The Effects of Established Trees on Woody Regeneration during Secondary Succession in Tropical Dry Forests

Understanding the mechanisms controlling secondary succession in tropical dry forests is important for the conservation and restoration of this highly threatened biome. Canopy‐forming trees in tropical forests strongly influence later stages of succession through their effect on woody plant regeneration. In dry forests, this may be complex given the seasonal interplay of water and light limitations. We reviewed observational and experimental studies to assess (1) the relative importance of positive and negative effects of established trees on regeneration; (2) the mechanisms underlying these effects; and (3) to test the ‘stress gradient hypothesis’ in successional tropical dry forests. The effects of established trees on seed dispersal, seed survival, and seed germination—either through direct changes to moisture and temperature regimes or mediated by seed dispersers and predators—are mainly positive. The balance between positive and negative effects on seedling establishment is more complex and depends on the season and leaf phenology of both trees and seedlings. Seedling survival is generally enhanced by established trees mitigating dry conditions. Established trees have counteracting effects on water and light availability that influence seedling growth. The probability of a positive effect of established trees on seedling survival decreases with increased rainfall, which supports the stress gradient hypothesis. Priorities for future research are experiments to test for facilitation and competition and their underlying mechanisms, long‐term studies evaluating how these effects change with ontogeny, and studies focusing on the species‐specificity of interactions.     

Effects of sea level rise on mangrove Avicennia population growth,colonization and establishment: Evidence from a field survey and greenhouse manipulation experiment

Mangroves will either face longer tidal inundation or retreat landwards in response to on-going accelerated sea level rise. However, little is known about the growth, regeneration or colonization of mangrove seedlings under the different tidal inundation regimes associated with accelerated sea level rise. In the present study, a field survey and a greenhouse mesocosm experiment were conducted to evaluate possible effects of accelerated sea level rise on colonization, establishment and seedling growth of a mangrove pioneer species, Avicennia marina. Avicennia populations at different elevations of the intertidal zone on Xiamen Island in Fujian Province, China showed distinctive patterns in both seedling density and plant age. The seedlings at lower elevations had less annual biomass accumulation and population productivity, but higher shoot to root ratios, suggesting that elevation has positive effects on seedling growth. The greenhouse mesocosm experiment with 1-year-old A. marina seedlings utilized five inundation periods (0, 2, 4, 6 and 12 h in a semidiurnal tidal cycle) and two inundation depths (root immersion and canopy immersion). Both inundation period and depth exerted significant and negative effects on biomass accumulation, photosynthetic rate, leaf electron transportation and water use efficiency. However, the negative effects of canopy immersion were more profound than root immersion. Canopy immersion exacerbated the effects of prolonged inundation, with no seedlings surviving under canopy immersion at the 12-hour treatment. These results suggest that at lower elevations with higher sea level, canopy immersion will have greater negative effects on seedling colonization, establishment and early growth of A. marina. This finding is instrumental in predicting the future dynamics of mangrove forests under increasing sea levels.     

Patterns of tree replacement: canopy effects on understory pattern in hemlock-northern hardwood forests

The effect of canopy trees on understory seedling and sapling distribution is examined in near-climax hemlock-northern hardwood forests in order to predict tree replacement patterns and assess compositional stability. Canopy trees and saplings were mapped in 65 0.1-ha plots in 16 tracts of old-growth forests dominated by Tsuga canadensis, Acer saccharum, Fagus grandifolia, Tilia americana, and Betula lutea in the northeastern United States. Seedlings were tallied in sub-plots. Canopy influence on individual saplings and sub-plots was calculated, using several indices for canopy species individually and in total. For each species sapling and seedling distributions were compared to those distributions expected if saplings were located independently of canopy influence. Non-random distributions indicated that sapling and seedling establishment or mortality were related to the species of nearby canopy trees. Hemlock canopy trees discriminate against beech and maple saplings while sugar maple canopy favors beech saplings relative to other species. Basswood canopy discourages growth of saplings of other species, but produces basal sprouts. Yellow birch saplings were rarely seen beneath intact canopy. Since trees in these forests are usually replaced by suppressed seedlings or saplings, canopy-understory interactions should influence replacement probabilities and, ultimately, stand composition. I suggest that hemlock and basswood tend to be self-replacing, maple and beech tend to replace each other, and birch survives as a fugitive by occupying occasional suitable gaps. This suggests that these species may co-exist within stands for long periods with little likelihood of successional elimination of any species. There is some suggestion of geographical variation in these patterns.     

Canopy Size Dependent Facilitations from the Native Shrub Rhodomyrtus tomentosa to the Early Establishment of Native Trees Castanopsis fissa and Syzygium hancei in Tropical China

The quantitative role of the canopy size of nurse shrubs on microenvironment and native tree establishment in degraded tropical lands has been seldom studied. In a 21‐month field experiment, we aimed to test the effect of a native shrub with different canopy sizes on the early establishment of native trees as part of the effort of forest restoration in tropical China. We examined the microenvironment, and the seedling establishment and growth of two native trees: Castanopsis fissa and Syzygium hancei in both open space (OS) microsite and microsite under the canopy of the native pioneer shrub Rhodomyrtus tomentosa. Shrub microsite was further divided into large canopy (LC), and medium canopy (MC) microsite, based on the shrub leaf area indices. Results showed that relative to OS, LC had higher soil nutrient concentration and water content, and lower photosynthetic active radiation (PAR), while MC had lower PAR and higher soil exchangeable Mg, K, and Ca. Survival and growth were mostly enhanced, while water stress and photoinhibition reduced for C. fissa seedlings in MC and S. hancei seedlings in LC. It is found that the beneficial effects of the native shrub on seedling establishment and growth result mostly from the improvement in nutrient and water availabilities, the reduction in plant stress caused by harsh summer light, and the specific ecological requirements of different tree species. We suggest that different canopy sizes of native shrub R. tomentosa may be explored to target different native trees and hence promote forest restoration in degraded tropical ecosystems.     

Short dry spells in the wet season increase mortality of tropical pioneer seedlings

Variation in plant species performance in response to water availability offers a potential axis for temporal and spatial habitat partitioning and may therefore affect community composition in tropical forests. We hypothesized that short dry spells during the wet season are a significant source of mortality for the newly emerging seedlings of pioneer species that recruit in treefall gaps in tropical forests. An analysis of a 49-year rainfall record for three forests across a rainfall gradient in central Panama confirmed that dry spells of ≥10 days during the wet season occur on average once a year in a deciduous forest, and once every other year in a semi-deciduous moist and an evergreen wet forest. The effect of wet season dry spells on the recruitment of pioneers was investigated by comparing seedling survival in rain-protected dry plots and irrigated control plots in four large artificially created treefall gaps in a semi-deciduous tropical forest. In rain-protected plots surface soil layers dried rapidly, leading to a strong gradient in water potential within the upper 10 cm of soil. Seedling survival for six pioneer species was significantly lower in rain-protected than in irrigated control plots after only 4 days. The strength of the irrigation effect differed among species, and first became apparent 3–10 days after treatments started. Root allocation patterns were significantly, or marginally significantly, different between species and between two groups of larger and smaller seeded species. However, they were not correlated with seedling drought sensitivity, suggesting allocation is not a key trait for drought sensitivity in pioneer seedlings. Our data provide strong evidence that short dry spells in the wet season differentially affect seedling survivorship of pioneer species, and may therefore have important implications to seedling demography and community dynamics.     

Variation in leaf resin composition between parent tree and progeny in Hymenaea: Implications for herbivory in the humid tropics

Variation in the sesquiterpene hydrocarbon leaf resins in the tropical leguminous genus Hymenaea is compared between parent tree, seedling and sapling progeny. Relatively large discrete quantitative variation in the leaf resins, known experimentally to display little phenotypic plasticity, has been classified into Compositional Types. Differences in Compositional Types in the leaves between parent tree and their seedling and sapling progeny are more pronounced in rain forest and related eocystems than in savanna and dry forests. A model is presented in which it is suggested that this variation in leaf resin may play an important role in defence against lepidopteran herbivores and thus also in seedling establishment under Hymenaea parent trees in rain forest and related ecosystems.     

Effects of drought and fire on seedling survival and growth under contrasting light conditions in a seasonal tropical forest

Question: How do tree seedlings differ in their responses to drought and fire under contrasting light conditions in a tropical seasonal forest? Location: Mae Klong Watershed Research Station, 100–900 m a.s.l, Kanchanaburi Province, western Thailand. Method: Seedlings of six trees, Dipterocarpus alatus, D. turbinatus, Shorea siamensis, Pterocarpus macrocarpus, Xylia xylocarpa var. kerrii and Sterculia macrophylla, were planted in a gap and under the closed canopy. For each light condition, we applied (1) continuous watering during the dry season (W); (2) ground fire during the dry season (F); (3) no watering/no fire (intact, I). Seedling survival and growth were followed. Results: Survival and growth rate were greater in the gap than under the closed canopy for all species, most dramatically for S. siamensis and P. macrocarpus. Dipterocarpus alatus and D. turbinatus had relatively high survival under the closed canopy, and watering during the dry season resulted in significantly higher survival rates for these two species. Watering during the dry season resulted in higher growth rates for five species. All seedlings of D. alatus and D. turbinatus failed to re‐sprout and died after fire. The survival rates during the dry season and after the fire treatment were higher for the seedlings grown in the canopy gap than in the shade for S. siamensis, P. macrocarpus, X. xylocarpa var. kerrii and S. macrophylla. The seedlings of these species in the canopy gap had higher allocation to below‐ground parts than those under the closed canopy, which may support the ability to sprout after fire. Conclusions: The light conditions during the rainy season greatly affect seedling survival and resistance to fire during the subsequent dry season. Our results suggest differentiation among species in terms of seedling adaptations to shade, drought and fire.     

The regeneration of pioneer tree species under browsing pressure of Sika deer in an evergreen oak forest

The effects of Sika deer (Cervus nippon) browsing on the regeneration of pioneer species were studied in relation to canopy gaps in a warm temperate evergreen oak forest in Kasugayama, Nara City. Four study sites, three in canopy gaps and one under a closed canopy, were selected and each divided into fenced and unfenced plots. Under the closed canopy, seedlings of all the pioneer species died irrespective of browsing pressure. However, in the canopy gap sites, seedlings of the pioneer species could establish and grow well. The seedling survival ratio in the fenced plots in the canopy gaps was >60% 1 year after germination. However, in the unfenced plots, only <20% of the seedlings survived 1 year, with all dying within 3 years after germination. Thus, the regeneration of pioneer trees in this forest was strongly inhibited by deer browsing. Successful regeneration of a pioneer,Zanthoxylum ailanthoides, occurred for several years even after two major wind disturbances during the past 90 years. This may be due to less browsing pressure from the deer.     

Posthurricane Seedling Structure in a Multi‐aged Tropical Dry Forest: Implications for Community Succession

Hurricane‐caused tree mortality in tropical dry forests occurs predominantly in early successional species. Consequently, hurricanes may accelerate succession in these forests. Forest regeneration, however, must be measured over an extended posthurricane time period to demonstrate this pattern. In this study, we recorded tree seedlings in 19 Florida Keys forests during May–August 1995, 3 years after Hurricane Andrew. For these forests—spanning a chronosequence from 14 to over 100 years since the most recent clearing—we used weighted averaging regression on relative abundances of pre‐hurricane trees to calculate a successional age optimum for each species; and used weighted averaging calibration to calculate inferred successional ages for stands based on pre‐hurricane trees and on posthurricane seedlings. To test the hypothesis that successional stage of seedlings exceeded successional stage of pre‐hurricane trees, we compared inferred stand ages based on posthurricane seedlings with those based on pre‐hurricane trees. Across the study area, inferred stand ages based on posthurricane seedlings were greater than those based on pre‐hurricane trees (P < 0.005); however, more seedlings in the youngest stands were early successional than in older stands. Of 29 species present both as pre‐hurricane trees and posthurricane seedlings, 23 had animal‐dispersed seeds. These results provide evidence that: (1) hurricanes do not ‘reset’ succession, and may accelerate succession; and (2) a strong legacy of stand successional age influences seedling assemblages in these forests.     

A Neighborhood Analysis of the Consequences of Quercus suber Decline for Regeneration Dynamics in Mediterranean Forests

In forests, the vulnerable seedling stage is largely influenced by the canopy, which modifies the surrounding environment. Consequently, any alteration in the characteristics of the canopy, such as those promoted by forest dieback, might impact regeneration dynamics. Our work analyzes the interaction between canopy neighbors and seedlings in Mediterranean forests affected by the decline of their dominant species (Quercus suber). Our objective was to understand how the impacts of neighbor trees and shrubs on recruitment could affect future dynamics of these declining forests. Seeds of the three dominant tree species (Quercus suber, Olea europaea and Quercus canariensis) were sown in six sites during two consecutive years. Using a spatially-explicit, neighborhood approach we developed models that explained the observed spatial variation in seedling emergence, survival, growth and photochemical efficiency as a function of the size, identity, health, abundance and distribution of adult trees and shrubs in the neighborhood. We found strong neighborhood effects for all the performance estimators, particularly seedling emergence and survival. Tree neighbors positively affected emergence, independently of species identity or health. Alternatively, seedling survival was much lower in neighborhoods dominated by defoliated and dead Q. suber trees than in neighborhoods dominated by healthy trees. For the two oak species, these negative effects were consistent over the three years of the experimental seedlings. These results indicate that ongoing changes in species’ relative abundance and canopy trees’ health might alter the successional trajectories of Mediterranean oak-forests through neighbor-specific impacts on seedlings. The recruitment failure of dominant late-successional oaks in the gaps opened after Q. suber death would indirectly favor the establishment of other coexisting woody species, such as drought-tolerant shrubs. This could lead current forests to shift into open systems with lower tree cover. Adult canopy decline would therefore represent an additional factor threatening the recruitment of Quercus forests worldwide.     

Winners and losers: tropical forest tree seedling survival across a West African forest–savanna transition

Forest encroachment into savanna is occurring at an unprecedented rate across tropical Africa, leading to a loss of valuable savanna habitat. One of the first stages of forest encroachment is the establishment of tree seedlings at the forest–savanna transition. This study examines the demographic bottleneck in the seedlings of five species of tropical forest pioneer trees in a forest–savanna transition zone in West Africa. Five species of tropical pioneer forest tree seedlings were planted in savanna, mixed/transition, and forest vegetation types and grown for 12 months, during which time fire occurred in the area. We examined seedling survival rates, height, and stem diameter before and after fire; and seedling biomass and starch allocation patterns after fire. Seedling survival rates were significantly affected by fire, drought, and vegetation type. Seedlings that preferentially allocated more resources to increasing root and leaf starch (starch storage helps recovery from fire) survived better in savanna environments (frequently burnt), while seedlings that allocated more resources to growth and resource‐capture traits (height, the number of leaves, stem diameter, specific leaf area, specific root length, root‐to‐shoot ratio) survived better in mixed/transition and forest environments. Larger (taller with a greater stem diameter) seedlings survived burning better than smaller seedlings. However, larger seedlings survived better than smaller ones even in the absence of fire. Bombax buonopozense was the forest species that survived best in the savanna environment, likely as a result of increased access to light allowing greater investment in belowground starch storage capacity and therefore a greater ability to cope with fire. Synthesis: Forest pioneer tree species survived best through fire and drought in the savanna compared to the other two vegetation types. This was likely a result of the open‐canopied savanna providing greater access to light, thereby releasing seedlings from light limitation and enabling them to make and store more starch. Fire can be used as a management tool for controlling forest encroachment into savanna as it significantly affects seedling survival. However, if rainfall increases as a result of global change factors, encroachment may be more difficult to control as seedling survival ostensibly increases when the pressure of drought is lifted. We propose B. buonopozense as an indicator species for forest encroachment into savanna in West African forest–savanna transitions.     

Individual Canopy‐tree Species Effects on Their Immediate Understory Microsite and Sapling Community Dynamics

Canopy trees are largely responsible for the environmental heterogeneity in the understory of tropical and subtropical species‐rich forests, which in turn may influence sapling community dynamics. We tested the effect of the specific identity of four cloud forest canopy trees on total solar radiation, canopy openness, soil moisture, litter depth, and soil temperature, as well as on the structure and dynamics of the sapling community growing beneath their canopies. We observed significant effects of the specific identity of canopy trees on most understory microenvironmental variables. Soil moisture was higher and canopy openness lower beneath Cornus disciflora. In turn, canopy openness and total solar radiation were higher beneath Oreopanax xalapensis, while the lowest soil moisture occurred beneath Quercus laurina. Moreover, Chiranthodendron pentadactylon was the only species having a positive effect on litter depth under its canopy. In spite of these between‐species environmental differences, only C. pentadactylon had significant, negative effects on sapling density and species richness, which may be associated to low seed germination and seedling establishment due to an increased litter depth in its vicinity. The relevance of the specific identity of canopy trees for natural regeneration processes and species richness maintenance depends on its potential to differentially affect sapling dynamics through species‐specific modifications of microenvironmental conditions.     

The role of nurse successional stages on species‐specific facilitation in drylands: Nurse traits and facilitation skills

Plant establishment is a challenge in semiarid environments due to intense and frequent drought periods. The presence of neighboring trees (nurses) can increase the establishment of seedlings (targets) by improving resource availability and microclimate. The nurse effect, however, might vary depending on nurse‐target species combinations but factors that predict this specificity are poorly known. We used a multispecies experiment to investigate the facilitation potential of trees from a range of successional stages, focusing on how nurse functional traits can predict species‐specific interaction outcomes. We conducted a factorial field experiment in a Brazilian semiarid tropical forest during a severe drought period. Sixty pairs of interacting tree species, 20 potential nurses, and three targets were used. Seedlings of all targets were planted both under and far from the nurse canopy, in a randomized block design replicated five times. Target growth and survival were monitored for 275 days from the beginning of the dry season, and interaction outcomes were calculated using the Relative Interaction Intensity (RII) index. Nurse functional traits such as successional stage, height, wood density, and canopy diameter were used as explanatory variables to predict RII values. The average effect of nurse species on target plants was in general positive, that is, seedling survival and growth increased under the nurse canopy. However, for growth pairwise interactions were significantly species specific. Successional stage was the only functional trait explaining RII values, with pioneer tree species being stronger facilitators than later successional trees. However, the explanation power of this variable was low, and positive, negative, or neutral interactions were found among nurse trees of all successional stages. Because seedling mortality during drought in semiarid systems is high, future studies should investigate how nurse traits related to water use could influence nurse facilitation skills.     

Canopy vs. soil effects of shrubs facilitating tree seedlings in Mediterranean montane ecosystems

Abstract. Question: Is the facilitative effect of nurse shrubs on early recruitment of trees mediated by a ‘canopy effect’(microclimate amelioration and protection from herbivores), a ‘soil effect’(modification of soil properties), or both? Location: Two successional montane shrublands at the Sierra Nevada Protected Area, SE Spain. Method: Seedlings of Quercus and Pinus species were planted in four experimental treatments: (1) under shrubs; (2) in open interspaces without vegetation; (3) under shrubs where the canopies were removed; (4) in open interspaces but covering seedlings with branches, mimicking a shrub canopy. Results: Both effects benefited seedling performance. However, microclimatic amelioration due to canopy shading had the strongest effect, which was particularly pronounced in the drier site. Below‐ground, shrubs did not modify soil physical characteristics, organic matter, total N and P, or water content, but significantly increased available K, which has been shown to improve seedling water‐use efficiency under drought conditions. Conclusions: We propose that in Mediterranean montane ecosystems, characterised by a severe summer drought, pioneer shrubs represent a major safe site for tree early recruitment during secondary succession, improving seedling survival during summer by the modification of both the above‐and below‐ground environment.     

Changes in tree phenology along natural regeneration in a seasonally dry tropical forest

The applicability of succession models from temperate and tropical wet forests to threatened seasonally dry tropical forests (SDTFs) is questioned. Plant phenology affects ecosystem functions and changes along forest regeneration gradient. To investigate the recovery of ecological functions after disturbances in a SDTF, we recorded the vegetative and reproductive phenologies for trees (DBH >5 cm) for 17 months in southeast Brazil in three successional stages: early (10–15 years after clearing), intermediate (25–30) and late (>50). The vegetative phenology of the 523 individuals was strongly seasonal, with 3% of individuals presenting green leaves in a deciduous dry season. Besides structural and floristic differences, phenological trends were similar between the later stages. Reproduction occurred with higher intensities in the early stage and in the advanced stages only in the dry season, providing key resources to local fauna. The studied SDTF is resilient to ecological functions, rapidly recovering functional processes. The integration of structural and functional knowledge of succession of STDFs may lead to better management of its secondary remnants. Our study suggests that classical forest succession theory developed for other ecosystems may not fully reflect the pattern of SDTF succession, an ecosystem that originally covered 42% of the earth's tropical and subtropical landmass.     

Episodic seedling growth in Allosyncarpia ternata,a lignotuberous,monsoon rainforest tree in northern Australia

On the western Arnhem Land Plateau, Northern Territory, Australia, seedlings of the canopy tree Allosyncarpia ternata S.T. Blake typically spend many years (perhaps decades) as small (<1 m), multistemmed plants on the forest floor. In this establishment phase, long periods of apparent inactivity are interrupted by episodes of rapid growth. This paper describes a 5‐year field‐monitoring program to examine the pattern of seedling growth and survival in allosyncarpia forest, and field and shadehouse measurements of lignotuber size. Individual seedlings may produce, each wet season, a number of fast‐growing stems, which then die back in the following dry season. As a result, mean annual above‐ground growth during this life stage is negligible. With each wet season, however, the seedling extends its below ground parts – a large lignotuber and a deep root system. After a number of years, when the lignotuber has grown large enough to sustain massive shoot growth, when a suitable light gap becomes available, and presumably when roots reach reliable dry‐season water supplies, the seedling grows rapidly. Thus, the shortage of saplings in allosyncarpia forest is due to the short time that individual plants spend at that particular growth‐stage, rather than to any dysfunction in recruitment.     

Litter mixture effects on tropical tree seedling growth--a greenhouse experiment

Decomposing litter provides critical nutrients for plants, particularly in nutrient-poor ecosystems such as tropical forests. We hypothesised that decomposing litter improves the performance of a variety of tropical tree seedlings, and that this litter effect varies depending on the species of litter present in litter mixtures. We addressed these hypotheses with a large pot experiment manipulating a range of different litter mixtures of contrasting quality and using seedlings of four tree species from the Amazonian forest of French Guiana. In contrast to our initial hypothesis, decomposing litter had either neutral or negative impacts on seedling growth, despite strongly different growth rates, biomass allocation patterns and leaf and root traits among tree species. Tree species varied in their responses to litter additions, which were further modified by species identity of the added litter. Our data show litter species-specific effects on growth, biomass allocation and leaf and root traits of tropical tree seedlings. These results suggest that a net nutrient release from decomposing litter does not necessarily improve tree seedling growth, even under nutrient-limiting conditions. In conclusion, litter layer composition may affect seedling establishment and recruitment success beyond litter-derived plant nutrient availability, which may contribute to tree species composition and dynamics in the studied tropical forest.     

桂西南石漠化区3种先锋树种对树冠下青冈和金银花幼苗生长的影响

为探讨桂西南石漠化区先锋树种对树冠下其他幼苗生长的影响,采取野外小区试验的方法,对茶条木(Delavaya toxocarpa)、银合欢(Leucaena leucocephala)和任豆(Zenia insignis)等先锋树种树冠下的青冈(Cyclobalanopsis glauca)和金银花(Lonicera maackii)幼苗的成活和生长进行了研究。结果表明,3种先锋树种能明显降低树冠下的光照强度,对土壤的物理性状亦能起到一定或比较明显的改善作用,但对土壤化学性状则没有或者改善作用较小。3种先锋树种对青冈幼苗的成活和生长具有比较明显的保育作用;任豆和银合欢对金银花幼苗的成活有保育作用,但对其幼苗生长具有抑制作用,而茶条木对金银花幼苗成活和生长均有较明显的抑制作用,且无论是保育作用还是抑制作用,3种先锋树种对树冠下同种幼苗株高或枝条的影响要大于对基径的影响。因此,该区植被修复可以选择茶条木、银合欢和任豆等先锋树种作为青冈幼苗的保育植物,而金银花则应选择这些树种的树冠外作为定植点,以减少或消除其对幼苗生长的不利影响。     

Facilitating Establishment of Advance Regeneration of Pterocarpus santalinus L.—An Endangered Tree Species from India

Red sanders (Pterocarpus santalinus L.) is an endangered and endemic tropical tree species from India in need of restoration. This study evaluated options for improving establishment of its advance regeneration in degraded forests. Using randomized complete block design, the effect of silvicultural treatments involving prescribed fire, in combination with disking, singling, disking with singling, and control (no treatment) on survival and growth of advanced regeneration were evaluated for a period of 2 years. Results indicate that the treatments served to ameliorate microsite conditions resulting in better survival and growth. Seedlings with fewer coppice shoots, treatments with a singling component, and treatments with disking component showed better survival and growth. The number and height of other neighboring seedlings and trees also influenced seedling establishment. Seedlings showed significantly higher survival results in the prescribed fire with disking (disking with prescribed burn [DPB]: 96%) and prescribed fires with disking and singling (singling plus disking with prescribed burn [SDPB]: 94%) treatments. Similarly, tall seedlings and those with larger root collar diameters accrued significantly higher volume growth in DPB (87%) and SDPB (97%) treatments. Although seedlings showed similar increments in DPB and SDPB treatments, better survival due to singling indicated the latter as the best option. In dense regeneration areas, preferential treatment of the taller and larger stump‐sized seedlings and, in limited regeneration areas that of smaller seedlings, may yield better results. Additionally, removal of competing vegetation and canopy opening may also help establishment of young regeneration. The results of this study have applications for restoration of endangered species in other tropical dry deciduous ecosystems worldwide.     

Composition and Dynamics of Functional Groups of Trees During Tropical Forest Succession in Northeastern Costa Rica

We compared the functional type composition of trees ≥10 cm dbh in eight secondary forest monitoring plots with logged and unlogged mature forest plots in lowland wet forests of Northeastern Costa Rica. Five plant functional types were delimited based on diameter growth rates and canopy height of 293 tree species. Mature forests had significantly higher relative abundance of understory trees and slow-growing canopy/emergent trees, but lower relative abundance of fast-growing canopy/emergent trees than secondary forests. Fast-growing subcanopy and canopy trees reached peak densities early in succession. Density of fast-growing canopy/emergent trees increased during the first 20 yr of succession, whereas basal area continued to increase beyond 40 yr. We also assigned canopy tree species to one of three colonization groups, based on the presence of seedlings, saplings, and trees in four secondary forest plots. Among 93 species evaluated, 68 percent were classified as regenerating pioneers (both trees and regeneration present), whereas only 6 percent were classified as nonregenerating pioneers (trees only) and 26 percent as forest colonizers (regeneration only). Slow-growing trees composed 72 percent of the seedling and sapling regeneration for forest colonizers, whereas fast-growing trees composed 63 percent of the seedlings and saplings of regenerating pioneers. Tree stature and growth rates capture much of the functional variation that appears to drive successional dynamics. Results further suggest strong linkages between functional types defined based on adult height and growth rates of large trees and abundance of seedling and sapling regeneration during secondary succession.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp