Fire, which is the dominant disturbance in the boreal forest, creates substantial heterogeneity in soil burn severity at patch and landscape scales. We present results from five field experiments in ...Yukon Territory, Canada, and Alaska, USA that document the effects of soil burn severity on the germination and establishment of four common boreal trees: Picea glauca, Picea mariana, Pinus contorta subsp. latifolia, and Populus tremuloides. Burn severity had strong positive effects on seed germination and net seedling establishment after 3 years. Growth of transplanted seedlings was also significantly higher on severely burned soils. Our data and a synthesis of the literature indicated a consistent, steep decline in conifer establishment on organic soils at depths greater than 2.5 cm. A meta-analysis of seedling responses found no difference in the magnitude of severity effects on germination versus net establishment. There were, however, significant differences in establishment but not germination responses among deciduous trees, spruce, and pine, suggesting that small-seeded species experience greater mortality on lightly burned, organic soils than large-seeded species. Together, our analyses indicate that variations in burn severity can influence multiple aspects of forest stand structure, by affecting the density and composition of tree seedlings that establish after fire. These effects are predicted to be most important in moderately-drained forest stands, where a high potential variability in soil burn severity is coupled with strong severity effects on tree recruitment.
This study quantifies the short-term effects of low-, moderate-, and high-severity fire on carbon pools and fluxes in the Eastern Cascades of Oregon. We surveyed 64 forest stands across four fires ...that burned 41,000 ha (35%) of the Metolius Watershed in 2002 and 2003, stratifying the landscape by burn severity (overstory tree mortality), forest type (ponderosa pine PP and mixed-conifer MC), and prefire biomass. Stand-scale C combustion ranged from 13 to 35% of prefire aboveground C pools (area − weighted mean = 22%). Across the sampled landscape, total estimated pyrogenic C emissions were equivalent to 2.5% of statewide anthropogenic CO₂ emissions from fossil fuel combustion and industrial processes for the same 2-year period. From low- to moderate- to high-severity ponderosa pine stands, average tree basal area mortality was 14, 49, and 100%, with parallel patterns in mixed-conifer stands (29, 58, 96%). Despite this decline in live aboveground C, total net primary productivity (NPP) was only 40% lower in high- versus low-severity stands, suggesting strong compensatory effects of non-tree vegetation on C uptake. Dead wood respiratory losses were small relative to total NPP (range: 10-35%), reflecting decomposition lags in this seasonally arid system. Although soil C, soil respiration, and fine root NPP were conserved across severity classes, net ecosystem production (NEP) declined with increasing severity, driven by trends in aboveground NPP. The high variability of C responses across this study underscores the need to account for landscape patterns of burn severity, particularly in regions such as the Pacific Northwest, where non-stand-replacement fire represents a large proportion of annual burned area.
Without canopy-opening fire disturbances, shade-tolerant, fire-sensitive species like red maple (Acer rubrum L.) proliferate in many historically oak-dominated forests of the eastern U.S. Here, we ...evaluate potential implications of increased red maple dominance in upland oak forests of Kentucky on rates of leaf litter decomposition and nitrogen (N) cycling. Over 5 years, we evaluated mass loss of leaf litter and changes in total N and carbon (C) within six leaf litter treatments comprised of scarlet oak, chestnut oak, and red maple, and three mixed treatments of increasing red maple contribution to the leaf litter pool (25, 50, and 75% red maple). Over a 1.5-year period, we conducted a plot-level leaf litter manipulation study using the same treatments plus a control and assessed changes in net nitrification, ammonification, and N mineralization within leaf litter and upper (0–5 cm depth) mineral soil horizons. Red maple leaf litter contained more “fast” decomposing material and initially lost mass faster than either oak species. All litter treatments immobilized N during initial stages of decomposition, but the degree of immobilization decreased with decreasing red maple contribution. The leaf litter plot-level experiment confirmed slower N mineralization rates for red maple only plots compared to chestnut oak plots. As red maple increases, initial leaf litter decomposition rates will increase, leading to lower fuel loads and more N immobilization from the surrounding environment. These changes may reduce forest flammability and resource availability and promote red maple expansion and thereby the “mesophication” of eastern forests of the U.S.
Browsing by free-living ungulates is a serious threat to forest regeneration. Although predictors of browsing and potential consequences are well researched, less information is available in the ...scientific literature about possible solutions to the problem. We investigated whether a large-scale game management system in a traditional sport hunting culture has the potential to effectively reduce browsing damage. Our analysis was based on browsing survey data from 2006 and 2009 covering more than 25,000km2 in Bavaria, Germany. After an initial assessment of browsing damage throughout Bavaria in 2006, game management plans were altered, and the effect of this intervention was assessed in 2009. Browsing damage clearly declined in 2009 in areas where the suggested deer harvests were increased in 2006 game management plans. This is the first report of a successful implementation of a large-scale game management system aiming at reducing browsing damage to facilitate unfenced forest regeneration.
This paper examines the effects of seed size and the depth of sand burial on seed germination and seedling development for Pinus thunbergii. Parl. Seeds from 20- to 30-year old trees grown in the ...coastal area of Yantai were divided into three size categories (large, medium, and small). The seeds were sown in pots with different depth of sand, and their germination and seedling growth during the first month were investigated. Results showed that large seeds possessed the highest 1000-seed weight and soluble sugar concentration. Large and medium seeds had a higher germination rate, germination index, vigor index, and seedling biomass than small seeds. With the increase in seed size, root mass ratio, root/shoot ratio, specific root length, and specific root area decreased, whereas leaf mass ratio increased. Sand burial depth significantly influenced seed germination and seedling growth, and the highest germination rate and seedling biomass were achieved with 2–3 cm sand burial. We also found that seedling biomass was positively related to germination rate, germination index, and vigor index, but was negatively related to mean germination time. Moreover, seedling biomass was negatively correlated with root mass ratio and root/shoot ratio, but positively correlated with leaf mass ratio, specific root length, and specific root area. The results suggest that seed size and sand burial depth are key factors in the regeneration of the coastal P. thunbergii forest.
QUESTIONS: What are the spatial patterns of adult trees and recruits in natural Picea abies forests? How are these patterns related to each other? Does the relationship differ before and after ...stand‐replacing disturbance? What are the ecological processes behind these spatial patterns? LOCATION: Mountain Picea abies forests in the Šumava Mts. (Bohemian Forest), Czech Republic, affected by a high‐severity outbreak of bark beetle (Ips typographus) that caused large‐scale dieback of the forest canopy. METHODS: We measured the spatial coordinates and heights of all recruits and the coordinates and DBH of all adult trees in nine plots across a wide range of recruit densities. We distinguished pre‐ and post‐disturbance recruits, trees killed by the disturbance and trees already dead before it. To analyse spatial relationship among these groups, we used univariate and bivariate pair‐correlation functions. To provide further insight into the mechanisms behind the observed patterns, we fitted Thomas and Matérn point processes to the observed data. RESULTS: Recruits formed tight clusters (2–9 m), whereas trees were distributed randomly or weakly clustered at short distances (1–2 m). Both pre‐disturbance and post‐disturbance recruits were highly clustered (cluster radii < 2 m) around trees before and after the stand–replacing disturbance. This fine‐scale pattern was likely driven by a combination of: (1) seed accumulation in tree wells during winter; (2) nurse effects of tree trunks extending the vegetation period, suppressing competitive vegetation and enhancing nutrient supply from decomposed litter; and (3) suitable seedbeds on some decaying wood. The Thomas point process fitted the observed pattern of decreasing recruit density with increasing distance from mature trees better than the Matérn process. CONCLUSIONS: Tree spatial pattern in mountain P. abies forests showed high resilience to stand‐replacing disturbance. After a self‐thinning of recruits tightly clustered around parental trees, their spatial pattern will mirror the pattern of trees that formed the stand before the disturbance. This ‘memory’ of tree spatial patterns is an important biological legacy and should be viewed as a fundamental property of natural P. abies forests.
Global warming is triggering some species to shift towards the poles or higher elevations, but spatial translocation is also influenced by land-use regime or intensity. The Himalayan climate is ...getting warmer and land use has changed, reducing in intensity in some areas. We estimated the upper species limit (USL) and tree limit of Abies spectabilis (D. Don) Spach and assessed whether these have changed over recent years. We hypothesise an upslope shift in response to enhanced temperature and changes in land-use intensity. Our four transects were located in treeline ecotones of two protected areas in Nepal, namely Manaslu Conservation Area (3 transects) and Gaurishankar Conservation Area (1 transect). Transects (20 m wide) ran from the USL of A. spectabilis down towards the treeline and beyond to the forest line. Length of each transect varied depending on local conditions. Co-ordinates, elevation, height and age of each A. spectabilis individual along the transects were recorded. We noted an upward shift of both the USL and the tree limit. The rate of shift was ca. 20 m per decade for the USL and 12 m per decade for the tree limit in the area of reduced land-use intensity and in the area with no change in land use, 5 m per decade for the USL, but almost nil for tree limit. The seedling density was higher below the treeline than above. Reduced intensity of land use was the dominant factor in upslope shift of A. spectabilis at both the USL and the tree limit.
•Phylogenetic ecology has seldom been used in restoration forests.•We looked at phylogenetic relations in the understory of single species stands.•We hypothesized overdispersed phylogenetic patterns ...due to negative interactions.•We did not observe a common phylogenetic pattern.•Phylogenetic structure responded to factors like dispersal and grass competition.
One approach in forest restoration is to plant trees that will establish an initial canopy to promote forest recovery through the colonization of other species. The identity of the planted tree affects which species are able to recruit in its understory. Here we evaluate the phylogenetic structure of young understory plant communities recruiting beneath eleven different species planted in single species stands and relate those structures with processes affecting community assembly. We expected the presence of negative biotic interactions between closely related overstory and understory species, as well as among related understory species, to lead to phylogenetic overdispersion. However, we did not find consistent phylogenetic patterns maybe due to the young age of the understory communities at the time of sampling. Most overstories showed a higher than expected presence of close relatives due to the recruitment of conspecifics, whereas, the higher recruitment of the ancient clade of Piperaceae beneath Fabaceae trees led to overdispersion. The presence of various Asteraceae species in understories that had been invaded by the grass, Saccharum spontaneum, led to significant clustering suggesting the conservatism of traits that allow overcoming the strong competition imposed by the grass. Phylogenetic patterns among the recruiting species showed that dispersal and competition are playing a role in shaping the communities. Our results highlight the importance of choosing an adequate set of species to plant in a restoration project since they dictate the subsequent regeneration of a forest community.
Addicted to Rubber Mann, Charles C
Science,
07/2009, Letnik:
325, Številka:
5940
Journal Article
Recenzirano
Odprti dostop
A rising tide of rubber plantations is eating away at Southeast Asian ecosystems. Can an ancient forest crop help wean the region off its monoculture habit?
1. Tree architecture is thought to allow species to partition horizontal and vertical light gradients in the forest canopy. Tree architecture is closely related to light capture, carbon gain and the ...efficiency with which trees reach the canopy. Previous studies that investigated how light gradients drive differentiation in tree architecture have produced inconsistent results, partially because of the differences in which tree species and ontogenetic stages were studied. 2. We examined the relationship between stem diameter, tree height, foliage height, crown width and life-history strategy over a broad size range of 200 randomly selected, co-occurring tree species in a lowland rainforest in Peninsular Malaysia. We developed a hierarchical Bayesian model to account for both intra-and interspecific variation and describe the relationships among tree architectural variables. We analysed interspecific variation in tree architectural variables in relation to adult stature and light requirement for species regeneration as a function of tree size. 3. There was little interspecific variation in architectural variables, this is partly because of large intraspecific variation in response to canopy heterogeneity, but it also suggests architectural convergence within this community. However, interspecific analyses showed that, for large-statured species, small size classes had thinner stems with narrow and shallow crowns, whereas large-size classes had wider crowns. Light-demanding species (as indicated by high sapling mortality in shaded conditions) showed weak trends in tree architecture and were only characterized by wide crowns at intermediate sizes. 4. In summary, tree architectural traits overlapped across the species community. This suggests that architectural convergence and equalizing effects occur in this diverse tropical forest and that community-wide allometric equations can be used to describe forest height and carbon storage. Light resource partitioning also occurs, indicating stabilizing effects. Interspecific architectural variation in relation to adult stature supports the theory of the trade-off between early reproduction and vegetative growth. In closed rainforests, adult stature imposes a stronger force on architectural differentiation of species than regeneration light requirements.
PDF
