Natural Regeneration Potential Research Articles

Seed rain and soil seed bank of Picea asperata Mast. in subalpine coniferous forest of western Sichuan, China

Dragon spruce (Picea asperata Mast.) is widely planted on clear-cuts from natural subalpine coniferous forests in western Sichuan. To assess the natural regeneration potential of this species in spruce plantations of different ages, field studies on the seed rain, seed bank, and seedling recruitment were conducted in 20-year, 30-year, and 60-year plantations, and in a retained natural forest ca. 150 years old for comparison. Moreover, a series of temperature and light regimes were also designed in March 2003 to test germination/dormancy responses of the P. asperata seeds to different conditions. In the plantations considered, both the densities of seed rain and soil seed bank increased with increasing stand age, whereas they were both low beneath the natural forest partially due to low adult density of P. asperata adult trees. P. asperata has a transient seed bank, and ca. 60% of seeds were found in the litter layer. Seed decay and seed predation were the two most important factors affecting soil seed bank dynamics, which caused a number of seed losses from the soil. Only a small fraction germinated and produced seedlings, and the indices of the losses from the seed bank via germination in the 30-year plantation, 60-year plantation and natural forest were 4.75, 5.10, and 2.80%, respectively. High seedling mortality was observed after seedling emergence, and most of the germinated seedlings died out within one growing season. The P. asperata seeds showed a high percent germination and no significant differences under most light and temperature regimes except for full sunlight or temperature below 5°C. In conclusion, despite a substantial number of seed produced, the high depletion of soil seed, the low seedling output, and high seedling mortality may obscure the natural regeneration potential of this tree species.

Harnessing nature to improve sustainability

Harnessing nature to improve sustainability

Validation of Forest Condition Monitoring Programme (ICP-Forests, level 1) cone index scores by measuring cone density using a field-of-view method

A measure of annual cone production is needed for evaluating potential seed crops and for the study of population changes of seed-eating species, but is rarely available in long time series or over extensive areas. The Forest Condition Monitoring (FCM) programme, which contributes to the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP-Forests), has been collecting coning data for Scots pine, Norway spruce and Sitka spruce since 1989, from plots located throughout Britain. A visual assessment system is used to measure a coning index at four levels of abundance as part of the overall crown health assessment. This study tested whether the FCM abundance assessment was related to coning density, and therefore its potential for wider use in future research. Data from the survey have been compared with a field-of-view method that assesses cone density, and the cone production represented by the FCM index has thus been determined. A direct relationship between increased cone index and increased cone density was found; the use of a four-level scoring system allows different cone densities to be distinguished with some reliability. Allocation of cone scores by surveyors from year to year was shown to be consistent except in the case of abundantly coning Sitka spruce. These findings indicate that the FCM programme scoring method does reflect cone production levels and that the data can be used to assess variation in coning between sites and between years. The resolution of the coning data is adequate for assessing the potential for natural regeneration of woodlands but not for selecting stands for seed collections. It is also appropriate for use as a measure of food resource to relate to population changes in seed-eating birds and mammals, and the long-term and Britain-wide nature of these data are of particular value. There is potential for the field-of-view method to be used more widely to evaluate the quality of cone data collected at ICP-Forest sites throughout Europe where the same cone index method has been employed.

Advanced regeneration and seedling establishment in small cutblocks in high-elevation spruce–fir forest at Sicamous Creek, southern British Columbia

We examined the potential of natural regeneration for stocking 1-ha patch cuts in high-elevation Engelmann spruce (Picea engelmannii Parry) – subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forests. Using the Sicamous Creek Silvicultural Systems site, which was harvested during winter 1994–1995, we established 1-m2 plots in patch cuts, forest edge, and untreated control forest. We marked and recorded microsite characteristics for all advanced regeneration and new recruits for up to 5 years; over 12 000 individuals were included. Advanced regeneration was abundant and was about one-quarter spruce. Spruce and fir germinants occurred in all years, but numbers varied greatly, with a very large cohort in 1998. Both advanced regeneration and new recruits were concentrated on decaying logs. Mortality of advanced regeneration was high in the patch cuts following harvest, but subsequent survival was good, approaching rates in the untreated forest within 4 years. Survival rates were higher for spruce than fir, but differed little among surface types and microtopographic positions. Survival of new recruits was high, approximately 50% the first year and 70% during the second, and was similar between spruce and fir. If the 1998 cohort has similar survival, the patch cuts could be adequately stocked. Use of natural regeneration, in combination with infill planting, is a viable option for stocking small openings in wet high-elevation forests in southern British Columbia.

Assessing the potential of natural woody species regeneration for the conversion of Norway spruce plantations on alluvial soils

In the perspective of the conversion of Norway spruce plantations, there is a need for foresters to assess the potential of the natural woody species regeneration. We studied 50 Norway spruce plantations on alluvial soils throughout the Grand-duche de Luxembourg and compared the regeneration characteristics (species composition, spatial heterogeneity) with 42 riverine deciduous stands (the target communities). Within the Norway spruce plantations, Fraxinus excelsior and Acer pseudoplatanus were the main regenerating species, probably because of their very good dispersal abilities. Norway spruce seedlings were quasi-absent. Low Norway spruce densities and base- rich soils (local factors) as well as proximity of riverine deciduous forests (regional factor) strongly favoured the regeneration of a suite of broad-leaved species. The thickness of Norway spruce litter did not appear to be a limiting factor, at least for large-seeded tree seedlings. The spatial heterogeneity of the woody regeneration was rather similar in coniferous and deciduous stands. We conclude that for the development of multifunctional forests, the spontaneous regeneration under low-dense Norway spruce stands on base-rich soils provides a valuable starting point.

Dispersal, germination, and survival of Populus nigra L. (Salicaceae) in changing hydrologic conditions

Improving our knowledge of regeneration processes in riparian woodlands could help guide restoration projects by enhancing the natural regeneration potential of riparian tree species. In western Europe, Populus nigra, is a major component of riparian woodlands, but the spatial extent of this species has decreased due to river management activities. In this study, the timing of Populus nigra seed dispersal and variations in seed germinability through time were monitored. An experiment was also devised to measure both seed germination and seedling survival in changing bydrologic conditions. The seed dispersal period lasted 12 weeks along the Garonne River. Individual poplar trees displayed variations in seed release patterns. On average, seed germinability remained rather low and close to 28%. However, large differences in germinability were observed between trees and over time. A continuously wet substrate was the most favorable condition for germination and seedling survival. A change from wet to submerged conditions increased germination and reduced seedling survival. In the case of a change from either wet or submerged to dry conditions, there was no survival possible if the dry conditions persisted more than one week. Substrate type had a significant effect on germinability only in moderate moisture conditions. Populus nigra tolerates decreases in the optimum minimum flow if coupled with at least a brief rise in river level on a weekly basis.

High altitude tropical secondary forests: a competitive carbon sink?

High altitude tropical regions have been heavily deforested and offer large areas for carbon offsets by secondary forest regeneration. However, a general assumption exists that productivity, and thus, carbon sequestration of high altitude forests is low, but the scarcity of data from high altitude tropical forests does not allow for a sound confirmation of this assumption. To determine the carbon sequestration potential of natural forest regeneration and reforestation efforts at high altitudes, aboveground biomass was quantified of several successional stages of two monospecific secondary forests in the high Ecuadorian Andes. The studied forests were, at 3200 m, an Alnus acuminata forest with 8-, 20-, 30- and 45-year-old stands and, at 3600 m, a Polylepis incana forest with 6-, 15- and 30-year-old stands and old growth forest without known age. Both trees are pioneer species. Additionally, a soil survey was conducted and leaf N/P ratios and N and P retranslocation rates were determined. Total aboveground biomass (TAGB) estimates of the oldest stages of the two forests were 241 Mg ha −1 for the Alnus and 366 Mg ha −1 for the Polylepis forest. Productivity, expressed as annual aboveground biomass accumulation (ABA) was in both forests highest in the establishment phase (14.2 and 15.0 Mg ha −1 per year at 8 and 6 years, respectively) due to high sapling numbers, and then slowed down significantly (5.9 and 6.9 Mg ha −1 per year, respectively at age 30). TAGB and ABA figures of the investigated forests are comparable to those of lowland tropical forests and do not indicate a significant decrease of these parameters at higher altitudes in the tropics. Analysis of site conditions, ecological requirements and ecophysiological properties of the tree species indicated that in both cases an optimal combination of these factors strongly favoured forest growth. It is not possible to verify whether our forests are representative for other high altitude tropical forests or if they should be treated as exceptional cases. The results do show, however, that high carbon offsets at high altitudes are possible.

Structural and Floristic Heterogeneity in a 30‐Year‐Old Costa Rican Rain Forest Restored on Pasture Through Natural Secondary Succession

AbstractRelatively little information exists on neotropical secondary rain forests that have progressed beyond the pioneer stages of succession, or on the potential of natural regeneration to restore forest on large areas. We determined the structural and floristic characteristics (10 cm dbh) of a 30‐year‐old secondary forest developing on a 32.5 ha pasture on hilly terrain, abandoned after use of moderate intensity. Ten 0.24 ha sample plots covered the range of site conditions. The forest was dominated by long‐lived pioneer tree species; overall, the majority of species (70%) was vertebrate dispersed but the majority of individuals (52%) was of wind‐dispersed species. Tree species, including the dominants, were a mixture of those present in old‐growth and adventives colonizing from agricultural land. The forest was very heterogeneous. Vochysia ferruginea‐dominated stands characterized slopes with soils of high exchangeable acidity, while the adventive Cordia alliodora dominated sites with gentler topography and soils of lower acidity. Structural differences between the two forest types were slight, but Cordia forest had significantly greater species diversity and absolute and relative abundances of vertebrate‐dispersed tree species than Vochysia forest, which had significantly greater absolute and relative abundances of wind‐dispersed tree species. These latter differences between forest types, as well as the wide structural variation of the forest as a whole, were probably largely due to spatial and temporal variation in seed rains, some of it linked to the characteristics of the dominant species. Rain forest restoration on large pastures may depend greatly on wind dispersal and adventive tree species, and techniques for silvicultural diagnosis must be developed as a basis for the management of heterogeneous successional stands. Studies of early colonization of pastures should be expanded to focus on the causes of heterogeneity in older forests.

Natural regeneration potential of the degraded Krkono?e forests

Self-regulating mechanisms and natural regeneration capacities still exist in the Krkonosˇe National Park, although the magnitude of these varies with altitude. A study of changes after forest decline and clear-cut with respect to the establishment of pioneer trees, changes in the herb layer, changes in humus profile characteristics and soil base status was conducted in the Krkonosˇe Mountains National Park in order to evaluate potentials for natural regeneration in forests affected by severe atmospheric deposition. Pioneer trees establish in both the upper and the lower supramontane zones. Even lowland species such as Fagus sylvatica appear to rejuvenate at high altitude, although in low numbers. Cover values of Betula pendula increase during clear-cut development, partly because they are avoided by deer; those of Sorbus aucuparia remain low due to browsing. In the upper supramontane zone changes in the herb layer are not significant: Calamagrostis villosa is dominant in (already declined) forests and remains so in clear-cut areas. In the lower supramontane zone Vaccinium myrtillus has its optimum in forests, while Deschampsia flexuosa strongly increases in clear-cut areas. Pioneer herbs establish after clear-cut. During clear-cut development, LF horizons decrease, due to a shift in input from low-decomposable spruce needles to easily decomposable grass (and later pioneer) litter. H horizons increase because of continuing decomposition and organic matter transfer from F to H horizons. At higher altitude, these processes occur at a lower rate. Pioneer trees have ameliorating effects on the soil via an increase in base elements and pH compared to spruce forests. There are only few indications that pioneer trees are severely hampered by dense grass carpets, which may occur in particular microhabitats escaping attention in the larger plot descriptions. High grass covers instead seem to have stimulating effects on seedling establishment via the improvement of the humus profile, which continues after pioneer trees grow up. Copyright © 2000 John Wiley & Sons, Ltd.

Determinants of sustainable CD4 lymphocyte count increases in response to antiretroviral therapy.

HIV-induced CD4 lymphocyte depletion is partially reversed by antiretroviral therapy but it is unclear if the degree to which the CD4 count rises depends on viral suppression (if so, the extent of viral suppression required to achieve a maximal CD4 count rise), whether the rise is sustainable and whether it occurs in patients with CD4 count <10 x 10(6) cells/l. We aimed to address these issues. We studied CD4 count and plasma HIV RNA values every 4 weeks for 72 weeks in 154 patients starting indinavir-containing regimens. Mean baseline HIV RNA and CD4 count were 4.8 log10 copies/ml and 180 x 10(6) cells/l, respectively. Overall, there was a mean increase in CD4 count of 143 x 10(6) cells/l by 72 weeks. The adjusted mean increase (adjusted for initial viral load, CD4 count and age) was strongly related to the mean viral suppression over the follow-up period (P < 0.0001). Importantly, there was a highly significant difference (P = 0.0004) in the rise in CD4 count between those with 2-3 log suppression (161 x 10(6) cells/l) and those with > 3 log suppression (314 x 10(6) cells/l; mean 3.6 log suppression in this group), suggesting that with even greater suppression the rise in CD4 lymphocytes may be still larger. We also studied whether CD4 counts were still rising after 72 weeks in patients with sustained suppression of at least 3 log in viral load. There was a significant (P = 0.004; paired t-test) rise in count of 43 x 10(6) cells/l between weeks 64 and 72 in these patients, suggesting that regeneration continues at least up to 72 weeks after therapy, provided virus replication continues to be suppressed. Patients with initial CD4 counts < 10 x 10(6) cells/l experienced no smaller rises than those at higher levels, even after adjustment for other factors. These results strongly support a direct causal relationship between HIV replication and CD4 lymphocyte count depletion. The rise in those with > 3 log suppression provides the best available indicator of the potential for natural CD4 regeneration in HIV-infected patients. However, since still greater CD4 count rises may be seen with more suppressive regimens, it may not be possible to study the intrinsic CD4 regenerative capacity until such regimens are available.

Differential recovery of a deepwater swamp forest across a gradient of disturbance intensity

On the Savannah River Site, South Carolina, USA, large areas of floodplain swamp forest of baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) were destroyed by the cumulative impacts of cooling-water discharges over a 35-year period of nuclear reactor operations. In one floodplain area, four years after thermal discharges ended, we analyzed the pattern of forest recovery across a disturbance gradient spanning from a site of chronic thermal impact and extensive sediment deposition to sites of intermittent thermal impact and little substrate change. Across this spatial gradient, we measured density and size structure of cypress and tupelo and assessed regeneration success in relation to density of surviving canopy trees and to substrate changes. Compared with undisturbed forest, canopy tree density was lower in all disturbed sites and decreased progressively with greater site disturbance. Density of trees regeneration decreased in parallel with declining canopy tree density; however, regeneration was particularly low in the site of chronic impact, where very few canopy trees had survived and where substrate had been modified by sedimentation. Size structures suggested that tree recruitment had occured synchronously during a 5-year period of regional drought and minimal river flooding. Thus, cypress-tupelo recovery was influenced both by availability of seed sources and by site conditions, but floodplain hydrology also affected regeneration. The pattern of differential recovery across the disturbance gradient has allowed the use of natural regeneration potential in efforts to restore the pre-disturbance forest, and it also illustrates several key factors in wetlands design.

Natural regeneration potential and early development of Shorea robusta Gaertn.f. forest after regeneration felling in the Bhabar-Terai zone in Nepal

In Nepal, the natural Shorea robusta (local name ‘sal’) dominated forests have been subject to selection felling, encroachment, uncontrolled grazing and annual forest fires for the past 30–50 years, and the forest cover has declined by about 1.3% per annum. The aim of this study was to obtain information on the natural regeneration potential of the Shorea robusta forests, when these forests are treated with different types of regeneration fellings, and when the areas are protected from grazing and forest fire. The study was conducted in a mature irregular ‘Moist Bhabar Sal’ forest. The main species were Shorea robusta, Terminalia tomentosa, Lagerstroemia parviflora, Sysigium cuminii and Ficus sp. The experiment consisted of three different regeneration felling methods: (1) regeneration felling with 75 sheltertrees ha −1; (2) regeneration felling with 25 sheltertrees ha −1; (3) regeneration fellings without sheltertrees. These areas were fenced and protected from fire and grazing. A control area was fenced and protected in the same forest. Bushes and advanced growth were cleaned from the harvested areas with only the smallest seedlings remaining (height less than 50 cm). The removal of Lantana camara and Eupatorium odoratum was done in the treated areas 14 months after the felling. Permanent plots were measured one growing season after the felling, and again 12 months later. The number of Shorea robusta seedlings was high after the felling, varying from 74500 to 91000 seedlings ha −1. During the dry period between the measurements, 4.2–10.2% of the seedlings died back, but an analysis of variance did not reveal any significant differences. The height development of the dominant 2000 seedlings ha −1 during the second growing season was the fastest in the area without sheltertrees (127 cm), and the lowest in the control area (81 cm). The results of the area without sheltertrees differed significantly from all the other treatments in Tukey's HSD test of means; other significant differences were not observed. Differences in diameter growth were more distinct than those for height; the growth in the area without sheltertrees was almost four times the growth in the control area. Significant differences were detected between all treatments, except between the areas where 25 and 75 sheltertrees were left. The die-back of Shorea robusta seedlings was not a problem in the treatment areas. Removal of old crop and protection led to the fast growth of already recruited seedlings.

Setting priorities for conservation of the conifer genetic resources of British Columbia

Gene conservation of native conifer species in British Columbia is considered necessary primarily to safeguard the future evolutionary potential of species to climate change, new biotic challenges and for commercial genetic improvement programs. The tactical options include: (i) maintaining existing protected areas, (ii) creating new reserves for in situ management, and (iii) ex situ collections of various types.A two-part strategy is presented, with emphasis on technical justifications, for the conservation of conifer tree genetic resources of 23 British Columbia species. Part I is a survey of the frequency of each species in current land reserves in BC. Part II outlines an approach that will aid in setting priorities for additional gene conservation activities for specific species. This process attempts to use information on: (i) levels of in situ protection, (ii) the status of each species in current provenance research and breeding programs, and (iii) the relative capabilities for natural regeneration for each species.Representation of the 23 native conifer species in the current network of protected areas is generally complete. For instance, western hemlock is under little threat, as extensive ex situ collections are in field tests; it is well protected in the current reserve network, and it has a great capacity for natural regeneration. At the other extreme, whitebark pine has no ex situ collections made to date, needs additional protection in some ecoregions of the province, and generally has poor natural regeneration potential. While implementation of our strategy will be an ongoing process (i.e. updating information from both new and old in situ reserves, and setting new priorities among species), several immediate issues have been noted. These include; (i) follow-up work in the area of population sampling for ex situ collections, (ii) "ground truthing" of current reserves where data are weak, and (iii) examining the merit of certain populations not located in BC (as they could be as important as those currently protected in BC).For the future, various broad management questions will need to be resolved, such as: (i) whether existing reserves will perpetuate the various gene pools, and what management will be appropriate for such areas, (ii) the impact of pollen migration from genetically improved production stands on reserve stands, and (iii) the role of commercially improved stands and the breeding populations themselves to meet gene conservation objectives. Key words: gene conservation, native conifers, British Columbia, tree genetics

Insect damage to cones and other mortality factors limiting natural regeneration potential of Swiss stone pine (Pinus cembra L) in the northern French Alps

Les degats d'insectes des cones et autres facteurs de mortalite limitant les potentialites de regeneration naturelle du pin cembro dans les Alpes francaises du Nord. Un suivi demographique de cones de pin cembro sur un cycle reproductif complet a ete realise en 1992 et 1993. Au total, 84 % de la production potentielle de graines a ete detruite. La majorite des pertes a ete causee par des facteurs abiotiques la premiere annee, et par des insectes pour les cones de deuxieme annee. L'entomofaune ne comprend que trois especes phytophages et differe largement de celle observee dans les autres essences des coniferes alpins.

Quebec's ecological framework for forest management: a case study in the boreal forest of Abitibi

The Quebec Ministry of Forests has developed an approach to ecological cartography designed to complement its traditional forest inventory and delimit homogeneous land units for forest management. The methodology consists of field work, map analysis and photointerpretation. Within the hierarchical classification, ecological regions reflecting regional climate are mapped at the 1:1 250 000 scale. Major physiographic ensembles and ecological districts, mapped at 1:250 000, express patterns of physiography, geology and geomorphology and ecological types (1:20 000) characterize surface deposits, drainage class, slope and potential climax forest. Using information drawn from ecological classification work in northwestern Quebec and applying the Ministry's standards, an ecological framework for two townships was developed. In addition to maps of each classification level, the framework includes interpretative documents such as schematic cross-sections of ecosystems and descriptive texts. Examples of management interpretations (natural regeneration potential and site preparation effect on competition) are presented. The classification approach and its future are evaluated.