Long-term Forest Succession Research Articles

Spatial structure and individual competition characteristics of secondary Mongolian oak mature forests in the mountainous area of eastern Liaoning Province, China.

The community structure of natural mature forests is determined by long-term forest succession, characterized by rational structure, rich biodiversity, and high ecological function. Understanding the spatial structure and formation mechanisms of mature forests is a fundamental prerequisite for forest management. We analyzed four structure parameters, including diameter structure, angular scale, size ratio, and mixture degree, as well as the Hegyi competition index, of secondary Quercus mongolica (Mongolian oak) mature forests in the mountainous area of eastern Liaoning Province. The results showed that Q. mongolica predominated the tree layer. In the sapling layer, Q. mongolica, Tilia amurensis, and Acer pictum were the dominant species. In the seedling layer, Acer pseudosieboldianum, T. amurensis, and A. amurensis dominated, with very few Q. mongolica seedlings. The overall diameter distribution of the stand showed an inverse "J" shape, while the diameter distribution of Q. mongolica, the dominant tree species, followed a normal distribution. The horizontal spatial structure of the stand was generally randomly distributed, with an average angle scale of 0.505, size ratio of 0.219, and mixture degree of 0.670 for Q. mongolica. From the perspective of spatial structure binary distribution, Q. mongolica individuals which had a random distribution exhibited greater growth advantages and higher levels of mixing, in comparison to other distribution types. Randomly distributed dominant and subdominant individuals made up nearly half individuals in the stand, and showed a high degree of mixing with surrounding trees. The stand-level individual tree competition index decreased with increasing diameter classes. When the diameter at breast height exceeded 20 cm, the competition index tended to stabilize (ΔCI<2). The competitive radius of individual Q. mongolica trees was 8 m, with intraspecific competition as the main pressure. Other species experienced competition pressure primarily from interspecific sources. Our results suggested that competition played an important role in shaping the spatial structure of secondary Q. mongolica mature forests.

Carbon stabilization pathways in soil aggregates during long-term forest succession: Implications from δ13C signatures

Forest restoration increases organic carbon (OC) sequestration mainly via the additional litter input and improvements in soil structure that result in biochemical and physical C stabilization over the short term. However, the pathways of long-term C stabilization in soil aggregates during forest succession are unclear. To characterize the long-term C fluxes, the aggregate-associated OC content and C flow pathways were examined over 160 years of secondary successional chronosequence from Lespedeza bicolor to Quercus liaotungensis. The contribution of plant-derived C (litters and fine roots) to aggregate-associated OC was assessed using 13C natural abundance. The proportion of macroaggregates increased but microaggregates decreased along forest succession, and the macroaggregate-associated OC content increased from 4.6 to 28 g kg−1 during succession. The 13C enrichment trend was common in all aggregate size classes: macroaggregates to silt and clay size classes. The maximum δ13C was −23‰ in the silt and clay size classes in the pioneer weed stage at 20−30 cm soil depth. The C pathways followed the trend from macroaggregates to silt and clay size classes. The intensity of the C flows decreased in the topsoil (<10 cm), but plant-derived C stocks within the aggregates increased during forest succession over the 160 years. Notably, fine roots made a greater contribution to the OC accumulation within aggregates than aboveground litter did. The microbial biomass was an important factor affecting fine root-derived C stocks in the aggregates. Concluding, this analysis of natural δ13C signature provides detailed insights into long-term C stabilization pathways associated with soil aggregates during forest succession.

Carbon Stabilization Pathways in Soil Aggregates During Long-Term Forest Succession: Implications from Δ13c Signatures

Carbon Stabilization Pathways in Soil Aggregates During Long-Term Forest Succession: Implications from Δ13c Signatures

Long-term forest succession improves plant diversity and soil quality but not significantly increase soil microbial diversity: Evidence from the Loess Plateau

Many studies have focused on the processes of vegetation succession, however, the dynamics of soil microbes and the synergy between vegetation and soil are still poorly understood following vegetation succession. This study focused on a forest succession sequence including farmland, grassland, shrubland (i.e., Hippophae rhamnoides), pioneer forest (i.e., Populus davidiana), and climax forest (i.e., Quercus liaotungensis) on the Loess Plateau of China, to explore plant and soil changes, as well as soil microbial community dynamics. The results showed that litter biomass, soil organic carbon (SOC), total nitrogen (TN) and the ratio of SOC to TN exhibited an increasing trend in the whole process of the forest succession, and NH4+, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and the ratio of dissolved organic carbon (DOC) to dissolved organic nitrogen (DON) had significantly increased before the shrubland stage, and then they were going to be stable. During the forest succession, the main bacterial phyla present were Proteobacteria, Actinobacteria, and Acidobacteria, and the predominant fungal phyla were Ascomycota and Basidiomycota. The soil microbial community composition was stable and did not change significantly, but the bacteria and fungal communities were associated with specific plant or soil properties. It was proved that the change of soil microbial community was closely related to vegetation and soil community changes. The results suggested that long-term forest succession not only improves plant diversity, but also improves soil biology and quality, even though it does not significantly increase soil microbial diversity. The findings enhance the understanding of the impact of soil microbial ecological characteristics and provide an important guidance for the sustainable management of forest ecosystems following long-term natural vegetation restoration.

Disturbance and Topography Shape Nitrogen Availability and δ15N over Long-Term Forest Succession

Forest disturbance and long-term succession towards old-growth are thought to increase nitrogen (N) availability and N loss, which should increase soil δ15N values. We examined soil and foliar patterns in N and δ15N, and soil N mineralization, across 800 years of forest succession in a topographically complex montane landscape influenced by human logging and wildfire. In contrast to expectations, we found that disturbance caused declines in surface mineral soil δ15N values, both in logged forests measured 40–50 years after disturbance, and in unlogged forests disturbed by severe wildfire within the last 200 years. Both symbiotic N fixation and N transfers from disturbed vegetation and detritus could lower soil δ15N values after disturbance. A more important role for symbiotic N fixation is suggested by lower soil δ15N values in slow-successional sites with slow canopy closure, which favors early-successional N fixers. Soil δ15N values increased only marginally throughout 800 years of succession, reflecting soil N uptake by vegetation and strong overall N retention. Although post-disturbance N inputs lowered surface soil δ15N values, steady-state mass balance calculations suggest that wildfire combustion of vegetation and detritus can dominate long-term N loss and increase whole-ecosystem δ15N. On steeper topography, declining soil δ15N values highlight erosion and accelerated soil turnover as an additional abiotic control on N balances. We conclude for N-limited montane forests that soil δ15N and N availability are less influenced by nitrate leaching and denitrification loss than by interactions between disturbance, N fixation, and erosion.

Carbon dynamics in the future forest: the importance of long‐term successional legacy and climate–fire interactions

Understanding how climate change may influence forest carbon (C) budgets requires knowledge of forest growth relationships with regional climate, long-term forest succession, and past and future disturbances, such as wildfires and timber harvesting events. We used a landscape-scale model of forest succession, wildfire, and C dynamics (LANDIS-II) to evaluate the effects of a changing climate (A2 and B1 IPCC emissions; Geophysical Fluid Dynamics Laboratory General Circulation Models) on total forest C, tree species composition, and wildfire dynamics in the Lake Tahoe Basin, California, and Nevada. The independent effects of temperature and precipitation were assessed within and among climate models. Results highlight the importance of modeling forest succession and stand development processes at the landscape scale for understanding the C cycle. Due primarily to landscape legacy effects of historic logging of the Comstock Era in the late 1880s, C sequestration may continue throughout the current century, and the forest will remain a C sink (Net Ecosystem Carbon Balance>0), regardless of climate regime. Climate change caused increases in temperatures limited simulated C sequestration potential because of augmented fire activity and reduced establishment ability of subalpine and upper montane trees. Higher temperatures influenced forest response more than reduced precipitation. As the forest reached its potential steady state, the forest could become C neutral or a C source, and climate change could accelerate this transition. The future of forest ecosystem C cycling in many forested systems worldwide may depend more on major disturbances and landscape legacies related to land use than on projected climate change alone.

Human intervened post-fire forest restoration in the Northern Great Hing’an Mountains: a review

The devastating fire in May 1987 in the northern Great Hing’an Mountains created a mosaic of burned severity. Subsequent log harvesting and tree planting complicated the restoration process. Based on intensive field work and GIS analysis for the burned area, we studied the landscape pattern change in relation with its influencing factors, the restoration of some ecosystem functions and the long-term effect of human planting on vegetation restoration. A post-fire vegetation restoration process was also established using spatial series instead of temporal series. The results indicated that coniferous forest, broad-leaved forest and mixed forest increased obviously in the burned area. Factors influencing the restoration process are ranked as the burned severity, way of restoration (planting, promoted restoration or natural restoration) and topographical factors. The latter was further ranked as the slope, elevation, slope position and aspect. Primary productivity, hydrological functions, habitats for wild animals and permanent frozen soil of the area have all largely been restored to the pre-fire level after more than 15 years. Parameters demonstrated a transitional character of the forest from the early succession stage to middle stage. LANDIS simulation for the long-term forest succession under pure natural restoration and human-intervened restoration indicated that post-fire tree planting largely influenced the age structure, spatial pattern and timber stock of dominant species such as Larix gmelini, Betula platyphylla and Pinus sylvestris var. mongolica. In general, the influence of post-fire human planting can remain for more than 200 years.

Using a forest patch model to predict the dynamics of stand structure in Swiss mountain forests

Forest patch models have been applied to simulate forest development and long-term forest succession in many studies. The main focus of these simulations has been on species composition and biomass in natural forests, but these models could also become useful for the prediction of other structural forest patterns such as size distributions. Up to now, most of these models have been validated by approaches such as comparison of simulation results with potential natural vegetation (PNV), or national forest inventory data. While these approaches may be appropriate to validate the simulated species composition, they are not sufficient in testing the prediction of other structural patterns. Thus, little is known about the accuracy of forest patch models in simulating structural forest patterns such as size distribution of different forest types. For this reason, we tested the forest patch model ForClim against empirical data from three Swiss mountain forests. The objectives of this study were: (i) to investigate the performance of ForClim in simulating structural forest patterns and (ii) to assess the influence of the regeneration, growth and mortality submodels of ForClim on the simulation results. Several shortcomings of the model were identified and quantified. In particular, the stress-induced mortality implemented in ForClim was found to overestimate the actual mortality rates. The excessive mortality was most likely caused by an inaccurate growth function or an overestimation of light competition. Once the stress-induced mortality was reduced, ForClim was able to reproduce structural forest patterns in an accurate manner. Based on these encouraging results, we suggest that ForClim as well as other forest patch models could become important tools for further applications in forest research.

Synthesizing published knowledge of boreal forest cover change for large-scale landscape dynamics modelling

We reviewed the published knowledge on forest succession in the North American boreal biome for its applicability in modelling forest cover change over large extents. At broader scales, forest succession can be viewed as forest cover change over time. Quantitative case studies of forest succession in peer-reviewed literature are reliable sources of information about changes in forest canopy composition. We reviewed the following aspects of forest succession in literature: disturbances; pathways of post-disturbance forest cover change; timing of successional steps; probabilities of post-disturbance forest cover change, and effects of geographic location and ecological site conditions on forest cover change. The results from studies in the literature, which were mostly based on sample plot observations, appeared to be sufficient to describe boreal forest cover change as a generalized discrete-state transition process, with the discrete states denoted by tree species dominance. In this paper, we outline an approach for incorporating published knowledge on forest succession into stochastic simulation models of boreal forest cover change in a standardized manner. We found that the lack of details in the literature on long-term forest succession, particularly on the influence of pre-disturbance forest cover composition, may be limiting factors in parameterizing simulation models. We suggest that the simulation models based on published information can provide a good foundation as null models, which can be further calibrated as detailed quantitative information on forest cover change becomes available. Key words: probabilistic model, transition matrix, boreal biome, landscape ecology

Macrofossil and Tree-Ring Evidence for a Long-Term Forest Succession and Mid-Holocene Hemlock Decline

Paludified dune fields in southern Québec provided a unique opportunity to analyze a mid-Holocene forest succession, ranging from xero-mesophilous forests to treed peatlands, which registered the hemlock decline, a major biostratigraphic event in eastern North America. Our fossil-tree chronology established from 66 radiocarbon dates of tree stems indicates that white pine and hemlock were present at the study site about 6000-5700 yr B.P. Hemlock reached a maximum 4900-4800 yr B.P. and then declined between 4600 and 3800 yr B.P.; the species recovered around 3700 yr B.P. and then decreased when white pine and eastern latch dominated the site after 3000 yr B.P. and between 2600 and 2200 yr B.P., respectively. Tree-ring signatures of fossil hemlocks suggest the continuous influence of biotic factors, possibly insect defoliators, throughout the record, as shown by recurrent suppressed-growth pattern. Microscopic examination of the hemlock fossil stems disclosed no evidence of fungal disease. The hemlock decline was probably caused by regional posthypsithermal climatic changes, toward moister conditions.

Comparison of taxon calibrations, modern analogue techniques, and forest‐stand simulation models for the quantitative reconstruction of past vegetation

AbstractWe compared results of three quantitative methods for reconstructing past vegetation, including (1) calibrations of per cent dominance vs. per cent pollen for individual tree taxa; (2) coefficients of dissimilarity between fossil and modern pollen assemblages; and (3) simulation modelling of long‐term forest succession. For calibration, we used 1684 modern pollen samples and 1742 forest‐inventory summaries from eastern North America. We applied the calibrations at 1 000‐year intervals to the 19000‐year pollen record from Anderson Pond, Tennessee. Dominance values reconstructed using taxon calibrations typically paralleled the changes in percentages of arboreal pollen. Dissimilarity values between fossil and modern pollen assemblages were lowest from 19 000 yr BP to 15 000 yr BP and from 9 000 yr BP to the present, indicating good modern analogues for both full‐glacial and Holocene time periods. During times of good analogue, forest composition estimated from forest inventories at the locations of best pollen analogues was similar to that reconstructed using taxon calibrations. Relatively poor modern analogues exist for late glacial and early Holocene pollen spectra from Anderson Pond. During times of poor analogues, forest composition reconstructed from taxon calibrations differed from that derived from analogue methods. FORET‐model simulations of forest‐stand biomass differed markedly from palaeovegetation estimates made from the other two methods. This is primarily because the FORET model is scaled to forest succession on 1/12‐ha forest plots rather than forest dynamics integrated over a broad landscape mosaic. Because they are based upon fundamental relationships of pollen production and dispersal, taxon calibrations provide the best available means for reconstructing forest history both during times of good and of poor analogues.