Pettit Neil E, Naiman Robert J
School of Aquatic and Fishery Sciences, Campus Box 355020, University of Washington, Seattle, Washington 98195, USA.
Ecology. 2007 Aug;88(8):2094-104. doi: 10.1890/06-1270.1.
Piles of large wood (LW) deposited by major floods in river corridors can interact with naturally occurring wildfires from uplands to impact the regeneration of riparian vegetation. This study examines the spatial and short-term temporal response of riparian vegetation and soil nutrients to fire along the Sabie River, South Africa, with special emphasis on the effects of burned LW piles. At the study site there were 112 species of plants recorded with 28% of species restricted to the burned plots. As expected, vegetation cover was significantly lower in burned plots as compared with the unburned plots 12 months postfire. There was a significant influence of LW on species richness with fewer species recorded in the LW plots. For both fire and LW treatments, plant cover showed a significant change over three years. After an initial increase from 12 to 24 months (postfire) there was a decline in plant cover after 36 months. Species community composition was distinctly different between burned and unburned plots 12 months postfire, and the presence of LW affected species composition for burned plots but not for unburned ones. Time series ordination of LW plots highlighted the changes in species composition over the three years of sampling. Of trees with accumulations of LW within 5 m of their base, 48% had been killed by fire as compared to only 4% with no LW accumulations in close proximity. Soil-available P was significantly higher in the burned plots and even higher with burned LW while there were no effects on soil total N. There was also a significant positive trend between available P in soils and plant vegetation cover. Soil-exchangeable K was also significantly higher and total C significantly lower in the burned and LW plots. Burned plots also had significantly higher soil electrical conductivity (EC) and soil pH. The patchy nature of the studied fire, whose complexity is exacerbated by the distribution of flood deposited LW, acted to create a mosaic of alternate successional states as the riparian community recovers from flooding and the subsequent fire. We suspect that the resultant heterogeneity will increase ecosystem resilience by providing flexibility in the form of more options for a system response to subsequent disturbances.
大洪水在河道中堆积的大量木材（LW）会与高地自然发生的野火相互作用，从而影响河岸植被的再生。本研究考察了南非萨比河沿岸河岸植被和土壤养分对火灾的空间和短期时间响应，特别强调了燃烧的LW堆的影响。在研究地点记录了112种植物，其中28%的物种仅限于燃烧区域。正如预期的那样，火灾后12个月，燃烧区域的植被覆盖度明显低于未燃烧区域。LW对物种丰富度有显著影响，LW区域记录的物种较少。对于火灾和LW处理，植物覆盖度在三年中都有显著变化。在火灾后12至24个月最初增加后，36个月后植物覆盖度下降。火灾后12个月，燃烧区域和未燃烧区域的物种群落组成明显不同，LW的存在影响了燃烧区域的物种组成，但对未燃烧区域没有影响。LW区域的时间序列排序突出了三年采样期间物种组成的变化。在基部5米范围内有LW堆积的树木中，48%被火烧死，而附近没有LW堆积的树木只有4%被火烧死。燃烧区域土壤有效磷显著更高，燃烧LW时甚至更高，而对土壤总氮没有影响。土壤有效磷与植物植被覆盖度之间也存在显著的正相关趋势。燃烧区域和LW区域的土壤交换性钾也显著更高，总碳显著更低。燃烧区域的土壤电导率（EC）和土壤pH也显著更高。所研究火灾的斑块性质，由于洪水沉积的LW分布而使其复杂性加剧，在河岸群落从洪水和随后的火灾中恢复时，形成了交替演替状态的镶嵌体。我们怀疑，由此产生的异质性将通过为系统应对后续干扰提供更多选择的形式来增加生态系统的恢复力。
