The role of disturbance severity and canopy closure on standing crop of understory plant species in ponderosa pine stands in northern Arizona,USA

Concerns about the long-term sustainability of overstocked dry conifer forests in western North America have provided impetus for treatments designed to enhance their productivity and native biodiversity. Dense forests are increasingly prone to large stand-replacing fires; yet, thinning and burning treatments, especially combined with other disturbances such as drought and grazing, may enhance populations of colonizing species, including a number of non-native species. Our study quantifies plant standing crop of major herbaceous species across contrasting stand structural types representing a range in disturbance severity in northern Arizona. The least disturbed unmanaged ponderosa pine stands had no non-native species, while non-native grasses constituted 7–11% of the understory plant standing crop in thinned and burned stands. Severely disturbed wildfire stands had a higher proportion of colonizing native species as well as non-native species than other structural types, and areas protected from grazing produced greater standing crop of native forbs compared to grazed unmanaged stands. Standing crop of understory plants in low basal area thinned and burned plots was similar to levels on wildfire plots, but was comprised of fewer non-native graminoids and native colonizing plants. Our results also indicate that size of canopy openings had a stronger influence on standing crop in low basal area plots, whereas tree density more strongly constrained understory plant standing crop in dense stands. These results imply that treatments resulting in clumped tree distribution and basal areas <10 m² ha⁻¹ will be more successful in restoring native understory plant biomass in dense stands. Multiple types and severity of disturbances, such as thinning, burning, grazing, and drought over short periods of time can create greater abundance of colonizing species. Spreading thinning and burning treatments over time may reduce the potential for non-native species colonization compared to immediately burning thinned stands.     

Fine root production and turnover in forest ecosystems in relation to stand and environmental characteristics

The production and turnover of fine roots (diameter ?2 mm) contributes significantly to carbon cycling in forest ecosystems. We compiled an up-to-date global database covering 186 stands from the literature and estimated fine root production (FRP) and fine root turnover (FRT) for boreal, temperate and tropical forests in order to study the relationships between FRP or FRT and environmental and stand variables. FRP for all plants (trees + understorey) was 311 ± 259 (n = 39), 428 ± 375 (n = 71) and 596 ± 478 g m⁻² a⁻¹ (n = 32) in the boreal, temperate and tropical forests, respectively, and the corresponding annual FRT rates were 0.77 ± 0.70, 1.21 ± 1.04 and 1.44 ± 0.76, respectively. When the FRP and FRT of trees were estimated separately for boreal and temperate forests the differences between the two biomes were insignificant. The mean FRP of trees for the two biomes combined was 306 ± 240 g m⁻² a⁻¹ (n = 86) and the annual FRT was 1.31 ± 1.43. Fine root biomass (FRB) was the most significant factor explaining the variation in FRP, and more so at the tree level than at the stand level, explaining 53% of the variation in FRP for trees at the tree level. The corresponding proportions at the stand level were 21% for all plants and 12% for trees. Latitude, mean annual temperature and annual precipitation each explained <20% of the variation in FRP or FRT. Fine root production and FRT estimates are highly dependent on the species included in the sampling, the sampling depth and the methods used for estimating FRP or calculating FRT. The results indicate that the variation in FRP on a global scale can be explained to a higher degree if we focus on tree roots separately from the roots of the understorey vegetation and on FRP at the tree level instead of FRP at the stand level or on FRT.     

Responses of oaks and tanoaks to the sudden oak death pathogen after 8 y of monitoring in two coastal California forests

Sudden oak death, caused by Phytophthora ramorum, is widely established in mesic forests of coastal central and northern California. In 2000, we placed 18 plots in two Marin County sites to monitor disease progression in coast live oaks (Quercus agrifolia), California black oaks (Q. kelloggii), and tanoaks (Lithocarpus densiflorus), the species that are most consistently killed by the pathogen in these areas. Through early 2008, the numbers of newly infected trees increased for all species. The infection rate for trees that were asymptomatic in 2000 was 5.0% y⁻¹ for coast live oaks, 4.1% y⁻¹ for black oaks and 10.0% y⁻¹ for tanoaks. Mortality rates were 3.1% y⁻¹ for coast live oaks, 2.4% y⁻¹ for black oaks, and 5.4% y⁻¹ for tanoaks. Mortality not attributed to P. ramorum was 0.54% y⁻¹ for coast live oaks, and 0.75% y⁻¹ for tanoaks. Weibull survival models of trees that were asymptomatic in 2000 provided overall median survival times of 13.7 y for coast live oaks, 13.8 y for black oaks, and 8.8 y for tanoaks. Survival of infected (bleeding) trees declined to 9.7 y for coast live oaks, 6.2 y for black oaks, and 5.8 y for tanoaks. Ambrosia beetle attacks on bleeding trees further reduced modeled survival times by 65–80%, reaffirming the earlier finding that beetle attacks on bleeding cankers considerably reduce survival. Across all plots, the modeled time for 90% of trees that were asymptomatic in 2000 to become infected is 36.5 y for coast live oaks and 15.4 y for tanoaks. There was a trend toward higher infection rates as tree diameter increased. Greater than 90% of living coast live oaks that failed during the study had extensive beetle tunneling at the site of the break. Disease intensity in coast live oaks at the plot level was positively associated with bay laurel (Umbellularia californica) basal area and negatively associated with Pacific madrone (Arbutus menziesii) basal area. This study demonstrates the use of survival modeling to characterize the effects of epidemic disease on different species and to project the future of forests infected with tree pathogens.     

Oak/Douglas-fir/sheep: A three-crop silvopastoral system

A small scale agroforestry study which was begun in 1952 was revisited in 1985 to evaluate the long-term influence of site preparation and grazing on tree growth and survival in a Douglas-fir (Pseudotsuga menziesii)-white oak (Quercus garryana)-sheep silvopastoral system. In 1952–1953, two-year-old Douglas-fir seedlings were planted at the rate of 2500 trees/ha under three levels of site preparation: (1) no treatment, (2) oak thinned by 50%, and (3) oak clearcut. From 1954 to 1960, yearling ewes grazed one-half of each of the three thinning treatments for 3–4 weeks each spring. The conifers have been undisturbed since grazing was discontinued in 1960. Survival of planted conifers averaged 64% in 1985 and did not vary among either site preparation or grazing treatments. From 1964 to 1985, trees on the thinned and clearcut plantations grew an average of 1060 and 990 cm in height, respectively, compared to 900 cm on the unthinned plantation. Diameter at breast height (dbh) averaged 3.8 and 5.6 cm greater on thinned or clearcut plantations, respectively, than on the unthinned control by 1985 (p < 0.05). Conifers on grazed plantations had increased height and dbh growth during the first 12 years of plantation life, averaging 63 cm taller (p < 0.10) and 0.7 cm greater in dbh (p < 0.05) than the ungrazed plots by 1964. By 1985 the difference in height (122 cm) and dbh (1.0 cm) between grazed and ungrazed plantations was not statistically significant. These data suggest that although site preparation can positively influence conifer growth, total clearfelling is no better than thinning oaks. Furthermore, proper grazing can increase height and dbh growth of the conifers during and immediately after the grazing years.     

Post-fire soil respiration in relation to burnt wood management in a Mediterranean mountain ecosystem

After a wildfire, the management of burnt wood may determine microclimatic conditions and microbiological activity with the potential to affect soil respiration. To experimentally analyze the effect on soil respiration, we manipulated a recently burned pine forest in a Mediterranean mountain (Sierra Nevada National and Natural Park, SE Spain). Three representative treatments of post-fire burnt wood management were established at two elevations: (1) “salvage logging” (SL), where all trees were cut, trunks removed, and branches chipped; (2) “non-intervention” (NI), leaving all burnt trees standing; and (3) “cut plus lopping” (CL), a treatment where burnt trees were felled, with the main branches lopped off, but left in situ partially covering the ground surface. Seasonal measurements were carried out over the course of two years. In addition, we performed continuous diurnal campaigns and an irrigation experiment to ascertain the roles of soil temperature and moisture in determining CO₂ fluxes across treatments. Soil CO₂ fluxes were highest in CL (average of 3.34 ± 0.19 μmol m⁻² s⁻¹) and the lowest in SL (2.21 ± 0.11 μmol m⁻² s⁻¹). Across seasons, basal values were registered during summer (average of 1.46 ± 0.04 μmol m⁻² s⁻¹), but increased during the humid seasons (up to 10.07 ± 1.08 μmol m⁻² s⁻¹ in spring in CL). Seasonal and treatment patterns were consistent at the two elevations (1477 and 2317 m a.s.l.), although respiration was half as high at the higher altitude.Respiration was mainly controlled by soil moisture. Watering during the summer drought boosted CO₂ effluxes (up to 37 ± 6 μmol m⁻² s⁻¹ just after water addition), which then decreased to basal values as the soil dried. About 64% of CO₂ emissions during the first 24 h could be attributed to the degasification of soil pores, with the rest likely related to biological processes. The patterns of CO₂ effluxes under experimental watering were similar to the seasonal tendencies, with the highest pulse in CL. Temperature, however, had a weak effect on soil respiration, with Q₁₀ values of ca. 1 across seasons and soil moisture conditions. These results represent a first step towards illustrating the effects of post-fire burnt wood management on soil respiration, and eventually carbon sequestration.     

Oak/Douglas-fir/sheep: A three-crop silvopastoral system

A small scale agroforestry study which was begun in 1952 was revisited in 1985 to evaluate the long-term influence of site preparation and grazing on tree growth and survival in a Douglas-fir (Pseudotsuga menziesii)-white oak (Quercus garryana)-sheep silvopastoral system. In 1952–1953, two-year-old Douglas-fir seedlings were planted at the rate of 2500 trees/ha under three levels of site preparation: (1) no treatment, (2) oak thinned by 50%, and (3) oak clearcut. From 1954 to 1960, yearling ewes grazed one-half of each of the three thinning treatments for 3–4 weeks each spring. The conifers have been undisturbed since grazing was discontinued in 1960. Survival of planted conifers averaged 64% in 1985 and did not vary among either site preparation or grazing treatments. From 1964 to 1985, trees on the thinned and clearcut plantations grew an average of 1060 and 990 cm in height, respectively, compared to 900 cm on the unthinned plantation. Diameter at breast height (dbh) averaged 3.8 and 5.6 cm greater on thinned or clearcut plantations, respectively, than on the unthinned control by 1985 (p < 0.05). Conifers on grazed plantations had increased height and dbh growth during the first 12 years of plantation life, averaging 63 cm taller (p < 0.10) and 0.7 cm greater in dbh (p < 0.05) than the ungrazed plots by 1964. By 1985 the difference in height (122 cm) and dbh (1.0 cm) between grazed and ungrazed plantations was not statistically significant. These data suggest that although site preparation can positively influence conifer growth, total clearfelling is no better than thinning oaks. Furthermore, proper grazing can increase height and dbh growth of the conifers during and immediately after the grazing years.     

Effects of winter selective tree harvest on soil microclimate and surface CO2 flux of a northern hardwood forest

Soil surface CO₂ flux (S_flux) is the second largest terrestrial ecosystem carbon flux, and may be affected by forest harvest. The effects of clearcutting on S_flux have been studied, but little is known about the effect of alternative harvesting methods such as selective tree harvest on S_flux. We measured S_flux before and after (i) the creation of forest canopy gaps (simulating group tree selection harvests) and (ii) mechanized winter harvest but no tree removal (simulating ground disturbance associated with logging). The experiment was carried out in a sugar maple dominated forest in the Flambeau River State Forest, Wisconsin. Pre-treatment measurements of soil moisture, temperature and S_flux were measured throughout the growing season of 2006. In January–February 2007, a harvester created the canopy gaps (200–380 m²). The mechanization treatment consisted of the harvester traveling through the plots for a similar amount of time as the gap plots, but no trees were cut. Soil moisture and temperature and S_flux were measured throughout the growing season for 1 year prior to harvest and for 2 years after harvest. Soil moisture and temperature were significantly greater in the gap than mechanized and control treatments. Instantaneous S_flux was positively correlated to soil moisture and soil temperature at 2 and 10 cm, but temperature at 10 cm was the single best predictor. Annual S_flux was not significantly different among treatments prior to winter 2007 harvest, and was not significantly different among treatments after harvest. Annual (+1 std. err.) S_flux averaged 967 + 72, 1011 + 72, and 1012 + 72 g C m⁻² year⁻¹ in the control, mechanized and gap treatments, respectively, for the 2-year post-treatment period. The results from this study suggest selective group tree harvest significantly increases soil moisture and temperature but does not significantly influence S_flux.     

Soil–atmosphere CO2, CH4 and N2O fluxes in boreal forestry-drained peatlands

Greenhouse gas emissions from managed peatlands are annually reported to the UNFCCC. For the estimation of greenhouse gas (GHG) balances on a country-wide basis, it is necessary to know how soil–atmosphere fluxes are associated with variables that are available for spatial upscaling. We measured momentary soil–atmosphere CO₂ (heterotrophic and total soil respiration), CH₄ and N₂O fluxes at 68 forestry-drained peatland sites in Finland over two growing seasons. We estimated annual CO₂ effluxes for the sites using site-specific temperature regressions and simulations in half-hourly time steps. Annual CH₄ and N₂O fluxes were interpolated from the measurements. We then tested how well climate and site variables derived from forest inventory results and weather statistics could be used to explain between-site variation in the annual fluxes. The estimated annual CO₂ effluxes ranged from 1165 to 4437 g m⁻² year⁻¹ (total soil respiration) and from 534 to 2455 g m⁻² year⁻¹ (heterotrophic soil respiration). Means of 95% confidence intervals were ±12% of total and ±22% of heterotrophic soil respiration. Estimated annual CO₂ efflux was strongly correlated with soil respiration at the reference temperature (10 °C) and with summer mean air temperature. Temperature sensitivity had little effect on the estimated annual fluxes. Models with tree stand stem volume, site type and summer mean air temperature as independent variables explained 56% of total and 57% of heterotrophic annual CO₂ effluxes. Adding summer mean water table depth to the models raised the explanatory power to 66% and 64% respectively. Most of the sites were small CH₄ sinks and N₂O sources. The interpolated annual CH₄ flux (range: −0.97 to 12.50 g m⁻² year⁻¹) was best explained by summer mean water table depth (r² = 64%) and rather weakly by tree stand stem volume (r² = 22%) and mire vegetation cover (r² = 15%). N₂O flux (range: −0.03 to 0.92 g m⁻² year⁻¹) was best explained by peat CN ratio (r² = 35%). Site type explained 13% of annual N₂O flux. We suggest that water table depth should be measured in national land-use inventories for improving the estimation of country-level GHG fluxes for peatlands.     

Factors causing variation in fine root biomass in forest ecosystems

Fine roots form one of the most significant components contributing to carbon cycling in forest ecosystems. We study here the effect of variation in root diameter classes, sampling depth and the inclusion of understorey vegetation root biomass in fine root biomass (FRB) estimates. The FRB estimates for different forest biomes are updated using a database of 512 forest stands compiled from the literature. We also investigate the relationships between environmental or forest stand variables and fine root biomass (≤2 mm in diameter) at the stand (g m⁻²) and tree level (g tree⁻¹). The FRB estimates extrapolated for the whole rooting depth were 526 ± 321 g m⁻², 775 ± 474 g m⁻² and 776 ± 518 g m⁻² for boreal, temperate and tropical forests, respectively, and were 26-67% higher than those based on the original sampling depths used. We found significant positive correlations between ≤1 and ≤2 mm diameter roots and between ≤2 and ≤5 mm roots. The FRB estimates, standardized to the ≤2 mm diameter class, were 34-60% higher and 25-29% smaller than those standardized to the ≤1 mm and ≤5 mm diameter classes, respectively. The FRB of the understorey vegetation accounted for 31% of the total FRB in boreal forests and 20% in temperate forests. The results indicate that environmental factors (latitude, mean annual precipitation, elevation, temperature) or forest stand factors (life form, age, basal area, density) can not explain a significant amount of the variation in the total FRB and a maximum of 30% that in the FRB of trees at the stand level, whereas the mean basal area of the forest stand can explain 49% of the total FRB and 79% of the FRB of trees at the tree level.     

Loblolly pine growth and soil nutrient stocks eight years after forest slash incorporation

Incorporation of forest slash during stand establishment is proposed as a means of increasing soil carbon and nutrient stocks. If effective, the increased soil carbon and nutrient status may result in increased aboveground tree growth. Eight years after study installation, the impact of forest slash incorporation into the soil on soil carbon and nutrient stocks, foliar nutrients and loblolly pine growth are examined on mineral and organic sites on the North Carolina Lower Coastal Plain. Treatments include leaving forest slash on the surface and flat planting (control); V-shear and bedding (conventional), mulch forest slash followed by bedding (strip mulch) and mulch forest slash and till into the soil followed by bedding (strip mulch till). After eight years, mulching and/or tillage did not have a significant impact (p > 0.05) on soil bulk density or soil chemical properties (pH, cation exchange capacity, soil nutrients). Additionally, neither tree foliar nutrients nor stand volume were significantly impacted. However, significant effects were observed for soil phosphorus contents and stand volume between the control plots and the other treatment plots. For example, the mean stand volumes on the mineral site were 24.49 ± 1.28, 38.16 ± 2.90, 44.59 ± 3.07 and 46.96 ± 2.74 m³ ha⁻¹ for the control, conventional, strip mulch and strip mulch till plots. These observations are more likely due to the effect of bedding rather than mulching or tillage of the forest slash. These results are consistent for the mineral and the organic sites. Considering the greater expense to install the mulch and tillage treatments, the lack of a treatment effect on soil carbon and nutrient stocks and tree growth does not justify these treatments on these sites.     

Linking tree biodiversity to belowground process in a young tropical plantation: Impacts on soil CO2 flux

This study examined the effect of tree species identity and diversity on soil respiration in a 3-year-old tropical tree biodiversity plantation in Central Panamá. We hypothesized that tree pairs in mixed-species plots would have higher soil respiration rates than those in monoculture plots as a result of increased primary productivity and complementarity leading to greater root and microbial biomass and soil respiration. In addition to soil respiration, we measured potential controls including root, tree, and microbial biomass, soil moisture, surface temperature, bulk density. Over the course of the wet season, soil respiration decreased from the June highs (7.2 ± 3.5 μmol CO₂/(m² s⁻¹) to a low of 2.3 ± 1.9 μmol CO₂/(m² s⁻¹) in the last 2 weeks of October. The lowest rates of soil respiration were at the peak of the dry season (1.0 ± 0.7 μmol CO₂/(m² s⁻¹)). Contrary to our hypothesis, soil respiration was 19–31% higher in monoculture than in pairs and plots with higher diversity in the dry and rainy seasons. Although tree biomass was significantly higher in pairs and plots with higher diversity, there were no significant differences in either root or microbial biomass between monoculture and two-species pairs. Path analyses allow the comparison of different pathways relating soil respiration to either biotic or abiotic controls factors. The path linking crown volume to soil temperature then respiration has the highest correlation, with a value of 0.560, suggesting that canopy controls on soil climate may drive soil respiration.     

Dissolved organic carbon and nitrogen leaching from Scots pine, Norway spruce and silver birch stands in southern Sweden

The effects of three common tree species - Scots pine, Norway spruce and silver birch - on leaching of dissolved organic carbon and dissolved nitrogen were studied in an experimental forest with podzolised soils in southern Sweden. We analyzed soil water collected with lysimeters and modeled water fluxes to estimate dissolved C and N fluxes. Specific UV absorbance (SUVA) was analyzed to get information about the quality of dissolved organic matter leached from the different stands. Under the O horizon, DOC concentrations and fluxes in the birch stands were lower than in the spruce and pine stands; annual fluxes were 21 g m⁻² y⁻¹ for birch and 38 g m⁻² y⁻¹ and 37 g C m⁻² y⁻¹ for spruce and pine, respectively. Under the B horizon, annual fluxes for all tree species ranged between 3 and 5 g C m⁻² y⁻¹, implying greater loss of DOC in the mineral soil in the coniferous stands than in the birch stands. We did not find any effect of tree species on the quality of the dissolved organic matter, as measured by SUVA, indicating that the chemical composition of the organic matter was similar in leachates from all three tree species. Substantial amounts of nitrogen was leached out of the soil profile at the bottom of the B horizon from the pine and birch stands, whereas the spruce stands seemed to retain most of the nitrogen in the soil. These differences in N leaching have implications for soil N budgets.     

Impact of Macrotermes termitaria as a source of heterogeneity on tree diversity and structure in a Sudanian savannah under controlled grazing and annual prescribed fire (Burkina Faso)

Macrotermes termitaria are conspicuous features of savannah ecosystems in the Sudanian and Sahelian zones of West Africa. The mounds, alive or abandoned, are a major source of heterogeneity in the landscape. The purpose of the present study was to assess the impact of termitaria on tree community in a state forest of the Sudanian regional centre (Tiogo forest, Burkina Faso), under controlled burning and grazing experiments. A comparative inventory was carried out in a split-plot experiment (16 subplots of 2500 m²): 8 subplots where fire regime and grazing were controlled and 8 subplots exposed to grazing and with annual prescribed fire since 1992. All tree individuals (≥1.5 m) were recorded, both on termitaria and outside and their basal area at stump level was measured. A total of 61 observed (or 65.7 ± 2.4 estimated) tree species were recorded on 28 Macrotermes subhyalinus mounds (54 observed species or 60.8 ± 3.3 estimated), the immediate surroundings (44 observed and 59.0 ± 0.0 estimated species) and the rest of subplots (56 observed and 63.6 ± 0.0 estimated). Specific density was higher on mounds in comparison with the surroundings (P < 0.05). Results showed that termitaria played a key role in maintaining higher species diversity as compared to their surroundings (P < 0.05). Differences in species diversity between termitaria and immediate surroundings appeared more pronounced in disturbed plots (submitted to both fire and grazing). Some species, such as Tamarindus indica, Boscia senegalensis, Cadaba farinosa, Capparis sepiaria and Maerua angolensis are found solely on termitaria. Besides, the density of trees was significantly higher on termitaria compared to the surrounding (P < 0.05), as well as total basal area per unit of 100 m² area (P < 0.05). We concluded that Macrotermes termitaria play an important role as a source of heterogeneity in this Sudanian savannah woodland ecosystem. This role is particularly important in ecosystems under stresses. Termitaria acted as refuge for tree vegetation. The density and dynamics of M. subhyalinus termitaria should, therefore, be taken into account in the global strategy of the forest resources management and conservation.     

Transpiration and hydraulic traits of old and regrowth eucalypt forest in southwestern Australia

We tested the hypothesis that overstorey of eucalypt forest dominated by tall, large diameter trees uses less water than regrowth stands in the high rainfall zone (>1100 mm year⁻¹) of the northern jarrah (Eucalyptus marginata) forest in southwestern Australia. We measured leaf area, cover, sapwood area and sapwood density at three paired old and regrowth stands. We also measured sapflow velocity at one paired stand (Dwellingup) from June 2007 to October 2008. Old stands had more basal area but less foliage cover, less leaf area and slightly thinner sapwood. The ratio of sapwood area to basal area decreased markedly as tree size increased. Sapwood area of the regrowth forest stands (6.6 ± 0.30 m² ha⁻¹) was nearly double that of the old stands (3.4 ± 0.17 m² ha⁻¹), despite larger basal area at the old stands. Leaf area index of the regrowth stands (2.1 ± 0.26) was only one-third larger than that at the old stands (1.5 ± 0.15); hence, the ratio of leaf area to sapwood area was larger in old stands than in regrowth stands (0.45 ± 0.022 m² cm⁻² versus 0.32 ± 0.045 m² cm⁻²). Our results are consistent with theories that trees have evolved to optimize carbon gain rather than maintain stomatal conductance. Neither sapwood density (540–650 kg m⁻³) nor sap velocity differed greatly between regrowth and old stands. At the old forest site, daily transpiration rose from 0.5 mm day⁻¹ in winter to 0.9 mm day⁻¹ in spring–summer, compared to 0.9 mm day⁻¹ and 1.8 mm day⁻¹ at the regrowth site. Annual water use by the overstorey trees was estimated to be ∼230 mm year⁻¹ for the old stand and ∼500 mm year⁻¹ at the regrowth stand, or 20% and 44% of annual rainfall. The overwhelming role of stand sapwood area in determining stand water use, combined with the marked changes in the ratio of sapwood area to basal area with tree age and size, suggest that stand overstorey structure can be managed to alter overstorey water use and catchment water yield. Silviculture to promote old-forest-like attributes may be a viable means of delivering multiple water and conservation benefits.     

Quercus calliprinos regrowth advantage under grazing in Mediterranean maquis and its management implications

The post disturbance natural succession of the Mediterranean maquis, which turns open and species-rich landscapes into dense, closed stands of sclerophyllous woody vegetation is a principal threat to plant and animal diversity. Therefore, in the absence of traditional agricultural disturbance, active management regimes that include cutting and grazing are proposed to preserve biodiversity. The Mediterranean woody vegetation in Israel is strongly dominated by one species - the evergreen sclerophyllous Quercus calliprinos (Kermes oak). We hypothesized that under cutting and grazing, the evergreen Q. calliprinos has a relative regrowth advantage over other competing tree species. Here we examined the effect of grazing and the effect of tree structural traits on the regrowth after clear cutting of all trees in our study plots at Mt. Meron LTER site, Israel. All trees were removed from five blocks of 2000 m² and each block was divided into two plots, five of which were exposed to grazing livestock while five were wire-fenced and ungrazed. The regrowth rate of Q. calliprinos under grazing was higher than that of all other tree species suggesting that in the long-term, under such a conservation management regime, the dominance of the evergreen sclerophyllous Q. calliprinos over the deciduous tree species will increase and consequently will decrease plant and animal diversity. Therefore, we conclude that to protect landscape and species diversity in Mediterranean ecosystems dominated by evergreen oaks, when cutting and grazing are applied, special care must be paid to trees that are more negatively affected by such treatment.     

Medicinal plants in old-growth, degraded and re-growth forests of NW Pakistan

Many old-growth forest stands in northwest Pakistan have been structurally transformed as a consequence of logging and livestock grazing, some of which are thereafter left to secondary succession. These forests represent an important resource for local inhabitants who gather and sell medicinal plants as part of their livelihood. With this in mind, the main objectives of our study were: (1) to assess differences in the structure of the tree layer and the abundance of medicinal plants among differently transformed forests, (2) to evaluate the recovery potential of medicinal plants under re-growth forests, and (3) to assess relationships between tree stand structural characteristics and the occurrence of medicinal plants.The first step of the study involved creating an approximate map covering an area of 90 km² for five forest-use types (old-growth forest, forest degraded by logging, derived woodland, agroforest and re-growth forest). Fifteen plots per forest-use type were randomly allocated at altitudes ranging from 2200 m to 2400 m asl, within which the abundance of 10 locally important medicinal herb species was assessed.The study stands differed greatly in tree basal area, which was highest in old-growth forest (48 m² ha⁻¹), lowest in agroforest areas (6 m² ha⁻¹) and intermediate in re-growth forest (20 m² ha⁻¹). All ten medicinal plant species were encountered in old-growth and in re-growth forests, but only five of these species also occurred on agroforest plots. The mean coverage of study medicinal plants was highest in old-growth forest (7%), low in forest degraded by logging, derived woodland and agroforest (0.3-2%), and intermediate in re-growth forest (4%). The Jaccard abundance based similarity index indicates a considerable similarity (0.6) between re-growth and old growth forest for both trees and medicinal plants. The overall abundance of medicinal plants increased with increasing tree basal area and canopy cover. The abundance of some particular species decreased; however, the most sought-after medicinal species Bergenia ciliata, Valeriana jatamansi and Viola cancescens increased with tree basal area within specific forest-use type and also across forest-use types. In conclusion, our data suggest that anthropogenic forest degradation leads to a reduction in the abundance of economically viable medicinal plants for the study region. It is further indicated that this can be reversed if degraded forests are allowed to regenerate.     

Impact of timber harvesting on litterfall inputs and benthic coarse particulate organic matter (CPOM) storage in a small stream draining a eucalyptus plantation

Eucalyptus plantations have a short rotation cycle and harvesting occurs every 12-15 years, with the potential to modify the ecological integrity of the small streams draining the harvested areas through the reduction of litterfall inputs. We studied litterfall inputs and benthic coarse particulate organic matter (CPOM) storage in a small headwater stream draining a eucalyptus (Eucalyptus globulus Labill.) plantation before and after clear felling of the plantation. We hypothesized that wood harvesting will result in a reduction of CPOM inputs and storage in the stream. Litterfall inputs ranged 530-700 g m⁻² y⁻¹ and were approximately halved (200-320 g m⁻² y⁻¹) after the harvesting of the eucalyptus trees. Bark and woody materials showed the largest reduction. Leaf inputs were initially reduced sharply, but, during the second year after the harvest, they recovered to about 90% of the values observed before the harvesting. Harvesting of the eucalyptus plantation caused an increase of benthic CPOM storage to 535 g m⁻², but this was a temporary effect and these materials were washed downstream of the study reach. One year after the harvesting, benthic CPOM was reduced below 15 g m⁻². Bark, twigs and other woody residues generated during the preparation of the logs for transportation were retained within the study site and represented the main component (>90%) of the benthic CPOM after timber harvesting. However, 2 years after the harvesting, low inputs of these materials caused an overall reduction of in-stream retention and residence time of benthic CPOM. Amount and composition of benthic CPOM changed quickly in response to alterations of the riparian forest, so we propose the use of CPOM as an indicator of the impact of forestry activities on the ecological functioning of small streams.     

Decomposition of Scots pine fine woody debris in boreal conditions: Implications for estimating carbon pools and fluxes

Litter quality and environmental effects on Scots pine (Pinus sylvestris L.) fine woody debris (FWD) decomposition were examined in three forestry-drained peatlands representing different site types along a climatic gradient from the north boreal (Northern Finland) to south (Southern Finland) and hemiboreal (Central Estonia) conditions. Decomposition (percent mass loss) of FWD with diameter ≤10 mm (twigs) and FWD with diameter >10 mm (branches) was measured using the litter bag method over 1–4-year periods. Overall, decomposition rates increased from north to south, the rate constants (k values) varying from 0.128 to 0.188 year⁻¹ and from 0.066 to 0.127 year⁻¹ for twigs and branches, respectively. On average, twigs had lost 34%, 19% and 19%, and branches 25%, 17% and 11% of their initial mass after 2 years of decomposition at the hemiboreal, south boreal and north boreal sites, respectively. After 4 years at the south boreal site the values were 48% for twigs and 42% for branches. Based on earlier studies, we suggest that the decomposition rates that we determined may be used for estimating Scots pine FWD decomposition in the boreal zone, also in upland forests. Explanatory models accounted for 50.4% and 71.2% of the total variation in FWD decomposition rates when the first two and all years were considered, respectively. The variables most related to FWD decomposition included the initial ash, water extractives and Klason lignin content of litter, and cumulative site precipitation minus potential evapotranspiration. Simulations of inputs and decomposition of Scots pine FWD and needle litter in south boreal conditions over a 60-year period showed that 72 g m⁻² of organic matter from FWD vs. 365 g m⁻² from needles accumulated in the forest floor. The annual inputs varied from 5.7 to 15.6 g m⁻² and from 92 to 152 g m⁻² for FWD and needles, respectively. Each thinning caused an increase in FWD inputs, up to 510 g m⁻², while the needle inputs did not change dramatically. Because the annual FWD inputs were lowered following the thinnings, the overall effect of thinnings on C accumulation from FWD was slightly negative. The contribution of FWD to soil C accumulation, relative to needle litter, seems to be rather minor in boreal Scots pine forests.     

Fuel deposition rates of montane and subalpine conifers in the central Sierra Nevada,California, USA

Fire managers and researchers need information on fuel deposition rates to estimate future changes in fuel bed characteristics, determine when forests transition to another fire behavior fuel model, estimate future changes in fuel bed characteristics, and parameterize and validate ecosystem process models. This information is lacking for many ecosystems including the Sierra Nevada in California, USA. We investigated fuel deposition rates and stand characteristics of seven montane and four subalpine conifers in the Sierra Nevada. We collected foliage, miscellaneous bark and crown fragments, cones, and woody fuel classes from four replicate plots each in four stem diameter size classes for each species, for a total of 176 sampling sites. We used these data to develop predictive equations for each fuel class and diameter size class of each species based on stem and crown characteristics. There were consistent species and diameter class differences in the annual amount of foliage and fragments deposited. Foliage deposition rates ranged from just over 50 g m⁻² year⁻¹ in small diameter mountain hemlock stands to ∼300 g m⁻² year⁻¹ for the three largest diameter classes of giant sequoia. The deposition rate for most woody fuel classes increased from the smallest diameter class stands to the largest diameter class stands. Woody fuel deposition rates varied among species as well. The rates for the smallest woody fuels ranged from 0.8 g m⁻² year⁻¹ for small diameter stands of Jeffrey pine to 126.9 g m⁻² year⁻¹ for very large diameter stands of mountain hemlock. Crown height and live crown ratio were the best predictors of fuel deposition rates for most fuel classes and species. Both characteristics reflect the amount of crown biomass including foliage and woody fuels. Relationships established in this study allow predictions of fuel loads to be made on a stand basis for each of these species under current and possible future conditions. These predictions can be used to estimate fuel treatment longevity, assist in determining fuel model transitions, and predict future changes in fuel bed characteristics.     

Above-ground biomass dynamics after reduced-impact logging in the Eastern Amazon

Changes in above-ground biomass (AGB) of 17 1 ha logged plots of terra firme rain forest in the eastern Amazon (Brazil, Paragominas) were monitored for four years (2004–2008) after reduced-impact logging. Over the same time period, we also monitored two 0.5 ha plots in adjacent unlogged forest. While AGB in the control plots changed little over the observation period (increased on average 1.4 Mg ha⁻¹), logging resulted in immediate reductions in ABG that averaged 94.5 Mg ha⁻¹ (±42.0), which represented 23% of the 410 Mg ha⁻¹ (±64.9) present just prior to harvesting. Felled trees (dbh > 55 cm) accounted for 73% (±15) of these immediate losses but only 18.9 Mg ha⁻¹ (±8.1) of biomass was removed in the extracted logs. During the first year after logging, the annual AGB balance (annual AGB gain by recruitment and growth − annual AGB loss by mortality) remained negative (−31.1 Mg ha⁻¹ year⁻¹; ±16.7), mainly due to continued high mortality rates of damaged trees. During the following three years (2005–2008), average net AGB accumulation in the logged plots was 2.6 Mg ha⁻¹ year⁻¹ (±4.6). Post-logging biomass recovery was mostly through growth (4.3 ± 1.5 Mg ha⁻¹ year⁻¹ for 2004–2005 and 6.8 ± 0.9 Mg ha⁻¹ year⁻¹ for 2005–2008), particularly of large trees. In contrast, tree recruitment contributed little to the observed increases in AGB (1.1 ± 0.6 Mg ha⁻¹ year⁻¹ for 2004–2005 and 3.1 ± 1.3 Mg ha⁻¹ year⁻¹ for 2005–2008). Plots with the lowest residual basal area after logging generally continued to lose more large trees (dbh ≥70 cm), and consequently showed the greatest AGB losses and the slowest overall AGB gains. If 100% AGB recovery is desired and the 30-year minimum cutting cycle defined by Brazilian law is adhered to, current logging intensities (6 trees ha⁻¹) need to be reduced by 40–50%. Such a reduction in logging intensity will reduce financial incomes to loggers, but might be compensated for by the payment of environmental services through the proposed REDD (reduced emissions from deforestation and forest degradation) mechanism of the United Nations Framework Convention on Climate Change.