Kimberley D. Brosofske

Microclimate in Forest Ecosystem and Landscape Ecology

Microclimate is the suite of climatic conditions measured in localized areas near the earths surface (Geiger 1965). These environmental variables, which include temperature, light, windspeed, and moisture, have been critical throughout human history, providing meaningful indicators for habitat selection and other activities. For example, for 2600 years the Chinese have used localized seasonal changes in temperature and precipitation to schedule their agricultural activities. In seminal studies, Shirley (1929, 1945) emphasized microclimate as a determinant of ecological patterns in both plant and animal communities and a driver of such processes as the growth and mortality of organisms. The importance of microclimate in influencing ecological processes such as plant regeneration and growth, soil resperation and growth, soil repiration, nutrient cycling, and wildlife habitat selection has became an essential component of current ecological research (Perry 1994). plant regeneration and growth, soil respiration, nutrient cycling, and

Characterizing historical and modern fire regimes in Michigan (USA): A landscape ecosystem approach

We studied the relationships of landscape ecosystems to historical and contemporary fire regimes across 4.3 million hectares in northern lower Michigan (USA). Changes in fire regimes were documented by comparing historical fire rotations in different landscape ecosystems to those occurring between 1985 and 2000. Previously published data and a synthesis of the literature were used to identify six forest-replacement fire regime categories with fire rotations ranging from very short (<100 years) to very long (>1,000 years). We derived spatially-explicit estimates of the susceptibility of landscape ecosystems to fire disturbance using Landtype Association maps as initial units of investigation. Each Landtype Association polygon was assigned to a fire regime category based on associations of ecological factors known to influence fire regimes. Spatial statistics were used to interpolate fire points recorded by the General Land Office. Historical fire rotations were determined by calculating the area burned for each category of fire regime and dividing this area by fifteen (years) to estimate area burned per annum. Modern fire rotations were estimated using data on fire location and size obtained from federal and state agencies. Landtype Associations networked into fire regime categories exhibited differences in both historical and modern fire rotations. Historical rotations varied by 23-fold across all fire rotation categories, and modern forest fire rotations by 13-fold. Modern fire rotations were an order of magnitude longer than historical rotations. The magnitude of these changes has important implications for forest health and understanding of ecological processes in most of the fire rotation categories that we identified.

Net Ecosystem Exchanges of Carbon, Water, and Energy in Young and Old-growth Douglas-Fir Forests

To be able to estimate the cumulative carbon budget at broader scales, it is essential to understand net ecosystem exchanges (NEE) of carbon and water in various ages and types of ecosystems. Using eddy-covariance (EC) in Douglas-fir dominated forests in the Wind River Valley, Washington, USA, we measured NEE of carbon, water, and energy from July through September in a 40-year-old stand (40YR) in 1998, a 20-year-old stand (20YR) in 1999, and a 450-year-old stand (450YR) during both years. All three stands were net carbon sinks during the dry, warm summers, with mean net daily accumulation of –0.30 g C m−2 d−1, –2.76 g C m−2 d−1, and –0.38 g C m−2 d−1, respectively, in the 20YR, 40YR, and 450YR (average of 1998, 1999) stands; but for individual years, the 450YR stand was a carbon source in 1998 (0.51 g C m−2 d−1) and a sink in 1999 (–1.26 g C m−2 d−1). The interannual differences for the summer months were apparent for cumulative carbon exchange at the 450YR stand, which had 46.9 g C m−2 loss in 1998 and 115.9 g C m−2 gain in 1999. As predicted, the 40YR stand assimilated the most carbon and lost the least amount of water to the atmosphere through evapotranspiration.

Hierarchical relationships between landscape structure and temperature in a managed forest landscape

Management may influence abiotic environments differently across time and spatial scale, greatly influencing perceptions of fragmentation of the landscape. It is vital to consider a priori the spatial scales that are most relevant to an investigation, and to reflect on the influence that scale may have on conclusions. While the importance of scale in understanding ecological patterns and processes has been widely recognized, few researchers have investigated how the relationships between pattern and process change across spatial and temporal scales. We used wavelet analysis to examine the multiscale structure of surface and soil temperature, measured every 5 m across a 3820 m transect within a national forest in northern Wisconsin. Temperature functioned as an indicator – or end product – of processes associated with energy budget dynamics, such as radiative inputs, evapotranspiration and convective losses across the landscape. We hoped to determine whether functional relationships between landscape structure and temperature could be generalized, by examining patterns and relationships at multiple spatial scales and time periods during the day. The pattern of temperature varied between surface and soil temperature and among daily time periods. Wavelet variances indicated that no single scale dominated the pattern in temperature at any time, though values were highest at finest scales and at midday. Using general linear models, we explained 38% to 60% of the variation in temperature along the transect. Broad categorical variables describing the vegetation patch in which a point was located and the closest vegetation patch of a different type (landscape context) were important in models of both surface and soil temperature across time periods. Variables associated with slope and microtopography were more commonly incorporated into models explaining variation in soil temperature, whereas variables associated with vegetation or ground cover explained more variation in surface temperature. We examined correlations between wavelet transforms of temperature and vegetation (i.e., structural) pattern to determine whether these associations occurred at predictable scales or were consistent across time. Correlations between transforms characteristically had two peaks; one at finer scales of 100 to 150 m and one at broader scales of >300 m. These scales differed among times of day and between surface and soil temperatures. Our results indicate that temperature structure is distinct from vegetation structure and is spatially and temporally dynamic. There did not appear to be any single scale at which it was more relevant to study temperature or this pattern-process relationship, although the strongest relationships between vegetation structure and temperature occurred within a predictable range of scales. Forest managers and conservation biologists must recognize the dynamic relationship between temperature and structure across landscapes and incorporate the landscape elements created by temperature-structure interactions into management decisions.

Disturbance and landscape dynamics in the Chequamegon National Forest Wisconsin, USA, from 1972 to 2001

Land uses, especially harvesting and road building, are considered to be the primary cause of forest fragmentation in many parts of the world. To test this perception, we (1) quantified changes and rates of change in vegetative composition and structure within the Washburn Ranger District in northern Wisconsin using Landsat images, (2) examined changes in landscape structure, (3) assessed changes within the area of road influence (ARI), and (4) investigated changes in landscape composition and structure within the context of forest management activities. Our landscape classifications included six dominant cover types: mixed hardwood (MH), jack pine (JP), red pine (RP), mixed hardwood/conifer (MHC), non-forested bare ground (NFBG), and regenerating forest or shrub (RFS). Increases in NFBG and RFS, by 196% and 28% respectively, reflect expansion of the pine-barrens. Windthrow in the mature hardwoods during the late 1970s and jack pine budworm outbreaks during the mid-1990s correlated with decreases in those classes over the corresponding intervals. A 69% decrease in mean patch size and a 60% increase in edge density reflect increased fragmentation. An inverse relationship existed between the compositional trends of forested (excluding JP) cover types and RFS and NFBG cover types. ARI covered 8% of the landscape affecting species composition within the MH, RFS, and NFBG. Results from this study are key in assessing the links between management activities and ecological consequences and thereby facilitate adaptive management.

The patch mosaic and ecological decomposition across spatial scales in a managed landscape of northern Wisconsin, USA

Summary Understanding landscape organization across scales is vital for determining the impacts of management and retaining structurally and functionally diverse ecosystems. We studied the relationships of a functional variable, decomposition, to microclimatic, vegetative and structural features at multiple scales in two distinct landscapes of northern Wisconsin, USA. We hoped to elucidate any characteristic resolutions of structure-process relationships on these landscapes, and to determine the validity of extrapolation of structure-process associations across scales and management regimes. We used a combination of ANOVA, wavelet, canonical discriminant, and correlation analyses and asked specifically whether: 1) specific combinations of microclimatic, structural, and vegetative features were consistently associated with differences in decomposition among management zones along transects (i.e., within landscapes); and 2) factors influencing decomposition were consistent among resolutions of analysis and depths within and between landscapes. Decomposition was greater on the pine barrens than the small block transect and greater at 4 cm depth than at the surface for both landscapes. Significant differences in decomposition occurred among management patches for both transects and depths, except 4 cm along the pine barrens. In general decomposition was faster for patch types with greater overstory cover at 1 cm (both transects) and lower at 4 cm (small block). Canonical discriminant analysis also separated management patches by overstory cover for both transects. Secondary vectors also separated patches along both transects by microclimate, independent from overstory effects on those variables. Dominant resolutions in the patterns of decomposition differed between transects and depths: 80 m (pine barrens, 1 cm); 500 m (pine barrens 4 cm); 160 m (small block, 1 cm); and 750 m (small block, 4 cm). At the 1 cm depth, the strongest correlations of wavelet transforms of decomposition with structural, microclimatic, and vegetation variables often differed in resolution from those dominant in the decomposition patterns. At the 4 cm depths, many of the strongest correlations occurred at the maximum resolutions examined. Although many important correlates differed between transects and depths within a transect, there were some consistencies. On both transects, surface and soil temperatures were strongly correlated (|r| > 0.40) with decomposition; soil temperatures were stronger correlates along the small block. The direction of association between decomposition and temperatures changed with depth, being negative at 1 cm and positive at 4 cm for both transects. Overstory was an important correlate (|r| > 0.50) for 3 of 4 transect-depth combinations. On both transects, correlations between decomposition and overstory peaked at different resolutions and were different signs (positive at 1 cm and negative at 4 cm) for the two decomposition depths. Along the pine barrens but not the small block, there were two peaks of resolutions of correlation that appeared consistently across variables. Thus, correlates of decomposition changed with scale as well as depth and management regime. This suggests that factors other than management may still be maintaining decomposition patterns on the landscapes. Further, patterns in and relationships to process variables should be examined at multiple scales to develop a comprehensive understanding of the mechanisms driving functional heterogeneity. Das Verstandnis der Landschaftsorganisation ist entscheidend fur die Bestimmung der Auswirkungen von Management und fur den Erhalt von strukturell und funktionell diversen Okosystemen. Wir untersuchten die Beziehungen zwischen einer funktionellen Variablen, der Zersetzung, und mikroklimatischen, Vegetations- und Struktureigenschaften auf multiplen Skalen in zwei unterschiedlichen Landschaften im nordlichen Wisconsin, USA. Wir hofften, charakteristische Losungen fur Struktur-Prozes-Beziehungen in den Landschaften aufzuklaren, sowie die Gultigkeit von Extrapolationen von Struktur-Prozess-Beziehungen uber Skalen und Management-Regimes zu bestimmen. Wir nutzten eine Kombination von ANOVA, “wavelet”-, kanonischer Diskriminanz- und Korrelationsanalysen und fragten uns insbesondere: (1) ob spezielle Kombinationen von mikroklimatischen, strukturellen und Vegetationseigenschaften durchweg mit Unterschieden in der Zersetzung zwischen den Managementzonen entlang der Transekte (d.h. innerhalb der Landschaften) verbunden waren; und (2) ob es bei verschiedenen Auflosungen der Analysen und Tiefen innerhalb und zwischen den Landschaften durchgangige Faktoren waren, die die Zersetzung beeinflusten. Die Zersetzung war in den beiden Landschaften in den Kieferodlandern groser als in den “small block”-Transekten; und in 4 cm Tiefe groser als an der Oberflache. Signifikante Unterschiede in der Zersetzung traten zwischen “Management-patches” sowohl fur die Transekte als auch die Tiefen auf; mit Ausnahme der 4 cm Tiefe in den Kieferodlandern. Im Allgemeinen war die Zersetzung in den “patch”-Typen mit groserer Oberholz-Deckung (overstorey) bei 1 cm schneller (beide Transekte), und bei 4 cm geringer (“small block”-Transekt). Die Kanonische Diskriminanzanalyse trennte ebenfalls gemanagte “patches” nach der Oberholz-Deckung bei beiden Transekten. Sekundare Vektoren) trennten ebenfalls “patches” nach dem Mikroklima, unabhangig vom Oberholz-Einfluss auf diese Variablen. Die dominanten Auflosungen in den Mustern der Zersetzung unterschieden sich zwischen den Transekten und Tiefen: 80 m (Kieferodlander, 1cm), 500 m (Kieferodlander, 4 cm), 160 m (“small block”-Transekt, 1 cm) und 750 m (“small block”-Transekt, 4 cm). Bei 1 cm Tiefe unterschieden sich die starksten Korrelationen der “wavelet”-Transformation der Zersetzung mit strukturellen, mikroklimatischen und Vegetationsvariablen haufig in der Auflosung von denen, die dominant in den Zersetzungsmustern waren. Bei 4 cm Tiefe fanden sich viele der starksten Korrelationen bei der maximalen betrachteten Auflosung. Obwohl sich viele, wichtige korrelierende Variablen (correlates) zwischen den Transekten und den Tiefen innerhalb eines Transektes unterschieden, gab es einige Gemeinsamkeiten. Auf beiden Transekten waren Oberflachen- und Bodentemperatur stark mit der Zersetzung korreliert (|r| > 0.40); die Bodentemperaturen waren die starker korrelierenden Variablen entlang des “small block”-Transekts. Die Richtung der Beziehung zwischen der Zersetzung und der Temperatur anderte sich mit der Tiefe und war negativ in 1 cm und positiv in 4 cm Tiefe bei beiden Transekten. Oberholz war eine wichtige korrelierende Variable (|r| > 0.50) bei 3 von 4 Transekt-Tiefen-Kombinationen. Bei beiden Transekten erreichten die Korrelationen zwischen Zersetzung und Oberholz ihren Hohepunkt bei verschiedenen Auflosungen und zeigten unterschiedliche Vorzeichen fur die beiden Zersetzungstiefen (positiv bei 1 cm, negativ bei 4 cm Tiefe). Entlang der Kieferodlander, jedoch nicht entlang des “small block”-Transekts, gab es zwei Hohepunkte der Auflosung der Korrelation, die bei den Variablen durchweg auftraten. Somit anderten sich die korrelierenden Variablen sowohl mit der Skala als auch mit der Tiefe und dem Management-Regime. Das legt nahe, dass andere Faktoren als das Management die Zersetzungs-Muster in den Landschaften aufrechterhalten. Weiterhin sollten Muster in und Beziehungen zwischen den Prozes-Variablen auf multiplen Skalen untersucht werden, um ein umfassendes Verstandnis der Mechanismen zu entwickeln, die die funktionelle Heterogenitat vorantreiben.