Although freshwater shorelines occupy extensive areas of the temperate zone, we still have few conceptual models for pattern and process in shoreline vegetation. This study uses multivariate vegetation data to describe vegetation-environment relationships in a set of riverine wetlands and then explores general relationships between pattern and process. Samples were collected from five marshes along the Ottawa River (eastern Canada) (n = 94 sample units). Detrended correspondence analysis was used to describe major gradients, and TWINSP AN was used to classify vegetation types. TWINSP AN produced four major classes dominated by Sparganium eurycarpum, Eleocharis smallii, Scirpus americanus, and Typha latifolia. Within each class, two associations could be recognized, differing in the degree to which one species managed to dominate the vegetation. Ordination showed that these vegetation types were arranged along two major axes: a standing crop and litter gradient, and a water depth gradient. Species richness was greatest just above the late August waterline in Eleocharis smallii vegetation that had low fertility, intermediate total biomass (250glm 2 ) and low littermass (30 g/m 2 ). Very high biomass (>400glm 2 ) was observed where indices of high fertility and low disturbance coincided. Low species richness in this Typha-dominated vegetation is thought to be a result of competitive exclusion. Exposure to waves, ice, and flowing water produced a fertility gradient. The least fertile sites had small evergreen species such as Eriocaulon septangulare and Ranunculus flammula. These species possessed traits associated with Grime's "stress tolerator" strategy. The three main factors controlling vegetation composition were water depth, the effects of spring flooding in removing litter, and the fertility gradient produced by waves and flowing water. These were incorporated into a conceptual model including both patterns and processes observed along the Ottawa River.

No abstract

The woody vegetation of 131 clear-cut, postlogged boreal forest stands in central Canada, previously dominated by Picea mariana (Mill.) BSP., is compared with 250 natural postfire stands from the same region. Each dataset represents a stand chronosequence on a range of substrate types. Correspondence analysis (CA) based ordination methods is used for structural and compositional comparison in order to address the question of the extent to which woody vegetation recovery and succession are similar between the two disturbance types. In addition, canonical CA is used as a general linear model strategy to examine unique and covariant influences on forest composition. The postlogged stand dataset had a much lower representation of conifer-dominated stands than the postfire dataset and a far greater proportion of stands dominated by poplars. Detrended and canonical CA on all 381 stands indicated a primary influence on stand composition due to site factors, but disturbance type and intensity, i.e. wildfire versus horse or mechanical hauling in postlogged stands, showed the strongest correlation of any single variable. Analyses of each dataset, separately, indicated similar predictability of vegetation composition from associated stand environmental and age data but regressions were weak (R 2 ~ 22%). Whereas skidding type and stand age were the most important correlates with the postlogged data, soil variables were the most prominent correlates with the postfire woody vegetation. In addition to Abies balsamea (L.) Mill. dominated woodland deriving from postfire succession, such forests also arose on a widespread basis in horse skidded, postlogged stands through the persistence of advanced growth seedlings. Mechanically skidded, postlogged stands show a wholesale conversion from conifer dominance, mostly Picea mariana, to dominance by Populus. It is concluded that both the qualitative nature and the intensity of boreal forest disturbance lead to different woody vegetation recovery patterns.Résumé: On a comparé la végétation ligneuse de 131 peuplements forestiers issus de coupes à blanc de pessières à épinette noire (Picea mariana [Mill.] BSP.) avec celle de 250 peuplements régénérés à la suite de feux naturels dans la partie centrale du Canada. Chaque groupe de données correspond à une chronoséquence couvrant plusieurs types de substrat. Une analyse des correspondances (CA) basée sur des méthodes d'ordination a été utilisée pour évaluer le degré de ressemblance de la végétation ligneuse en phase de rétablissement et de succession en fonction des deux types de perturbation. De plus, une analyse canonique a servi de modèle général linéaire afin d'examiner d'autres effets possibles sur la composition forestière des peuplements. Le groupe des données associé à la coupe renferme moins de peuplements conifériens, mais une plus grande proportion de peuplements feuillus (peupliers) que le groupe relié au feu. L'analyse des correspondances des 381 peuplements montre que les facteurs stationnels exercent un effet marqué sur la comp...

Ordination models of approximate environmental and dynamic relationship between eight boreal tree species were constructed based upon principal components analysis and Kruskal's nonmetric multidimensional scaling. The assumptions inherent in these models are stated and discussed. The data consisted of 152 forest stands from the closed-crown boreal forest zone of Ontario and Quebec south of James Bay. Sequential forest succession, as demonstrated by similar techniques for a section of the Wisconsin evergreen–hardwood forest, is not common in the region of boreal forest studied. However, for those species in common between this and the Wisconsin study, similar dynamic pathways are indicated despite differences in sample size and field technique. Tree species developmental pathways, as indicated by 'succession vectors' on the ordination models are, for the most part, short and circular with the exception of Abies balsamea (balsam fir). This reflects the reestablishment of similar, relatively monospecific forest stands following catastrophic forest destruction by fire and (or) other agencies. Where catastrophe does not intervene, deciduous primary forest species may be succeeded by an understory of A. balsamea or by Picea mariana (black spruce). Equally, some forest stands of primary establishment may become decadent with little or no subsequent tree growth. These observations are discussed with respect to the general notion of forest succession.

The North American mid‐continent population of lesser snow geese (Anser caerulescens caerulescens) breeds in coastal areas of the Hudson Bay region. Breeding success is highly variable, particularly during recent decades. The availability of long‐term data sets of weather and the breeding success of geese allowed us to determine whether climatic variables in spring and early summer (May–June) are reliable predictors of different attributes of the reproductive biology of snow geese. A large region of strong anomalous cooling in north‐eastern North America has been the dominant anomalous climatic feature since the mid‐1970s. The cooling which becomes established during winter persists into spring and early summer when migration, nesting and hatching of geese are occurring. Redundancy analysis (RDA) of the data sets was made to identify dominant correlations and regression relationships between climatic and goose variables. Individual goose response variables were further explored with stepwise multiple regression and bipartial regression. 96.7% of year‐to‐year variance in the goose data was explained by the selected climatic data. The first four orthogonal axes out of seven possible axes explained 92.2% of the total variance. Date of last snow on the ground and mean daily temperature from 6 to 20 May formed the lowest and highest predictor scores, respectively. Initiation date and hatching date at the low end and total clutch size and clutch size at hatch at the high end were associated with these extremes, particularly in certain years. Days of freezing rain in May and total rainfall were correlated with nest failure. Bivariate correlation/regression showed that the most parsimonious model for nest initiation day was based on four climatic predictors, for hatching day four predictors, and for clutch size at hatch, nine predictors. Both the multiple regression analyses and the redundancy analyses confirm the high degree of predictability of goose reproductive variables from selected climatic variables. As discussed, the correlations reflect both direct and indirect effects of climate on the reproductive biology of geese. The correlations are strongest in the early season and weaken by early summer.