Juan A. Blanco

Yield decline in Chinese-fir plantations: a simulation investigation with implications for model complexity

A variety of competing hypotheses have been described to explain yield decline in Chinese-fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations. The difficulty in implementing field experiments suggests ecosystem modeling as a viable option for examining alternative hypotheses. We present a conceptual model of Chinese-fir yield decline and explore its merits using the ecosystem-based FORECAST model. Model results suggest that yield decline is caused primarily by a decline in soil fertility, largely as a consequence of slash burning in conjunction with short rotations. However, as tree leaf area declines, there is a transition (over subsequent rotations) from seed rain based competition to bud bank based competition, increasing the competitive impact of minor vegetation on tree growth. Short rotations increase understory survival between rotations and may cause a gradual shift from tree dominance to shrub/herb dominance over subsequent rotations. These effects are most evident on nutrient-poor sites, but...

Testing the performance of a forest ecosystem model (FORECAST) against 29 years of field data in a Pseudotsuga menziesii plantation

The ability of the forest ecosystem management model FORECAST to project a 29-year record of stand response to factorial thinning and fertilization treatments in a Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation at Shawnigan Lake (Vancouver Island, British Columbia, Canada) was assessed. Model performance was evaluated firstly using for calibration a regional data set and secondly with site-specific data from control plots. Model output was compared against field measurements of height, diameter, stem density, component biomass (aboveground), and litterfall rates and estimates of nutrient uptake, foliar N efficiency, and understory vegetation biomass. When calibrated with regional data, results from graphical comparisons, three measures of goodness-of-fit, and equivalence testing demonstrated that FORECAST can produce predictions of good to moderate accuracy depending on the variable of interest. Model performance was generally better when compared with field measurements (e.g., top height, ...

Effects of nitrogen deposition on carbon sequestration in Chinese fir forest ecosystems.

Nitrogen deposition and its ecological effects on forest ecosystems have received global attention. We used the ecosystem model FORECAST to assess the effects of nitrogen deposition on carbon sequestration in Chinese fir planted forests in SE China. This topic is important as China is intensifying its reforestation efforts to increase forest carbon sequestration for combating climate change impacts, using Chinese fir as the most important plantation species. A series of scenarios including seven N deposition levels (1, 5, 10, 20, 30, 40 and 50kg ha(-1)y(-1)), three management regime (rotation lengths of 15, 30 and 50 years) and two site qualities (nutrient poor and fertile sites) were defined for the simulations. Our results showed that N deposition increased carbon sequestration in Chinese fir forests, but the efficiency of the increasing effect is reduced as N deposition levels increase. When N deposition levels exceeded 20-30kg ha(-1)y(-1), the incremental effects of N deposition on forest C pools were marginal. This suggests that N deposition levels above 20-30kg ha(-1)y(-1) could lead to N saturation in Chinese fir forest soils. Any additional amounts of N input from deposition would likely be leached out. Total above-ground C was more sensitive to N deposition than to rotation length and site quality. It was also estimated that the contributions of N deposition to C sequestration in all Chinese fir forests in South-East China are 7.4×10(6)MgCy(-1) under the current N deposition levels (5 to 10kg ha(-1)y(-1)) and could reach up to 16×10(6)MgCy(-1) if N deposition continues increasing and reaches levels of 7.5 to 15kg N ha(-1)y(-1).

Thinning affects nutrient resorption and nutrient‐use efficiency in two Pinus sylvestris stands in the Pyrenees

Needle chemical composition was measured, and nutrient resorption, nutrient-use efficiency (NUE), and other indexes were estimated for 24 months in two contrasting natural Pinus sylvestris L. forests in the western Pyrenees in Spain. For each location (Aspurz, 650 m elevation, 7% slope; Garde, 1335 m elevation, 40% slope), there were three reference plots (P0), three plots with 20% of the basal area removed (P20), and three with 30% of the basal area removed (P30). Needle P, Ca, and Mg concentrations were higher in Garde, but N concentration was higher for Aspurz, without differences for K. Nutrient-resorption efficiency of P was higher in Aspurz, of Mg higher in Garde, and there were no differences between sites in N and K. Nutrient-resorption proficiency was significantly higher in the site with lower soil nutrient availability, i.e., for P, Ca, and Mg in Aspurz, but N in Garde (no differences in K); this may be an indicator of nutrient conservation strategy. Annual nutrient productivity (A) was higher for all nutrients in Aspurz, whereas the mean residence time (MRT) was higher in Garde in all nutrients but P. NUE was significantly higher in Garde for all nutrients but P, which was more efficiently used in Aspurz. In both sites, N, P, and K concentrations were higher in the 2002 cohort, Ca in the 2000 cohort, and maximum Mg was found in the 2001 cohort. Thinning caused a reduction of Mg concentration in the 2001 cohort in Aspurz, an increase of Ca resorption proficiency in Aspurz and Mg resorption at both sites, and reduction of P, K, and Mg nutrient response efficiency (NRE) in Garde. Thinning may have caused an increase of the C:Mg ratio through facilitating the development of more biosynthesis apparatus in a more illuminated canopy, but it seemed not to affect resorption in a significant way. Changes in NRE in Garde after thinning show that forest management can affect how trees use nutrients. Our results indicate that the strategy to optimize NUE is different in each stand. In Aspurz (a Mediterranean ecosystem), pine trees carried out resorption more efficiently, while in Garde (a continental forest), trees used nutrients for longer periods of time and reduced their efficiency in using the available soil nutrients after reduced competition by thinning.

Relationship between Monokaryotic Growth Rate and Mating Type in the Edible Basidiomycete Pleurotus ostreatus

ABSTRACT The edible fungus Pleurotus ostreatus (oyster mushroom) is an industrially produced heterothallic homobasidiomycete whose mating is controlled by a bifactorial tetrapolar genetic system. Two mating loci (matA and matB) control different steps of hyphal fusion, nuclear migration, and nuclear sorting during the onset and progress of the dikaryotic growth. Previous studies have shown that the segregation of the alleles present at thematB locus differs from that expected for a single locus because (i) new nonparental B alleles appeared in the progeny and (ii) there was a distortion in the segregation of the genomic regions close to this mating locus. In this study, we pursued these observations by using a genetic approach based on the identification of molecular markers linked to the matBlocus that allowed us to dissect it into two genetically linked subunits (matBα and matBβ) and to correlate the presence of specific matBα and matAalleles with differences in monokaryotic growth rate. The availability of these molecular markers and the mating type dependence of growth rate in monokaryons can be helpful for marker-assisted selection of fast-growing monokaryons to be used in the construction of dikaryons able to colonize the substrate faster than the competitors responsible for reductions in the industrial yield of this fungus.

Effects of thinning on nutrient content pools in two Pinus sylvestris forests in the western Pyrenees

Abstract Nutrient content [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg)] in needles, branches and stems before (P0, not thinned) and after thinning (P20 and P30, 20% and 30% of basal area removed, respectively) was studied in 37- and 32-year-old Pinus sylvestris L. forests in the western Pyrenees: Garde and Aspurz. Thinning significantly decreased all nutrient pools in P20 and P30 relative to P0 on both sites, but no significant differences were found between P20 and P30 owing to low statistical power. Thinning increased the differences between the two forests for total above-ground content of P and Mg, and for the content of N, P and K in the 1999 needles cohort. The former result was due in part to the higher concentration of P (needles and branches) and Mg (needles) in Garde. Therefore, the importance of needles relative to the other nutrient pools increased for N and P after thinning. This may have resulted from the fact that the removal of dead trees with low needle biomass was greater in Garde than in Aspurz. Based on the percentage of basal area removed, nutrient removal in Garde for P30 was higher than expected, apparently owing to an increase in branch removal relative to P20. These results indicate that effects of thinning on nutrient pools were influenced by differences in stand structure and nutrient tissue concentrations between sites.

Forests may need centuries to recover their original productivity after continuous intensive management: an example from Douglas-fir stands

How long would it take for forests to recover their original productivity following continuous intensive management if they are left untouched? This issue was explored using the model FORECAST, calibrated and validated for coastal Douglas-fir stands on Vancouver Island (western Canada). Three types of forest management (production of timber, pulp, and biomass) were simulated, being different in utilization level and rotation length (stem-only and 75-year rotation for timber production, whole-tree and 30-year rotation for pulp/fiber, and whole-tree and 15-year rotations for biomass production). Management was simulated for 150 years, followed by several cycles of natural growth without management ending with a stand-replacing windstorm with a return time of 200 years. Productivity-related ecological variables in previously managed stands were compared to natural forests. Stands developed after management for timber would quickly reach values similar to non-managed forests for tree and understory total biomass, stored carbon, available nitrogen and soil organic matter (SOM). However, intensive management regimes designed for fiber and biomass production would cause a decrease in SOM and nutrient availability, increasing understory biomass. As a consequence, stands recovering from intensive management would need at least two stand-replacing events (400 years) to reach a productivity status similar to non-managed stands. Stands developed after management for biomass would take much longer, up to 600 or 800 years to recover similar values of SOM and understory biomass, respectively. Current fertilization prescriptions will likely be not enough to stop a quick drop in forest productivity associated with intensive management. Intensifying forest management to achieve short-term objectives could produce a reduction of stand productivity that would influence tree growth for very long time (up to several centuries), if such management is continuously implemented at the same stand. Some of these effects could be reduced if one rotation of intensive management (for pulp or bioenergy) is followed by a rotation of management for timber, or by leaving the forest without management for an equivalent time.

Significant increase in ecosystem C can be achieved with sustainable forest management in subtropical plantation forests

Subtropical planted forests are rapidly expanding. They are traditionally managed for intensive, short-term goals that often lead to long-term yield decline and reduced carbon sequestration capacity. Here we show how it is possible to increase and sustain carbon stored in subtropical forest plantations if management is switched towards more sustainable forestry. We first conducted a literature review to explore possible management factors that contribute to the potentials in ecosystem C in tropical and subtropical plantations. We found that broadleaves plantations have significantly higher ecosystem C than conifer plantations. In addition, ecosystem C increases with plantation age, and reaches a peak with intermediate stand densities of 1500–2500 trees ha−1. We then used the FORECAST model to simulate the regional implications of switching from traditional to sustainable management regimes, using Chinese fir (Cunninghamia lanceolata) plantations in subtropical China as a study case. We randomly simulated 200 traditional short-rotation pure stands and 200 sustainably-managed mixed Chinese fir – Phoebe bournei plantations, for 120 years. Our results showed that mixed, sustainably-managed plantations have on average 67.5% more ecosystem C than traditional pure conifer plantations. If all pure plantations were gradually transformed into mixed plantations during the next 10 years, carbon stocks could rise in 2050 by 260.22 TgC in east-central China. Assuming similar differences for temperate and boreal plantations, if sustainable forestry practices were applied to all new forest plantation types in China, stored carbon could increase by 1,482.80 TgC in 2050. Such an increase would be equivalent to a yearly sequestration rate of 40.08 TgC yr−1, offsetting 1.9% of China’s annual emissions in 2010. More importantly, this C increase can be sustained in the long term through the maintenance of higher amounts of soil organic carbon and the production of timber products with longer life spans.

Increased complementarity in water-limited environments in Scots pine and European beech mixtures under climate change

Ramon y Cajal contract, Grant/Award Number:RYC‐2011‐08082; Spanish Ministry of Economy and Competitiveness, Grant/AwardNumber: AGL2012‐33465; mobility aid,Grant/Award Number: EEBB‐I‐15‐09220; Spanish Predoctoral Research Grant, Grant/Award Number: BES‐2013‐066705.

Tree‐to‐tree competition in mixed European beech–Scots pine forests has different impacts on growth and water‐use efficiency depending on site conditions

Mixed conifer–hardwood forests can be more productive than pure forests and they are increasingly considered as ecosystems that could provide adaptation strategies in the face of global change. However, the combined effects of tree-to-tree competition, rising atmospheric CO2 concentrations and climate on such mixtures remain poorly characterized and understood. To fill this research gap, we reconstructed 34-year series (1980–2013) of growth (basal area increment, BAI) and intrinsic water-use efficiency (iWUE) of Scots pine (Pinus sylvestris L.)–European beech (Fagus sylvatica L.) mixed stands at two climatically contrasting sites located in the southwestern Pyrenees. We also gathered data on tree-to-tree competition and climate variables in order to test the hypotheses that (1) radial growth will be greater when exposed to inter- than to intraspecific competition, that is, when species complementarity occurs and (2) enhanced iWUE could be linked to improved stem radial growth. Growth of both species was reduced when intraspecific competition increased. Species complementarity was linked to improved growth of Scots pine at the continental site, while competition overrode any complementarity advantage at the drought-prone Mediterranean site. Beech growth did not show any significant response to pine admixture likely due to shade tolerance and the highly competitive nature of this species. Increasing interspecific competition drove recent iWUE changes, which increased in Scots pine but decreased in European beech. The iWUE enhancement did not involve any growth improvement in Scots pine. However, the positive BAI-iWUE relationship found for beech suggests an enhanced beech growth in drought-prone sites due to improved water use. Synthesis. Complementarity may enhance growth in mixed forests. However, water scarcity can constrict light-related complementarity for shade intolerant species (Scots pine) in drought-prone sites. Basal area increment–intrinsic water-use efficiency relationships were negative for Scots pine and positive for European beech. These contrasting behaviours have got implications for coping with the expected increasing drought events in Scots pine–European beech mixtures located near the ecological limit of the two species. Complementarity effects between tree species should be considered to avoid overestimating the degree of future carbon uptake by mixed conifer–broadleaf forests.