查看更多>>摘要：? 2021 Elsevier B.V.Post-fire landscapes are the frontline of forest ecosystem change. As such, they represent opportunities to foster conditions that are better adapted to future climate and wildfires with post-fire management. In western US landscapes, post-fire management has been mostly defined by short-term emergency mitigation measures, salvage harvest to recover economic value, and replanting to achieve full stocking. These approaches are largely incongruent with ecologically based forest management due to their limited scope and objectives. Here, we develop a framework for ecologically based post-fire management. Post-fire management principles are to (i) protect large-diameter trees and fire refugia; (ii) anticipate future fuel accumulation from post-fire tree mortality; (iii) reinitiate and maintain stabilizing fire-vegetation feedbacks; (iv) differentiate between climate- and dispersal-mediated transitions to non-forest; and (v) align species composition and structure with future fire regimes and climate. Stand-scale management strategies to implement these principles include (i) maintain or enhance forest resilience; (ii) restore forest conditions and resist transition to non-forest; and (iii) accept or facilitate transition to non-forest. Determining where and over what extent to deploy these stand-scale strategies in large, burned landscapes is informed by a post-fire landscape evaluation, and expressed with a landscape prescription. A post-fire landscape evaluation is a data-driven characterization of current vegetation conditions, including the immediate changes caused by wildfire, and includes a departure analysis—an evaluation of current conditions against reference conditions. The landscape prescription provides guidance about the distribution of different successional patches and their sizes across the topographic template and identifies priority areas for different post-fire treatments. We develop a geospatial framework to integrate ecological principles with a post-fire landscape evaluation that can be readily applied to management planning after wildfire. We illustrate application of these principles through the development of landscape prescriptions for two watersheds, each burned in a recent large fire, in northeast Washington, USA. Use of ecologically based post-fire management principles and landscape evaluations can help shift often contentious debates over salvage harvesting towards a more productive dialogue around how to best adapt landscapes to future conditions.
Kafuti C.Van den Bulcke J.Van Acker J.De Mil T....
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查看更多>>摘要：? 2021 Elsevier B.V.Reliable tree height-diameter (H-D) allometric equations are a key tool for the estimation of forest productivity and Above Ground Biomass (AGB). Most existing H-D allometric equations developed for the tropical region are based on large-scale multi-species datasets, and their use to derive information on productivity and AGB at the species level is prone to uncertainties. The single-species H-D allometric equations available are mainly focused on monocultures or stands with simple tree species mixtures and did not account for the site effects. Here we measured the height and diameter of 2,288 trees of the emergent tree species Pericopsis elata (Harms) Meeuwen in the Democratic Republic of the Congo (DRC) and in Cameroon. We first examined how accurate multispecies H-D allometric equations are in predicting the total height of P. elata. We then tested whether single-species H-D allometric equations vary between sites. We developed the first H-D allometric equation of P. elata and tested whether and how stand-level and environmental variables induce changes in H-D allometric relationship of P. elata at the regional level. We additionally evaluated whether tree-level variables are important at the local level where climate and stand development stage are expected to be less variable. We found that pantropical, regional and local H-D allometric equations significantly underestimate the total height of P. elata. The local multi-species H-D allometric equation developed for Yangambi showed the highest underestimation in all the studied sites. This result supports the need for an H-D allometric equation specific for P. elata. The species-level H-D allometric equation developed showed significant underestimations for trees from the disturbed and undisturbed forests in DRC, while overestimations were observed for similar sites in Cameroon. Using a mixed-effect H-D allometric equation, we showed that even within a single species, a substantial variation exists between sites. This variation showed to be driven by the differences in the maximum asymptotic height (Hmax) between sites. We found that P. elata trees are taller and attain higher Hmax in DRC than in Cameroon. The basal area showed to be a significant covariate accounting for the site effects at the regional-scale where climate variables showed minor effects. However, at the local-scale, none of climate or stand variables showed to be significant. Local-scale variation showed to be associated with differences in light availability, highlighting the potential of management options that shape the local environment in driving species productivity.
查看更多>>摘要：? 2021 Elsevier B.V.This study is one of several investigating the biological effects of silvicultural systems at the Montane Alternative Silvicultural Systems (MASS) project located on Vancouver Island in British Columbia (BC). We compared understory vegetation cover and diversity under four silvicultural systems (clearcutting, patch cutting, dispersed retention, and shelterwood) to an adjacent old-growth forest. Long-term plots were measured pre-harvest and at intervals up to 26 years post-harvest. We also compared vegetation response to fertilization and vegetation control treatments. All harvesting resulted in a short-term reduction in understory cover from logging debris and ground disturbance. Recovery from disturbance varied by species, life-form and system. Understory tree species returned to pre-harvest cover after 15 years and significantly exceeded initial cover after 26 years. Shrubs returned to pre-harvest cover after 5–10 years and continued to increase in most systems. Herb cover was low in the pre-harvest forest but increased rapidly in years three through 10 due to herbaceous colonizers; this was least pronounced in the shelterwood. Herbs have declined rapidly since year fifteen. Forest floor bryophytes were reduced to less than 5% cover in all systems except the shelterwood and they remain at one-third or less of their pre-harvest cover. The shelterwood retained more stand structure and plant species from the original old-growth forest than other systems immediately after logging, except for the retained patches. All the harvesting treatments increased species richness and diversity compared to the pre-harvest forest. The increase in total species and abundance was highest for year 15 when early-seral colonizers were still present, and many pre-harvest species had returned. By year 26, richness and diversity began to decrease as early-seral species were lost. For overall species diversity of vascular plants and forest floor bryophytes, silvicultural system did not have an effect after 26 years. All the late-seral herbs that occur at MASS were present after harvesting but several were locally eliminated or had reduced abundance in cut areas. We found no significant edge effects into retention patches, which had comparable species richness and diversity to the pre-harvest old growth—suggesting that aggregated retention can be effective for maintaining late-seral species. Silvicultural system had more significant long-term effects on shrubs and bryophytes than early vegetation control.
查看更多>>摘要：? 2021 Elsevier B.V.Permanent sample plots were installed in two generations of operationally-established loblolly pine plantations across the southeastern US. The first population, established with non-genetically improved seedlings, did not receive mid-rotation fertilizer or competition control treatments. Approximately 20 years later, using consistent protocols for plot locations and tree measurements, permanent plots were installed in operationally-established plantings with genetically improved seedlings and receiving mid-rotation fertilizer and release treatments. These two studies, both of which reflect contemporary plantation management at the time they were initiated, were analyzed to examine the impact of changing management intensity and environmental influences on carrying capacity. Results showed that the second generation of plantings generally exhibited substantial increases in site index, as well as in maximum stand density. Assuming a constant rotation age of 25 years and computing mean annual increment using an empirical yield function fitted to the overall data, gave an estimated increase in volume production of 47% for the region. The estimated productivity gains were disparate by physiographic regions with the Piedmont showing an estimated increase of 83%, Atlantic Coastal Plain 64%, and Gulf Coastal Plain 34%. All physiographic regions can be assumed to have benefitted from increased levels of atmospheric CO2. The extraordinary increase in the Piedmont from one generation to the next likely resulted from a combination of factors, including maintaining more trees at maximum stand density and disproportionate gains in improved soil quality and climate change, as compared to the two coastal plain regions.
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