History of Sugar Maple Decline Introduction Sugar Maple Dectines
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History of Sugar Maple Decline Uav~dH. Houston' Abstract Certain ecophysiolog!cal character!sttcs of sugar maple have made it easy to exploit these values. Sugar maples frt~it Only a few episodes of sugar maple dieback or decline were prolificaily; seeds, which mature in the fali, are readily recorded during the first half of the 20th Century. In coritrast, dispersed by wind and germinate the foliowirtg spring. Wei! the last 50 years have provided nume!ous reports of both over 5,000,000 seeds per acre are common in good seed urban and forest diebackideciine. In the late 1950s. a years and, establishment is ofteri highly successful. Carpets defoliation-triggered decline. termed rnaple blight, that of young seedlings are common. and the ability of shade- occurred in Wisconsin prompted the first compreherrsive, suppressed seed!ings and sap!rngs to respond when multidiscipl~rrarystudy of a sugar maple decline. Tha? re!eased has enabled the species to become a predominant research, and other investigations since, provided the component of many forest types. Sugar rnaple does best on conceptual framework for a model of sequential, stress- deep soils that are moderately coarse-textured, moist and initiated cause and effect for diebacudeciine disease. Many weii-drained (Godman e: al. 1990). cases of ilrban maple diebackfdecline have been attributed to soil compaction, drought, impeded soil water availability, Sugar Maple Dectines or toxic effects of road deicing sait. Most cases of forest or sugarbush decline have been associated with the initiating Although records are lacking, it is highly probable that sugar stresses of ir\secl defoiiation or drought. singiy or in concert. maple has long experienced serious episodes of diebacW Mortality of stressed trees is often caused or hastened when decline. Many of the environmental stresses affecting today's roots or twigs are invaded by opportunistic, secondary forests occurred in pre-European settlement times; drotights. organisms, espectalty the root rot fungi Arillilfaria spp. (and ~nsectdefoliation, fire, aarnagiriy winds, and ice storms were probably Xylaria sp.). In the past two decades, freez~ngof no strangers to those early forests. Although opinior~svary. roots associated with periods of thaw-freeze and of deep the effects of these disturbances. especially, perhaps, f~re cold, especiaiiy when snow cover was rninin.lal or lacking, and windstorms, created mosaics of both uneven-aged and have been correlated with major decline cptsodcs In eastern even-aged forests of differing successional stayes (Clawson Canada and northern New England and New York. An 1983, 1-oucks 1983). Old, uneven-aged stands contained a hypothesis that dieback results when death of roots leads to high proportion of mature and overrnature trees--those transpiration-stress and vessel cavitation Is supported by considered most susceptible to many of the stress factors observations that diebaciddeciine episodes attributed lo that trigger declines. As colonization ensued, activities such droughts appear correlated temporaliy with prior root-freeze as iogging, clearing, burning, pasturing, and sugaring events. Such events are now Delievcd ri:sponsib!e for the intensified drarnaticaily. Areas best si~itedfor tree growth serioirs maple dicbackideclirje probletns in southern Ouebec were ofreri those most desired for agricultural uses. Much of !n the 1980-1990s that at first ware hypothesized to result :he old growth forest ivas removed, especially during the from atmospheric deposition. While atmospheric deposition latter half of the 19th century. Reestabiishment of forests on has been disco~intedas a direct cause of maple declines. land withdrawn froni agriculture has resulted in large areas the long-term and perhaps complex effects on tree health of of relatively even-aged forests that, during the fatter half of deposltion-hastened changes in soil ctienlistry. especially in the 20th century purportedly began reaching an age of areas with soils susceptible to acidification, are the primary increased susceptibility to stress events. sut~jcctsof current investigations. While a few reports of maple diebacWdeclines appeared in introduction the first half of the 20th century (Hartley and Merrill 1915; Marsden 1950; McKenzie 19431, ~twas not until after 1950 Sagar rnapie (Acer saccharurn Marsh.) has rr:any highly that accounts of such problems become numerous. Several valued qualities. its lony life. pleasing !orm. and bri!liant fal! reviews present the chrono!ogies and presumed causes of color have made it a favored tree for gracing dooryards and sugar maple diebackidecline episodes (e.g. Allen et al. 1992; roadsides from New England to the Lake States. Its hard, but Houston 1985, 1987; Mcflveen et al. 1986; Millers et al, easily-worked, light-coiored wood is widely used for flooring. 1989; Sinctair 1964; Westing 1966). The purpose of this brief furniture, and many specialty products. Wood with uniquely paper is not to restate what was presented in those reviews, figured patteins, including "bird's eye", "curfey", or but, rather. to discgss the main themes that seem most "fiddleback is highly prized for fine woodworking. Further, pertinent to the present situation. the romanticism arid economic values associated with spring saptlows and mapfe sugaring are as strong today as in The Mature of Sugar Maple DiebacWdectirae colc;nial trn'tes. One conceptuai model of sugar maple diebackideclines in torest sttuations was structured around !he premise that disease msn~festation(progressive crown dieback sometimes ieadng to continued tree decline and death) 'Research Plant i'athologist (Retired), USOA Forest Service, results when one or more predisposing (sensu str!cto) stress 5f Mill Pond Road. Hamden. CT 06514 ----- Sugar PJap:e Ecology 2nd :iealtfi: P;7ceedings of an k:!cm:ional~,vmpnriam G?R-NE-2661 19 factors reduccs resistance to invasion by opportunistic; action arc ab!e to invade altered trssues suc~essiully.The secondary-action organisms !hat resuit In death of tissues- model above indicates that although host changes sufficient sometimes of trees je.9. Houston 1981. 19921. This model to allow organism attack can occur after a singie severe evolved initially from research on "maple blight, a diebacW stress event, such changes usually follow muitipie or deciine of sugar maple in northeastern Wisconsin, trigyered repeated events. Arrows are to be read as "leads to". by insect defoliation (Anonymous 1961, Giese et a!. 1964). A complex of insects irtcluding several species of leafroilers The statements of this model can be construed as and the maple webworm, Tetraiqaha asperate!/;, (Clem.) summaries of several important relationships: caused severe defoliatfon on about 10,009 acres in the mid- !ate 1950s (Giese and Benjamin 1964). Dead and dying i) Dieback of trees or tissues often results from the trees and saplings usually iveie attacked aggressively by effects of the stress factor(s) alone. With abatement of Armillaria sp. (Houston and Kuntz 1964). Severely damaged stress. and in the absence of significant colonization by stands, prior to being defoliated, had low basal area and saprogens or secondary insects. dieback often ceases and density, and a high proportion (r 50%) of sugar maple. trees recover. The dieback phase can be viewed as a During the 10 months prior to the onset of mortairiy, the survival mechanism whereby the tree adjusts to its recently region had below-normal precipitation (-8.3 inches) (Skilling encountered adverse environment. 1 964). ii) Stress alone, if sufficiently severe, prolonged, or L.ater studies elsewhere confirmed the defoliation str~ssi repeated, can cause continued or repeated dieback and Armilidria association and clarified the biochemical basis for +/en death. Numerous reports exist of tree mortality the lowered resistance of defoliation-affected tissues to following either unusually severe and prolonged drought or attack by this opportunrst (Parker and Houston 1971; Wargo ep~sodesof severe defoliation, especially if repeated. 1972: 'Wargo el ai. 1972;Wargo and Houston 1973). Another perhaps even in the same growing season, Even one severe opportunist, Steganosporiclrn ovaturn (Pers.) S.J. Hughes, defoiiatior; occurring concomitantly or sequentially with appeared to hasten the death of defoliation or drought- drought can result in high tree mortality. stressed fw~gsand branches (Hibben 1959, Wargo and Houston 1974). Research on several other stress-initiated iii) Usualiy, however, the dec!ine phase, wherein vitality problems (e.9.. Appel and Stipes 1984, Ehrlich 1934. lessens and trees succumb. is the consequence of organism Houston 1994a. Schoeneweiss 1981a. b. Wargo 1977. invasion of stress-altered tissues. Recovery from this phase 1983) tias validated the ctrror?ological and spatial prerrtises depends on many factors including the vi!a!ity of the tree, of the following sttnple, general model for diebacGdecline the partrcular tissues invaded, the relatrve aggressiveness of diseases: the organisrn(s), and the degree of invasion. 1. 14eaitkiy trees + stress --t Altered trees (tissues) iv) Where and when the dieback phase occurs is closely (dieback begins) related to where and when the triggering stress(es) occurs. The decline and mortality phase is related, rn addition, to the 2. Altered trees + more stress --r Trees (tissues) altered temporal afid sparial distrtbutions of the organisms of further (dieback contirlues) secondary action. 0 D These summary statements point out the inherent