Linking Restoration and Ecological Succession (Springer ... - Inecol

54 David A. Wardle and Duane A. Peltzer
Table 3.1 Retrogressive successional trends that occur in lake islands in
northern Sweden as a result of prolonged absence of wildfire. Sources of
information are Wardle et al. (1997, 2003, 2004b) and Wardle and Zackrisson
(2005).
Response variable
Aboveground:
Trend
Tree vegetation Shift from domination by Pinus sylvestris to
Betula pubescens to Picea abies
Understory vegetation Shift from domination by Vaccinium
myrtillus to Vaccinium vitis-idaea to
Empetrum hermaphroditum
Tree and understory biomass Continual decline
NPP Continual decline
Light interception by vegetation Continual decline
Vascular plant diversity Strong increase
Intensity of effects of plant species Continual decline
removals on ecosystem properties
Moss biomass Slight increase
N fixation by mosses Strong increase
Belowground:
Polyphenol concentrations in soil Continual increase
Decomposer microbial biomass Continual decline
Litter decomposition rate Continual decline
Soil carbon sequestration Strong increase
N mineralization rate Continual decline
Mineral N concentration Continual decline
Ratio of mineral N to organic N Continual decline
Ratio of soil N to P Continual increase
The ecological impacts of long-term suppression or absence of wildfire have
been investigated over the past decade through a “natural experiment” involving
forested islands in Lake Uddjaure and Lake Hornavan in northern Sweden
(Wardle et al. 1997, 2003, and 2004b, Wardle and Zackrisson 2005) (Table 3.1)
(see Fig. 3.3). This system allows significant replication of discrete independent
ecosystems (each island effectively operates as a separate system) at ecologically
meaningful spatial scales. The main extrinsic driver that varies across
these islands is wildfire caused by lightning strike; large islands burn more often
than smaller ones simply because they have a larger area to be intercepted
by lightning. Thus, some of the largest islands have burned in the past 100 years
while some of the smallest have not burned for 5000 years. These islands therefore
represent a secondary successional gradient induced by fire history. This
variation across islands in fire history impacts vegetation composition. Thus,
the largest (most frequently burned) islands are dominated by relatively rapidgrowing
early successional plant species such as Pinus sylvestris and Vaccinium
myrtillus, the middle sized islands are dominated by Betula pubescens and Vaccinium
vitis-idaea, and the smallest islands are dominated by slow-growing,
late successional species such as Picea abies and Empetrum hermaphroditum
(Wardle et al. 1997). Picea and Empetrum are well known to contain high levels
of secondary metabolites such as polyphenols in their tissues (Nilsson and
Wardle 2005), so that with increasing time since fire there is a shift from plants
that invest their C in growth to those that invest C in defense. Concomitant with