An empirical cohort model for management of Terra Firme forests in the Brazilian Amazon

A model to project forest growth in the Terra Firme forests of the eastern Amazon is described. It is based on 12–17 years measurements from experimental plots at Jarí and Tapajós. Forest stands are represented by cohorts of species group, diameter, and defect. There are 54 species groups, with a robust diameter increment function fitted to each, tables of mortality by crown and defect status, and recruit lists by disturbance level and locality. Stand level functions partition trees by crown status, and modify growth for stand density. Recruitment is a function of basal-area losses. Evaluation compares model performance with two experiments involving heavy felling in Tapajos State Forest. At one site, total bole volume growth of all species over 45 cm DBH was 2.56 m³ ha⁻¹ year⁻¹ over 17 years, whereas the model projected 3.13 m³ ha⁻¹ year⁻¹. At the other site, actual growth over 12 years was 0.39 m³ ha⁻¹ year⁻¹, with the model giving an identical result. Both felled and control plots are compared in the study and accurately simulated. Some weaknesses in the model are discussed.     

Use of a gradient of N-deposition to calculate effect-related soil and vegetation measures in deciduous forests

Deposition of N and S has increased since the 1950s in most European countries and N accumulates in ecosystems that are not N saturated. This study shows long-term effects of a (modelled) N deposition of 7–17 kg N ha⁻¹ per year on biological and chemical processes in soil, vegetation composition, and functional types of field-layer plant species in deciduous forests. Soil pH largely determined the response of the soil processes, emphasising the importance to compare soils of similar acidity regarding the effects of N deposition. The most pronounced effects were demonstrated for the most acid study plots. When we compared regions with a deposition of 7 and 17 kg N ha⁻¹ per year we found a 40–80% higher soil N mineralisation rate, 2–90% higher nitrification rate and 10–25% lower C:N ratio in the region with the highest deposition. Similar but smaller differences were indicated when regions with a deposition of 7 and 10 kg N ha⁻¹ per year were compared. Number of species was lower in the regions with the highest deposition. Literature data for plants on N concentration, nitrate reductase activity (NRA), growth rates, morphology and height were calculated on a site basis. They varied to different extent between the regions. The N concentration was 7–24% higher in the regions with the highest N deposition. We argue that the effect-related critical load based on our results should be set to a N deposition of 7–10 kg N ha⁻¹ per year. Critical loads for a subdivision of deciduous forests would give lower critical loads for the most acid soils compared to less acid soil.     

The impact of hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) on balsam fir and spruce in New Brunswick, Canada

In 1989, the first recorded outbreak of hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) occurred in New Brunswick, Canada. Data were collected from ten plots established in an area infested from 1992–1994, to assess impacts of hemlock looper. Ocular and branch sample assessments of current defoliation and ocular assessments of total defoliation (all age classes of foliage) were conducted for balsam fir (Abies balsamea [L.] Mill.), white spruce (Picea glauca [Moench] Voss), and black spruce (Picea mariana (Mill.) B.S.P.). Stand response was assessed and related to cumulative defoliation. Ocular assessments were found to accurately estimate defoliation, which was significantly related to tree mortality. Ninety-two percent of balsam fir trees that had cumulative defoliation >90% died. Mortality of balsam fir was significantly (p < 0.05) related to tree size, in both lightly and severely defoliated plots; trees with DBH <11 cm sustained 22–48% higher mortality than larger trees. Mortality of balsam fir, in terms of both percent stems/ha and m³/ha merchantable volume, increased exponentially in relation to three estimates of cumulative (summed) plot mean defoliation. The strongest relationships (r² = 0.75–0.79) were between mortality and the ocular defoliation assessment for 1990–1993 foliage. Tree mortality caused by the looper outbreak ranged from 4–14% stems/ha in lightly defoliated and from 32–100% in severely defoliated plots; merchantable volume killed was 3–14 m³/ha and 51–119 m³/ha, respectively. Relationships between mortality and defoliation were similar when defoliation was assessed for 1987–1993 and 1990–1993 foliage age classes.     

Burning of Amazonian forest in Ariquemes, Rondônia, Brazil: biomass, charcoal formation and burning efficiency

Biomass burning in tropical forests – the normal practice to prepare land for agriculture and ranching – has been a major source of CO₂ emitted to the atmosphere. Mass transformations by burning are still little studied in the tropics. The present study estimated parameters, such as the stock of carbon contained in the biomass, burning efficiency and the formation of charcoal and ashes in a tropical moist forest. Two sets of plots arranged in the form of ‘stars' (720 m² total) were installed in a 3.5 ha area of forest that had been felled for planting pasture at Fazenda Nova Vida, Ariquemes, Rondônia. Each ‘star' had six rays measuring 2 m × 30 m; alternating rays were designated for pre-burn and post-burn measurements. All above-ground biomass present in the plots was weighed directly before the burn in the pre-burn rays and after the burn in the post-burn rays. Pieces of wood with diameter ≥10 cm also had their biomasses estimated from volume estimates, using line-intersect sampling (LIS) in order to increase the area of sampling and to allow volume loss to be estimated as an increment based on individual pieces measured before, and after, the burn at the same point (as opposed to inferring change as a difference between independent estimates of stocks). The initial above-ground biomass (dry weight) before the burn was estimated at 306.5 ± 48.6 (mean ± SE) Mg ha⁻¹, with an additional 4.5 Mg ha⁻¹ for trees left standing. Carbon stock in the initial biomass (including trees left standing) was 141.3 (Mg C) ha⁻¹. After burning, carbon stock was reduced by 36.8% (burning efficiency). The stocks of charcoal and ash formed in the burn were, respectively, 6.4 ± 2.7 and 5.7 ± 1.0 Mg ha⁻¹. The destructive and nondestructive (LIS) methods did not differ significantly (t-test, p > 0.05) in estimating post-burn stocks of wood and charcoal. The results of this study contribute to improving the estimates of parameters needed for global carbon calculations and point to ways in which estimates of these parameters could be further improved.     

Woody vegetation structure and composition along a protection gradient in a miombo ecosystem of western Tanzania

Fully protected areas such as National Parks are often assumed to be the best way to conserve plant diversity and maintain intact forest composition and structure. To evaluate this assertion, we sampled trees in areas with four different levels of protection: a National Park, where the protection level is very high, a Game Controlled Area which allows tourist hunting of big game animals, a Forest Reserve which allows selective harvest of trees, and an Open Area where human populations have unrestricted access to forest resources. All four land management areas had healthy size-class distributions with greater numbers of juvenile trees (2–10 cm DBH) than adults. Surprisingly, mean stem density of trees was highest (947 stems ha⁻¹) in the Game Controlled Area but was lowest (635 stems ha⁻¹) in the National Park. The former had the highest basal area value (24 m² ha⁻¹) while the human-inhabited Open Area had the lowest (11 m² ha⁻¹). Species richness in the Forest Reserve and Game Controlled Area was significantly higher than in the other areas. The total number of plots with unique species not found anywhere else was lowest in the National. Our measures of forest structure and composition therefore show that fully protected National Parks do not necessarily conserve the greatest diversity of tree species or unique species, indicating that a suite of different types of protection strategies may be the key to conservation of trees in these African dry tropical forests.     

Influence of artificial gaps in tropical forest on survival, growth, and Phytolyma lata attack on Milicia excelsa

Milicia excelsa and M. regia are important timber species in moist tropical areas of Africa. They have not been successfully grown largely because of attacks by gall-forming psyllids in the genus Phytolyma. Our objectives were to evaluate the growth of planted Milicia seedlings and incidence of psyllid attack in small (4.2 m²), medium (18.5 m²) and large (>500 m²) artificial gaps in the Bobiri Forest Reserve in the Moist Semi-Deciduous Forest of Ghana. After 13 months, height and diameter growth of Milicia seedlings were significantly greater in the medium and large gaps than in the small gaps. Insect attacks occurred first and most severely in the large gaps, but spread to gaps of all sizes between the 11th and 13th months after planting. While gap size significantly affected the susceptibility of seedlings to psyllid attack, it is not the only factor important in determining susceptibility of Milicia excelsa under field conditions. We conclude that gap sizes in the range of 10–50 m², where irradiances are from 30–60% of full sunlight, in forests similar to those at the study site, seem to be most suitable for regeneration of Milicia.     

Population structure of Carapa guianensis in two forest types in the southwestern Brazilian Amazon

Carapa guianensis Aublet. is a tropical tree with strong multiple-use characteristics, and is valued for both the high quality oil extracted from its seeds and as a timber resource. This study compares the population structure of this economically important rainforest tree in two contrasting forest types: occasionally inundated and terra firme forests. Main study objectives were (a) to assess the density, spatial distribution, and size class structure of C. guianensis in these two forest types and (b) to use patterns of abundance, distribution and demographic structure to help infer key demographic stages or ecological variables that merit special focus for management. Four 400 m × 400 m plots, two in each forest type, were established to determine distribution and density patterns of C. guianensis ≥10 cm diameter at breast height (dbh) at the landscape level, and 32 10 m × 10 m subplots were randomly nested within each of the larger plots to measure individuals <10 cm dbh. Larger individuals (≥10 cm dbh) were found at higher densities in occasionally inundated forest than in terra firme forest: 25.7 trees ha⁻¹ and 14.6 trees ha⁻¹, respectively. Mean density of C. guianensis individuals <10 cm dbh was also higher in occasionally inundated forests, but variation of regeneration density among the subplots was high. Spatial distribution methods revealed a tendency toward clumping in both forest types, and both had similar size class structures, suggesting that both environments are suitable for C. guianensis. This new finding illustrates the potential for C. guianensis management in terra firme forests. High densities and clumped distributions in both forest types are also indices favorable for sustainable species management. Finally, several ecological variables (tree density and reproductive potential) were sufficiently different between terra firme and occasionally inundated forests to recommend stratification by forest type when conducting further studies on key ecological and management variables of C. guianensis.     

Regeneration of timber trees in a logged tropical forest in North Bolivia

For sustainable forest management, it is important to know the response of timber species to the change in environment caused by logging. We performed a 2-year study on germination, survival and growth of four timber species, Cedrela odorata, Swietenia macrophylla, Hymenaea courbaril, and Cariniana micrantha, and one non-commercial species Tachigali vasquezii. We sowed seeds of these species in five microenvironments: log landing, gap-crown and gap-trunk, skidder trail and understory, in a tropical lowland moist rain forest in northern Bolivia. We related seed and seedling performance to light availability, soil compaction, and plant competition. Germination did not differ significantly between microenvironments but survival of germinated seeds for most species was significantly higher (P < 0.05) in the log landing (46–100%) than in the understory (0–7%). After 2 years, the tallest plants were always found in the log landing (119–190 cm) and the smallest in the understory (12–26 cm) caused by a higher relative height growth rate (RHGR) in the log landing (0.003–0.004 cm cm⁻¹ per day) compared to the understory (0.000–0.001 cm cm⁻¹ per day). During the first year RHGR was positively related to canopy openness for all species and negatively to the number of overtopping competitors for three species. During the second year also water infiltration explained observed variation to RHGR. These results show that abandoned log landings and logging gaps are suitable environments for the regeneration of timber species studied. This finding suggests that the removal of competitors in log landings and logging gaps combined with leaving seed trees near these microenvironments or sowing seeds, will improve regeneration of timber species in tropical forests.     

Forest structure and C stocks in natural Fagus sylvatica forest in southern Europe: The effects of past management

Managed forests often differ substantially from undisturbed forests in terms of tree structure and diversity. By altering the forest structure, management may affect the C stored in biomass and soil. A survey of 58 natural stands located in the south-westernmost limit of European beech forests was carried out to assess how the C pools are affected by the changes in tree structural diversity resulting from past management. The mean tree density, basal area and the number of large trees found in unmanaged forests were similar to those corresponding to virgin beech forests in Central Europe, whereas large live trees were totally absent from partially cut stands. Analysis of the Evenness index and the Gini coefficient indicated high structural diversity in the three stand types. The results of the Kolmogorov–Smirnov test used to compare the diameter distributions of each group revealed significant differences between stand types in terms of distributions of total tree species and of Fagus sylvatica.

The mean C stocks in the whole ecosystem – trees, litter layer and mineral soil – ranged from 220 to 770 Mg ha⁻¹ (average 380 Mg ha⁻¹). Tree biomass (above and belowground), which averaged 293 Mg C ha⁻¹, constituted the main C pool of the system (50–97%). The statistical test (Kolmogorov–Smirnov) revealed differences in the distribution of C pools in tree biomass between unmanaged and partially cut stands. As a consequence of the presence of large trees, in some unmanaged stands the C stock in tree biomass was as high as 500–600 Mg C ha⁻¹. In the partially cut stands, most of the C was mainly accumulated in trees smaller than 20 cm dbh, whereas in unmanaged stands the 30% of tree C pool was found in trees larger than 50 cm dbh. Furthermore, many unmanaged stands showed a larger C pool in the litter layer. The C content of mineral soils ranged from 40 to 260 Mg C ha⁻¹ and it was especially high in umbrisols. In conclusion, the implementation of protective measures in these fragile ecosystems may help to maintain the highly heterogeneous tree structure and enhance the role of both soils and trees as long-term C sinks.     

Management of advanced regeneration in secondary forests of the Brazilian Amazon

Gap formation is a critical process for plant establishment that may be absent or infrequent in second-growth forests, negatively influencing their ability to become diverse mature forest. I simulated treefall gaps within a 10-year-old secondary forest established on a clear-cut area, because cut areas may have a greater potential for economic exploitation than areas used for pastures and shifting cultivation. I explored the effects of varying degrees of canopy opening on the growth of plants already established as advanced regeneration. Five intensities of canopy opening were created: total removal (100%), 80–90%, 50–60%, 20–30% and a 0% control. Only trees >5 cm DBH were cut. The established plant community was diverse, and comprised 37 families and 126 species and morpho-species, of which 72% had some use reported in the literature. I found that the canopy opening treatments resulted in very little disturbance to the established seedling and sapling community, with no significant increase in mortality, but had a strong positive effect on their growth. Light levels reaching the understory were increased from 1% of incident photosynthetic active radiation in control plots to 35% in 100% canopy opening plots. During the first year, differences in plant growth were not significant, but by the second year, differential plant growth associated with canopy opening became evident. Most seedlings (51%) grew approximately 25 cm in height, and approximately one quarter grew more than 25 cm. Only 2.6% of the seedlings decreased in height, and 12% did not grow at all. Fifty percent canopy removal resulted in an almost threefold increase in plant height compared to control plots (0.52 ± 0.4 m and 0.20 ± 0.2 m, respectively), and was not significantly different from 80 or 100% removal. This indicates that intermediate levels of canopy removal had positive effects and total removal was unnecessary to stimulate the best growth responses. I conclude that regeneration of diverse mature forest can be accelerated under some conditions by partial removal of secondary forest canopy.     

Structure, allometry, and biomass of plantation Metasequoia glyptostroboides in Japan

We quantified structural features and the aboveground biomass of the deciduous conifer, Metasequoia glyptostroboides (Hu and Cheng) in six plantations in central Japan. In order to derive biomass estimates we dissected 14 M. glyptostroboides trees into three structural components (stem wood, branch wood and foliage) to develop allometric equations relating the mass of these components and of the whole tree to diameter at breast height (DBH). We found robust relationships at the branch and whole tree level that allow accurate prediction of component and whole tree biomass. Dominant tree height was similar within five older (>40 years) plantations (27–33 m) and shorter in a 20-year-old plantation (18 m). Average stem diameter varied from 12.8 cm in the youngest stand to greater than 35 cm in the oldest stand.

Metasequoia have relatively compact crowns distributed over the top 30% of the tree although the youngest stand had the deepest crown relative to tree height (up to 38%). At the individual tree level in older stands, 87% of the aboveground biomass was allocated to the stem, 9% to branch wood and 4% to foliage. We found little difference in the relative distribution of above ground biomass among the stands with the exception of lower foliage biomass in larger diameter trees. Total aboveground biomass of the older stands varied twofold, ranging from a maximum of 450 Mg ha⁻¹ in a 42-year-old stand to a minimum of 196 Mg ha⁻¹ in a 48-year-old stand. Total above ground biomass of the 20-year-old stand was 176 Mg ha⁻¹.     

The effects of clearcutting on snowshoe hare (Lepus americanus) relative abundance in central Labrador

To assess the effects of clearcutting on snowshoe hare (Lepus americanus) relative abundance, we surveyed pellets in 1 m² circular plots and, vegetation and browse surveys in 4.5 m² circular plots among four different aged clearcut (30, 20, 10, 5 years post-harvest) and mature forests (>150 years old) in central Labrador, Canada. Data were modelled at three grain sizes: transect (4400 m²), plot (314 m²) and subplot scales (4.5 m²). Betula papyrifera, distance from mature forest edge, tree and herb cover as well as remotely sensed forest inventory data were used as predictors for hare pellets. We found pellet abundance was 5 and 37 times greater (new and old pellets, respectively) in clearcut stands 30 years old than the next highest in 20 year old cuts. There were few hare pellets in the remaining stand ages. B. papyrifera was the most proportionately used browse species and most important of our fine-detailed vegetation in predicting hare pellets. The coarse-detailed, forest inventory and topographic data better predicted hare pellets than the fine-detailed vegetation data.     

Pre-commercial thinning effects on growth, yield and mortality in even-aged paper birch stands in British Columbia

The aim of this study was to quantify 5-year growth, yield and mortality responses of 9- to 13-year-old naturally regenerated, even-aged paper birch (Betula papyrifera Marsh.) stands to pre-commercial thinning in interior British Columbia. The study included four residual densities (9902–21,807 stems ha⁻¹ (unthinned control), 3000, 1000 and 400 stems ha⁻¹) and four sites with 3-fold within-site replication in a randomised block design. The largest, straightest, undamaged trees were selected to leave during thinning. Thinning reduced stand basal area from 5.90 m² ha⁻¹ in the control to 2.50, 1.53 and 0.85 m² ha⁻¹ in the three thinning treatments, representing 42, 26 and 15% of control basal area, respectively. After 5 years, total stand volume per plot remained lower in the three thinning treatments than the control (50.20, 30.07, 18.99 and 11.86 m³ in the control, 3000, 1000 and 400 stems ha⁻¹ treatments), whereas mean stand diameter, diameter increment, height, and height increment were increased by thinning, and top height (tallest 100 trees ha⁻¹) was unaffected. When a select group of crop trees (largest 250 trees ha⁻¹) in the thinning treatments was compared with the equivalent group in the control, there was a significant increase in mean diameter, diameter increment, basal area, basal area increment, and volume increment. Mean height, height increment, top height, and total volume were unaffected by thinning. Crop tree diameter increment was the greatest following thinning to 400 stems ha⁻¹ for all diameter classes. Thinning to 1000 stems ha⁻¹ resulted in lower diameter increment than thinning to 400 stems ha⁻¹ but tended to have higher volume increment. Dominant trees responded similarly to subdominant trees at 400 stems ha⁻¹, but showed the greatest response at 3000 stems ha⁻¹. Results suggest that pre-commercial thinning of 9–13-year-old stands to 1000 stems ha⁻¹ would improve growth of individual trees without seriously under-utilising site resources.     

What the soil reveals: Potential total ecosystem C stores of the Pacific Northwest region, USA

How much organic C can a region naturally store in its ecosystems? How can this be determined, when land management has altered the vegetation of the landscape substantially? The answers may lie in the soil: this study synthesized the spatial distribution of soil properties derived from the state soils geographic database with empirical measurements of old-growth forest ecosystem C to yield a regional distribution of potential maximum total-ecosystem organic C stores. The region under consideration is 179,000 square kilometers extending from the southern Oregon border to the northern Washington border, and from the Pacific Ocean to the east side of the Cascade Mountains. Total ecosystem organic C (TEC) was measured in 16 diverse old-growth forests encompassing 35 stands and 79 pedons to a depth of 100 cm. The TEC ranged between 185 and 1200 Mg C ha⁻¹. On an average, 63% of TEC was in the vegetation, 13% in woody detritus, 3% in the forest floor, 7% in the 0–20 cm mineral soil, and 13% in 20–100 cm mineral soil. The TEC was strongly related to soil organic C (SOC) in the 0–20 cm mineral soil, yielding a monotonically increasing, curvilinear relation. To apply this relation to estimate the TEC distribution throughout the region, 211 map units of the state soils geographic database (STATSGO) were used. The SOC in the 0–20 cm mineral soil of the map units was consistent with values from previously measured pedons distributed throughout the region. Resampling of 13 second-growth forests 25 years after initial sampling indicated no regional change in mineral SOC, and supported the use of a static state soils map. The SOC spatial distribution combined with the quantitative old-growth TEC–SOC relation yielded an estimate of potential TEC storage throughout the region under the hypothetical condition of old-growth forest coverage. The area-weighted TEC was 760 Mg C ha⁻¹. This is 100 Mg C ha⁻¹ more than a previous estimate based on a coarser resolution of six physiographic provinces, and 400 Mg C ha⁻¹ more than current regional stores. The map of potential TEC may be useful in forecasting regional C dynamics and in land-management decisions related to C sequestration.     

Carbon and nitrogen in forest soils: Potential indicators for sustainable management of eucalypt forests in south-eastern Australia

Soil organic matter (SOM) has been adopted as an indicator of soil fertility based on the rationale that SOM contributes significantly to soil physical, chemical, and biological properties that affect vital ecosystem processes of forests in Australia. A study was undertaken to evaluate the utility of SOM as an indicator of SFM at two long-term experimental sites in native eucalypt forests, including Silvertop Ash (E. sieberi L. Johnson) and Mountain Ash (E. regnans F. Muell.) in Victoria. This study examines the relative contributions made by various sources of carbon in soil profiles (0–30 cm) of forest soils, viz. mineral soil (<2 mm), plant residues, charcoal (>2 mm), and rock fragments (>2 mm). The long-term changes in these fractions in response to management-induced soil physical disturbance and fire (unburnt, moderate and high intensity) were evaluated. After 10 years, carbon levels in the fine soil fraction (soil <2 mm including fine charcoal) were similar across the range of fire disturbance classes in Mountain Ash forest (20–25 kg/m²) and Silvertop Ash forest (7–8 kg/m²). Likewise differences in carbon associated with other fractions, viz. microbial biomass, labile carbon, plant residues and rock fragments were comparatively small and could not be attributed to fire disturbance. Burning increased the charcoal carbon fraction from 5 to 23 kg/m² in Mountain Ash forest and from 1 to 3 kg/m² in Silvertop Ash forest. Taking into account, the percentage area affected by fire, increases in total soil carbon in these forests were estimated at 25 and 7 t/ha, respectively.

The effects of physical disturbance of soils were examined at one site in Mountain Ash forest where soil cultivation was used as site preparation rather than the standard practice of burning of logging residues. Total carbon in soil profiles decreased from 29 to 21 kg/m² where soil disturbance was severe, i.e. topsoil removed and subsoil disturbed. This was mainly due to a decrease in charcoal carbon from 6.8 to 1.7 kg/m² but severe soil disturbance also increased the amount of carbon associated with rock fragments from 1.6 to 3.5 kg/m².

Management-induced fire increased the coarse charcoal content of soil profiles substantially, thus increasing total carbon content as well as the proportion of recalcitrant carbon in SOM. In contrast, there was little change in the carbon content of the fine soil fraction including the labile and biologically active fractions indicating that these SOM fractions most relevant to ecosystem processes showed little long-term impact from soil disturbance and fire. Conventional sampling of the fine soil fraction (<2 mm) only represented between 50% and 70% of total carbon in the soil profiles. In contrast, total nitrogen in this fraction represented between 75% and 90% of the nitrogen in soil profiles and was less affected by changes in the contributions of N made by coarse fractions. Monitoring of soil N rather than C as an indicator of soil fertility and SFM may be more appropriate for forest soils with significant charcoal content.     

Responses of soil carbon, nitrogen and cations to the frequency and seasonality of prescribed burning in a Cape Cod oak-pine forest

Fire is an important component of the historic disturbance regime of oak and pine forests that occupy sandy soils of the coastal outwash plain of the northeastern US. Today prescribed fire is used for fuel reduction and for restoration and maintenance of habitat for rare plant and animal, animal species. We evaluated the effects of the frequency and seasonality of prescribed burning on the soils of a Cape Cod, Massachusetts's coastal oak-pine forest. We compared soil bulk density, pH and acidity, total extractable cations and total soil carbon (C) and nitrogen (N) in unburned plots and in plots burned over a 12-year period, along a gradient of frequency (every 1–4 years), in either spring (March/April) or summer (July/August). Summer burning decreased soil organic horizon thickness more than spring burning, but only summer burning every 1–2 years reduced organic horizons compared with controls. Burning increased soil bulk density of the organic horizon only in the annual summer burns and did not affect bulk density of mineral soil. Burn frequency had no effect on pH in organic soil, but burning every year in summer increased pH of organic soil from 4.01 to 4.95 and of mineral soil from 4.20 to 4.79. Burning had no significant effect on organic or mineral soil percent C, percent N, C:N, soil exchangeable Ca²⁺, Mg²⁺, K⁺ or total soil C or N. Overall effects of burning on soil chemistry were minor. Our results suggest that annual summer burns may be required to reduce soil organic matter thickness to produce conditions that would regularly allow seed germination for oak and for grassland species that are conservation targets. Managers may have to look to other measures, such as combinations of fire with mechanical treatments (e.g., soil scarification) to further promote grasses and forbs in forests where establishment of these plants is a high priority.     

Physiological and growth responses of three sizes of containerized Picea mariana seedlings outplanted with and without vegetation control

Three different stock sizes of containerized black spruce (Picea mariana [Mill.] B.S.P.) seedlings were planted in an abandoned agricultural field. The small planting stock was of a conventional type produced in 110 cm³ containers. The experimental medium and large stock types were produced in 340 and 700 cm³ containers, respectively. Gas exchange, xylem water potential and dry masses were measured six times during each of the first two growing seasons in field plots with and without vegetation control. During the first growing season, the effect of planting shock masked most physiological and growth differences among seedling types. During the second growing season, in plots with vegetation control, small and medium seedlings had similar values of physiological variables and of growth as measured by relative growth rates (RGR), but the large seedlings showed lower values of both net photosynthesis and of RGR, a difference attributed to low initial quality of the root system in the larger seedlings. In plots without vegetation control, the trend was identical, but differences were not significant; the greater height of the larger seedlings, and the resulting greater access to light, compensated for their lower initial quality. The similarity in response between the medium and the small seedlings shows that a fourfold increase in shoot size (1.68–6.82 g) in the initial size and a doubling of the shoot : root ratio (2.17–4.54) of the planting stock did not result in increased planting shock or reduced growth in these containerized conifer stock types. The results also show the importance of the interaction between stock height and the vertical light profile created by the competing vegetation in the final assessment of stock performance.     

Effect of natural disturbances on the abundance of Norway spruce (Picea abies (L.) Karst.) regeneration in nemoral forests of the southern boreal zone

The impact of natural disturbances on the canopy (trees ≥14 m high) and sapling stratum (>0.3 and ≤14 m high) composition was studied in nemoral old-growth forests located within the southern boreal zone in Central Russia (Central Forest Reserve, 32°29′–33°01′E, 56°26′–56°31′N). I hypothesized that the current disturbance regime does not allow the maintenance of current spruce abundance in the canopy, and, as a result, there is a continuous shift in the canopy composition towards a greater abundance of deciduous species. Three 300×20 m² transects were established to estimate the proportions of stand under non-closed unexpanded canopy gaps. Data on sapling composition of 49 canopy gaps were used to analyze pattern of gap refuting in these forests. Additionally, data from three forest inventories showed changes in canopy composition over a period from 1972 to 1990.

The current status of nemoral forests is characterized by the high proportion of stand area under treefall gaps (71%). The loss of spruce from the canopy caused by treefalls (53% of the total basal area of gap-makers) was slightly greater than its canopy abundance (45%). Canopy gaps of all sizes encouraged spruce regeneration which might be due to a decrease in sapling mortality and/or more active recruitment of spruce seedlings. After a gap was formed, the presence of spruce in sapling strata increased. However, within both small (<200 m² in size) and large (>200 m²) gaps, tall (>6 m) spruce saplings did not reach the level of its abundance in the tree canopy. In gaps, tall (>6 m) saplings of lime (Tilia cordata) and elm (Ulmus glabra) grew more quickly than those of spruce and maple. These data suggested a decrease in canopy spruce and an increase in deciduous species in the near future which supported the original hypothesis. Analysis of forest inventory records revealed similar changes in the canopy structure over the past two decades. However, the observed high proportion of stand area under gaps implies that for the next few decades large areas of nemoral communities will be occupied by relatively young stands. This may, in turn, decrease the frequency of large-scale treefalls revegetated mainly by deciduous saplings.     

Biogeochemical impacts of clearfelling and reforestation on blanket peatland streams I. phosphorus

Forest drains and streams on blanket peatland in western Ireland were sampled weekly, 1996–2000, using continuous, depth-proportional passive sampling, and analysed for molybdate-reactive phosphorus (MRP) by the acid–antimony-molybdate method. The study area was largely clearfelled and partly reforested with wind-rowing, drainage, planting, and aerially applied rock phosphate equivalent to 70 kg P/ha. Further felled areas were not wind-rowed, drained or fertilised for reforestation. Catchment areas were of the following orders: 1 ha (two forest drains); 10–20 ha (two semi-permanent drains, one permanent stream); 1–3 km² (three permanent streams). Streamwater from three undisturbed closed-canopy-forest catchments had pre-felling median concentrations of MRP (all values are μg MRP l⁻¹) of 9 (catchment approximately 1 km²), 13 (1 ha) and 93 (1 ha). Clearfelling was associated with large increases (maxima 305, 4164 and 3530 μg MRP l⁻¹) in MRP concentrations in each case. Following protracted mechanical operations in four other catchments of ca. 1 km², 20, 10 and 10 ha, with apparently existing elevated MRP concentrations (medians 41, 328, 102, 214 μg MRP l⁻¹) fertilising gave major rises (maxima 218, 2723, 806, 2323 μg MRP l⁻¹). The three smaller catchments showed subsequent exponential-type declines, while the 1 km² catchment had sustained high values (median 74 μg MRP l⁻¹) over the remaining study period. The higher values in this one larger stream were seasonally cyclical, with a late summer maximum. Annual median MRP values above 70 μg l⁻¹ represent a seriously polluted state for these streams, which qualify as waterways under relevant statutes, but it is not clear what implications these results have for downstream river-water quality in larger channels.     

Tree regeneration responses to microsite characteristics following a severe tornado in the Georgia Piedmont, USA

For 3 years following a severe, November 1992 tornado, abundance and growth of tree regeneration in intact forest-floor and windthrow-pit microsites were studied in three mixed pine and hardwood stands in the Georgia Piedmont, USA. The research had two objectives: (1) determine if performance of tree regeneration differed between microsite types and between pre- and post-tornado cohorts on intact forest-floor microsites, and (2) determine if variation in light and soil water availability from the disturbance affected performance of eight species artificially seeded into intact forest-floor microsites. Near each of the 42 sample points (12–20 per site) spaced on 15 m grids, species and height of tree seedlings were recorded within a 1 m radius plot of intact forest floor and the nearest windthrow pit. Intact forest-floor microsites were dominated by two late-successional species, Acer rubrum (3.5 pre-tornado stems per m² and 1.8 post-tornado stems per m²) and Ostrya virginiana (2.6 post-tornado stems per m²), while windthrow pits were dominated by an early successional species, Liriodendron tulipifera (1.7 stems per m²). Although seedling survival did not vary significantly among species or microsite types, first-year height of seedlings in intact forest-floor microsites (24 cm) was significantly greater than those in windthrow-pit microsites (19 cm). Second-year height growth of new seedlings of Cornus florida in intact forest-floor microsites (52 cm) significantly exceeded that of many other combinations of species and microsite type. Species artificially-seeded into intact forest-floor microsites in 1994 and 1995 varied considerably in emergence (<1–24%), survival (<1–16%), and height (5–15 cm), and those with the heaviest seed survived best. From 1994 to 1995, average gap fraction, an index of light availability, decreased 17% from 0.23 to 0.19. Soil water content in 1995 under gap fractions of greater than 0.3 (21%) averaged significantly less than under gap fractions of either 0.1–0.3 (24%) or less than 0.1 (26%). Significant positive correlations were detected for relationships of emergence and survival of several species to soil water content. Overall rankings of seedling performance between microsites (intact forest floor>windthrow pits), between cohorts (pre-tornado>post-tornado origin), and among species (mid- to late->early-successional species) indicate that advanced regeneration and new seedlings of A. rubrum, O. virginiana, and C. florida will be long-term dominants of the understory because of their high abundance, initial growth responses, and shade tolerance.