringham (2001 [this issue]) explain in the lead article of this forum why this concept is not valid for the California shrublands, and they present evidence that the presuppression fire regime had been one of standreplacing crown fires. We show here that the idea of unnatural fuel buildup is also invalid for the boreal and subalpine forest, another closed-canopy ecosystem with a crown-fire regime ( Johnson 1992). Despite differences in climate and vegetation between chaparral and boreal forest, many of the basic arguments and explanations we present are similar to those of Keeley and Fotheringham. Fire Regime of the Boreal Forest

Bird community structure along a trekking corridor of Sikkim Himalaya: a conservation perspective

Bird community structure was studied in the Yuksam–Dzongri trekking corridor of the Sikkim Himalaya, India. Nineteen transects with a total of 266 samplings were made in the forests along the corridor during June 1997 to June 1999. Human utilised forest (open canopy forest) and relatively unutilised forest (closed canopy forest) were designated for the study at two ecological zones, i.e. lower forest (1780–2350 m a.s.l.) and upper forest (2350–3600 m) depending on the natural resources utilisation pattern by local community living in the area and for tourism purposes. There were visible changes in the open and closed canopy forests in diameters at breast height class distribution of trees leading to distinct variation in the habitat types. Among the 143 species of birds observed during the study, a handful of species were found as habitat specific and about 40% were common to all the four habitat types. Both bird species richness and diversity were higher at the open canopy conditions compared with closed canopy, but the differences were not statistically significant. On the other hand, both the indices showed strong and significant negative relationship with the elevation. These diversity indices were also significantly higher during the summer compared with the winter season. The open canopy conditions exhibited comparatively more species of birds that were perturbated by human settlements than those species found at the closed canopy (mostly forest interior) and vice versa. Though the study could not trace out the effect of patch size brought about by human caused disturbances, the Yuksam–Dzongri trekking corridor possesses diverse habitat types as well as bird species resulted from heterogeneous habitat conditions. It is therefore important to emphasise disturbance study for threshold level assessment so that generalists as well as forest interior species could be managed through conservation efforts.

6000 years of forest dynamics in Suserup Skov, a seminatural Danish woodland

1 The history of a forest stand over the last 6000 years has been reconstructed by studying pollen, macrofossils and charcoal from a small, wet hollow in Suserup Skov on the island of Sjaelland in eastern Denmark. 2 The earliest recorded forest was Tilia-dominated but contained an intimate mixture of many different tree species that included Acer campestre, A. platanoides, Alnus glutinosa, Betula pubescens, Corylus avellana, Frangula alnus, Fraxinus excelsior, Malus sylvestris, Populus tremula, Pinus sylvestris, Quercus robur, Q. petraea, Salix spp., Sorbus aucuparia, Tilia cordata and T. platyphyllos. The preserved fruits of T. platyphyllos confirm its hitherto doubtful status as a native member of the Danish flora. 3 The present-day woodland developed after a period of intensive anthropogenic disturbance between ≈ 600 bc and ad 900, during which time open canopy conditions prevailed at Suserup. Fagus sylvatica and Fraxinus excelsior are the dominant trees at present, together with some Quercus robur and Ulmus glabra. 4 Charcoal was present in the sediments from most time periods except at the Ulmus decline. In the last 1000 years of the sequence — the period of Fagus dominance — charcoal counts were consistently low. 5 Pinus sylvestris was a natural component of this primarily deciduous forest, and the last macrofossil find dates from c. ad 900. Macrofossil Pinus cone scales recorded c. ad 1800 originate from planted individuals. Prior to Fagus dominance, the forest had an open structure partly caused by frequent, low-intensity fires associated with the presence of Pinus sylvestris. 6 The replacement of Tilia by Fagus in this forest was catalysed by human activity. If the forest had not been so disturbed, the rich diversity of trees would most probably have persisted up to the present time, with only a moderate-sized Fagus population.

Dynamics of forests with Araucariaceae in the western Pacific

Abstract. Several species of Araucaria and Agathis (Araucariaceae) occur as canopy emergents in rain forests of the western pacific region, often representing major components of total stand biomass. New data from permanent forest plots (and other published work) for three species (Araucaria hunsteinii from New Guinea, A. laubenfelsii from New Caledonia, and Agathis australis from New Zealand) are used to test the validity of the temporal stand replacement model proposed by Ogden (1985) and Ogden &amp; Stewart (1995) to explain the structural and compositional properties of New Zealand rain forests containing the conifer Agathis australis. Here we propose the model as a general one which explains the stand dynamics of rain forests with Araucariaceae across a range of sites and species in the western Pacific.Forest stands representing putative stages in the model were examined for changes through time in species recruitment, growth and survivorship, and stand richness, density and basal area. Support for the model was found on the basis of: 1. Evidence for a phase of massive conifer recruitment following landscape‐scale disturbances (e.g. by fire at the Huapai site, New Zealand for Agathis australis); 2. Increasing species richness of angiosperm trees in the pole stage of forest stand development (i.e. as the initial cohort of conifers reach tree size; &gt;10 cm DBH); 3. A high turnover rate for angiosperms (&lt;100 yr), and low turnover for conifers (≥ 100 yr) in the pole stage, but similar turnover rates for both components (50–100 yr) as forests enter the mature to senescent phase for the initial conifer cohort; 4. Very low rates of recruitment for conifers within mature stands, and projected forest compositions which show increasing dominance by angiosperm tree species; 5. A low probability of conifer recruitment in large canopy gaps created by conifer tree falls during the initial cohort senescent phase, which could produce a second generation low density stand in the absence of landscape scale disturbance; 6. Evidence that each of the three species examined required open canopy conditions (canopy openness &gt; 10 %) for successful recruitment.The evidence presented here supports the temporal stand replacement model, but more long‐term supporting data are needed, especially for the phase immediately following landscape level disturbance.

Tree Regeneration and Species Diversity Following Conventional and Uniform Spacing Methods of Selective Cutting in a Subtropical Humid Forest Reserve1

ABSTRACTThere are a variety of ways to diminish the negative impacts of forest management for timber on biodiversity. A pilot project using a uniform spacing method of selective cutting was recently implemented in the 5340 ha Guarani Reserve, Misiones, Argentina, to design adequate management schemes for the subtropical forests of the region. Uniform spacing involves moderate timber harvesting and careful selection of remnant trees. In this article we compare tree regeneration in forests experimentally cut by diameter limit and uniform spacing methods. Seedlings of five size classes from 10 cm to 3 m in height were sampled using rectangular nested plots. Three years after cutting, an average of 54,330 and 22,270 seedling/ha (all height classes combined) of commercial and non‐commercial species were found in the forest cut by uniform spacing and by minimum diameter, respectively. In an adjacent uncut forest there were 34,900 seedlings/ha, and in another forest cut by minimum diameters 30 years ago there were 50,000 seedlings/ha, The forest cut by uniform spacing had the highest number of commercial seedlings/ha, with three times as many as the forest cut by minimum diameter three years ago and twice as many as the forest treated by minimum diameters 30 years ago. The forest cut by uniform spacing and the forest treated by minimum diameters 30 years ago had the highest diversity of understory plants other than trees, as well as heterogeneous canopy cover, while the other two forests had a predominance of bamboo in the understory and more open canopy conditions. Although lack of site replication limits interpretation of the results, these early findings suggest that the uniform spacing method can be an ecologically sound forest management option for the region.

Gap-phase regeneration in longleaf pine wiregrass ecosystems

Naturally regenerated seedlings of longleaf pine are typically observed to cluster in the center of tree fall canopy gaps and be encircled by a wide zone from which they are generally excluded. Twelve representative canopy gaps distributed across 600 ha of a naturally regenerated uneven-aged longleaf pine forest in the sandhills of north central Florida were examined to determine which aboveground and belowground factors are responsible for development of this seedling exclusionary zone. Within 12 m of adult trees growing along the gap edge, significantly fewer longleaf pine seedlings were present. The canopy of overstory trees, however, extended only 4–5 m into the gap. The relatively open structure of the longleaf pine canopy (57% cover) allowed photosynthetically active radiation (PAR) to be evenly distributed upon the forest floor across each canopy gap. Thus, light availability was not related to pine seedling clustering near gap centers. Significantly greater forest litter mass beneath adult trees (5 Mg ha −1) could result in fires more intense than would be supported by the litter mass near gap centers (2.5 Mg ha −1). However, litter mass was significantly elevated only within 4 m of the gap edge. The fine root biomass within 12 m of the gap edge (3–4.5 Mg ha −1) was two to six times that measured near the gap center and most closely coincided with the width of the seedling exclusionary zone along the margin of each gap. Thus, while the canopy of adjacent adult trees may indirectly influence seedling mortality through deposition of needle litter and greater fire intensity within 4 m of the gap edge, the root systems of these adults also appear to directly compete with seedlings within 12–16 m of the gap edge for limited site resources. To effectively regenerate and sustain longleaf pine wiregrass ecosystems, caution should be used in prescribing single-tree selection harvest methods so as not to create gap openings so small (<30 m diameter) that intraspecific competition from adult trees totally excludes seedlings. Group selection methods may prove more effective in creating canopy gaps of sizes suitable (≥40 m diameter) for ensuring that intraspecific competition from adults is maintained at a level which allows for survival and growth of seedlings. Shelterwood and deferment methods may also prove useful where more open canopy conditions are desired. However, the pine seedlings' need for light cannot be used as an appropriate rationale for application of clearcutting methods.

Effects of late growing‐season and late dormant‐season prescribed fire on herbaceous vegetation in restored pine‐grassland communities

Abstract. We compared the effects of late dormant‐season and late growing‐season prescribed fires on herbaceous species in restored shortleaf pine‐ (Pinus echinata) grassland communities in the Ouachita Highlands of western Arkansas. Herbaceous species richness, diversity, and total forb and legume abundance increased following fire. Late growing‐season burns reduced distribution and abundance of panicums (primarily Panicum boscii, P. dichotomum, and P. linearifolium) while late dormant‐season burns increased Panicum distribution and abundance. Density of legumes (such as Stylosanthes biflora) increased following frequent or annual dormant‐season fires. However, season of fire influenced the distribution and abundance of fewer than 10 % of the species. Fire plays an essential role in pine‐grassland communities by creating and maintaining open canopy conditions that perpetuate understory herbaceous plant communities.