Kathleen L. Kavanagh

Consequences of Environmental Service Payments for Forest Retention and Recruitment in a Costa Rican Biological Corridor

Compensation to landowners for forest-derived environmental services has gained international recognition as a mechanism to combat forest loss and fragmentation. This approach is widely promoted, although there is little evidence demonstrating that environmental service payments encourage forest stewardship and conservation. Costa Rica provides a unique case study in which a 1996 Forestry Law initiated environmental service payments and prohibited forest conversion to other land uses. We examined these novel policies to determine their influence on landowner decisions that affect forest change, carbon services, and connectivity in a 2425 km² biological corridor. We used Landsat images to compare land-cover changes before and after 1996, and linked these data to landowner surveys investigating land-use decisions. Carbon stocks and storage in secondary forests were also examined. Forest change observations were corroborated by landowner survey data, indicating that the 1996 Forestry Law and environmental service payments contributed positively to forest retention and recruitment. Socioeconomic conditions also favored forest protection. Rates of natural forest loss declined from -1.43% to -0.10%/yr after 1996. Forest cover and connectivity were maintained through tree plantations and secondary forest recruitment, although forest heterogeneity increased as these forest types sometimes replaced natural forest. Carbon storage in secondary forest approached levels in primary forest after 25-30 yr of succession, although few landowners retained natural regeneration. Secondary forests will persist as minor landscape components without legal or financial incentives. The Costa Rican experience provides evidence that environmental service payments can be effective in retaining natural forest and recruiting tree cover within biological corridors.

Fire effects on gross inorganic N transformation in riparian soils in coniferous forests of central Idaho, USA: wildfires v. prescribed fires

We investigated differences between wildfires and prescribed fires in their effects on nitrogen (N) dynamics in mineral soils collected from riparian coniferous forests of central Idaho, USA. Specifically, we investigated how the two types of fires affected inorganic N concentrations, microbial biomass N and gross transformation rates of inorganic N in mineral soils relative to their corresponding unburnt controls. There was no significant difference in soil NH4+ concentrations between burnt and control soils in either type of fires. However, wildfires significantly reduced gross ammonification and microbial NH4+ uptake rates relative to their controls (P = 0.05 and 0.08). No such effect was found in soils burnt by the prescribed fires relative to their controls. Burnt soils had significantly higher NO3– concentrations than control soils when all the data were pooled (P = 0.08). The elevated NO3– concentrations in the soils burnt by either type of fire were not caused by increased gross nitrification, but likely by significantly reduced microbial NO3– uptake (P ≤ 0.02). We concluded that controlled prescribed fires conducted in early spring had less of an effect on soil N dynamics than wildfires in the region.

Selection for improved growth and wood quality in lodgepole pine: effects on phenology, hydraulic architecture and growth of seedlings

Selection for both growth and wood quality is the primary goal of many tree breeding programs. In order to investigate the impacts of such selection on adaptive traits, observations were made on phenology, drought resistance, xylem conductance and xylem vulnerability to cavitation of 2-year-old seedlings of lodgepole pine (Pinus contorta Dougl. Ex Loud var. latifolia Engelm) from four subpopulations: (1) fast height growth and high wood density (FH); (2) slow height growth and high density (SH); (3) fast height growth and low density (FL); and (4) slow height growth and low density (SL). Results showed that the impact of the selection on phenology was minor; differences in growth among subpopulations were mainly attributable to maximal growth rate and the duration of the period of rapid growth. The FL subpopulation showed a significantly stronger productivity decline in response to moderate drought compared to the two slower-growing subpopulations. The FH subpopulation showed significantly higher xylem specific conductivity than the two slower-growing subpopulations, and greater resistance to cavitation than the other three subpopulations, suggesting the possibility of selecting families that combine fast growth, high wood density and drought tolerance.

Constraining 3‐PG with a new δ13C submodel: a test using the δ13C of tree rings

A semi-mechanistic forest growth model, 3-PG (Physiological Principles Predicting Growth), was extended to calculate δ(13)C in tree rings. The δ(13)C estimates were based on the models existing description of carbon assimilation and canopy conductance. The model was tested in two ~80-year-old natural stands of Abies grandis (grand fir) in northern Idaho. We used as many independent measurements as possible to parameterize the model. Measured parameters included quantum yield, specific leaf area, soil water content and litterfall rate. Predictions were compared with measurements of transpiration by sap flux, stem biomass, tree diameter growth, leaf area index and δ(13)C. Sensitivity analysis showed that the models predictions of δ(13)C were sensitive to key parameters controlling carbon assimilation and canopy conductance, which would have allowed it to fail had the model been parameterized or programmed incorrectly. Instead, the simulated δ(13)C of tree rings was no different from measurements (P > 0.05). The δ(13)C submodel provides a convenient means of constraining parameter space and avoiding model artefacts. This δ(13)C test may be applied to any forest growth model that includes realistic simulations of carbon assimilation and transpiration.

Comparing the Influence of Wildfire and Prescribed Burns on Watershed Nitrogen Biogeochemistry Using 15N Natural Abundance in Terrestrial and Aquatic Ecosystem Components

We evaluated differences in the effects of three low-severity spring prescribed burns and four wildfires on nitrogen (N) biogeochemistry in Rocky Mountain headwater watersheds. We compared paired (burned/unburned) watersheds of four wildfires and three spring prescribed burns for three growing seasons post-fire. To better understand fire effects on the entire watershed ecosystem, we measured N concentrations and δ15N in both the terrestrial and aquatic ecosystems components, i.e., soil, understory plants in upland and riparian areas, streamwater, and in-stream moss. In addition, we measured nitrate reductase activity in foliage of Spiraea betulifolia, a dominant understory species. We found increases of δ15N and N concentrations in both terrestrial and aquatic ecosystem N pools after wildfire, but responses were limited to terrestrial N pools after prescribed burns indicating that N transfer from terrestrial to aquatic ecosystem components did not occur in low-severity prescribed burns. Foliar δ15N differed between wildfire and prescribed burn sites; the δ15N of foliage of upland plants was enriched by 2.9 ‰ (difference between burned and unburned watersheds) in the first two years after wildfire, but only 1.3 ‰ after prescribed burns. In-stream moss δ15N in wildfire-burned watersheds was enriched by 1.3 ‰, but there was no response by moss in prescription-burned watersheds, mirroring patterns of streamwater nitrate concentrations. S. betulifolia showed significantly higher nitrate reductase activity two years after wildfires relative to corresponding unburned watersheds, but no such difference was found after prescribed burns. These responses are consistent with less altered N biogeochemistry after prescribed burns relative to wildfire. We concluded that δ15N values in terrestrial and aquatic plants and streamwater nitrate concentrations after fire can be useful indicators of the magnitude and duration of fire effects and the fate of post-fire available N.

Wildfire effects on physiological properties in conifers of central Idaho forests, USA

Key messageConifers which substantially lost foliage in wildfires were also reduced in their relative hydraulic capacity, resulting in little change in water use efficiency.AbstractWildfires are a natural and ubiquitous component of many forests. Fire-induced damages can lead to immediate tree mortality or a prolonged state of decline. However, physiological mechanisms behind the phenomenon are not well understood. We investigated physiological properties of conifers that survived wildfire 2 year post-fire in central Idaho, USA. In 2005, we set up a burned plot at each of three sites, where the independent wildfires damaged dominant conifers in 2003, paired with a comparable adjacent control plot without any fire damage. At each burned plot, we assessed physical damages in the burned conifers. At each plot in a given site, we repeatedly measured physiological characteristics in five trees of a dominant conifer species (Pseudotsuga menziesii or Pinus contorta) to compare burned and control plots across the three sites during the 2005 growing season. Growth of the burned conifers was significantly reduced post-fire. Leaf area of burned conifers was significantly reduced due to scorching, which, in theory, should have led to increased stomatal conductance (gs) and leaf specific conductance (KL). However, we did not find significant differences in KL between burned and control conifers, and gs was sometimes even lower in burned than control conifers. These results indicate the wildfires reduced capacity of hydraulic apparatus in the surviving conifers, partly due to reduced sapwood area associated with the decreased stem growth post-fire. This was supported by our finding that integrated water use efficiency, assessed via δ13C of woody materials and foliage, was not significantly affected by the wildfires.

513C in Pentaclethra macroloba trees growing at forest edges in north-eastern Costa Rica

Fragmented forest landscapes with large proportions of edge area are common in the tropics, though little is known about functional responses of trees to edge effects. Foliar δ 13 C can increase our understanding of tree function, as these values reflect changes in c i /c a as trees respond to environmental gradients. We expected that foliar δ 13 C would be enriched, indicating a decline in c i /c a , in Pentaclethra macroloba trees growing at forest edges in north-eastern Costa Rica. We also anticipated this isotopic shift in δ 13 C values of soil carbon and soil respired CO 2 . Three transects perpendicular to forest edges were established at three study sites, and six plots per transect were located 0–300 m from edges. Within plots, foliage, soil and soil respired CO 2 were collected for isotopic analyses. Foliar δ 13 C, thus c i /c a , and soil carbon δ 13 C did not vary along the edge to interior gradient. δ 13 C for canopy and understorey foliage averaged −29.7‰ and −32.5‰, respectively, while soil carbon δ 13 C averaged −28.0‰. Soil respired CO 2 δ 13 C ranged from −29.2‰ to −28.6‰ and was significantly depleted within 50 m of edges. The predominant lack of functional responses at forest edges indicates that P. macroloba trees are robust and these forests are minimally influenced by edge effects.