Daniel Houle

Consequences of climate change for biogeochemical cycling in forests of northeastern North America.

A critical component of assessing the impacts of climate change on forest ecosystems involves understanding associated changes in the biogeochemical cycling of elements. Evidence from research on northeastern North American forests shows that direct effects of climate change will evoke changes in biogeochemical cycling by altering plant physiology, forest productivity, and soil physical, chemical, and biological processes. Indirect effects, largely mediated by changes in species composition, length of growing season, and hydrology, will also be important. The case study presented here uses the quantitative biogeochemical model PnET-BGC to test assumptions about the direct and indirect effects of climate change on a northern hardwood forest ecosystem. Modeling results indicate an overall increase in net primary production due to a longer growing season, an increase in NO3– leaching due to large increases in net mineralization and nitrification, and slight declines in mineral weathering due to a reduction i...

Projections of future soil temperature and water content for three southern Quebec forested sites

AbstractThe impacts of climate change on future soil temperature Ts and soil moisture Ms of northern forests are uncertain. In this study, the authors first calibrated Ts and Ms models [Forest Soil Temperature Model (ForSTeM) and Forest Hydrology Model (ForHyM), respectively] using long-term observations of Ts and Ms at different depths measured at three forest sites in eastern Canada. The two models were then used to project Ts and Ms for the period 1971–2100 using historical and future climate scenarios generated by one regional and five global climate models. Results indicate good model performance by ForSTeM and ForHyM in predicting observed Ts and Ms values at various depths for the three sites. Projected annual-mean Ts at these sites increased between 1.1° and 1.9°C and between 1.9° and 3.3°C from the present 30-yr averages (1971–2000) to the periods 2040–69 and 2070–99, respectively. Increases as high as 5.0°C were projected at the black spruce site during the growing season (June) for the period 2...

IMPACT OF NUTRIENT REMOVAL THROUGH HARVESTING ON THE SUSTAINABILITY OF THE BOREAL FOREST

The cycling of base cations (K, Ca, Mg, and Na) was investigated in a boreal balsam fir forest (the Lake Laflamme Watershed) between 1999 and 2005. Base cation budgets were calculated for the soil rooting zone that included atmospheric deposition and soil leaching losses, two scenarios of tree uptake (whole-tree and stem-only harvesting), and three scenarios of mineral weathering, leading to six different scenarios. In every scenario there was a net accumulation of Mg within the soil exchangeable reservoir, while Ca accumulated in four scenarios. Potassium was lost in five of the six scenarios. Contrary to Ca and Mg, immobilization of K within tree biomass (69 mol x ha(-1) x yr(-1)) was the main pathway of K losses from the soil exchangeable reservoir, being five times higher than losses via soil leaching (14 mol x ha(-1) x yr(-1)). The amounts of K contained within the aboveground biomass and the exchangeable soil reservoir were 3.3 kmol/ha and 4.2 kmol/ha, respectively. Whole-tree harvesting may thus remove 44% of the K that is readily available for cycling in the short term, making this forest sensitive to commercial forestry operations. Similar values of annual K uptake as well as a similar distribution of K between tree biomass and soil exchangeable reservoirs at 14 other coniferous sites, distributed throughout the boreal forest of Quebec, suggest that the Lake Laflamme Watershed results can be extrapolated to a much larger area. Stem-only harvesting, which would reduce K exports due to biomass removal by 60%, should be used for these types of forest.

Role of SO4 adsorption and desorption in the long-term S budget of a coniferous catchment on the Canadian Shield

The hypothesis that SO4 desorption can explain apparent long term net SO4-S losses (5 kg·ha−1·yr−1 on average) at the Lake Laflamme catchment from 1982 to 1991 is examined. Field observations show that SO4 concentrations in the soil solution are strongly buffered during percolation through the Bf horizon. In the Bf horizon, SO4 exchange reactions between the adsorbed and aqueous compartments are rapid (hours). Most (≈60%) of the adsorbed SO4 may be readily desorbed with deionized water. These observations and the presence of an important adsorbed SO4-S reservoir in the Bf horizon (113 kg·ha−1) as compared with annual wet SO4-S deposition (7 kg·ha−1), suggest that on the short-term, adsorption and desorption reactions can control dissolved SO4 concentration in the Bf horizon. To examine whether SO4 adsorption/desorption could explain long-term SO4-S losses by the catchment, an aggregated Langmuir isotherm for the Bf horizon was used to calculate the catchments resilience to changing SO4-S loads. The results indicate that the soil should adjust rapidly (within 4 years) to changing SO4-S loads and that SO4 desorption alone cannot explain long-term net SO4-S losses. Other possibilities, such as an underestimation of dry deposition or the weathering of S-bearing minerals also appear unlikely. Our results suggest a net release of SO4-S from the soil organic S reservoirs (1230 kg·ha−1) present in the catchment.

Effects of two silvicultural practices on soil fauna abundance in a northern hardwood forest, Quebec, Canada

Soil fauna play a key role in soil fertility and productivity of forest ecosystems and represent an important base of terrestrial food chains. The impact of forest management on soil fauna should be considered when sustainable forest management and conservation of biodiversity are desired. We evaluated the impact of selective cutting and strip clearcutting on soil fauna abundance in a northern hardwood forest of the Lower Laurentians of Quebec. Twelve years after strip clearcutting, the abundance of carabid beetles (Coleoptera: Carabidae), collembolans (Hexapoda: Collembola) and snails (Stylommatophora: Sigmurethra) was greater in the strip clearcuts than the adjacent undisturbed strips. Snails and millipedes (Polydesmida: Polydesmidae) were more abundant in the selective cuts 6 to 8 yr after treatment. Spiders (Arachnida) were the only organism whose abundance was lower in the selective cuts than in the adjacent undisturbed forest . No significant negative effect of the silvicultural treatments was noted...

Soil organic sulfur dynamics in a coniferous forest

Sulfate microbial immobilization and the mineralization of organic S were measured in vitro in soil horizons (LFH, Ae, Bhf, Bf and C) of the Lake Laflamme watershed (47°17′ N, 71°14′ O) using 35SO4. LFH samples immobilized from 23 to 77% of the added 35SO4 within 2 to 11 days. The 35SO4 microbial immobilization increased with temperature and reached an asymptote after a few days. The mineral soil generally immobilized less than 20% of the added 35SO4, and an asymptote was reached after 2 days. An isotopic equilibrium was rapidly reached in mineral horizons. A two-compartment (SO4 and organic S) model adequately described 35SO4 microbial immobilization kinetics. The active organic reservoir in the whole soil profile represented less than 1% of the total organic S. The average concentrations of dissolved organic S (DOS) in the soil solutions leaving the LFH, Bhf and Bf horizons were respectively 334, 282 and 143 µg⋅L−1. Assuming that the DOS decrease with soil depth corresponded to the quantities adsorbed in the B horizons, we estimated that 12 800 kg⋅ha−1 of organic S could have been formed since the last glaciation, which is about 13 times the size of the actual B horizons reservoirs. Our results suggest that the organic S reservoirs present in mineral forest soils are mostly formed by the DOS adsorption resulting from incomplete litter decomposition in the humus layer. The capability of these horizons to immobilize SO4 from the soil solution would be restricted to a 1% active fraction composed of microorganisms. Despite their refractory nature, these reservoirs can, however, be slowly decomposed by microorganisms and contribute to the S-SO4 export from the watershed in the long term.

Sulfur speciation and distribution in soils and aboveground biomass of a boreal coniferous forest

Major sulfur pools are quantified in soils and aboveground biomass of a coniferous boreal forest. Total ecosystem S averages 1395 kg·ha−1 of which 98% is found in the soil, with 89% being in the mineral horizons. Organic S dominates in soil, tree parts (trunks, branches + foliage, roots) and litterfall, ranging from 77 to 99% of total S concentration. Carbon-bonded S, ester sulfate and SO4-S in soil profiles range respectively from 51–68%, 29–37% and 1–14% of total S concentrations and account respectively for 57, 33 and 10% of total S on an areal basis. Adsorbed SO4 accounts for 82% of total SO4, and can be predicted from Al bound to organic matter, amorphous Al and pH (r2 = 0.81). There is a strong relationship between % carbon and carbon-bonded S in 4 of the 5 soil horizons studied which represent over 95% of the total soil organic matter, whereas ester sulfate is related to % carbon in 3 soil horizons representing only 37% of the soil organic matter. An analysis of atmospheric S loading and S data for 10 forested sites in Europe and North America suggests that the size of the organic S pool in forested systems is independent of atmospheric loading.

Effects of a spruce budworm outbreak on element export below the rooting zone: a case study for a balsam fir forest

Abstract• Spruce budworm outbreaks are among the major natural disturbances affecting the dynamics and functioning of Canadian boreal forests. However, the element losses potentially associated with spruce budworm outbreaks have not been quantified.• We evaluated the influence of spruce budworm outbreaks on nutrient export from boreal forest soils by comparing nutrient leaching losses during a spruce budworm outbreaks episode (1981–1984) to an unperturbed period (1999–2003) in a calibrated catchment located in a balsam fir forest.• Nutrient soil leaching losses were significantly higher during the spruce budworm outbreaks (1981–1984) for N-NO3 (30.1 fold), K (8.3 fold), N-NH4 (6.2 fold), Mg (2.7 fold) and SO4 (2.2 fold), as compared to an unperturbed period (1999–2003). When the recurrence of spruce budworm outbreaks (33 years) and a plausible average length of such events (5 years) are taken into consideration, it is estimated that in the long term, 5.6 more NO3, 1.5 more K and 1.2 more NH4 are leached from the soil profile during outbreaks.• The important leaching losses during spruce budworm outbreaks, when added to the losses due to tree harvesting and fire (and acid deposition for K), may have considerable effects on soil fertility and ecosystem sustainability.Résumé• Les épidémies de la tordeuse des bourgeons de l’épinette sont parmi les principales perturbations naturelles qui affectent la dynamique et le fonctionnement des forêts boréales canadiennes. Toutefois, les éléments potentiellement perdus associés à une épidémie de la tordeuse des bourgeons de l’épinette n’ont pas été quantifiés.• Nous avons évalué l’influence des épidémies de tordeuse des bourgeons de l’épinette sur l’exportation des éléments nutritifs des sols de la forêt boréale, en comparant les pertes par lessivage des éléments nutritifs au cours d’un épisode d’épidémie de la tordeuse des bourgeons de l’épinette (1981–1984) à une période non perturbée (1999–2003) dans un bassin versant calibré situé dans une forêt de sapin baumier.• Les pertes par lessivage des éléments nutritifs du sol ont été significativement plus élevées au cours de l’épidémie de la tordeuse des bourgeons de l’épinette (1981–1984) pour N-NO3 (30,1 fois), K (8,3 fois), N-NH4 (6,2 fois), Mg (2,7 fois) and SO4 (2,2 fois), de N-NO3 (par rapport à une période non perturbée (1999–2003). Quand la répétition des épidémies de tordeuse des bourgeons de l’épinette (33 ans) et une durée moyenne plausible de ces événements (5 ans) sont prises en considération, il est estimé que dans le long terme, 5,6 fois plus de NO3, 1,5 fois plus de K et 1,2 fois plus de NH4 sont lessivés du profil du sol durant les épidémies.• Les importantes pertes par lessivage lors des épidémies de tordeuse des bourgeons de l’épinette, ajoutées aux pertes dues à la récolte des arbres et au feu (et des dépôts acides pour K), peuvent avoir des effets considérables sur la fertilité des sols et la durabilité de l’écosystème.

RECENT RECOVERY OF LAKE WATER QUALITY IN SOUTHERN QUEBEC FOLLOWING REDUCTIONS IN SULFUR EMISSIONS

Since 1985, monitoring activities have been conducted in a networkof 43 lakes comprising the Québec portion of the Long-Range Transport of Airborne Pollutants (LRTAP) program. The results to date indicate that Québec lakes generally are responding positively to the generalized decline in precipitation sulfate (SO42-), with 40 of the 43 lakes now showing steep declines in SO42- concentrations. The drop in SO42- was associated with a significant decrease in Ca2+ concentrations in 77% of the lakes (67% for Mg2+ concentrations). Overall, the acid-neutralizing capacity was increasing in 19 lakes and decreasing only in three, while 21 lakes showed no temporal trends. Compared with previous trend studies of the LRTAP-Québec network for the period of 1985–1993, the longer period (1985–1999) shows a clear improvement, with the proportion of lakes that were acidifying changing from 24 to 7% and with the proportion of lakes that were recovering changing from 16 to 35%. These observations suggest that the recent drop in SO42- deposition in the northeastern U.S. and eastern Canada was significant enough to allow chemical recovery for a significant proportion of Québec lakes.

Foliar and wood chemistry of sugar maple along a gradient of soil acidity and stand health

The decline of sugar maple (Acer saccharum Marsh.) in forest of north-eastern North America is an important environmental issue. In this study, relationships between, soil, wood and foliar chemistry were assessed for 17 stands distributed within a large area of the Quebec sugar maple forest and that were growing on soils with a strong gradient of acidity and base saturation. There were many significant relationships between variables describing the acid-base status of the top-B soil (Ca and Mg concentrations, exchangeable acidity and base saturation) and Ca and Mn concentrations and Ca/Mn and Mg/Mn in tree tissues. Manganese was the element that showed the strongest inverse non-linear relationships with top-B soil base saturation with variance explanation of 71 and 65%, for wood and foliage, respectively. The 17 sites were divided in two groups according to their level of decline. The declining stands had significantly higher wood Mn and Mg concentrations and lower Ca/Mn ratios and significantly higher foliar Mn and lower Ca and Al concentrations. It was impossible to determine if these differences were a cause or a symptom of sugar maple health. However, the increase in Mn concentrations in tree tissues with increasing soil acidity, as well as the higher Mn concentrations in declining as compared to healthy stands suggest that Mn, as well as low Ca availability, could be an important contributing factor in the sugar maple decline.