Timothy D. Perkins

Primary and secondary causes and consequences of contemporary forest decline

Realization that forest decline (Waldsterben) has become an ecological crisis throughout the developed world has resulted in massive research efforts to determine the causes of declines. It is now recognized that no single causal factor is responsible, but that there are a variety of anthropogenic causal factor complexes interacting with natural events and processes that, together, induce stresses in forests that culminate in declines of individual plants and of ecosystems.It is the thesis of this article that forest declines involve all biotic and abiotic facets and parameters of forested ecosystems and that the declines are themselves new causal factor complexes that continue to affect the stability of forested ecosystems independently of the initial causal factor complexes. Lacking direct field or laboratory studies on these cascades of causes and effects, this article attempts to utilize the growing body of information on plant physiological ecology to provide a heuristic framework for evaluating long-term forest declines.AbstraktDie Erkenntnis, daß das Waldsterben zu einer ökologischen Krise in der gesamten entwickelten Welt geworden ist, hat zu massiven Forschungsanstrengungen nach den Ursachen geführt. Es ist mittlerweile anerkannt, daß nicht ein einzelner verursachender Umstand verantwortlich ist, sondern, daß es sich um eine Vielzahl anthropogener Faktoren im Wechselspiel mit natürlichen Vorgängen handelt; die im Zusammenwirken Stresse in den Wäldern hervorrufen und im Niedergang einzelner Pflanzen oder ganzer Waldökosysteme ihren Ausdruck finden.Dieser Artikel unterstüzt die These, daß das Waldsterben alle biotischen und abiotischen Facetten und Parameter eines Waldökosystems einbezieht und daß die Zerfallsprozesse selbst neue Ursachenkomplexe darstellen, die unabhängig von den ursprünglichen Ursachen, fortgesetzt die Stabilität der Waldökosysteme angreifen. Ohne direkte Feldoder Laboruntersuchungen dieser Kaskaden von Ursache und Wirkung versucht dieser Artikel die ständig wachsende Masse der Information über Pflanzen-ökologie und -physiologie zu nutzen, um ein heuristiches Gitternetz für die Auswertung der Langzeiteffekte des Waldsterbens aufzustellen.

Chapter 4 Maple Syrup—Production, Composition, Chemistry, and Sensory Characteristics

Maple syrup is made from sap exuded from stems of the genus Acer during the springtime. Sap is a dilute solution of primarily water and sucrose, with varying amounts of amino and organic acids and phenolic substances. When concentrated, usually by heating, a series of complex reactions produce a wide variety of flavor compounds that vary due to processing and other management factors, seasonal changes in sap chemistry, and microbial contamination. Color also forms during thermal evaporation. Flavor and color together are the primary factors determining maple syrup grade, and syrup can range from very light-colored and delicate-flavored to very dark-colored and strong-flavored.

Assessing cold tolerance in Picea using chlorophyll fluorescence

Chlorophyll fluorescence measurements were performed on field-collected red spruce foliage exposed to controlled freezing temperatures to determine the utility of chlorophyll fluorescence kinetics in assessing low temperature tolerance. No significant decreases in fluorescence relative to unfrozen control foliage were observed at progressively lower temperatures until a critical temperature was reached, whereupon rapid, irreversible decreases in fluorescence occurred. Weekly comparisons between cold tolerance estimates derived using chlorophyll fluorescence inflection point temperatures and foliar visual lt20 (temperature at which 20% of foliage exhibited necrosis) estimates were also made throughout the winter of 1991–1992. No significant differences in weekly cold tolerance estimates between the two methods were evident. The weekly absolute difference in mean cold tolerance using the two methods was 3.0°C. These results indicate that chlorophyll fluorescence is a rapid, consistent, and reproducible method of determining low temperature tolerance of spruce foliage.

Contribution of anthocyanins to the antioxidant capacity of juvenile and senescing sugar maple (Acer saccharum) leaves

Foliar anthocyanins are hypothesised to provide an additional source of photoprotection from photooxidative stress to the leaves in which they occur through their ability to scavenge excess free radical species. Although demonstrated to significantly enhance the antioxidant status of red morphs of fully expanded leaves of some species, the contribution of anthocyanins to the antioxidant capacity of the juvenile and senescing leaves in which they frequently occur has not been examined. Antioxidant activity of extracts from anthocyanic and non-anthocyanic juvenile and senescing sugar maple (Acer saccharum Marsh.) leaves from similar light environments was assessed using the stable free radical 1,1-diphenyl-2-picryl hydrazyl (DPPH). Anthocyanin content was significantly correlated with antioxidant activity in extracts of anthocyanic juvenile leaves but only weakly correlated in extracts of anthocyanic senescing leaves. In addition, the antioxidant activity of anthocyanic and non-anthocyanic leaves was equal in both juvenile and senescing leaves. Thus, although anthocyanins may contribute to the antioxidant capacity of anthocyanic juvenile and senescing sugar maple leaves, these results are not consistent with the hypothesis that anthocyanins provide an enhancement to the photoprotection available in either leaf type through free radical scavenging. The results suggest anthocyanins may be part of alternative strategies employed by anthocyanic juvenile and senescing maple leaves to achieve similar levels of antioxidant capacity as their non-anthocyanic counterparts to cope with the same set of environmental challenges.

Anthocyanin influence on light absorption within juvenile and senescing sugar maple leaves - do anthocyanins function as photoprotective visible light screens?

Foliar anthocyanins are hypothesised to function as photoprotective visible light screens, preventing over-excitation of the photosynthetic system, and decreasing the likelihood of photo-oxidative stress by absorbing green light and reducing the amount of light available to be absorbed by chloroplasts in deeper tissue layers. Chlorophyll fluorescence imaging was used to test the hypothesis that anthocyanins in the palisade mesophyll of juvenile and senescing sugar maple (Acer saccharum Marsh.) leaves function as visible light screens by assessing their influence on light absorption profiles within leaves. We hypothesised that an effective anthocyanic light screen should reduce light absorption, particularly of green wavelengths, by chloroplasts in the spongy mesophyll. Both anthocyanic juvenile and senescing leaves absorbed greater amounts of green light than corresponding nonanthocyanic leaves. However, profiles of green light absorption by chlorophyll within anthocyanic leaves were not shifted to reflect reduced absorption of green light by spongy mesophyll chloroplasts. Further, the spongy mesophyll of both anthocyanic juvenile and senescing leaves absorbed proportions of green light equal to or greater than the spongy mesophyll of corresponding nonanthocyanic leaves. These results indicate that though they may provide a general source of photoprotection by reducing the total quantity of light available to be absorbed by chlorophyll, the anthocyanins in juvenile and senescing sugar maple leaves do not attenuate light in a manner consistent with that expected for an anthocyanic screen in the palisade mesophyll.

Techniques for pollution monitoring in remote sites: I. Near real-time rainfall pH and depth

A flow-through system for in situ, near real-time, sequential measurements of rainfall pH and depth was developed for monitoring of precipitation in sites lacking electric power. The system is easily fabricated from readily available instruments and materials, portable, relatively inexpensive and requires minimal maintenance. It also operates independently of AC power making it ideal for use in remote areas. Initial field testing of this system on Camels Hump, Vermont, took place over the period of July to August 1990, during which twenty-seven individual storm events were monitored. The system proved to be robust and reliable, providing rainfall pH and depth information with high (programmable) temporal resolution for unattended periods of up to a week.

Techniques for pollution monitoring in remote sites. II: Ozone

An O3 monitoring system for use in remote sites lacking AC line power was developed. A chemiluminescent O3 monitor, ethylene delivery system, and a DC power supply were combined to allow unattended O3 measurements over extended periods of time. A Campbell Scientific 21X micrologger in combination with a relay was used to control the ethylene delivery solenoid and O3 analyzer power, and to record results. The system was tested over a six week period in late summer 1990 and gave results comparable to those from surrounding sites.

Identifying Sustainable Practices for Tapping and Sap Collection from Birch Trees: Optimum Timing of Tapping Initiation and the Volume of Nonconductive Wood Associated with Taphole Wounds

Experiments were conducted to determine two pieces of information essential to identify practices necessary to ensure tapping trees for birch sap collection is both sustainable and profitable—the selection of the time to initiate tapping birch trees to obtain maximum yields, and the volume of nonconductive wood (NCW) associated with taphole wounds in birch trees. The yields obtained from various timing treatments varied between sapflow seasons, but indicate that using test tapholes to choose the appropriate time to initiate tapping is likely to result in optimum yields from birch trees. The volume of NCW associated with taphole wounds in birch trees was highly variable and generally quite large, averaging 220 times the volume of the taphole drilled, and requiring relatively high radial growth rates to maintain NCW at sustainable levels over the long-term. However, more conservative tapping practices, including reduced taphole depth and increased dropline length, as well as thinning and other stand management practices, can be used to reduce the minimum growth rates required. Producers can use this information to ensure that they use tapping practices that will result in sustainable outcomes and obtain the maximum possible sap yields from their trees.

Techniques for pollution monitoring in remote sites: III. Near real-time monitoring of cloud water conductivity and pH

A semi-portable flow-through cloud water monitoring system was developed for measurements of cloud water conductivity and pH in remote sites lacking AC line power. This system was tested from May to September on Camels Hump mountain, Vermont. High temporal resolution data from seven cloud events were collected during the 1991 growing season. Mean cloud water conductivity and pH for all events was 467 μmhos cm−1 and 3.2, respectively. The highest conductivity was 997 (μmhos cm−1 recorded on 19 September 1991 and the lowest pH of 2.9 was recorded during several events over the summer. Data from this system may be used to achieve a better understanding of the chemical environment in areas experiencing forest decline.