Conversion Of Old-growth Forests Research Articles

Greater soil carbon losses from secondary than old-growth tropical forests

Tropical forests play a crucial role in mediating the global carbon cycle and climate. Southeast Asian tropical forests are experiencing ongoing threats of deforestation and degradation. There is an urgent need to determine how the conversion from primary forest to secondary forest coverage may impact C stocks and cycling. While old-growth forests typically contain larger stores of C aboveground than secondary forests, past research has found varied results for belowground soil C storage and fluxes between tropical forest types. We examined differences in annual soil C efflux in a 2-ha old-growth and an adjacent 2-ha 70-year-old secondary ForestGEO plots in Bukit Timah Nature Reserve in Singapore. We hypothesized that the secondary forest would have greater soil C efflux rates than the old-growth forest and explored several potential drivers of soil C efflux including abiotic and biotic factors such as soil moisture, fine root biomass, and ectomycorrhizal association. We found that the hypothesis was supported, suggesting that belowground carbon dynamics fundamentally differ with forest age. Additionally, we found that fine root biomass was the best predictor of soil C efflux in the secondary forest and soil moisture in the old-growth forest. The difference in soil C efflux between forest types indicates that with continued degradation of old-growth forests in Southeast Asia, conversion of old-growth forests into secondary forests may drive greater C loss from soils even after 70 years of regrowth.

Land-use trajectories for sustainable land system transformations: Identifying leverage points in a global biodiversity hotspot

Sustainable land-system transformations are necessary to avert biodiversity and climate collapse. However, it remains unclear where entry points for transformations exist in complex land systems. Here, we conceptualize land systems along land-use trajectories, which allows us to identify and evaluate leverage points, i.e., entry points on the trajectory where targeted interventions have particular leverage to influence land-use decisions. We apply this framework in the biodiversity hotspot Madagascar. In the northeast, smallholder agriculture results in a land-use trajectory originating in old-growth forests and spanning from forest fragments to shifting hill rice cultivation and vanilla agroforests. Integrating interdisciplinary empirical data on seven taxa, five ecosystem services, and three measures of agricultural productivity, we assess trade-offs and cobenefits of land-use decisions at three leverage points along the trajectory. These trade-offs and cobenefits differ between leverage points: Two leverage points are situated at the conversion of old-growth forests and forest fragments to shifting cultivation and agroforestry, resulting in considerable trade-offs, especially between endemic biodiversity and agricultural productivity. Here, interventions enabling smallholders to conserve forests are necessary. This is urgent since ongoing forest loss threatens to eliminate these leverage points due to path dependency. The third leverage point allows for the restoration of land under shifting cultivation through vanilla agroforests and offers cobenefits between restoration goals and agricultural productivity. The co-occurring leverage points highlight that conservation and restoration are simultaneously necessary to avert collapse of multifunctional mosaic landscapes. Methodologically, the framework highlights the importance of considering path dependency along trajectories to achieve sustainable land-system transformations.

Forest structure and biomass reflects the variable effects of fire and land use 15 and 29 years following fire in the western Cascades, Oregon

The mixed severity fire regime of western Oregon forests creates a complex post-fire landscape mosaic with patches of low, moderate and high overstory tree mortality. Conversion of old-growth forests into plantations and post-fire salvage logging are widespread land uses that dramatically affect structure, biomass and carbon stocks. Few studies, however, have quantified the complex responses to wildfire and land management (i.e. logging and post-fire salvage logging) over long time periods. We quantified total aboveground biomass and composition in forest stands following low, moderate, and high severity fires 15 (2002 Apple Fire) and 29 years (1991 Warner Creek Fire) following fire in low elevation, old-growth forests dominated by Douglas-fir (Pseudotsuga menziesii). We also sampled post-fire responses in forest plantations (harvested prior to fire) and salvage-logged sites (harvested after fire) in the same fires. Fire severity had dramatic effects on the partitioning of total aboveground biomass (TAGB). Most of the TAGB in high severity fires was sequestered in dead trees (>43%) and downed wood (>29%) while live trees comprised the largest component of TAGB (>62%) in low severity fires. In spite of differences in overstory mortality, there was no significant difference in the TAGB between the low, moderate and high severity fires 15 years following fire (Apple Fire). Similarly, there was no significant difference between the low and high severity burns 29 years following fire (Warner Creek Fire). Managed forests (salvage and plantations) had significantly lower post-fire aboveground biomass and carbon storage that the natural forests. The TAGB of salvage logged sites was 49% and 42% that of the high severity sites at the Apple Fire and Warner Creek Fire, respectively. The mean TAGB of plantations was lowest of all fire and land use scenarios. At the Warner Creek Fire, TAGB of the plantations were <30% of that of the high severity fire sites (e.g. 326 and 984 Mg ha−1, respectively). This equates to a difference in aboveground carbon in the managed compared to the natural stands of 553 Mg CO2e ha−1 at the Apple Fire and 781 Mg CO2e ha−1 at the Warner Creek Fire. This research highlights the management tradeoffs involving values relating to carbon storage and wood harvest following fires.

How much primary coastal temperate rain forest should society retain? Carbon uptake, recreation, and other values

In this study, average and marginal approaches for determining optimal preservation of primary forests on British Columbia's coast are compared. When the market values from timber, mushrooms, etc., and nonmarket benefits (e.g., carbon sink, preservation values) of preserving old-growth forests are considered (where the opportunity cost of preserving such forests are the benefits of commercial forestry foregone), the average method recommends harvest of all remaining old growth. For the marginal approach, a deterministic optimal control model is solved to compute socially optimal stocks of old growth. In this case, the numerical results indicate that large-scale conversion of old-growth forests cannot be justified on economic grounds.