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Plants go with the flow: predicting spatial distribution of plant species in the boreal forest
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main objectives of this thesis are to study if a topographic wetness index (TWI) could be used as a tool for predicting the spatial distribution of vascular plant species richness in the boreal forest as well as to study congruence in species richness between vascular plants, liverworts, mosses and lichens. A wetness index ln(a/tanβ) based on topography was used to assign a specific TWI-value to every 20 x 20m grid in two 25 km2 boreal forest landscapes (differing in average soil pH) in northern Sweden. Soil pH is known to be influenced by groundwater and to affect plant species richness in other biomes. Therefore, the relationships between plant species richness, TWI and soil pH were also studied.

The results showed that the majority of the investigated boreal forest landscapes were relatively dry and species-poor, whereas interspersed patches linked to areas with relatively high TWI had species-rich vegetation including the species of the drier parts of the landscape. There was a positive relationship between species richness of vascular plants and the TWI in both landscapes, but varied with average soil pH. TWI explained 30 % and 52 % of the variation in plant species richness in the landscape with lower and higher pH, respectively. The proportion of regionally uncommon plants also increased with TWI. Testing different calculation methods of the TWI resulted in a large variation in correlation strengths between the various TWI-values and different measured variables (species richness of vascular plants, soil pH, groundwater flow and soil moisture). The relationship between plant species richness and TWI could be further improved with some of the calculation methods.

When studying correlations in species richness using data sets from boreal forest in northern Sweden, strong positive correlations among vascular plants, mosses and liverworts were found, but no significant correlation between macrolichens and any of the other groups. This result could be explained by that the species number of each of the three related groups increases with ambient moisture, whereas the species number of macrolichens is weakly associated with moisture.

In conclusion, the TWI could become a useful tool in conservation management for identifying areas of special interest prior to field inventories. Since vascular plants can be used as an indicator taxon for species richness of mosses and liverworts, high TWI-values indicate areas of species hotspots of these taxa.

Abstract [sv]

Syftet med avhandlingen är att dels studera om ett topografiskt fuktighetsindex skulle kunna vara användbart för att förutsäga fördelningen av kärlväxters artrikedom i boreal skog, dels att studera om den rumsliga fördelningen av artrikedom hos kärlväxter, blad- och levermossor samt lavar sammanfaller.

Ett fuktighetsindex, ln(a/tanβ), som bara är baserat på topografi användes för att beräkna ett indexvärde för varje 20 x 20 m grid i två 25 km2 stora boreala skogslandskap (med i medeltal olika mark-pH) i norra Sverige. Det är känt att mark-pH påverkas av grundvatten och att pH i sin tur påverkar artrikedom hos kärlväxter i andra biom. Därför studerades även sambanden mellan kärlväxters artrikedom, mark pH och TWI.

Resultaten visade att större delen av det studerade boreala landskapet var relativt torrt och artfattigt, medan mindre utspridda områden med höga TWI-värden var artrika på kärlväxter och här växte även arter som återfanns i de torra delarna av skogen. Sambandet mellan artrikedom hos kärlväxter och TWI var positivt i båda landskapen, men påverkades av de olika nivåerna på mark-pH. TWI förklarade 30 % av variationen i artrikedom i området med lägre mark-pH respektive 50 % i området med högre mark-pH. Andelen kärlväxter som klassificeras som icke vanliga i respektive region ökade också med TWI. Med andra beräkningsmetoder för TWI visade det sig att styrkan på korrelationerna mellan TWI och olika uppmätta variabler (artrikedom hos kärlväxter, mark-pH, grundvattennivå och markfuktighet) varierade mycket. Sambandet mellan artrikedom hos kärlväxter och TWI kunde förbättras ytterligare med vissa beräkningsmetoder.

Då korrelationer i artrikedom studerades användes ett dataset från boreal skog i norra Sverige. Resultaten visade på starka, positiva korrelationer mellan kärlväxter, blad- och levermossor, men inga korrelationer mellan någon av dessa grupper och lavar. Detta kunde förklaras med att artrikedom hos de tre korrelerande organismgrupperna ökar med ökad fuktighet, medan artrikedom hos lavar inte är kopplat till fukt.

Huvudslutsatsen i avhandlingen är att TWI, som endast är baserad på topograpfiskt data, skulle kunna bli ett värdefullt redskap i naturvårdsplanering för att identifiera särskilt intressanta skogsområden innan man gör fältinventeringar. Eftersom studien visar att kärlväxter kan användas som en indikator grupp för artrikedom hos blad- och levermossor indikerar höga TWI-värden områden med hög artrikedom även vad gäller dessa taxa.

Place, publisher, year, edition, pages
Umeå: Ekologi och geovetenskap , 2004. , 29 p.
Keyword [en]
Ecology, boreal forest, vascular plant, species richness, wetness index, soil pH, bryophyte, lichen, substrate, stand age, plot size
Keyword [sv]
Ekologi
National Category
Ecology
Research subject
Ecological Botany
Identifiers
URN: urn:nbn:se:umu:diva-315ISBN: 91-7305-705-3 (print)OAI: oai:DiVA.org:umu-315DiVA: diva2:143067
Public defence
2004-10-01, P.O. Bäckströms sal, Skogshögskolan, Sveriges Lantrbuksuniversitet, Umeå, 10:00
Opponent
Supervisors
Available from: 2004-09-13 Created: 2004-09-13Bibliographically approved
List of papers
1. Plant species number predicted by a topography based groundwater-flow index
Open this publication in new window or tab >>Plant species number predicted by a topography based groundwater-flow index
2005 (English)In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 8, no 4, 430-441 p.Article in journal (Refereed) Published
Abstract [en]

The lack of a clear understanding of the factors governing the often-great variation of species numbers over entire landscapes confounds attempts to manage biodiversity. We hypothesized that in a topographically variable boreal forest landscape the availability of shallow groundwater is a major determinant of plant species numbers. We then developed a topographically derived hydrologic index based on multidirectional flow algorithms to account for the variation in availability of such groundwater in the landscape. We found a positive correlation between species numbers of vascular plants in plots ranging from 0.01 to 200 m2 and the hydrologic index. Generally, the landscape was relatively dry and species-poor, but interspersed patches with shallow groundwater had high species numbers and high proportions of regionally uncommon plant species. The index explained 30% of the variation in vascular plant number and correlated quite well (rs = 0.50) with groundwater level, but not as well with a community H+concentration value (instead of community pH, rs = −0.31), based on species composition. In addition, we found a very strong correlation between species number and the community H+ concentration value (rs−0.84). The hydrologic index is a useful tool for the identification of spatial of species number patterns across entire landscapes. This is an important step in identifying the areas most in need of protection or restoration, designing survey techniques, and understanding the fundamental processes that control the spatial distribution of species.

Place, publisher, year, edition, pages
New York, N.Y.: Springer, 2005
Keyword
species richness, wetness index, boreal forest, vascular plants, slope, nestedness, scale dependence
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-4096 (URN)10.1007/PL00021513 (DOI)
Available from: 2004-09-13 Created: 2004-09-13 Last updated: 2017-12-14Bibliographically approved
2. The importance of soil moisture and pH for the spatial variation of plant species numbers in boreal forests.
Open this publication in new window or tab >>The importance of soil moisture and pH for the spatial variation of plant species numbers in boreal forests.
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-4097 (URN)
Available from: 2004-09-13 Created: 2004-09-13 Last updated: 2013-02-07
3. On the calculation of the topographic wetness index: evaluation of different methods based on field observations.
Open this publication in new window or tab >>On the calculation of the topographic wetness index: evaluation of different methods based on field observations.
2006 (English)In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 10, no 1, 101-112 p.Article in journal (Refereed) Published
Abstract [en]

The topographic wetness index (TWI, ln(a/tan beta)), which combines local upslope contributing area and slope, is commonly used to quantify topographic control on hydrological processes. Methods of computing this index differ primarily in the way the upslope contributing area is calculated. In this study we compared a number of calculation methods for TWI and evaluated them in terms of their correlation with the following measured variables: vascular plant species richness, soil pH, groundwater level, soil moisture, and a constructed wetness degree. The TWI was calculated by varying six parameters affecting the distribution of accumulated area among downslope cells and by varying the way the slope was calculated. All possible combinations of these parameters were calculated for two separate boreal forest sites in northern Sweden. We did not find a calculation method that performed best for all measured variables; rather the best methods seemed to be variable and site specific. However, we were able to identify some general characteristics of the best methods for different groups of measured variables. The results provide guiding principles for choosing the best method for estimating species richness, soil pH, groundwater level, and soil moisture by the TWI derived from digital elevation models.

Identifiers
urn:nbn:se:umu:diva-4098 (URN)
Available from: 2004-09-13 Created: 2004-09-13 Last updated: 2017-12-14Bibliographically approved
4. Correlation in species numbers among vascular plants, mosses, liverworts and lichens in boreal forests: effects of plot size, substrate affiliation, and stand age.
Open this publication in new window or tab >>Correlation in species numbers among vascular plants, mosses, liverworts and lichens in boreal forests: effects of plot size, substrate affiliation, and stand age.
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4099 (URN)
Available from: 2004-09-13 Created: 2004-09-13 Last updated: 2010-01-13Bibliographically approved

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